Cathode active material for all-solid battery, and all-solid battery comprising same

Abstract

The present invention relates to a cathode active material for all-solid battery in a secondary particle form formed by aggregating a plurality of primary particles, wherein the secondary particles have an average particle diameter (D50) of 2-7 μm, and the cathode active material has a particle surface aspect resistance (PSAR) of 5-9 kΩ·μm2.

Description

Cathode active material for all-solid-state batteries and all-solid-state batteries containing the same

[0001] The present invention relates to a positive electrode active material for an all-solid-state battery and an all-solid-state battery including the same.

[0002]

[0003] Research on the safety issues and energy density of high-capacity batteries is attracting attention, and all-solid-state batteries are gaining attention as next-generation batteries.

[0004] All-solid-state batteries replace liquid electrolytes that are prone to explosion with solid electrolytes, so they do not use flammable solvents within the battery, and thus do not cause ignition or explosion due to reactions such as the decomposition reaction of conventional electrolytes, thereby ensuring the safety of the battery.

[0005] Additionally, since lithium metal or a lithium alloy can be used as the negative electrode material, the energy density for the mass and volume of the battery can be improved.

[0006] However, solid electrolytes generally have lower lithium ion conductivity than liquid electrolytes, so improving rate characteristics is an important technological challenge in all-solid-state batteries.

[0007]

[0008] Accordingly, one object of the present invention is to provide a positive electrode active material for an all-solid-state battery with improved rate characteristics and an all-solid-state battery including the same.

[0009]

[0010] One embodiment of the present invention is a positive electrode active material in the form of secondary particles formed by agglomeration of a plurality of primary particles, wherein the secondary particles have an average particle diameter (D50) of 2 to 7 μm, and the positive electrode active material has a particle surface aspect resistance (PSAR) of 5 to 9 kΩ·μm. 2 Provides a cathode active material for an all-solid-state battery.

[0011] The above positive electrode active material may include a lithium metal oxide having a nickel-containing layered crystal structure and a coating layer disposed on the lithium metal oxide.

[0012] The content of nickel in the above lithium metal oxide may be 70 mol% or more based on the total mole number of metals excluding lithium.

[0013] The above coating layer may contain a lithium ion conductive oxide.

[0014] The above lithium ion conductive oxide can be represented by the following chemical formula 1.

[0015] [Chemical Formula 1]

[0016] Li x1 D y1 O z1

[0017] In the above chemical formula 1, 0≤x1≤3, 0 <y1≤2, 0<z1≤4이고, D는 Zr, Nb, Ti, V, B, P 또는 이들의 조합이다.

[0018] The above lithium ion conductive oxide can be represented by the following chemical formula 2.

[0019] [Chemical Formula 2]

[0020] Li x2 Zr y2 O z2

[0021] In the above chemical formula 2, 0.5≤x2≤2.2, 0.9≤y2≤1.1, 2.6≤z≤3.4.

[0022] The above lithium metal oxide can be represented by the following chemical formula 3.

[0023] [Chemical Formula 3]

[0024] Li a [Ni x3 Co y3 Mn z3 M w ]O2

[0025] In the above chemical formula 3, 0.8≤a≤1.3, 0.7≤x3<1, 0≤y3≤0.3, 0≤z3≤0.3, 0≤w≤0.2, x3+y3+z3+w=1, and M is Zr, Al, B, Y, Ti, Nb, W, V, Cr, Mo, Ta, Fe, Cu, Zn, Ga, Ge, Ru, Rh, Sn, Sb, Re, Ir, Pt, Pb, Bi, Na, K, Rb, Cs, Ca, Sr, Ba, Mg, Si, Sc or a combination thereof.

[0026]

[0027] Another embodiment of the present invention provides a positive electrode for an all-solid-state battery comprising the positive electrode active material described above.

[0028] Another embodiment of the present invention provides an all-solid-state battery including the positive electrode for the all-solid-state battery.

[0029]

[0030] According to one embodiment of the present invention, the cathode active material for an all-solid-state battery can have improved rate characteristics as the particle surface resistivity constant is controlled.

[0031]

[0032] Figure 1 is an example of an SEM image of a positive electrode active material for an all-solid-state battery.

[0033] Figure 2 is an image segmented into individual primary particle units using image software from the SEM image of Figure 1.

[0034] Figure 3 is a conceptual diagram showing the process of calculating the average active area assuming that the primary particle is spherical.

[0035] The terms first, second, and third, etc., are used to describe, but are not limited to, various parts, components, regions, layers, and / or sections. These terms are used solely to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Accordingly, a first part, component, region, layer, or section described below may be referred to as a second part, component, region, layer, or section without departing from the scope of the present invention.

[0036] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the present invention. As used herein, the singular forms "singular" and "comprising" include plural forms as well, unless the context clearly dictates otherwise. The word "comprising" as used herein specifies a particular feature, region, integer, step, operation, element, and / or component, but does not exclude the presence or addition of other features, regions, integers, steps, operations, elements, and / or components.

[0037] When a part is referred to as being "on" or "over" another part, it can be directly on or over the other part, or there may be other parts intervening. Conversely, when a part is referred to as being "directly on" another part, there are no other parts intervening.

[0038] Although not defined otherwise, all terms, including technical and scientific terms, used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention pertains. Terms defined in commonly used dictionaries are further interpreted to have meanings consistent with the relevant technical literature and the present disclosure, and are not to be construed as ideal or overly formal unless otherwise defined.

[0039] Also, unless otherwise stated, % means weight%, and 1 ppm is 0.0001 weight%.

[0040] In this specification, the term "combination(s) thereof" described in the expression in the Makushi format means one or more mixtures or combinations selected from the group consisting of the components described in the expression in the Makushi format, and means including any one or more selected from the group consisting of said components.

[0041] Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement them. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein.

[0042]

[0043] 1. Cathode active material for all-solid-state batteries

[0044] All-solid-state batteries generally use inorganic solid electrolyte powder as the electrolyte, and unlike general lithium-ion batteries that use liquid electrolytes, their characteristics are largely determined by the surface contact area between the positive electrode active material and the solid electrolyte, surface reaction characteristics, and whether physical surface contact is maintained after expansion / contraction during the charge / discharge process.

[0045] In particular, solid electrolytes generally have the issue of lower ionic conductivity compared to liquid electrolytes, so research on the quantitative properties of positive electrode active materials for all-solid-state batteries that can improve rate characteristics is necessary.

[0046] Accordingly, the inventors of the present invention have conducted repeated research on a method for improving the rate characteristics of an all-solid-state battery, and as a result, have found that it is important to control the surface contact area (hereinafter referred to as “active area” in this specification) of the positive electrode active material for an all-solid-state battery and the solid electrolyte, and the particle surface resistivity constant (PSAR, particle sufrace aspect resistance) calculated using the resistance of the positive electrode active material, thereby completing the present invention.

[0047]

[0048] More specifically, the positive electrode active material for an all-solid-state battery according to one embodiment of the present invention may be in the form of secondary particles formed by agglomeration of a plurality of primary particles.

[0049] In this specification, “secondary particle” means an aggregate, i.e., a secondary structure, in which tens to hundreds of primary particles are aggregated together by physical or chemical bonding between the primary particles without any intentional aggregation or assembly process for the primary particles.

[0050] In addition, “primary particle” refers to the smallest particle unit that can be distinguished as a single lump when observing the cross-section of the positive electrode active material through a scanning electron microscope (SEM), and may be composed of one crystal grain or multiple crystal grains.

[0051] Additionally, “crystal grain” refers to a distinct region in which atoms within a primary particle form a lattice structure with a certain orientation.

[0052]

[0053] In addition, the secondary particles may have an average particle diameter (D50) of 2 to 7 μm, and more specifically, 3 to 6 μm. If the average particle diameter (D50) of the secondary particles is too small, the positive electrode mixture density may become too low, making it difficult to realize high energy density. If the average particle diameter (D50) of the secondary particles is too large, the migration path of lithium ions in the positive electrode active material may become too long, resulting in deterioration of rate characteristics and resistance characteristics. In addition, when the average particle diameter (D50) of the secondary particles satisfies the above range, the rate characteristic improvement effect by adjusting the particle surface resistivity constant of the positive electrode active material described below within the range according to the present invention can be more preferably realized.

[0054] In this specification, the average particle diameter (D50) can be defined as the particle diameter corresponding to 50% of the volume accumulation amount in the particle diameter distribution curve. The average particle diameter (D50) can be measured using, for example, the laser diffraction method.

[0055]

[0056] In particular, the positive electrode active material for an all-solid-state battery according to one embodiment of the present invention has a particle surface aspect resistance (PSAR) of 5 to 9 kΩ·μm. 2 and more specifically, 5 to 8 kΩ·μm 2 It could be.

[0057] The above particle surface resistivity constant can be calculated by multiplying the average active area of ​​the positive electrode active material and the resistance of the positive electrode active material.

[0058] That is, the particle surface resistivity constant can satisfy the following relationship 1.

[0059] [Relationship 1]

[0060] Particle surface resistivity constant (PSAR) = Average active area of ​​positive electrode active material × Resistance of positive electrode active material

[0061] At this time, in this specification, the “active area” of the positive electrode active material means the surface contact area between the positive electrode active material and the solid electrolyte.

[0062]

[0063] First, a method for deriving the average active area of ​​the positive electrode active material is described.

[0064] The average active area of ​​the positive electrode active material can be obtained by using the SEM image and image software of the positive electrode active material as follows.

[0065] More specifically, first, a scanning electron microscope (SEM) image of a positive electrode active material for an all-solid-state battery in the form of a secondary particle formed by agglomeration of multiple primary particles is obtained. Figure 1 is an example of an SEM image of a positive electrode active material for an all-solid-state battery.

[0066] Next, the average radius of the primary particles and the average number of primary particles present in the secondary particles are derived from the SEM images. Fig. 2 is an example of a software image showing the process of deriving the average radius of the primary particles and the average number of primary particles present in the secondary particles.

[0067] Referring to Fig. 2, the boundaries of individual primary particles within secondary particles can be removed through image software, and then the outlines of individual primary particles can be detected to derive an image segmented into individual primary particle units. Through this software image, the average radius of the primary particles and the average number of primary particles present within the secondary particles can be derived. Meanwhile, the number of primary particles at this time refers to the number of primary particles located on the surface of the positive electrode active material observed in the two-dimensional SEM image, and does not mean the number of all primary particles present within the actual three-dimensional positive electrode active material.

[0068] At this time, the average radius of the primary particles derived above may be an area-based average radius calculated based on the area of ​​the primary particles. More specifically, the area-based average radius may be calculated by measuring the area (pixel) occupied by each primary particle within the secondary particle using image software in the SEM image derived from the first step, specifying the radius of a circle having the same area as the radius of each primary particle, and obtaining the average value of the radius of each primary particle within the secondary particle.

[0069] Meanwhile, the average radius of the primary particles derived above and the average number of primary particles present in the secondary particles can be averaged by measuring the values ​​for 10 different secondary particles within the positive electrode active material sample. This can reduce measurement deviation and error.

[0070] Next, the average active area is derived from the average radius of the primary particles derived above and the average number of primary particles present in the secondary particles.

[0071] At this time, the average active area derived above may be a spherical reference average active area derived by assuming that the primary particle is spherical.

[0072] More specifically, Fig. 3 is a conceptual diagram illustrating a process for deriving a spherical reference average active area by assuming that the primary particles are spherical. Referring to Fig. 3, the spherical reference average active area can be calculated using the following method. First, the average radius of the primary particles derived using the above method is assumed to be the radius of the spherical particles. Then, half of the total area of ​​the spherical particles is assumed to be the active area that is in direct contact with the solid electrolyte. Then, the average active area of ​​the positive electrode active material can be calculated by multiplying the active area of ​​each primary particle derived through this by the average number of primary particles present in the secondary particles.

[0073]

[0074] Next, a method for measuring the resistance of the positive electrode active material is described.

[0075] The resistance of the positive electrode active material can be measured using a surface resistance analyzer on a pressed positive electrode active material powder. At this time, the measurement can be performed at a pressure of 25 MPa for 15 seconds, with a sample diameter of approximately 11 mm.

[0076]

[0077] The average active area of ​​the positive electrode active material derived by the above series of methods and the resistance can be multiplied to obtain the particle surface resistivity constant of the positive electrode active material.

[0078] At this time, the particle surface resistivity constant of the positive electrode active material according to the present invention is 5 to 9 kΩ·μm. 2 and more specifically, 5 to 8 kΩ·μm 2 It could be.

[0079] The present inventors calculated the particle surface resistivity constant for a cathode active material for a secondary particle all-solid-state battery using the above method, and experimentally studied the correlation between these particle surface resistivity constants and the capacity or rate characteristics of the all-solid-state battery. As a result, they found that the rate characteristics were maximized, especially, when the particle surface resistivity constant satisfied the above range. The present inventors believe that this is due to the following reasons. The resistance of a cathode active material refers to the sum of the resistance elements that impede the flow of charges passing through the cathode material. This is due to a complex interaction of not only the resistance characteristics of the material itself but also the influence of the area through which charges flow (i.e., the active area). In other words, even for the same material, a small contact area (i.e., the active area) results in a large measured resistance. In addition, during low-rate discharge, the influence of other physical properties is relatively large, so the match between the particle surface resistivity constant and the charge-discharge capacity is not high. However, during high-rate discharge, the influence of resistance relatively increases, so that the match between the particle surface resistivity constant and the charge-discharge capacity is high. Therefore, the particle surface resistivity constant according to the present invention is a parameter that considers both the resistance of the positive electrode material and the area through which charges flow (active area), and appears to have a large correlation with the charge-discharge capacity, especially during high-rate discharge.

[0080]

[0081] Hereinafter, other configurations of the positive electrode active material for an all-solid-state battery according to one embodiment of the present invention will be described in more detail.

[0082] A cathode active material for an all-solid-state battery according to one embodiment of the present invention may include a lithium metal oxide having a nickel-containing layered crystal structure and a coating layer disposed on the lithium metal oxide.

[0083] The lithium metal oxide having a nickel-containing layered crystal structure may further contain nickel and, if necessary, cobalt and / or manganese, and may further contain other doping elements.

[0084] At this time, the content of nickel in the lithium metal oxide may be 70 mol% or more based on the total mole number of metals excluding lithium, and more specifically, 75 mol% or 80 mol% or more. Accordingly, the high-capacity characteristics of the battery can be realized.

[0085] In addition, the coating layer may contain a lithium ion conductive oxide. By containing a lithium ion conductive oxide in the coating layer, not only can the effect of improving life characteristics be achieved through suppression of side reactions with the electrolyte due to the coating layer covering, but also the effect of preserving capacity and rate characteristics can be achieved simultaneously.

[0086] Meanwhile, the coating layer can be formed by a wet coating method using a fluid coating layer device. Accordingly, the entire surface of the lithium metal oxide secondary particle can be covered with a coating layer having a very thin and uniform thickness, thereby more preferably implementing the effect of the coating layer.

[0087]

[0088] The above lithium ion conductive oxide can be more specifically represented by the following chemical formula 1.

[0089] [Chemical Formula 1]

[0090] Li x1 D y1 O z1

[0091] In the above chemical formula 1, 0≤x1≤3, 0 <y1≤2, 0<z1≤4이고, D는 Zr, Nb, Ti, V, B, P 또는 이들의 조합이다.

[0092]

[0093] The above lithium ion conductive oxide can be more specifically represented by the following chemical formula 2.

[0094] [Chemical Formula 2]

[0095] Li x2 Zr y2 O z2

[0096] In the above chemical formula 2, 0.5≤x2≤2.2, 0.9≤y2≤1.1, 2.6≤z≤3.4.

[0097]

[0098] The above lithium metal oxide can be more specifically represented by the following chemical formula 3.

[0099] [Chemical Formula 3]

[0100] Li a [Ni x3 Co y3 Mn z3 M w ]O2

[0101] In the above chemical formula 3, 0.8≤a≤1.3, 0.7≤x3<1, 0≤y3≤0.3, 0≤z3≤0.3, 0≤w≤0.2, x3+y3+z3+w=1, and M is Zr, Al, B, Y, Ti, Nb, W, V, Cr, Mo, Ta, Fe, Cu, Zn, Ga, Ge, Ru, Rh, Sn, Sb, Re, Ir, Pt, Pb, Bi, Na, K, Rb, Cs, Ca, Sr, Ba, Mg, Si, Sc or a combination thereof.

[0102] In the lithium metal oxide of the above chemical formula 1, lithium may be included in an amount corresponding to a, that is, 0.8≤a≤1.3. If a is too small, the capacity may be reduced, and if a is too large, the strength of the sintered positive electrode active material may be increased, making pulverization difficult, and the amount of gas generated may increase due to an increase in lithium byproducts. Considering the effect of improving the capacity characteristics of the positive electrode active material according to the control of the lithium content and the sinterability balance during the production of the active material, the lithium may be included in an amount of 0.9≤a≤1.1 more preferably.

[0103] In the lithium metal oxide of the above chemical formula 1, nickel may be included in an amount corresponding to x3, that is, 0.7≤x3<1, and more specifically, 0.75≤x3<1 or 0.80≤x3<1. When the nickel content satisfies the above range, it is possible to achieve high capacity of the battery.

[0104] In the lithium metal oxide of the above chemical formula 1, cobalt may be included in a content corresponding to y3, i.e., 0≤y3≤0.3. If the cobalt content is too low, grain size growth may be inhibited and output characteristics may deteriorate. If the cobalt content is too high, manufacturing costs may increase and reversible capacity may decrease.

[0105] In the lithium metal oxide of the above chemical formula 1, manganese may be included in a content corresponding to z3, i.e., 0≤z3≤0.3. If the manganese content is too low, the production cost may increase and the stability of the active material may decrease. If the manganese content is too high, the capacity and output characteristics of the battery may decrease.

[0106] In the lithium metal oxide of the above chemical formula 1, M, which is another doping element, may be included in a content corresponding to w, that is, 0≤w1≤0.2. At this time, M may be Zr, Al, B, Y, Ti, Nb, W, V, Cr, Mo, Ta, Fe, Cu, Zn, Ga, Ge, Ru, Rh, Sn, Sb, Re, Ir, Pt, Pb, Bi, Na, K, Rb, Cs, Ca, Sr, Ba, Mg, Si, Sc or a combination thereof. The content of the other doping element may be appropriately selected to implement other doping effects.

[0107]

[0108] 2. All-solid-state battery

[0109] Another embodiment of the present invention provides a positive electrode comprising the positive electrode active material for an all-solid-state battery described above.

[0110] More specifically, the positive electrode may include a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, and the positive electrode active material layer may include the positive electrode active material for the all-solid-state battery described above, a sulfide-based solid electrolyte, and a conductive material. In addition, the positive electrode active material layer may further include a binder.

[0111] At this time, the sulfide-based solid electrolyte may be, for example, a sulfide-based solid electrolyte having an argyrodite-based crystal structure.

[0112] The sulfide-based solid electrolyte having the above-mentioned argyrodite-based crystal structure may be, for example, Li6PS5Cl, Li6PS5Br, Li6PS5I, or a combination thereof, but is not limited thereto.

[0113] The sulfide-based solid electrolyte having the above argyrodite-based crystal structure may have at least a portion of the crystal structure doped with a doping element.

[0114] The above-mentioned conductive material may be, for example, graphite, carbon black, acetylene black, Ketjen black, carbon nanofibers, carbon nanotubes, or a combination thereof.

[0115] The binder may be, for example, polyvinylidene fluoride, styrene butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, vinylidene fluoride / hexafluoropropylene copolymer, polyacrylonitrile, polymethyl methacrylate, or a combination thereof.

[0116] The above-described positive electrode active material layer may further include additives such as fillers, coating agents, dispersants, and ion conductive aids in addition to the above-described positive electrode active material, solid electrolyte, binder, and conductive agent.

[0117]

[0118] Another embodiment of the present invention provides an all-solid-state battery comprising a positive electrode, a negative electrode, and a solid electrolyte layer disposed therebetween, wherein the positive electrode comprises the positive electrode active material for an all-solid-state battery as described above.

[0119] Description of the above anodes is omitted as they have been explained previously.

[0120] The above solid electrolyte layer may include a sulfide-based solid electrolyte.

[0121] The above sulfide-based solid electrolyte is, for example, Li 7-x PS 6-x Cl x , 0≤x≤2, Li 7-x PS 6-x Br x , 0≤x≤2, and Li 7-x PS 6-x I x , may be an argyrodite-type compound including at least one selected from 0≤x≤2. In particular, the sulfide-based solid electrolyte may be an argyrodite-type compound including at least one selected from Li6PS5Cl, Li6PS5Br, and Li6PS5I. However, the present invention is not limited thereto.

[0122] The above sulfide-based solid electrolyte may have at least a portion of the crystal structure of the above-described argyrodite-type compound doped with a doping element.

[0123] The above solid electrolyte layer may further include a binder. The binder included in the solid electrolyte layer may be, but is not limited to, styrene butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, etc., and any binder used in the relevant technical field may be used. The binder of the solid electrolyte layer may be the same as or different from the binder included in the positive electrode active material layer and the negative electrode active material layer.

[0124]

[0125] The above negative electrode may include a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector, and the negative electrode active material layer may include a negative electrode active material.

[0126] The above negative active material includes a material capable of reversibly intercalating / deintercalating lithium ions, lithium metal, an alloy of lithium metal, a material capable of doping and dedoping lithium, or a transition metal oxide.

[0127] The material capable of reversibly intercalating / deintercalating the lithium ions is a carbon material, and any carbon-based negative electrode active material generally used in lithium ion secondary batteries can be used, and representative examples thereof include crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon include graphite such as natural graphite or artificial graphite in an amorphous, plate-like, flake-like, spherical, or fibrous form, and examples of the amorphous carbon include soft carbon (low-temperature calcined carbon) or hard carbon, mesophase pitch carbide, calcined coke, etc.

[0128] As the above lithium metal alloy, an alloy of lithium and a metal selected from the group consisting of Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn can be used.

[0129] Materials capable of doping and dedoping the lithium include Si, SiOx (0< x < 2), Si-Y alloy (wherein Y is an element selected from the group consisting of alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, transition metals, rare earth elements, and combinations thereof, and is not Si), Sn, SnO2, Sn-Y (wherein Y is an element selected from the group consisting of alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, transition metals, rare earth elements, and combinations thereof, and is not Sn), and at least one of these may be mixed with SiO2 for use. The above element Y may be selected from the group consisting of Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ti, Ge, P, As, Sb, Bi, S, Se, Te, Po, and combinations thereof.

[0130] Examples of the above transition metal oxides include vanadium oxide, lithium vanadium oxide, etc.

[0131] The above negative active material layer also includes a binder and may optionally further include a conductive material.

[0132] The above binder serves to adhere the negative electrode active material particles well to each other and also to adhere the negative electrode active material well to the current collector, and representative examples thereof include, but are not limited to, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc.

[0133] The above conductive material is used to provide conductivity to the electrode, and in the battery to be formed, any material that does not cause a chemical change and is electronically conductive can be used. Examples of conductive materials that can be used include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, and carbon fiber; metal-based materials such as metal powder or metal fiber such as copper, nickel, aluminum, and silver; conductive polymer materials such as polyphenylene derivatives; or conductive materials containing mixtures thereof.

[0134] The current collector may be selected from the group consisting of copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, polymer substrate coated with a conductive metal, and combinations thereof.

[0135]

[0136] Hereinafter, embodiments of the present invention will be described in more detail through examples. However, the following examples are merely preferred embodiments of the present invention, and the present invention is not limited to the following examples.

[0137]

[0138] Example 1

[0139] (1) Manufacturing of positive electrode active material

[0140] (lithium metal oxide formation) Ni 0.85 Co 0.12 Mn 0.03 A mixture was formed by mixing a metal hydroxide precursor with a composition of (OH)2 and LiOH·H2O as a lithium raw material at a molar ratio of 1:1.02.

[0141] 1 kg of the above mixture was loaded into a tube and fired at a temperature of 720°C for 8 hours. During the firing, pure O2 was supplied so that the O2 concentration could be maintained at 99% or higher, so that LiNi 0.85 Co 0.12 Mn 0.03 Lithium metal oxide with O2 composition was formed.

[0142] (Preparation of coating solution) Next, lithium was dissolved in dehydrated ethanol, and zirconium(IV) tetrapropoxide (70 wt. % in 1-propanol) was added and stirred to prepare a coating solution containing lithium ions and zirconium ions. At this time, the concentration of zirconium ions in the coating solution was set to 0.11 mol / L.

[0143] (Coating solution spraying) 420 mL of coating solution was sprayed onto 1 kg of the lithium transition metal oxide formed above using a fluid coating device (MP-01, POWREX).

[0144] (Coating heat treatment) After that, the lithium transition metal oxide sprayed with the above coating solution was loaded into Saggar, and then heat treated at 300°C for 3 hours while supplying oxygen in a box-type electric furnace, thereby manufacturing a cathode active material in which an amorphous coating layer of Li2ZrO3 was formed on the surface of the lithium transition metal oxide.

[0145] (2) Lithium secondary battery manufacturing

[0146] A mixture paste was prepared by mixing 75 wt% of the above-mentioned manufactured positive electrode active material, 22 wt% of argyrodite solid electrolyte (Li6PS5Cl), and 3 wt% of Super C65 as a conductive material with a solvent containing a small amount of binder dissolved therein. An electrode plate was manufactured using the mixture paste, and the plate was dried to prepare a composite electrode plate for the positive electrode.

[0147] First, 100 mg of argyrodite solid electrolyte (Li6PS5Cl) that functions as a separator was loaded into a jig for evaluating an all-solid-state battery, and pressurized at 300 MPa or more to a thickness of approximately 800 μm. Then, a positive electrode plate was placed on one side, and a second pressurization was performed to manufacture the positive electrode part.

[0148] Afterwards, a Li-In alloy was placed on the other side and appropriate pressure was applied to produce a battery for evaluating all-solid-state batteries.

[0149]

[0150] Example 2

[0151] At the lithium metal oxide formation stage, Ni 0.85 Co 0.12 Mn 0.03 A cathode active material and an all-solid-state battery were manufactured in the same manner as in Example 1, except that the metal hydroxide precursor of (OH)2 composition and LiOH·H2O as a lithium raw material were mixed at a molar ratio of 1:1.03 and the calcination temperature was set to 730°C.

[0152]

[0153] Example 3

[0154] In the lithium metal oxide formation step, a positive electrode active material and an all-solid-state battery were manufactured in the same manner as in Example 1, except that the sintering temperature was set to 730°C.

[0155]

[0156] Comparative Example 1

[0157] At the lithium metal oxide formation stage, Ni 0.83 Co 0.12 Mn0.05 A cathode active material and an all-solid-state battery were manufactured in the same manner as in Example 1, except that the metal hydroxide precursor of (OH)2 composition and LiOH·H2O as a lithium raw material were mixed at a molar ratio of 1:1.03.

[0158]

[0159] Comparative Example 2

[0160] At the lithium metal oxide formation stage, Ni 0.83 Co 0.12 Mn 0.05 A cathode active material and an all-solid-state battery were manufactured in the same manner as in Example 1, except that the metal hydroxide precursor of (OH)2 composition and LiOH·H2O as a lithium raw material were mixed at a molar ratio of 1:1.03 and the calcination temperature was set to 730°C.

[0161]

[0162] Comparative Example 3

[0163] At the lithium metal oxide formation stage, Ni 0.85 Co 0.12 Mn 0.03 A cathode active material and an all-solid-state battery were manufactured in the same manner as in Example 1, except that the metal hydroxide precursor of (OH)2 composition and LiOH·H2O as a lithium raw material were mixed at a molar ratio of 1:1.03 and the calcination temperature was set to 730°C.

[0164]

[0165] Tables 1 and 2 below summarize the results of Experimental Examples 1 and 2 described below.

[0166] Secondary particle average diameter (D50, μm) Primary particle average radius (μm) Average number of primary particles in secondary particles Average active area (μm) 2 )Resistance (Ω)PSAR (kΩ· μm 2)Example 13.8620.229276.00091.26176.496.98Example 24.1800.243256.00095.21177.097.34Example 33.9300.218321.00096.21976.297.34Comparative Example 14.1800.258296.000123.50081.9210.12Comparative Example 23.7720.259306.000128.59281.1210.43Comparative Example 33.8890.263310.000134.67778.7110.60

[0167] Initial Capacity Rate Characteristics Charge Capacity Discharge Capacity Initial Efficiency 0.1C 0.5C 1.0C 0.5C / 0.1C 1.0C / 0.1C mAh / g mAh / g % mAh / g mAh / g mAh / g % % Example 1 226.2 23 213.175 0.94 2212.448 197.139 184.54 0 9 2.79 4 8 6.863 Example 2 226.2 9 5 212.63 6 0.94 0 211.97 6 196.929 181.25 8 9 2.90 185.509 Example 3 221.60 3209.58 20.94 6 209.130 193.90 177.00 9 2.71 7 8 4.641 Comparative Example 1215.499203.0500.942202.448184.619166.03991.19382.015Comparative Example 2216.774205.7790.949205.291188.197168.09891.67381.883Comparative Example 3220.853208.0400.942207.505188.226166.94990.70980.456

[0168]

[0169] Experimental Example 1: Analysis of the properties of positive electrode active materials

[0170] (1) Evaluation of secondary particle average diameter (D50)

[0171] For the active material powder, the particle size corresponding to 50% of the cumulative volume was measured using the laser diffraction method.

[0172] (2) Evaluation of the average radius of primary particles, evaluation of the average number of primary particles in secondary particles

[0173] SEM (scanning electron microscope) images were obtained from the positive electrode active material samples prepared in the above examples and comparative examples. The magnification of the SEM images was 15,000x.

[0174] Thereafter, the average radius of the primary particles and the average number of primary particles present in the secondary particles were derived from the SEM images. At this time, the average radius based on area was calculated.

[0175] Specifically, the area-based average radius was calculated by measuring the area (pixel) occupied by each primary particle within the secondary particle using image software on the SEM image derived from the first step, specifying the radius of a circle with the same area as the radius of each primary particle, and calculating the average value of the radius of each primary particle within the secondary particle.

[0176] In addition, the number of primary particles present within the secondary particles was calculated from the SEM image using image software. In this case, the number of primary particles refers to the number of primary particles located on the surface of the positive electrode active material observed in the two-dimensional SEM image, and does not refer to the number of all primary particles present within the actual three-dimensional positive electrode active material.

[0177] Meanwhile, the average radius of the primary particles and the average number of primary particles present in the secondary particles were finally derived as the average values ​​of the values ​​measured for 10 different secondary particles in the positive electrode active material sample.

[0178] (3) Average active area evaluation

[0179] The average active area was derived from the average radius of the primary particles derived above and the average number of primary particles present in the secondary particles. At this time, the average active area based on a sphere was derived.

[0180] Referring to Fig. 3, the average active area based on a sphere can be calculated using the following method. First, the average radius of the primary particles derived above is assumed to be the radius of the spherical particles. Then, half of the total area of ​​the spherical particles is assumed to be the active area in direct contact with the solid electrolyte. Then, the average active area of ​​the positive electrode active material can be calculated by multiplying the active area of ​​each primary particle derived through this by the average number of primary particles present in the secondary particles.

[0181] (4) Resistance evaluation

[0182] The resistance of the positive electrode active material was measured using a surface resistance analyzer on a pressed positive electrode active material powder. The measurement pressure was maintained at 25 MPa for 15 seconds, and the sample diameter was approximately 11 mm.

[0183] (5) Evaluation of particle surface aspect resistance (PSAR)

[0184] The particle surface resistivity constant was calculated by multiplying the average active area and resistance derived above.

[0185] That is, the particle surface resistivity constant satisfies the following relationship 1.

[0186] [Relationship 1]

[0187] Particle surface resistivity constant (PSAR) = Average active area of ​​positive electrode active material × Resistance of positive electrode active material

[0188]

[0189] Experimental Example 2: Evaluation of the electrochemical properties of an all-solid-state battery.

[0190] (1) Initial capacity and initial efficiency evaluation

[0191] After fabricating the all-solid-state battery half-cell, it was aged at 25°C for 12 hours and then subjected to charge-discharge tests at 30°C. To evaluate the initial capacity, the reference capacity was set to 210 mAh / g, and the battery was charged to 4.25 V at a constant current of 0.1 C. After switching to constant voltage, the battery was charged until the end current reached 0.05 C. After a 10-minute rest time after charging, the battery was discharged to 2.5 V at a constant current of 0.1 C, using the reference capacity of 200 mAh / g.

[0192] (2) Rate characteristic evaluation

[0193] The rate characteristics were evaluated by comparing the initial discharge capacity at 0.1C charge-0.1C discharge and the initial discharge capacity at 0.1C charge-0.5C / 1.0C discharge.

[0194]

[0195] Referring to Table 1 and Table 2, it was confirmed that the particle surface resistivity constant (PSAR) of the derived positive electrode active material had a nearly linear correlation with the electrochemical characteristics of the all-solid-state battery, especially the rate characteristics, and that the correlation was very large.

[0196] Specifically, the particle surface resistivity constant is 5 to 9 kΩ·μm. 2 In the case of Examples 1 to 3, which are in the range, it was confirmed that the 0.5C discharge capacity was 190 mAh / g or more, the 1.0C discharge capacity was 170 mAh / g or more, the 0.5C / 0.1C rate characteristic was 92.0% or more, and the 1.0C / 0.1C rate characteristic was 83.0% or more, which was implemented very well.

[0197] On the other hand, in the case of Comparative Examples 1 to 3 in which the particle surface resistivity constant is outside the above range, it was confirmed that the 0.5C discharge capacity, 1.0C discharge capacity, 0.5C / 0.1C rate characteristics, and 1.0C / 0.1C rate characteristics were lower than in Examples 1 to 3.

[0198]

[0199] Although the preferred embodiments of the present invention have been described above, the present invention is not limited thereto, and various modifications can be made within the scope of the patent claims, the detailed description of the invention, and the attached drawings, and it is obvious that this also falls within the scope of the present invention.

[0200] Accordingly, the actual scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A cathode active material in the form of a secondary particle formed by the agglomeration of multiple primary particles. The above secondary particles have an average particle diameter (D50) of 2 to 7 μm, and the positive electrode active material has a particle surface aspect resistance (PSAR) of 5 to 9 kΩ·μm. 2 Cathode active material for all-solid-state batteries.

2. In paragraph 1, The above cathode active material is an all-solid-state battery cathode active material including a lithium metal oxide having a nickel-containing layered crystal structure and a coating layer disposed on the lithium metal oxide.

3. In paragraph 2, A cathode active material for an all-solid-state battery, wherein the nickel content in the lithium metal oxide is 70 mol% or more based on the total mole number of metals excluding lithium.

4. In paragraph 2, The above coating layer is a cathode active material for an all-solid-state battery containing a lithium ion conductive oxide.

5. In paragraph 4, The above lithium ion conductive oxide is a cathode active material for an all-solid-state battery represented by the following chemical formula 1: [Chemical Formula 1] Li x1 D y1 Oh z1 In the above chemical formula 1, 0≤x1≤3, 0 <y1≤2, 0<z1≤4이고, D는 Zr, Nb, Ti, V, B, P 또는 이들의 조합이다.

6. In paragraph 4, The above lithium ion conductive oxide is a cathode active material for an all-solid-state battery represented by the following chemical formula 2: [Chemical formula 2] Li x2 Zr y2 About z2 In the above chemical formula 2, 0.5≤x2≤2.2, 0.9≤y2≤1.1, 2.6≤z≤3.

4.

7. In paragraph 2, The above lithium metal oxide is a cathode active material for a lithium secondary battery represented by the following chemical formula 3: [Chemical Formula 3] Li a [Ni x3 Co y3 Mr z3 M w ]O2 In the chemical formula 3, 0.8≤a≤1.3, 0.7≤x3<1, 0≤y3≤0.3, 0≤z3≤0.3, 0≤w≤0.2, and x3+y3+z3+w=1, and M is Zr, Al, B, Y, Ti, Nb, W, V, Cr, Mo, Ta, Fe, Cu, Zn, Ga, Ge, Ru, Rh, Sn, Sb, Re, Ir, Pt, Pb, Bi, Na, K, Rb, Cs, Ca, Sr, Ba, Mg, Si, Sc or a combination thereof.

8. A cathode for an all-solid-state battery comprising the cathode active material of clause 1.

9. An all-solid-state battery comprising the positive electrode for an all-solid-state battery of clause 8.

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