Positive electrode active material for lithium secondary battery and method for producing the same, positive electrode for lithium secondary battery including the same, lithium secondary battery, and all-solid-state secondary battery

Abstract

The present invention relates to a positive electrode active material for lithium secondary batteries, which comprises particles containing a lithium transition metal composite oxide and a coating layer containing ZrO2 and Li6Zr2O7 located on the surface of the particles, a method for producing the same, and a positive electrode, lithium secondary battery, and all-solid-state secondary battery that include the same.

Description

[Technical Field]

[0001] The present invention relates to a positive electrode active material for a lithium secondary battery, a method for producing the same, a positive electrode for a lithium secondary battery containing the same, a lithium secondary battery, and an all-solid-state secondary battery. [Background technology]

[0002] Lithium secondary batteries, which have high energy density yet are easy to carry, are primarily used as power sources for mobile information terminals such as mobile phones, laptops, and smartphones. Recently, active research has been conducted into using high-energy-density lithium secondary batteries as power sources for hybrid and electric vehicles or as power storage sources.

[0003] Various positive electrode active materials have been investigated to realize lithium secondary batteries suitable for these applications. Among these, lithium nickel oxide, lithium nickel manganese cobalt composite oxide, lithium nickel cobalt aluminum composite oxide, and lithium cobalt oxide are commonly used as positive electrode active materials. However, these positive electrode active materials suffer from structural collapse or cracking after repeated charge / discharge cycles, resulting in reduced long-term life of the lithium secondary battery and increased resistance, resulting in unsatisfactory capacity characteristics. Therefore, there is a need for the development of new positive electrode active materials that can achieve high capacity and high energy density while maintaining long-term life characteristics.

[0004] Recently, development of all-solid-state secondary batteries has been actively pursued in response to reports of the risk of explosion of batteries using liquid electrolytes. However, solid electrolytes have lower ionic conductivity than liquid electrolytes, which creates problems such as resistance at the interface with solid particles, such as the cathode active material, in the battery, and the formation of a depletion layer at the solid-solid junction, resulting in reduced ionic conductivity. There is a need for the development of cathode active materials that can be used with such solid electrolytes, as well as cathode active materials that can improve the overall performance of all-solid-state secondary batteries, including their capacity and long-life characteristics. Summary of the Invention [Problem to be solved by the invention]

[0005] The coating layer on the surface of the positive electrode active material improves the structural stability of the positive electrode active material and increases ionic conductivity, and mass production is made possible by applying a dry coating method that does not use organic solvents. In batteries that use solid electrolytes, the coating layer eliminates the problem of depletion layers between solid particles and suppresses reactions between the positive electrode active material and the solid electrolyte, solving interface problems. The coating layer also improves the capacity and life characteristics of lithium secondary batteries. [Means for solving the problem]

[0006] In one embodiment, there is provided a positive electrode active material for a lithium secondary battery, comprising particles containing a lithium transition metal composite oxide, and a coating layer located on the surface of the particles and containing ZrO2 and Li6Zr2O7.

[0007] In one embodiment, there is provided a method for producing a positive electrode active material for a lithium secondary battery, the method comprising dry-mixing 100 parts by mole of particles containing a lithium transition metal composite oxide and 0.1 to 0.6 parts by mole of a zirconium raw material, followed by heat treatment at 420°C to 580°C.

[0008] In one embodiment, a positive electrode for a lithium secondary battery is provided that includes a positive electrode active material.

[0009] In one embodiment, a lithium secondary battery is provided that includes a positive electrode, a negative electrode, and an electrolyte.

[0010] In one embodiment, an all-solid-state secondary battery is provided that includes a positive electrode, a negative electrode, and a solid electrolyte layer located between the positive electrode and the negative electrode. [Effects of the Invention]

[0011] According to one embodiment, a positive electrode active material for a lithium secondary battery includes a coating layer of a mixed phase of ZrO and LiZrO, which improves structural stability and ionic conductivity. For example, the reaction with sulfide-based solid electrolyte particles is effectively suppressed, thereby improving capacity characteristics and life characteristics.

[0012] A method for manufacturing a positive electrode active material for a lithium secondary battery according to an embodiment employs a dry coating method, which is advantageous for mass production and enables the formation of a good coating layer with a uniform thickness, thereby improving not only the productivity and economy of the positive electrode active material but also the capacity characteristics and life characteristics.

[0013] A positive electrode for a lithium secondary battery according to an embodiment, and a lithium secondary battery and an all-solid-state secondary battery including the positive electrode can achieve excellent capacity characteristics and life characteristics. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a cross-sectional view schematically illustrating an all-solid-state secondary battery according to an embodiment. [Figure 2] 1 is a cross-sectional view schematically illustrating an all-solid-state secondary battery according to an embodiment. [Figure 3] 1 is a graph showing the initial charge capacity (gray bars) and the initial discharge capacity (black bars) of the batteries of Examples 1 to 5 and Comparative Examples 1 to 8. [Figure 4] 1 is a graph showing the initial discharge capacity (black bars) and the 100-cycle capacity retention rate (dotted line) of the batteries of Examples 1 to 5 and Comparative Examples 1 to 8. [Figure 5]1 is a graph showing the capacity retention rate as a function of the number of cycles, that is, the life characteristics, for Example 3 and Comparative Examples 3, 4, 6, and 7. [Figure 6] 1 shows scanning electron microscopy (SEM) images of the surfaces of large particles (left) and small particles (right) in the positive electrode active material of Example 3. [Figure 7] 1 shows SEM images of the surfaces of large and small particles in Comparative Example 1. [Figure 8] 10 shows SEM images of the surfaces of large and small particles in Comparative Example 3. [Figure 9] 10 shows SEM images of the surfaces of large and small particles in Comparative Example 4. [Figure 10] 10 shows SEM images of the surfaces of large and small particles in Comparative Example 5. [Figure 11] 10 shows SEM images of the surfaces of large and small particles in Comparative Example 6. [Figure 12] 1 shows SEM-EDS (SEM-Energy Dispersive X-ray Spectroscopy) images of the surfaces of large particles (left side) and small particles (right side) in the positive electrode active material of Example 3. [Figure 13] 1 shows SEM-EDS images of large and small particles in Comparative Example 1. [Figure 14] 10 shows SEM-EDS images of large and small particles in Comparative Example 3. [Figure 15] 10 shows SEM-EDS images of large and small particles in Comparative Example 4. [Figure 16] 10 shows SEM-EDS images of large and small particles in Comparative Example 5. [Figure 17] 10 shows SEM-EDS images of large and small particles in Comparative Example 6. [Figure 18] 1 is an image showing the distribution of Zr and Ni obtained by analyzing a cross section of a small particle in the positive electrode active material of Example 4 by STEM-EDS (Scanning Transmission Electron Microscopy-EDS). [Figure 19]1 is a high-resolution transmission electron microscopy (HRTEM) image of a cross section of a small particle in the positive electrode active material of Example 4. [Figure 20] This is the result of performing an Inverse Fast Fourier Transform (IFFT) on the area indicated by the square box in FIG. [Figure 21] The image in Figure 20 shows an enlarged view of the ZrO2 region (left) and an enlarged view of the Li6Zr2O7 region (right). DETAILED DESCRIPTION OF THE INVENTION

[0015] Although the present invention may be embodied in many different forms, it is not limited to the embodiments set forth herein.

[0016] The terms used herein are merely used to describe exemplary embodiments and are not intended to limit the present invention. The singular expressions include the plural expressions unless the context clearly indicates otherwise.

[0017] As used herein, "combinations thereof" refers to mixtures, laminates, composites, copolymers, alloys, blends, reaction products, and the like of compositions.

[0018] It should be understood that the terms "comprises," "includes," or "has" are intended to specify the presence of embodied features, numbers, steps, components, or combinations thereof, but do not preclude the possible presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0019] In the drawings, the thickness of various layers and regions is exaggerated for clarity, and similar parts are designated by the same reference numerals throughout the specification. When a layer, film, region, plate, or other part is said to be "on" or "above" another part, this includes not only the case where it is "directly on" another part, but also the case where there is another part between them. Conversely, when a part is said to be "directly on" another part, it means that there is no other part between them.

[0020] Furthermore, the term "layer" as used herein includes not only shapes formed on the entire surface when observed in a plan view, but also shapes formed on a portion of the surface.

[0021] The average particle size can be measured by a method well known to those skilled in the art, for example, by using a particle size analyzer or by using a transmission electron microscope image or a scanning electron microscope image. Alternatively, the average particle size can be calculated by measuring using a dynamic light scattering method, counting the number of particles in each particle size range, and then calculating the average particle size. Unless otherwise defined, the average particle size is the diameter (D) of particles whose cumulative volume is 50% by volume in the particle size distribution. 50 ) and unless otherwise defined, the average particle size is the diameter (D) of the particle that makes up 50% of the cumulative volume in the particle size distribution obtained by measuring the size (diameter or length of the major axis) of 20 or more particles randomly selected in a scanning electron microscope image. 50 ) may be taken as the average particle size.

[0022] Here, "or" is not to be construed in an exclusive sense; for example, "A or B" is to be construed as including A, B, A+B, etc.

[0023] The term "metal" is understood to include general metals, transition metals, and metalloids.

[0024] positive electrode active material A positive electrode active material for a lithium secondary battery according to one embodiment includes particles containing a lithium transition metal composite oxide and a coating layer containing ZrO2 and Li6Zr2O7 located on the surface of the particles.

[0025] Here, the term "lithium secondary battery" is used as a concept including lithium ion batteries, semi-solid batteries, polymer batteries, all-solid batteries, etc., which use non-aqueous electrolytes. The positive electrode active material has advantages such as low reactivity with solid electrolytes and low interfacial resistance between solid particles, making it advantageous for application to all-solid batteries, semi-solid batteries, etc. As an example, the positive electrode active material may be a positive electrode active material for all-solid secondary batteries.

[0026] Coating layer According to one embodiment, the coating layer of the positive electrode active material includes a mixed phase of ZrO2 and Li6Zr2O7. The coating layer may include ZrO2, which has relatively high crystallinity, and Li6Zr2O7, which has lower crystallinity. The presence or absence of ZrO2 and Li6Zr2O7 can be determined, for example, through inverse FFT analysis of an HRTEM image. The coating layer containing ZrO2 and Li6Zr2O7 can further facilitate the movement of lithium ions on the surface of the positive electrode active material, improve the structural stability of the positive electrode active material, and reduce reactivity with the solid electrolyte, thereby improving interfacial resistance.

[0027] Here, the coating layer can be expressed as a buffer layer, a protective layer, or the like.

[0028] The coating layer may further include an amorphous region. For example, the coating layer may include a ZrO2 crystalline phase, a Li6Zr2O7 crystalline phase, and a Zr-containing amorphous region. Such a coating layer has a thin and uniform thickness and can improve lithium ion conductivity and the life characteristics of the positive electrode active material.

[0029] The coating layer may be in the form of a continuous film or islands. The coating layer may be prepared by a dry coating method described below, and may be well-formed with a uniform thickness on the surface of the positive electrode active material without agglomeration or localized presence of the coating. For example, the coating layer may be present in the form of a continuous and uniform film on the surface of particles containing a lithium transition metal composite oxide. In this case, the capacity and life characteristics of the positive electrode active material may be further improved.

[0030] The thickness of the coating layer may be 5 nm to 300 nm, for example, 5 nm to 200 nm, 5 nm to 100 nm, 5 nm to 80 nm, or 10 nm to 50 nm. When the coating layer has a thickness within this range, an increase in resistance due to the coating can be suppressed, the positive electrode active material can be effectively protected, and ion conductivity can be improved, thereby improving the electrochemical characteristics of the lithium secondary battery.

[0031] According to an embodiment, the coating layer may be formed on the surface of the positive electrode active material with a uniform thickness, without being locally present or aggregated. For example, the standard deviation of the thickness of the coating layer may be 10% or less, or 5% or less, relative to the diameter of the positive electrode active material, and may be 100 nm or less, 50 nm or less, or 30 nm or less.

[0032] The Zr content of the coating layer may be 0.1 to 0.6 molar parts, for example, 0.1 to 0.5 molar parts, or 0.1 to 0.4 molar parts, relative to 100 molar parts of the particles containing the lithium transition metal composite oxide. The Zr content of the coating layer may be 0.1 to 6 wt. % relative to 100 wt. % of the positive electrode active material, for example, 0.5 to 6 wt. % or 1 to 5.5 wt. The Zr content of the coating layer may be 0.1 to 10 atomic %, for example, 0.1 to 8 atomic %, 0.1 to 7 atomic %, 0.5 to 6.5 atomic %, or 1 to 6 atomic %. When the Zr content is within the above range, the coating layer adequately protects the positive electrode active material without acting as a resistor and is uniformly thick without agglomerating or being present locally on the surface of the positive electrode active material, thereby effectively improving the lifespan characteristics of the positive electrode active material without reducing its capacity. If the Zr content is too high, the coating layer may become too thick and act as a resistor, which may reduce the charge / discharge capacity of the positive electrode active material. Conversely, if the Zr content is too low, the coating layer may not adequately function as a buffer, which may reduce the lifespan characteristics of the positive electrode active material.

[0033] Lithium transition metal composite oxide particles In one embodiment of the positive electrode active material, the lithium transition metal composite oxide particles refer to a type of core having a particle shape containing a lithium transition metal composite oxide, and may be any commonly used positive electrode active material without limitation. The lithium transition metal composite oxide particles may be a compound capable of reversible intercalation and deintercalation of lithium, and may include a compound represented by any one of the following chemical formulas:

[0034] Li a A 1-b X b D2(0.90≦a≦1.8, 0≦b≦0.5); Li a A 1-b X b O2-c D c (0.90≦a≦1.8、0≦b≦0.5、0≦c≦0.05); Li a HAVE BEEN 1-b X b O 2-c D c (0.90≦a≦1.8、0≦b≦0.5、0≦c≦0.05); Li a HAVE BEEN 2-b X b O 4-c D c (0.90≦a≦1.8、0≦b≦0.5、0≦c≦0.05); Li a Ni 1-b-c Co b X c D α (0.90≦a≦1.8、0≦b≦0.5、0≦c≦0.5、0<α≦2); Li a Ni 1-b-c Co b X c O 2-α T α (0.90≦a≦1.8、0≦b≦0.5、0≦c≦0.05、0<α<2); Li a Ni 1-b-c Co b X c O 2-α T2(0.90≦a≦1.8、0≦b≦0.5、0≦c≦0.05、0<α<2); Li a Ni 1-b-c Mr b X c D α (0.90≦a≦1.8、0≦b≦0.5、0≦c≦0.05、0<α≦2); Li a Ni 1-b-c Mr b X c O 2-α T α (0.90≦a≦1.8、0≦b≦0.5、0≦c≦0.05、0<α<2); Li a Ni 1-b-c Mr b X c O2-α T2(0.90≦a≦1.8、0≦b≦0.5、0≦c≦0.05、0<α<2); Li a Ni b E c G d O2(0.90≦a≦1.8、0≦b≦0.9、0≦c≦0.5、0.001≦d≦0.1); Li a Ni b Co c Mn d G e O2(0.90≦a≦1.8、0≦b≦0.9、0≦c≦0.5、0≦d≦0.5、0.001≦e≦0.1); Li a NiG b O2(0.90≦a≦1.8、0.001≦b≦0.1); Li a CoG b O2(0.90≦a≦1.8、0.001≦b≦0.1); Li a Mn 1-b G b O2(0.90≦a≦1.8、0.001≦b≦0.1); Li a Mn2G b O4(0.90≦a≦1.8、0.001≦b≦0.1); Li a Mn 1-g G g PO4(0.90≦a≦1.8、0≦g≦0.5); QO2;QS2;LiQS2; V2O5;LiV2O5; LiZO2; LiNiVO4; Li (3-f) J2(PO4)3(0≦f≦2); Li (3-f) Fe2(PO4)3(0≦f≦2); Li a FePO4(0.90≦a≦1.8)。 In the above chemical formula, A is selected from the group consisting of Ni, Co, Mn, and combinations thereof; X is selected from the group consisting of Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, rare earth elements, and combinations thereof; D is selected from the group consisting of O, F, S, P, and combinations thereof; E is selected from the group consisting of Co, Mn, and combinations thereof; T is selected from the group consisting of F, S, P, and combinations thereof; G is selected from the group consisting of Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, and combinations thereof; Q is selected from the group consisting of Ti, Mo, Mn, and combinations thereof; Z is selected from the group consisting of Cr, V, Fe, Sc, Y, and combinations thereof; and J is selected from the group consisting of V, Cr, Mn, Co, Ni, Cu, and combinations thereof.

[0035] The lithium transition metal composite oxide can include, for example, lithium cobalt oxide (LCO), lithium nickel oxide (LNO), lithium nickel cobalt oxide (NC), lithium nickel cobalt aluminum oxide (NCA), lithium nickel cobalt manganese oxide (NCM), lithium nickel manganese oxide (NM), lithium manganese oxide (LMO), lithium iron phosphate oxide (LFP), or a combination thereof.

[0036] The lithium transition metal composite oxide may be, for example, a lithium nickel-based oxide represented by the following chemical formula 1, a lithium cobalt-based oxide represented by the following chemical formula 2, a lithium iron phosphate-based compound represented by the following chemical formula 3, or a cobalt-free lithium nickel-manganese-based oxide represented by the following chemical formula 4.

[0037] [Chemical formula 1] Li a1 Ni x1 M 1 y1 M 2 z1 O 2-b1 X b1 In the above chemical formula 1, 0.9≦a1≦1.8, 0.3≦x1≦1, 0≦y1≦0.7, 0≦z1≦0.7, 0.9≦x1+y1+z1≦1.1, and 0≦b1≦0.1; M 1 and M 2 are each independently one or more elements selected from the group consisting of Al, B, Ba, Ca, Ce, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Zn, and Zr, and X is one or more elements selected from the group consisting of F, P, and S.

[0038] [Chemical formula 2] Li a2 Co x2 M 3 y2 O 2-b2 X b2 In the above chemical formula 2, 0.9≦a2≦1.8, 0.7≦x2≦1, 0≦y2≦0.3, 0.9≦x2+y2≦1.1, and 0≦b2≦0.1; M 3 is one or more elements selected from the group consisting of Al, B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mn, Mo, Ni, Se, Si, Sn, Sr, Ti, V, W, Y, Zn, and Zr, and X is one or more elements selected from the group consisting of F, P, and S.

[0039] [Chemical formula 3] Li a3 Fe x3 M 4 y3 PO 4-b3 X b3 In the above chemical formula 3, 0.9≦a3≦1.8, 0.6≦x3≦1, 0≦y3≦0.4, and 0≦b3≦0.1; M 4 is one or more elements selected from the group consisting of Al, B, Ba, Ca, Ce, Co, Cr, Cu, Mg, Mn, Mo, Ni, Se, Si, Sn, Sr, Ti, V, W, Y, Zn, and Zr, and X is one or more elements selected from the group consisting of F, P, and S.

[0040] [Chemical formula 4] Lia4 Ni x4 Mn y4 M 5 z4 O 2-b4 X b4 In the above chemical formula 4, 0.9 ≦ a4 ≦ 1.8, 0.8 ≦ x4 < 1, 0 < y4 ≦ 0.2, 0 ≦ z4 ≦ 0.2, 0.9 ≦ x4 + y4 + z4 ≦ 1.1, and 0 ≦ b4 ≦ 0.1, and M 5 is one or more elements selected from the group consisting of Al, B, Ba, Ca, Ce, Cr, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, and Zr, and X is one or more elements selected from the group consisting of F, P, and S.

[0041] As an example, the lithium transition metal composite oxide may be a lithium nickel-based oxide represented by Chemical Formula 1, for example, a high-nickel-based oxide. That is, the content of nickel with respect to 100 mol% of the metal excluding lithium in the lithium transition metal composite oxide may be 80 mol% or more, or 90 mol% or more, or 91 mol% or more, or 94 mol% or more. In Chemical Formula 1, 0.8 ≦ x1 ≦ 1, 0 ≦ y1 ≦ 0.2, and 0 ≦ z1 ≦ 0.2 may be satisfied, or 0.9 ≦ x1 ≦ 1, 0 ≦ y1 ≦ 0.1, and 0 ≦ z1 ≦ 0.1 may be satisfied, or 0.91 ≦ x1 ≦ 1, 0 ≦ y1 ≦ 0.09, and 0 ≦ z1 ≦ 0.09 may be satisfied; 0.94 ≦ x1 ≦ 1, 0 ≦ y1 ≦ 0.06, and 0 ≦ z1 ≦ 0.06 may be satisfied. As an example, 0.8 ≦ x1 < 1, 0 < y1 ≦ 0.2, and 0 ≦ z1 ≦ 0.2 or 0.9 ≦ x1 < 1, 0 < y1 ≦ 0.1, and 0 ≦ z1 ≦ 0.1 may be satisfied. The high-nickel-based oxide can achieve a high capacity and is suitable for application to the recently required high-capacity and high-density lithium secondary batteries. However, the positive electrode active material containing the high-nickel-based oxide has a large volume change of about 8% due to charge and discharge, so it is difficult to maintain long-term contact with the solid electrolyte. By introducing a coating layer according to one embodiment, it is possible to smooth the movement of lithium ions while realizing long-term adhesion between solid particles.

[0042] The average particle size (D50) of the particles containing the lithium transition metal composite oxide may be 1 μm to 25 μm, for example, 2 μm to 20 μm, or 3 μm to 18 μm. Here, the average particle size may be determined by measuring the sizes (diameter or major axis length) of 20 or more randomly selected particles in an electron micrograph such as a scanning electron microscope to obtain a particle size distribution, and then taking the diameter (D50) of the particles whose cumulative volume in the particle size distribution accounts for 50% by volume as the average particle size.

[0043] Particles containing a lithium transition metal composite oxide may be in the form of secondary particles formed by agglomeration of multiple primary particles, single particles, or a mixture of these. Secondary particles can also be considered to be in the form of a polycrystal. A single particle refers to a particle that exists independently and does not have a grain boundary within it. It can also refer to a single particle, a monolith structure, a single structure, or a non-agglomerated particle in which particles exist in an independent phase without agglomeration, morphologically. For example, it may be a single crystal.

[0044] For example, particles containing a lithium transition metal composite oxide may include large particles with an average particle size of 9 μm to 25 μm and small particles with an average particle size of 1 μm to 8 μm. In this case, the large particles may be contained in an amount of 60 wt% to 95 wt% and the small particles may be contained in an amount of 5 wt% to 40 wt%, relative to a total of 100 wt% of the large and small particles. For example, the large particles may be contained in an amount of 70 wt% to 90 wt% and the small particles may be contained in an amount of 10 wt% to 30 wt%. When formed by mixing large particles and small particles, a battery with a high energy density can be realized.

[0045] The large particles are in the form of secondary particles made up of a plurality of primary particles, and the small particles may be in the form of secondary particles made up of a plurality of primary particles or in the form of a single particle.

[0046] The average particle size of the large particles may be 9 μm to 20 μm, or 10 μm to 15 μm. The average particle size of the small particles may be 1 μm to 7 μm, 1 μm to 6 μm, or 2 μm to 5 μm. Here, the average particle size may also be determined by measuring the sizes (diameter or major axis length) of 20 or more randomly selected particles in an electron micrograph such as a scanning electron microscope to obtain a particle size distribution, and then taking the diameter (D50) of the particle whose cumulative volume in the particle size distribution accounts for 50% by volume as the average particle size.

[0047] Method for producing positive electrode active material In one embodiment, a method for producing a cathode active material is provided, comprising dry-mixing 100 mol parts of particles containing a lithium transition metal composite oxide and 0.1 mol to 0.6 mol parts of a zirconium raw material, followed by heat treatment at 420°C to 580°C. The cathode active material can be produced using this method. This method employs a dry coating process, eliminating the need for organic solvents and expensive coating materials, allowing existing equipment to be used, making it economical, environmentally friendly, and feasible for mass production. This method can synthesize a cathode active material having a coating layer containing ZrO2 and Li6Zr2O7. The coating layer can be synthesized with an appropriate content and thickness in a favorable shape, thereby producing a cathode active material with improved capacity and life characteristics. This cathode active material has low reactivity with sulfide-based solid electrolyte particles and low interfacial resistance, making it suitable for use in all-solid-state secondary batteries and other applications, resulting in improved capacity, rate, and life characteristics.

[0048] The lithium transition metal composite oxide has been described above, and therefore a detailed description thereof will be omitted.

[0049] The zirconium raw material is a compound containing zirconium element and can be applied without limitation as long as it is a compound that can be dry mixed. The zirconium raw material may be, for example, a zirconium-containing oxide, a zirconium-containing sulfide, a zirconium-containing carbonate, a zirconium-containing hydroxide, etc., such as zirconium oxide, zirconium sulfide, zirconium carbonate, zirconium hydroxide, or a combination thereof.

[0050] The zirconium raw material is mixed in an amount of 0.1 to 0.6 molar parts per 100 molar parts of particles containing a lithium transition metal composite oxide, e.g., 0.1 to 0.5 molar parts or 0.1 to 0.4 molar parts. When the zirconium raw material is added in this range, a coating layer of appropriate content and thickness is formed, which can adequately protect the positive electrode active material. The coating layer may be uniformly thick, without agglomeration or localized presence on the surface of the positive electrode active material. If the content of the zirconium raw material exceeds 0.6 molar parts, the coating layer may become too thick and act as a resistive layer, which may reduce the charge / discharge capacity of the positive electrode active material. Conversely, if the content of the zirconium raw material is less than 0.1 molar parts, the zirconium raw material may not adequately function as a buffer, which may reduce the lifespan of the positive electrode active material.

[0051] For example, the zirconium raw material may be in the form of nanoparticles. The zirconium raw material may be in the form of particles, and the average particle size (D50) of the particles may be, for example, 10 nm to 500 nm, 10 nm to 500 nm, or 50 nm to 500 nm. For example, the zirconium raw material may be particles containing zirconium oxide, and the average particle size (D50) of the particles may be 10 nm to 500 nm. In this case, it may be advantageous to synthesize a coating layer of an appropriate thickness.

[0052] In the method for manufacturing a positive electrode active material according to an embodiment, dry mixing means mixing without a solvent, and can be understood as a solid-phase coating method, which is distinguished from wet coating and liquid-phase coating.

[0053] In one embodiment of a method for manufacturing a cathode active material, a coating layer containing a mixed phase of ZrO2 and Li6Zr2O7 and having a uniform thickness can be formed by dry-mixing followed by heat treatment at 420°C to 580°C. The heat treatment temperature may be, for example, 430°C to 570°C, 440°C to 560°C, 450°C to 550°C, or 460°C to 530°C. Heat treatment within this temperature range allows for the synthesis of a coating layer with an appropriate crystalline phase, which effectively functions as a buffer without acting as a resistor, thereby improving the capacity and life characteristics of the cathode active material. For example, if the heat treatment temperature is less than 420°C, the coating layer may not form an appropriate crystalline phase and may only act as a resistor, resulting in a decrease in the capacity characteristics of the cathode active material. If the heat treatment temperature exceeds 580°C, the coating material may aggregate or be coated only locally, reducing the buffer effect. In addition, zirconium may be absorbed into the positive electrode active material, preventing it from fulfilling its buffering function and resulting in reduced capacity and life characteristics.

[0054] The heat treatment can be carried out in an oxygen atmosphere for, for example, 5 to 25 hours, or 10 to 20 hours. Under such conditions, a good coating layer can be formed.

[0055] In one embodiment, when particles containing a lithium transition metal composite oxide and a zirconium raw material are dry-mixed, a lithium raw material can be mixed in together. The lithium raw material can be any lithium-containing compound that can be dry-mixed. The lithium raw material can be, for example, Li2CO3, LiOH, hydrates thereof, or a combination thereof. The lithium raw material can be mixed in an amount of more than 1 to 4 molar parts per 1 molar part of the zirconium raw material, for example, more than 1 to 3 molar parts, or 2 to 4 molar parts. Mixing the lithium raw materials together and heat-treating them is advantageous for forming a lithium zirconium oxide, e.g., Li6Zr2O7, crystalline phase in the coating layer, which can increase lithium ion conductivity and provide a coating layer of appropriate thickness and good morphology.

[0056] positive electrode In one embodiment, a positive electrode for a lithium secondary battery is provided, which includes the positive electrode active material described above or a positive electrode active material produced by the method described above. The positive electrode for a lithium secondary battery may include a current collector and a positive electrode active material layer disposed on the current collector. The positive electrode active material layer includes the positive electrode active material described above and may further include a binder and / or a conductive material.

[0057] The binder serves to firmly adhere the positive electrode active material particles to each other and to firmly adhere the positive electrode active material to the current collector. Representative examples of the binder include, but are not limited to, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl 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, and nylon.

[0058] The content of the binder in the positive electrode active material layer may be approximately 1 wt % to 5 wt % based on the total weight of the positive electrode active material layer.

[0059] The conductive material is used to impart conductivity to the electrode, and any material that is electron-conductive and does not cause a chemical change in the constructed battery 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, carbon fiber, carbon nanofiber, and carbon nanotube; metal-based materials in the form of metal powder or metal fiber containing copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; and conductive materials containing mixtures of these.

[0060] The content of the conductive material in the positive electrode active material layer may be 1 wt % to 5 wt % based on the total weight of the positive electrode active material layer.

[0061] The positive electrode current collector may be made of aluminum foil, but is not limited to this.

[0062] Meanwhile, the cathode according to one embodiment may be a cathode for an all-solid-state secondary battery, for example. The surface coating layer of the cathode active material acts as a buffer, reducing reactivity with a solid electrolyte, particularly a sulfide-based solid electrolyte, and eliminating problems that occur at the interface of solid particles, thereby improving the capacity characteristics and life characteristics of the all-solid-state secondary battery.

[0063] The positive electrode for the all-solid-state secondary battery may include the positive electrode active material, a binder, a conductive material, etc., and may further include a solid electrolyte.

[0064] solid electrolyte The solid electrolyte may be an inorganic solid electrolyte such as a sulfide-based solid electrolyte or an oxide-based solid electrolyte.

[0065] In one embodiment, the solid electrolyte may be a sulfide-based solid electrolyte having excellent ionic conductivity. Examples of sulfide-based solid electrolyte particles include Li2S-P2S5, Li2S-P2S5-LiX (X is a halogen element, such as I 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, and Li2S-P2S5-Z. m S n (m and n are integers, and Z is Ge, Zn, or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q (p, q are integers, and M is P, Si, Ge, B, Al, Ga, or In), or a combination thereof.

[0066] For example, such sulfide-based solid electrolytes can be obtained by mixing Li2S and P2S5 in a molar ratio of 50:50 to 90:10 or 50:50 to 80:20 and selectively heat-treating the mixture. Within this mixing ratio range, sulfide-based solid electrolytes with excellent ionic conductivity can be produced. The addition of other components, such as SiS2, GeS2, or B2S3, can further improve ionic conductivity.

[0067] Mechanical milling and solution milling can be used to mix sulfur-containing raw materials to produce sulfide-based solid electrolytes. Mechanical milling involves placing the starting materials in a ball mill reactor and vigorously stirring them to finely mix the starting materials. When using the solution milling method, the starting materials are mixed in a solvent to obtain a solid electrolyte as a precipitate. Furthermore, when heat-treated after mixing, the crystals of the solid electrolyte become even stronger, improving ionic conductivity. For example, sulfide-based solid electrolytes can be produced by mixing sulfur-containing raw materials and heat-treating them two or more times. In this case, a sulfide-based solid electrolyte with high ionic conductivity and robustness can be produced.

[0068] For example, sulfide-based solid electrolyte particles according to one embodiment can be manufactured through a first heat treatment in which sulfur-containing raw materials are mixed and fired at 120°C to 350°C, and a second heat treatment in which the result of the first heat treatment is mixed and fired at 350°C to 800°C. The first and second heat treatments can be performed in an inert gas or nitrogen atmosphere. The first heat treatment can be performed for 1 hour to 10 hours, and the second heat treatment can be performed for 5 hours to 20 hours. The first heat treatment can achieve the effect of milling small raw materials, and the second heat treatment can synthesize the final solid electrolyte. By performing these two or more heat treatments, a high-performance sulfide-based solid electrolyte with high ionic conductivity and robustness can be obtained, and such a solid electrolyte can be suitable for mass production. The temperature of the first heat treatment can be, for example, 150°C to 330°C or 200°C to 300°C, and the temperature of the second heat treatment can be, for example, 380°C to 700°C or 400°C to 600°C.

[0069] For example, sulfide-based solid electrolyte particles may include argyrodite-type sulfides. Argyrodite-type sulfide-based solid electrolyte particles have an ionic conductivity of 10, which is the ionic conductivity of a typical liquid electrolyte at room temperature. -4 ~10 -2 It has high ionic conductivity close to the S / cm range, and can form a tight bond between the positive electrode active material and the solid electrolyte without inducing a decrease in ionic conductivity, and can also form a tight interface between the electrode layer and the solid electrolyte layer. All-solid-state secondary batteries containing this material can improve battery performance such as rate capability, coulombic efficiency, and life characteristics.

[0070] The argyrodite-type sulfide-based solid electrolyte particles may contain, for example, a compound represented by the following chemical formula 11.

[0071] [Chemical formula 11] (Li a M 1 b M 2 c )(P dM 3 e )(S f M 4 g )X h In Chemical Formula 11 above, 4 ≤ a ≤ 8, and M 1 is Mg, Cu, Ag, or a combination thereof, 0 ≤ b < 0.5, and M 2 is Na, K, or a combination thereof, 0 ≤ c < 0.5, and M 3 is Sn, Zn, Si, Sb, Ge, or a combination thereof, 0 < d < 4, 0 ≤ e < 1, and M 4 is O, SO n or a combination thereof, 1.5 ≤ n ≤ 5, 3 ≤ f ≤ 12, 0 ≤ g < 2, X is F, Cl, Br, I, or a combination thereof, and 0 ≤ h ≤ 2.

[0072] As an example, in Chemical Formula 11, the halogen compound element (X) is necessarily included, and in this case, it can be expressed as 0 < h ≤ 2. As an example, in Chemical Formula 11, M 1 element is necessarily included, and in this case, it can be expressed as 0 < b < 0.5. In Chemical Formula 11, M 3 can be understood as the element substituted at the position of P, and 0 < e < 1 may also be satisfied. In Chemical Formula 11, M 4 is substituted at the position of S, and as an example, 0 < g < 2 may also be satisfied, and f which is the ratio of S may be, for example, 3 ≤ f ≤ 7. When M 4 is SO n , SO n may be, for example, S4O6, S3O6, S2O3, S2O4, S2O5, S2O6, S2O7, S2O8, SO4, or SO5, etc., and as an example, it may be SO4.

[0073] As an example, in Chemical Formula 11, a + b + c + h = 7, d + e = 1, and f + g + h = 6 may also be satisfied.

[0074] As a specific example, the argyrodite-type sulfide-based solid electrolyte particles are Li3PS4, Li7P3S 11, Li7PS6, Li6PS5Cl, Li6PS5Br, Li 5.8 PS 4.8 Cl 1.2 , Li 6.2 PS 5.2 Br 0.8 , Li 5.75 PS 4.75 Cl 1.25 , (Li 5.69 Cu 0.06 )PS 4.75 Cl 1.25 , (Li 5.72 Cu 0.03 )PS 4.75 Cl 1.25 , (Li 5.69 Cu 0.06 )P(S 4.70 (SO4) 0.05 )Cl 1.25 , (Li 5.69 Cu 0.06 )P(S 4.60 (SO4) 0.15 )Cl 1.25 , (Li 5.72 Cu 0.03 )P(S 4.725 (SO4) 0.025 )Cl 1.25 , (Li 5.72 Na 0.03 )P(S 4.725 (SO4) 0.025 )Cl 1.25 , Li 5.75 P(S 4.725 (SO4) 0.025 )Cl 1.25 , or combinations thereof, but are not limited to these.

[0075] The argyrodite-type sulfide-based solid electrolyte can be prepared by mixing, for example, lithium sulfide and phosphorus sulfide, and optionally, lithium halide. After mixing, the mixture can be heat-treated. The heat treatment can include, for example, two or more heat treatment steps. Here, preparing the argyrodite-type sulfide-based solid electrolyte can include, for example, a first heat treatment in which raw materials are mixed and fired at 120°C to 350°C, and a second heat treatment in which the result of the first heat treatment is mixed again and fired at 350°C to 800°C.

[0076] The average particle size (D50) of the sulfide-based solid electrolyte particles may be, for example, 0.1 μm to 5.0 μm or 0.1 μm to 3.0 μm, or may be small particles of 0.1 μm to 1.9 μm or large particles of 2.0 μm to 5.0 μm. The sulfide-based solid electrolyte particles may be a mixture of small particles with an average particle size of 0.1 μm to 1.9 μm and large particles with an average particle size of 2.0 μm to 5.0 μm. The average particle size of the sulfide-based solid electrolyte particles may be measured using an electron microscope image; for example, the size (diameter or major axis length) of approximately 20 particles may be measured using a scanning electron microscope image to obtain a particle size distribution, from which the D50 may be calculated.

[0077] The solid electrolyte may contain an oxide-based inorganic solid electrolyte in addition to the sulfide-based material. The oxide-based inorganic solid electrolyte may be, for example, Li 1+x Ti 2-x Al(PO4)3(LTAP)(0≦x≦4), Li 1+x+y Al x Ti 2-x Si y P 3-y O 12 (0 <x<2、0≦y<3)、BaTiO3、Pb(Zr、Ti)O3(PZT)、Pb 1-x La x Zr 1-y Ti y O3(PLZT)(0≦x<1, 0≦y<1), PB(Mg3Nb 2 / 3 )O3-PbTiO3 (PMN-PT), HfO2, SrTiO3, SnO2, CeO2, Na2O, MgO, NiO, CaO, BaO, ZnO, ZrO2, Y2O3, Al2O3, TiO2, SiO2, lithium phosphate (Li3PO4), lithium titanium phosphate (Li x Ti y (PO4)3,0 <x<2、0<y<3)、Li 1+x+y (Al,Ga) x (Ti, Ge) 2-x Si y P 3-y O 12 (0≦x≦1, 0≦y≦1), lithium lanthanum titanate (Lix La y TiO3, where 0 < x < 2 and 0 < y < 3), Li2O, LiAlO2, Li2O - Al2O3 - SiO2 - P2O5 - TiO2 - GeO2 - based ceramics, Garnet - based ceramics Li 3+x La3M2O 12 (M = Te, Nb, or Zr; x is an integer from 1 to 10), or mixtures thereof can be included.

[0078] The solid electrolyte is in particle form, and the average particle size (D50) may be 5.0 μm or less, for example, 0.1 μm to 5.0 μm, 0.5 μm to 5.0 μm, 0.5 μm to 4.0 μm, 0.5 μm to 3.0 μm, 0.5 μm to 2.0 μm, or 0.5 μm to 1.0 μm. Such a solid electrolyte can effectively penetrate between the positive electrode active materials and has excellent contact with the positive electrode active materials and connectivity between the solid electrolyte particles.

[0079] Based on 100% by weight of the positive electrode active material layer, the solid electrolyte may be contained in an amount of 0.1% to 35% by weight, for example, 1% to 35% by weight, 5% to 30% by weight, 8% to 25% by weight, or 10% to 20% by weight.

[0080] Also, based on 100% by weight of the total of the positive electrode active material and the solid electrolyte in the positive electrode active material layer, 65% to 99% by weight of the positive electrode active material and 1% to 35% by weight of the solid electrolyte may be included. For example, 80% to 90% by weight of the positive electrode active material and 10% to 20% by weight of the solid electrolyte may be included. When the solid electrolyte is contained in the positive electrode in such an amount, the efficiency and life characteristics of the all - solid - state battery can be improved without reducing the capacity.

[0081] Lithium secondary battery In one embodiment, a lithium secondary battery is provided that includes a cathode including the cathode active material, an anode, and an electrolyte. Here, the lithium secondary battery can be understood as a broader concept, including lithium ion batteries using a non-aqueous electrolyte, lithium metal batteries using lithium metal as the anode, and all-solid-state secondary batteries in which a solid electrolyte layer is interposed between the cathode and anode.

[0082] Lithium-ion battery As an example, a lithium ion battery will be described, which employs the above-mentioned positive electrode active material and uses a non-aqueous electrolyte solution as the electrolyte.

[0083] A lithium secondary battery according to one embodiment may include a battery cell including a positive electrode, a negative electrode facing the positive electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte impregnating the positive electrode, the negative electrode, and the separator; a battery container including the battery cell; and a sealing member sealing the battery container.

[0084] negative electrode A negative electrode for a lithium secondary battery includes a current collector and a negative electrode active material layer located on the current collector. The negative electrode active material layer includes a negative electrode active material and may further include a binder and / or a conductive material.

[0085] The negative electrode active material includes a material capable of reversibly intercalating / deintercalating lithium ions, lithium metal, a lithium metal alloy, a material capable of being doped and dedoped with lithium, or a transition metal oxide.

[0086] The material capable of reversibly intercalating / deintercalating lithium ions may be a carbon-based negative electrode active material, such as crystalline carbon, amorphous carbon, or a combination thereof. Examples of crystalline carbon include graphite, such as amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite. Examples of amorphous carbon include soft or hard carbon, mesophase pitch carbide, and calcined coke.

[0087] As the alloy of lithium metal, 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.

[0088] As the substance capable of doping and undoping lithium, an Si-based negative electrode active material or an Sn-based negative electrode active material can be used. As the Si-based negative electrode active material, silicon, a silicon-carbon composite, SiO x (0 < x < 2), an Si-Q alloy (Q is an element selected from the group consisting of an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element, a Group 15 element, a Group 16 element, a transition metal, a rare earth element, and combinations thereof, and is not Si), and as the Sn-based negative electrode active material, Sn, SnO2, an Sn-R alloy (R is an element selected from the group consisting of an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element, a Group 15 element, a Group 16 element, a transition metal, a rare earth element, and combinations thereof, and is not Sn), etc. can be mentioned, and at least one of these can also be used by mixing with SiO2. As the elements Q and R, 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, Tl, Ge, P, As, Sb, Bi, S, Se, Te, Po, and combinations thereof can be used.

[0089] As an example, the negative electrode active material can include silicon-carbon composite particles. The average particle size (D50) of the silicon-carbon composite particles may be, for example, 0.5 μm to 20 μm. With respect to 100% by weight of the silicon-carbon composite particles, silicon may be contained at 10% to 60% by weight, and carbon may be contained at 40% to 90% by weight. The silicon-carbon composite particles can include, for example, a core containing silicon particles and a carbon coating layer located on the surface of the core. The average particle size (D50) of the silicon particles in the core may be 10 nm to 1 μm, or 10 nm to 200 nm. The silicon particles may exist alone as silicon, or may be in the form of a silicon alloy, or may exist in an oxidized form. The oxidized form of silicon is SiO x It can be represented by (0 < x < 2). Also, the thickness of the carbon coating layer may be about 5 nm to 100 nm.

[0090] As an example, the silicon-carbon composite particles can include a core containing silicon particles and crystalline carbon, and a carbon coating layer located on the surface of the core and containing amorphous carbon. As an example, in the silicon-carbon composite particles, amorphous carbon may exist only in the carbon coating layer and not in the core. The crystalline carbon may be artificial graphite, natural graphite, or a combination thereof, and the amorphous carbon may be formed from coal-based pitch, mesophase pitch, petroleum-based pitch, coal-based oil, petroleum-based middle oil, or a polymer resin (such as a phenol resin, a furan resin, a polyimide resin, etc.). At this time, with respect to 100% by weight of the silicon-carbon composite particles, the content of the crystalline carbon may be 10% to 70% by weight, and the content of the amorphous carbon may be 20% to 40% by weight.

[0091] In the silicon-carbon composite particles, the core can include voids in the central portion. The radius of the voids may be 30% to 50% of the length of the radius of the silicon-carbon composite particles.

[0092] Silicon-carbon composite particles effectively suppress problems such as volume expansion, structural collapse, or particle crushing during charge and discharge, preventing the phenomenon of conductive pathways being disconnected, and can achieve high capacity and high efficiency, making them advantageous for use under high voltage and high-speed charging conditions.

[0093] The Si-based or Sn-based negative electrode active material can be used in combination with a carbon-based negative electrode active material. When the Si-based or Sn-based negative electrode active material and the carbon-based negative electrode active material are used in combination, the mixing ratio by weight may be 1:99 to 90:10.

[0094] The content of the negative electrode active material relative to 100% by weight of the negative electrode active material layer may be 95% by weight to 99% by weight.

[0095] In one embodiment, the negative electrode active material layer further includes a binder and may optionally further include a conductive material. The binder content may be 1 wt% to 5 wt% relative to 100 wt% of the negative electrode active material layer. When the conductive material is further included, the negative electrode active material layer may include 90 wt% to 98 wt% of the negative electrode active material, 1 wt% to 5 wt% of the binder, and 1 wt% to 5 wt% of the conductive material.

[0096] The binder serves to firmly adhere the negative electrode active material particles to each other and to the current collector, and may be a water-insoluble binder, a water-soluble binder, or a combination thereof.

[0097] The water-insoluble binder may include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, ethylene propylene copolymers, polystyrene, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or combinations thereof.

[0098] The water-soluble binder may be a rubber-based binder or a polymeric resin binder. The rubber-based binder may be selected from styrene-butadiene rubber, acrylated styrene-butadiene rubber, acrylonitrile-butadiene rubber, acrylic rubber, butyl rubber, fluororubber, and combinations thereof. The polymeric resin binder may be selected from polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0099] When a water-soluble binder is used as the negative electrode binder, a cellulose-based compound can be further included as a thickener to impart viscosity. Examples of the cellulose-based compound include carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, and alkali metal salts thereof, and a mixture of at least one of these compounds can be used. Examples of the alkali metal include sodium, potassium, and lithium. The amount of the thickener used can be 0.1 to 3 parts by weight per 100 parts by weight of the negative electrode active material.

[0100] The conductive material is used to impart conductivity to the electrode, and any material that is electron-conductive and does not cause a chemical change in the constructed battery 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, carbon fiber, carbon nanofiber, and carbon nanotube; metal-based materials in the form of metal powder or metal fiber, including copper, nickel, aluminum, and silver; conductive polymers such as polyphenylene derivatives; and conductive materials including mixtures of these.

[0101] The negative electrode current collector may be selected from the group consisting of copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof.

[0102] electrolyte The electrolyte includes a non-aqueous organic solvent and a lithium salt.

[0103] The non-aqueous organic solvent acts as a medium through which ions involved in the electrochemical reaction of the battery can move. Non-aqueous organic solvents can be carbonates, esters, ethers, ketones, alcohols, or aprotic solvents. Carbonate solvents include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC). Examples of the ester solvent include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone, decanolide, valerolactone, mevalonolactone, caprolactone, etc. Examples of the ether solvent include dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, etc. Examples of the ketone solvent include cyclohexanone, etc. In addition, examples of alcoholic solvents that can be used include ethyl alcohol and isopropyl alcohol, and examples of aprotic solvents that can be used include nitriles such as R-CN (where R is a hydrocarbon group having 2 to 20 carbon atoms and having a linear, branched, or cyclic structure, which may contain a double bond, an aromatic ring, or an ether bond), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, and sulfolanes.

[0104] The non-aqueous organic solvent may be used alone or in combination of two or more thereof. When two or more thereof are used in combination, the mixing ratio may be appropriately adjusted depending on the desired battery performance, which should be widely understood by those skilled in the art.

[0105] In addition, in the case of carbonate-based solvents, cyclic carbonates and chain carbonates can be mixed and used. In this case, when the cyclic carbonate and chain carbonate are mixed in a volume ratio of about 1:1 to about 1:9, the performance of the electrolyte can be excellent.

[0106] The non-aqueous organic solvent may further include an aromatic hydrocarbon organic solvent in addition to the carbonate solvent, and the carbonate solvent and the aromatic hydrocarbon organic solvent may be mixed in a volume ratio of about 1:1 to about 30:1.

[0107] As the aromatic hydrocarbon solvent, an aromatic hydrocarbon compound represented by the following chemical formula I can be used.

[0108] [ka] [Chemical formula I] In the above chemical formula I, R 4 ~R 9 are the same or different and are selected from the group consisting of hydrogen, halogen, alkyl groups having 1 to 10 carbon atoms, haloalkyl groups having 1 to 10 carbon atoms, and combinations thereof.

[0109] Specific examples of aromatic hydrocarbon solvents include benzene, fluorobenzene, 1,2-difluorobenzene, 1,3-difluorobenzene, 1,4-difluorobenzene, 1,2,3-trifluorobenzene, 1,2,4-trifluorobenzene, chlorobenzene, 1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene, 1,2,3-trichlorobenzene, 1,2,4-trichlorobenzene, iodobenzene, 1,2-diiodobenzene, 1,3-diiodobenzene, 1,4-diiodobenzene, 1,2,3-triiodobenzene, 1,2,4-triiodobenzene, and triiodobenzene. Examples of suitable toluene include toluene, fluorotoluene, 2,3-difluorotoluene, 2,4-difluorotoluene, 2,5-difluorotoluene, 2,3,4-trifluorotoluene, 2,3,5-trifluorotoluene, chlorotoluene, 2,3-dichlorotoluene, 2,4-dichlorotoluene, 2,5-dichlorotoluene, 2,3,4-trichlorotoluene, 2,3,5-trichlorotoluene, iodotoluene, 2,3-diiodotoluene, 2,4-diiodotoluene, 2,5-diiodotoluene, 2,3,4-triiodotoluene, 2,3,5-triiodotoluene, xylene, or combinations thereof.

[0110] The electrolyte may further contain vinylene carbonate or an ethylene carbonate-based compound of the following formula II as a life-promoting additive to improve the battery life.

[0111] [ka] [Chemical formula II] In the above chemical formula II, R 10 and R 11 are the same or different and are selected from the group consisting of hydrogen, a halogen group, a cyano group, a nitro group, and a fluorinated alkyl group having 1 to 5 carbon atoms; R 10 and R 11 At least one of R is selected from the group consisting of a halogen group, a cyano group, a nitro group, and a fluorinated alkyl group having 1 to 5 carbon atoms, provided that R 10and R 11 Neither of these is hydrogen.

[0112] Representative examples of ethylene carbonate compounds include difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate, fluoroethylene carbonate, etc. When such a life-improving additive is further used, the amount used can be appropriately adjusted.

[0113] The lithium salt is dissolved in a non-aqueous organic solvent and acts as a source of lithium ions in the battery, enabling basic lithium secondary battery operation and facilitating the movement of lithium ions between the positive electrode and the negative electrode.

[0114] The lithium salt may be applied without any limitation on type, and may include, for example, LiPF, LiBF, LiSbF, LiAsF, LiClO, LiAlO, LiAlCl, LiPOF, LiCl, LiI, LiSCN, LiN(CN), lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LiDFOB), lithium difluorobis(oxalato)phosphate (LiDFBP), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(pentafluoroethanesulfonyl)imide (LiBETI), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, or a combination thereof.

[0115] The lithium salt concentration is preferably within the range of 0.1 M to 2.0 M. If the lithium salt concentration is within this range, the electrolyte has appropriate conductivity and viscosity, thereby exhibiting excellent electrolyte performance and allowing lithium ions to migrate effectively.

[0116] Separator The separator separates the positive and negative electrodes and provides a path for lithium ions to move. Any separator commonly used in lithium-ion batteries can be used. Separators can have low resistance to electrolyte ion movement and excellent electrolyte humidification. For example, separators can include glass fiber, polyester, polyethylene, polypropylene, polytetrafluoroethylene, or a combination thereof, and can be in the form of a nonwoven or woven fabric. For example, polyolefin-based polymer separators such as polyethylene and polypropylene are commonly used in lithium-ion batteries. Coated separators containing ceramic components or polymer materials can also be used to improve heat resistance or mechanical strength, and can be used in either a single-layer or multi-layer structure.

[0117] All-solid-state secondary battery In one embodiment, an all-solid-state secondary battery is provided that includes the aforementioned positive electrode and negative electrode, and a solid electrolyte layer located between the positive electrode and the negative electrode.

[0118] FIG. 1 is a cross-sectional view of an all-solid-state secondary battery according to an embodiment. Referring to FIG. 1, the all-solid-state secondary battery 100 may have a structure in which an electrode assembly including a negative electrode 400 including a negative electrode current collector 401 and a negative electrode active material layer 403, a solid electrolyte layer 300, and a positive electrode 200 including a positive electrode active material layer 203 and a positive electrode current collector 201 is stacked and housed in a battery case. The all-solid-state secondary battery 100 may further include an elastic layer 500 on the outer surface of at least one of the positive electrode 200 and the negative electrode 400. Although FIG. 1 shows one electrode assembly including the negative electrode 400, the solid electrolyte layer 300, and the positive electrode 200, two or more electrode assemblies may also be stacked to fabricate an all-solid-state secondary battery.

[0119] negative electrode The negative electrode for the all-solid-state secondary battery may be, for example, the same negative electrode as that described for the lithium ion battery.

[0120] Alternatively, the negative electrode for the all-solid-state secondary battery may be a deposition-type negative electrode, which does not include a negative electrode active material when the battery is assembled, but has lithium metal or the like deposited or electrodeposited on the negative electrode during battery charging, and serves as the negative electrode active material.

[0121] FIG. 2 is a schematic cross-sectional view of an all-solid-state secondary battery including a deposition-type anode. Referring to FIG. 2, the deposition-type anode 400′ may include a current collector 401 and an anode coating layer 405 disposed on the current collector. An all-solid-state secondary battery including this deposition-type anode 400′ is initially charged without the presence of an anode active material. During charging, high-density lithium metal is deposited or electrodeposited between the current collector 401 and the anode coating layer 405 or on the anode coating layer 405, forming a lithium metal layer 404, which serves as the anode active material. Thus, in an all-solid-state secondary battery that has been charged at least once, the deposition-type anode 400′ may include, for example, the current collector 401, the lithium metal layer 404 disposed on the current collector, and the anode coating layer 405 disposed on the metal layer. The lithium metal layer 404 refers to a layer formed by deposition of lithium metal during the charging process of the battery and may be referred to as a metal layer, a lithium layer, a lithium electrodeposition layer, or an anode active material layer.

[0122] The anode coating layer 405 may also be referred to as a lithium electrodeposition induction layer or an anode catalyst layer, and may include a metal, a carbon material, or a combination thereof that acts as a catalyst.

[0123] The metal may be a lithophilic metal, such as gold, platinum, palladium, silicon, silver, aluminum, bismuth, tin, zinc, or a combination thereof, and may consist of one of these or various types of alloys. When the metal is in particulate form, its average particle size (D50) may be about 4 μm or less, for example, from 10 nm to 4 μm.

[0124] The carbon material may be, for example, crystalline carbon, amorphous carbon, or a combination thereof. The crystalline carbon may be, for example, natural graphite, artificial graphite, mesophase carbon microbeads, or a combination thereof. The amorphous carbon may be, for example, carbon black, activated carbon, acetylene black, denka black, ketjen black, or a combination thereof.

[0125] When the anode coating layer 405 includes both a metal and a carbon material, the mixing ratio of the metal to the carbon material may be, for example, 1:10 to 2:1 by weight. In this case, the deposition of lithium metal can be effectively promoted, and the characteristics of the all-solid-state secondary battery can be improved. The anode coating layer 405 can include, for example, a carbon material supporting a catalytic metal, or a mixture of metal particles and carbon material particles.

[0126] For example, the negative electrode coating layer 405 may contain metal and amorphous carbon, which can effectively promote the deposition of lithium metal.

[0127] The negative electrode coating layer 405 may further include a binder, for example, a conductive binder, and may further include common additives such as a filler, a dispersant, and an ion conductive agent.

[0128] The thickness of the negative electrode coating layer 405 may be, for example, 100 nm to 20 μm, or 500 nm to 10 μm, or 1 μm to 5 μm.

[0129] For example, the deposition-type negative electrode 400′ may further include a thin film on the surface of the current collector, i.e., between the current collector and the negative electrode coating layer. The thin film may include an element capable of forming an alloy with lithium. The element capable of forming an alloy with lithium may be, for example, gold, silver, zinc, tin, indium, silicon, aluminum, bismuth, etc., and may be composed of one of these or various types of alloys. The thin film may further flatten the deposition morphology of the lithium metal layer 404, thereby further improving the characteristics of the all-solid-state secondary battery. The thin film may be formed by, for example, a vacuum deposition method, a sputtering method, a plating method, or the like. The thin film may have a thickness of, for example, 1 nm to 500 nm.

[0130] The lithium metal layer 404 can include lithium metal or a lithium alloy, such as a Li-Al alloy, a Li-Sn alloy, a Li-In alloy, a Li-Ag alloy, a Li-Au alloy, a Li-Zn alloy, a Li-Ge alloy, or a Li-Si alloy.

[0131] The thickness of the lithium metal layer 404 may be 1 μm to 500 μm, 1 μm to 200 μm, 1 μm to 100 μm, or 1 μm to 50 μm. If the lithium metal layer 404 is too thin, it may not function as a lithium reservoir, and if it is too thick, the battery volume may increase, resulting in reduced performance.

[0132] When such a deposition-type anode is used, the anode coating layer 405 can protect the lithium metal layer 404 and suppress the deposition and growth of lithium dendrites, thereby suppressing short circuits and capacity reduction in the all-solid-state battery and improving its lifespan.

[0133] solid electrolyte layer The solid electrolyte layer 300 may include a sulfide-based solid electrolyte, an oxide-based solid electrolyte, etc. The sulfide-based solid electrolyte and the oxide-based solid electrolyte have been described above, and therefore detailed description thereof will be omitted.

[0134] Meanwhile, the average particle size (D50) of the solid electrolyte contained in the solid electrolyte layer 300 may be larger than the average particle size (D50) of the solid electrolyte contained in the cathode 200. In this case, the energy density of the all-solid-state secondary battery can be maximized while increasing the mobility of lithium ions, thereby improving overall performance. For example, the average particle size (D50) of the solid electrolyte contained in the cathode 200 may be 0.1 μm to 1.9 μm, or 0.1 μm to 1.0 μm, and the average particle size (D50) of the solid electrolyte contained in the solid electrolyte layer 300 may be 2.0 μm to 5.0 μm, or 2.0 μm to 4.0 μm, or 2.5 μm to 3.5 μm. When these particle size ranges are satisfied, the energy density of the all-solid-state secondary battery can be maximized while facilitating the transfer of lithium ions and reducing resistance, thereby improving overall performance of the all-solid-state secondary battery. Here, the average particle size (D50) of the solid electrolyte may be measured using a particle size analyzer using a laser diffraction method.

[0135] The solid electrolyte layer 300 may further include a binder in addition to the solid electrolyte. The binder may be, but is not limited to, styrene butadiene rubber, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, an acrylate-based polymer, or a combination thereof. Any binder commonly used in the art may be used. The acrylate-based polymer may be, for example, butyl acrylate, polyacrylate, polymethacrylate, or a combination thereof.

[0136] The solid electrolyte layer 300 can be formed by adding a solid electrolyte to a binder solution, coating the binder solution on a substrate film, and drying the solution. The solvent for the binder solution may be isobutyryl isobutyrate, xylene, toluene, benzene, hexane, or a combination thereof. The process for forming the solid electrolyte layer is widely known in the art, and therefore, a detailed description thereof will be omitted.

[0137] The thickness of the solid electrolyte layer 300 may be, for example, 10 μm to 150 μm.

[0138] The solid electrolyte layer 300 may further include an alkali metal salt, and / or an ionic liquid, and / or a conductive polymer.

[0139] The alkali metal salt may be, for example, a lithium salt. The content of the lithium salt in the solid electrolyte layer may be 1 M or more, for example, 1 M to 4 M. In this case, the lithium salt can improve the ion conductivity by increasing the lithium ion mobility in the solid electrolyte layer.

[0140] The lithium salt may be applied without any limitation on type, and may include, for example, LiPF, LiBF, LiSbF, LiAsF, LiClO, LiAlO, LiAlCl, LiPOF, LiCl, LiI, LiSCN, LiN(CN), lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LiDFOB), lithium difluorobis(oxalato)phosphate (LiDFBP), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(pentafluoroethanesulfonyl)imide (LiBETI), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, or a combination thereof.

[0141] For example, the lithium salt may be an imide-based lithium salt such as LiTFSI, LiFSI, LiBETI, or a combination thereof. The imide-based lithium salt can maintain or improve ionic conductivity by appropriately maintaining chemical reactivity with the ionic liquid.

[0142] An ionic liquid is a salt that has a melting point below room temperature, is in a liquid state at room temperature, and is composed only of ions, or is a room-temperature molten salt.

[0143] The ionic liquid comprises: a) one or more cations selected from ammonium, pyrrolidinium, pyridinium, pyrimidinium, imidazolium, piperidinium, pyrazolium, oxazolium, pyridazinium, phosphonium, sulfonium, triazolium, and mixtures thereof; and b) BF4 - , PF6 - , AsF6 - , SbF6 - , AlCl4 - , HSO4 - , ClO4 - , CH3SO3 - , CF3CO2 - , Cl - , Br - , I - , BF4 - , SO4 - , CF3SO3 - , (FSO2)2N - , (C2F5SO2)2N - , (C2F5SO2)(CF3SO2)N - , and (CF3SO2)2N - The compound may contain one or more anions selected from the following:

[0144] The ionic liquid may be, for example, one or more selected from the group consisting of N-methyl-N-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide, N-butyl-N-methylpyrrolidinium bis(3-trifluoromethylsulfonyl)imide, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide, and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide.

[0145] The weight ratio of solid electrolyte to ionic liquid in the solid electrolyte layer may be 0.1:99.9 to 90:10, for example, 10:90 to 90:10, 20:80 to 90:10, 30:70 to 90:10, 40:60 to 90:10, or 50:50 to 90:10. A solid electrolyte layer satisfying this range can increase the electrochemical contact area with the electrode, maintaining or improving ionic conductivity. This can improve the energy density, discharge capacity, rate characteristics, etc. of the all-solid-state secondary battery.

[0146] The all-solid-state secondary battery may be a unit cell having a structure of positive electrode / solid electrolyte layer / negative electrode, a bi-cell having a structure of positive electrode / solid electrolyte layer / negative electrode / solid electrolyte layer / positive electrode, or a stacked battery in which the unit battery structure is repeated.

[0147] The shape of the all-solid-state secondary battery is not particularly limited, and may be, for example, a coin type, a button type, a sheet type, a laminated type, a cylindrical type, a flat type, or the like. Furthermore, the all-solid-state secondary battery can also be applied to large batteries used in electric vehicles, etc. For example, the all-solid-state secondary battery can also be used in hybrid vehicles such as plug-in hybrid electric vehicles (PHEVs). Furthermore, the all-solid-state secondary battery can also be used in fields requiring large amounts of power storage, such as electric bicycles or power tools. Furthermore, the all-solid-state secondary battery can also be used in various fields, such as portable electronic devices.

[0148] Examples of the present invention and comparative examples are described below. The following examples are merely examples of the present invention, and the present invention is not limited to the following examples. [Example]

[0149] Example 1 (0.25 mol%, 460°C) 1. Production of positive electrode active material The composition is LiNi 0.945 Co 0.04 Al 0.015 O2, with an average particle size (D50) of approximately 14 μm and a secondary particle form, and the composition is LiNi0.94 Co 0.04 Mn 0.02 A composite oxide was prepared by mixing 100 mol parts of the composite oxide with 0.25 mol parts of zirconium oxide (ZrO2) and 0.5 mol parts of anhydrous lithium hydroxide (LiOH) in a weight ratio of 8:2. The composite oxide was mixed with 0.25 mol parts of zirconium oxide (ZrO2) and 0.5 mol parts of anhydrous lithium hydroxide (LiOH) in a Henschel mixer. The mixer was operated at low, medium, and high speeds to ensure a uniform coating without layer separation. The mixture was then heat-treated at 460°C for 15 hours in an oxygen atmosphere to produce the final cathode active material with a coating layer.

[0150] 2. Fabrication of the positive electrode The cathode composition was prepared by mixing 84.9 wt% of the prepared cathode active material, 13.61 wt% of Li6PS5Cl argyrodite-type solid electrolyte, 1 wt% of PVdF binder, 0.35 wt% of carbon nanotube conductive material, and 0.14 wt% of hydrogenated nitrile butadiene rubber (HNBR) as a dispersant in an isobutyryl isobutyrate (IBIB) solvent. The mixture was applied to a cathode current collector, dried, and then rolled (hydrostatic pressing (WIP), 500 MPa, 85°C, 30 min) to prepare a cathode.

[0151] 3. Manufacturing of all-solid-state secondary batteries An Ag / C composite was prepared by mixing carbon black with a primary particle size of approximately 30 nm and silver (Ag) with an average particle size (D50) of approximately 60 nm in a weight ratio of 3:1. An anode coating layer composition was prepared by adding 0.25 g of the composite to 2 g of NMP solution containing 7 wt% polyvinylidene fluoride binder and mixing. This was applied to an anode current collector and dried to prepare a deposition-type anode with an anode coating layer formed on the current collector.

[0152] An argyrodite-type solid electrolyte of Li6PS5Cl was mixed with an IBIB solvent containing an acrylic binder to prepare a composition for forming a solid electrolyte layer. The composition was cast onto a release film and dried at room temperature to prepare a solid electrolyte layer.

[0153] The prepared positive electrode, negative electrode, and solid electrolyte layer were cut, and the solid electrolyte layer was laminated on the positive electrode, followed by laminating the negative electrode on top of that. This was sealed into a pouch and isostatically pressed at 80°C and 500 MPa for 30 minutes to produce an all-solid-state secondary battery.

[0154] Example 2 (0.125 mol%, 500°C) A cathode active material and an all-solid-state secondary battery were manufactured in substantially the same manner as in Example 1, except that 0.125 mol parts of zirconium oxide and 0.25 mol parts of anhydrous lithium hydroxide (LiOH) were mixed as a coating agent during the cathode active material manufacturing process, and the coating heat treatment temperature was changed to 500°C.

[0155] Example 3 (0.25 mol%, 500°C) A positive electrode active material and an all-solid-state secondary battery were manufactured in substantially the same manner as in Example 1, except that the coating heat treatment temperature was changed to 500°C during the positive electrode active material manufacturing process.

[0156] Example 4 (0.375 mol%, 500°C) A positive electrode active material and an all-solid-state secondary battery were manufactured in substantially the same manner as in Example 1, except that 0.375 mol parts of zirconium oxide and 0.75 mol parts of anhydrous lithium hydroxide (LiOH) were mixed during the positive electrode active material manufacturing process, and the coating heat treatment temperature was changed to 500°C.

[0157] Example 5 (0.25 mol%, 540°C) A positive electrode active material and an all-solid-state secondary battery were manufactured in substantially the same manner as in Example 1, except that the coating heat treatment temperature was changed to 540°C during the positive electrode active material manufacturing process.

[0158] Comparative example 1 (0.25mol%, 300℃) A positive electrode active material and an all-solid-state secondary battery were manufactured in substantially the same manner as in Example 1, except that the coating heat treatment temperature was changed to 300°C during the positive electrode active material manufacturing process.

[0159] Comparative example 2 (0.25mol%, 400℃) A positive electrode active material and an all-solid-state secondary battery were manufactured in substantially the same manner as in Example 1, except that the coating heat treatment temperature was changed to 400°C during the positive electrode active material manufacturing process.

[0160] Comparative example 3 (0.05mol%, 500℃) A positive electrode active material and an all-solid-state secondary battery were manufactured in substantially the same manner as in Example 2, except that 0.05 mol parts of zirconium oxide and 0.10 mol parts of anhydrous lithium hydroxide (LiOH) were mixed during the preparation of the positive electrode active material.

[0161] Comparative example 4 (0.75mol%, 500℃) A positive electrode active material and an all-solid-state secondary battery were manufactured in substantially the same manner as in Example 2, except that 0.75 mol parts of zirconium oxide and 1.5 mol parts of anhydrous lithium hydroxide (LiOH) were mixed during the preparation of the positive electrode active material.

[0162] Comparative example 5 (0.25mol%, 600℃) A positive electrode active material and an all-solid-state secondary battery were manufactured in substantially the same manner as in Example 1, except that the coating heat treatment temperature was changed to 600° C. during the positive electrode active material manufacturing process.

[0163] Comparative example 6 (0.25mol%, 700℃) A positive electrode active material and an all-solid-state secondary battery were manufactured in substantially the same manner as in Example 1, except that the coating heat treatment temperature was changed to 700°C during the positive electrode active material manufacturing process.

[0164] Comparative Example 7 (no coating layer) A cathode active material and an all-solid-state secondary battery were manufactured in substantially the same manner as in Example 1, except that a coating layer was not formed on the cathode active material and the composite oxide prepared in Example 1 itself was used as the cathode active material.

[0165] Comparative Example 8 (wet coating, 0.25 mol%, 300°C) The composite oxide prepared in Example 1 was coated using a wet method. Dehydrated 2-propanol, a methanol solution containing 10% lithium methoxide, and zirconium isopropoxide were mixed in a molar ratio of 200:2:1, and the composite oxide was dispersed therein. The solvent was evaporated in a vacuum at 50°C while irradiating with ultrasound to prevent aggregation of the composite oxide particles. The resulting material was filtered and heat-treated in an air atmosphere at 300°C for 1 hour, yielding a cathode active material coated with approximately 0.25 wt% of a buffer layer containing Li2CO3, LiOH, and ZrO2.

[0166] An all-solid-state secondary battery was produced in substantially the same manner as in Example 1, except that the obtained material was used as the positive electrode active material.

[0167] To facilitate understanding, the positive electrode active material design details of Examples 1 to 5 and Comparative Examples 1 to 8 are briefly shown in Table 1 below.

[0168] [Table 1]

[0169] Evaluation example 1: Evaluation of initial charge / discharge capacity of all-solid-state secondary batteries The all-solid-state secondary batteries produced in Examples 1 to 5 and Comparative Examples 1 to 8 were initially charged and discharged at a constant current of 0.1 C at 45°C up to an upper voltage of 4.25 V, and at a constant voltage of 0.05 C, followed by discharging at 0.1 C to a cut-off voltage of 2.5 V. Table 2 below shows the initial charge capacity and initial discharge capacity, as well as the ratio of the latter to the former, calculated as efficiency. Figure 3 also shows the initial charge capacity (gray bars) and initial discharge capacity (black bars) for Examples 1 to 5 and Comparative Examples 1 to 8.

[0170] [Table 2]

[0171] Referring to Table 2 and FIG. 3, compared to Comparative Example 8, which uses a conventional technology of wet-coating a buffer layer using an expensive metal alkoxide raw material in an organic solvent, Examples 1 to 5 use dry-coating, a mass-producible method, and can secure a capacity equivalent to or higher than that of Comparative Example 8.

[0172] In Comparative Examples 1 and 2, the coating heat treatment temperature was lower than that of the Examples, so the coating layer did not form a proper crystalline phase and acted only as a resistor, resulting in a low initial charge / discharge capacity.

[0173] In Comparative Example 3, the content of zirconium oxide as a coating agent was lower than in the Examples, and the coating layer was thin. However, the lithium hydroxide added during the coating process thickened the residual lithium layer, which acted as a buffer layer during the initial charging stage, and this is believed to have resulted in a slightly higher initial charge / discharge capacity compared to Comparative Example 7, in which no coating was performed.

[0174] In Comparative Example 4, the content of zirconium oxide as a coating agent was higher than in the Examples, and it was confirmed that the excessively thick coating layer acted as a resistance layer, resulting in a lower initial charge / discharge capacity.

[0175] In Comparative Examples 5 and 6, the coating heat treatment temperature was higher than in the Examples. If the temperature for forming the crystalline phase after coating is too high, the coating material aggregates, reducing the coating effect, or is absorbed into the positive electrode active material, ultimately resulting in a low initial charge / discharge capacity.

[0176] In Comparative Example 8, where wet coating was performed, the initial discharge capacity was similar to that of the Examples, but the initial charge capacity was reduced. This is believed to be because the coating layer acted only as a resistive layer, not as a lithium ion transport layer.

[0177] Evaluation example 2: Lifetime characteristics evaluation of all-solid-state secondary batteries The all-solid-state secondary batteries of Examples 1 to 5 and Comparative Examples 1 to 8 were subjected to initial charge and discharge as in Evaluation Example 1. Charge and discharge were repeated 100 times at 0.33 C and 0.33 C in a voltage range of 2.5 V to 4.25 V at 45°C, and the ratio of the 100th discharge capacity to the single discharge capacity, i.e., the in-life capacity retention, was evaluated. The results are shown in Table 3 below, and the initial discharge capacity (black bars) and the 100th capacity retention (dotted line) are shown in Figure 4. Furthermore, the capacity retention as a function of the number of cycles for Example 3 and Comparative Examples 3, 4, 6, and 7 are shown in Figure 5.

[0178] [Table 3] Referring to Table 3 or FIGS. 4 and 5, it can be seen that Examples 1 to 5, which were dry-coated, had a better capacity retention rate during life than Comparative Example 8, which was wet-coated.

[0179] In Comparative Examples 1 and 2, the coating heat treatment temperature was lower than that of the Examples. The life capacity retention rate was similar to that of the Examples, but as mentioned above, the coating layer did not form an appropriate crystalline phase and acted only as a resistive layer, resulting in a low initial discharge capacity.

[0180] In Comparative Example 3, the content of zirconium oxide, a coating agent, was lower than in the Examples. The residual lithium layer, which was thickened by the additional lithium hydroxide added during the coating process, initially acted as a buffer layer, resulting in a relatively high initial charge / discharge capacity. However, as shown in Figure 5, the buffer layer decomposed during the battery's life and did not exert its full effect, ultimately resulting in a low capacity retention rate during the battery's life.

[0181] In Comparative Example 4, the content of zirconium oxide, the coating agent, was higher than in the Examples. If the coating layer was too thick, the capacity retention rate during life was high, but it acted as a resistance layer, resulting in a low initial charge / discharge capacity.

[0182] As in Comparative Examples 5 and 6, when the heat treatment temperature for forming the crystalline phase after coating is increased, the coating materials aggregate, reducing the coating effect and decreasing the initial discharge capacity and capacity retention rate during life.

[0183] Evaluation example 3: Surface coating condition evaluation The surfaces of the positive electrode active materials prepared in Example 3, Comparative Example 1, and Comparative Examples 3 to 6 were photographed with an SEM at 50,000 magnification (BSE mode), and the photographs are shown in Figures 6 to 11. In each figure, the image on the left corresponds to large particles, and the image on the right corresponds to small particles. Figure 6 is an SEM image of the surfaces of large and small particles in Example 3, and Figure 7 is an SEM image of the surfaces of large and small particles in Comparative Example 1. Figure 8 is an SEM image of the surfaces of large and small particles in Comparative Example 3, and Figure 9 is an SEM image of the surfaces of large and small particles in Comparative Example 4. Figure 10 is an SEM image of the surfaces of large and small particles in Comparative Example 5, and Figure 11 is an SEM image of the surfaces of large and small particles in Comparative Example 6.

[0184] Comparing Figures 6 to 11, it can be seen that the surface coating layer disappears and becomes clean in Comparative Example 5 (Figure 10), where the coating heat treatment temperature is 600°C, and Comparative Example 5 (Figure 11), where the coating heat treatment temperature is 700°C. Also, although the coating heat treatment temperature is the same as Example 3 at 500°C, Comparative Example 3 (Figure 8), where 0.05 mol parts of zirconium oxide are coated, has an obscured surface coating layer, while Comparative Example 4 (Figure 9), where 0.754 mol parts of zirconium oxide are coated, has a thick coating and some of it is agglomerated.

[0185] That is, it can be seen that the performance of the all-solid-state secondary battery can be ensured as long as the surface coating layer is not too thick or too thin.

[0186] Evaluation example 4: Zr distribution analysis using SEM-EDS The surfaces of the positive electrode active materials prepared in Example 3, Comparative Example 1, and Comparative Examples 3 to 6 were photographed with an SEM, and the distribution of Zr was confirmed by EDS. The results are shown in Figures 12 to 17. In each figure, the image on the left shows large particles, and the image on the right shows small particles, with Zr highlighted in yellow. Figure 12 shows SEM-EDS images of large and small particles in Example 3, and Figure 13 shows SEM-EDS images of large and small particles in Comparative Example 1. Figure 14 shows SEM-EDS images of large and small particles in Comparative Example 3, and Figure 15 shows SEM-EDS images of large and small particles in Comparative Example 4. Figure 16 shows SEM-EDS images of large and small particles in Comparative Example 5, and Figure 17 shows SEM-EDS images of large and small particles in Comparative Example 6.

[0187] In addition, the Zr content in each area indicated by a square box in Figures 12 to 17 was analyzed by EDS, and the results are shown in Table 4 below. In Table 4, the unit of each value is atomic %.

[0188] [Table 4]

[0189] Although the heat treatment temperature was the same at 500°C, Comparative Example 3, which had a small coating of zirconium oxide at 0.05 mol parts, had a smaller amount of Zr coated on the surface and was less uniform than Example 3, as can be seen in Table 4, Figure 14, and Figure 12. Furthermore, Comparative Example 4, which had an excessive coating of zirconium oxide at 0.75 mol parts, had Zr agglomerated on the surface as can be seen in Figure 15, and Table 4 shows very large coating non-uniformity. In other words, Comparative Example 3 had an insufficient coating layer, resulting in poor life characteristics as shown in Figure 5, while Comparative Example 4 had an excessively thick coating layer with many agglomerated areas, resulting in low initial discharge capacity as can be seen in Figure 4.

[0190] Comparing Example 3, Comparative Example 1, and Comparative Examples 5 and 6, which were all coated with 0.25 mol parts of zirconium oxide but had different heat treatment temperatures, Comparative Example 1, which had a low heat treatment temperature of 300°C, did not form lithium zirconium oxide (Li6Zr2O7), and was not detected as being bright as shown in Figure 13. It can also be seen from Table 4 that the Zr content varied greatly depending on the position.

[0191] In contrast, Comparative Example 5, which was coated with 0.25 mol parts of zirconium oxide but heat-treated at 600°C, a higher temperature than Example 3, had a large amount of Zr agglomerated as shown in Figure 15, and the positional variation in Zr content was greater than in Example 3, as can be seen in Table 4. Furthermore, the surface of Comparative Example 6, which was heat-treated at 700°C, was clean as shown in Figure 11, and the amount of Zr detected was significantly lower as shown in Figure 17 and Table 4. This is thought to be due to the coating material being absorbed into the active material or excessive agglomeration during heat treatment at 700°C.

[0192] Evaluation example 5: Coating layer crystalline phase analysis using STEM-EDS and HRTEM To analyze the crystalline phase of the coating layer, a cross section of a small particle in the positive electrode active material prepared in Example 4 was analyzed by STEM-EDS, and the results are shown in Figure 18. The light green highlight in Figure 18 indicates Zr. Figure 18 confirms that Zr was very uniformly coated on the surface of the positive electrode active material. The thickness of the Zr-containing coating layer was confirmed to be approximately 130 nm.

[0193] Figure 19 is an HRTEM image of a cross section of a small particle in the positive electrode active material of Example 4. In Figure 19, a thickly coated portion on the surface of the positive electrode active material was selected and marked with a white square box. An Inverse Fast Fourier Transform (IFFT) was performed on this region, and the results are shown in Figure 20. The ZrO2 region in Figure 20 is enlarged and shown on the left side of Figure 21, and the Li6Zr2O7 region is enlarged and shown on the right side of Figure 21. As can be seen from Figures 20 and 21, the coating layer contains ZrO2 crystalline phases, Li6Zr2O7 crystalline phases, and amorphous portions containing Zr.

[0194] Although the preferred embodiments have been described in detail above, the scope of the present invention is not limited to these, and various modifications and improvements made by those skilled in the art using the basic concepts defined in the following claims also fall within the scope of the present invention. [Explanation of symbols]

[0195] 100: All-solid-state secondary battery 200: Positive electrode 201: Positive electrode current collector 203: Positive electrode active material layer 300: Solid electrolyte layer 400: Negative electrode 401:Negative electrode current collector 403:Negative electrode active material layer 400': Deposition type negative electrode 404: Lithium metal layer 405: Negative electrode coating layer 500: Elastic layer

Claims

1. Particles containing a lithium transition metal composite oxide, and ZrO located on the surface of the particles ２ and Li ６ Zr ２ O ７ A positive electrode active material for a lithium secondary battery, comprising a coating layer containing

2. The coating layer is made of ZrO ２ Crystal phase, Li ６ Zr ２ O ７ 2. The positive electrode active material for a lithium secondary battery according to claim 1, comprising a crystalline phase and a Zr-containing amorphous region.

3. The positive electrode active material for a lithium secondary battery according to claim 1 , wherein the coating layer has a continuous film form or an island form.

4. 2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the coating layer has a thickness of 5 nm to 300 nm.

5. 2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the coating layer has a Zr content of 0.1 to 0.6 parts by mole relative to 100 parts by mole of the particles containing the lithium transition metal composite oxide.

6. 2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the coating layer has a Zr content of 0.1 to 6 wt % based on 100 wt % of the positive electrode active material.

7. 2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the lithium transition metal composite oxide is a lithium nickel-based oxide represented by the following Chemical Formula 1, a lithium cobalt-based oxide represented by the following Chemical Formula 2, a lithium iron phosphate-based compound represented by the following Chemical Formula 3, or a cobalt-free lithium nickel-manganese-based oxide represented by the following Chemical Formula 4: [Chemical formula 1] Li ａ１ Ni ｘ１ M １ ｙ１ M ２ ｚ１ O ２－ｂ１ X ｂ１ In the above chemical formula 1, 0.9≦a1≦1.8, 0.3≦x1≦1, 0≦y1≦0.7, 0≦z1≦0.7, 0.9≦x1+y1+z1≦1.1, and 0≦b1≦0.1; M １ and M ２ are each independently one or more elements selected from the group consisting of Al, B, Ba, Ca, Ce, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Zn, and Zr, and X is one or more elements selected from the group consisting of F, P, and S; [Chemical formula 2] Li ａ２ Co ｘ２ M ３ ｙ２ O ２－ｂ２ X ｂ２ In the above chemical formula 2, 0.9≦a2≦1.8, 0.7≦x2≦1, 0≦y2≦0.3, 0.9≦x2+y2≦1.1, and 0≦b2≦0.1; M ３ is one or more elements selected from the group consisting of Al, B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mn, Mo, Ni, Se, Si, Sn, Sr, Ti, V, W, Y, Zn, and Zr, and X is one or more elements selected from the group consisting of F, P, and S; [Chemical formula 3] Li ａ３ Fe ｘ３ M ４ ｙ３ PO ４－ｂ３ X ｂ３ In the above chemical formula 3, 0.9≦a3≦1.8, 0.6≦x3≦1, 0≦y3≦0.4, and 0≦b3≦0.1; M ４ is one or more elements selected from the group consisting of Al, B, Ba, Ca, Ce, Co, Cr, Cu, Mg, Mn, Mo, Ni, Se, Si, Sn, Sr, Ti, V, W, Y, Zn, and Zr, and X is one or more elements selected from the group consisting of F, P, and S; [Chemical formula 4] Li ａ４ Ni ｘ４ Mn ｙ４ M ５ ｚ４ O ２－ｂ４ X ｂ４ In the above chemical formula 4, 0.9≦a4≦1.8, 0.8≦x4<1, 0<y4≦0.2, 0≦z4≦0.2, 0.9≦x4+y4+z4≦1.1, and 0≦b4≦0.1; M ５ is one or more elements selected from the group consisting of Al, B, Ba, Ca, Ce, Cr, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, and Zr, and X is one or more elements selected from the group consisting of F, P, and S.

8. 8. The positive electrode active material for a lithium secondary battery according to claim 7, wherein the lithium transition metal composite oxide is a lithium nickel-based oxide represented by Chemical Formula 1 and is a high nickel-based oxide satisfying 0.8≦x1<1, 0<y1≦0.2, and 0≦z1≦0.

2.

9. 8. The positive electrode active material for a lithium secondary battery according to claim 7, wherein the lithium transition metal composite oxide is a lithium nickel-based oxide represented by Chemical Formula 1 and is a high nickel-based oxide satisfying 0.9≦x1<1, 0<y1≦0.1, and 0≦z1≦0.

1.

10. 2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the particles containing the lithium transition metal composite oxide have an average particle size of 1 μm to 25 μm.

11. 2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the particles containing the lithium transition metal composite oxide include large particles having an average particle size of 9 μm to 25 μm and small particles having an average particle size of 1 μm to 8 μm.

12. 12. The positive electrode active material for a lithium secondary battery according to claim 11, wherein the large particles are contained in an amount of 60% by weight to 95% by weight and the small particles are contained in an amount of 5% by weight to 40% by weight, based on a total of 100% by weight of the large particles and the small particles.

13. The large particles are in the form of secondary particles composed of a plurality of primary particles, The positive electrode active material for a lithium secondary battery according to claim 11, wherein the small particles are in the form of secondary particles consisting of a plurality of primary particles or in the form of single particles.

14. A method for producing a positive electrode active material for a lithium secondary battery, comprising dry-mixing 100 parts by mole of particles containing a lithium transition metal composite oxide and 0.1 to 0.6 parts by mole of a zirconium raw material, followed by heat treatment at 420°C to 580°C.

15. The method for producing a positive electrode active material for a lithium secondary battery according to claim 14, wherein when the particles containing the lithium transition metal composite oxide and the zirconium raw material are dry mixed, a lithium raw material is also mixed.

16. The method for producing a positive electrode active material for a lithium secondary battery according to claim 15, wherein the lithium raw material is mixed in an amount of more than 1 molar part to 4 molar parts or less with respect to 1 molar part of the zirconium raw material.

17. The method for producing a positive electrode active material for a lithium secondary battery according to claim 14, wherein the heat treatment is carried out in an oxygen atmosphere for 5 to 25 hours.

18. 15. The method for producing a positive electrode active material for a lithium secondary battery according to claim 14, wherein the zirconium raw material is particles containing zirconium oxide, and the average particle size (D50) of the particles is 10 nm to 500 nm.

19. 15. The method for producing a positive electrode active material for a lithium secondary battery according to claim 14, wherein the lithium transition metal composite oxide is a lithium nickel-based oxide represented by the following Chemical Formula 1, a lithium cobalt-based oxide represented by the following Chemical Formula 2, a lithium iron phosphate-based compound represented by the following Chemical Formula 3, or a cobalt-free lithium nickel-manganese-based oxide represented by the following Chemical Formula 4: [Chemical formula 1] Li ａ１ Ni ｘ１ M １ ｙ１ M ２ ｚ１ O ２－ｂ１ X ｂ１ In the above chemical formula 1, 0.9≦a1≦1.8, 0.3≦x1≦1, 0≦y1≦0.7, 0≦z1≦0.7, 0.9≦x1+y1+z1≦1.1, and 0≦b1≦0.1; M １ and M ２ are each independently one or more elements selected from the group consisting of Al, B, Ba, Ca, Ce, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Zn, and Zr, and X is one or more elements selected from the group consisting of F, P, and S; [Chemical formula 2] Li ａ２ Co ｘ２ M ３ ｙ２ O ２－ｂ２ X ｂ２ In the above chemical formula 2, 0.9≦a2≦1.8, 0.7≦x2≦1, 0≦y2≦0.3, 0.9≦x2+y2≦1.1, and 0≦b2≦0.1; M ３ is one or more elements selected from the group consisting of Al, B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mn, Mo, Ni, Se, Si, Sn, Sr, Ti, V, W, Y, Zn, and Zr, and X is one or more elements selected from the group consisting of F, P, and S; [Chemical formula 3] Li ａ３ Fe ｘ３ M ４ ｙ３ PO ４－ｂ３ X ｂ３ In the above chemical formula 3, 0.9≦a3≦1.8, 0.6≦x3≦1, 0≦y3≦0.4, and 0≦b3≦0.1; M ４ is one or more elements selected from the group consisting of Al, B, Ba, Ca, Ce, Co, Cr, Cu, Mg, Mn, Mo, Ni, Se, Si, Sn, Sr, Ti, V, W, Y, Zn, and Zr, and X is one or more elements selected from the group consisting of F, P, and S; [Chemical formula 4] Li ａ４ Ni ｘ４ Mn ｙ４ M ５ ｚ４ O ２－ｂ４ X ｂ４ In the above chemical formula 4, 0.9≦a4≦1.8, 0.8≦x4<1, 0<y4≦0.2, 0≦z4≦0.2, 0.9≦x4+y4+z4≦1.1, and 0≦b4≦0.1; M ５ is one or more elements selected from the group consisting of Al, B, Ba, Ca, Ce, Cr, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, and Zr, and X is one or more elements selected from the group consisting of F, P, and S.

20. 15. The method for producing a positive electrode active material for a lithium secondary battery according to claim 14, wherein the lithium transition metal composite oxide is a lithium nickel-based oxide represented by Chemical Formula 1 and is a high nickel-based oxide that satisfies 0.8≦x1<1, 0<y1≦0.2, and 0≦z1≦0.

2.

21. 15. The method for producing a positive electrode active material for a lithium secondary battery according to claim 14, wherein the particles containing the lithium transition metal composite oxide include large particles having an average particle size of 9 μm to 25 μm and small particles having an average particle size of 2 μm to 8 μm.

22. 22. The method for producing a positive electrode active material for a lithium secondary battery according to claim 21, wherein the large particles are contained in an amount of 60% by weight to 95% by weight and the small particles are contained in an amount of 5% by weight to 40% by weight, based on a total of 100% by weight of the large particles and the small particles.

23. The large particles are in the form of secondary particles composed of a plurality of primary particles, 22. The method of claim 21, wherein the small particles are in the form of secondary particles consisting of a plurality of primary particles or in the form of single particles.

24. A positive electrode for a lithium secondary battery, comprising the positive electrode active material according to any one of claims 1 to 13.

25. The positive electrode for a lithium secondary battery according to claim 24 , wherein the positive electrode further comprises a sulfide-based solid electrolyte.

26. 26. The positive electrode for a lithium secondary battery according to claim 25, wherein the positive electrode contains 65% by weight to 99% by weight of a positive electrode active material and 1% by weight to 35% by weight of a sulfide-based solid electrolyte, relative to a total of 100% by weight of the positive electrode active material and the sulfide-based solid electrolyte.

27. 26. The positive electrode for a lithium secondary battery according to claim 25, wherein the sulfide-based solid electrolyte comprises an argyrodite-type sulfide and is in the form of particles, and the average particle size (D50) of the particles is 0.1 μm to 3.0 μm.

28. 25. The positive electrode according to claim 24. a negative electrode, and A lithium secondary battery, including an electrolyte.

29. 25. The positive electrode according to claim 24. a negative electrode, and an all-solid-state secondary battery comprising a solid electrolyte layer located between the positive electrode and the negative electrode;

30. the negative electrode includes a current collector and a negative electrode coating layer disposed on the current collector and containing a lithophilic metal, a carbon material, or a combination thereof; 30. The all-solid-state secondary battery according to claim 29, comprising a lithium metal layer formed by charging between the current collector and the negative electrode coating layer.

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