Cathode active material for lithium secondary battery and lithium secondary battery including the same

Abstract

A positive electrode active material for a lithium secondary battery according to embodiments of the present invention comprises lithium-transition metal composite oxide particles having a single particle form and a first coating layer formed on the surface of the lithium-transition metal composite oxide particles and comprising a La-Zr-O compound. By forming the lithium-transition metal composite oxide particles as single particles and forming a coating layer on their surface, lifespan characteristics and capacity characteristics can be improved.

Description

Technology Field

[0001] The present invention relates to a positive electrode active material for a lithium secondary battery and a lithium secondary battery comprising the same. More specifically, the invention relates to a positive electrode active material for a lithium secondary battery comprising a lithium-transition metal composite oxide and a lithium secondary battery comprising the same. Background Technology

[0003] Rechargeable batteries are batteries capable of repeated charging and discharging, and with the advancement of the information and communication and display industries, they are widely applied as power sources for portable electronic communication devices such as camcorders, mobile phones, and laptop PCs. Furthermore, recently, battery packs containing rechargeable batteries are being developed and applied as power sources for eco-friendly vehicles, such as hybrid cars.

[0004] Examples of secondary batteries include lithium-ion batteries, nickel-cadmium batteries, and nickel-hydrogen batteries; among these, lithium-ion batteries are being actively developed and applied due to their high operating voltage and energy density per unit weight, as well as advantages in charging speed and weight reduction.

[0005] For example, a lithium secondary battery may include an electrode assembly comprising a positive electrode, a negative electrode, and a separator, and an electrolyte impregnating the electrode assembly. The lithium secondary battery may further include an outer casing, for example, in the form of a pouch, that accommodates the electrode assembly and the electrolyte.

[0006] A lithium metal oxide is used as the positive electrode active material of the above-mentioned lithium secondary battery, and it is desirable that it possesses high capacity, high power output, and long lifespan characteristics. However, if the above-mentioned lithium metal oxide is designed with a high-power composition, thermal and mechanical stability may be reduced, which may lead to a decrease in the lifespan characteristics and operational reliability of the lithium secondary battery.

[0007] For example, Korean Patent Publication No. 10-2017-0093085 discloses a cathode active material comprising a transition metal compound and an ion adsorption binder, but there are limitations in ensuring sufficient lifespan characteristics and stability. Prior art literature

[0008] Korean Patent Publication No. 10-2017-0093085 The problem to be solved

[0009] One objective of the present invention is to provide a positive electrode active material for a lithium secondary battery having excellent operational stability and reliability.

[0010] One objective of the present invention is to provide a lithium secondary battery comprising a positive electrode active material having excellent operational stability and reliability. means of solving the problem

[0012] A positive electrode active material for a lithium secondary battery according to embodiments of the present invention comprises: lithium-transition metal composite oxide particles having a single particle form; and a first coating layer formed on the surface of the lithium-transition metal composite oxide particles and comprising a La-Zr-O compound.

[0013] In some embodiments, a second coating layer formed on the surface of the first coating layer and comprising a Li-BO compound may be further included.

[0014] In some embodiments, the La-Zr-O compound may be derived from a first flux containing lanthanum and a second flux containing zirconium.

[0015] In some embodiments, the first flux may be La(OH)3 and the second flux may be Zr(OH)4.

[0016] In some embodiments, the grain size of the lithium-transition metal composite oxide particles measured by XRD analysis is 300 to 600 nm, and the grain size can be measured using Formula 1 below:

[0017] [Equation 1]

[0018]

[0019] (In Equation 1, L is the grain size (nm), λ is the X-ray wavelength (nm), β is the full width at half maximum of the (003) plane peak (rad), and θ is the diffraction angle (rad).

[0020] In some embodiments, the average particle size (D50) of the lithium-transition metal composite oxide particles may be less than 3.0 μm.

[0021] In some embodiments, the La-Zr-O compound is doped or coated with a metal, and the metal may be at least one of Mg, Ca, Al, Ti, W, Ta, P, and Nb.

[0022] In some embodiments, the single particle form may include a monolithic form formed by attaching or closely adhering 2 to 10 single particles to each other.

[0023] In some embodiments, when the surface of the lithium-transition metal composite oxide particles is measured by XPS (X-ray Photoelectron Spectrometer) analysis, a La (4d) peak at 102 eV and a Zr (3d) peak at 128.8 eV may be observed.

[0024] In some embodiments, the La-Zr-O compound is a garnet-structured Li7La3Zr2O 12 It may not include.

[0025] A method for manufacturing a positive electrode active material for a lithium secondary battery according to embodiments of the present invention comprises the steps of: preparing a lithium precursor and a transition metal precursor; mixing the lithium precursor, the transition metal precursor, a first flux and a second flux; and calcining the mixed lithium precursor, the transition metal precursor, the first flux and the second flux to form lithium-transition metal composite oxide particles having a first coating layer comprising a La-Zr-O compound formed on the surface.

[0026] In some embodiments, the first flux may have an average particle size (D50) of 1 μm or less.

[0027] In some embodiments, the first flux is La(OH)3 and the second flux is Zr(OH)4, and the lanthanum content in the first flux may be 500 to 2,000 ppm relative to the total weight of the lithium-transition metal composite oxide particles.

[0028] In some embodiments, the zirconium content included in the second flux may be 500 to 2,000 ppm relative to the total weight of the lithium-transition metal composite oxide particles.

[0029] In some embodiments, the step of adding boron and heat-treating to form a second coating layer containing a Li-BO compound on the surface of the first coating layer may be further included.

[0030] In some embodiments, a metal hydroxide is further added in the step of mixing the lithium precursor, the transition metal precursor, the first flux and the second flux, and the metal hydroxide may be at least one hydroxide selected from Mg, Ca, Al, Ti, W, Ta, P, and Nb.

[0031] In some embodiments, the lithium-transition metal composite oxide particles may have a composition represented by the following chemical formula 1:

[0032] [Chemical Formula 1]

[0033] Li a Ni x M 1-x O 2+y

[0034] (In Chemical Formula 1, a is 0.9≤a≤1.5, x is x≥0.6, y is -0.1≤y≤0.1, and M is one or more elements selected from Na, Mg, Ca, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Co, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, or Zr).

[0035] In some embodiments, the temperature at which the sintering is performed may satisfy the following Equations 2 and 3:

[0036] [Equation 2]

[0037] t1-15 ≤ T1(℃) ≤ t1+15

[0038] (In Equation 2, t1 is the temperature according to Equation 3 below, and T1 is the temperature at which the above firing is performed)

[0039] [Equation 3]

[0040] t1(℃) = (-520)*x + 1285

[0041] (In Equation 3, x is x from Equation 1 above).

[0042] A lithium secondary battery according to embodiments of the present invention comprises: a positive electrode comprising a positive electrode active material layer comprising the positive electrode active material for a lithium secondary battery described above; and a negative electrode facing the positive electrode. Effects of the invention

[0044] A positive electrode active material according to embodiments of the present invention may include a lithium-transition metal composite oxide particle having a single particle form and a first coating layer formed on the surface of the lithium-transition metal composite oxide particle and comprising a La-Zr-O compound.

[0045] When the lithium-transition metal composite oxide particles are single particles, cracking of the lithium-transition metal composite oxide particles is reduced, and the BET surface area where the cathode active material reacts with the electrolyte can be reduced. Accordingly, lifespan characteristics such as the capacity retention rate of the secondary battery can be improved. In addition, the electrical conductivity of the surface of the lithium-transition metal composite oxide particles is increased by the first coating layer, thereby maintaining good output characteristics of the secondary battery.

[0046] In some embodiments, a second coating layer containing a Li-BO compound may be formed on the surface of the first coating layer. In this case, the output characteristics and capacity characteristics of the secondary battery may be improved as the ion conductivity is enhanced.

[0047] In a method for manufacturing an anode active material according to embodiments of the present invention, a fluxing agent may be mixed with a lithium precursor and a transition metal precursor, and then calcined. In this case, a single particle may be smoothly formed by the fluxing agent, and a first coating layer may be formed on the surface of the single particle. Accordingly, the above-described effect can be realized by the single particle and the first coating layer. Brief explanation of the drawing

[0049] FIG. 1 is a schematic cross-sectional view showing a positive electrode active material according to exemplary embodiments. FIG. 2 is an SEM image taken to measure the particle size of lithium-transition metal composite oxide particles according to exemplary embodiments. FIG. 3 is a process flow diagram for explaining a method for manufacturing a positive electrode active material according to exemplary embodiments. FIG. 4 is SEM images illustrating the grinding process of a flux according to exemplary embodiments. FIG. 5 is a schematic flowchart illustrating the process of forming a positive electrode active material according to exemplary embodiments. Figure 6 is an SEM image illustrating the phenomenon of solution reprecipitation caused by a flux. FIGS. 7 and FIGS. 8 are schematic plan and cross-sectional views, respectively, showing a lithium secondary battery according to exemplary embodiments. Figure 9 shows SEM images of the surfaces of the positive electrode active materials of Example 1, Comparative Example 1, and Comparative Example 2. Figure 10 is a graph showing the elemental signal on the surface of the positive electrode active material of Example 1 measured through XPS analysis. FIG. 11 is a graph showing the change in capacity according to the repeated charging and discharging of a secondary battery according to the examples and comparative examples. Specific details for implementing the invention

[0050] Embodiments of the present invention provide a positive electrode active material comprising lithium-transition metal composite oxide particles and a lithium secondary battery comprising the same.

[0051] Hereinafter, embodiments of the present invention will be described in detail. However, this is merely illustrative and the present invention is not limited to the specific embodiments described illustratively.

[0052] FIG. 1 is a schematic cross-sectional view showing a positive electrode active material according to exemplary embodiments. Specifically, FIG. 1 (a) is a cross-sectional view showing a positive electrode active material in which a first coating layer is formed on the surface of a lithium-transition metal composite oxide particle. FIG. 1 (b) is a cross-sectional view showing a positive electrode active material in which a first coating layer is formed on the surface of a lithium-transition metal composite oxide particle and a second coating layer is formed on the surface of the first coating layer.

[0053] Referring to FIG. 1, in exemplary embodiments, the positive active material may include a lithium-transition metal composite oxide particle (50) having a single particle form and a first coating layer (60) formed on the surface of the lithium-transition metal composite oxide particle (50) and comprising a La-Zr-O compound.

[0054] The term “single particle form” used in this application is used to mean excluding secondary particles formed by the aggregation of a plurality of primary particles, for example. For example, the lithium-transition metal composite oxide particles (50) are substantially composed of particles in a single particle form, and secondary particle structures formed by the assembly or aggregation of primary particles may be excluded.

[0055] The term “single particle form” as used in this application does not exclude, for example, a range of 2 to 10 single particles being attached or closely bonded to each other to form a single body form.

[0056] In some embodiments, the lithium-transition metal composite oxide particle (50) may include a structure in which a plurality of primary particles are merged together as a single unit and converted substantially into a single particle.

[0057] For example, the lithium-transition metal composite oxide particles (50) may have a granular or spherical single particle form.

[0058] For example, the lithium-transition metal composite oxide particles (50) may include nickel (Ni) and may further include at least one of cobalt (Co) or manganese (Mn).

[0059] For example, the lithium-transition metal composite oxide particles (50) can be represented by the following chemical formula 1.

[0060] [Chemical Formula 1]

[0061] Li a Ni x M 1-x O 2+y

[0062] In Chemical Formula 1, a can be 0.9≤a≤1.5, x can be x≥0.6, and y can be -0.1≤y≤0.1. M can represent one or more elements selected from Na, Mg, Ca, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Co, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, or Zr.

[0063] In some preferred embodiments, the molar ratio or concentration x of Ni in Formula 1 may be 0.8 or higher, more preferably exceeding 0.8, and in some embodiments may be 0.98 or higher.

[0064] For example, when adopting a high-nickel (High-Ni) composition in which x is 0.8 or higher, the calcination of the lithium-transition metal composite oxide particles (50) can be performed at a relatively low temperature. Accordingly, in the manufacturing process of the positive electrode active material for a lithium secondary battery described later, the lithium-transition metal composite oxide particles (50) in the form of single particles can be formed at a relatively low temperature.

[0065] Ni can be provided as a transition metal associated with the output and capacity of the lithium secondary battery. Therefore, by employing a High-Ni composition in the lithium-transition metal composite oxide particles (50) as described above, a high-output cathode and a high-output lithium secondary battery can be provided.

[0066] However, as the Ni content increases, the long-term storage stability and lifespan stability of the anode or secondary battery may relatively decrease. However, according to exemplary embodiments, lifespan stability and capacity retention characteristics can be improved through Mn while maintaining electrical conductivity by including Co.

[0067] For example, lithium-transition metal composite oxide particles may be in the form of secondary particles formed by the dense aggregation of primary particles. However, in this case, micro-cracks may form inside the secondary particles during charging and discharging of the battery, and side reactions between the electrolyte and the positive electrode active material may be promoted, which may generate gas inside the battery. Consequently, the lifespan characteristics of the secondary battery may deteriorate with repeated charging and discharging.

[0068] In exemplary embodiments of the present invention, the lithium-transition metal composite oxide particles (50) may have a single particle form. In this case, cracking of the particles may be reduced, and the BET surface area reacting with the electrolyte may be reduced. Accordingly, the lifespan characteristics of the secondary battery and the capacity retention rate during repeated charge and discharge cycles may be improved.

[0069] For example, sintering may be performed at a relatively low temperature to form a high-Ni lithium-transition metal composite oxide (50) having a single particle form. However, in this case, residual lithium may increase on the surface of the lithium-transition metal composite oxide particles (50), which may reduce the electrical conductivity of the particle surface. Accordingly, the output characteristics and capacity characteristics of the secondary battery may be somewhat degraded.

[0070] In exemplary embodiments of the present invention, a first coating layer (60) comprising a lanthanum-zirconium-oxygen (La-Zr-O) compound may be formed on the surface of a lithium-transition metal composite oxide particle (50). In this case, the ionic conductivity of the surface of the lithium-transition metal composite oxide particle (50) may be increased. Accordingly, it is possible to prevent a decrease in capacity characteristics and output characteristics while forming a positive electrode active material of high-Ni composition in a single-particle structure.

[0071] For example, the above La-Zr-O compound may include various types of compounds containing La, Zr, and O.

[0072] In exemplary embodiments, the La-Zr-O compound may be derived from the first flux and the second flux described below.

[0073] For example, as described below, the first coating layer (60) can be formed together with the formation of single particles due to the fluxes. In this case, the La-Zr-O compound derived from the flux may further contain lithium, but Li7La3Zr2O having a garnet structure 12 It may not include. Therefore, when a first coating layer (60) is formed together with a lithium-transition metal composite oxide particle (50) in the form of a single particle as in the embodiments of the present invention, the La-Zr-O compound is Li7La3Zr2O having a garnet structure. 12 It may not include.

[0074] In some embodiments, as illustrated in FIG. 1(b), a second coating layer (70) comprising an ion-conducting Li-BO compound may be formed on the surface of the first coating layer (60) described above. In this case, as electrical conductivity is improved by the first coating layer (60), ion conductivity may also be improved by the second coating layer (70). Accordingly, the capacity characteristics and output characteristics of the secondary battery may be further improved.

[0075] In some embodiments, the La-Zr-O compound included in the first coating layer (60) may be derived from a first flux containing lanthanum and a second flux containing zirconium.

[0076] In some embodiments, La(OH)3 may be used as the first flux and Zr(OH)4 may be used as the second flux.

[0077] For example, a first flux and a second flux may be introduced during the manufacturing process of the lithium-transition metal composite oxide (50) described later. In this case, the first flux (e.g., La(OH)3) and the second flux (e.g., Zr(OH)4) react with a lithium precursor (e.g., LiOH) to form a lithium-transition metal composite oxide particle (50) in the form of a single particle, and a first coating layer (60) may be formed on the surface of the lithium-transition metal composite oxide particle (50). Accordingly, sufficient ion conductivity can be secured while forming an anode active material having a single particle structure of high-Ni composition.

[0078] In some embodiments, the crystal grain size of the lithium-transition metal composite oxide particles (50) measured by XRD analysis may be 300 to 600 nm. When the crystal grain size satisfies the above range, the lithium-transition metal composite oxide particles (50) in the form of single particles can be formed, while preventing the decrease in durability and cracking of the cathode active material due to excessively small particle size.

[0079] In exemplary embodiments, "grain size" is a value measured through X-ray diffraction (XRD) analysis. The grain size can be obtained by calculating it using the Scherrer equation (Equation 1 below) with the full width at half maximum (FWHM) obtained through XRD analysis.

[0080] [Equation 1]

[0081]

[0082] In Equation 1 above, L represents the grain size (nm), λ represents the X-ray wavelength (nm), β represents the full width at half maximum of the corresponding peak (rad), and θ represents the diffraction angle (rad). According to exemplary embodiments, the full width at half maximum in XRD analysis for grain size measurement can be measured from the peak of the (003) plane.

[0083] In some embodiments, β in Equation 1 above may be a half-width value corrected from a value derived from the equipment. In one embodiment, Si may be used as a standard material to reflect the value derived from the equipment. In this case, the half-width profile of Si over the entire 2θ range may be fitted to express the equipment-derived half-width as a function of 2θ. Subsequently, a value obtained by subtracting the equipment-derived half-width value at the corresponding 2θ from the function may be used as β.

[0084] In some embodiments, the average particle size (D50) of the lithium-transition metal composite oxide particles (50) may be less than 3.0 μm. In this case, the lithium-transition metal composite oxide particles (50) in the form of single particles may be formed due to the introduction of sufficient first and second fluxes.

[0085] In some embodiments, the average particle size (D50) of the lithium-transition metal composite oxide particles (50) may be 2.0 to 2.9 μm. In this case, the lithium-transition metal composite oxide particles (50) in the form of single particles can be formed, while preventing the degradation of lifespan characteristics caused by cracks in the positive electrode active material that occur during the electrode pressing process.

[0086] In the present invention, "average particle size" or "D50" may refer to the particle size at which the cumulative percentage of volume in the particle size distribution obtained from the particle volume corresponds to 50%.

[0087] For example, the above average particle size can be measured using a particle size analyzer (PSA).

[0088] FIG. 2 is an SEM image taken to measure the particle size of lithium-transition metal composite oxide particles according to exemplary embodiments.

[0089] Referring to FIG. 2, the average particle size can be determined by obtaining a cross-sectional image through ion milling for a positive electrode active material containing lithium-transition metal composite oxide particles (50), and measuring the average size of 50 single particles from the cross-sectional image.

[0090] In some embodiments, the La-Zr-O compound of the first coating layer (60) may be doped or coated with an additional metal. For example, the metal to be doped or coated may be at least one of Mg, Ca, Al, Ti, W, Ta, P, and Nb.

[0091] In this case, a metal with high electrical conductivity is doped into the layered structure of the aforementioned La-Zr-O compound to improve the output and capacity characteristics of the positive electrode active material. Accordingly, the output characteristics of the secondary battery can be maintained even when the positive electrode active material having a high-Ni composition is manufactured as a single particle.

[0092] FIG. 3 is a process flow diagram for explaining a method for manufacturing a positive electrode active material according to exemplary embodiments.

[0093] Hereinafter, a method for manufacturing according to exemplary embodiments of a positive electrode active material for a lithium secondary battery described above with reference to FIG. 3 is provided.

[0094] Referring to FIG. 3, a lithium precursor and a transition metal precursor can be prepared (e.g., step S10).

[0095] The above lithium precursor may include, for example, lithium carbonate, lithium nitrate, lithium acetate, lithium oxide, lithium hydroxide, etc. These may be used alone or in combination of two or more.

[0096] For example, a transition metal precursor can be prepared through a co-precipitation reaction of metal salts. The metal salts may include nickel salts, manganese salts, and cobalt salts.

[0097] Examples of the above nickel salts include nickel sulfate, nickel hydroxide, nickel nitrate, nickel acetate, and hydrates thereof. Examples of the above manganese salts include manganese sulfate, manganese acetate, and hydrates thereof. Examples of the above cobalt salts include cobalt sulfate, cobalt nitrate, cobalt carbonate, and hydrates thereof.

[0098] The above metal salts can be mixed with a precipitating agent and / or a chelating agent in a ratio satisfying the content or concentration ratio of each metal described with reference to Chemical Formula 1 to prepare an aqueous solution. The above aqueous solution can be co-precipitated in a reactor to prepare a transition metal precursor.

[0099] The above precipitating agent may include alkaline compounds such as sodium hydroxide (NaOH) and sodium carbonate (Na2CO3). The above chelating agent may include, for example, water ammonia (e.g., NH4OH) and ammonium carbonate (e.g., NH3HCO3).

[0100] The temperature of the above co-precipitation reaction can be controlled, for example, in the range of about 40°C to 60°C. The reaction time can be controlled in the range of about 24 to 72 hours.

[0101] In exemplary embodiments, the prepared lithium precursor, transition metal precursor, the first flux and the second flux described above can be mixed (e.g., step S20).

[0102] For example, the first flux may be La(OH)3 and the second flux may be Zr(OH)4. In this case, a first coating layer (60) containing a La-Zr-O compound may be formed on the surface of the lithium-transition metal composite oxide particles (50) in the subsequent calcination process.

[0103] In some embodiments, the method may further include a step of grinding the first flux (e.g., La(OH)3) before introducing the first flux and the second flux. In this case, the particle size may be sufficiently reduced to improve reactivity with the lithium precursor and the transition metal precursor. Accordingly, the formation of the lithium-transition metal composite oxide particles (50) and the first coating layer (60) in the form of single particles can be performed smoothly.

[0104] FIG. 4 is SEM images illustrating the grinding process of a flux according to exemplary embodiments.

[0105] Referring to FIG. 4, the first flux powder can be ground to have an average particle size of 1 μm or less. In this case, lithium-transition metal composite oxide particles (50) having a uniform single particle shape can be formed. Accordingly, the degradation of the capacity and lifespan characteristics of the secondary battery due to the non-uniform single particle shape can be prevented.

[0106] For example, a jet mill can be used for the above fine grinding.

[0107] In some embodiments, La(OH)3 may be used as the first flux, and the lanthanum content included in the first flux may be 500 to 2,000 ppm relative to the total weight of the lithium-transition metal composite oxide particles (50). Preferably, the lanthanum content included in the first flux may be 500 to 1,000 ppm relative to the total weight of the lithium-transition metal composite oxide particles (50).

[0108] When the above-mentioned range of lanthanum content is satisfied, the first flux is sufficiently introduced to form single particles, thereby preventing the formation of non-uniform large particles. Accordingly, the lifespan characteristics and output characteristics of the secondary battery can be improved together.

[0109] In some embodiments, Zr(OH)4 may be used as the second flux, and the zirconium content in the second flux may be 300 to 2,000 ppm relative to the total weight of the lithium-transition metal composite oxide particles (50). Preferably, the zirconium content in the second flux may be 500 to 1,000 ppm relative to the total weight of the lithium-transition metal composite oxide particles (50).

[0110] When the above-described zirconium content range is satisfied, the second flux is sufficiently introduced together with the first flux to form a single particle and form a first coating layer containing a La-Zr-O compound.

[0111] A lithium-transition metal composite oxide particle (50) can be formed by calcining a mixed lithium precursor, a transition metal precursor, a first flux, and a second flux to form a first coating layer (60) containing a La-Zr-O compound on the surface (e.g., step S30).

[0112] FIG. 5 is a schematic flowchart illustrating the process of forming a positive electrode active material according to exemplary embodiments.

[0113] In Figure 5, the flux is indicated as a relatively small dot between the lithium precursor and transition metal precursor clusters.

[0114] Referring to FIG. 5, the lithium precursor, transition metal precursor, and flux can be prepared in a mixed powder state through the mixing process described above (e.g., step S20) (e.g., step S31).

[0115] For example, when lithium precursors and transition metal precursors are mixed and calcined without adding a flux, each particle may grow to form secondary particles rather than single particles. In this case, gas may be generated due to particle cracking caused by repeated charging and discharging. Consequently, the capacity retention rate of the secondary battery may decrease.

[0116] As illustrated in FIG. 5, when the aforementioned fluxes (first flux and second flux) are introduced and mixed, the flux and the lithium precursor may react to form a liquid intermediate. In this case, as the intermediate reacts with the transition metal precursor, a rearrangement phenomenon may occur to reduce surface tension (e.g., step S32).

[0117] Figure 6 is an SEM image illustrating the solution re-precipitation phenomenon caused by a flux. For example, La(OH)3 introduced as the first flux can induce solution re-precipitation after the aforementioned realignment phenomenon.

[0118] Referring to FIG. 6, after the above rearrangement, a solution reprecipitation phenomenon occurs, which can reduce the pores inside the lithium-transition metal composite oxide particles (e.g., step S33).

[0119] For example, the above-mentioned reprecipitated lithium-transition metal composite oxide particles may undergo densification and take on a single-particle form (e.g., step S34). In this case, particle cracking and gas generation due to repeated charging and discharging of the secondary battery are reduced, thereby improving the lifespan characteristics of the battery.

[0120] In some embodiments, after performing the above-described calcination (e.g., S30), boron may be introduced onto the first coating layer (60) and heat treated. In this case, a second coating layer (70) containing a Li-BO compound may be formed on the first coating layer (60). Accordingly, the surface ion conductivity of the positive electrode active material may be increased, thereby improving the output characteristics of the secondary battery. For example, the heat treatment may be performed at 200 to 400°C.

[0121] For example, the first flux may have an ionic radius larger than that of nickel, cobalt, and manganese. For example, La contained in La(OH)3 3+The ionic radius of is 103.2 pm, and Ni 2+ The ionic radius of is 83 pm, Co 3+ The ionic radius of is 68.5 pm, Mn 4+ The ionic radius of can be 67 pm. In this case, since the ionic radius of the La ion is large, it cannot be included in the layered structure, and a La-Zr-O compound can be formed on the surface of the lithium-transition metal composite oxide particles together with Zr derived from the second flux. Accordingly, the above-described effect of improving lifespan characteristics can be realized.

[0122] In some embodiments, a metal hydroxide may be further added during the step of adding and mixing the first and second fluxes described above. For example, a metal hydroxide may be added together with La(OH)3 and Zr(OH)4 to a mixture of a lithium precursor and a transition metal precursor. In this case, the metal may be doped or coated onto the La-Zr-O compound contained in the first coating layer (60), thereby improving the electrical conductivity of the positive electrode active material.

[0123] For example, the metal may be at least one of Mg, Ca, Al, Ti, W, Ta, P, and Nb.

[0124] In some embodiments, the temperature at which the above-described sintering (e.g., step S30) is performed may satisfy the following Equations 2 and 3.

[0125] [Equation 2]

[0126] t1-15 ≤ T1(℃) ≤ t1+15

[0127] In Equation 2, t1 is a temperature according to Equation 3 below, and T1 may be the temperature at which the above firing is performed.

[0128] [Equation 3]

[0129] t1(℃) = (-520)*x + 1285

[0130] In Formula 3, x may be the x in Formula 1 described above.

[0131] When the above temperature range is satisfied, lithium-transition metal composite oxide particles (50) can be formed in the form of single particles having an appropriate average particle size and crystal grain size.

[0132] In some embodiments, a metal oxide coating layer may be further formed on the lithium-transition metal composite oxide particles formed according to steps S10 to S30 described above.

[0133] For example, a metal oxide coating layer can be further formed on the lithium-transition metal composite oxide particles by mixing the lithium-transition metal composite oxide particles and the metal oxide and then heat-treating. In this case, cracks on the particle surface caused by collisions between particles during the jet mill process can be eliminated. Accordingly, the lifespan characteristics of the secondary battery can be improved.

[0134] The metal oxide may be, for example, at least one oxide of Al, Mg, Ca, Al, Ti, W, Ta, P, and Nb. For example, the metal oxide may be Al2O3.

[0135] In some embodiments, the lithium-transition metal composite oxide particles formed with the above-described metal oxide coating layer can be washed with water.

[0136] For example, a metal oxide coating layer can be formed on the lithium-transition metal composite oxide particles, mixed with water in a 1:1 volume ratio, stirred, and then washed and dried. Accordingly, residual lithium remaining on the surface of the lithium-transition metal composite oxide particles can be removed, thereby improving the output characteristics and lifespan characteristics of the secondary battery.

[0137] In some embodiments, a boron-containing coating layer may be further formed on the washed and dried lithium-transition metal composite oxide particles.

[0138] For example, a boron-containing coating layer can be further formed on the lithium-transition metal composite oxide particles by mixing the washed and dried lithium-transition metal composite oxide particles with boric acid (H3BO3) and then heat-treating. Accordingly, the ionic conductivity of the positive electrode active material is improved, and the output characteristics of the secondary battery can be improved.

[0139] FIGS. 7 and FIGS. 8 are schematic plan and cross-sectional views, respectively, showing a lithium secondary battery according to exemplary embodiments.

[0140] Hereinafter, a lithium secondary battery comprising a positive electrode including a positive electrode active material for a lithium secondary battery as described above with reference to FIGS. 7 and 8 is provided.

[0141] Referring to FIGS. 7 and 8, a lithium secondary battery may include a positive electrode (100) containing a positive active material, a negative electrode (130), and a separator (140).

[0142] The positive electrode (100) may include a positive electrode active material layer (110) formed by applying a positive electrode active material containing the above-described lithium-transition metal oxide particles (50) to a positive electrode current collector (105).

[0143] For example, a slurry can be prepared by mixing and stirring lithium-transition metal oxide particles (50), on which a first coating layer (60) containing a La-Zr-O compound is formed on the surface, with a binder, a conductive material and / or a dispersant, etc., in a solvent. After coating the slurry onto an anode current collector (105), the anode can be manufactured by compressing and drying.

[0144] The positive current collector (105) may include, for example, stainless steel, nickel, aluminum, titanium, copper, or an alloy thereof, and preferably may include aluminum or an aluminum alloy.

[0145] The above binder may include, for example, organic binders such as vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidenefluoride (PVDF), polyacrylonitrile, and polymethylmethacrylate, or water-based binders such as styrene-butadiene rubber (SBR), and may be used together with a thickener such as carboxymethyl cellulose (CMC).

[0146] For example, a PVDF-based binder can be used as a binder for forming the positive electrode. In this case, the amount of binder for forming the positive electrode active material layer (110) can be reduced and the amount of the positive electrode active material can be increased relatively, thereby improving the output and capacity of the secondary battery.

[0147] The above conductive material may be included to promote electron transfer between active material particles. For example, the conductive material may include carbon-based conductive materials such as graphite, carbon black, graphene, carbon nanotubes, etc., and / or metal-based conductive materials such as perovskite materials such as tin, tin oxide, titanium oxide, LaSrCoO3, LaSrMnO3, etc.

[0148] The negative electrode (130) may include a negative electrode current collector (125) and a negative electrode active material layer (120) formed by coating a negative electrode active material onto the negative electrode current collector (125).

[0149] The above-mentioned negative electrode active material may be any material known in the art capable of absorbing and extracting lithium ions without special limitation. For example, carbon-based materials such as crystalline carbon, amorphous carbon, carbon composites, and carbon fibers; lithium alloys; silicon or tin, etc. may be used. Examples of the above-mentioned amorphous carbon include hard carbon, coke, mesocarbon microbeads (MCMB) calcined at 1500°C or lower, and mesophase pitch-based carbon fibers (MPCF). Examples of the above-mentioned crystalline carbon include graphite-based carbon such as natural graphite, graphitized coke, graphitized MCMB, and graphitized MPCF. Elements included in the above-mentioned lithium alloy may include aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, or indium.

[0150] The negative current collector (125) may include, for example, gold, stainless steel, nickel, aluminum, titanium, copper, or an alloy thereof, and preferably may include copper or a copper alloy.

[0151] In some embodiments, the cathode active material may be mixed and stirred with a binder, a conductive material and / or a dispersant, etc., in a solvent to prepare a slurry. The cathode (130) may be prepared by coating the slurry onto the cathode current collector, and then compressing and drying it.

[0152] Materials substantially identical or similar to the materials described above may be used as the binder and conductive material. In some embodiments, the binder for forming the cathode may include, for example, a water-based binder such as styrene-butadiene rubber (SBR) for compatibility with carbon-based active materials, and may be used together with a thickener such as carboxymethyl cellulose (CMC).

[0153] A separator (140) may be interposed between the anode (100) and the cathode (130). The separator (140) may include a porous polymer film made of a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, an ethylene / methacrylate copolymer, etc. The separator (140) may also include a nonwoven fabric formed of high-melting-point glass fibers, polyethylene terephthalate fibers, etc.

[0154] According to exemplary embodiments, an electrode cell is defined by an anode (100), a cathode (130), and a separator (140), and a plurality of said electrode cells may be stacked to form, for example, an electrode assembly (150) in the form of a jelly roll. For example, the electrode assembly (150) may be formed by winding, laminating, folding, etc., of the separator (140).

[0155] The above electrode assembly may be housed together with an electrolyte within an outer case (160) to define a lithium secondary battery. According to exemplary embodiments, a non-aqueous electrolyte may be used as the electrolyte.

[0156] The non-aqueous electrolyte comprises a lithium salt as an electrolyte and an organic solvent, and the lithium salt is, for example, Li + X - It is expressed as and the anion (X) of the above lithium salt - As F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P- , CF3SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - Examples of the back can be given.

[0157] Examples of the above organic solvents may include propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethylmethyl carbonate (EMC), methylpropyl carbonate, dipropyl carbonate, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, sulfolane, gamma-butyrolactone, propylene sulfite, and tetrahydrofuran. These may be used individually or in combination of two or more.

[0158] As illustrated in FIG. 7, electrode tabs (positive tabs and negative tabs) may protrude from the positive current collector (105) and negative current collector (125) belonging to each electrode cell, respectively, and extend to one side of the outer case (160). The electrode tabs may be fused together with the one side of the outer case (160) to form electrode leads (positive lead (107) and negative lead (127)) that extend or are exposed to the outside of the outer case (160).

[0159] The above lithium secondary battery can be manufactured in, for example, a cylindrical, prismatic, pouch, or coin type using a can.

[0160] Hereinafter, preferred embodiments are presented to aid in understanding the present invention; however, these embodiments are merely illustrative of the invention and are not intended to limit the appended claims. It is obvious to those skilled in the art that various changes and modifications to the embodiments are possible within the scope and spirit of the invention, and that such variations and modifications fall within the scope of the appended claims.

[0161] Example 1

[0162] (1) Preparation of lithium precursor and transition metal precursor (S10)

[0163] NiSO4, CoSO4, and MnSO4 were mixed in a ratio of 0.94:0.05:0.01 using distilled water from which internal dissolved oxygen had been removed by bubbling with N2 for 24 hours. The above solution was introduced into a reactor at 50°C, and a co-precipitation reaction was carried out for 48 hours using NaOH and NH4OH as a precipitating agent and a chelating agent, respectively, to produce Ni as a transition metal precursor 0.94 Co 0.05 Mn 0.01 (OH)2 was obtained. The obtained precursor was dried at 80°C for 12 hours, and then re-dried at 110°C for 12 hours.

[0164] In the above composition (e.g., Ni 94%), the appropriate firing temperature range according to Equations 2 and 3 is 781.2 to 811.2°C.

[0165] (2) Mixing process (S20)

[0166] The above lithium hydroxide, the above transition metal precursor, La(OH)3 as a first flux, and Zr(OH)4 as a second flux were introduced into a dry high-speed mixer and mixed. La(OH)2 was introduced so that the lanthanum content was 1,000 ppm relative to the total weight of the lithium-transition metal composite oxide particles to be obtained, and Zr(OH)4 was introduced so that the zirconium content was 1,000 ppm relative to the total weight of the lithium-transition metal composite oxide particles to be obtained.

[0167] (3) Sintering (S30)

[0168] Mixed lithium hydroxide, transition metal precursor, La(OH)3, and Zr(OH)4 were placed in a calcination furnace, and oxygen was supplied at a flow rate of 100 mL / min to maintain the oxygen concentration inside the furnace at 95% or higher, while the temperature was raised to approximately 795°C at a heating rate of 2°C / min. The heated temperature was maintained for 10 hours. After calcination, fine grinding was performed using a jet mill to obtain the cathode active material.

[0169] (4) Formation of a metal oxide coating layer

[0170] Al2O3- with an average particle size of 30 to 70 nm was added to the obtained lithium-transition metal composite oxide particles in a dry high-speed mixer and uniformly mixed for 5 minutes to prepare a mixture. At this time, the Al2O3 was added in an amount of 1,000 ppm relative to the total weight of the lithium-transition metal composite oxide particles.

[0171] The above mixture was placed in a kiln and heated to 700°C at a rate of 2°C / min, and then maintained at 700°C for 10 hours. During the heating and maintenance, oxygen gas was continuously passed through at a flow rate of 10 mL / min.

[0172] After the completion of calcination, natural cooling to room temperature was performed, followed by grinding and classification to obtain lithium-transition metal composite oxide particles coated with metal oxide. Through the aforementioned coating and heat treatment, cracks on the particle surface caused by collisions between particles during the jet mill process were reduced.

[0173] (5) Washing, drying, and formation of boron-containing coating layer

[0174] The lithium-transition metal composite oxide particles coated with the above metal oxide were mixed with water in a 1:1 volume ratio, stirred for 10 minutes, filtered, and washed with water. The filtered lithium-transition metal composite oxide particles were dried at 130°C for 12 hours.

[0175] Washed and dried lithium-transition metal composite oxide particles and H3BO3 at a ratio of 1,000 ppm relative to the total weight of the particles were fed into a dry high-speed mixer and uniformly mixed for 5 minutes to prepare a mixture. Specifically, the dried lithium-transition metal composite oxide particles and H3BO3 at a ratio of 1,000 ppm relative to the total weight of the particles were placed into a calcination furnace in an oxygen atmosphere and heated to 300°C at a rate of 2°C / min while mixing dry. After heating, the temperature was maintained for 10 hours to produce lithium-transition metal composite oxide particles with a boron-containing coating layer formed thereon.

[0176] (6) Lithium secondary battery manufacturing

[0177] A secondary battery was manufactured using the aforementioned positive active material. Specifically, a positive composite was prepared by mixing the positive active material, Denka Black as a conductive material, and PVDF as a binder in a mass ratio of 93:5:2, respectively. After coating the composite onto an aluminum current collector, the positive was manufactured through drying and pressing. After pressing, the target electrode density of the positive was adjusted to 3.6 to 3.7 g / cc.

[0178] Lithium metal was used as the negative electrode active material.

[0179] As described above, the anode and cathode manufactured were stacked by notching them into circular shapes with diameters of Φ14 and Φ16, respectively, and an electrode cell was formed by interposing a separator (polyethylene, thickness 13㎛) notched to Φ19 between the anode and cathode. The electrode cell was placed inside a coin cell outer casing with a diameter of 20mm and a height of 1.6mm, and an electrolyte was injected to assemble it, and it was aged for more than 12 hours so that the electrolyte could be impregnated into the electrode.

[0180] The electrolyte used was 1M LiPF6 dissolved in a mixed solvent of EC / EMC (30 / 70; volume ratio).

[0181] Formation charging and discharging were performed on the secondary battery manufactured as described above (charging conditions CC-CV 0.1C 4.3V 0.005C CUT-OFF, discharging conditions CC 0.1C 3V CUT-OFF).

[0182] Example 2

[0183] A positive electrode active material and a lithium secondary battery were obtained in the same manner as in Example 1, except that the temperature was raised to 782℃ during the calcination step.

[0184] Example 3

[0185] A positive electrode active material and a lithium secondary battery were obtained in the same manner as in Example 1, except that the temperature was raised to 810℃ during the calcination step.

[0186] Example 4

[0187] A positive electrode active material and a lithium secondary battery were obtained in the same manner as in Example 1, except that (NH4)H2PO4 was additionally added during the metal oxide coating so that the phosphorus (P) content was 1,000 ppm relative to the total weight of the lithium-transition metal composite oxide particles to be obtained.

[0188] Example 5

[0189] A positive electrode active material and a lithium secondary battery were obtained in the same manner as in Example 1, except that the temperature was raised to 775℃ during the calcination step.

[0190] Example 6

[0191] A positive electrode active material and a lithium secondary battery were obtained in the same manner as in Example 1, except that the temperature was raised to 830°C during the calcination step.

[0192] Example 7

[0193] A positive electrode active material and a lithium secondary battery were obtained in the same manner as in Example 1, except that La(OH)3 was added such that the lanthanum content was 450 ppm relative to the total weight of the lithium-transition metal composite oxide particles to be obtained.

[0194] Example 8

[0195] A positive electrode active material and a lithium secondary battery were obtained in the same manner as in Example 1, except that La(OH)3 was added such that the lanthanum content was 2,050 ppm relative to the total weight of the lithium-transition metal composite oxide particles to be obtained.

[0196] Comparative Example 1

[0197] A positive electrode active material and a lithium secondary battery were obtained in the same manner as in Example 1, except that the first and second fluxes were not added, and the temperature was raised to 845°C during the calcination step.

[0198] Comparative Example 2

[0199] A positive electrode active material and a lithium secondary battery were obtained using the same method as Comparative Example 1, except that the temperature was raised to 795℃ during the calcination step.

[0200] For the cathode active materials prepared according to the above-described examples and comparative examples, the grain size was calculated using XRD analysis and the above-described Equation 1.

[0201] Meanwhile, specific XRD analysis equipment / conditions are as listed in Table 1 below.

[0202] XRD(X-Ray Diffractometer) EMPYREAN Maker PANalytical Anode material Cu K-Alpha1 wavelength 1.540598 Å Generator voltage 45 kV Tube current 40 mA Scan Range 10~120 o Scan Step Size 0.0065 o Divergence slit 1 / 4 o Antiscatter slit 1 / 2 o

[0203] In addition to the grain size obtained through the XRD analysis above, the ratio of Ni among the transition metals, whether a flux was added, the BET specific surface area, the firing temperature, and the amount of lanthanum added for the above-described examples and comparative examples are shown in Table 2 below.

[0204] division Ni ratio (%) Whether to add flux Heat-treated metal Firing temperature (°C) La input amount (ppm) BET specific surface area (m²) 2 / g) Grain size (nm) D50(㎛) Example 1 94 O Al 795 1,000 0.63 428 2.65 Example 2 94 O Al 782 1,000 0.68 330 2.29 Example 3 94 O Al 810 1,000 0.55 571 2.29 Example 4 94 O Al+P 795 1,000 0.61 440 2.70 Example 5 94 O Al 775 1,000 - 285 3.11 Example 6 94 O Al 830 1,000 - 650 3.05 Example 7 94 O Al 795 450 - 285 3.10 Example 8 94 O Al 795 2,050 - 456 3.21 Comparative Example 1 94 Χ Al 845 - 0.48 738 3.8 Comparative Example 2 94 Χ Al 795 - 0.72 200 3.5

[0205] Referring to Table 2 above, Examples 1 to 4, in which the firing temperature satisfies Equations 2 and 3 and the lanthanum input amount is 500 to 2,000 ppm, had a crystal grain size of 300 to 600 nm and an average grain diameter (D50) of 3.0 μm or less.

[0206] However, in Example 5, the firing temperature was below the temperature range according to Equations 2 and 3, the temperature was relatively low, so the densification (S34) process was performed less, and the crystal grain size was formed relatively smaller compared to Examples 1 to 4, and the average grain size was measured to be relatively higher.

[0207] In addition, Example 6, in which the firing temperature exceeds the temperature range according to Equations 2 and 3, had a relatively higher grain size and average grain diameter compared to Examples 1 to 4 due to particle aggregation caused by under-firing.

[0208] In addition, in Example 7, where the lanthanum input amount was less than 500 ppm, the flux did not react sufficiently with the lithium precursor, so the single-grain formation was relatively less performed. Accordingly, a relatively smaller grain size was measured compared to Examples 1 to 4.

[0209] In addition, in Example 8, where the lanthanum input amount exceeded 2,000 ppm, the flux reacted non-uniformly with a number of transition metal precursors, and a relatively large average particle size was measured compared to Examples 1 to 4.

[0210] In the case of Comparative Examples 1 and 2, in which no flux was added, no or almost no single particle shape was formed, so relatively very high or low grain size and particle size were measured.

[0211] FIG. 9 shows SEM images of the surfaces of the positive electrode active materials of Example 1, Comparative Example 1, and Comparative Example 2. Specifically, FIG. 8 (a), (b), and (c) are SEM images of the surfaces of the positive electrode active materials of Example 1, Comparative Example 1, and Comparative Example 2, respectively.

[0212] Referring to FIG. 9, Example 1, in which a flux was added, formed an anode active material having a single particle form. However, Comparative Example 1, in which the calcination temperature was higher than the range of Equations 2 and 3 and no flux was added, formed a single particle with a very non-uniform particle size, and Comparative Example 2, in which the range of Equations 2 and 3 was satisfied but no flux was added, formed an anode active material having a secondary particle form with a polycrystalline structure.

[0214] Experimental example

[0215] (1) Measurement of cation mixing ratio

[0216] Cation mixing can refer to a phenomenon in which Ni ions are located in the Li layer, for example, in the layered structure of lithium-transition metal composite oxide particles. If the ratio of cation mixing is high, the discharge capacity may decrease.

[0217] The cation mixing ratio of the positive electrode active material according to the above-described examples and comparative examples was measured using the Rietveld Method.

[0218] Specifically, XRD peaks were measured, and lattice constants were refined using the least squares method or the Rawlay method. Subsequently, XRD simulations were performed on a structural model constructed by estimating the arrangement of each atom based on crystallographic findings and chemical composition. Through the simulations, the ratio of Ni ions occupying the Li sites (3a sites) of the cathode active material was calculated.

[0219] (2) Measurement of initial charge / discharge capacity and evaluation of initial capacity efficiency

[0220] A lithium secondary battery manufactured according to the above-described examples and comparative examples was charged (CC-CV 0.1 C 4.3V 0.005C CUT-OFF) in a 25℃ chamber, and the battery capacity (initial charge capacity) was measured, and then discharged (CC 0.1C 3.0V CUT-OFF) and the battery capacity (initial discharge capacity) was measured.

[0221] The initial capacity efficiency was evaluated by converting the value obtained by dividing the measured initial discharge capacity by the measured initial charge capacity into a percentage (%).

[0222] (3) Measurement of capacity retention rate (lifespan characteristic) during repeated charging and discharging

[0223] For lithium secondary batteries according to the examples and comparative examples, charging (CC / CV 0.5C 4.3V 0.05C CUT-OFF) and discharging (CC 1.0C 3.0V CUT-OFF) were repeated 50 times, and the life retention rate was evaluated as a percentage of the value obtained by dividing the discharge capacity at 50 cycles by the discharge capacity at 1 cycle.

[0224] The evaluation results are shown in Table 3 below.

[0225] division Cation mixing ratio (%) Initial charge capacity (mAh / g) Initial discharge capacity (mAh / g) Initial capacity efficiency (%) Capacity retention rate (%) Example 1 0.94 252.0 216.9 86.1 90.4 Example 2 1.27 252.1 220.3 87.4 91.7 Example 3 2.3 247.9 215.9 87.1 93.0 Example 4 0.82 252.6 218.6 86.6 93.9 Example 5 1.25 251.8 216.1 85.8 90.5 Example 6 2.45 249.0 213.6 85.7 89.0 Example 7 1.68 247.8 213.9 86.3 89.1 Example 8 1.72 247.5 213.4 86.2 90.2 Comparative Example 1 5.1 244.4 205.8 84.2 85.4 Comparative Example 2 3.5 245.0 209.3 85.4 87.2

[0226] Referring to Table 3, the examples in which a single particle and a first coating layer were formed by adding a fluxing agent showed a lower overall cation mixing ratio, excellent lifespan characteristics, and good initial capacity efficiency compared to the comparative examples.

[0227] Figure 10 is a graph showing the elemental signals on the surface of the positive electrode active material of Example 1 measured through XPS (X-ray photoelectron spectrometer) analysis. Specifically, Figure 9 is a graph showing the La and Zr components of the La-Zr-O compound present on the surface of the lithium-transition metal composite oxide particles of Example 1.

[0228] The above XPS analysis was performed under the following conditions.

[0229] 1) X-ray type: Source - Al Ka, Beam size 50 um

[0230] 2) Analyzer: CAE Mode

[0231] 3) Number of scans: 2(survey scan), 10-50 (Narrow Scan)

[0232] 4) Pass energy: 150eV (survey Scan), 20eV (Narrow Scan)

[0233] Referring to FIG. 10, in Example 1, a La-Zr-O compound was formed on the surface of lithium-transition metal composite oxide particles by introducing a first flux and a second flux, so the XPS analysis results clearly showed a La (4d) peak at 102 eV and a Zr (3d) peak at 128.8 eV.

[0234] Example 5, in which the firing temperature is below the temperature range according to Equations 2 and 3, has a relatively low temperature, so the densification (S34) process is performed less, and the capacity retention rate was measured to be relatively lower compared to Examples 1 to 4.

[0235] In addition, Example 6, in which the firing temperature exceeds the temperature range according to Equations 2 and 3, was measured to have a relatively lower capacity retention rate compared to Examples 1 to 4 due to particle aggregation caused by under-firing.

[0236] In addition, Example 7, in which the lanthanum input amount was less than 500 ppm, did not sufficiently react with the lithium precursor, resulting in relatively less single-particle formation. Accordingly, it exhibited relatively lower capacity and output characteristics compared to Examples 1 to 4.

[0237] In addition, Example 8, in which the lanthanum input amount exceeded 2,000 ppm, showed a relatively lower capacity efficiency compared to Examples 1 to 4 because the flux reacted non-uniformly with a number of transition metal precursors.

[0238] In the case of Comparative Example 1, where the firing temperature exceeded the temperature range according to Equations 2 and 3 and no flux was added, single particles were formed due to high-temperature firing, but the average particle size of the particles increased significantly, exhibiting very low capacity characteristics compared to the examples.

[0239] In addition, in the case of Comparative Example 2, which had a low calcination temperature but did not add a flux, no or almost no single particles were formed, resulting in a significantly lower capacity retention rate during repeated charge and discharge cycles, and lower capacity characteristics compared to the examples were confirmed.

[0240] FIG. 11 is a graph showing the change in capacity according to the repeated charging and discharging of secondary batteries according to the examples and comparative examples. Specifically, FIG. 10 is a graph showing the capacity retention rate of Examples 1 to 4 and Comparative Examples 1 and 2 for a positive electrode active material having a Ni composition of 94%.

[0241] Referring to FIG. 11, in the case of the embodiments in which a single particle and a first coating layer were formed by adding a flux, an excellent capacity retention rate was secured compared to the comparative examples in which no flux was added.

[0242] In particular, in the case of Example 4, which is reinforced by adding (NH4)H2PO4 during the formation of the metal oxide coating layer to include phosphorus in the coating layer, the particle surface cracks caused by collisions between particles during the jet mill process in the aforementioned calcination (S30) process are effectively protected, and the lifespan characteristics are improved compared to Example 1. Explanation of the symbols

[0244] 50: Lithium-transition metal complex oxide particles 60: 1st coating layer 70: 2nd coating layer 100: Anode 105: Anode current collector 110: Positive electrode active material layer 120: Negative electrode active material layer 125: Cathode current collector 130: Cathode 120: Cathode active material layer 125: Cathode current collector 140: Separator 160: Case

Claims

Claim 1 A positive electrode active material for a lithium secondary battery comprising: lithium-transition metal composite oxide particles having a single particle form; and a first coating layer formed on the surface of the lithium-transition metal composite oxide particles and comprising a La-Zr-O compound, wherein the grain size of the lithium-transition metal composite oxide particles measured by XRD analysis is 300 to 600 nm, and the grain size is measured by the following Equation 1: [Equation 1] (In Equation 1, L is the grain size (nm), λ is the X-ray wavelength (nm), β is the full width at half maximum of the (003) plane peak (rad), and θ is the diffraction angle (rad). Claim 2 A positive electrode active material for a lithium secondary battery according to claim 1, further comprising a second coating layer formed on the surface of the first coating layer and comprising a Li-BO compound. Claim 3 A positive electrode active material for a lithium secondary battery according to claim 1, wherein the La-Zr-O compound is derived from a first flux containing lanthanum and a second flux containing zirconium. Claim 4 A positive electrode active material for a lithium secondary battery according to claim 3, wherein the first flux is La(OH)3 and the second flux is Zr(OH)4. Claim 5 delete Claim 6 A positive electrode active material for a lithium secondary battery according to claim 1, wherein the average particle size (D50) of the lithium-transition metal composite oxide particles is less than 3.0 μm. Claim 7 A positive electrode active material for a lithium secondary battery according to claim 1, wherein the La-Zr-O compound is doped or coated with a metal, and the metal is at least one of Mg, Ca, Al, Ti, W, Ta, P, and Nb. Claim 8 A positive electrode active material for a lithium secondary battery according to claim 1, wherein the single particle form comprises a monolithic form formed by 2 to 10 single particles being attached or closely bonded to each other. Claim 9 A positive electrode active material for a lithium secondary battery according to claim 1, wherein a La peak is observed at 102 eV and a Zr peak is observed at 128.8 eV when the surface of the lithium-transition metal composite oxide particles is measured by XPS (X-ray Photoelectron Spectrometer) analysis. Claim 10 In claim 1, the La-Zr-O compound is Li7La3Zr2O with a garnet structure 12 A positive electrode active material for a lithium secondary battery that does not contain Claim 11 A method for manufacturing a positive electrode active material for a lithium secondary battery, comprising the steps of: preparing a lithium precursor and a transition metal precursor; mixing the lithium precursor, the transition metal precursor, a first flux and a second flux; and calcining the mixed lithium precursor, the transition metal precursor, the first flux and the second flux to form lithium-transition metal composite oxide particles having a first coating layer comprising a La-Zr-O compound formed on the surface. Claim 12 A method for manufacturing a positive electrode active material for a lithium secondary battery according to claim 11, wherein the first flux has an average particle size (D50) of 1 μm or less. Claim 13 A method for manufacturing a positive electrode active material for a lithium secondary battery according to claim 11, wherein the first flux is La(OH)3 and the second flux is Zr(OH)4, and the lanthanum content included in the first flux is 500 to 2,000 ppm relative to the total weight of the lithium-transition metal composite oxide particles. Claim 14 A method for manufacturing a positive electrode active material for a lithium secondary battery according to claim 13, wherein the zirconium content included in the second flux is 500 to 2,000 ppm relative to the total weight of the lithium-transition metal composite oxide particles. Claim 15 A method for manufacturing a positive electrode active material for a lithium secondary battery according to claim 11, further comprising the step of adding boron and heat-treating to form a second coating layer containing a Li-BO compound on the surface of the first coating layer. Claim 16 A method for manufacturing a positive electrode active material for a lithium secondary battery according to claim 11, wherein a metal hydroxide is further added in the step of mixing the lithium precursor, the transition metal precursor, the first flux and the second flux, and the metal hydroxide is at least one hydroxide selected from Mg, Ca, Al, Ti, W, Ta, P and Nb. Claim 17 A method for manufacturing a positive electrode active material for a lithium secondary battery according to claim 11, wherein the lithium-transition metal composite oxide particles have a composition represented by the following chemical formula 1: [Chemical Formula 1]Li a Ni x M 1-x O 2+y (In Chemical Formula 1, a is 0.9≤a≤1.5, x is x≥0.6, y is -0.1≤y≤0.1, and M is one or more elements selected from Na, Mg, Ca, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Co, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, or Zr). Claim 18 A method for manufacturing a positive electrode active material for a lithium secondary battery according to claim 17, wherein the temperature at which the calcination is performed satisfies the following Equations 2 and 3: [Equation 2] t1-15 ≤ T1(°C) ≤ t1+15 (wherein 2, t1 is the temperature according to Equation 3 below, and T1 is the temperature at which the calcination is performed) [Equation 3] t1(°C) = (-520)*x + 1285 (wherein x is x in Equation 1). Claim 19 A lithium secondary battery comprising: a positive electrode comprising a positive electrode active material layer comprising a positive electrode active material for a lithium secondary battery according to claim 1; and a negative electrode facing the positive electrode.

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