Cathode active material, preparation method therefor, cathode including same, and lithium secondary battery including same

Abstract

The present invention relates to a cathode active material, a preparation method therefor, a cathode including same, and a lithium secondary battery including same, wherein the cathode active material comprises: a lithium transition metal oxide containing nickel in a content of 50 mol% or more among the total metal elements excluding lithium and being in the form of single-particles; and a coating layer provided on a part or the entirety of the surface of the lithium transition metal oxide and including cobalt (Co) and titanium (Ti), with the content of titanium ranging from 0.01mol% to 0.2mol% (both inclusive) on the basis of the total mole number of the cathode active material, and as a result of X-ray diffraction analysis, the X-ray diffraction pattern includes a first peak appearing in a 2θ angle range of 37 degrees to 37.8 degrees and a second peak appearing in a 2θ angle range of 43 degrees to 44 degrees.

Description

A positive electrode active material, a method for manufacturing the same, a positive electrode including the same, and a lithium secondary battery including the same

[0001] Cross-citation with related application(s)

[0002] The present application claims the benefit of the filing date of Patent No. 10-2024-0164440 filed with the Korean Intellectual Property Office on November 18, 2024, the contents of which are incorporated herein.

[0003] The present invention relates to a positive electrode active material, a method for manufacturing the same, a positive electrode including the same, and a lithium secondary battery including the same.

[0004] Lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMnO2 or LiMn2O4, etc.), and lithium iron phosphate compounds (LiFePO4) have been used as cathode active materials for lithium secondary batteries. Furthermore, as a method to improve the low thermal stability of LiNiO2 while maintaining its excellent reversible capacity, lithium composite metal oxides (hereinafter simply referred to as 'NCM-based lithium composite transition metal oxides' or 'NCA-based lithium composite transition metal oxides') in which a portion of the nickel (Ni) is substituted with cobalt (Co) or manganese (Mn) / aluminum (Al) have been developed. However, conventionally developed NCM-based and NCA-based lithium composite transition metal oxides had limitations in application due to insufficient capacity characteristics.

[0005] To address these issues, recent research has focused on increasing the Ni content in NCM-based and NCA-based lithium composite transition metal oxides. However, high-concentration nickel cathode active materials present problems such as gas generation due to surface phase changes and surface degradation upon contact with the electrolyte, reduced lifespan capacity and resistance, and a rapid decline in thermal stability.

[0006] Many studies incorporating doping and coating technologies are being conducted to ensure the thermal stability of Ni-rich High-Ni NCM / NCA lithium composite transition metal oxides. For example, phosphate-based coating layers have been used; however, this still presented issues with low ionic conductivity, and problems regarding structural collapse due to volume changes in the Ni-rich cathode active material persisted, leading to the emergence of the need for oxide-based coatings.

[0007] The present invention relates to a positive electrode active material, a method for manufacturing the same, a positive electrode including the same, and a lithium secondary battery including the same.

[0008] The present invention relates to a lithium transition metal oxide in the form of a single particle, wherein the nickel content among all metal elements excluding lithium is 50 mol% or more; and

[0009] It includes a coating layer provided on part or all of the surface of the lithium transition metal oxide, and

[0010] The above coating layer comprises cobalt (Co) and titanium (Ti), and

[0011] The content of the above titanium is 0.01 mol% or more and 0.2 mol% or less based on the total molar amount of the cathode active material, and

[0012] As a result of X-ray diffraction analysis, a positive electrode active material is provided that includes a first peak appearing in the range of 2θ angles from 37 degrees to 37.8 degrees and a second peak appearing in the range of 2θ angles from 43 degrees to 44 degrees.

[0013] In addition, the present invention comprises the step of preparing a mixture including a lithium transition metal oxide, a cobalt precursor, and a titanium precursor in a single-particle form, wherein the nickel content among all metal elements excluding lithium is 50 mol% or more; and

[0014] A method for manufacturing the above-described positive active material is provided, comprising the step of heat-treating the above mixture.

[0015] In addition, the present invention provides a positive electrode comprising the positive electrode active material described above.

[0016] In addition, the present invention provides a lithium secondary battery comprising the anode described above.

[0017] The positive active material of the present invention has the effect of improved structural stability with reduced surface phase change.

[0018] When the positive active material of the present invention is applied to a positive electrode or a lithium secondary battery, it has the effect of improving high-temperature storage stability.

[0019] The positive active material of the present invention has the effect of improving high-temperature long-term performance when applied to a positive electrode or a lithium secondary battery.

[0020] Figures 1 to 4 are X-ray diffraction analysis spectra according to Experimental Example 1.

[0021] The present specification will be described in detail below.

[0022] Terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted in a meaning and concept consistent with the technical idea of ​​the invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe his invention.

[0023] Unless otherwise defined in this specification, all technical and scientific terms have the same meaning as generally understood by those skilled in the art to which the invention pertains. The terms used in the description of the invention are merely for the purpose of effectively describing specific embodiments and are not intended to limit the invention.

[0024] The singular forms used in this specification include plural forms unless the phrases clearly indicate otherwise.

[0025] As used in this specification, the meaning of “includes” specifies certain characteristics, regions, integers, steps, actions, elements, and / or components, and does not exclude the existence or addition of other specific characteristics, regions, integers, steps, actions, elements, components, and / or groups.

[0026] The present invention is capable of various modifications and may take various forms, and specific embodiments are illustrated and described in detail below. However, this is not intended to limit the invention to the specific disclosed forms, and it should be understood that the invention includes all modifications, equivalents, and substitutions that fall within the spirit and scope of the invention.

[0027] In this specification, where the positional relationship between two parts is described, for example, using expressions such as 'on', 'on the upper part', 'on the lower part', 'next to', etc., one or more other parts may be located between the two parts unless expressions such as 'immediately' or 'directly' are used.

[0028] In this specification, when temporal sequences are described, for example, using expressions such as ‘after,’ ‘following,’ ‘next,’ or ‘before,’ cases that are not continuous may be included unless expressions such as ‘immediately’ or ‘directly’ are used.

[0029] In this specification, the 'anode active material' may be a composition comprising one or more lithium transition metal oxides.

[0030] In this specification, a 'Primary Particle' is a basic unit that forms a 'Secondary Particle,' which is an aggregate of particles, and the Primary Particle and the Secondary Particle are distinguished by the presence or absence of particle aggregation. When multiple Primary Particles aggregate to form a Secondary Particle, a particle interface existing between the Primary Particles may exist within the Secondary Particle. The Primary Particle may refer to the smallest unit demarcated by the particle interface when observing the positive electrode active material using a Scanning Electron Microscope (SEM). Additionally, the Primary Particle may refer to a particle in a state where the positive electrode active material containing the Secondary Particle has been sufficiently crushed in a grinder or disperser.

[0031] In this specification, 'Single Particle' refers to a secondary particle form in which the number of primary particles constituting the secondary particle is small; it may be a single particle form consisting of one primary particle, or a secondary particle form in which several primary particles are aggregated. In other words, it is a concept distinct from a secondary particle formed by the aggregation of hundreds of primary particles. Specifically, it may refer to a form in which the secondary particle consists of 40 or fewer, 30 or fewer, 20 or fewer, 10 or fewer, 5 or fewer, or 3 or fewer primary particles. In this case, particle breakage can be prevented even at high electrode densities. Furthermore, compared to a secondary particle in which hundreds of primary particles are aggregated, breakage during rolling is suppressed, enabling the realization of high energy density and preventing lifespan degradation caused by particle breakage.

[0032] In this specification, 'Particle Size' refers to the diameter of an individual particle. In this case, if the particle is a perfect sphere, it refers to the diameter of the sphere. Additionally, if the particle is not a perfect sphere, it may refer to the diameter of a virtual perfect sphere having the same volume as the particle. Alternatively, it may refer to the diameter of a virtual circle having the same area as the cross-section of the particle as confirmed by an optical microscope image, such as a scanning electron microscope; the diameter of the largest circle that may be contained within the cross-section of the particle as confirmed by the optical microscope image (Maximum Inscribed Circle Diameter); or the diameter of the smallest circle that completely surrounds the cross-section of the particle as confirmed by the optical microscope image.

[0033] In this specification, 'Mean Particle Size' refers to a statistical representative value representing a sample containing several particles. For example, it may be the Number Mean Particle Size calculated by dividing the sum of the diameters of individual particles in the sample by the number of particles, or it may be the Mean Particle Size (Dn) derived by a method using a particle size analyzer as described below.

[0034] The above method for measuring particle size or average particle size may use a method using a particle size analyzer (PSD) or a scanning electron microscope image analysis method.

[0035] The method using the particle size analyzer described above is a laser diffraction analysis method that irradiates a dispersion solution containing dispersed cathode active material with a laser and analyzes the pattern of scattered light using an optical model. It enables statistical analysis of the entire sample and allows for fast and automated analysis. By utilizing the particle size analyzer, it is possible to derive and analyze volume distribution curves or volume accumulation distribution curves that accumulate from smallest to largest particle sizes.

[0036] In the present specification, the structure, type of components, and crystallinity contained within the positive electrode active material can be confirmed through an X-ray diffraction pattern derived through X-ray diffraction analysis, and X-ray diffraction analysis can be performed using an X-ray diffraction (XRD) analysis instrument (product name: D4-endavor, manufacturer: Bruker), and in addition to the above instrument, instruments used in the industry may be appropriately employed.

[0037] In this specification, the peak intensity refers to the number of X-rays detected per unit time by an X-ray diffraction analysis device and may be expressed as intensity(count).

[0038] In this specification, unless otherwise stated, the cobalt and titanium mentioned herein may be present in the coating layer.

[0039] The present invention relates to a lithium transition metal oxide in the form of a single particle, wherein the nickel content among all metal elements excluding lithium is 50 mol% or more; and

[0040] It includes a coating layer provided on part or all of the surface of the lithium transition metal oxide, and

[0041] The above coating layer comprises cobalt (Co) and titanium (Ti), and

[0042] The content of the above titanium is 0.01 mol% or more and 0.2 mol% or less based on the total molar amount of the cathode active material, and

[0043] As a result of X-ray diffraction analysis, a positive electrode active material is provided that includes a first peak appearing in the range of 2θ angles from 37 degrees to 37.8 degrees and a second peak appearing in the range of 2θ angles from 43 degrees to 44 degrees.

[0044] The positive electrode active material of the present invention comprises a lithium transition metal oxide and a coating layer provided on a part or all of the surface of the lithium transition metal oxide. Additionally, a region having the same composition as the coating layer may be provided in a part of the interior of the lithium transition metal oxide, and a region within the interior of the lithium transition metal oxide having the same composition as the coating layer is also included within the scope of the coating layer.

[0045] In the present invention, the nickel content among the total metal elements excluding lithium in the lithium transition metal oxide may be 50 mol% or more. Specifically, it may be 55 mol% or more, 58 mol% or more, 60 mol% or more, 62 mol% or more, 65 mol% or more, or 68 mol% or more. Additionally, it may be 95 mol% or less, 90 mol% or less, 85 mol% or less, or 80 mol% or less. When lithium transition metal oxide particles with a high Ni content as described above are applied, a high capacity can be achieved. In particular, the lithium transition metal oxide may be a nickel-cobalt-manganese (NCM) oxide.

[0046] In the present invention, the lithium transition metal oxide may be in the form of a single particle. The description of the single particle or the single particle form is as described above, and in this case, thermal stability can be improved and the occurrence of side reactions can be improved.

[0047] In the case of conventional high-nickel (Ni-rich) cathode active materials, surface degradation occurs at the surface where the cathode active material contacts the electrolyte due to side reactions with the electrolyte, resulting in gas generation and a decrease in lifespan and resistance. Furthermore, on the surface of single-particle lithium transition metal oxides, a degraded NiO layer exists that has not been converted into a nickel-cobalt-manganese (NCM) oxide layered structure due to high calcination temperatures; this acts as battery resistance or causes a reduction in capacity.

[0048] The cathode active material of the present invention solves the aforementioned problem by having a coating layer that includes both cobalt (Co) and titanium (Ti). The cobalt (Co) and titanium (Ti) are doped into the interior of the lithium transition metal oxide or coated on its surface to prevent structural collapse of the lithium transition metal oxide, suppress contact with the electrolyte, and particularly improve long-term high-temperature performance. Specifically, the titanium coating prevents the lithium transition metal oxide from reacting with the electrolyte and causing the transition metal to leach into the electrolyte, while the cobalt ensures high ionic conductivity. In other words, by coating with both cobalt and titanium, structural stability and battery performance can be secured simultaneously.

[0049] In the present invention, the titanium content may be 0.01 mol% or more and 0.2 mol% or less based on the total molar amount of the cathode active material. Preferably, it may be 0.012 mol% or more, 0.014 mol% or more, 0.016 mol% or more, 0.018 mol% or more, 0.02 mol% or more, or 0.022 mol% or more. Additionally, it may be 0.18 mol% or less, 0.15 mol% or less, 0.1 mol% or less, 0.08 mol% or less, or 0.06 mol% or less. Within the above numerical range, the structural stability of the lithium transition metal oxide may be improved.

[0050] In the present invention, the positive electrode active material may include a first peak appearing in the range of 2θ angles from 37 degrees to 37.8 degrees and a second peak appearing in the range of 2θ angles from 43 degrees to 44 degrees, based on the results of X-ray diffraction analysis. In this case, the first peak is a peak related to cobalt (Co), specifically a peak due to the LiCoO2 phase. The second peak is a peak related to titanium (Ti), specifically a peak due to the Li2TiO3 phase. By doping both cobalt and titanium and including both the LiCoO2 phase and the Li2TiO3 phase, the positive electrode active material of the present invention can secure structural stability due to titanium and high ionic conductivity due to cobalt.

[0051] In the present invention, the positive active material may have a value calculated by the following mathematical formula 1 of 0.1 or more and 2.5 or less.

[0052] [Mathematical Formula 1]

[0053] I2 / I1

[0054] In mathematical formula 1,

[0055] I1 is the intensity of the first peak mentioned above, and

[0056] I2 is the intensity of the second peak mentioned above.

[0057] In the present invention, the value calculated by the above mathematical formula 1 may be 0.3 or more, 0.5 or more, 0.7 or more, 1 or more, 1.05 or more, or 1.1 or more. Additionally, it may be 2 or less, 1.8 or less, 1.6 or less, 1.5 or less, 1.4 or less, or 1.3 or less. Within the above numerical range, the ratio of the LiCoO2 phase and the Li2TiO3 phase is controlled, and structural stability by titanium and high ionic conductivity by cobalt can both be secured.

[0058] In the present invention, the X-ray diffraction pattern may include a third peak that appears in the range of a 2θ angle of 35.9 degrees or more and 36.2 degrees or less. The third peak may be a peak due to titanium (Ti), specifically an additional peak due to Li2TiO3. The third peak is a peak associated with titanium (Ti) and appears as the amount of titanium (Ti) increases, or is observed when the content of titanium (Ti) relative to cobalt (Co) is above a certain ratio.

[0059] In the present invention, the positive active material may have a value calculated by the following mathematical formula 2 of 0.5 or more and 2 or less.

[0060] [Mathematical Formula 2]

[0061] I3 / I1

[0062] In mathematical formula 2,

[0063] I1 is the intensity of the first peak mentioned above, and

[0064] I3 is the intensity of the third peak mentioned above.

[0065] In the present invention, the value calculated by the above mathematical formula 2 may be 0.6 or more, 0.7 or more, 0.8 or more, 0.9 or more, 0.95 or more, or 1 or more. Additionally, it may be 1.8 or less, 1.6 or less, 1.4 or less, 1.2 or less, 1.1 or less, or 1.05 or less. Within the above numerical range, the ratio of the LiCoO2 phase and the Li2TiO3 phase is controlled, and structural stability by titanium and high ionic conductivity by cobalt can both be secured.

[0066] In the present invention, the titanium content may be 0.5 mol% or more and 10 mol% or less based on the total molar amount of cobalt and titanium. Preferably, it may be 0.6 mol% or more, 0.7 mol% or more, 0.8 mol% or more, 0.9 mol% or more, 1 mol% or more, 1.1 mol% or more, or 1.2 mol% or more. Additionally, it may be 8 mol% or less, 6 mol% or less, 4 mol% or less, 3 mol% or less, or 2.5 mol% or less. Within the above numerical range, structural stability provided by titanium and high ionic conductivity provided by cobalt can both be secured.

[0067] In the present invention, the cobalt content may be 1 mol% or more and 4 mol% or less based on the total molar amount of the cathode active material. Preferably, it may be 1.2 mol% or more, 1.5 mol% or more, 1.7 mol% or more, or 1.9 mol% or more. Additionally, it may be 3.8 mol% or less, 3.5 mol% or less, 3 mol% or less, 2.5 mol% or less, 2.3 mol% or less, or 2.1 mol% or less. Within this range, it can contribute to the structural stabilization effect of the lithium transition metal oxide.

[0068] In the present invention, the coating layer may comprise one or more of ions, oxides, lithium oxides, or composites thereof, each of cobalt and titanium or both. For example, it may exist in an oxide state such as CoO, Co2O3, and TiO2 within the coating layer, or exist in a lithium oxide state such as LiCoO2 and Li2TiO3 by reacting with lithium byproducts present on the surface of a lithium transition metal oxide, or have a composite form such as LiCoO2TiO2, CoOLi2TiO3, and Li2OCoOLi2TiO3. Preferably, it may be in the form of a lithium oxide such as LiCoO2 and Li2TiO3, and these exist on the surface of the lithium transition metal oxide in a particulate state.

[0069] At this time, the cobalt (Co) and titanium (Ti) participating in the doping diffuse into the surface of the lithium transition metal oxide particles, thereby having the effect of surface doping. During the above doping, cobalt (Co) and titanium (Ti) may exist in ionic form.

[0070] Since cobalt (Co) included in the above coating layer is an element advantageous for forming a layered structure, when a coating layer is formed using cobalt, a stable crystal structure is formed on the surface of the positive electrode active material, which reduces lithium ion diffusion resistance and suppresses crystal structure deformation and particle cracking during charging and discharging, thereby achieving the effect of improving lifespan characteristics.

[0071] Titanium (Ti) included in the above coating layer can improve the stability of the layered structure and surface stability of the lithium transition metal oxide, suppress phase transitions, effectively suppress the increase in resistance, especially under high voltage and high temperature conditions, improve high temperature life performance, and reduce the amount of gas generated.

[0072] In addition, the coating layer containing cobalt (Co) and titanium (Ti) in the present invention exists on the surface of lithium transition metal oxide particles in various forms as described above, thereby minimizing direct contact between the lithium transition metal oxide and the electrolyte.

[0073] In the present invention, the thickness of the coating layer may be 1 nm or more and 200 nm or less. Preferably, it may be 1 nm or more, 5 nm or more, or 10 nm or more. Additionally, it may be 150 nm or less or 100 nm or less. Within the above numerical range, the reaction between the lithium transition metal oxide particles and the electrolyte can be stably suppressed while ensuring lithium ion conductivity. Specifically, if the thickness of the coating layer is too thin, it may be difficult to ensure the stability of the coating layer. Furthermore, if the thickness of the coating layer is too thin, uncoated areas may occur partially on the surface of the lithium transition metal oxide particles, and there is a risk that high-resistance regions may be formed at those areas due to the reaction between the lithium transition metal oxide particles and the electrolyte. However, if the thickness of the coating layer is too thick, the lithium ion conductivity may decrease.

[0074] In the present invention, the coating layer may be provided discontinuously on the surface of the lithium transition metal oxide. The discontinuously provided coating layer implies the formation of a thick coating layer in which the doping of cobalt onto the surface of the positive electrode active material is suppressed to the maximum extent. Due to the discontinuously provided coating layer, the surface protection effect of the positive electrode active material can be maximized.

[0075] In the present invention, the coating layer may be located on 60% or more, 70% or more, 80% or more, 90% or more, or the entire surface area based on the total surface area of ​​the lithium transition metal oxide particles. At this time, the upper limit of the coating area of ​​the coating layer is not specifically restricted, but for example, it may be 100% or less, 99% or less, 98% or less, 97% or less, 96% or less, 95% or less, 94% or less, 93% or less, 92% or less, 91% or less, or 90% or less. However, in order to ensure that the above-described effect resulting from the introduction of the coating layer is sufficiently manifested, it is preferable that the coating layer be located on the entire surface area of ​​the lithium transition metal oxide particles. If 40% or more of the surface of the lithium transition metal oxide particles is not coated, there is a risk that the lithium transition metal oxide particles and the electrolyte will react at those points to form a high-resistance atmosphere.

[0076] In the present invention, the lithium transition metal oxide may be represented by the following chemical formula 1.

[0077] [Chemical Formula 1]

[0078] Li 1+t Ni a Co b M 1 c M 2 d O2

[0079] In the above chemical formula 1,

[0080] M 1 It includes Mn, Al, or a combination thereof,

[0081] M 2 ... comprises W, Zr, Y, Ba, Ca, Ti, V, Mg, Ta, Nb, or a combination thereof, and

[0082] -0.2≤t≤1, 0.5≤a<1, 0 <b≤0.4, 0<c≤0.4, 0≤d≤0.05, a+b+c+d=1이다.

[0083] The above M 1 is Mn, Al, or a combination thereof, preferably Mn or a combination of Mn and Al.

[0084] The above M 2 comprises W, Zr, Y, Ba, Ca, Ti, V, Mg, Ta, Nb, or a combination thereof. Preferably, it may be one or more selected from the group consisting of Zr, Y, Mg, and Ti, and more preferably, it may be Zr, Y, or a combination thereof. M 2 Although the element is not necessarily included, if included in an appropriate amount, it can play a role in promoting grain growth during sintering or improving crystal structure stability.

[0085] The above t represents the molar ratio of excess lithium in the lithium transition metal oxide and may be -0.1 or greater, -0.05 or greater, or 0 or greater. Additionally, it may be 1 or less, 0.9 or less, 0.8 or less, 0.7 or less, 0.6 or less, 0.5 or less, 0.4 or less, 0.3 or less, 0.2 or less, 0.15 or less, 0.1 or less, 0.07 or less, 0.05 or less, or 0.03 or less.

[0086] The above 'a' represents the molar ratio of nickel among all metals excluding lithium in the lithium transition metal oxide, and may be 0.55 or more, 0.58 or more, 0.6 or more, 0.62 or more, 0.65 or more, or 0.68 or more. Additionally, it may be less than 1.0, 0.95 or less, 0.9 or less, 0.85 or less, or 0.8 or less.

[0087] The above b represents the molar ratio of cobalt among all metals excluding lithium in the lithium transition metal oxide, and may be greater than 0, 0.01 or more, 0.02 or more, 0.03 or more, 0.04 or more, or 0.05 or more. Additionally, it may be 0.3 or less, 0.25 or less, 0.2 or less, or 0.1 or less.

[0088] The above c is M among the total metals excluding lithium in the lithium transition metal oxide. 1 It represents the molar ratio and may be greater than 0, 0.05 or more, 0.1 or more, 0.15 or more, or 0.2 or more. Additionally, it may be 0.38 or less, 0.35 or less, or 0.3 or less.

[0089] The above d is M among the total metals excluding lithium in the lithium transition metal oxide. 2 It represents the molar ratio of an element and may be 0. Or, it may be 0.01 or greater, or 0.02 or greater. Also, it may be 0.05 or less, or 0.04 or less.

[0090] In the present invention, the average particle size of the lithium transition metal oxide may be 2 μm or more and 50 μm or less. Additionally, it may be 3 μm or more, 4 μm or more, or 5 μm or more. Furthermore, it may be 30 μm or less, 25 μm or less, 20 μm or less, or 15 μm or less. If the particle size of the lithium transition metal oxide particles is too small, controlling the particles is not easy, which may cause difficulties in the manufacturing process. On the other hand, if the particle size of the lithium transition metal oxide particles is too large, losses may occur in terms of rolling density, capacity, etc. Therefore, it is preferable for the lithium transition metal oxide particles to have a particle size within the range described above.

[0091] The present invention provides a method for manufacturing the above-described positive electrode active material, comprising the steps of: preparing a mixture comprising a lithium transition metal oxide, a cobalt precursor, and a titanium precursor in a single-particle form, wherein the nickel content among all metal elements excluding lithium is 50 mol% or more; and heat-treating the mixture.

[0092] The above lithium transition metal oxide may be manufactured by purchasing a commercially available product or by using a method for manufacturing lithium transition metal oxide known in the relevant technical field. For example, the above lithium transition metal oxide may be manufactured by mixing a lithium raw material and a nickel-based precursor and then calcining the mixture. In this case, calcination is intended to crystallize the lithium and transition metal materials to produce the lithium transition metal oxide, and differs from the heat treatment described later, which is performed for the purpose of coating the surface of the lithium transition metal oxide.

[0093] The above lithium raw material may be, for example, one or more selected from the group consisting of lithium carbonate (Li2CO3), lithium hydroxide (LiOHH2O), anhydrous lithium hydroxide (LiOH), LiNO3, CH3COOLi, and Li2(COO)2, and preferably may be lithium carbonate (Li2CO3), lithium hydroxide (LiOH·H2O), or a combination thereof.

[0094] The above calcination is a heat treatment for forming single particles and is not particularly limited, but can generally be formed by increasing the calcination temperature to under-calcination, or by using additives that aid in under-calcination or by changing the starting material. For example, it can be formed by under-calcination at 800°C to 1,000°C for 10 to 25 hours under an oxygen atmosphere. In addition, the above calcination may include a first calcination and a second calcination in two stages, the first calcination is as described above, and the second calcination can be performed in an air atmosphere.

[0095] Additionally, the above-mentioned calcination may be performed under an oxygen atmosphere for 5 to 35 hours, preferably 5 to 20 hours, and more preferably 6 to 15 hours. In this specification, an oxygen atmosphere refers to an atmosphere containing a sufficient amount of oxygen for calcination, including an atmospheric atmosphere. In particular, it is preferable to perform the calcination in an atmosphere where the oxygen partial pressure is higher than that of an atmospheric atmosphere.

[0096] The above cobalt precursor may be an oxide, hydroxide, oxyhydroxide, halide, nitrate, carbonate, acetate, oxalate, citrate, carboxylate, or sulfate containing cobalt, and more specifically, may be Co(OH)2, Co3O4, CoOOH, Co(OCOCH3)2·4H2O, Co(NO3)2·6H2O, CoC2O4, or Co(SO4)2·7H2O, and any one or more of these may be used.

[0097] The above titanium precursor may be an oxide, hydroxide, oxyhydroxide, halogen, nitrate, carbonate, acetate, oxalate, citrate, carboxylate, sulfate, sulfide, or a combination thereof containing titanium, and more specifically, may be TiO2, Ti(OBu)4, TiB2, TiC, TiF3, Ti(NO3)4, TiCl2, Ti4P3, etc., but is not limited thereto.

[0098] In the present invention, the step of preparing the mixture may be performed by mixing raw materials. Additionally, the mixing may be solid-state mixing or liquid-state mixing, and is not specifically limited in the present invention.

[0099] In the present invention, the step of heat-treating the mixture is intended to form a coating layer by fixing cobalt and titanium to the surface of the lithium transition metal oxide.

[0100] In the present invention, the step of heat-treating the mixture may be performed at a heat treatment temperature of 800°C or higher and 1,000°C or lower. Preferably, the heat treatment temperature may be 820°C or higher, 840°C or higher, 850°C or higher, or 860°C or higher. Additionally, it may be 980°C or lower, 960°C or lower, 940°C or lower, 920°C or lower, 900°C or lower, or 890°C or lower. Within the above numerical ranges, a uniform coating layer can be formed by sufficiently reacting the cobalt precursor and the titanium precursor with the lithium byproduct on the surface. On the other hand, if the heat treatment temperature is below the above range, unreacted cobalt (Co) and titanium (Ti) byproducts may be formed.

[0101] In the present invention, the step of heat-treating the mixture can be performed under an oxygen atmosphere.

[0102] In the present invention, the step of heat-treating the mixture may be performed for a heat treatment time of 3 hours or more and 20 hours or less. Preferably, the heat treatment time may be 4 hours or more, 6 hours or more, or 8 hours or more. Additionally, it may be 16 hours or less, 12 hours or less, or 10 hours or less. Within the above numerical ranges, a coating layer of appropriate thickness may be formed and production efficiency may be improved.

[0103] In particular, the present invention can achieve the effect of reducing the content of residual lithium by-products on the surface of a lithium transition metal oxide by proceeding with a reaction with residual lithium by-products remaining on the surface of the lithium transition metal oxide without using an additional lithium (Li) precursor as a precursor for the coating layer.

[0104] By performing the steps described above, an anode active material comprising the lithium transition metal oxide and a coating layer in which cobalt (Co) and titanium (Ti) are doped into the lithium transition metal oxide or coated on the surface can be manufactured.

[0105] The present invention provides a positive electrode comprising the positive electrode active material described above.

[0106] In the present invention, the anode comprises an anode active material layer comprising the anode active material described above. Specifically, the anode comprises an anode current collector and an anode active material layer formed on the anode current collector and comprising the anode active material. Since the anode active material has been described above, a detailed description is omitted, and only the remaining components are described in detail below.

[0107] In the present invention, the positive current collector is not particularly limited as long as it is conductive without causing chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surfaces treated with carbon, nickel, titanium, silver, etc. may be used. In addition, the positive current collector may typically have a thickness of 3 μm or more and 500 μm or less, and may form fine irregularities on the surface of the current collector to increase the adhesion of the positive active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0108] In the present invention, the positive active material layer may include a conductive material and a binder together with the positive active material. At this time, the content of the positive active material may be 80% to 99% by weight, more specifically 85% to 98.5% by weight, based on the total weight of the positive active material layer, and excellent capacity characteristics may be exhibited within this range.

[0109] In the present invention, the conductive material is used to impart conductivity to the electrode, and can be used without special limitations as long as it has electronic conductivity without causing chemical changes. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fibers; metal powder or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and one of these alone or a mixture of two or more may be used. The content of the conductive material may be 0.1% to 15% by weight with respect to the total weight of the positive electrode active material layer.

[0110] In the present invention, the binder serves to improve adhesion between positive active material particles and adhesion between the positive active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these alone or a mixture of two or more may be used. The content of the binder may be 0.1% to 15% by weight based on the total weight of the positive active material layer.

[0111] In the present invention, the anode may be manufactured according to a conventional anode manufacturing method. Specifically, it may be manufactured by applying a composition for forming an anode active material layer, prepared by dissolving or dispersing the anode active material and, optionally, a binder and a conductive material in a solvent, onto an anode current collector, and then drying and rolling. At this time, the types and contents of the anode active material, binder, and conductive material are as described above. Alternatively, the anode may be manufactured by casting the composition for forming an anode active material layer onto a separate support, and then laminating the film obtained by peeling from the support onto an anode current collector.

[0112] In the present invention, the solvent may be a solvent generally used in the relevant technical field, and may include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and one of these alone or a mixture of two or more may be used. The amount of solvent used is sufficient if it has a viscosity that dissolves or disperses the anode active material, conductive material, and binder, taking into account the coating thickness of the slurry and the manufacturing yield, and subsequently provides excellent thickness uniformity when coated for anode manufacturing.

[0113] The present invention provides an electrochemical device comprising the anode described above. Specifically, the electrochemical device may be a battery, a capacitor, etc., and more specifically, may be a lithium secondary battery.

[0114] The present invention provides a lithium secondary battery comprising the anode described above.

[0115] In the present invention, the lithium secondary battery comprises a positive electrode, a negative electrode, a separator and an electrolyte provided between the positive electrode and the negative electrode.

[0116] In addition, the lithium secondary battery may optionally further include a battery container that accommodates the electrode assembly of the positive electrode, negative electrode, and separator, and a sealing member that seals the battery container.

[0117] In the present invention, the cathode comprises a cathode current collector and a cathode active material layer provided on the cathode current collector.

[0118] In the present invention, the negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy may be used. In addition, the negative electrode current collector may typically have a thickness of 3 μm to 500 μm, and, similar to the positive electrode current collector, fine irregularities may be formed on the surface of the current collector to strengthen the bonding strength of the negative electrode active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0119] In the present invention, the negative electrode active material layer further comprises a binder, a conductive material, and a combination thereof in addition to the negative electrode active material.

[0120] In the present invention, the negative electrode active material may be a compound capable of reversible intercalation and deintercalation of lithium. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; and SiO₂ βExamples include metal oxides capable of doping and dedoping lithium, such as (0<β<2), SnO2, vanadium oxide, and lithium vanadium oxide; or composites comprising the metal compound and carbonaceous material, such as Si-C composites or Sn-C composites, and any one or more of these may be used. Additionally, a metallic lithium thin film may be used as the negative electrode active material. Furthermore, low-crystallinity carbon and high-crystallinity carbon may both be used as the carbonaceous material. Representative examples of low-crystallinity carbon include soft carbon and hard carbon, while representative examples of high-crystallinity carbon include amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleum and coal tar pitch-derived cokes.

[0121] In the present invention, the content of the negative electrode active material may be 80% to 99% by weight based on the total weight of the negative electrode active material layer.

[0122] In the present invention, the binder is a component that assists in the bonding between the conductive material, the active material, and the current collector, and can typically be added in an amount of 0.1% to 10% by weight relative to the total weight of the negative active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0123] In the present invention, the conductive material may be added as a component to further improve the conductivity of the negative electrode active material in an amount of 10% by weight or less, specifically 5% by weight or less, based on the total weight of the negative electrode active material layer. Such conductive material is not particularly limited as long as it is conductive without causing chemical changes in the battery, and for example, graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black; conductive fibers such as carbon fibers or metal fibers; metal powders such as carbon fluoride, aluminum, or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives, etc. may be used.

[0124] In the present invention, the negative electrode active material layer may be manufactured by applying and drying a composition for forming a negative electrode active material layer, prepared by dissolving or dispersing a negative electrode active material and optionally a binder and a conductive material in a solvent, on a negative electrode current collector, or by casting the composition for forming a negative electrode active material layer onto a separate support and then laminating the film obtained by peeling from the support onto a negative electrode current collector.

[0125] In the present invention, the separator separates the negative electrode and the positive electrode and provides a pathway for the movement of lithium ions. Any separator commonly used in lithium secondary batteries may be used without special limitations, and it is particularly desirable that it has low resistance to the movement of electrolyte ions and excellent electrolyte moisture retention capacity. Specifically, a porous polymer film, such as a porous polymer film made of a polyolefin-based polymer like an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof may be used. In addition, a conventional porous nonwoven fabric, such as a nonwoven fabric made of high-melting-point glass fibers or polyethylene terephthalate fibers, may be used. Furthermore, a coated separator containing ceramic components or polymer materials may be used to ensure heat resistance or mechanical strength, and may optionally be used in a single-layer or multi-layer structure.

[0126] In the present invention, the electrolyte may include, but is not limited to, an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, a molten inorganic electrolyte, etc., which are usable in the manufacture of a lithium secondary battery. Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0127] In the present invention, the organic solvent may be used without special limitations as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvent may be an ester-based solvent such as methyl acetate, ethyl acetate, γ-butyrolactone, or ε-caprolactone; an ether-based solvent such as dibutyl ether or tetrahydrofuran; a ketone-based solvent such as cyclohexanone; or an aromatic hydrocarbon-based solvent such as benzene or fluorobenzene. Carbonate-based solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethylmethyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol-based solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a straight-chain, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may include a double aromatic ring or ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes may be used. Among these, a carbonate-based solvent is preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant that can improve the charge and discharge performance of the battery, and a low-viscosity linear carbonate-based compound (e.g., ethylmethyl carbonate, dimethyl carbonate or diethyl carbonate, etc.) is more preferred.In this case, using a mixture of cyclic carbonate and chain carbonate in a volume ratio of about 1:1 to about 1:9 can result in excellent performance of the electrolyte.

[0128] In the present invention, the lithium salt can be used without special limitations as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the lithium salt may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. The concentration of the lithium salt is preferably used within the range of 0.1 to 5.0 M, specifically 0.1 to 3.0 M. When the concentration of the lithium salt falls within the above range, the electrolyte has appropriate conductivity and viscosity, so it can exhibit excellent electrolyte performance and allow lithium ions to move effectively.

[0129] In the present invention, in addition to the electrolyte components, the electrolyte may further include one or more additives for the purpose of improving the lifespan characteristics of the battery, suppressing the decrease in battery capacity, and improving the discharge capacity of the battery, such as, for example, a haloalkylene carbonate-based compound such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, triamide hexaphosphate, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride. In this case, the additive may be included in an amount of 0.1 to 10 weight%, specifically 0.1 to 5 weight%, based on the total weight of the electrolyte.

[0130] As described above, since the lithium secondary battery containing the positive electrode active material according to the present invention exhibits excellent lifespan and capacity characteristics, it is useful in portable devices such as mobile phones, laptop computers, and digital cameras, as well as in the field of electric vehicles such as hybrid electric vehicles (HEVs).

[0131] Accordingly, according to another embodiment of the present invention, a battery module comprising the lithium secondary battery as a unit cell and a battery pack comprising the same are provided.

[0132] The above battery module or battery pack can be used as a power source for one or more medium-to-large devices, including a power tool; an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); or a power storage system.

[0133] There are no specific restrictions on the external shape of the above lithium secondary battery, but it may be a cylindrical type using a can, a prismatic type, a pouch type, or a coin type.

[0134] The above lithium secondary battery can be used not only as a battery cell used as a power source for small devices, but can also preferably be used as a unit cell in a medium-to-large battery module containing a plurality of battery cells.

[0135] The operation and effects of the invention will be explained in more detail through the specific embodiments described below. However, these are presented merely as examples to aid in understanding the invention. The following embodiments are not intended to limit the scope of the invention in any way, and it will be obvious to those skilled in the art that various changes and modifications are possible within the scope and technical spirit of the invention.

[0136] <Examples and Comparative Examples>

[0137] <Example 1>

[0138] Cathode active material precursor [Composition: Ni 0.70 Co 0.07 Mn 0.23 LiNi is mixed with [OH]2 and Li2CO3 as a lithium raw material in a molar ratio of 1.05:1 (=Li:(Ni+Co+Mn)), placed in an alumina crucible, and calcined at 910°C for 8 hours under an oxygen atmosphere. 0.7 Co 0.7 Mn 0.23 A lithium transition metal oxide with an O2 structure was prepared.

[0139] The above lithium transition metal oxide was ground, and a mixture was prepared by mixing a cobalt precursor (Co(OH)2) and a titanium precursor (TiO2) to form a coating layer on the ground lithium transition metal oxide.

[0140] At this time, the cobalt precursor was mixed in an amount such that the cobalt (Co) content was 2 mol% based on the total molar amount of the total cathode active material, and the titanium precursor was mixed in an amount such that the titanium (Ti) content was 0.05 mol% based on the total molar amount of the total cathode active material. At this time, the molar ratio of Co:Ti was set to 1:0.025.

[0141] A positive electrode active material having a coating layer formed on a lithium transition metal oxide was prepared by placing the obtained mixture into an alumina crucible and heat-treating it at a temperature of 870°C for 9 hours under an oxygen atmosphere.

[0142] <Example 2>

[0143] A cathode active material was prepared in the same manner as in Example 1, except that the content of the titanium precursor (TiO2) was changed so that the titanium (Ti) content was 0.025 mol% based on the total molar amount of the cathode active material. At this time, the molar ratio of Co:Ti was set to 1:0.0125.

[0144] <Comparative Example 1>

[0145] A positive electrode active material was prepared in the same manner as in Example 1, except that a coating layer was not formed.

[0146] <Comparative Example 2>

[0147] A positive electrode active material was prepared in the same manner as in Example 1, except that a titanium precursor was not mixed when forming the coating layer, and the content of the cobalt precursor was changed so that the content of cobalt (Co) was 2 mol% based on the total molar amount of the positive electrode active material.

[0148] <Comparative Example 3>

[0149] A positive electrode active material was prepared in the same manner as in Example 1, except that a cobalt precursor was not mixed when forming the coating layer, and the content of the titanium precursor was changed so that the titanium (Ti) content was 0.05 mol% based on the total molar amount of the positive electrode active material.

[0150] <Comparative Example 4>

[0151] A positive electrode active material was prepared in the same manner as in Example 1, except that a cobalt precursor (Co(OH)2) and a niobium precursor (Nb2O5) were mixed into a mixture for forming a coating layer. At this time, the content of the cobalt precursor was adjusted so that the content of cobalt (Co) was 2 mol% based on the total molar amount of the positive electrode active material, and the content of the niobium precursor was adjusted so that the content of niobium (Nb) was 0.025 mol%.

[0152] <Comparative Example 5>

[0153] A cathode active material was prepared in the same manner as in Example 1, except that the content of the titanium precursor was changed so that the titanium (Ti) content was 0.3 mol% based on the total molar amount of the cathode active material.

[0154] <Experimental Example>

[0155] <Experimental Example 1>

[0156] X-ray diffraction analysis using CuKα rays was performed on the positive active materials of the above examples and comparative examples (model name: MiniFlex600, manufacturer: Rigaku) ​​to derive X-ray diffraction patterns, and the results are shown in Table 1 and Figures 1 to 4 below. The X-ray diffraction pattern analysis was performed under conditions of a scan range of 10 to 80 degrees, a scan speed of 1.5 degrees / min, a voltage of 40 kV, and a current of 15 mA.

[0157] The presence or absence (detection / non-detection) of the first peak appearing in the range of 2θ angles from 37 degrees to 37.8 degrees, the second peak appearing in the range of 2θ angles from 43 degrees to 44 degrees, and the third peak appearing in the range of 2θ angles from 35.9 degrees to 36.2 degrees was confirmed, and the peak intensity ratio according to Equation 1 or Equation 2 below was calculated and recorded in Table 1 below. In cases where the first to third peaks did not appear and the peak intensity ratio could not be calculated, it was indicated as '-'.

[0158] Meanwhile, the X-ray diffraction pattern spectra of the positive electrode active materials of Example 1 and Comparative Example 1 are shown in FIG. 1, and enlarged images are shown in FIG. 2 to 4. In this case, (a) of FIG. 1 to 4 represents the result of Example 1, and (b) represents the result of Comparative Example 1, respectively.

[0159] [Mathematical Formula 1]

[0160] I2 / I1

[0161] [Mathematical Formula 2]

[0162] I3 / I1

[0163] In mathematical formulas 1 and 2,

[0164] I1 is the intensity of the first peak mentioned above, and

[0165] I2 is the intensity of the second peak mentioned above, and

[0166] I3 is the intensity of the third peak mentioned above.

[0167] <Experimental Example 2: Evaluation of Battery Characteristics>

[0168] A composition for forming an anode active material layer was prepared by adding each of the anode active materials prepared in Examples 1 to 2 and Comparative Examples 1 to 4, Super P conductive material, and PVdF (Kureha, KF9709) binder in a weight ratio of 95:3:2 to an N-methylpyrrolidone (NMP) (Daejeong Chemical Co.) solvent.

[0169] A composition for forming an anode active material layer was applied to one side of an aluminum foil current collector with a thickness of 20 μm, and dried at a temperature of 130°C for 3 hours to form an anode active material layer. Subsequently, an anode was manufactured by rolling using a roll pressing method so that the porosity of the anode active material layer after rolling becomes 20 volume%.

[0170] A cathode slurry was prepared by mixing a cathode active material, in which natural graphite and artificial graphite were mixed in a weight ratio of 5:5, a Super C conductive material, an additive (Daicel, DAICEL2200), and a binder (ZEON, BML302) in a weight ratio of 95.6:1.0:2.3:1.1. The cathode slurry was applied to one side of a copper current collector, dried at 130°C, and rolled to produce a cathode.

[0171] An electrode assembly was prepared by interposing a porous polyethylene separator between the positive and negative electrodes. This was placed inside a battery case, and a pouch-type monocell battery was prepared by injecting an electrolyte solution in which 0.7 M LiPF6 and 0.3 M LiFSI were dissolved in an organic solvent mixed with ethylene carbonate (EC):ethyl methyl carbonate (EMC) in a volume ratio of 3:7.

[0172] [High-temperature life characteristics]

[0173] Each monocell was charged to 4.4V using the CC-CV method (0.1C) at 25℃ and discharged to 2.5V using the CC method (0.1C). After setting the SOC state based on the measured discharge capacity, the initial resistance (Ω) was measured at 25℃.

[0174] The SOC50 resistance is a value calculated by applying a 2.5C discharge current at SOC50 for 30 seconds at 25℃ to measure the voltage drop, and then dividing the voltage drop during the initial 10 seconds by the applied current.

[0175] A total of 300 cycles of charging and discharging were repeated, with one cycle consisting of charging to 4.4V at 45℃ using the CC-CV method (0.33C) and discharging to 2.5V using the CC method (0.33C). After measuring the discharge capacity in the first cycle and the 300th cycle, the percentage of the discharge capacity of the 300th cycle relative to the discharge capacity of the first cycle (capacity retention rate (%)) was calculated.

[0176] The resistance was calculated based on the voltage drop and applied current values ​​when a fully charged monocell at 4.4V was discharged at 0.5C for 60 seconds. A total of 300 cycles of charging and discharging were repeated, with one cycle defined as a 0.7C / 0.5C discharge cycle at 45℃. After measuring the discharge resistance in the first cycle and the 300th cycle, the percentage of the discharge resistance of the 300th cycle relative to the discharge resistance of the first cycle (resistance increase rate (%)) was calculated.

[0177] [Equation 1]

[0178] Capacity Retention Rate (%) = (Discharge Capacity at 300 Cycles / Discharge Capacity at 1 Cycle) x 100

[0179] [Equation 2]

[0180] Resistance increase rate (%) = (Discharge resistance at 300 cycles / Discharge resistance at 1 cycle) x 100

[0181] [High-temperature storage characteristics]

[0182] Each monocell was subjected to a formation process at 25°C at a rate of 0.1C for 3 hours, then charged to 4.4V at 25°C at a rate of 0.33C under CC-CV conditions, and discharged to 2.5V at a rate of 0.33C under CC conditions. Three cycles of initial charge and discharge were performed, with the above charge and discharge counting as one cycle. Subsequently, the cells were charged to 4.4V at a rate of 0.33C under CC-CV conditions, stored at 60°C for 12 weeks (SOC; state of charge, 100%), and then discharged to 2.5V at a rate of 0.33C under CC conditions, after which the capacity retention rate and resistance increase rate were measured.

[0183] [Equation 3]

[0184] Capacity retention rate after high-temperature storage (%) = (Discharge capacity after 12 weeks / Discharge capacity before high-temperature storage) × 100

[0185] [Equation 4]

[0186] Resistance increase rate after high-temperature storage (%) = [(Resistance value after 12 weeks of high-temperature storage / Resistance value before high-temperature storage) × 100)] - 100 (%)

[0187] [High-temperature storage gas growth rate]

[0188] For each monocell, the amount of gas generated was measured by storing it at 60°C at 100% SOC for 12 weeks, and the increase rate (%) was calculated by comparing it with the amount of gas generated before storage.

[0189] Classification Example 1 Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Experimental Example 1 1st Peak Detected Not Detected Detected Not Detected Detected 2nd Peak Detected Not Detected Not Detected Detected Not Detected 3rd Peak Detected Not Detected Not Detected Not Detected Not Detected Mathematical Formula 11.2 1.15 ----2.8 Mathematical Formula 21.0 32 ----- 2.24 Experimental Example 2(a)1.45 1.5 31.6 1.6 1.5 91.6 42.15(b)90.28 9.18 7.5 87 87.38 7.18 7.5(c)129.8 133.4 14 615 6.6 138.2 14 2.6 21 4.2(d)71.36 9.4 16 6.45 9.7 61.5 64.7 64.2(e)469.2 47 5.16 21.39 39 74 6.16 89.2 76 5.5(f)20.6 21.2 23.6 24.5 23.4 24 21.1(a): Initial resistance (ohm)(b): Capacitance retention rate (%) of high-temperature life characteristics (@300cy)(c): Resistance growth rate (%) of high-temperature life characteristics (@300cy)(d): High-temperature storage characteristics Capacity retention rate (%) (e) at (@60℃ / 12W): Resistance increase rate (%) (f) of high-temperature storage characteristics (@60℃ / 12W): High-temperature storage gas increase rate (@60℃ / 12W: %)

[0190] From the results of Experimental Example 1, the cobalt (Co) related peak derived from LiCO3 is observed in the range of 37 to 37.8 degrees, and the titanium (Ti) related peak derived from Li2TiO3 is observed in the range of 35.9 to 36.2 degrees and 43 to 44 degrees.

[0191] Cobalt (Co) and titanium (Ti) peaks were observed together in the cathode active materials of Examples 1 and 2. In particular, Example 1 used a high content of titanium (Ti), and an additional peak was identified in the range of 35.9 to 36.2 degrees.

[0192] The positive active material of Comparative Example 1 did not form a coating layer, so no peaks related to them were observed, and the positive active material of Comparative Example 2 used only cobalt (Co) as the coating layer, so no peaks related to titanium (Ti) were observed.

[0193] In Comparative Example 3, the positive active material used only titanium (Ti) as the coating layer, so no cobalt (Co) related peaks were observed, and in Comparative Example 4, only cobalt (Co) related peaks were observed.

[0194] Looking at the XRD spectrum of Fig. 1, there is almost no difference in the peaks of the cathode active materials of Example 1 and Comparative Example 1, but looking at the magnified images of Figs. 2 to 4, differences in peaks at 37 to 37.8 degrees (Fig. 2), 35.9 to 36.2 degrees (Fig. 3), and 43 to 44 degrees (Fig. 4) could be confirmed.

[0195] The battery using the positive active material of Comparative Example 1, which did not have a coating layer formed, had low high-temperature life characteristics, and after high-temperature storage, the capacity and resistance characteristics deteriorated and the amount of gas generated increased.

[0196] Batteries containing positive electrode active materials that use only cobalt (Co) as the coating layer (Comparative Example 2) or only titanium (Ti) (Comparative Example 3) showed reduced lifespan characteristics and high-temperature storage characteristics.

[0197] In addition, it was confirmed that although the coating layer contains both cobalt and titanium, if the titanium content is too high, the storage growth rate at high temperatures is too high and the capacity retention rate is low, making it unsuitable for use in lithium secondary batteries (Comparative Example 5).

[0198] On the other hand, it was confirmed that the battery containing the positive active material of Examples 1 and 2 had a low initial resistance value, excellent lifespan characteristics and high-temperature storage characteristics at high temperatures, and also showed a low gas increase rate.

Claims

1. A lithium transition metal oxide in the form of a single particle, wherein the nickel content among all metal elements excluding lithium is 50 mol% or more; and It includes a coating layer provided on part or all of the surface of the lithium transition metal oxide, and The above coating layer comprises cobalt (Co) and titanium (Ti), and The content of the above titanium is 0.01 mol% or more and 0.2 mol% or less based on the total molar amount of the cathode active material, and A positive active material comprising, as a result of X-ray diffraction analysis, a first peak appearing in the range of a 2θ angle of 37 degrees or more and 37.8 degrees or less, and a second peak appearing in the range of a 2θ angle of 43 degrees or more and 44 degrees or less.

2. In Claim 1, A positive active material having a value calculated by the following mathematical formula 1 of 0.1 or more and 2.5 or less: [Mathematical Formula 1] I2 / I1 In mathematical formula 1, I1 is the intensity of the first peak mentioned above, and I2 is the intensity of the second peak mentioned above.

3. In Claim 1, A positive active material comprising a third peak that appears in the X-ray diffraction pattern in the range of a 2θ angle of 35.9 degrees or more and 36.2 degrees or less.

4. In Claim 3, A positive active material having a value calculated by the following mathematical formula 2 of 0.5 or more and 2 or less: [Mathematical Formula 2] I3 / I1 In mathematical formula 2, I1 is the intensity of the first peak mentioned above, and I3 is the intensity of the third peak mentioned above.

5. In Claim 1, A positive electrode active material having a titanium content of 0.5 mol% or more and 10 mol% or less based on the total molar amount of cobalt and titanium.

6. In Claim 1, A positive electrode active material having a cobalt content of 1 mol% or more and 4 mol% or less based on the total molar amount of the positive electrode active material.

7. In Claim 1, The above coating layer is a positive electrode active material comprising one or more of ions, oxides, lithium oxides, or complexes thereof, each of cobalt and titanium or both.

8. In Claim 1, A positive active material having a coating layer thickness of 1 nm or more and 200 nm or less.

9. In Claim 1, A positive electrode active material having the above coating layer discontinuously provided on the surface of the lithium transition metal oxide.

10. In Claim 1, A positive active material in which the above lithium transition metal oxide is represented by the following chemical formula 1: [Chemical Formula 1] Li 1+t Ni a Co b M 1 c M 2 d O2 In the above chemical formula 1, M 1 It includes Mn, Al, or a combination thereof, M 2 ... comprises W, Zr, Y, Ba, Ca, Ti, V, Mg, Ta, Nb, or a combination thereof, and -0.2≤t≤1, 0.5≤a<1, 0 <b≤0.4, 0<c≤0.4, 0≤d≤0.05, a+b+c+d=1이다.

11. A step of preparing a mixture comprising a lithium transition metal oxide, a cobalt precursor, and a titanium precursor in a single-particle form, wherein the nickel content among all metal elements excluding lithium is 50 mol% or more; and A method for manufacturing an anode active material according to any one of claims 1 to 10, comprising the step of heat-treating the above mixture.

12. In Claim 11, A method for manufacturing an anode active material in which the step of heat-treating the above mixture is performed at a heat treatment temperature of 800°C or higher and 1,000°C or lower.

13. A positive electrode comprising a positive electrode active material according to any one of claims 1 to 10.

14. A lithium secondary battery comprising a positive electrode according to claim 13.

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