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

Abstract

The present specification provides a cathode active material, a preparation method therefor, a cathode for a lithium secondary battery, comprising same, and a lithium secondary battery comprising same, the cathode active material comprising: a lithium transition metal oxide in a single particle form in which nickel content is 50 mol% or more on the basis of the total metal elements excluding lithium; a coating layer provided on a part or all of the surface of the lithium transition metal oxide; a first metal doped into the lithium transition metal oxide; and a second metal doped into the coating layer, wherein a value calculated using mathematical relation 1 is 5 to 6.

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. 10-2024-0164441 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, in the case of high-concentration nickel cathode active materials with high nickel content, there have been 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;

[0009] A coating layer provided on part or all of the surface of the above lithium transition metal oxide;

[0010] A first metal doped inside the lithium transition metal oxide; and

[0011] It includes a second metal doped in the above coating layer,

[0012] A positive active material is provided having a value calculated by the following mathematical formula 1 that is 5 or more and 6 or less.

[0013] [Mathematical Formula 1]

[0014] R H / L =I L / I H

[0015] In mathematical formula 1,

[0016] I L is the intensity of the first peak appearing at a 2θ angle of 32.5 to 33 degrees in the X-ray diffraction pattern, and

[0017] I H is the intensity of the second peak appearing at an angle of 2θ of 37 to 38 degrees in the X-ray diffraction pattern.

[0018] In addition, the present invention comprises the step of preparing a first mixture including a positive electrode active material precursor, a first lithium raw material, and a first metal raw material;

[0019] A step of producing a lithium transition metal oxide in the form of single particles by first calcining the above first mixture, wherein the nickel content among the total metal elements excluding lithium is 50 mol% or more;

[0020] A step of preparing a second mixture comprising the above lithium transition metal oxide, a second lithium raw material, and a second metal raw material; and

[0021] The present invention provides a method for manufacturing the above-described positive electrode active material, comprising the step of secondarily calcining the above-described second mixture to form a coating layer on part or all of the surface of the lithium transition metal oxide.

[0022] In addition, the present invention provides a positive electrode for a lithium secondary battery comprising the positive electrode active material described above.

[0023] In addition, the present invention provides a lithium secondary battery comprising the anode described above.

[0024] The positive active material of the present invention has the effect of improving structural stability.

[0025] 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 characteristics.

[0026] When the positive electrode 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 life characteristics.

[0027] Figure 1 is a scanning electron microscope image of the positive electrode active material according to Example 1.

[0028] Figures 2 and 3 are X-ray diffraction patterns of the positive active material according to Example 1.

[0029] The present invention will be described in more detail below.

[0030] 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.

[0031] 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.

[0032] The singular forms used in this specification include plural forms unless the phrases clearly indicate otherwise.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] In this specification, the term 'at least one' should be understood to include all combinations that can be presented from one or more related items.

[0038] In this specification, the 'anode active material' may be a composition comprising one or more of the above-described lithium transition metal oxides.

[0039] In this specification, 'metal element' may mean any metal element excluding lithium, unless otherwise defined. More specifically, it may mean transition metals excluding lithium.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] In this specification, 'peak' may mean 'major peak'. For example, the first peak appearing at 2θ angles of 32.5 to 33 degrees may mean the major peak with the strongest intensity among 2θ angles of 32.5 to 33 degrees.

[0048] In this specification, 'main peak' means the peak with the strongest intensity among the peaks observed in the measured 2θ angle range.

[0049] In this specification, '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).

[0050] 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;

[0051] A coating layer provided on part or all of the surface of the above lithium transition metal oxide;

[0052] A first metal doped inside the lithium transition metal oxide; and

[0053] It includes a second metal doped in the above coating layer,

[0054] A positive active material is provided having a value calculated by the following mathematical formula 1 that is 5 or more and 6 or less.

[0055] [Mathematical Formula 1]

[0056] R H / L =I L / I H

[0057] In mathematical formula 1,

[0058] I L is the intensity of the first peak appearing at a 2θ angle of 32.5 to 33 degrees in the X-ray diffraction pattern, and

[0059] I H is the intensity of the second peak appearing at an angle of 2θ of 37 to 38 degrees in the X-ray diffraction pattern.

[0060] 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.

[0061] 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.

[0062] 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 prevented.

[0063] 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.

[0064] The positive electrode active material of the present invention comprises a first metal doped inside the lithium transition metal oxide and a second metal doped in the coating layer, and the above-mentioned problem was solved by controlling the value calculated by Equation 1 to be between 5 and 6. Specifically, the crystal structure of the surface of the positive electrode active material is stably formed, thereby reducing the lithium ion diffusion resistance and suppressing crystal structure deformation and particle cracking during charging and discharging, which resulted in improved lifespan characteristics. Furthermore, the stability of the layered structure and surface stability of the lithium transition metal oxide were improved, phase transitions were suppressed, and the increase in resistance, particularly under high voltage and high temperature conditions, was effectively suppressed, thereby improving high-temperature lifespan performance. The first metal is a metal element doped inside the lithium transition metal oxide, and the second metal is a metal element coated on part or all of the surface of the lithium transition metal oxide to form a coating layer.

[0065] In the present invention, the value of the positive electrode active material calculated by the above mathematical formula 1 may be 5 or more and 6 or less. The value calculated by the above mathematical formula 1 is I L The first peak, representing Lithium Yttrium Oxide expressed as, and I H It refers to the ratio of the second peak, which represents lithium cobalt oxide expressed as . By adjusting the value calculated by the above mathematical formula 1, the ratio of the lithium yttrium oxide phase to the lithium cobalt oxide phase is controlled, thereby minimizing surface phase changes of the cathode active material and suppressing side reactions with the electrolyte, while improving high-temperature long-term performance by having high lifespan characteristics at high temperatures and excellent storage stability. The lithium yttrium oxide may be LiYO2, and the lithium cobalt oxide may be LiCO2.

[0066] In the present invention, the value calculated by the above mathematical formula 1 may be 5 or more, 5.1 or more, 5.2 or more, 5.3 or more, or 5.4 or more. Additionally, it may be 6 or less, 5.9 or less, 5.8 or less, 5.7 or less, 5.6 or less, or 5.5 or less. Within the above numerical range, the surface phase change of the cathode active material is minimal, side reactions with the electrolyte are suppressed, and high-temperature long-term performance can be improved by having high lifespan characteristics and excellent storage stability at high temperatures. For example, the peak intensity ratio (R H / L A case where ) is less than 5 indicates that the lithium yttrium oxide content is low or the lithium cobalt oxide content is excessively high. Batteries using cathode active materials having the above value of less than 5 exhibit very high initial resistance, and the resistance growth rate at high temperatures and after high-temperature storage increase significantly. In addition, the peak intensity ratio (R H / L When ) exceeds 6, it is because lithium yttrium oxide is used excessively or the content of lithium cobalt oxide is low. In this case, the initial resistance is very high, and the resistance growth rate at high temperatures and the resistance growth rate after high-temperature storage may increase significantly.

[0067] In the present invention, the X-ray diffraction analysis method may use a known X-ray diffraction apparatus. Specifically, using a Bruker D8 Endeavor (light source: Cu-Kα, λ=1.54Å) equipped with a LynxEye XE-T-position sensitive detector, a sample of the positive active material powder to be measured is placed in a groove of a general powder holder, the surface of the sample is leveled using a slide glass, and the sample is filled so that its height matches the edge of the holder. Then, measurements can be taken under conditions of a step size of 0.02 degrees and a total scan time of approximately 20 minutes for the FDS 0.5 degree, 2θ angle of 15 degrees to 90 degrees region.

[0068] In the present invention, the presence and intensity of the first peak are peaks indicating the presence of a first metal, and specifically may be related to yttrium (Y). More specifically, it is a peak indicating lithium yttrium oxide obtained by the reaction of yttrium (Y) with lithium. A higher value of the peak intensity within the above range indicates an increase in the content of lithium yttrium oxide within the cathode active material.

[0069] In the present invention, the presence and intensity of the second peak are peaks indicating the presence of a second metal, and may be related to cobalt (Co). More specifically, it may be a peak indicating lithium cobalt oxide obtained by the reaction of cobalt (Co) and lithium (Li). A higher value of the peak intensity within the above range indicates an increase in the content of lithium cobalt oxide within the cathode active material.

[0070] Meanwhile, in the cathode active material of the present invention, an increase in the content of lithium yttrium oxide implies an increase in the content of yttrium (Y) doped into the lithium cobalt-based oxide. When lithium yttrium oxide is included within an appropriate content range, it can prevent structural collapse of the lithium transition metal oxide and achieve surface structure stabilization; however, if used excessively, it acts as a resistor, hindering the insertion and extraction of lithium ions, thereby degrading output characteristics and raising concerns about reduced long-term lifespan characteristics.

[0071] Furthermore, increasing the lithium cobalt oxide content implies an increase in the amount of lithium cobalt oxide coated on the surface of the lithium cobalt-based oxide. While the inclusion of lithium cobalt oxide within an appropriate range can suppress phase transitions and prevent contact with the electrolyte, excessive use acts as resistance or causes cobalt (Co) ions to penetrate too deeply into the lithium cobalt-based oxide, leading to a higher proportion of the NiO reduction layer on the surface of the cathode active material, which also results in a deterioration of long-term lifespan characteristics.

[0072] In particular, the cathode active material of the present invention is manufactured through a process of forming lithium yttrium oxide via yttrium (Y) doping, followed by forming lithium cobalt oxide using cobalt (Co) and lithium (Li). At this time, lithium (Li) is consumed to form the subsequent lithium cobalt oxide, thereby reducing the formation of lithium yttrium oxide within the cathode active material after coating. Consequently, as the content of lithium yttrium oxide within the cathode active material decreases, the aforementioned effect cannot be sufficiently secured.

[0073] In the present invention, the lithium cobalt oxide To compensate for the decrease in lithium yttrium oxide content due to lithium consumption for formation, additional lithium is compensated during the coating process so that the cathode active material contains lithium yttrium oxide and lithium cobalt oxide at appropriate levels.

[0074] In the present invention, the above I L It may be 2,500 or more, 2,700 or more, 3,000 or more, or 3,300 or more. Also, it may be 3,800 or less, 3,600 or less, 3,500 or less, or 3,450 or less.

[0075] In the present invention, the above I H It may be 450 or more, 500 or more, 550 or more, or 580 or more. Also, it may be 900 or less, 800 or less, 700 or less, or 650 or less.

[0076] The above I L and I H represents the number of X-rays detected per unit time by an X-ray diffraction analysis device and can be expressed as intensity(count).

[0077] In the present invention, the second metal may include cobalt (Co). Specifically, the second metal may be in the form of one or more of an ion, an oxide, a lithium oxide, or a complex thereof on the surface of a lithium transition metal oxide.

[0078] In the present invention, the content of the second metal may be 1,000 ppm or more and 50,000 ppm or less based on the total weight of the lithium transition metal oxide. Preferably, it may be 2,000 ppm or more, 4,000 ppm or more, 6,000 ppm or more, 8,000 ppm or more, 10,000 ppm or more, 12,000 ppm or more, 14,000 ppm or more, 16,000 ppm or more, 18,000 ppm or more, or 19,000 ppm or more. Additionally, it may be 45,000 ppm or less, 40,000 ppm or less, 36,000 ppm or less, 32,000 ppm or less, 28,000 ppm or less, 24,000 ppm or less, or 20,000 ppm or less. In the above numerical range, the effect of the second metal doping is sufficiently expressed, and the second metal remaining as a byproduct prevents a decrease in battery capacity, and the value calculated by the above-described mathematical formula 1 can satisfy a range of 5 or more and 6 or less.

[0079] In the present invention, the coating layer further comprises lithium, and the lithium content may be 1.05 mol% or more and 2.4 mol% or less based on the total molar amount of metal elements included in the lithium transition metal oxide and the coating layer. Preferably, it may be 1.06 mol% or more, 1.08 mol% or more, 1.1 mol% or more, 1.12 mol% or more, or 1.14 mol% or more. Additionally, it may be 2.35 mol% or less, 2.3 mol% or less, 2.25 mol% or less, 2.2 mol% or less, 2.15 mol% or less, 2.1 mol% or less, or 2.05 mol% or less. Within the above numerical range, the lithium compensation effect can be sufficiently manifested, and by preventing unreacted lithium from remaining as a byproduct, the degradation of battery capacity when applied to a lithium secondary battery can be prevented. Furthermore, the range in which the value calculated by the above-described mathematical formula 1 is 5 or more and 6 or less can be satisfied.

[0080] In the present invention, the coating layer may include lithium cobalt oxide. The lithium cobalt oxide may be LiCoO2. Additionally, the lithium cobalt oxide may be in the form of particles. In this case, the lithium cobalt oxide has the effect of suppressing phase transition and suppressing contact with the electrolyte.

[0081] In the present invention, the first metal may include yttrium (Y). The yttrium (Y) may be in one or more forms among an ion, an oxide, a lithium oxide, or a complex thereof within the lithium transition metal oxide, and preferably reacts with lithium to exist in the form of lithium yttrium oxide. The lithium yttrium oxide can prevent structural collapse of the lithium transition metal oxide and stably form a surface structure.

[0082] In the present invention, the content of the first metal may be 500 ppm or more and 10,000 ppm or less based on the total weight of the lithium transition metal oxide. Preferably, it may be 1,000 ppm or more, 1,500 ppm or more, 2,000 ppm or more, 2,400 ppm or more, 2,600 ppm or more, or 2,800 ppm or more. Additionally, it may be 9,000 ppm or less, 8,000 ppm or less, 7,000 ppm or less, 6,000 ppm or less, 5,000 ppm or less, or 4,000 ppm or less. Within the above numerical range, the effect of the first metal doping is sufficiently manifested, the first metal can be prevented from remaining as a byproduct and reducing the battery capacity, and the range in which the value calculated by the above-described mathematical formula 1 is 5 or more and 6 or less can be satisfied.

[0083] In the present invention, the positive electrode active material may include a third peak appearing at an X-ray diffraction angle of 18 to 19 degrees, a fourth peak appearing at 43 to 46 degrees, or a combination thereof. The third peak and the fourth peak may each be characteristic peaks indicating that the lithium transition metal oxide has a layered structure.

[0084] 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.

[0085] In the present invention, the coating layer may be provided on a part or the whole of the surface of the lithium transition metal oxide. Specifically, it may be formed over the entire surface of the lithium transition metal oxide particles or discontinuously. Preferably, the discontinuously distributed 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, and the surface protection effect of the positive electrode active material can be maximized due to this coating layer.

[0086] 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.

[0087] In the present invention, the lithium transition metal oxide may be a nickel-cobalt-manganese oxide (NCM) comprising nickel, cobalt, and manganese. Furthermore, in the case of a high-nickel (Ni-rich) cathode active material, surface degradation occurs due to side reactions with the electrolyte at the surface of the cathode active material where the cathode active material comes into contact with the electrolyte, leading to problems such as reduced lifespan and resistance. Additionally, on the surface of the lithium transition metal oxide in single-particle form, a NiO degradation layer exists that has not been converted into a nickel-cobalt-manganese (NCM) oxide layered structure due to the high calcination temperature, which acts as battery resistance or causes a reduction in capacity.

[0088] In the present invention, the lithium transition metal oxide can be represented by the following chemical formula 1.

[0089] [Chemical Formula 1]

[0090] Li 1+t Ni a Co b M 1 c M2 d O2

[0091] In the above chemical formula 1,

[0092] M 1 It includes Mn, Al, or a combination thereof,

[0093] M 2 ... comprises W, Zr, Y, Ba, Ca, Ti, V, Mg, Ta, Nb, or a combination thereof, and

[0094] -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.

[0095] The above M 1 is Mn, Al, or a combination thereof, preferably Mn or a combination of Mn and Al.

[0096] 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.

[0097] 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 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.

[0098] 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.

[0099] 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.

[0100] 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.

[0101] The above d is M among the total metals excluding lithium in the lithium transition metal oxide. 2 It represents the molar ratio of 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.

[0102] 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.

[0103] The present invention comprises the step of preparing a first mixture comprising a positive electrode active material precursor, a first lithium raw material, and a first metal raw material;

[0104] A step of producing a lithium transition metal oxide in the form of single particles by first calcining the above first mixture, wherein the nickel content among the total metal elements excluding lithium is 50 mol% or more;

[0105] A step of preparing a second mixture comprising the above lithium transition metal oxide, a second lithium raw material, and a second metal raw material; and

[0106] The present invention provides a method for manufacturing the above-described positive electrode active material, comprising the step of secondarily calcining the above-described second mixture to form a coating layer on part or all of the surface of the lithium transition metal oxide.

[0107] In the present invention, a coating layer is formed on the surface of a lithium transition metal oxide by the steps of: preparing a second mixture comprising the lithium transition metal oxide, a second lithium raw material, and a second metal raw material; and performing a second calcination of the second mixture to form a coating layer on a part or all of the surface of the lithium transition metal oxide. At this time, by changing the mixing state and conditions of the second mixture and the conditions of the second calcination, an anode active material satisfying the above-described mathematical formula 1 can be produced.

[0108] In the present invention, the content of lithium derived from the second lithium raw material may be 1.05 mol% or more and 2.4 mol% or less based on the total molar amount of the metal component of the second mixture. Preferably, it may be 1.06 mol% or more, 1.08 mol% or more, 1.1 mol% or more, 1.12 mol% or more, or 1.14 mol% or more. Additionally, it may be 2.35 mol% or less, 2.3 mol% or less, 2.25 mol% or less, 2.2 mol% or less, 2.15 mol% or less, 2.1 mol% or less, or 2.05 mol% or less. Within the above numerical range, the lithium compensation effect can be sufficiently manifested, and by preventing unreacted lithium from remaining as a byproduct, the reduction of battery capacity when applied to a lithium secondary battery can be prevented. Furthermore, the range in which the value calculated by the above-described mathematical formula 1 is 5 or more and 6 or less can be satisfied. At this time, the total number of moles of the metal components of the second mixture may refer to the total number of moles of transition metals in the second mixture. Specifically, the total number of moles of nickel, cobalt, and manganese in the second mixture (Me 2 It can mean =Ni+Co+Mn).

[0109] In the present invention, the secondary firing is intended to form a coating layer by fixing a second metal and lithium (Li) to the surface of a lithium transition metal oxide.

[0110] In the present invention, the calcination temperature of the secondary calcination may be 600°C or higher and 900°C or lower. Preferably, it may be 650°C or higher, 700°C or higher, 750°C or higher, or 780°C or higher. Additionally, it may be 880°C or lower, 860°C or lower, or 840°C or lower. Within the above numerical range, the lithium insertion rate is improved, and the surface of the calcined product can be prevented from degenerating into a rock salt structure.

[0111] In the present invention, the firing time of the secondary firing may be 1 hour or more and 20 hours or less. Preferably, it may be 2 hours or more, 3 hours or more, 4 hours or more, or 5 hours or more. Additionally, it may be 19 hours or less, 18 hours or less, or 16 hours or less.

[0112] In the present invention, the secondary calcination may be performed under an oxidizing atmosphere. At this time, the oxygen concentration may be 10% or more and 100% or less, or 20% or more and 90% or less.

[0113] In the present invention, the firing temperature of the first firing may be 800°C or higher and 1,000°C or lower. Preferably, it may be 850°C or higher, 860°C or higher, 880°C or higher, or 900°C or higher. Additionally, it may be 990°C or lower, 980°C or lower, 970°C or lower, or 960°C or lower. Within the above numerical range, there is an effect of a high degree of crystallization of the first fired product. The firing temperature may be the final firing temperature of the first firing step.

[0114] In the present invention, the firing time of the first firing may be 1 hour or more and 20 hours or less. Preferably, it may be 2 hours or more, 3 hours or more, 4 hours or more, or 5 hours or more. Additionally, it may be 18 hours or less, 16 hours or less, 12 hours or less, or 10 hours or less.

[0115] In the present invention, the heating rate of the first firing may be 0.5℃ / min or higher and 5℃ / min or lower. Preferably, it may be 0.7℃ / min or higher, 0.9℃ / min or higher, 1℃ / min or higher, 1.1℃ / min or higher, or 1.2℃ / min or higher. Additionally, it may be 4℃ / min or lower, 3℃ / min or lower, 2℃ / min or lower, or 1.5℃ / min or lower. Within the above numerical ranges, a first fired product with a stable structure can be produced.

[0116] In the present invention, the first calcination may be performed under an oxidizing atmosphere. At this time, the oxygen concentration may be 10% or more and 100% or less, or 20% or more and 90% or less.

[0117] In the present invention, the content of lithium derived from the first lithium raw material may be 1 mol% or more and 10 mol% or less based on the total molar amount of the metal component of the cathode active material precursor. Preferably, it may be 2 mol% or more or 3 mol% or more. Additionally, it may be 9 mol% or less, 8 mol% or less, 7 mol% or less, 6 mol% or less, or 5 mol% or less. Within the above numerical range, the structural stability of the cathode active material is improved, and excessive residual lithium generation can be prevented. At this time, the total molar amount of the metal component of the cathode active material precursor may refer to the total molar amount of transition metals in the cathode active material precursor. Specifically, the total molar amount of nickel, cobalt, and manganese (Me 0 It can mean =Ni+Co+Mn).

[0118] In the present invention, the positive active material precursor is used in which the nickel content among the metal elements is 50 mol% or more, and may be represented, for example, by the following chemical formula 2 or chemical formula 3.

[0119] [Chemical Formula 2]

[0120] [Ni a2 Co b2 M' c2 M'' d2 ](OH)2

[0121] [Chemical Formula 3]

[0122] [Ni a3 Co b3 M' c3 M'' d3 ]O·OH

[0123] In the above chemical formulas 2 and 3,

[0124] M ' is M of the above-described chemical formula 1. 1The explanation for can be applied,

[0125] M '' is M of the above-described chemical formula 1. 2 The explanation for can be applied,

[0126] a2 and a3 can each be subject to the description of a in Chemical Formula 1 described above, and

[0127] The description of b in Chemical Formula 1 described above can be applied to b2 and b3, respectively, and

[0128] c2 and c3 can each be subject to the description of c of Chemical Formula 1 described above, and

[0129] a2+b2+c2+d2=1, and

[0130] a3+b3+c3+d3=1.

[0131] In the present invention, the first lithium raw material and the second lithium raw material are each the same or different and may be at least one selected from the group consisting of lithium carbonate (Li2CO3), lithium hydroxide (LiOH), anhydrous lithium hydroxide (LiOH), LiNO3, CH3COOLi, and Li2(COO)2, and preferably may be lithium carbonate (Li2CO3), lithium hydroxide (LiOH), or a combination thereof.

[0132] In the present invention, the first metal raw material may be an oxide, hydroxide, oxyhydroxide, halide, nitrate, carbonate, acetate, oxalate, citrate, carboxylate, sulfate, or sulfide containing the first metal, and more specifically, may be one or more selected from Y2O3, Y(OH)3, YCl3, Y(NO3)3, YSZ, Y2(SO4)3, and Y2S3, and more specifically, one or more selected from Y2O3 and Y(OH)3, and even more specifically, may be Y2O3.

[0133] In the present invention, the second metal raw material may be an oxide, hydroxide, oxyhydroxide, halide, nitrate, carbonate, acetate, oxalate, citrate, carboxylate, or sulfate containing the second metal, 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.

[0134] In the present invention, the step of preparing the first mixture and the step of preparing the second mixture are not particularly limited as long as they involve mixing each raw material, and may proceed as a solid-state mixing or a liquid-state mixing.

[0135] The present invention provides a positive electrode comprising the positive electrode active material described above.

[0136] 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.

[0137] 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.

[0138] 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.

[0139] 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.

[0140] 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.

[0141] 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.

[0142] 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.

[0143] 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.

[0144] The present invention provides a lithium secondary battery comprising the anode described above.

[0145] 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.

[0146] 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.

[0147] In the present invention, the cathode comprises a cathode current collector and a cathode active material layer provided on the cathode current collector.

[0148] 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.

[0149] 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.

[0150] 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.

[0151] 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.

[0152] 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.

[0153] 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.

[0154] 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.

[0155] 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.

[0156] 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.

[0157] 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.

[0158] 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.

[0159] 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.

[0160] 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).

[0161] 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.

[0162] 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.

[0163] 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.

[0164] 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.

[0165] 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.

[0166] <Examples and Comparative Examples>

[0167] <Example 1>

[0168] Cathode active material precursor [Composition: Ni 0.7 Co 0.07 Mn 0.23 (OH)2], a first mixture was prepared by mixing Li2CO3 as a first lithium raw material and Y2O3 as a first metal raw material. At this time, lithium (Li derived from the first lithium raw material) 1 ) and the total moles of the metal component of the positive electrode active material precursor (Me 0 The ratio of =Ni+Co+Mn) (Li 1 :Me 0 The ratio was 1.04:1. In addition, the first metal raw material was mixed so that the Y content was 3,000 ppm based on the total weight of the total cathode active material precursor.

[0169] A lithium transition metal oxide doped with yttrium (Y) was prepared by placing the above first mixture into an alumina crucible and calcining it at a temperature of 910°C for 8 hours under an oxygen atmosphere.

[0170] After grinding the above lithium transition metal oxide, a second mixture was prepared by mixing Co(OH)2 as a second metal raw material and LiOH as a second lithium raw material. At this time, the second metal raw material was mixed such that the Co content was 19,500 ppm based on the total weight of the lithium transition metal oxide. In addition, lithium (Li derived from the second lithium raw material 2 ) and the total moles of the metal component of the second mixture (Me 2 The ratio of =Ni+Co+Mn) (Li 2 :Me 2 ) was 1.15:100.

[0171] Subsequently, the second mixture was placed in an alumina crucible and heat-treated at a temperature of 800°C for 15 hours under an oxygen atmosphere to produce an anode active material.

[0172] <Example 2>

[0173] Lithium derived from second lithium raw materials (Li 2) and the total moles of the metal component of the second mixture (Me 2 The ratio of =Ni+Co+Mn) (Li 2 :Me 2 A positive electrode active material was prepared in the same manner as in Example 1, except that the ratio was changed to 2:100.

[0174] <Comparative Example 1>

[0175] Lithium derived from second lithium raw materials (Li 2 ) and the total moles of the metal component of the second mixture (Me 2 The ratio of =Ni+Co+Mn) (Li 2 :Me 2 A positive electrode active material was prepared in the same manner as in Example 1, except that the ratio was changed to 0.5:100.

[0176] <Comparative Example 2>

[0177] Lithium derived from second lithium raw materials (Li 2 ) and the total moles of the metal component of the second mixture (Me 2 The ratio of =Ni+Co+Mn) (Li 2 :Me 2 A positive electrode active material was prepared in the same manner as in Example 1, except that the ratio was changed to 1:100.

[0178] <Comparative Example 3>

[0179] Lithium derived from second lithium raw materials (Li 2 ) and the total moles of the metal component of the second mixture (Me 2 The ratio of =Ni+Co+Mn) (Li 2 :Me 2 A positive electrode active material was prepared in the same manner as in Example 1, except that the ratio was changed to 2.5:100.

[0180] <Experimental Example>

[0181] <Experimental Example 1: Observation of Appearance>

[0182] The cathode active materials prepared in the examples and preparation examples were observed using a scanning electron microscope (SEM, FEI, Inspect F) (High Voltage: 5kV, Magnification: 5k, WD: 10.2mm, Beam spot size: 3.5, SE MODE).

[0183] Figure 1 is a scanning electron microscope image of the positive electrode active material prepared in Example 1. Referring to Figure 1, it was confirmed that the particles of the positive electrode active material have a single particle form consisting of one primary particle or a secondary particle form in which 2 to 10 primary particles are aggregated. It was confirmed that this has a different shape from the conventional spherical secondary particles formed by the aggregation of tens to hundreds of primary particles.

[0184] <Experimental Example 2: X-ray Diffraction Analysis>

[0185] X-ray diffraction analysis was performed on the positive active materials of the above examples and comparative examples.

[0186] Using a Bruker D8 Endeavor (light source: Cu-Kα, λ=1.54Å) equipped with a LynxEye XE-T-position sensitive detector, a sample of the positive active material powder to be measured was placed in the groove of a general powder holder, the surface of the sample was leveled using a slide glass, and the sample was filled so that its height matched the edge of the holder. Then, measurements were taken for the FDS 0.5°, 2θ=15° to 90° range under the conditions of step size=0.02° and total scan time=approx. 20 minutes.

[0187] Figure 2 is an X-ray diffraction pattern of the positive electrode active material of Example 1, and Figure 3 is an enlarged image thereof.

[0188] From FIGS. 2 and 3, a first peak appearing at a 2θ angle of 32.5 to 33 degrees and a second peak appearing at a 2θ angle of 37 to 38 degrees could be identified. The ratio of the intensity of the peak with the greatest intensity in the corresponding region (R H / L = I L / I H ) was calculated and recorded in Table 1 below. The cathode active materials of the remaining examples and comparative examples were analyzed in the same manner.

[0189] Meanwhile, by confirming the third peak appearing at 2θ angles of 18 to 19 degrees and the fourth peak appearing at 43 to 46 degrees, it was confirmed that the lithium transition metal oxide has a layered structure.

[0190] It was confirmed that the positive active materials of Examples 1 and 2 have a value calculated by Equation 1 of 5 or higher and 6 or lower, and that the positive active materials of Comparative Examples 1 to 3 fall outside this range.

[0191] Specifically, the positive electrode active materials of Comparative Examples 1 and 2 have a peak intensity (I) associated with lithium yttrium oxide (LiYO2). L ) was low, which means that the formation of the lithium yttrium oxide was insufficient because less Li was used when forming the coating layer.

[0192] Conversely, the cathode active material of Comparative Example 3 has a peak intensity (I) associated with lithium yttrium oxide due to a sufficient supply of Li during the formation of the coating layer. L ) increased, but the intensity of the peak associated with lithium cobalt oxide (LiCoO2) (I H As ) decreases, R H / L The figures increased significantly.

[0193] <Experimental Example 3: Battery Performance Evaluation>

[0194] A composition for forming an anode active material layer was prepared by adding the anode active material, Super P conductive material, and PVdF (Kureha, KF9709) binder prepared in each of the examples and comparative examples to an N-methylpyrrolidone (NMP) (Daejeong Chemical Co.) solvent in a weight ratio of 95:3:2.

[0195] 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%.

[0196] A cathode slurry was prepared by mixing a cathode active material, consisting of natural graphite and artificial graphite mixed in a weight ratio of 5:5, a Super C conductive material, an additive (Daicel, DAICEL2200), and a binder (ZEON, BML302) in water at 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 manufacture a cathode.

[0197] 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.

[0198] [High-temperature life characteristics evaluation]

[0199] 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 SOC-50 resistance (Ω) was measured at 25℃.

[0200] The SOC-50 resistance is a value calculated by applying a 2.5C discharge current at SOC-50 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.

[0201] A total of 100 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 and 100th cycles, the percentage of the discharge capacity of the 100th cycle relative to the discharge capacity of the first cycle (capacity retention rate (%)) was calculated.

[0202] 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 100 cycles of charging and discharging were repeated, with a cycle of 0.7C / 0.5C discharge at 45℃ defined as one cycle. After measuring the discharge resistance in the first cycle and the 100th cycle, the percentage of the discharge resistance of the 100th cycle relative to the discharge resistance of the first cycle (resistance increase rate (%)) was calculated.

[0203] [Mathematical Formula 2]

[0204] Capacity retention rate (%) = (Discharge capacity at 100 cycles / Discharge capacity at 1 cycle) * 100

[0205] [Mathematical Formula 3]

[0206] Resistance increase rate (%) = (Discharge resistance at 100 cycles / Discharge resistance at 1 cycle) * 100

[0207] [Evaluation of High-Temperature Storage Characteristics]

[0208] 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 2 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.

[0209] [Mathematical Formula 4]

[0210] Capacity retention rate (%) = (Discharge capacity after high-temperature storage / Discharge capacity before high-temperature storage) * 100

[0211] [Mathematical Formula 5]

[0212] Resistance increase rate (%) = [(Resistance value after high-temperature storage / Resistance value before high-temperature storage) * 100)] - 100 (%)

[0213] Classification Example 1 Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 Experimental Example 2I L 3,3023,4141,2152,3023,461I H 61358912,1501,841524 Mathematical Formula 15.3875.7960.11.256.6 Experimental Example 3 Initial Resistance (ohm) 1.44 1.45 1.61 1.49 1.58 High Temperature Life Characteristics (%) Capacitance Retention Rate 95.5% 95.3% 94.2% 94.9% 94.9% Resistance Growth Rate 62.7% 71.3% 101.2% 96.8% 84.4% High Temperature Storage Characteristics (%) Capacitance Retention Rate 91.7% 91.3% 85.7% 98.8% 90.6% Resistance Growth Rate 158.8% 167.2% 208.5% 183% 197%

[0214] It was confirmed that the battery containing the positive active material of Examples 1 and 2 had a low initial resistance value and excellent lifespan characteristics and high-temperature storage characteristics at high temperatures.

[0215] On the other hand, the battery using the positive active material of Comparative Example 1, which had a value of 0.1 calculated by Equation 1, had a very high initial resistance value, and the positive active material of Comparative Example 1, which had a value of 1.25 calculated by Equation 1, showed a tendency for the initial resistance value to decrease compared to Comparative Example 1. However, the lifespan characteristics and high-temperature storage characteristics of both batteries using the positive active materials of Comparative Examples 1 and 2 deteriorated.

[0216] In addition, the battery using the positive active material of Comparative Example 3, which has a value of 6.6 calculated by Equation 1, showed an increased initial resistance value compared to the battery of Example 1, and also exhibited a tendency for the lifespan characteristics and high-temperature storage characteristics to decrease.

[0217] Although the present invention has been described above by limited embodiments, the present invention is not limited thereto, and it is obvious that various modifications and variations are possible within the scope of the technical spirit of the present invention and the equivalent scope of the claims described below by those skilled in the art to which the present invention belongs.

Claims

1. A lithium transition metal oxide in single-particle form, wherein the nickel content among all metal elements excluding lithium is 50 mol% or more; A coating layer provided on part or all of the surface of the above lithium transition metal oxide; A first metal doped inside the lithium transition metal oxide; and It includes a second metal doped in the above coating layer, Anode active material having a value of 5 or more and 6 or less calculated by the following mathematical formula 1: [Mathematical Formula 1] R H / L =I L / I H In mathematical formula 1, I L is the intensity of the first peak appearing at a 2θ angle of 32.5 to 33 degrees in the X-ray diffraction pattern, and I H is the intensity of the second peak appearing at an angle of 2θ of 37 to 38 degrees in the X-ray diffraction pattern.

2. In Claim 1, The above-mentioned second metal is a positive active material containing cobalt (Co).

3. In Claim 1, A positive electrode active material having a content of the second metal of 1,000 ppm or more and 50,000 ppm or less based on the total weight of the lithium transition metal oxide.

4. In Claim 1, A positive electrode active material in which the coating layer further comprises lithium, and the lithium content is 1.05 mol% or more and 2.4 mol% or less based on the total molar amount of metal elements included in the lithium transition metal oxide and the coating layer.

5. In Claim 1, The above coating layer is a positive active material containing lithium cobalt oxide.

6. In Claim 1, The above-mentioned first metal is a positive active material containing yttrium (Y).

7. In Claim 1, A positive electrode active material having a content of the first metal of 500 ppm or more and 10,000 ppm or less based on the total weight of the lithium transition metal oxide.

8. In Claim 1, A positive active material comprising an X-ray diffraction pattern having a third peak appearing at a 2θ angle of 18 to 19 degrees, a fourth peak appearing at 43 to 46 degrees, or a combination thereof.

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

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 first mixture comprising a positive electrode active material precursor, a first lithium raw material, and a first metal raw material; A step of producing a lithium transition metal oxide in the form of single particles by first calcining the above first mixture, wherein the nickel content among the total metal elements excluding lithium is 50 mol% or more; A step of preparing a second mixture comprising the above lithium transition metal oxide, a second lithium raw material, and a second metal raw material; and A method for manufacturing an anode active material according to any one of claims 1 to 10, comprising the step of secondarily calcining the second mixture to form a coating layer on part or all of the surface of the lithium transition metal oxide.

12. In Claim 11, A method for manufacturing a positive electrode active material in which the lithium content derived from the second lithium raw material is 1.05 mol% or more and 2.4 mol% or less based on the total molar amount of the metal component of the second mixture.

13. In Claim 11, A method for manufacturing an anode active material in which the calcination temperature of the above secondary calcination is 600℃ or higher and 900℃ or lower.

14. A positive electrode for a lithium secondary battery comprising a positive electrode active material according to any one of claims 1 to 10.

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

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