Positive electrode active material, and positive electrode and lithium secondary battery comprising same

Abstract

The present invention relates to a positive electrode active material comprising a single-particle lithium nickel-based oxide expressed by [Chemical formula 1], and a coating layer disposed on the surface of the single-particle lithium nickel-based oxide, wherein the ratio RPI2 / RPI1 of RPI2 defined by Formula 2 below against RPI1 defined by Formula 1 below is 1-1.3. [Chemica formula 1] Lix[NiaCobM1 cM2 d]O2 In Chemical formula 1 above, M1 is Mn, Al, or a combination thereof, M2 comprises at least one selected from the group consisting of Ti, Mg, Zr, Y, Ba, Ca, Sr, W, Ta, Nb, and Mo, and 0.9≤x≤1.1, 0.8≤a<1, 0<b<0.2, 0<c<0.2, 0≤d<0.1. [Formula 1] RPI1=I2 / I1 [Formula 2] RPI2=I3 / I1 In Formula 1 and Formula 2 above, I1, I2 , and I3 are values obtained by manufacturing an electrode comprising the positive electrode active material and then measuring the X-ray diffraction pattern; I1 is the minimum value of peak intensity appearing in the region in which 2θ=37°-38° in the X-ray diffraction pattern; I2 is the average value of peak intensities appearing in the region in which 2θ=37.3°- 37.5°; and I3 is the average value of peak intensities appearing in the region in which 2θ=37.0°- 37.2°.

Description

Cathode active material, cathode containing same, and lithium secondary battery

[0001] This application claims the benefit of priority from Korean Patent Application No. 10-2023-0189043, filed December 21, 2023, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to a cathode active material, a cathode including the same, and a lithium secondary battery, and more particularly, to a high-capacity single-particle cathode active material having excellent life characteristics, and a cathode including the cathode active material and a lithium secondary battery.

[0003] Lithium nickel cobalt manganese oxide, containing nickel, cobalt, and manganese, boasts excellent capacity characteristics and is widely used as a cathode active material in battery applications requiring high capacity. Recently, demand for high-power, high-capacity batteries, such as those for electric vehicles, has been increasing, leading to a gradual increase in the nickel content in cathode active materials.

[0004] However, when the nickel content in the positive electrode active material increases, the capacity characteristics are improved, but when charge and discharge are repeated, the highly reactive Ni +4 There is a problem that a large amount of ions are generated, causing structural collapse of the positive electrode active material, which increases the rate of deterioration of the positive electrode active material, resulting in a decrease in life characteristics and battery safety. In particular, performance deterioration occurs rapidly when exposed to high temperatures.

[0005] In addition, conventional lithium nickel cobalt manganese oxide generally has a spherical secondary particle form in which tens to hundreds of primary particles are aggregated. When lithium nickel cobalt manganese oxide in the form of secondary particles is applied, there is a problem in that the primary particles are easily broken during the rolling process during the manufacture of the positive electrode, and cracks occur inside the particles during the charge and discharge process. When the particles of the positive electrode active material are broken or cracked, the contact area with the electrolyte increases, which increases gas generation and active material degradation due to side reactions with the electrolyte, and this causes a decrease in the life characteristics. This deterioration in the life characteristics becomes more severe as the nickel content in the positive electrode active material increases.

[0006] Therefore, there is a need for the development of a cathode active material that can achieve high capacity due to its high nickel content while also having excellent life cycle characteristics.

[0007] The present invention is intended to solve the above problems, and to provide a single particle type positive electrode active material that is formed to have a specific XRD pattern and thus can excellently implement both capacity and lifespan characteristics.

[0008] In addition, the present invention seeks to provide a positive electrode and a lithium secondary battery capable of excellently implementing both capacity and lifespan characteristics by including the positive electrode active material as described above.

[0009] According to one embodiment, the present invention provides a cathode active material comprising a single-particle lithium nickel-based oxide represented by the following [chemical formula 1]; and a coating layer disposed on the surface of the single-particle lithium nickel-based oxide, wherein the ratio RPI2 / RPI1 of RPI2 defined by the following formula 2 to RPI1 defined by the following formula 1 is 1 to 1.3.

[0010] [Chemical Formula 1]

[0011] Li x [Ni a Co b M 1c M 2 d ]O2

[0012] In the above chemical formula 1, M 1 is Mn, Al or a combination thereof, and M 2 It includes at least one selected from the group consisting of Ti, Mg, Zr, Y, Ba, Ca, Sr, W, Ta, Nb, and Mo, and 0.9≤x≤1.1, 0.8≤a<1, 0 <b<0.2, 0<c<0.2, 0≤d<0.1임.

[0013] [Formula 1] RPI1=I2 / I1

[0014] In the above formula 1, I1 and I2 are values ​​obtained by measuring an X-ray diffraction pattern after manufacturing an electrode including the positive electrode active material, I1 is the minimum value of the peak intensity (Intensity) appearing in the region of 2θ=37° to 38° in the X-ray diffraction pattern for the positive electrode active material, and I2 is the average value of the peak intensity (Intensity) appearing in the region of 2θ=37.3° to 37.5° in the X-ray diffraction pattern for the positive electrode active material.

[0015] [Formula 2] RPI2=I3 / I1

[0016] In the above formula 2, I1 and I3 are values ​​obtained by measuring an X-ray diffraction pattern after manufacturing an electrode including the positive electrode active material, I1 is the minimum value of the peak intensity (Intensity) appearing in the region of 2θ=37° to 38° in the X-ray diffraction pattern for the positive electrode active material, and I3 is the average value of the peak intensity (Intensity) appearing in the region of 2θ=37.0° to 37.2° in the X-ray diffraction pattern for the positive electrode active material.

[0017] The above RPI1 may be 1.07 to 1.5, preferably 1.08 to 1.4, more preferably 1.09 to 1.3, and the above RPI2 may be 1.1 to 2, preferably 1.1 to 1.8, more preferably 1.2 to 1.6.

[0018] Also, the above RPI1 and the above The sum of RPI2 (RPI1+RPI2) may be 2.2 to 2.6, preferably 2.2 to 2.5.

[0019] Meanwhile, the coating layer may include Co, and preferably may include Co and Al.

[0020] The above single particle lithium nickel-based oxide may include 30 or fewer nodules, preferably 1 to 25 nodules, more preferably 1 to 15 nodules, and the nodules may have an average particle diameter of 0.8 µm to 4.0 µm, preferably 0.8 µm to 3 µm, more preferably 1.0 µm to 3.0 µm.

[0021] More preferably, the single particle lithium nickel oxide may be represented by the following [Chemical Formula 1-1].

[0022] [Chemical Formula 1-1]

[0023] Li x [Ni a Co b Mn c1 Al C2 M 2 d ]O2

[0024] In the above chemical formula 1-1, M 2 It includes at least one selected from the group consisting of Ti, Mg, Zr, Y, Ba, Ca, Sr, W, Ta, Nb, and Mo, and 0.9≤x≤1.1, 0.8≤a<1, 0 <b<0.2, 0<c1<0.15, 0<c2<0.05, 0≤d<0.1이다.

[0025] Meanwhile, the positive electrode active material may contain nickel in an amount of 80 mol% to 99 mol%, cobalt in an amount of 0.1 mol% to 20 mol%, manganese in an amount of 0.1 mol% to 20 mol%, and aluminum in an amount of 5 mol% or less, of all metals excluding lithium.

[0026] In addition, the above positive electrode active material is D50 It may be 3 ㎛ to 10 ㎛, preferably 3 ㎛ to 8 ㎛, and more preferably 4 ㎛ to 7 ㎛.

[0027] According to another embodiment, the present invention provides a positive electrode comprising the positive electrode active material of the present invention described above and a lithium secondary battery comprising the positive electrode.

[0028] The cathode active material according to the present invention includes a single particle lithium nickel oxide having a high Ni content of 80 mol% or more, so that the generation of fine particles due to particle breakage during electrode manufacturing is small and side reactions with the electrolyte are minimized, so that the lifespan degradation due to side reactions with the electrolyte can be effectively suppressed.

[0029] In addition, the positive electrode active material according to the present invention is characterized in that RPI2 / RPI1 is formed so as to satisfy a specific range. At this time, the RPI2 / RPI1 is an indicator indicating the coating and doping ratio of cobalt present on the surface of positive electrode active material particles. According to the research of the inventors of the present invention, in the case of a positive electrode active material having a Ni content of 80 mol% or more, particularly, 90 mol% or more and having a single particle shape, when the ratio of cobalt doped on the particle surface and cobalt coated on the particle surface satisfies a specific ratio, that is, RPI2 / RPI1 satisfies 1 to 1.3, it was found that there is an effect of significantly improving the life characteristics. This effect is unique to high-nickel single particle positive electrode active materials, and when the particle shape or Ni content of the positive electrode active material is different, the effect of improving the life characteristics is minimal even if RPI2 / RPI1 satisfies 1 to 1.3.

[0030] Figure 1 is a scanning electron microscope (SEM) photograph of a positive electrode active material manufactured according to Example 1.

[0031] Figure 2 is a scanning electron microscope (SEM) photograph of the positive electrode active material manufactured by Comparative Example 1.

[0032] Figure 3 is a scanning electron microscope (SEM) photograph of the positive electrode active material manufactured by Comparative Example 2.

[0033] Figure 4 is an X-ray diffraction pattern of an electrode including a positive electrode active material manufactured by an example and a comparative example.

[0034] Terms or words used in this specification and the scope of the claims should not be interpreted as limited to their usual or dictionary meanings, but should be interpreted as meanings and concepts that conform to the technical idea of ​​the present invention, based on the principle that the inventor can appropriately define the concept of the term to explain his or her own invention in the best way.

[0035] In the present invention, “single particle type” means a particle composed of 30 or fewer nodules, and is a concept that includes a single particle composed of one nodule and a pseudo-single particle which is a composite of 2 to 30 nodules.

[0036] The above “nodule” is a sub-particle unit that constitutes a single particle and a pseudo-single particle, and may be a single crystal without a crystalline grain boundary, or a polycrystal with no apparent grain boundary when observed under a magnification of 5,000 to 20,000 times using a scanning electron microscope.

[0037] In the present invention, "secondary particle" refers to a particle formed by agglomeration of a plurality of primary particles, for example, tens to hundreds of primary particles. Specifically, the secondary particle may be an aggregate of more than 30 primary particles.

[0038] In the present invention, “particle” is a concept including any one or all of a single particle, a pseudo-single particle, a primary particle, a nodule, and a secondary particle.

[0039] In the present invention, the average particle diameter (D) of the nodules or primary particles mean) means the arithmetic mean value calculated after measuring the particle size of nodules or primary particles observed in scanning electron microscope images.

[0040] In the present invention, "average particle diameter D 50 " refers to the particle size corresponding to 50% of the volume cumulative particle size distribution of the target powder, and can be measured using the laser diffraction method. For example, after dispersing the target powder in a dispersion medium, it can be measured by introducing it into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000), irradiating it with ultrasonic waves of about 28 kHz at an output of 60 W, obtaining a volume cumulative particle size distribution graph, and then calculating the particle size corresponding to 50% of the volume cumulative amount.

[0041] Meanwhile, in the present invention, X-ray diffraction pattern analysis was performed in the following manner.

[0042] First, a cathode slurry was prepared by mixing the cathode active material to be measured: conductive agent (carbon black): binder (PVdF) in a weight ratio of 96:2:2 in N-methylpyrrolidone, and the cathode slurry was applied onto an aluminum current collector and then dried to prepare a sample electrode. Then, the sample electrode was mounted on a Bruker D8 Endeavor (light source: Cu-Kα, λ=1.54Å) equipped with a LynxEye XE-T-position sensitive detector, and measured under the conditions of 2θ=30°~60°, total scan time=approximately 70 minutes.

[0043]

[0044] Hereinafter, the present invention will be described in more detail.

[0045] positive electrode active material

[0046] The present invention provides a cathode active material comprising a single-particle lithium nickel-based oxide represented by the following [chemical formula 1]; and a coating layer disposed on the surface of the single-particle lithium nickel-based oxide, wherein the ratio RPI2 / RPI1 of RPI2 defined by the following formula 2 to RPI1 defined by the following formula 1 is 1 to 1.3.

[0047] [Chemical Formula 1]

[0048] Li x [Ni a Co b M 1 c M 2 d ]O2

[0049] In the above chemical formula 1, M 1 is Mn, Al or a combination thereof, and M 2 It contains at least one selected from the group consisting of Zr, W, Ti, Mg, Ba, Ca, Ta, Nb and Mo, and 0.9≤x≤1.1, 0.8≤a<1, 0 <b<0.2, 0<c<0.2, 0≤d<0.1이다.

[0050] [Formula 1] RPI1=I2 / I1

[0051] In the above formula 1, I1 and I2 are values ​​obtained by measuring an X-ray diffraction pattern after manufacturing an electrode including the positive electrode active material, I1 is the minimum value of the peak intensity (Intensity) appearing in the region of 2θ=37° to 38° in the X-ray diffraction pattern for the positive electrode active material, and I2 is the average value of the peak intensity (Intensity) appearing in the region of 2θ=37.3° to 37.5° in the X-ray diffraction pattern for the positive electrode active material.

[0052] [Formula 2] RPI2=I3 / I1

[0053] In the above formula 2, I1 and I3 are values ​​obtained by measuring an X-ray diffraction pattern after manufacturing an electrode including the positive electrode active material, I1 is the minimum value of the peak intensity (Intensity) appearing in the region of 2θ=37° to 38° in the X-ray diffraction pattern for the positive electrode active material, and I3 is the average value of the peak intensity (Intensity) appearing in the region of 2θ=37.0° to 37.2° in the X-ray diffraction pattern for the positive electrode active material.

[0054] In the X-ray diffraction pattern of an electrode containing a positive electrode active material, a peak appearing in the region where 2θ is 37° to 38° appears when a layered crystal structure exists in the positive electrode active material. Among these, a peak appearing in the region where 2θ is 37.3° to 37.5° appears when a layered structure in the form of lithium cobalt oxide (LCO) exists in the positive electrode active material, and a peak appearing in the region where 2θ is 37.0° to 37.2° appears when a layered structure in the form of lithium nickel cobalt manganese oxide exists in the positive electrode active material.

[0055] Meanwhile, when cobalt is coated, the lithium byproducts present on the surface of the positive electrode active material react with cobalt to form lithium cobalt oxide, and when cobalt is doped, cobalt diffuses into the crystal structure inside the positive electrode active material particles, so it forms lithium nickel cobalt manganese oxide. Therefore, when the amount of cobalt present in the coating form increases, I2 / I1 (= RPI1) increases, and when the amount of cobalt present in the doping form increases, I3 / I1 (= RPI2) increases. Therefore, RPI1 can be used as an indicator representing the proportion of coated cobalt, and RPI2 can be used as an indicator representing the proportion of doped cobalt.

[0056] Meanwhile, according to the research of the present inventors, unlike the positive electrode active material containing less than 80 mol% of Ni or in the form of secondary particles, in the case of the positive electrode active material containing 80 mol% or more of Ni, particularly, 90 mol% or more of Ni, and in the form of single particles, it was found that when the ratio of cobalt doped on the particle surface to cobalt coated on the particle surface satisfies the range of the present invention, that is, when RPI2 / RPI1 is 1 to 1.3, there is a significantly improved lifespan characteristic. It is believed that the reason why the lifespan characteristic is improved when RPI2 / RPI1 is 1 to 1.3 is because direct contact between nickel and the electrolyte is blocked by lithium cobalt oxide present on the surface of the positive electrode active material, thereby suppressing interfacial side reactions.

[0057] Meanwhile, the RPI1 may be 1.07 to 1.5, preferably 1.08 to 1.4, and more preferably 1.09 to 1.3. When the above range is satisfied, a dot (island)-shaped Co coating layer may be formed on the surface of the positive electrode active material, thereby effectively suppressing side reactions with the electrolyte.

[0058] The above RPI2 may be 1.1 to 2, preferably 1.1 to 1.8, and more preferably 1.2 to 1.6. When the above range is satisfied, Co can be appropriately doped on the surface of the single-particle lithium nickel-based oxide to obtain a resistance improvement effect.

[0059] Also, the above RPI1 and the above The sum of RPI2 (RPI1+RPI2) may be 2.2 to 2.6, preferably 2.2 to 2.5. When the above range is satisfied, cobalt coating and doping are sufficiently formed, thereby improving resistance and life characteristics.

[0060]

[0061] The above RPI1 and RPI2 may vary depending on the content of lithium byproducts present on the surface of the single-particle lithium nickel-based oxide during the manufacture of the positive electrode active material, the type and content of the coating element, or the heat treatment conditions during the coating. Therefore, by controlling the content of lithium byproducts present on the surface of the single-particle lithium nickel-based oxide, the type and content of the coating element, or the coating conditions during the manufacture of the positive electrode active material, a positive electrode active material having the desired RPI1 and RPI2 can be manufactured.

[0062]

[0063] Meanwhile, the single-particle lithium nickel-based oxide may include 30 or fewer nodules, preferably 1 to 25, and more preferably 1 to 15. The single-particle lithium nickel-based oxide has a small number of nodules constituting the particles, and thus the intra-particle interface is small, resulting in a small contact area with the electrolyte. Therefore, compared to lithium nickel-based oxide in the form of secondary particles in which 40 to several hundred primary particles are aggregated, which has been commonly used in the past, the side reaction with the electrolyte is small, and accordingly, the amount of gas generated is also significantly less. Therefore, when the single-particle lithium nickel-based oxide is applied as a cathode active material, excellent cycle characteristics can be obtained.

[0064] Meanwhile, the average particle size of the nodules may be 0.8 µm to 4.0 µm, preferably 0.8 µm to 3 µm, and more preferably 1.0 µm to 3.0 µm. When the average particle size of the nodules satisfies the above range, particle breakage is minimized during electrode manufacturing, and resistance increase can be more effectively suppressed. At this time, the average particle size of the nodules refers to a value obtained by measuring the particle sizes of nodules observed in SEM images obtained by analyzing the positive electrode active material powder with a scanning electron microscope, and then calculating the arithmetic mean of the measured values.

[0065]

[0066] The above single particle lithium nickel oxide may be a lithium transition metal oxide containing nickel, manganese and cobalt, and may be, for example, represented by the following [chemical formula 1].

[0067] [Chemical Formula 1]

[0068] Li x [Ni a Co b M 1 c M 2 d ]O2

[0069] In the above chemical formula 1, the M 1 is Mn, Al or a combination thereof, and preferably may be Mn or a combination of Mn and Al.

[0070] Above M 2 It may contain one or more elements selected from the group consisting of Ti, Mg, Zr, Y, Ba, Ca, Sr, W, Ta, Nb, and Mo. M 2 When elements are included, the structural stability of lithium nickel oxide particles is improved, enabling better performance of life characteristics.

[0071] The above x represents the lithium molar ratio in the lithium nickel-based oxide, and may be -0.9≤x≤1.1, 1≤x≤1.1, or 1≤x≤1.07. When x satisfies the above range, a stable layered crystal structure can be formed.

[0072] The above a represents the molar ratio of nickel among all metals excluding lithium in the lithium nickel-based oxide, and may be 0.8≤a<1, 0.83≤a≤0.98, 0.85≤a≤0.98, or 0.90≤a≤0.98. When a satisfies the above range, high capacity can be achieved.

[0073] The above b represents the molar ratio of cobalt among all metals excluding lithium in the lithium nickel oxide, and is 0. <b<0.2, 0.01≤b≤0.2 또는 0.01≤b≤0.1일 수 있다.

[0074] The above c is M of all metals except lithium in lithium nickel oxide. 1 It represents the molar ratio of elements, 0 <c<0.2, 0.01≤c≤0.2 또는 0.01≤c≤0.1일 수 있다.

[0075] The above d is M of all metals except lithium in lithium nickel oxide. 2 It represents the molar ratio of elements, and can be 0≤d≤0.1, or 0≤d≤0.05. M 2 When the molar ratio of the elements satisfies the above range, both the structural stability and capacity of the positive electrode active material can be excellent.

[0076]

[0077] More specifically, the single particle lithium nickel oxide may be represented by the following [Chemical Formula 1-1].

[0078] [Chemical Formula 1-1]

[0079] Li x [Ni a Co b Mn c1 Al C2 M 2 d ]O2

[0080] In the above chemical formula 1-1, M 2, x, a, b, d are the same as defined in the above chemical formula 1. Meanwhile, c1 represents the molar ratio of the Mn element among the total metals excluding lithium in the lithium nickel-based oxide, and is 0 <c1<0.15, 또는 0.01≤c1≤0.1일 수 있고, 상기 c2는 리튬 니켈계 산화물 내 리튬을 제외한 전체 금속 중 Al 원소의 몰비를 나타내는 것으로, 0<c2<0.05, 또는 0.01≤c2≤0.05일 수 있다. 상기와 같이 단입자형 리튬 니켈계 산화물이 Mn 및 Al을 동시에 포함할 경우 양극 활물질의 입자 구조 안정성이 더욱 개선되는 효과를 얻을 수 있다. 다만, Al의 함량이 너무 높을 경우, 용량 특성이 저하될 수 있으므로, Mn 및 Al의 함량은 상기 범위를 만족하는 것이 바람직하다.

[0081]

[0082] Next, the positive electrode active material according to the present invention includes the coating layer on the surface of the single particle lithium nickel-based oxide.

[0083] Preferably, the coating layer may contain Co, and more preferably, may contain Co and Al. In the case of single-particle lithium nickel-based oxide, there is a problem that the resistance characteristics are reduced because the high temperature firing is performed during the manufacturing process, an electrically inactive rock salt structure is formed on the particle surface, and the lithium migration distance inside the particle is long. However, when a coating layer containing Co is formed, the rock salt structure on the particle surface is converted into a layered structure during the coating layer formation process, so that the resistance characteristics can be improved. In addition, when Co and Al are included together in the coating layer, the coating layer formation is more smoothly performed than when Co is coated alone, and it is easier for RPI2 / RPI1 to form a positive electrode active material satisfying the scope of the present invention.

[0084]

[0085] Meanwhile, in the positive electrode active material including a single-particle lithium nickel-based oxide and a coating layer, the content of nickel among the total metals excluding lithium may be 80 mol% to 99 mol%, preferably 83 mol% to 98 mol%, 85 mol% to 98 mol%, or 90 mol% to 98 mol%, the content of cobalt may be 0.1 mol% to 20 mol%, 0.1 mol% to 15 mol%, or 1 mol% to 10 mol%, the content of manganese may be 0.1 mol% to 20 mol%, 0.1 mol% to 15 mol%, or 1 mol% to 10 mol%, and the content of aluminum may be 5 mol% or less, 0.1 mol% to 5 mol%, or 0.1 mol% to 4 mol%. When the content of each metal component in the total positive electrode active material satisfies the above range, the capacity characteristics and particle structure stability can be excellently implemented.

[0086]

[0087] Meanwhile, the positive electrode active material is D 50 It may be 3.0㎛ to 8.0㎛, preferably 3.0㎛ to 7.5㎛. More preferably, it is preferably about 3.5㎛ to 7.5㎛. D of lithium nickel-based oxide 50 If this is too small, the processability during electrode manufacturing may be poor, the electrolyte impregnation may be poor, and the electrochemical properties may increase. 50 If this is too large, there is a problem that the resistance increases and the output characteristics deteriorate.

[0088]

[0089] In addition, the above positive electrode active material is D 50 The single particle size ratio, which is the ratio of the average particle diameter of the nodules to the single particle size ratio, may be 0.1 to 1, preferably 0.2 to 0.8, and more preferably 0.4 to 0.7. When the single particle size ratio of the positive electrode active material satisfies the above range, the life characteristics are further improved.

[0090]

[0091] The cathode active material according to the present invention can be manufactured by a method of manufacturing a single-particle lithium nickel-based oxide by calcining a mixture of a transition metal precursor and a lithium raw material, and mixing and heat-treating the single-particle lithium nickel-based oxide with a coating raw material.

[0092] First, a single-particle lithium nickel oxide is manufactured by mixing and calcining a transition metal precursor and a lithium raw material.

[0093] At this time, the transition metal precursors include nickel and cobalt, and optionally M 1 and M 2 A hydroxide containing the element can be used. The transition metal precursor can be purchased and used as a commercially available precursor, or can be manufactured using a precursor manufacturing method known in the art, such as a coprecipitation method.

[0094] As the above lithium raw material, lithium-containing sulfate, nitrate, acetate, carbonate, oxalate, citrate, halide, hydroxide or oxyhydroxide may be used, and for example, Li2CO3, LiNO3, LiNO2, LiOH, LiOHㆍH2O, LiH, LiF, LiCl, LiBr, LiI, CH3COOLi, Li2O, Li2SO4, CH3COOLi, Li3C6H5O7 or a mixture thereof may be used.

[0095] Meanwhile, the lithium raw material and the positive electrode active material precursor may be mixed so that the molar ratio of Li: total metal in the precursor is 1:1 to 1.1:1, preferably 1:1 to 1.05:1, more preferably 1.01:1 to 1.03:1. When the mixing ratio of the lithium raw material and the metal in the positive electrode active material precursor satisfies the above range, the layered crystal structure of the positive electrode active material is well developed, so that a positive electrode active material with excellent capacity characteristics and structural stability can be manufactured.

[0096] Meanwhile, the sintering is performed at a temperature capable of forming a single-particle lithium nickel-based oxide. In order to form a single-particle lithium nickel-based oxide, the sintering should be performed at a higher temperature than that used in the conventional secondary particle lithium nickel-based oxide production. For example, when the precursor composition is the same, the sintering should be performed at a temperature that is about 30°C to 100°C higher than that used in the conventional secondary particle lithium nickel-based oxide production. The sintering temperature for producing a single-particle lithium nickel-based oxide may vary depending on the metal composition in the precursor. For example, when a high-nickel (High-Ni) single-particle lithium nickel-based oxide having a nickel (Ni) content of 80 mol% or more is to be produced, the sintering temperature may be about 800°C to 1000°C, preferably about 800°C to 950°C, and more preferably about 850°C to 950°C. When the sintering temperature satisfies the above range, a single-particle lithium nickel-based oxide having excellent electrochemical properties can be produced. When the sintering temperature is less than 800℃, a cathode active material in the form of secondary particles is produced, and when it exceeds 1000℃, excessive sintering occurs and a layered crystal structure is not properly formed, resulting in a deterioration in electrochemical properties.

[0097] In addition, the above-mentioned calcination can be performed for 6 to 35 hours, preferably 6 to 20 hours, and more preferably 6 to 15 hours under an oxygen atmosphere. When the calcination time satisfies the above range, a single-particle lithium nickel-based oxide can be formed. If the primary calcination time is too short, particle growth is insufficient, and a secondary particle lithium nickel-based oxide is formed, and if it is too long, a rock salt phase may occur, which may deteriorate the electrochemical characteristics of the active material. In the present specification, an oxygen atmosphere means an atmosphere containing oxygen sufficient for calcination, including an air atmosphere. In particular, it is preferable to perform the calcination in an atmosphere having a higher oxygen partial pressure than an air atmosphere.

[0098]

[0099] Meanwhile, M may be added as needed during the above firing. 1 Contains Raw materials and / or M 2 The raw materials contained can be mixed and fired together, the above M 1 Contains raw materials and M 2 Contains raw materials M 1 Metal or M 2 It may be an acetate, carbonate, nitrate, sulfate, halite, sulfide or oxide of the metal.

[0100]

[0101] The single-particle lithium nickel-based oxide manufactured as described above preferably contains 0.4 to 3 wt%, 0.5 to 2 wt%, or 0.5 to 1.5 wt% of lithium byproduct. When the lithium byproduct content of the single-particle lithium nickel-based oxide satisfies the above range, it is easy to manufacture a cathode active material that satisfies the RPI2 / RPI1 ratio of 1 to 1.3.

[0102]

[0103] If necessary, an additional step may be performed to control the content of lithium byproducts present on the surface of the single-particle lithium nickel-based oxide particles. For example, the content of lithium byproducts on the surface of the lithium nickel-based oxide particles may be controlled by performing additional processes such as washing or heat treatment. As described above, the RPI1 and RIP2 values ​​of the positive electrode active material may change depending on the content of lithium byproducts on the surface of the lithium nickel-based oxide. Therefore, by performing such additional processes, the ratio of RPI2 / RPI1 may be controlled within the range of the present invention.

[0104]

[0105] Next, the single particle lithium nickel oxide and the coating raw material are mixed and heat treated to form a coating layer.

[0106] The above coating raw material may include a Co-containing raw material, and preferably may include a Co-containing raw material and an Al-containing raw material. The Co-containing raw material may be cobalt oxide, cobalt carbonate, etc., such as cobalt hydroxide, CoO, Co2O3, Co3O4, etc., and the Al-containing raw material may be aluminum oxide, aluminum hydroxide, etc., such as Al2O3, etc., but is not limited thereto.

[0107] Meanwhile, the Co-containing raw material may be mixed in an amount such that the Co content is 0.5 mol% to 4 mol%, preferably 1 mol% to 3 mol%, based on 100 mol of the single-particle lithium nickel-based oxide. When the mixing amount of the Co-containing raw material satisfies the above range, it can react with the residual lithium on the surface of the lithium nickel-based oxide at an appropriate ratio to form a coating layer in the form of lithium cobalt oxide.

[0108] In addition, the Al-containing raw material may be mixed in an amount such that the Al content is 0.01 mol% to 2 mol%, preferably 0.01 mol% to 1 mol%, based on 100 mol of the single-particle lithium nickel-based oxide. When the mixing amount of the Al-containing raw material satisfies the above range, it helps to strengthen the layered structure on the surface of the positive electrode active material, so that the Co-containing coating layer can be well formed.

[0109] Meanwhile, the heat treatment temperature can be appropriately adjusted depending on the type of coating raw material, and preferably, it can be 500°C to 800°C or 600°C to 750°C.

[0110] When the content and temperature of the coating raw material satisfy the above range, it is easy to manufacture a positive electrode active material having a ratio of RPI2 / RPI1 of 1 to 1.3.

[0111]

[0112] anode

[0113] Next, the anode of the present invention will be described.

[0114] The positive electrode according to the present invention comprises the positive electrode active material according to the present invention described above, and may further comprise a positive electrode conductive material and a positive electrode binder, if necessary. Specifically, the positive electrode comprises a positive electrode current collector, a positive electrode active material layer formed on at least one surface of the positive electrode current collector, and the positive electrode active material layer comprises a positive electrode active material, a positive electrode conductive material, and a positive electrode binder. Meanwhile, since the positive electrode active material is the same as described above, a detailed description thereof will be omitted.

[0115]

[0116] The positive electrode current collector is not particularly limited as long as it is conductive and does not cause a chemical change in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. may be used. In addition, the positive electrode current collector may typically have a thickness of 3 to 500 μm, and fine unevenness may be formed on the surface of the positive electrode current collector to increase the adhesion of the positive electrode active material. For example, the positive electrode current collector may be used in various forms such as a film, sheet, foil, net, porous body, foam, or non-woven fabric.

[0117]

[0118] Meanwhile, the positive electrode active material may be included in an amount of 93 wt% to 99 wt%, preferably 95 wt% to 98 wt%, and more preferably 95 wt% to 97 wt%, based on the total weight of the positive electrode active material layer, i.e., the total amount of the positive electrode active material, the positive electrode conductive material, and the positive electrode binder. When the content of the positive electrode active material satisfies the above range, a high energy density can be realized.

[0119]

[0120] Next, the positive electrode conductive material is used to provide conductivity to the positive electrode, and in the battery to be formed, as long as it does not cause a chemical change and has electronic conductivity, it can be used without any particular limitation. 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, summer black, carbon fiber, carbon nanotube, etc.; metal powder or metal fiber such as copper, nickel, aluminum, silver, etc.; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, etc., and one of these may be used alone or a mixture of two or more may be used.

[0121] The above-mentioned positive electrode conductive material may be included in an amount of 0.1 to 10 wt%, preferably 0.5 to 8 wt%, and more preferably 1 to 5 wt%, based on the total weight of the positive electrode active material layer.

[0122] Next, the positive electrode binder serves to improve adhesion between positive electrode active material particles and adhesion between the positive electrode active material and the positive electrode current collector. Specific examples thereof include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these may be used alone or a mixture of two or more thereof may be used.

[0123] The above positive electrode binder may be included in an amount of 0.5 wt% to 5 wt%, preferably 1 wt% to 4 wt%, and more preferably 1 wt% to 3 wt%, based on the total weight of the positive electrode active material layer.

[0124]

[0125] The positive electrode can be manufactured according to a conventional positive electrode manufacturing method. For example, the positive electrode can be manufactured by mixing a positive electrode active material, a positive electrode binder, and / or a positive electrode conductive material in a solvent to manufacture a positive electrode slurry, applying the positive electrode slurry onto a positive electrode current collector, and then drying and rolling the resulting film, or by casting the positive electrode slurry onto a separate support, and then peeling the resulting film from the support and laminating the resulting film onto a positive electrode current collector.

[0126] Meanwhile, solvents commonly used in the art may be used as the solvent for the positive electrode slurry, and examples thereof include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, and water, which may be used alone or in combination of two or more. The amount of the solvent used is sufficient to dissolve or disperse the positive electrode active material, conductive material, and binder in consideration of the coating thickness and manufacturing yield of the slurry, and to have a viscosity that can exhibit excellent thickness uniformity when applied thereafter for manufacturing the positive electrode.

[0127]

[0128] lithium secondary battery

[0129] Next, a lithium secondary battery according to the present invention will be described.

[0130]

[0131] The lithium secondary battery of the present invention comprises the positive electrode according to the present invention. Specifically, the lithium secondary battery comprises a positive electrode, a negative electrode positioned opposite the positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, wherein the positive electrode is as described above.

[0132] In addition, the lithium secondary battery may optionally further include a battery container that houses the electrode assembly of the positive electrode, negative electrode, and separator, and a sealing member that seals the battery container.

[0133]

[0134] In the above lithium secondary battery, the negative electrode includes a negative electrode current collector and a negative electrode active material layer positioned on the negative electrode current collector.

[0135] 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., aluminum-cadmium alloy, etc. can be used. In addition, the negative electrode current collector can typically have a thickness of 3 to 500 ㎛, and like the positive electrode current collector, fine unevenness can be formed on the surface of the current collector to strengthen the bonding strength of the negative electrode active material. For example, it can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric, etc.

[0136] The above negative electrode active material layer optionally includes a negative electrode binder and a negative electrode conductive material together with the negative electrode active material.

[0137] As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. 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 alloy, Sn alloy, or Al alloy; SiO β (0 <β< 2), metal oxides capable of doping and dedoping lithium, such as SnO2, vanadium oxide, and lithium vanadium oxide; or composites containing the above metal compounds and carbonaceous materials, such as Si-C composites or Sn-C composites, and any one or a mixture of two or more of these may be used.

[0138] In addition, a metallic lithium thin film may be used as the negative electrode active material. In addition, both low-crystalline carbon and high-crystalline carbon may be used as the carbon material. Representative examples of low-crystalline carbon include soft carbon and hard carbon, and representative examples of high-crystalline carbon include amorphous, plate-like, flaky, spherical or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch derived cokes.

[0139] The above-described negative electrode conductive material is used to provide conductivity to the electrode, and in the battery to be formed, as long as it does not cause a chemical change and has electronic conductivity, it can be used without any particular limitation. 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, carbon fiber, and carbon nanotube; metal powders 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 the like. One type alone or a mixture of two or more types of these may be used. The negative electrode conductive material may typically be included in an amount of 1 to 30 wt%, preferably 1 to 20 wt%, and more preferably 1 to 10 wt%, based on the total weight of the negative electrode active material layer.

[0140] The above negative electrode binder serves to improve adhesion between negative electrode active material particles and adhesion between the negative electrode active material and the negative electrode current collector. Specific examples thereof include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these may be used alone or a mixture of two or more thereof. The above negative electrode binder may be included in an amount of 1 to 30 wt%, preferably 1 to 20 wt%, and more preferably 1 to 10 wt%, based on the total weight of the negative electrode active material layer.

[0141] The above-described negative electrode active material layer may be manufactured by, for example, applying and drying a negative electrode slurry containing a negative electrode active material, and optionally a negative electrode binder and a negative electrode conductive material, onto a negative electrode current collector, or by casting the negative electrode slurry onto a separate support and then laminating the resulting film onto a negative electrode current collector by peeling it off from the support.

[0142]

[0143] Meanwhile, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. Any separator commonly used in lithium secondary batteries can be used without special restrictions, and in particular, one having low resistance to ion movement of the electrolyte and excellent electrolyte moisture retention capacity is preferable. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin polymer such as 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, can be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc. can also be used. In addition, a coated separator containing a ceramic component or a polymer material to secure heat resistance or mechanical strength can be used, and can optionally be used in a single-layer or multi-layer structure.

[0144]

[0145] In addition, examples of the electrolyte used in the present invention include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

[0146]

[0147] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0148] The organic solvent may be used without any particular limitation 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 include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; Carbonate solvents such as dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (wherein R is a C2 to C20 linear, branched, or cyclic hydrocarbon group, and may include a double-bonded aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes can be used. Among these, a carbonate solvent is preferable, 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 / discharge performance of the battery and a linear carbonate compound having low viscosity (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate, etc.) is more preferable.

[0149]

[0150] The lithium salt may be used without any particular limitation 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, LiAl04, 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 within the range of 0.1 to 5.0 M, and preferably 0.1 to 3.0 M. When the concentration of the lithium salt is within the above range, the electrolyte can exhibit excellent electrolyte performance because it has appropriate conductivity and viscosity, and lithium ions can move effectively.

[0151]

[0152] In addition to the electrolyte components, the electrolyte may further include additives for the purpose of improving the life characteristics of the battery, suppressing battery capacity decrease, and improving the discharge capacity of the battery. For example, the additives may include haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ethers, ethylene diamine, n-glyme, hexamethylphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, either singly or in mixtures, but are not limited thereto. The additives may be included in an amount of 0.1 to 10 wt%, preferably 0.1 to 5 wt%, based on the total weight of the electrolyte.

[0153]

[0154] As described above, a lithium secondary battery including a cathode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics, and capacity retention, and is therefore useful in portable devices such as mobile phones, laptop computers, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs).

[0155] Accordingly, according to another embodiment of the present invention, a battery module including the lithium secondary battery as a unit cell and a battery pack including the same are provided.

[0156] The above battery module or battery pack can be used as a power source for one or more medium- to large-sized devices, such as a power tool; an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); or a power storage system.

[0157]

[0158] Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement them. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein.

[0159]

[0160] Example 1

[0161] Nickel-cobalt-manganese hydroxide with a molar ratio of Ni:Co:Mn of 93:6:1 and lithium hydroxide were mixed so that the molar ratio of transition metal (Ni+Co+Mn):Li was 1:1.02, and then calcined at 870°C for 13 hours to produce a single-particle lithium nickel-based oxide.

[0162] Then, the single-particle lithium nickel oxide, cobalt hydroxide, and alumina were mixed in a weight ratio of 97:2.5:0.5, and heat-treated at 700°C to prepare a cathode active material. Fig. 1 shows an SEM image of the cathode active material prepared according to the above method.

[0163]

[0164] Example 2

[0165] A cathode active material was prepared in the same manner as in Example 1, except that nickel-cobalt-manganese hydroxide having a molar ratio of Ni:Co:Mn of 88:10:2 was used.

[0166]

[0167] Example 3

[0168] A cathode active material was prepared in the same manner as in Example 1, except that single-particle lithium nickel oxide, cobalt hydroxide, and alumina were mixed in a weight ratio of 97.5:2.3:0.2.

[0169]

[0170] Comparative Example 1

[0171] Nickel-cobalt-manganese hydroxide with a molar ratio of Ni:Co:Mn of 93:6:1 and lithium hydroxide were mixed so that the molar ratio of transition metal (Ni+Co+Mn):Li was 1:1.03, and then calcined at 860°C for 11 hours to produce a lithium nickel oxide in the form of single particles.

[0172] Then, the lithium nickel oxide, cobalt hydroxide, and alumina were mixed in a weight ratio of 97:2.5:0.5, and heat-treated at 750°C to produce a cathode active material. Figure 2 shows an SEM image of the cathode active material produced by the above method.

[0173]

[0174] Comparative Example 2

[0175] Nickel-cobalt-manganese hydroxide with a molar ratio of Ni:Co:Mn of 93:6:1 and lithium hydroxide were mixed so that the molar ratio of transition metal (Ni+Co+Mn):Li was 1:1.07, and then calcined at 880°C for 11 hours to produce a lithium nickel oxide in the form of single particles.

[0176] Then, the lithium nickel oxide, cobalt hydroxide, and alumina were mixed in a weight ratio of 97:2.5:0.5, and heat-treated at 800°C to produce a cathode active material. Fig. 3 shows an SEM image of the cathode active material produced according to the above method.

[0177]

[0178] Comparative Example 3

[0179] Nickel-cobalt-manganese hydroxide with a molar ratio of Ni:Co:Mn of 93:6:1 and lithium hydroxide were mixed so that the molar ratio of transition metal (Ni+Co+Mn):Li was 1:1.03, and then calcined at 870°C for 13 hours to produce a lithium nickel-based oxide in the form of single particles.

[0180] Then, the lithium nickel oxide, cobalt hydroxide, and alumina were mixed in a weight ratio of 96.5:3:0.5, and heat-treated at 600°C to manufacture a cathode active material.

[0181]

[0182] Experimental Example 1: Measurement of lithium byproduct content

[0183] 10 g of the lithium nickel-based oxide prepared by the methods of Examples 1 to 3 and Comparative Examples 1 to 3 was retaken, placed in distilled water, stirred for 5 minutes, and then titrated with a 0.1 N HCl solution. The pH curve was differentiated with respect to the volume of the obtained HCl solution to obtain the inflection point, and the lithium byproduct content (wt%) in the lithium nickel-based oxide before the formation of the coating layer was measured using this. The measurement results are shown in [Table 1] below.

[0184] Lithium byproduct (weight %) Example 10.73 Example 20.77 Example 30.73 Comparative Example 10.91 Comparative Example 21.09 Comparative Example 30.76

[0185] Experimental Example 2: XRD Analysis

[0186] Each of the positive electrode active materials, carbon black conductive agent, and PVdF binder manufactured according to Examples 1 to 3 and Comparative Examples 1 to 3 was mixed in N-methylpyrrolidone at a weight ratio of 96:2:2 to manufacture a positive electrode slurry. The positive electrode slurry was applied to one surface of an aluminum current collector and dried to manufacture a sample electrode.

[0187] X-ray diffraction pattern analysis was performed on the above sample electrode to measure the RPI1 and RPI2 values. The measurement results are shown in Fig. 4 and Table 2 below.

[0188] RPI1RPI2RPI2 / RPI1Example 11.1771.1941.014Example 21.1041.3491.222Example 31.1531.2761.107Comparative Example 11.0981.5301.393Comparative Example 21.0611.8271.722Comparative Example 31.0851.0650.981

[0189] Experimental Example 3: Measurement of Life Characteristics

[0190] The positive electrode active material, carbon black conductive agent, and PVDF binder manufactured in Examples 1 to 3 and Comparative Examples 1 to 3, respectively, were mixed in N-methylpyrrolidone at a weight ratio of 96:2:2 to manufacture a positive electrode slurry. The positive electrode slurry was applied to one surface of an aluminum current collector, dried, and then rolled to manufacture a positive electrode.

[0191] A negative electrode slurry was prepared by mixing a negative electrode active material (natural graphite), a conductive agent (carbon black), styrene-butadiene rubber, and carboxymethyl cellulose in a weight ratio of 95:2:2:1 in water, and the slurry was applied to one surface of a copper current collector, dried, and then rolled to prepare a negative electrode.

[0192] An electrode assembly was manufactured by interposing a separator between the positive and negative electrodes, and then positioning it inside a battery case, and then injecting an electrolyte into the case to manufacture a lithium secondary battery.

[0193]

[0194] For each lithium secondary battery manufactured above, 600 charge-discharge cycles were performed, in which one cycle was defined as charging at 0.5C in CC-CV mode at 45°C to 4.25V and discharging at a constant current of 1C to 2.5V, and then the capacity retention rate was measured to evaluate the life characteristics. The measurement results are shown in [Table 3] below.

[0195] Capacity retention rate (%) Example 178 Example 279 Example 376 Comparative Example 171 Comparative Example 268 Comparative Example 372

[0196] Through the above [Table 3], it can be confirmed that the lithium secondary batteries of Examples 1 to 3, which applied a positive electrode active material having an RPI2 / RPI1 of 1 to 1.3, have superior life characteristics compared to the lithium secondary batteries of Comparative Examples 1 to 2, which applied a positive electrode active material having an RPI2 / RPI1 exceeding 1.3, and the lithium secondary battery of Comparative Example 3, which applied a positive electrode active material having an RPI2 / RPI1 of less than 1.

Claims

1. A cathode active material comprising a single particle lithium nickel-based oxide represented by the following [chemical formula 1]; and a coating layer disposed on the surface of the single particle lithium nickel-based oxide, The above cathode active material is a cathode active material in which the ratio RPI2 / RPI1, defined by Equation 2 below, to RPI1, defined by Equation 1 below, is 1 to 1.

3. [Chemical Formula 1] Li x [Ni a Co b M 1 c M 2 d ]O2 In the above chemical formula 1, M 1 is Mn, Al or a combination of these, and M 2 It includes at least one selected from the group consisting of Ti, Mg, Zr, Y, Ba, Ca, Sr, W, Ta, Nb, and Mo, and 0.9≤x≤1.1, 0.8≤a<1, 0 <b<0.2, 0<c<0.2, 0≤d<0.1임. [Formula 1] RPI1=I2 / I1 In the above Equation 1, the I1 and I2 are values ​​obtained by measuring an X-ray diffraction pattern after manufacturing an electrode including the positive electrode active material, and I1 is the minimum value of the peak intensity (Intensity) appearing in the region of 2θ=37° to 38° in the X-ray diffraction pattern for the positive electrode active material, and I2 is the average value of the peak intensity (Intensity) appearing in the region of 2θ=37.3° to 37.5° in the X-ray diffraction pattern for the positive electrode active material. [Formula 2] RPI2=I3 / I1 In the above Equation 2, the I1 and I3 are values ​​obtained by measuring an X-ray diffraction pattern after manufacturing an electrode including the positive electrode active material, and I1 is the minimum value of the peak intensity (Intensity) appearing in the region of 2θ=37° to 38° in the X-ray diffraction pattern for the positive electrode active material, and I3 is the average value of the peak intensity (Intensity) appearing in the region of 2θ=37.0° to 37.2° in the X-ray diffraction pattern for the positive electrode active material.

2. In paragraph 1, The above RPI1 is a positive electrode active material having a value of 1.07 to 1.

5.

3. In paragraph 1, The above RPI2 is a positive electrode active material of 1.1 to 2.

4. In paragraph 1, The above RPI1 and the above A cathode active material having a sum of RPI2 (RPI1+RPI2) of 2.2 to 2.

6.

5. In paragraph 1, The above coating layer is a cathode active material containing Co.

6. In paragraph 1, The above coating layer is a positive electrode active material further containing Al.

7. In paragraph 1, The above single particle lithium nickel-based oxide is a cathode active material comprising 30 or fewer nodules.

8. In paragraph 7, The above nodule is a positive electrode active material having an average particle diameter of 0.8 ㎛ to 4.0 ㎛.

9. In paragraph 1, The above single particle lithium nickel oxide is a cathode active material represented by the following [chemical formula 1-1]. [Chemical Formula 1-1] Li x [Ni a Co b Mr c1 Al C2 M 2 d ]O2 In the above chemical formula 1-1, M 2 It includes at least one selected from the group consisting of Ti, Mg, Zr, Y, Ba, Ca, Sr, W, Ta, Nb, and Mo, and 0.9≤x≤1.1, 0.8≤a<1, 0 <b<0.2, 0<c1<0.15, 0<c2<0.05, 0≤d<0.1임.

10. In paragraph 1, The above cathode active material is a cathode active material containing nickel in an amount of 80 mol% to 99 mol%, cobalt in an amount of 0.1 mol% to 20 mol%, manganese in an amount of 0.1 mol% to 20 mol%, and aluminum in an amount of 5 mol% or less of all metals excluding lithium.

11. In paragraph 1, The above positive electrode active material is D 50 This positive electrode active material is 3㎛ to 10㎛.

12. A positive electrode comprising the positive electrode active material of any one of claims 1 to 11.

13. A lithium secondary battery comprising the positive electrode, negative electrode and electrolyte of claim 12.

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