Positive electrode active material powder for lithium secondary battery, preparation method thereof, positive electrode for lithium secondary battery and lithium secondary battery

Abstract

The present invention relates to a positive electrode active material powder for a lithium secondary battery, a positive electrode including the same, and a lithium secondary battery. The positive electrode active material powder includes single particles each composed of one nodule or quasi-single particles in the form of a composite of 30 or fewer nodules of a lithium composite transition metal oxide. Among them, the positive electrode active material powder satisfies Expression 1, where D mean is the average particle diameter of the nodules measured using an electron backscatter diffraction (EBSD) pattern analyzer, and d press is the pressing density measured after putting 5 g of the positive electrode active material powder into a circular mold with a diameter of 2 cm and pressing it under a pressure of 2000 kgf, and D 50 is a value corresponding to 50% of the cumulative volume in the particle size distribution of the positive electrode active material powder. [Expression 1] 0.5 ≤ D mean × d press / D 50 ≤ 3

Description

Technical Field

[0001] This application claims priority to and the benefit of Korean Patent Application No. 10-2021-0121307, filed on September 10, 2021, the disclosure of which is incorporated herein by reference in its entirety.

[0002] The present invention relates to positive electrode active material powder for lithium secondary batteries, a preparation method thereof, a positive electrode for lithium secondary batteries and a lithium secondary battery, and more specifically, to positive electrode active material powder containing lithium composite transition metal oxide in the form of single particles and / or quasi-single particles, and a positive electrode and a lithium secondary battery containing the same. Background Art

[0003] A lithium secondary battery is generally composed of a positive electrode, a negative electrode, a separator, and an electrolyte, and the positive electrode and the negative electrode include an active material capable of intercalating and deintercalating lithium ions.

[0004] As a positive electrode active material for lithium secondary batteries, lithium cobalt oxide (LiCoO 2 ), lithium nickel oxide (LiNiO 2 ), lithium manganese oxide (LiMnO 2 、LiMnO 4 etc.) and lithium iron phosphate compounds (LiFePO 4 ) and the like. Among those listed above, lithium cobalt oxide has a high operating voltage and excellent capacity characteristics, but since cobalt as a raw material for lithium cobalt oxide is expensive and the supply is unstable, it is difficult to commercialize lithium cobalt oxide for large-capacity batteries. Lithium nickel oxide has poor structural stability, so it is difficult to achieve sufficient life characteristics. At the same time, lithium manganese oxide has excellent stability, but poor capacity characteristics. Therefore, lithium composite transition metal oxides containing at least two transition metals have been developed to make up for the shortcomings of lithium transition metal oxides containing Ni, Co or Mn alone, and in particular, lithium nickel cobalt manganese oxides containing Ni, Co and Mn have been widely used in the field of electric vehicle batteries.

[0005] Conventional lithium nickel cobalt manganese oxide is usually in the form of spherical secondary particles formed by agglomeration of tens to hundreds of primary particles. In the case of lithium nickel cobalt manganese oxide in the form of secondary particles formed by agglomeration of many primary particles, the primary particles are easily detached during the rolling process when manufacturing the positive electrode, that is, the particles are broken, and cracks are generated inside the particles during the charge and discharge process. When the positive electrode active material particles are broken or cracked, the contact area with the electrolyte increases, thereby increasing the gas generation caused by the side reaction with the electrolyte and the degradation of the active material, and therefore, the life characteristics are deteriorated.

[0006] In addition, recently, the demand for high-output and high-capacity batteries such as batteries for electric vehicles has increased, so the nickel content in the positive electrode active material has gradually increased. When the nickel content in the positive electrode active material increases, the initial capacity characteristics are improved, but with repeated charging and discharging, a large amount of highly reactive Ni is generated. +4 ions, and thus the structure of the positive electrode active material collapses. As a result, the degradation rate of the positive electrode active material increases, and thus the life characteristics and battery stability decrease. Summary of the invention

[0007] Technical Solution

[0008] The present invention is completed in order to solve the above-mentioned problems, and aims to provide a positive electrode active material capable of suppressing particle breakage and cracking during the electrode manufacturing process and the charge and discharge process.

[0009] The present invention also aims to provide a positive electrode and a lithium secondary battery having improved high-temperature life characteristics, high-temperature storage characteristics, and initial resistance characteristics by including the positive electrode active material.

[0010] Technical Solution

[0011] One aspect of the present invention provides a positive electrode active material powder for a lithium secondary battery, which comprises a lithium composite transition metal oxide in the form of a single particle consisting of one nodule and / or a quasi-single particle as a composite of 30 or less nodules, and satisfies the following Expression 1:

[0012] [Expression 1]

[0013] 0.5≤D mean ×d press / D 50 ≤3

[0014] Among them, D mean is the average particle size of nodules measured using an electron backscatter diffraction (EBSD) spectrometer.

[0015] d press is the compaction density measured after 5 g of the positive electrode active material powder is put into a circular mold with a diameter of 2 cm and pressed at a pressure of 2000 kgf, and

[0016] D 50 It is a value corresponding to 50% of the cumulative volume in the particle size distribution of the positive electrode active material powder.

[0017] Another aspect of the present invention provides a positive electrode, which includes the positive electrode active material powder of the present invention.

[0018] Another aspect of the present invention provides a lithium secondary battery comprising the positive electrode of the present invention.

[0019] Beneficial Effects

[0020] Since the positive electrode active material powder for lithium secondary batteries of the present invention contains a lithium composite transition metal oxide in the form of a single particle and / or a quasi-single particle with excellent particle strength, particle crushing or cracking caused by the rolling process when manufacturing the electrode is reduced. Therefore, gas generation caused by side reactions with the electrolyte and degradation of the positive electrode active material are reduced, thereby achieving excellent life characteristics and high temperature characteristics.

[0021] In addition, since the positive electrode active material powder for lithium secondary batteries of the present invention meets specific levels of particle size and calendering density, the crushing of particles during electrode manufacturing is minimized to reduce gas generation, and the change of crystal structure during charging and discharging is minimized, so high temperature life characteristics and high temperature storage characteristics can be excellent. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Since the drawings attached to this specification illustrate exemplary embodiments of the present invention and are used together with the above content of the present invention to help understand the technical concept of the present invention, the present invention should not be interpreted restrictively based on the drawings. At the same time, in order to emphasize a clearer description, the shapes, sizes, scales or ratios of the elements in the drawings included in this specification may be exaggerated.

[0023] Figure 1 is a scanning electron microscope (SEM) image of the positive electrode active material powder prepared in Example 1.

[0024] Figure 2 is a SEM image of the positive electrode active material powder prepared in Comparative Example 1.

[0025] Figure 3 : is a graph showing the change rate of the full width at half maximum (FWHM) of the (003) peak of the coin cell using the positive electrode active material powder prepared in Example 1 according to the state of charge (SOC).

[0026] Figure 4 is a graph showing the (003) peak FWHM change rate of the positive electrode active material prepared in Comparative Example 1 with SOC.

[0027] Figure 5 : is a graph showing the change in cell volume when batteries using each of the positive electrode active materials prepared in Examples 1 and 2 and Comparative Examples 1 and 2 are stored at high temperature.

[0028] Figure 6 is a graph showing the capacity retention rate of batteries including each of the positive electrode active materials prepared in Examples 1 and 2 and Comparative Examples 1 and 2 according to the number of cycles. DETAILED DESCRIPTION

[0029] The terms and words used in this specification and claims should not be interpreted as limited to the common meanings or meanings in dictionaries, and should be interpreted with meanings and concepts consistent with the technical scope of the present invention based on the principle that the inventor can appropriately define the concepts of the terms to best describe the present invention.

[0030] It should be understood that the terms "comprises," "comprising," and / or "having" when used herein specify the presence of stated features, integers, steps, components, or combinations thereof, but do not preclude the presence or addition of one or more other features, integers, steps, components, or combinations thereof.

[0031] In the present disclosure, a "single particle" is a particle composed of a single nodule. The "nuclide" of the present disclosure refers to a particle unit body constituting a single particle and a quasi-single particle. The nodule may be a single crystal without any crystal grain boundary, or may be a polycrystal in which no grain boundary appears when observed in a field of view of 5000 to 20000 times using a scanning electron microscope (SEM). In the present disclosure, a "quasi-single particle" refers to a particle that is a composite formed by 30 or less nodules.

[0032] In the present disclosure, "secondary particles" refer to particles formed by agglomeration of a plurality of tens to hundreds of primary particles. More specifically, secondary particles are agglomerates of 50 or more primary particles.

[0033] In the present disclosure, when "particles" are described, any one or all of single particles, quasi-single particles, primary particles, nodules, and secondary particles may be encompassed.

[0034] In the present invention, “D mean ” refers to the average particle size of nodules measured using an electron backscatter diffraction (EBSD) spectrometer. The EBSD analysis was performed as follows: an electrode was manufactured using the positive electrode active material powder to be measured, the electrode was cut by ion milling (HITACHI IM-500, accelerating voltage: 6 kV) before the rolling process to obtain a cross section, and the cross section was measured using a FE-SEM device (JEOL JSM-7900F). In this case, the measurement was performed on a scale of about 400±10 primary particles under the conditions of an accelerating voltage of 15 kV and a WD of 15 mm.

[0035] In the present invention, “D 50 ” refers to the particle size corresponding to 50% of the cumulative volume in the particle size distribution of the positive electrode active material powder. The average particle size (D 50) can be measured by a laser diffraction method. For example, the average particle size can be measured by the following process: a positive electrode active material powder is dispersed in a dispersion medium, the resultant is put into a commercially available laser diffraction particle size analyzer (e.g., Microtrac MT 3000), ultrasonic waves are irradiated at a frequency of about 28 kHz and an output of 60 W, a volume cumulative particle size distribution graph is obtained, and a particle size corresponding to 50% of the cumulative volume is determined.

[0036] In the present invention, “d press ” refers to the pressing density of the positive electrode active material powder measured using HPRM-1000. Specifically, the pressing density can be obtained by the following process: 5 g of the positive electrode active material powder is put into a cylindrical mold, the mold containing the positive electrode active material powder is pressurized at a pressure of 2000 kgf, and the height of the pressurized mold is measured using a vernier caliper.

[0037] In the present invention, the "specific surface area" can be measured by the BET method. Specifically, the specific surface area can be calculated from the amount of nitrogen adsorbed at liquid nitrogen temperature (77K) using BELSORP-miniⅡ (commercially available from BEL Japan).

[0038] Hereinafter, the present invention will be described in further detail.

[0039] Positive electrode active material powder

[0040] The cathode active material powder of the present invention comprises a lithium composite transition metal oxide in the form of a single particle or a quasi-single particle consisting of one nodule, and the quasi-single particle is a composite of 30 or less nodules, preferably 2 to 20 nodules, more preferably 2 to 10 nodules.

[0041] Since the lithium composite transition metal oxide in the form of single particles and / or quasi-single particles has higher particle strength than conventional lithium composite transition metal oxides in the form of secondary particles in which tens to hundreds of primary particles are aggregated, the particles are less broken during calendering.

[0042] In addition, since the number of sub-parts (i.e., nodules) constituting the single particles and / or quasi-single particles of the lithium composite transition metal oxide in the form of single particles or quasi-single particles of the present invention is small, the changes caused by the volume expansion / contraction of the sub-parts (i.e., nodules) during charging and discharging are small, and therefore, the generation of cracks inside the particles is significantly reduced.

[0043] In particular, the inventors of the present invention found that when a positive electrode active material powder that satisfies the following Expression 1 is used, the crushing of particles during electrode manufacturing is minimized to reduce gas generation, and the change of crystal structure during charge and discharge is minimized, thereby enhancing the initial resistance characteristics, high temperature life characteristics and high temperature storage characteristics.

[0044] [Expression 1]

[0045] 0.5≤D mean ×d press / D 50 ≤3

[0046] Among them, D mean is the average particle size of nodules in the positive electrode active material powder measured using an electron backscatter diffraction (EBSD) spectrometer, d press is the compaction density measured after 5 g of the positive electrode active material powder is put into a circular mold with a diameter of 2 cm and pressed at a pressure of 2000 kgf, and D 50 It is a value corresponding to 50% of the cumulative volume in the particle size distribution of the positive electrode active material powder.

[0047] When D mean ×d press / D 50 When the value of is less than 0.5, the particles are severely crushed during the process of rolling the positive electrode or charging and discharging the lithium secondary battery, so gas generation increases at high temperatures and the life characteristics deteriorate. On the other hand, when D mean ×d press / D 50 When the value of exceeds 3, the initial resistance of the lithium secondary battery increases. More preferably, D mean ×d press / D 50 The value of can be 0.8 to 3 or 1 to 3.

[0048] Meanwhile, the positive electrode active material powder of the present invention may have a change rate of the (003) peak full width at half maximum (FWHM) during charge and discharge of 25% or less, preferably 20% or less, more preferably 3 to 15%.

[0049] The (003) peak FWHM change rate (unit: %) can be defined by the following Expression 2.

[0050] [Expression 2]

[0051] (003) peak FWHM change rate = [{(003) peak FWHM at SOC 60% – (003) peak FWHM at SOC 0%} / {(003) peak FWHM at SOC 0%}] × 100

[0052] The (003) peak FWHM change rate can be measured by an X-ray diffraction method, specifically, by the following method.

[0053] An electrode is fabricated using the positive electrode active material powder, and then assembled to form an experimental coin cell for operando XRD with a Kapton film window. XRD measurements are carried out by 2θ scanning in transmission mode using Mo-target X-rays. A first slit of 1 / 4 degree, Soller slits (both the first and the second) of 0.02 rad, and a second mask of 1.68 mm are used. The region from 7 degrees to 30 degrees in 2θ is measured every 0.014 degrees, such that each scan takes about 6 minutes. During the measurement, charging and discharging are carried out at a slow rate of 0.05C to maintain a state close to equilibrium, measured up to 4.25V, held in the CV state for one hour, and then discharged to 2.5V. FWHM analysis can be performed up to SOC 60%. In this case, FWHM is a value obtained by fitting the entire spectrum (multiple peaks) using only the crystal system information instead of a complete structure model, and the split pseudo-Voigt function is used for fitting.

[0054] A lower rate of change in the FWHM of the (003) peak represented by Expression 2 of 25% or less means that the strain change in the crystal structure of the positive electrode active material during charging and discharging is small. Therefore, the deterioration of the positive electrode active material is reduced, and thus excellent life characteristics can be achieved.

[0055] Meanwhile, the positive electrode active material of the present invention may contain a lithium composite transition metal oxide, specifically a lithium composite transition metal oxide having a composition represented by the following Chemical Formula 1.

[0056] [Chemical Formula 1]

[0057] Li 1+x Ni a Co b M 1 c M 2 d O 2

[0058] In Chemical Formula 1, M 1 is Mn, Al, or a combination thereof, M 2 is one or more selected from the group consisting of W, Zr, Y, Ba, Ca, Ti, Mg, Ta, and Nb, and satisfies 0 ≤ x ≤ 0.5, 0.8 ≤ a < 1, 0 < b < 0.2, 0 < c < 0.2, and 0 ≤ d ≤ 0.05.

[0059] In Chemical Formula 1, M 1 is Mn, Al, or a combination thereof, preferably Mn or a combination of Mn and Al, M 2is one or more selected from the group consisting of Zr, W, Y, Ba, Ca, Ti, Mg, Ta, and Nb, preferably one or more selected from the group consisting of Zr, Y, Mg, and Ti, more preferably Zr, Y, or a combination thereof. Although it does not necessarily contain the M 2 element, when an appropriate amount of the M 2 element is contained, it can be used to promote grain growth during firing or enhance the stability of the crystal structure.

[0060] 1 + x represents the molar fraction of lithium in the lithium composite transition metal oxide, and x can satisfy 0 ≤ x ≤ 0.5, 0 ≤ x ≤ 0.3, or 0 ≤ x ≤ 0.2.

[0061] a represents the molar fraction of nickel among all metals other than lithium in the lithium composite transition metal oxide, and can satisfy 0.8 ≤ a < 1, 0.8 < a ≤ 0.95, or 0.82 ≤ a ≤ 0.95.

[0062] b represents the molar fraction of cobalt among all metals other than lithium in the lithium composite transition metal oxide, and can satisfy 0 < b < 0.2, 0.01 ≤ b < 0.2, or 0.01 ≤ b ≤ 0.15.

[0063] c represents the molar fraction of M 1 among all metals other than lithium in the lithium composite transition metal oxide, and can satisfy 0 < c < 0.2, 0.01 ≤ c < 0.2, or 0.01 ≤ c ≤ 0.15.

[0064] d represents the molar fraction of M 2 among all metals other than lithium in the lithium composite transition metal oxide, and can satisfy 0 ≤ d ≤ 0.05, 0 ≤ d ≤ 0.02, or 0 ≤ d ≤ 0.01.

[0065] The positive electrode active material powder of the present invention may include nodules having an average particle size (D mean ) of 0.5 to 3.5 μm. Specifically, D mean can be 0.5 μm or more, 1.0 μm or more, or 1.5 μm or more, and D mean can be 3.5 μm or less, 3 μm or less, 2.5 μm or less, or 2.0 μm or less. When the average particle size (D mean ) of the nodules is less than 0.5 μm, the specific surface area of the entire positive electrode active material increases, so the side reaction with the electrolyte may increase. On the other hand, when D mean exceeds 3.5 μm, the lithium mobility in the positive electrode active material decreases, so the output characteristics of the battery may deteriorate.

[0066] The positive electrode active material powder of the present invention is a pressed density (d press ) may be 3 g / cc or more, preferably 3 to 5 g / cc or 3 to 4 g / cc, more preferably 3 to 3.5 g / cc. When the compaction density of the positive electrode active material powder satisfies the above range, high energy density can be achieved.

[0067] The positive electrode active material powder of the present invention has a D 50 (which is a value corresponding to 50% of the cumulative volume in the particle size distribution of the powder) may be 2 to 10 μm. Specifically, D 50 It may be 2 μm or more, 3 μm or more, 4 μm or more, 5 μm or more, or 6 μm or more, and D 50 It can be 10 μm or less, 9 μm or less, 8 μm or less, or 7 μm or less. 50 When D is less than 2 μm, the specific surface area of ​​the entire positive electrode active material increases, and thus the side reaction with the electrolyte may increase. 50 When it exceeds 10 μm, lithium mobility in the positive electrode active material decreases, and thus the output characteristics of the battery may deteriorate.

[0068] At the same time, the lithium composite transition metal oxide may also include a coating on the surface of its particles, which coating includes one or more coating elements selected from the group consisting of Al, Ti, W, B, F, P, Mg, Ni, Co, Fe, Cr, V, Cu, Ca, Zn, Zr, Nb, Mo, Sr, Sb, Bi, Si and S.

[0069] When the coating layer exists on the surface of the lithium composite transition metal oxide particle, the contact between the electrolyte and the lithium composite transition metal oxide is suppressed by the coating layer, and thus, the dissolution of the transition metal or the gas generation caused by the side reaction with the electrolyte can be reduced.

[0070] Preferably, the coating layer may include Co as a coating element. When the coating layer including Co is formed on the particle surface of the lithium composite transition metal oxide in the form of a single particle and / or a quasi-single particle, a side reaction with an electrolyte may be suppressed and output may also be improved.

[0071] Meanwhile, the BET specific surface area of ​​the positive electrode active material powder of the present invention may be 0.1 to 1 m 2 / g, preferably 0.3 to 1 m 2 / g, more preferably 0.5 to 1 m 2When the BET specific surface area of ​​the positive electrode active material powder satisfies the above range, the side reaction with the electrolyte can be properly controlled, and the lithium ion mobility at the interface between the positive electrode active material and the electrolyte can be ensured to be above a certain level.

[0072] Method for preparing positive electrode active material

[0073] Next, a method for preparing the positive electrode active material powder of the present invention will be described.

[0074] The method for preparing the positive electrode active material powder of the present invention comprises the following steps: (S1) adding a 1 A transition metal-containing solution of a cation, an alkaline aqueous solution and an ammonium solution are co-precipitated to prepare a positive electrode active material precursor; and (S2) the positive electrode active material precursor is mixed with a lithium raw material and the resulting mixture is heat-treated to prepare a positive electrode active material powder.

[0075] In addition, the prepared positive electrode active material powder contains a lithium composite transition metal oxide in the form of a single particle consisting of one nodule and / or a quasi-single particle that is a composite of 30 or less nodules, and satisfies the following Expression 1:

[0076] [Expression 1]

[0077] 0.5≤D mean ×d press / D 50 ≤3

[0078] Among them, D mean is the average particle size of nodules measured using an electron backscatter diffraction (EBSD) spectrometer, d press is the compaction density measured after 5 g of the positive electrode active material powder is put into a circular mold with a diameter of 2 cm and pressed at a pressure of 2000 kgf, and D 50 It is a value corresponding to 50% of the cumulative volume in the particle size distribution of the positive electrode active material powder.

[0079] Regarding Expression 1, since the above description also applies, redundant description will be omitted.

[0080] Hereinafter, each step of the method for preparing the positive electrode active material powder will be described in detail.

[0081] First, a nickel (Ni), cobalt (Co) and M 1 For example, the solution containing transition metals may include a nickel-containing raw material, a cobalt-containing raw material, and a M-containing raw material. 1 Raw materials, and containing M 1 The raw material may be a manganese-containing raw material and / or an aluminum-containing raw material.

[0082] Then, the transition metal-containing solution may be co-precipitated by adding a complex-forming agent containing ammonium cations and an alkaline aqueous solution to prepare a positive electrode active material precursor.

[0083] The nickel-containing raw material may be, for example, nickel-containing acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide or oxyhydroxide, and specifically Ni(OH) 2 、NiO、NiOOH、NiCO 3 ·2Ni(OH) 2 ·4H 2 O、NiC 2 O 2 ·2H 2 O.Ni(NO 3 ) 2 6H 2 O、NiSO 4 、NiSO 4 6H 2 O, fatty acid nickel salt, nickel halide or a combination thereof, but the present invention is not limited thereto.

[0084] The cobalt-containing raw material may be, for example, a cobalt-containing acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide or oxyhydroxide, and specifically Co(OH) 2 、CoOOH、Co(OCOCH 3 ) 2 ·4H 2 O、Co(NO 3 ) 2 6H 2 O. CoSO 4 、Co(SO 4 ) 2 7H 2 O or a combination thereof, but the present invention is not limited thereto.

[0085] The manganese-containing raw material may be, for example, manganese-containing acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide, oxyhydroxide or a combination thereof, specifically: manganese oxide, such as Mn 2 O 3 、MnO 2 or Mn 3 O 4 etc.; manganese salts, such as MnCO 3 、Mn(NO 3 ) 2 、MnSO 4 , manganese acetate, manganese dicarboxylate, manganese citrate or manganese salt of fatty acid; manganese oxyhydroxide, manganese chloride or a combination thereof, but the present invention is not limited thereto.

[0086] The aluminum-containing raw material may be, for example, Al 2 O 3 、Al(OH) 3 、Al(NO 3 ) 3 、Al 2 (SO 4 ) 3 、(HO) 2 AlCH 3 CO 2 HOAl(CH 3 CO 2 ) 2 、Al(CH 3 CO 2 ) 3 , aluminum halide or a combination thereof.

[0087] The solution containing transition metals can be prepared by the following process: a raw material containing nickel, a raw material containing cobalt and a raw material containing M 1 The raw materials are added to a solvent, specifically water or a solvent mixture of an organic solvent (such as alcohol, etc.) that can be uniformly mixed with water and water, or an aqueous solution containing a nickel raw material, an aqueous solution containing a cobalt raw material and an aqueous solution containing M 1 The aqueous solutions of the raw materials are mixed.

[0088] The complex forming agent containing ammonium cations may be, for example, NH 4 OH, (NH 4 ) 2 SO 4 NH 4 NO 3 NH 4 Cl, CH 3 COONH 4 NH 4 ) 2 CO 3 Or a combination thereof, but the present invention is not limited thereto. Meanwhile, the complex forming agent containing ammonium cations can be used in the form of an aqueous solution, in which case, as a solvent, water or a mixture of an organic solvent (specifically alcohol, etc.) that can be uniformly mixed with water and water can be used.

[0089] The alkaline compound can be, for example, NaOH, KOH or Ca(OH) 2 The basic compound can also be used in the form of an aqueous solution, in which case, as the solvent, water or a mixture of an organic solvent (specifically, alcohol, etc.) that can be uniformly mixed with water and water can be used.

[0090] The basic compound is added to adjust the pH of the reaction solution, and the added amount may be such that the pH of the metal solution becomes 8 to 12.

[0091] The coprecipitation may be performed in an inert atmosphere such as a nitrogen or argon atmosphere at a temperature ranging from 35°C to 80°C.

[0092] Therefore, it is possible to prepare a 1 Cationic positive electrode active material precursor.

[0093] Nickel-Cobalt-M 1 The positive electrode active material precursor particles formed by the hydroxide are prepared by the above method and precipitated in the reaction solution. 1 The concentration of the raw materials can prepare a positive electrode active material precursor having a nickel (Ni) content of 80 mol% or more, preferably 82 mol% or more of the total metal content. The precipitated positive electrode active material precursor particles can be separated and dried by conventional methods to prepare a positive electrode active material precursor.

[0094] At the same time, the tap density of the prepared positive active material precursor may be less than 2.2 g / cc, preferably 1.2 to 2.1 g / cc, and more preferably 1.4 to 2.0 g / cc. When the tap density of the positive active material precursor satisfies the above range, it is easy to form a lithium composite transition metal oxide in the form of a single particle and / or a quasi-single particle, and the size of the nodules is appropriately adjusted, so that a positive active material powder satisfying Expression 1 can be formed. Since the formation of single particles and quasi-single particles depends on the process conditions, when the tap density of the positive active material precursor varies outside the above range, a lithium composite transition metal oxide in the desired form may not necessarily be formed. If the tap density is outside the range, an active material in the form of secondary particles may be formed instead.

[0095] Then, the positive electrode active material precursor and the lithium raw material are mixed and heat-treated.

[0096] As the lithium raw material, lithium-containing sulfate, nitrate, acetate, carbonate, oxalate, citrate, halide, hydroxide or oxyhydroxide can be used, and the lithium raw material is not particularly limited as long as it can be dissolved in water. Specifically, the lithium raw material can be Li 2 CO 3 、LiNO 3 、LiNO 2 、LiOH、LiOH·H 2 O, LiH, LiF, LiCl, LiBr, LiI, CH 3 COOLi, Li 2 O. Li 2 SO4、CH 3COOLi or Li 3 C 6 H 5 O 7 etc., which may be used alone or in combination of two or more thereof.

[0097] The positive electrode active material precursor and the lithium raw material may be mixed in a molar ratio of 1:1 to 1.2. The positive electrode active material precursor and the lithium raw material may be mixed in a molar ratio of, for example, about 1:1, about 1:1.05, about 1:1.10, about 1:1.15, or about 1:1.20, but the present invention is not limited thereto.

[0098] In the case of a nickel-rich NCM-based lithium composite transition metal oxide having a nickel (Ni) content of 80 mol % or more, the heat treatment may be performed at a temperature range of 750°C to 1000°C. For example, the heat treatment is preferably performed at a temperature range of 800°C to 925°C, more preferably 850°C to 910°C. The formation of the positive electrode active material powder in the form of single particles and / or quasi-single particles is affected by the heat treatment temperature conditions. Therefore, when the heat treatment is performed at the above temperature, the D of the prepared positive electrode active material powder is mean ×d press / D 50 The value may be 0.5 to 3.0. Therefore, in the case of the prepared positive electrode active material, the crushing of particles and the strain in the crystal structure during the rolling process or the charging and discharging process of the lithium secondary battery including it can be reduced, and the initial resistance characteristics can be improved. However, if the heat treatment is performed at a temperature outside the above range, the positive electrode active material powder may be formed into secondary particles instead of single particles and / or quasi-single particles, and may not have a D value of 0.5 to 3.0. mean ×d press / D 50 Value. Appropriate heat treatment conditions (i.e., will produce D mean ×d press / D 50 The condition of the positive electrode active material powder having a D value of 0.5 to 3.0) may vary based on the characteristics of the positive electrode active material precursor (e.g., the tap density of the precursor), the composition and molar ratio of the elements in the precursor, and the presence of any additives. For example, when an additive is used in the heat treatment, the heat treatment can be performed at a lower temperature than the above temperature, but still achieve a single particle / quasi-single particle structure and have a D value of 0.5 to 3.0. mean ×d press / D 50 The additives may be, for example, Zr, Mg, Sr or Y, and in order to produce a desired D mean ×d press / D 50 For powders with high value, the appropriate lower temperature must be adjusted according to the type and content of additives.

[0099] The heat treatment may be performed in air or oxygen atmosphere for, for example, 4 to 12 hours. Specifically, the heat treatment may be performed for, for example, 4 hours or more, 6 hours or more, 8 hours or more, or 10 hours or more and 12 hours or less, 10 hours or less, 8 hours or less, or 6 hours or less.

[0100] At the same time, in order to prepare the 2 The lithium composite transition metal oxide of the metal can be further added with M during the coprecipitation or sintering process. 2 In this case, the raw material containing M 2 The raw material of metal can be M 2 Acetates, carbonates, nitrates, sulfates, halides, sulfides or oxides of metals.

[0101] Meanwhile, in order to form a coating on the surface of the lithium composite transition metal oxide, after the heat treatment, the lithium composite transition metal oxide prepared by the heat treatment may be further mixed with the coating source material and the resulting mixture may be heat treated. In this case, the mixing may be performed by solid phase mixing or liquid phase mixing, and the heat treatment may be performed at an appropriate temperature according to the coating source material. For example, the heat treatment for the coating process may be performed in a temperature range of 200°C to 700°C or 300°C to 600°C, but the present invention is not limited thereto.

[0102] In addition, it is preferred that, when preparing the positive active material powder of the present invention, a washing process is not performed after the heat treatment. Conventionally, when preparing nickel-rich NCM-type lithium composite transition metal oxides, a washing process is usually performed after the heat treatment to reduce the amount of lithium by-products. However, according to research conducted by the inventors of the present invention, when a washing process is performed when preparing lithium composite transition metal oxides in the form of single particles and / or quasi-single particles, the surface properties of the lithium composite transition metal oxide deteriorate during the washing process, and thus the resistance increases. Therefore, it is preferred that, when preparing the positive active material powder of the present invention, the lithium remaining on the surface of the lithium composite transition metal oxide is consumed by forming a coating without performing a washing process. As described above, when the positive active material is prepared without washing the lithium composite transition metal oxide, the increase in resistance caused by surface defects can be suppressed.

[0103] positive electrode

[0104] The positive electrode of the present invention includes the positive electrode active material powder of the present invention described above. Specifically, the positive electrode includes a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector, and the positive electrode active material layer includes the positive electrode active material powder of the present invention. Since the positive electrode active material powder has been described above, its detailed description will be omitted, and only the remaining components will be described in detail.

[0105] The positive electrode collector may include a highly conductive metal, and there is no particular limitation, as long as the positive electrode active material layer is easily adhered thereto and the positive electrode collector is not reactive within the voltage range of the battery. As the positive electrode collector, for example, stainless steel, aluminum, nickel, titanium, heat-treated carbon, aluminum or stainless steel whose surface is treated with carbon, nickel, titanium or silver, etc., may be used. Moreover, the positive electrode collector may generally have a thickness of 3 μm to 500 μm, and fine concavo-convex objects may be formed on its surface to increase the adhesion of the positive electrode active material. For example, the positive electrode collector may be used in any of various forms, such as a film, a sheet, a foil, a mesh, a porous material, a foam, and a non-woven fabric.

[0106] The positive electrode active material layer may optionally include a conductive material and a binder in addition to the positive electrode active material powder, if necessary.

[0107] In this case, the positive electrode active material powder may be contained in an amount of 80 to 99 wt %, more specifically 85 to 98.5 wt % relative to the total weight of the positive electrode active material layer. When the positive electrode active material powder is contained in such an amount, excellent capacity characteristics may be exhibited.

[0108] The conductive material is used to impart conductivity to the electrode, and any conductive material that does not cause chemical changes in the battery and has conductivity can be used without particular limitation. Specific examples thereof include: graphite, such as natural graphite and artificial graphite; carbon materials, such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; powders or fibers of metals such as copper, nickel, aluminum, and silver; conductive tubes, such as carbon nanotubes; conductive whiskers, such as zinc oxide and potassium titanate; conductive metal oxides, such as titanium oxide; and conductive polymers, such as polyphenylene derivatives, which can be used alone or in combination of two or more thereof. The content of the conductive material may be 0.1 to 15% by weight relative to the total weight of the positive electrode active material layer.

[0109] The binder plays a role in enhancing the adhesion between the positive active material particles and the adhesion between the positive active material and the current collector. Its specific examples include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, polymethyl methacrylate, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluororubber, polyacrylic acid, polymers whose hydrogen is replaced by Li, Na or Ca, and various copolymers thereof, which can be used alone or in combination with two or more thereof. Relative to the total weight of the positive active material layer, the content of the binder can be 0.1 to 15 weight %.

[0110] In addition to using the above-mentioned positive electrode active material powder, the positive electrode can be manufactured by a conventional method for manufacturing a positive electrode. Specifically, the positive electrode can be manufactured by the following process: a positive electrode slurry composition prepared by dissolving or dispersing the above-mentioned positive electrode active material powder and an optional binder, a conductive material and a dispersant in a solvent is applied to a positive electrode current collector and dried and rolled.

[0111] The solvent may be a commonly used solvent in the art, examples of which include dimethyl sulfoxide (DMSO), isopropanol, N-methylpyrrolidone (NMP), dimethylformamide (DMF), acetone and water, etc., which may be used alone or in combination of two or more thereof. As long as it can dissolve and disperse the positive electrode active material, the conductive material, the binder and the dispersant in consideration of the coating thickness and the manufacturing yield of the slurry, and achieves a viscosity that can exhibit excellent thickness uniformity when coated to manufacture the positive electrode, the amount of the solvent is sufficient.

[0112] In addition, as another method, the positive electrode may be manufactured by laminating a film obtained by casting the positive electrode slurry composition on a separate support and removing it from the support on a positive electrode current collector.

[0113] Electrochemical Devices

[0114] Next, the electrochemical device of the present invention will be described. The electrochemical device of the present invention includes the above-mentioned positive electrode of the present invention. The electrochemical device may be specifically a battery or a capacitor, and more specifically, a lithium secondary battery.

[0115] The lithium secondary battery specifically includes a positive electrode, a negative electrode disposed to face the positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte. Since the positive electrode is the same as above, its detailed description will be omitted, and only the remaining configuration will be described in detail.

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

[0117] In a lithium secondary battery, the negative electrode includes a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0118] The negative electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, heat-treated carbon, copper or stainless steel whose surface is treated with carbon, nickel, titanium or silver, or aluminum-cadmium alloy, etc. can be used. Moreover, the negative electrode current collector can generally have a thickness of 3μm to 500μm. Moreover, similar to the positive electrode current collector, the negative electrode current collector may be formed with fine concave-convex objects on its surface to increase the adhesion of the negative electrode active material. For example, the negative electrode current collector can be used in any of various forms, such as a film, a sheet, a foil, a net, a porous material, a foam, and a non-woven fabric.

[0119] The negative electrode active material layer includes a negative electrode active material and optionally a binder and a conductive material.

[0120] As the negative electrode active material, a compound that can reversibly intercalate and deintercalate lithium can be used. Specific examples thereof include: carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metal compounds that can alloy with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, and Al alloys; metal oxides that can be doped and dedoped with lithium, such as SiO β (0<β<2), SnO 2 , vanadium oxides and lithium vanadium oxides; and composites comprising metal compounds and carbonaceous materials, such as Si-C composites and Sn-C composites, which can be used alone or in combination of two or more thereof. In addition, lithium metal films can be used as negative electrode active materials. In addition, as carbon materials, both low-crystallinity carbon and high-crystallinity carbon can be used. Representative examples of low-crystallinity carbon include soft carbon and hard carbon, and representative examples of high-crystallinity carbon include amorphous, plate-like, flaky, spherical or fibrous natural graphite or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-type carbon fibers, mesophase carbon microbeads, mesophase pitch and high-temperature calcined carbon, such as coke derived from petroleum or coal tar pitch, etc.

[0121] The negative electrode active material may be contained in an amount of 80 wt % to 99 wt % relative to the total weight of the negative electrode active material layer.

[0122] The binder plays a role in helping the bonding between the conductive material, the active material and the current collector, and its content is generally 0.1 wt % to 10 wt % relative to the total weight of the negative electrode active material layer. Examples of binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene butadiene rubber, nitrile rubber, fluororubber and various copolymers thereof.

[0123] The conductive material is a component for enhancing the conductivity of the negative electrode active material, and its content can be 10% by weight or less, preferably 5% by weight or less, relative to the total weight of the negative electrode active material layer. There is no particular limitation on this conductive material as long as it does not cause chemical changes in the battery and has conductivity. For example, graphite, such as natural graphite or artificial graphite, etc.; carbon black, such as acetylene black, Ketjen black, channel black, furnace black, lamp black or thermal black, etc.; conductive fibers, such as carbon fibers or metal fibers, etc.; carbon fluorides; metal powders containing aluminum or nickel, etc.; conductive whiskers, such as zinc oxide or potassium titanate, etc.; conductive metal oxides, such as titanium oxide, etc.; or conductive materials such as polyphenylene derivatives.

[0124] The negative electrode active material layer may be formed by applying a negative electrode slurry composition prepared by dissolving or dispersing the negative electrode active material and optionally a binder and a conductive material in a solvent onto a negative electrode collector and drying it, or by laminating a film obtained by casting the negative electrode slurry composition on a separate support and removing it from the support onto the negative electrode collector.

[0125] At the same time, in lithium secondary batteries, the separator plays the role of separating the negative electrode from the positive electrode and providing a channel for lithium ion migration. As a separator, any separator commonly used in lithium secondary batteries can be used without particular limitation, and in particular, it is preferred that the migration of electrolyte ions shows low resistance and has excellent electrolyte impregnation ability. Specifically, a porous polymer film can be used, such as a porous polymer film made of a polyolefin polymer (such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer or ethylene / methacrylate copolymer, etc.) or a stacked structure having more than two layers thereof. In addition, conventional porous non-woven fabrics can be used, for example, non-woven fabrics made of high melting point glass fiber or polyethylene terephthalate fiber, etc. In addition, in order to ensure heat resistance or mechanical strength, a coated separator including a ceramic component or a polymer material and optionally a single layer or multilayer structure can be used.

[0126] In addition, as the electrolyte used in the present invention, an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel polymer electrolyte, an inorganic solid electrolyte or a molten inorganic electrolyte that can be used to manufacture a lithium secondary battery can be used, but the present invention is not limited thereto.

[0127] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0128] As the organic solvent, any organic solvent that can be used as a medium through which ions participating in the electrochemical reaction of the battery can migrate can be used without particular limitation. Specifically, the organic solvent can be: an ester solvent, such as methyl acetate, ethyl acetate, γ-butyrolactone or ε-caprolactone, etc.; an ether solvent, such as dibutyl ether or tetrahydrofuran, etc.; a ketone solvent, such as cyclohexanone, etc.; an aromatic hydrocarbon solvent, such as benzene or fluorobenzene, etc.; a carbonate solvent, such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC) or propylene carbonate (PC), etc.; an alcohol solvent, such as ethanol or isopropanol, etc.; or a nitrile, such as R-CN (R is a C2-C20 hydrocarbon group having a linear, branched or cyclic structure, and may include a double-bonded aromatic ring or an ether bond), etc.; an amide, such as dimethylformamide, etc.; a dioxolane, such as 1,3-dioxolane, etc.; or cyclopentane sulfone. Among those listed above, carbonate solvents are preferred, and more preferred are mixtures of cyclic carbonate compounds (e.g., EC, PC, etc.) having high ionic conductivity and high dielectric constant and linear carbonate compounds (e.g., EMC, DMC, DEC, etc.) having low viscosity, which can improve the charge and discharge performance of the battery.

[0129] As the lithium salt, any compound that can provide lithium ions used in lithium secondary batteries can be used without particular limitation. Specifically, as the anion of the lithium salt, a compound selected from the group consisting of F - , Cl - Br - ,I - 、NO 3 - 、N(CN) 2 - , BF 4 - CF 3 CF 2 SO 3 - ,(CF 3 SO 2 ) 2 N - 、(FSO 2 ) 2 N - CF 3CF 2 (CF 3 ) 2 CO - ,(CF 3 SO 2 ) 2 CH - , (SF 5 ) 3 C - ,(CF 3 SO 2 ) 3 C - CF 3 (CF 2 ) 7 SO 3 - CF 3 CO 2 - , CH 3 CO 2 - 、SCN - and (CF 3 CF 2 SO 2 ) 2 N - At least one of the group consisting of, and as the lithium salt, LiPF 6 、LiClO 4 、LiAsF 6 , LiBF 4 、LiSbF 6 、LiAlO 4 、LiAlCl 4 、LiCF 3 SO 3 ,LiC 4 F 9 SO 3 、LiN(C 2 F 5 SO 3 ) 2 、LiN(C 2 F 5 SO 2 ) 2 、LiN(CF 3 SO 2 ) 2 , LiCl, LiI or LiB(C 2 O 4 ) 2The lithium salt is preferably used in a concentration range of 0.1 M to 2.0 M. When the concentration of the lithium salt falls within the above range, the electrolyte has appropriate levels of conductivity and viscosity and thus can exhibit excellent electrolyte performance, and lithium ions can efficiently migrate.

[0130] For the purpose of enhancing the life characteristics of the battery, inhibiting the reduction of the battery capacity or increasing the discharge capacity of the battery, in addition to the above-mentioned electrolyte components, the electrolyte may further include at least one additive selected from halogenated alkylene carbonate compounds (such as difluoroethylene carbonate), pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glycol ether, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N, N-substituted imidazolidinones, ethylene glycol dialkyl ethers, ammonium salts, pyrroles, 2-methoxyethanol and aluminum chloride, etc. In this case, the content of the additive may be 0.1 wt% to 5 wt% relative to the total weight of the electrolyte.

[0131] Implementation

[0132] Hereinafter, the present invention will be described in detail with reference to embodiments so that those skilled in the art can easily implement the present invention. However, the present invention can be implemented in many different forms and is therefore not limited to the embodiments described herein.

[0133] Example 1

[0134] 4 L of distilled water was put into a coprecipitation reactor (capacity: 20 L). Then, while maintaining the temperature at 50 °C, 3.2 mol / L of transition metal solution (mixed with NiSO 4 、CoSO 4 and MnSO 4 , so that the molar ratio of nickel: cobalt: manganese is 0.83: 0.11: 0.06) and 28 wt% ammonia solution were continuously added to the reactor at 300 mL / hr and 42 mL / hr, respectively. The stirring speed of the impeller was set to 400 rpm, and 40 wt% sodium hydroxide solution was added to maintain the pH at 9.3. Then, coprecipitation was performed for 10 hours to form precursor particles, and the precursor particles were separated, washed, and then dried in an oven set at 130° C. to prepare a precursor (tap density: 1.8 g / cc).

[0135] The Ni synthesized by coprecipitation 0.83 Co 0.11 Mn 0.06 (OH) 2 The precursor was mixed with LiOH so that the molar ratio of Li / Me(Ni+Co+Mn) became 1.05, and the resulting mixture was heat-treated at 870°C for 10 hours under an oxygen atmosphere to prepare a LiNi 0.83 Co0.11 Mn 0.06 O 2 The scanning electron microscope (SEM) image of the prepared positive electrode active material powder is shown in Figure 1 middle.

[0136] Example 2

[0137] In addition to Ni 0.83 Co 0.11 Mn 0.06 (OH) 2 A positive electrode active material powder was prepared in the same manner as in Example 1, except that the precursor was mixed with LiOH so that the molar ratio of Li / Me (Ni, Co, Mn) was 1.05, and the resulting mixture was heat-treated at 900° C. for 10 hours under an oxygen atmosphere.

[0138] Comparative Example 1

[0139] In addition to Ni 0.83 Co 0.11 Mn 0.06 (OH) 2 The precursor was mixed with LiOH so that the molar ratio of Li / Me (Ni, Co, Mn) was 1.05, and the resulting mixture was heat-treated at 780° C. for 10 hours under an oxygen atmosphere. A positive electrode active material powder was prepared in the same manner as in Example 1. The SEM image of the prepared positive electrode active material powder is shown in Figure 2 middle.

[0140] Comparative Example 2

[0141] In addition to Ni 0.83 Co 0.11 Mn 0.06 (OH) 2 A positive electrode active material powder was prepared in the same manner as in Example 1, except that the precursor was mixed with LiOH so that the molar ratio of Li / Me (Ni, Co, Mn) was 1.05, and the resulting mixture was heat-treated at 950° C. for 10 hours under an oxygen atmosphere.

[0142] Experimental Example 1

[0143] The D of each positive electrode active material powder prepared in Examples 1 and 2 and Comparative Examples 1 and 2 was measured. mean d press and D 50 , and calculate D mean ×d press / D 50 The value of .

[0144] D meanis the average particle size of nodules measured using an electron backscatter diffraction (EBSD) spectrometer, d press It is the compaction density measured after 5 g of positive electrode active material powder is put into a circular mold with a diameter of 2 cm and pressed at a pressure of 2000 kgf. 50 It is a value corresponding to 50% of the cumulative volume in the particle size distribution measured by a laser diffraction method.

[0145] [Table 1]

[0146] Example 1 Example 2 Comparative Example 1 Comparative Example 2 <![CDATA[D mean ]]> 1.2 3 0.4 4 <![CDATA[d press ]]> 3.12 3.22 2.55 3.35 <![CDATA[D 50 ]]> 3.4 3.5 3.45 4.3 <![CDATA[D mean ×d press / D 50 Value]]> 1.10 2.76 0.30 3.12

[0147] It can be confirmed that Examples 1 and 2 satisfy 0.5≤D mean ×d press / D 50 ≤3, while Comparative Example 1 exhibits a D value less than 0.5 mean ×d press / D 50 value, and Comparative Example 2 exhibits a D greater than 3 mean ×d press / D 50 value.

[0148] Experimental Example 2

[0149] The (003) peak full width at half maximum (FWHM) of each positive electrode active material powder prepared in Example 1 and Comparative Example 1 was measured by X-ray diffraction (XRD) by the following method, and the (003) peak FWHM change rate was calculated using the measurement results.

[0150] First, a coin cell containing a positive electrode active material powder is manufactured. In this case, the coin cell is manufactured as an operando XRD coin cell with a Kapton film window for XRD analysis. Then, the in-situ XRD is measured in transmission mode while the coin cell is charged and discharged. During the XRD measurement, a Mo target X-ray is used as the light source, and the measurement is performed by 2θ scanning in transmission mode. A first slit of 1 / 4 degree, a Soller slit of 0.02rad (both the first and the second) and a second mask of 1.68mm are used. The area from 7 degrees to 30 degrees in 2θ is measured every 0.014 degrees, so that each scan takes about 6 minutes. During the measurement, charging and discharging are performed at 0.05C, and the CV state is maintained for one hour after measuring to 4.25V, and then discharged to 2.5V. A high-energy XRD Empyrean is used as a measuring instrument.

[0151] The (003) peak FWHM change rate was calculated by: [{(003) peak FWHM at SOC 60%−(003) peak FWHM at SOC 0%} / {(003) peak FWHM at SOC 0%}]×100.

[0152] The measurement results are shown in Figure 3 and Figure 4 middle. Figure 3 and Figure 4 Graphs showing the FWHM change rates of the positive electrode active material powders of Example 1 and Comparative Example 1 according to SOC, respectively.

[0153] Reference Figure 3 and Figure 4 , it can be confirmed that Example 1 exhibits a (003) peak FWHM change rate of 15% or less, and Comparative Example 1 exhibits a (003) peak FWHM change rate of more than 60%. Therefore, in the case of Example 1, it can be seen that even when charged to SOC 60% or discharged to SOC 0%, there is almost no change in the strain in the crystal size and structure, and the crushing of particles and the stress applied to the crystal structure during charging and discharging are reduced.

[0154] Experimental Example 3

[0155] A coin half-cell including each positive electrode active material powder prepared in Examples 1 and 2 and Comparative Examples 1 and 2 was manufactured and then charged to 4.25 V. Then, two electrodes (loading amount: 400 mg) charged at 4.25 V and a separator were placed on the lower plate of the coin cell and fixed with a gasket, and then 15 μl of electrolyte (DEC REF.) was vacuum injected twice, and each side was vacuum sealed to a thickness of 1 cm using a 6.5×5 cm aluminum bag (Al bag). In this case, vacuum sealing refers to single-cell vacuum sealing under the conditions of 95 kPa / 93 kPa. The coin half-cell manufactured as described above was then stored in a convection oven set at 60°C for 8 weeks, and the gas generation was evaluated by comparing the volume changes of the cells, and the results are shown in FIG. Figure 5 middle.

[0156] Reference Figure 5 , the cells using the positive electrode active material powders of Examples 1 and 2 showed a cell volume change of less than 0.2 mL after 8 weeks of storage, which was significantly lower than the cell volume change of the cells using the positive electrode active material powders of Comparative Examples 1 and 2. This shows that when the positive electrode active material powder of the present invention is applied, the high temperature storage characteristics of the battery are improved.

[0157] Experimental Example 4

[0158] A single cell including a positive electrode and a negative electrode was manufactured. The positive electrode was manufactured by coating each positive electrode active material powder prepared in Examples 1 and 2 and Comparative Examples 1 and 2 onto a current collector and drying it. A 5:5 mixture of natural graphite and artificial graphite was used as the negative electrode active material to manufacture the negative electrode, so that it contained 95.6% by weight of the negative electrode active material, 0.9% by weight of the conductive material, and 3.4% by weight of the binder. The loading of the negative electrode was 10.7 mg / cm 2 , the N / P ratio of the negative electrode and the positive electrode is fixed at 1.08.

[0159] The capacity retention rate (%) of the single battery cell including each positive electrode active material powder prepared in Examples 1 and 2 and Comparative Examples 1 and 2 was measured for 300 cycles at 45° C., and the results are shown in Figure 6 middle.

[0160] Reference Figure 6 It can be confirmed that under the condition of 300 cycles, the single cells using the positive electrode active material powders prepared in Examples 1 and 2 showed a capacity retention rate of more than 92%, while the single cells using the positive electrode active material powders prepared in Comparative Examples 1 and 2 showed a capacity retention rate of 87% and 85%, respectively. That is, it can be seen that when the positive electrode active material powder of the present invention is applied, the high temperature life characteristics are improved.

[0161] Experimental Example 5 - Measurement of Initial Resistance Value

[0162] A coin half cell including each positive electrode active material powder prepared in Examples 1 and 2 and Comparative Examples 1 and 2 was manufactured, and its initial resistance value was measured. Based on the first cycle discharge capacity measured at 0.1C, the initial resistance value was calculated as the voltage change rate when a current of 1C was applied for 60 seconds after setting 0.2C and SOC 10% in the second cycle.

[0163] The initial resistance values ​​of Examples 1 and 2 and Comparative Examples 1 and 2 are shown in Table 2 below.

[0164] [Table 2]

[0165]

[0166] Referring to the results of Table 2, when the positive electrode active material powders prepared in Examples 1 and 2 were applied, it was found that the initial resistance value at SOC 10% was lower than the initial resistance value at SOC 10% when the positive electrode active material powders prepared in Comparative Examples 1 and 2 were applied. Therefore, it can be seen that when the positive electrode active material powder of the present invention is applied to a battery, the initial resistance characteristics are improved.

Claims

1. A positive electrode active material powder for a lithium secondary battery, comprising a lithium composite transition metal oxide in the form of at least one of a single particle consisting of one nodule and a quasi-single particle which is a composite of 30 or less nodules, in, The positive electrode active material powder satisfies the following Expression 1: [Expression 1] 0.5≤D mean ×d press / D 50 ≤3 Among them, D mean is the average particle size of the nodules measured using an electron backscatter diffraction (EBSD) spectrometer, d press is the compaction density measured after 5 g of the positive electrode active material powder is put into a circular mold with a diameter of 2 cm and pressed at a pressure of 2000 kgf, and D 50 is the value corresponding to 50% of the cumulative volume in the particle size distribution of the positive electrode active material powder, D 50 It is not less than 2 μm and less than 10 μm.

2. The positive electrode active material powder according to claim 1, in, The lithium composite transition metal oxide has a composition represented by the following chemical formula 1: [Chemical formula 1] Li 1+x Ni a Co b M 1 c M 2 d O 2 In Chemical Formula 1, M 1 is Mn, Al, or a combination thereof, and M 2 is one or more selected from the group consisting of W, Zr, Y, Ba, Ca, Ti, Mg, Ta, and Nb, and satisfies 0 ≤ x ≤ 0.5, 0.8 ≤ a < 1, 0 < b < 0.2, 0 < c < 0.2, and 0 ≤ d ≤ 0.

05.

3. The positive electrode active material powder according to claim 2, in, In Chemical Formula 1, 0.82≤a≤0.95 is satisfied.

4. The positive electrode active material powder according to claim 1, in, The change rate of the full width at half maximum (FWHM) of the (003) peak of the positive electrode active material powder represented by the following Expression 2 is 25% or less: [Expression 2] (003) peak FWHM change rate=[{(003) peak FWHM at SOC 60%−(003) peak FWHM at SOC 0%} / {(003) peak FWHM at SOC 0%}]×100.

5. The positive electrode active material powder according to claim 4, in, The (003) peak FWHM change rate of the positive electrode active material powder is 15% or less.

6. The positive electrode active material powder according to claim 1, in, The D mean 0.5 to 3.5 μm.

7. The positive electrode active material powder according to claim 1, in, The d press 3 to 5 g / cc.

8. The positive electrode active material powder according to claim 1, in, The lithium composite transition metal oxide also includes a coating disposed on the surface of at least one form of the single particle and the quasi-single particle, wherein the coating includes one or more coating elements selected from the group consisting of Al, Ti, W, B, F, P, Mg, Ni, Co, Fe, Cr, V, Cu, Ca, Zn, Zr, Nb, Mo, Sr, Sb, Bi, Si and S.

9. The positive electrode active material powder according to claim 1, in, The BET specific surface area of ​​the positive electrode active material powder is 0.1 m 2 / g to 1m 2 / g. 10 . A positive electrode for a lithium secondary battery, comprising the positive electrode active material powder according to claim 1 . A lithium secondary battery comprising the positive electrode according to claim 10.

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