Positive electrode material powder and method for producing the same

Abstract

This invention relates to a cathode material powder and its preparation method. The cathode material powder comprises single-particle lithium-nickel-based oxide, wherein the amount of nickel in the metal other than lithium is 80 mol% or more, and wherein the cathode material powder has a density of 5.0 μm or more. 50 And has 280×10 ‑6 The following is the crystal strain.

Description

Technical Field

[0001] This application claims priority to Korean Patent Application No. 10-2024-0014418, filed on January 30, 2024, the entire contents of which are incorporated herein by reference.

[0002] This invention relates to having controlled D 50 A cathode material powder with crystal strain, its preparation method, and a cathode and lithium secondary battery including the cathode material powder. Background Technology

[0003] Industries that use lithium-ion batteries, such as mobile phones, laptops, and electric vehicles, have actively engaged in research and development efforts to improve their performance. Lithium-ion batteries generate electrical energy through oxidation and reduction reactions as lithium ions are inserted into and extracted from the positive and negative electrodes.

[0004] Lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, and lithium iron phosphate compounds are mainly used as positive electrode active materials for lithium secondary batteries. In addition, as a method to improve the low thermal stability while maintaining the excellent reversible capacity of lithium nickel oxide, lithium composite metal oxides (hereinafter referred to as "NCM oxides") in which part of the nickel is replaced by cobalt and manganese have been developed.

[0005] Recently, with the increasing demand for high-output, high-capacity batteries (such as those used in electric vehicles), there has been a growing effort to increase the nickel content in NCM oxides. However, the application of high-Ni NCM oxides as cathode materials is limited by the significant instability in their crystal structure due to cation mixing and oxygen desorption, as well as the large amount of lithium impurities remaining on their surfaces. This is because they generate a large amount of gas during high-temperature storage or charging and discharging. Summary of the Invention

[0006] [Technical Issues]

[0007] The present invention aims to provide a cathode material powder that can simultaneously achieve high capacity, particle durability and resistivity, and a method for preparing the same.

[0008] [Technical Solution]

[0009] [1] This invention provides a cathode material powder comprising a single-particle lithium nickel-based oxide, wherein the amount of nickel in the metal other than lithium is 80 mol% or more, and wherein the cathode material powder has a D of 5.0 μm or more. 50 And has 280×10 -6 The following is the crystal strain.

[0010] [2] The present invention provides the positive electrode material powder of [1] above, wherein the cation mixing ratio of the positive electrode material powder is less than 1.0 at%.

[0011] [3] The present invention provides the cathode material powder of [1] or [2] above, wherein the particle size reduction rate (K) of the cathode material powder according to mathematical formula 1 is 20% to 30%.

[0012] [Mathematical Expression 1]

[0013] Particle size reduction rate (K) =

[0014] In mathematical formula 1, D 50 It is the D of the positive electrode material powder 50 ,and D 50 The D value was measured after the cathode material powder was placed into a circular mold with a diameter of 13 mm and pressed with a force of 9 tons. 50 .

[0015] [4] The present invention provides a positive electrode material powder of at least one of [1] to [3] above, wherein the positive electrode material powder has a D of 0.5 μm or more. min .

[0016] [5] The present invention provides a positive electrode material powder of at least one of [1] to [4] above, wherein the positive electrode material powder has a density of 10 μm to 20 μm. max .

[0017] [6] The present invention provides a positive electrode material powder of at least one of [1] to [5] above, wherein the positive electrode material powder has a pellet density of 3.50 g / cc or more, wherein the pellet density is a value obtained by dividing the weight of the positive electrode material powder by the volume of the pellet after preparing a pellet by placing the positive electrode material powder in a circular mold with a diameter of 13 mm and pressing the positive electrode material powder with a force of 9 tons.

[0018] [7] The present invention provides a positive electrode material powder of at least one of [1] to [6] above, wherein the tap density of the positive electrode material powder is 2.00 g / cc to 2.50 g / cc.

[0019] [8] The present invention provides a positive electrode material powder of at least one of [1] to [7] above, wherein the lithium nickel-based oxide has the composition of chemical formula 1.

[0020] [9] The present invention provides a positive electrode material powder of at least one of [1] to [8] above, wherein the amount of nickel in the metal other than lithium of the lithium nickel-based oxide is 85 mol% or more.

[0021]

[10] The present invention provides a positive electrode material powder of at least one of [1] to [9] above, wherein the positive electrode material powder further includes a coating containing cobalt (Co) on the surface of the lithium nickel-based oxide particles.

[0022]

[11] The present invention provides a method for preparing a cathode material powder of at least one of [1] to

[10] above, the method comprising the following steps: preparing a mixture by mixing a precursor having a nickel content of more than 80 mol% with a lithium raw material; sintering the mixture at 750°C to 890°C for a first time; and sintering the sintered body subjected to the first sintering at 660°C to 750°C for a second time for 9 to 14 hours.

[0023]

[12] The present invention provides the method described in

[11] above, wherein the method further comprises the step of grinding the sintered body subjected to the secondary sintering at a speed of 1,000 rpm to 2,500 rpm.

[0024]

[13] The present invention provides the method described in

[11] or

[12] above, wherein the method does not include a washing step after the secondary sintering.

[0025]

[14] The present invention provides a positive electrode comprising a positive electrode material powder comprising at least one of [1] to

[10] above.

[0026]

[15] The present invention provides a lithium secondary battery comprising: a positive electrode as described in

[14] above; a negative electrode comprising a negative electrode active material; a separator disposed between the positive electrode and the negative electrode; and an electrolyte.

[0027] [Beneficial Effects]

[0028] This invention provides D 50 The numerical range of crystal strain can be used to optimize the particle size reduction rate of cathode material powders containing high-nickel (high-Ni) lithium nickel-based oxides before / after rolling. This is because D... 50 The particle size reduction rate of the cathode material powder with crystal strain satisfying the scope of the present invention is optimized, thus the cathode material powder has the advantage of excellent lithium migration and less fine powder generation during the rolling process.

[0029] Therefore, cathode material powder can help improve the cycle performance of lithium secondary batteries and reduce gas generation during high-temperature storage. Attached Figure Description

[0030] Figure 1 This is a scanning electron microscope (SEM) image of the cathode material powder prepared in Example 1.

[0031] Figure 2 This is an SEM image of the cathode material powder prepared in Example 2.

[0032] Figure 3 This is a SEM image of the cathode material powder prepared in Comparative Example 1.

[0033] Figure 4 This is a SEM image of the cathode material powder prepared in Comparative Example 2.

[0034] Figure 5 This is a SEM image of the cathode material powder prepared in Comparative Example 3.

[0035] Figure 6 This is a graph showing the volume change of a battery cell using the cathode material powders of the examples and comparative examples during high-temperature storage.

[0036] Figure 7 This is a SEM image of the cathode material powder prepared in Comparative Example 4. Detailed Implementation

[0037] The invention will be described in more detail below in order to provide a clearer understanding of it.

[0038] In this invention, "single-particle type" refers to a particle composed of 30 or fewer nodules, which includes the concept of a single particle composed of one nodule and a quasi-single particle as a complex of 2 to 30 nodules.

[0039] "Nodules" are sub-particle units that make up single particles and quasi-single particles. Nodules can be single crystals without crystal boundaries, or polycrystalline particles that do not appear to have grain boundaries when observed using a scanning electron microscope with a field of view of 5,000 to 20,000 times.

[0040] In this invention, "particle" is a concept that includes any or all of single particles, quasi-single particles, primary particles, and nodules.

[0041] In this invention, "D" 50 “D” min "and "D max"These refer to the particle sizes corresponding to the 50% volumetric cumulative particle size, minimum particle size, and maximum particle size in the volumetric cumulative particle size distribution of the corresponding powder, which can be measured using laser diffraction. For example, after dispersing the positive electrode active material powder in a dispersion medium, the dispersion medium is introduced into a commercially available laser diffraction particle size analyzer (e.g., Malvern Panalytical Ltd., Mastersizer 3000) and irradiated with ultrasound at approximately 28 kHz at an output of 60 W to obtain the volumetric cumulative particle size distribution map, and D..." 50 The particle size can be measured by obtaining the particle size at the 50% volume accumulation point in the resulting volumetric cumulative particle size distribution map.

[0042] In this invention, "cation mixing ratio" refers to the total amount of nickel ions (Ni ions) mixed with the lithium sites (Li sites) in the lithium layer of a layered lithium nickel-based oxide. 2+ The ratio (at%) can be measured by X-ray diffraction (XRD) analysis.

[0043] In this invention, "at%" refers to atomic percentage.

[0044] In this invention, “crystal strain” is a value indicating the lattice distortion caused by defects, i.e., the degree of lattice deformation, where it is a dimensionless number and can be measured by Rietveld refinement analysis of XRD data.

[0045] After placing the sample into the recess of a holder for general powders, leveling the sample surface with a glass slide, and filling the sample to match its height to the edge of the holder, X-ray diffraction analysis was performed using a Bruker D8 Endeavor (light source: Cu Kα, λ=1.54) equipped with a LynxEye XE-T position-sensitive detector, with a fixed divergence slit (FDS) of 0.5° and a 2θ range of 15° to 90°, at a step size of 0.02° and a total scan time of approximately 20 minutes. Rietveld refinement was applied to the measurement data, taking into account the charge at each site (+3 for metal at transition metal sites and +2 for Ni at Li sites) and cation mixing. Instrument broadening during analysis was performed using the fundamental parametric method (FPA) implemented in the Bruker TOPAS program, and the entire peak value within the measurement range was used during fitting. Only the Lorentz contribution was used as the first principle (FP) available in the peak type to fit the peak shape.

[0046] In this invention, "compacted density" can be obtained by placing a certain amount of sample into a cylindrical force sensor or a circular mold and applying force to compress it into a compacted object shape, then calculating the density from the weight and volume of the compacted object. For example, compacted density can be measured using an automatic pelletizer (Auto Pellet Press, 3887.4) from Carver, Inc. or a pelletizer (Pellet Press, 4350.L) from Carver, Inc.

[0047] In this invention, "tap density" can be measured using methods commonly used in the art (as a method for measuring the degree to which a sample is filled per unit volume). For example, tap density can be density (sample weight / volume), which is calculated as the amount of volume that changes when a constant force is applied to a measuring container containing the sample, according to the measuring apparatus and methods specified in ASTM B527. Specifically, tap density can be measured by horizontal vibration using a tap density analyzer from Micromeritics Instrument Corporation up to a force of 10⁸ N.

[0048] The components of the present invention will be described in more detail below.

[0049] Positive electrode material powder

[0050] The cathode material powder of the embodiments of the present invention comprises a single-particle lithium nickel-based oxide, wherein the amount of nickel in the metal other than lithium is 80 mol% or more, and wherein the cathode material powder has a D of 5 μm or more. 50 And has 280×10 -6 The following is the crystal strain.

[0051] To overcome the aforementioned limitations of the high-Ni cathode material in this invention, the cathode material has been controlled to be in the form of single particles, rather than the conventional secondary particle form in which tens to hundreds of particles are aggregated. Because the contact area between the single-particle cathode material and the electrolyte solution is smaller than that between the secondary particle cathode material and the electrolyte solution, the particle strength is excellent, and the side reactions with the electrolyte solution are less, resulting in reduced particle cracking during electrode fabrication. Therefore, it can help reduce the amount of gas generated in lithium secondary batteries.

[0052] However, single-particle cathode materials have relatively disadvantageous properties in terms of resistance due to the fact that the small interface between primary particles (which becomes the migration path of lithium ions in the particles) results in low lithium mobility, and the surface structure is easily altered to a rock salt phase, i.e., an electrochemically inactive phase. This is because single-particle cathode materials are prepared at relatively high sintering temperatures, and due to the high sintering temperatures, excessive lithium by-products remain on the surface. The introduction of a washing process to remove lithium by-products damages the surface structure.

[0053] In other words, obtaining a cathode material that achieves an excellent balance in capacity characteristics, particle durability, and resistivity characteristics, rather than favoring a particular property, is a difficult task.

[0054] Therefore, the inventors introduced D of the positive electrode material powder. 50 And crystal strain were used as indicators for selecting this cathode material, and the D in it was confirmed 50 The diameter is greater than 5.0 μm and the crystal strain is 280 × 10⁻⁶. -6 In the following cases, in cathode materials with a nickel content of more than 80 mol% and in single-particle form, it is possible to ensure that the capacity characteristics, particle durability and resistance characteristics are all above a certain level.

[0055] Specifically, the crystal strain of the cathode material powder is greater than 280 × 10⁻⁶. -6 In this case, due to the reduced structural stability, there is a problem of reduced initial charge capacity.

[0056] However, in the D of the cathode material powder 50 At particle sizes smaller than 5 μm, conductivity is difficult to ensure due to the low density between particles, and high-temperature durability is difficult to maintain due to the increased amount of fine powder generated during rolling. Therefore, even if the range of crystal strain is met, the same effect may not be achieved. Furthermore, for D... 50 For single particles smaller than 5 μm, the increased amount of fine powder due to high crushing intensity can lead to decreased phase stability of the slurry, reduced solids content during electrode coating, slurry gelation, and increased viscosity. Furthermore, since this may affect coating speed, it can also adversely impact process productivity. Specifically, the Do of the cathode material powder... 50 It can be from 5.0 μm to 8.5 μm, specifically from 5.0 μm to 7.0 μm, and more specifically from 5.0 μm to 6.0 μm.

[0057] The cation mixing ratio of the cathode material powder can be less than 1.0 at%, less than 0.8 at%, less than 0.5 at%, less than 0.3 at%, or less than 0.1 at%. This is because the cathode material powder of the present invention has low crystal strain and optimized D...50 The crystal structure exhibits excellent stability and maintains a uniform grain size, thus enabling the achievement of a low cation mixing ratio. Since cation mixing refers to the presence of Li atoms with similar ionic radii... + and Ni 2+ The phenomenon of exchanging sites to form crystals, therefore, if the cation mixing ratio is high, it exists in Li + Ni in the space layer 2+ It can be found in Li + During insertion and deintercalation, it acts as a resistive component to reduce charging and discharging efficiency, and therefore a cation mixing ratio of less than 1.0 at% is desired.

[0058] The particle size reduction rate (K) of the cathode material powder according to the following mathematical formula 1 can be 20% to 30%.

[0059] [Mathematical Expression 1]

[0060] Particle size reduction rate (K) =

[0061] In mathematical formula 1, D 50 It is the D of the positive electrode material powder 50 ,and D 50 The D value was measured after the cathode material powder was placed into a circular mold with a diameter of 13 mm and pressed with a force of 9 tons. 50 .

[0062] D 50 The diameter is greater than 5.0 μm and the crystal strain is 280 × 10⁻⁶. -6 In the following cases, since both the stability of the crystal structure and the uniformity of the particle size are ensured to minimize particle breakage, the particle size reduction rate can be controlled as described above.

[0063] When the particle size reduction rate (K) is less than 20%, the smaller interface between primary particles (which becomes the diffusion path for lithium ions in the particles) increases the diffusion path for lithium ions, thus reducing lithium mobility. Consequently, the increase in resistance may be enhanced with cycling. Furthermore, when the particle size reduction rate (K) is greater than 30%, the increased amount of fine powder generated during rolling due to the remaining small-sized particles after filling the gaps between large-sized particles leads to increased gas generation during high-temperature storage and potentially reduced lifetime characteristics. Preferably, the particle size reduction rate (K) can be 21% to 29%, more preferably 23% to 28%.

[0064] D in mathematical formula 1 50 and D 50'Represents the particle size of the cathode material powder before and after rolling during electrode preparation.

[0065] D of cathode material powder min The particle size can be greater than 0.5 μm, specifically greater than 0.6 μm, and can be less than 2.0 μm or less than 1.5 μm. Furthermore, the Do of the cathode material powder... max It can be from 10 μm to 20 μm, specifically from 11 μm to 15 μm.

[0066] The compaction density of the cathode material powder can be 3.50 g / cc or higher, preferably 3.55 g / cc or higher, more preferably 3.60 g / cc or higher, and in this case, high density is easily achieved due to excellent rollability. However, when considering its applicability to D... 50 Under actual rolling conditions for single particles larger than 5.0 μm, the compaction density can be below 3.75 g / cc.

[0067] In addition, the tap density of the cathode material powder can be from 2.00 g / cc to 2.50 g / cc, preferably from 2.10 g / cc to 2.50 g / cc, and more preferably from 2.20 g / cc to 2.40 g / cc.

[0068] When the compaction density and vibration density are within the above range, the energy density can be increased by adjusting the roll compaction density to the desired level.

[0069] According to embodiments of the present invention, the nickel content in the metals other than lithium in the lithium-nickel based oxide can be 85 mol% or more, preferably 90 mol% or more, more preferably 93 mol% or more, but can be 99 mol% or less. In this case, there is an advantage of being able to achieve high capacity.

[0070] In addition, lithium nickel-based oxides may have the following chemical formula 1.

[0071] [Chemical Formula 1]

[0072] Li 1+x (Ni a Co b M 1 c M 2 d O2

[0073] In chemical formula 1, M 1 It is manganese (Mn), aluminum (Al), or a combination thereof. M 2is selected from at least one of the group consisting of barium (Ba), calcium (Ca), zirconium (Zr), titanium (Ti), magnesium (Mg), tantalum (Ta), niobium (Nb), molybdenum (Mo), tungsten (W), copper (Cu), iron (Fe), vanadium (V), chromium (Cr), zinc (Zn), indium (In), yttrium (Y), lanthanum (La), strontium (Sr), gallium (Ga), scandium (Sc), gadolinium (Gd), samarium (Sm), cerium (Ce), and boron (B), and x, a, b, c, and d respectively satisfy 0 ≤ x ≤ 0.50, 0.80 ≤ a < 1, 0 < b ≤ 0.20, 0 ≤ c ≤ 0.20, 0 ≤ d ≤ 0.10, and a + b + c + d = 1.

[0074] 1 + x represents the molar ratio of lithium in the lithium nickel-based oxide, where x can satisfy 0 ≤ x ≤ 0.20 or 0 ≤ x ≤ 0.10. When the molar ratio of lithium satisfies the above range, a crystal structure can be stably formed.

[0075] a represents the molar ratio of nickel in all metals other than lithium in the lithium nickel-based oxide, where a can satisfy 0.85 ≤ a < 1, 0.90 ≤ a < 1, or 0.93 ≤ a < 1. When the molar ratio of nickel satisfies the above range, a high energy density can be exhibited to achieve a high capacity.

[0076] b represents the molar ratio of cobalt in all metals other than lithium in the lithium nickel-based oxide, where b can satisfy 0 < b ≤ 0.12, 0 < b ≤ 0.09, or 0 < b ≤ 0.07. When the molar ratio of cobalt satisfies the above range, good resistance characteristics and output characteristics can be achieved.

[0077] c represents the molar ratio of element M in all metals other than lithium in the lithium nickel-based oxide 1 where c can satisfy 0 < c ≤ 0.12, 0 < c ≤ 0.07, or 0 < c ≤ 0.05. M 1 can be Mn; or a combination of Mn and Al, and can preferably be Mn.

[0078] d represents the molar ratio of element M in all metals other than lithium in the lithium nickel-based oxide 2 where d can satisfy 0 ≤ d ≤ 0.08, 0 ≤ d ≤ 0.05, or 0 ≤ d ≤ 0.03.

[0079] The positive electrode material powder may include a coating containing cobalt (Co) element on the surface of the lithium nickel-based oxide particles. More specifically, the coating may include Li e CoO2 (0 < e < 1), which is a reaction product of Co and lithium by-products. In this case, since the contact between the lithium nickel-based oxide and the electrolyte solution is inhibited by the coating, the side reaction with the electrolyte solution is reduced, and thus the effect of improving the life characteristics can be obtained.

[0080] The cathode material powder can be a single particle consisting of a single nodule and / or a quasi-single particle as a composite of 30 or fewer nodules, preferably 2 to 20, more preferably 2 to 10 nodules, or it can be a form including these. Preferably, the cathode material powder of the present invention can be composed of a combination of cathode active material particles in the form of single particles and quasi-single particles. This is because when the number of nodules constituting the cathode active material particles is greater than 30, the effect of improving high-temperature storage characteristics may be reduced due to increased particle breakage during electrode preparation and increased occurrence of internal cracks due to the volume expansion / contraction of nodules during charging and discharging.

[0081] Preparation method of cathode material powder

[0082] The preparation method of the cathode material powder of the present invention will be described below.

[0083] The method for preparing the cathode material powder according to the embodiments of the present invention includes the following steps: preparing a mixture by mixing a precursor having a nickel content of 80 mol% or more with a lithium raw material; sintering the mixture once at 750°C to 890°C; and sintering the sintered body that has undergone the first sintering at 660°C to 750°C for 9 to 14 hours.

[0084] The following steps will be described.

[0085] In the step of preparing the mixture by mixing a precursor having a nickel content of more than 80 mol% with a lithium feedstock, the precursor having a nickel content of more than 80 mol% is first mixed with the lithium feedstock in a reactor.

[0086] The precursor may be in the form of hydroxide, oxide or carbonate, specifically in the form of hydroxide, and more specifically may have the composition of the following chemical formula 2.

[0087] [Chemical Formula 2]

[0088] Ni a1 Co b1 M 1 c1 M 2 d1 (OH)2

[0089] In chemical formula 2, M 1 It is Mn, Al, or a combination thereof. M 2is at least one selected from the group consisting of Ba, Ca, Zr, Ti, Mg, Ta, Nb, Mo, W, Cu, Fe, V, Cr, Zn, In, Y, La, Sr, Ga, Sc, Gd, Sm, Ce, and B, a1, b1, c1, and d1 respectively satisfy 0.80 ≤ a1 < 1, 0 < b1 ≤ 0.20, 0 ≤ c1 ≤ 0.20, 0 ≤ d1 ≤ 0.10, and a1 + b1 + c1 + d = 1.

[0090] a1 represents the molar ratio of nickel among all metals other than lithium in the precursor, where a1 can satisfy 0.85 ≤ a1 < 1, 0.90 ≤ a1 < 1, or 0.93 ≤ a1 < 1.

[0091] b1 represents the molar ratio of cobalt among all metals other than lithium in the precursor, where b1 can satisfy 0 < b1 ≤ 0.12, 0 < b1 ≤ 0.09, or 0 < b1 ≤ 0.07.

[0092] c1 represents the molar ratio of element M 1 among all metals other than lithium in the precursor, where c1 can satisfy 0 < c1 ≤ 0.12, 0 < c1 ≤ 0.07, or 0 < c1 ≤ 0.05. M 1 can be Mn; or a combination of Mn and Al.

[0093] d1 represents the molar ratio of element M 2 among all metals other than lithium in the precursor, where d1 can satisfy 0 ≤ d1 ≤ 0.08, 0 ≤ d1 ≤ 0.05, or 0 ≤ d1 ≤ 0.03.

[0094] Commercially available precursors can be purchased and used as the precursor, or the precursor can be prepared according to methods known and used in the art for preparing precursors.

[0095] As the lithium raw material, lithium-containing sulfates, nitrates, acetates, carbonates, oxalates, citrates, halides, hydroxides, or hydroxyoxides can be used, and for example, Li2CO3, LiNO3, LiNO2, LiOH, LiOH·H2O, LiH, LiF, LiCl, LiBr, LiI, CH3COOLi, Li2O, Li2SO4, CH3COOLi, Li3C6H5O7, or mixtures thereof can be used.

[0096] The lithium raw material and the precursor can be mixed such that the molar ratio of lithium (Li) to all metals in the precursor is 1:1 to 1.2:1, preferably 1:1 to 1.1:1. When the mixing ratio of the lithium raw material to the metals in the precursor satisfies the above range, due to the well-developed layered crystal structure of the lithium nickel-based oxide, a cathode material with excellent capacity characteristics and structural stability can be prepared.

[0097] Next, there is a step of sintering the mixture to prepare a single-particle type sintered body. Specifically, sintering includes primary sintering and secondary sintering, and the primary sintering can be carried out by sintering the mixture for 8 hours to 16 hours at 750 °C to 890 °C, preferably 800 °C to 890 °C, more preferably 800 °C to 850 °C in an oxygen atmosphere. The primary sintering is a step of increasing the structural integrity of the lithium nickel-based oxide and single-particle formation. Considering that the higher the sintering temperature, the better the particle growth reaction occurs, thus increasing the degree of single-particle formation, it is desirable that the primary sintering temperature be above 750 °C. However, considering that when over-sintering occurs during primary sintering, the reactivity between the precursor and the lithium raw material decreases, and if the amount of Li2O increases due to high-temperature sintering, it is easily converted to LiOH, and LiOH can be easily converted to Li2CO3, causing side reactions with the electrolyte solution and gas generation, it is desirable that the primary sintering temperature be below 890 °C. In this article, the oxygen atmosphere refers to an atmosphere that contains sufficient oxygen for sintering in addition to the air atmosphere. In particular, it is desirable to carry out sintering in an atmosphere with an oxygen partial pressure higher than that of the air atmosphere.

[0098] The secondary sintering can be carried out on the sintered body that has undergone primary sintering at 600 °C to 750 °C, preferably 660 °C to 720 °C, more preferably 680 °C to 700 °C in an oxygen atmosphere. In addition, the secondary sintering can be carried out for 9 hours to 14 hours, preferably 10 hours to 14 hours, more preferably 10 hours to 12 hours. Since the secondary sintering is carried out to increase the degree of single-particle formation, it is desirable that the temperature of the secondary sintering be above 660 °C, but considering that too high a sintering temperature can increase the strain and cation mixing ratio, it is desirable that the secondary sintering temperature not be greater than 750 °C.

[0099] A coating raw material containing Co element can be added during the secondary sintering, and in this case, the lithium by-products remaining on the surface of the sintered body react with the coating raw material to form a coating containing a LCO-like phase (specifically Li e CoO2(0 < e < 1)) on the surface of the lithium nickel-based oxide particles. Since the coating including the Co element not only has an effect of improving the life, but also the lithium by-products remaining on the surface are consumed during the formation of the coating, there is also an effect of reducing the side reactions caused by the lithium by-products.

[0100] In this case, the coating raw material can be at least one selected from the group consisting of Co(OH)2, CoO, Co2O3, Co3O4, CoO(OH), and Co(OCOCH3)2, and based on the total molar number of the primary sintered body, the addition amount of the coating raw material can be 1 mol% to 10 mol%, preferably 2 mol% to 5 mol%.

[0101] The preparation method of cathode material powder may not require a washing step after sintering. When preparing high-NiNCM oxides with a nickel content of 80 mol% or more, a washing process is usually performed after sintering to remove lithium byproducts present on the particle surface. However, since the surface properties of lithium nickel-based oxides deteriorate during the washing process, increasing resistivity, it is desirable that this method exclude the washing step.

[0102] Since the cobalt coating in this invention can prevent side reactions caused by lithium byproducts, the washing step can be omitted, thus solving the problem of increased resistance due to washing.

[0103] Furthermore, a grinding step of the sintered body can be performed after the secondary sintering. Specifically, the method for preparing the cathode material powder according to embodiments of the present invention may further include a step of grinding the sintered body subjected to secondary sintering at a speed of 1,000 rpm to 2,500 rpm, preferably 1,200 rpm to 2,300 rpm.

[0104] The grinding process is used to remove large particles and obtain a cathode material powder with a particle size within a desired range. Aggregation and / or agglomeration between adjacent particles can occur during the high-temperature sintering process to produce large particles, which can lead to deterioration of the rolling characteristics. Therefore, in this invention, large particles can be removed by performing a grinding process, and a particle size with the aforementioned D can ultimately be formed. 50 The positive electrode material powder.

[0105] Grinding can be performed using common grinding methods known in the art, such as jet milling, and the speed refers to the classifier speed.

[0106] It is desirable to perform grinding in an atmosphere with low moisture content (e.g., in a dry air atmosphere). This is because when lithium nickel-based oxides are exposed to moisture, the generation of lithium byproducts increases and the surface properties of the active material may deteriorate.

[0107] positive electrode

[0108] Next, the positive electrode of the present invention will be described.

[0109] The positive electrode of the present invention includes the above-described positive electrode material powder. Specifically, the positive electrode includes: a positive electrode current collector; and a positive electrode active material layer disposed on the positive electrode current collector and containing the above-described positive electrode material powder. Since the positive electrode material powder has already been described above, the description of the positive electrode material powder will be omitted, and components other than the positive electrode material powder will be described below.

[0110] In the positive electrode, there are no particular restrictions on the positive electrode current collector, as long as it is conductive and does not cause adverse chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, sintered carbon, or aluminum or stainless steel surface-treated with one of carbon, nickel, titanium, silver, etc., can be used. Furthermore, the thickness of the positive electrode current collector can typically range from 3 μm to 500 μm, and microscopic irregularities can be formed on the surface of the current collector to improve the adhesion of the positive electrode material powder. For example, the positive electrode current collector can be used in various shapes such as films, sheets, foils, meshes, porous bodies, foams, and nonwoven fabrics.

[0111] In addition to the aforementioned cathode material powder, the cathode active material layer may also contain conductive agents and binders.

[0112] Based on the total weight of the positive electrode active material layer, the content of the positive electrode material powder can typically be 80% to 99% by weight, preferably 90% to 98% by weight, and more preferably 95% to 97% by weight.

[0113] Conductive agents are used to provide conductivity to the electrodes. Any conductive agent can be used without particular limitation, as long as it has suitable electronic conductivity and does not cause chemical changes in the battery. Specific examples of conductive agents can be: graphite, such as natural and artificial graphite; carbon black, such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermally cracked carbon black; carbonaceous materials, such as carbon fibers and carbon nanotubes; metal powders or fibers, such as copper, nickel, aluminum, and silver; conductive whiskers, such as zinc oxide whiskers or potassium titanate whiskers; conductive metal oxides, such as titanium oxide; or conductive polymers, such as polyphenylene derivatives, and any one or a mixture of two or more of these can be used. Based on the total weight of the positive electrode active material layer, the content of the conductive agent is typically from 0.5% to 20% by weight, preferably from 1% to 10% by weight, and more preferably from 1% to 5% by weight.

[0114] The adhesive improves the adhesion between the positive electrode active material particles and the adhesion between the positive electrode active material and the positive electrode current collector. Specific examples of the adhesive can be polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and any one or a mixture of two or more thereof can be used. Based on the total weight of the positive electrode active material layer, the adhesive content can be from 0.5% by weight to 20% by weight, preferably from 1% by weight to 10% by weight, more preferably from 1% by weight to 5% by weight.

[0115] The positive electrode can be prepared according to common methods for preparing positive electrodes. For example, after preparing a positive electrode slurry by mixing positive electrode material powder, binder and / or conductive agent in a solvent and coating it onto a positive electrode current collector, the positive electrode can be prepared by drying and rolling the coated positive electrode current collector.

[0116] The solvent can be one commonly used in the art. Solvents may include dimethyl sulfoxide (DMSO), isopropanol, N-methylpyrrolidone (NMP), acetone, and water, and any one or a mixture of two or more of these may be used. Considering the coating thickness and manufacturing yield of the slurry, the amount of solvent used may be sufficient if it can dissolve or disperse the cathode material powder, conductive material, and binder, and has a viscosity that provides excellent thickness uniformity during the subsequent coating process for preparing the cathode.

[0117] As another method, the positive electrode can be prepared by casting the positive electrode slurry onto a separate support and then pressing the film layer peeled off from the support onto the positive electrode current collector.

[0118] Lithium secondary batteries

[0119] Next, the lithium secondary battery of the present invention will be described.

[0120] A lithium-ion secondary battery specifically includes a positive electrode, a negative electrode containing a negative electrode active material, a separator disposed between the positive and negative electrodes, and an electrolyte. Since the positive electrode is the same as described above, its detailed description will be omitted, and only the remaining components will be described in detail below.

[0121] Additionally, the lithium secondary battery may optionally include a battery container housing an electrode assembly containing a positive electrode, a negative electrode, and a separator, as well as a sealing member for sealing the battery container.

[0122] In a lithium secondary battery, the negative electrode includes a negative electrode current collector and a layer of negative electrode active material disposed on the negative electrode current collector.

[0123] There are no particular limitations on the negative electrode current collector, as long as it has high conductivity and does not cause adverse chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, sintered carbon, or copper or stainless steel with a surface treatment of carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloys can be used. Furthermore, the thickness of the negative electrode current collector can typically range from 3 μm to 500 μm, and similar to the positive electrode current collector, microscopic irregularities can be formed on the surface of the current collector to improve the adhesion of the negative electrode active material. For example, the negative electrode current collector can be used in various shapes such as films, sheets, foils, meshes, porous bodies, foams, and nonwoven fabrics.

[0124] In addition to the negative electrode active material, the negative electrode active material layer may optionally include a binder and a conductive material.

[0125] Compounds capable of reversibly inserting and de-intercalating lithium can be used as anode active materials. Specific examples of anode active materials can be: carbonaceous materials, such as artificial graphite, natural graphite, graphitized carbon fibers, and amorphous carbon; metallic materials that can be alloyed with lithium, such as silicon (Si), aluminum (Al), tin (Sn), lead (Pb), zinc (Zn), bismuth (Bi), indium (In), magnesium (Mg), gallium (Ga), cadmium (Cd), Si alloys, Sn alloys, or Al alloys; and metal oxides that can be doped and de-doped with lithium, such as SiO₂. β (0<β<2), SnO2, vanadium oxide and lithium vanadium oxide; or a composite containing metallic and carbonaceous materials, such as a Si-C composite or a Sn-C composite, and any one or a mixture of two or more of them may be used.

[0126] In one embodiment of the invention, the negative electrode active material may be graphite, a Si-containing material, or a mixture thereof, specifically graphite, and more specifically a mixture of artificial graphite and natural graphite. Furthermore, a lithium metal thin film may be used as the negative electrode active material. Based on the total weight of the negative electrode active material layer, the content of the negative electrode active material may be from 80% to 99% by weight.

[0127] Adhesives are components that facilitate adhesion between conductive agents, active materials, and current collectors, wherein the adhesive content is typically from 0.1% to 10% by weight, based on the total weight of the negative electrode active material layer. Examples of adhesives include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile rubber, fluororubber, and various copolymers thereof.

[0128] A conductive agent is a component used to further improve the conductivity of the negative electrode active material. Based on the total weight of the negative electrode active material layer, the content of the conductive agent can be less than 10% by weight, preferably less than 5% by weight. There are no particular limitations on the conductive agent, as long as it is conductive without causing chemical changes in the battery. Examples of conductive agents that can be used include: conductive materials such as graphite (e.g., natural or artificial graphite); carbon black (e.g., acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermally cracked carbon black); conductive fibers such as carbon fibers or metal fibers; fluorocarbons; metal powders such as aluminum and nickel powders; conductive whiskers such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides such as titanium oxide; or polyphenylene derivatives.

[0129] The negative electrode active material layer can be prepared by coating a negative electrode material mixture (which is prepared by dissolving or dispersing the negative electrode active material and optional binder and conductive agent in a solvent) onto the negative electrode current collector and drying the coated negative electrode current collector, or by casting the negative electrode material mixture onto a separate support and then pressing the film layer separated from the support onto the negative electrode current collector.

[0130] In lithium-ion secondary batteries, the separator separates the negative and positive electrodes and provides a migration channel for lithium ions. Any separator can be used without particular limitation, as long as it is commonly used in lithium-ion secondary batteries. In particular, separators with high electrolyte retention capacity and low resistance to electrolyte ion migration can be used. Specifically, porous polymer membranes can be used, such as porous polymer membranes prepared from polyolefin polymers (e.g., ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, or ethylene / methacrylate copolymers, etc.), or laminates of two or more layers thereof. Alternatively, conventional porous nonwoven fabrics can be used, such as nonwoven fabrics formed from high-melting-point glass fibers or polyethylene terephthalate fibers. Moreover, coated separators including ceramic components or polymer materials can be used to ensure heat resistance or mechanical strength, and separators with single-layer or multi-layer structures can be optionally used.

[0131] In addition, the electrolyte used in this invention may include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, inorganic solid electrolytes or molten inorganic electrolytes that can be used to manufacture lithium secondary batteries, but this invention is not limited thereto.

[0132] Specifically, the electrolyte may contain organic solvents and lithium salts.

[0133] As organic solvents, any organic solvent can be used without particular limitation, as long as it can serve as a medium through which ions participating in the electrochemical reaction of the battery can move. Specifically, organic solvents that can be used include: ester solvents, such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents, such as dibutyl ether and tetrahydrofuran; ketone solvents, such as cyclohexanone; aromatic solvents, such as benzene and fluorobenzene; or carbonate solvents, such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), or propylene carbonate (PC); alcohol solvents, such as ethanol and isopropanol; nitriles, such as R-CN (where R is a straight-chain, branched, or cyclic C2-C20 hydrocarbon group, which may include double-bonded aromatic rings or ether bonds); amides, such as dimethylformamide; dioxolane, such as 1,3-dioxolane; or sulfolane. Among these solvents, carbonate solvents are preferred, and mixtures of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and high dielectric constant and low viscosity linear carbonate compounds (e.g., ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate) are even more preferred, as they can improve the charge / discharge performance of the battery.

[0134] Lithium salts can be used without particular restrictions, as long as they are compounds that can provide lithium ions for use in lithium secondary batteries. Specifically, the anion of the lithium salt can be selected from F... - Cl - ,Br - I - NO3 - N(CN)2 - BF4 - CF3CF2SO3 - (CF3SO2)2N - (FSO2)2N - CF3CF2(CF3)2CO - (CF3SO2)2CH - (SF5)3C - (CF3SO2)3C - CF3(CF2)7SO3 - CF3CO2 - CH3CO2 - SCN - and (CF3CF2SO2)2N -At least one of the groups consisting of. Specifically, the lithium salt can be at least one selected from the group consisting of LiPF6, LiN(SO2F)2 (LiFSI), LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO2, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, and LiB(C2O4)2, and more specifically, a mixture of LiPF6 and LiN(SO2F)2 (LiFSI). The concentration of the lithium salt can be from 0.1 M to 4.0 M, preferably from 0.5 M to 3.0 M, and more preferably from 1.0 M to 2.0 M. If the concentration of the lithium salt is within the above range, excellent electrolyte performance can be obtained because the electrolyte can have suitable conductivity and viscosity, and lithium ions can move efficiently.

[0135] When the lithium salt is a mixture of LiPF6 and LiN(SO2F)2 (LiFSI), the molar ratio of LiPF6:LiFSI can be from 5:5 to 9:1, preferably from 6:4 to 8:2.

[0136] To improve battery life characteristics, suppress battery capacity reduction, and improve battery discharge capacity, in addition to the electrolyte components mentioned above, the electrolyte may also contain at least one additive, such as alkylene carbonate halogenates (e.g., ethylene difluorocarbonate), pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glycol diether, hexamethylphosphotriamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolides, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride. In this case, the additive content may be from 0.1% by weight to 5% by weight, based on the total weight of the electrolyte.

[0137] The shape of the lithium secondary battery of the present invention is not particularly limited, but can be cylindrical, prismatic, pouch or coin-shaped.

[0138] As described above, since the lithium secondary battery including the positive electrode material powder of the present invention stably exhibits high-temperature performance, the lithium secondary battery can not only be used as a battery cell for powering small devices such as mobile phones, laptops and digital cameras, but also preferably as a cell battery for battery modules of medium and large devices including multiple battery cells.

[0139] Examples of medium and large units can be power tools, electric vehicles, hybrid vehicles, plug-in hybrid vehicles, and energy storage systems, but medium and large units are not limited to these.

[0140] According to another embodiment of the present invention, a battery module including the above-described lithium secondary battery as a unit battery and a battery pack including the battery module are provided.

[0141] In the following, embodiments of the invention will be described in detail in a manner readily available to those skilled in the art to which this invention pertains.

[0142] [Example: Preparation of cathode material powder]

[0143] Example 1

[0144] D with approximately 5.0 μm 50 And by Ni 0.93 Co 0.05 Mn 0.02 The precursor (OH)₂ and LiOH were placed in a Henschel mixer (700 L) and mixed at a center speed of 400 rpm for 20 minutes. In this case, LiOH was added in an amount such that the molar ratio of Li:(Ni+Co+Mn) was 1.05:1. The mixed powder was placed in an alumina crucible with dimensions of 330 mm × 330 mm and sintered once at 800 °C for 10 hours in an oxygen (O₂) atmosphere. Subsequently, based on the total molar amount of the first sintered body, 2 mol% Co(OH)₂ was added, and a second sintering was performed at 700 °C for 10 hours to form a Co coating. The Li[Ni]O₂ coating was prepared by grinding the sintered powder at a step speed of 2,000 rpm in a dry air atmosphere using a jet mill. 0.93 Co 0.05 Mn 0.02 The cathode material powder is composed of O2. Images of the prepared cathode material powder observed using scanning electron microscopy at magnifications of 10.0 K and 5.00 K are shown in the image. Figure 1 As shown in the image.

[0145] Example 2

[0146] D with approximately 5.0 μm 50 And by Ni 0.80 Co 0.10 Mn 0.10The precursor (OH)₂ and LiOH were placed in a Henschel mixer (700 L) and mixed at a center speed of 400 rpm for 20 minutes. In this case, LiOH was added in an amount such that the molar ratio of Li:(Ni+Co+Mn) was 1.05:1. The mixed powder was placed in an alumina crucible with dimensions of 330 mm × 330 mm and sintered once at 800 °C for 10 hours in an oxygen (O₂) atmosphere. Subsequently, based on the total molar amount of the first sintered body, 2 mol% Co(OH)₂ was added, and a second sintering was performed at 700 °C for 10 hours. The Li[Ni]₂ precursor and LiOH were then prepared by grinding the sintered powder at a step speed of 2,000 rpm in a dry air atmosphere using a jet mill. 0.80 Co 0.10 Mn 0.10 The cathode material powder is composed of O2. Images of the prepared cathode material powder observed using scanning electron microscopy at magnifications of 10.0 K and 5.00 K are shown in the image. Figure 2 As shown in the image.

[0147] Comparative Example 1.

[0148] The cathode material powder was prepared in the same manner as in Example 1, except that D was used. 50 The precursor is 3.5 μm thick. Images of the prepared cathode material powder observed using scanning electron microscopy at magnifications of 10.0 K and 5.00 K are shown in the figure. Figure 3 As shown in the image.

[0149] Compare Example 2.

[0150] The cathode material powder was prepared in the same manner as in Example 1, except that a secondary sintering was performed at 700°C for 8 hours. Images of the prepared cathode material powder were observed using a scanning electron microscope at magnifications of 10.0 K and 5.00 K. Figure 4 As shown in the image.

[0151] Comparative Example 3.

[0152] The cathode material powder was prepared in the same manner as in Example 1, except that a secondary sintering was performed at 700°C for 15 hours. Images of the prepared cathode material powder were observed using a scanning electron microscope at magnifications of 10.0 K and 5.00 K. Figure 5 As shown in the image.

[0153] Comparative Example 4.

[0154] The cathode material powder was prepared in the same manner as in Example 1, except that D was used. 50The precursor is 4.3 μm. Images of the prepared cathode material powder observed using scanning electron microscopy at magnifications of 10.0 K and 5.00 K are shown in the figure. Figure 7 As shown in the image.

[0155] [Experimental Example]

[0156] Experimental Example 1. Powder Characterization

[0157] (1) Measurement of particle size reduction rate

[0158] Particle size analysis

[0159] After dispersing 0.1 g of each cathode material powder prepared in the examples and comparative examples in a dispersion medium, the dispersion medium was introduced into a laser diffraction particle size analyzer (Malvern Panalytical Ltd., Mastersizer 3000) and irradiated with ultrasound at approximately 28 kHz at an output of 60 W to measure the D-value of each cathode material powder. 50 D min and D max The measurement results are shown in Table 1 below.

[0160] Crystal strain and cation mixing ratio

[0161] The XRD data obtained by X-ray diffraction analysis of the cathode material powders prepared in the examples and examples were analyzed using the Rietveld refinement method to measure crystal strain. The excess Ni value confirmed by Rietveld refinement was used to obtain the cation mixing ratio, and the results are listed in Table 1 below.

[0162] In this configuration, after placing the sample into the recess of a holder for general powders, leveling the sample surface using a glass slide, and filling the sample to match its height to the edge of the holder, X-ray diffraction analysis was performed using a Bruker D8 Endeavor (light source: Cu Kα, λ=1.54) equipped with a LynxEye XE-T position-sensitive detector, with a fixed divergence slit (FDS) of 0.5° and a 2θ range of 15° to 90°, at a step size of 0.02° and a total scan time of approximately 20 minutes. Rietveld refinement was applied to the measurement data, taking into account the charge at each site (+3 for metal at transition metal sites and +2 for Ni at Li sites) and cation mixing. Instrument broadening during analysis was performed using the fundamental parametric method (FPA) implemented in the Bruker TOPAS program, and the entire peak value within the measurement range was used during fitting. Only the Lorentz contribution was used as the first principle (FP) among the peak types available for fitting to fit the peak shape.

[0163] D 50 'Measurement'

[0164] Three grams of each cathode material powder prepared in the examples and comparative examples were collected and placed into a circular mold with a diameter of 13 mm. An automatic pelletizer (Auto Pellet Press, Carver, Inc., 3887.4) was used to apply force until the force reached 9 tons, thereby preparing granules. After redispersing the prepared granules in a dispersion medium, the dispersion medium was introduced into a laser diffraction particle size analyzer (Malvern Panalytical Ltd., Mastersizer 3000) and irradiated with ultrasound at approximately 28 kHz at an output of 60 W to measure the D-value of each pressed cathode material powder. 50 The measurement results are listed in Table 1 below as D. 50 '.

[0165] Calculation of particle size reduction rate

[0166] By measuring the D of each positive electrode material as described above 50 and D 50 The particle size reduction rate obtained by substituting the value into mathematical formula 1 is listed as K in Table 1 below.

[0167] (2) Compacted density and vibration compaction density

[0168] Measurement of compacted density

[0169] Three g of each cathode material powder prepared in the examples and comparative examples were collected and placed into a circular mold with a diameter of 13 mm. An automatic pelletizer (Auto Pellet Press, Carver, Inc., 3887.4) was used to apply force until the force reached 9 tons, thereby preparing a compacted object. After measuring the height of the prepared compacted object and calculating its volume based on this, the compaction density, calculated by dividing the weight of the cathode material powder by the volume of the compacted object, is listed in Table 1 below.

[0170] Measurement of tap density

[0171] The tap density of each cathode material powder prepared in the examples and comparative examples was measured using a GEOPYC 1360 tap density analyzer from Micromeritics Instrument Corporation. Specifically, 10 g of each cathode material powder prepared in the examples and comparative examples was collected and filled into a container with a diameter of 19 mm. The container was then vibrated horizontally until a force of 108 N was applied to measure the tap density, which is listed in Table 1 below.

[0172] Table 1

[0173] Experimental Example 2. Single Cell Performance Evaluation

[0174] (1) Fabrication of a single battery cell

[0175] The cathode material powders prepared in the examples and comparative examples, carbon black as a conductive agent, and PVDF as a binder were mixed in NMP solvent at a weight ratio of 96.5:1.5:2.0 to prepare cathode slurries. The cathode slurries were coated on one surface of an aluminum current collector, dried at 130°C, and then rolled to prepare the cathodes.

[0176] A negative electrode slurry was prepared by adding graphite (as the negative electrode active material), carbon black (as the conductive agent), and styrene-butadiene rubber (SBR) (as the binder) to distilled water in a weight ratio of 95.0:3.5:1.5. The negative electrode slurry was then coated onto one surface of a copper current collector, dried at 130°C, and then rolled to prepare the negative electrode.

[0177] An electrode assembly was prepared by placing a porous polyethylene separator between the prepared positive and negative electrodes. The electrode assembly was then placed in a battery casing, and an electrolyte solution was injected into the casing to prepare a single battery cell. An electrolyte solution was prepared by dissolving 0.7 M LiPF6 and 0.3 M LiFSI in a mixed organic solvent, in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a volume ratio of 3:7.

[0178] (2) Cyclic performance evaluation

[0179] Each single cell prepared in (1) above was charged to 4.2 V at a constant current of 0.3 C, each single cell was charged at 0.05 C and a constant voltage, and then each single cell was discharged to 2.5 V at 0.3 C. This was set as one cycle, and the capacity retention rate and resistance increase rate were measured when a total of 600 cycles were performed.

[0180] Specifically, discharge capacity and resistance were measured at the 1st, 100th, 300th, and 600th cycles, and the discharge capacity retention rate and resistance increase rate relative to the 1st cycle were calculated at the 100th, 300th, and 600th cycles. The results are listed in Table 2 below. A CRC (cell cycler) 05-10 (WONIK PNE Co., LTD) was used as the measuring instrument.

[0181] (3) Assessment of gas production

[0182] After the formation process of each single cell prepared in (1) above, each single cell was charged to 4.20 V at 25°C with a constant current (CC) of 0.3 C (reference capacity 1C = 40 mAh / g), and then charged with a constant voltage (CV) until the charging current reached 0.05 C (cutoff current). Subsequently, while storing each single cell in the chamber at 60°C, the single cells were removed from the chamber at weekly intervals, and the volume change was calculated using Archimedes' principle applied through a hydrometer (MATSUHAKU, TWD-150DM). The results were... Figure 6 The average weekly volume change was calculated based on measurements taken over 8 weeks and is listed in Table 2 below.

[0183] Table 2

[0184] According to Table 2 and Figure 6 The results confirm the use of D with a diameter greater than 5.0 μm. 50 and 280×10 -6 The cells using the cathode materials in Examples 1 and 2 of the following crystal strain exhibit better results than the cells using the cathode materials in Comparative Examples 1 to 4 in terms of capacity retention, resistance increase rate, and gas generation.

[0185] Based on Comparative Examples 1 to 3, it can be confirmed that when the crystal strain is greater than 280 × 10⁻⁶, -6 In the case of high-temperature storage, the amount of gas generated increases while the lifetime and electrical resistance characteristics decrease. Specifically, for Comparative Examples 2 and 3, where the particle size reduction rate is outside the range of 20% to 30%, it can be confirmed that the lifetime and electrical resistance characteristics are further reduced compared to those of Comparative Example 1. For D... 50 Comparative Example 1, with a crystal strain smaller than 5.0 μm, exhibited a capacity retention rate similar to that of the Examples of Comparative Examples 2 and 3, as the crystal strain was lower and the particle size reduction rate was 20% to 30%. However, with the increase in the number of cycles, the increase in resistance was more pronounced, and it was confirmed that the amount of gas generated increased significantly.

[0186] Furthermore, regarding D among them 50 Comparative Example 4, with a crystal strain less than 5.0 μm, showed that even with a crystal strain of 280 × 10⁻⁶, -6 The following results show that its lifespan and resistance characteristics are also reduced compared to the previous embodiment, and it can be confirmed that the amount of gas generated is also significantly increased.

Claims

1. A positive electrode material powder, comprising: Single-particle lithium nickel-based oxide, wherein the amount of nickel in the metals other than lithium is 80 mol% or more, in, The cathode material powder has a density of 5.0 μm or higher. 50 And has 280×10 -6 The following is the crystal strain.

2. The positive electrode material powder as described in claim 1, wherein, The cation mixing ratio of the positive electrode material powder is 1.0 at% or less.

3. The positive electrode material powder as described in claim 1, wherein, The particle size reduction rate K of the positive electrode material powder according to Mathematical Formula 1 is 20% to 30%: [Mathematical Formula 1] Particle size reduction rate K = Wherein, in Mathematical Formula 1, D 50 It is the D of the positive electrode material powder 50 ,and D 50 The D value was measured after the cathode material powder was placed into a circular mold with a diameter of 13 mm and pressed with a force of 9 tons. 50 .

4. The positive electrode material powder as described in claim 1, wherein, The cathode material powder has a density of 0.5 μm or higher. min .

5. The positive electrode material powder as described in claim 1, wherein, The cathode material powder has a density of 10 μm to 20 μm. max .

6. The positive electrode material powder as described in claim 1, wherein, The tap density of the positive electrode material powder is 3.50 g / cc or more, Wherein, the tap density is a value obtained by dividing the weight of the positive electrode material powder by the volume of the compact after preparing the compact by putting the positive electrode material powder into a circular mold with a diameter of 13 mm and pressing the positive electrode material powder with a force of 9 tons.

7. The positive electrode material powder as described in claim 1, wherein, The bulk density of the positive electrode material powder is 2.00 g / cc to 2.50 g / cc.

8. The positive electrode material powder as described in claim 1, wherein, The lithium nickel-based oxide has the composition of Chemical Formula 1: [Chemical Formula 1] Li 1+x (Ni a Co b M 1 c M 2 d )O2 Wherein, in Chemical Formula 1, M 1 It is Mn, Al, or a combination thereof. M 2 It is selected from at least one of the following groups: Ba, Ca, Zr, Ti, Mg, Ta, Nb, Mo, W, Cu, Fe, V, Cr, Zn, In, Y, La, Sr, Ga, Sc, Gd, Sm, Ce, and B. x, a, b, c, and d respectively satisfy 0 ≤ x ≤ 0.50, 0.80 ≤ a < 1, 0 < b ≤ 0.20, 0 ≤ c ≤ 0.20, 0 ≤ d ≤ 0.10, and a + b + c + d = 1.

9. The positive electrode material powder as described in claim 1, wherein, The amount of nickel in the metals other than lithium in the lithium nickel-based oxide is 85 mol% or more.

10. The positive electrode material powder according to claim 1, further comprising a coating containing cobalt (Co) element on the surface of the lithium nickel-based oxide particles.

11. A method for preparing the positive electrode material powder according to claim 1, the method comprising the following steps: Preparing a mixture by mixing a precursor having a nickel amount of 80 mol% or more with a lithium raw material; Performing a first sintering on the mixture at 750 °C to 890 °C; and Performing a second sintering on the sintered body subjected to the first sintering at 660 °C to 750 °C for 9 hours to 14 hours.

12. The method according to claim 11, further comprising a step of grinding the sintered body subjected to the second sintering at a speed of 1,000 rpm to 2,500 rpm.

13. The method of claim 11, wherein, The method does not include a washing step after the second sintering.

14. A positive electrode, comprising the positive electrode material powder according to claim 1.

15. A lithium secondary battery, comprising: The positive electrode according to claim 14; A negative electrode containing a negative electrode active material; A separator disposed between the positive electrode and the negative electrode; And An electrolyte.

Images