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

Abstract

The present invention relates to a positive electrode active material, a method for preparing the same, and a lithium secondary battery comprising the same. Specifically, the positive electrode active material according to the present invention comprises: a lithium nickel-based oxide in which the nickel content is 70 mol% or more among all metal elements other than lithium; a first coating layer formed on the lithium nickel-based oxide; and a second coating layer formed on the first coating layer, in which the first coating layer contains a coating element M1 (M1 is at least one selected from the group consisting of nickel (Ni), cobalt (Co), and aluminum (Al)), the second coating layer contains a coating element M2 (M2 is titanium (Ti)), and the content of the coating element M2 is calculated based on the total content of Ni, Co, lithium (Li), and oxygen (O) contained in the lithium nickel-based oxide as measured by X-ray photoelectron spectroscopy (XPS). The content of titanium contained in the second coating layer as measured by XPS may be 0.7 at% to 3.3 at%.

Description

[0001] Cross-reference to related applications

[0002] This application claims priority to Korean Patent Application No. 10-2023-0140699, filed on October 19, 2023, and Korean Patent Application No. 10-2024-0139814, filed on October 14, 2024, the disclosures of which are incorporated herein by reference. Technical Field

[0003] This invention relates to a positive electrode active material and a positive electrode and a lithium secondary battery comprising the positive electrode active material. More specifically, it relates to a positive electrode active material that improves high-temperature stability by comprising a coating containing a specific concentration of thermally stable titanium dioxide (TiO2), and a positive electrode and a lithium secondary battery that improve high-temperature stability by comprising the positive electrode active material. Background Technology

[0004] With technological advancements and increasing demand for mobile devices, the need for secondary batteries as an energy source has grown significantly. Among these secondary batteries, lithium-ion batteries, characterized by high energy density, high voltage, long cycle life, and low self-discharge rate, are seeing continuous commercial expansion.

[0005] Lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMnO2 or LiMn2O4), or lithium iron phosphate compounds (LiFePO4) have been used as positive electrode active materials for lithium secondary batteries. Among these, lithium cobalt oxide has the advantages of high operating voltage and excellent capacity characteristics; however, its commercial application in high-capacity batteries is difficult due to the high price and unstable supply of cobalt, a raw material. Lithium nickel oxide suffers from poor structural stability, making it difficult to achieve sufficient lifetime characteristics. Lithium manganese oxide exhibits excellent stability but suffers from poor capacity characteristics. Therefore, lithium composite transition metal oxides containing two or more transition metals have been developed to overcome the limitations of lithium transition metal oxides containing only nickel (Ni), cobalt (Co), or manganese (Mn). Lithium nickel cobalt manganese oxide containing Ni, Co, and Mn has been widely used in the field of electric vehicle batteries.

[0006] Conventional lithium nickel cobalt manganese oxides typically exist as spherical secondary particles aggregated from tens or hundreds of primary particles. However, for these secondary particle forms of lithium nickel cobalt manganese oxides with numerous primary particles, there are issues such as particle breakage due to primary particle detachment during the rolling process in cathode fabrication, and cracking within the particles during charge and discharge. When particle breakage or cracking occurs in the cathode active material, it exacerbates the degradation of the active material.

[0007] In particular, with the increasing demand for high-energy-density lithium-ion batteries, the nickel content in cathode active materials tends to gradually increase. However, for cathode active materials with high nickel content, repeated charge-discharge cycles generate large amounts of highly reactive Ni. +4 The ions cause structural collapse of the positive electrode active material, resulting in an increased rate of degradation of the positive electrode active material, which in turn degrades its lifespan and reduces battery safety.

[0008] Therefore, there is a need to develop a positive electrode active material that can simultaneously achieve high capacity and high thermal stability. Summary of the Invention

[0009] Technical issues

[0010] One aspect of the present invention provides a positive electrode active material with excellent thermal stability.

[0011] Another aspect of the present invention provides a positive electrode comprising the positive electrode active material and a lithium secondary battery having excellent thermal stability by comprising the positive electrode.

[0012] Technical solution

[0013] [1] The present invention provides a positive electrode active material comprising: a lithium nickel oxide having a nickel content of 70 mol% or more in all metal elements except lithium; a first coating formed on the lithium nickel oxide; and a second coating formed on the first coating. The first coating comprises a coating element M1 (M1 is at least one selected from the group consisting of nickel (Ni), cobalt (Co) and aluminum (Al)). The second coating contains coating element M2 (M2 is titanium (Ti)). Based on the total content of Ni, Co, lithium (Li) and oxygen (O) in the lithium nickel oxide as measured by X-ray photoelectron spectroscopy (XPS), the content of titanium in the second coating as measured by XPS is 0.7 atomic% to 3.3 atomic%.

[0014] [2] The present invention provides the positive electrode active material of [1] above, wherein the lithium nickel oxide particles are represented by Formula 1: [Formula 1] Li a Ni b Co c M ' d M '' e O2 In Equation 1, M ' It is manganese (Mn), aluminum (Al) or a combination thereof. M '' The element is selected from at least one element in the group consisting of Al, zirconium (Zr), tungsten (W), titanium (Ti), magnesium (Mg), calcium (Ca), and strontium (Sr), and 0.8 ≤ a ≤ 1.2, 0.7 ≤ b < 1.0, 0 <c<0.3,0<d<0.3,0≤e≤0.2。

[0015] [3] The present invention provides the positive electrode active material of [1] or [2] above, wherein the lithium nickel oxide particles are in the form of a single particle consisting of a primary particle, or in the form of a quasi-single particle as an aggregate of 30 or fewer primary particles.

[0016] [4] The present invention provides a positive electrode active material of at least one of [1] to [3] above, wherein the average particle size (D) of the lithium nickel oxide particles is [missing information]. 50 The thickness ranges from 1.0 μm to 8.0 μm.

[0017] [5] The present invention provides a positive electrode active material of at least one of [1] to [4] above, wherein a first coating is continuously coated on the surface of lithium nickel oxide particles.

[0018] [6] The present invention provides a positive electrode active material of at least one of [1] to [5] above, wherein the first coating comprises Al2O3 and Co3O4.

[0019] [7] The present invention provides a positive electrode active material of at least one of [1] to [6] above, wherein the second coating is discontinuously distributed on the surface of the first coating.

[0020] [8] The present invention provides a positive electrode active material of at least one of [1] to [7] above, wherein the second coating comprises titanium dioxide (TiO2).

[0021] [9] The present invention provides a positive electrode active material of at least one of [1] to [8] above, wherein the average particle size (D) of titanium dioxide (TiO2) is 50 The range is 20 nm to 150 nm.

[0022]

[10] The present invention provides a positive electrode active material of at least one of [1] to [9] above, wherein the content of titanium dioxide (TiO2) is 1000 ppm to 2000 ppm based on the total amount of the positive electrode active material.

[0023]

[11] The present invention provides a positive electrode active material of at least one of [1] to

[10] above, wherein the content of the first coating and the second coating is 2.3% to 2.5% by weight based on the total amount of the positive electrode active material.

[0024]

[12] The present invention provides a positive electrode active material of at least one of [1] to

[11] above, wherein the weight ratio of the first coating to the second coating is 1:0.04 to 1:0.1.

[0025]

[13] The present invention provides a positive electrode active material of at least one of [1] to

[12] above, wherein the content of titanium in the second coating, as measured by XPS, is from 0.7 atomic% to 3.0 atomic% based on the total content of Ni, Co, Li and oxygen (O) contained in the lithium nickel oxide as measured by XPS.

[0026]

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

[13] above, wherein the maximum heat flux of the positive electrode active material measured by differential scanning calorimetry (DSC) is less than 11 W / g.

[0027]

[15] The present invention provides a method for preparing a positive electrode active material of at least one of [1] to

[17] above, comprising: preparing a transition metal precursor containing nickel (Ni), cobalt (Co) and manganese (Mn) and wherein the content of nickel in all metal elements is more than 70 mol%; A transition metal precursor is mixed with a lithium-containing raw material and sintered once to form a lithium nickel oxide. Lithium nickel oxide is mixed with aluminum and cobalt precursors and then sintered twice to form a first coating containing coating element M1 (M1 is at least one selected from Ni, Co and aluminum (Al)) on the lithium nickel oxide. The lithium nickel oxide with the first coating is mixed with a titanium precursor and sintered three times to form a second coating containing coating element M2 (M2 is titanium (Ti)) on the surface of the first coating.

[0028]

[16] The present invention provides the method described in

[15] above, wherein the transition metal precursor is represented by Formula 2: [Equation 2] Ni x Co y Mn z M 3 q (OH)2 In Equation 2, M 3 It is selected from at least one of the groups consisting of Mn, Al, Zr, W, Ti, Mg, Ca, and Sr, and 0.7 ≤ x ≤ 1.0, 0 <y≤0.3,0<z<0.3,0≤q≤0.2。

[0029]

[17] The present invention provides the method described in

[15] or

[16] above, wherein the first sintering is performed at a temperature of 800°C to 890°C.

[0030]

[18] The present invention provides a method of at least one of

[15] to

[17] above, wherein the secondary sintering is performed at a temperature of 600°C to 790°C.

[0031]

[19] The present invention provides a method of at least one of

[15] to

[18] above, wherein the three sinterings are performed at a temperature of 600°C to 700°C.

[0032]

[20] The present invention provides a method of at least one of

[15] to

[19] above, wherein the molar ratio of the lithium nickel oxide having the first coating to the titanium precursor is 100:0.1 to 100:0.3.

[0033]

[21] The present invention provides a positive electrode for a lithium secondary battery, comprising at least one of the positive electrode active materials described in [1] to

[14] above.

[0034]

[22] The present invention provides a lithium secondary battery comprising the positive electrode of the above

[21] for a lithium secondary battery.

[0035] Beneficial effects

[0036] The positive electrode active material of the present invention ensures excellent thermal stability and surface durability by including a coating containing a specific concentration of highly thermally stable titanium dioxide (TiO2) on the surface of single-particle lithium nickel oxide particles. Therefore, using the positive electrode active material of the present invention, lithium secondary batteries with improved high-temperature stability and reduced initial resistance can be achieved. Attached Figure Description

[0037] The accompanying drawings, which are attached to this specification, illustrate preferred embodiments of the invention by way of example and, together with the detailed description of the invention provided below, serve to further understand the technical concept of the invention. Therefore, the invention should not be interpreted solely based on the contents of these drawings.

[0038] Figure 1 and Figure 2 This is a scanning electron microscope (SEM) image of the positive electrode active material containing the second coating prepared in Example 1 of the present invention.

[0039] Figure 3 The figure shows the XPS (X-ray photoelectron spectroscopy) results of the second coating of the positive electrode active material prepared in Example 1 of the present invention.

[0040] Figure 4 The figure shows the XPS results of the second coating of the positive electrode active material prepared in Example 2 of the present invention.

[0041] Figure 5 The figure shows the XPS results of the second coating of the positive electrode active material prepared in Example 3 of the present invention.

[0042] Figure 6 A graph showing the differential scanning calorimetry (DSC) results of the lithium secondary battery in Experimental Example 2 for comparison.

[0043] Figure 7 The figure shows the initial resistance evaluation results of the lithium secondary battery in Experiment Example 3. Detailed Implementation

[0044] It should be understood that the words or terms used in the specification and claims should not be interpreted as having the meaning defined in a common dictionary, but rather should be further understood as having meanings consistent with their meanings in the context of the related technology and the technical concept of the invention, based on the principle that the inventor can appropriately define the meanings of words or terms to best interpret the invention.

[0045] It should also be understood that the terms “comprising,” “including,” or “having” in this specification specify the presence of the said features, numbers, steps, elements, or combinations thereof, but do not exclude the presence or addition of one or more other features, numbers, steps, elements, or combinations thereof.

[0046] The term "upper" in this specification refers not only to the case where one component is directly formed on the upper surface of another component, but also to the case where there may be intermediate components.

[0047] In this specification, unless otherwise expressly stated, “%” represents weight.

[0048] In this specification, "single particle" refers to a particle consisting of a single nodule. In this invention, "quasi-single particle" refers to a composite particle formed from 30 or fewer nodules.

[0049] A "nodule" refers to a particle unit that constitutes a single particle or quasi-single particle. This nodule can be a single crystal without grain boundaries, or a polycrystalline material that does not appear to have grain boundaries when observed using scanning electron microscopy (SEM) or electron backscatter diffraction (EBSD) at a magnification of 5000x to 20000x. The average grain size of the nodule is the arithmetic mean calculated after measuring the grain size of the nodules observed by SEM or EBSD.

[0050] In this specification, "D" min “D” 50 "and "D max "D" refers to the particle size value measured using laser diffraction to determine the volumetric cumulative distribution of the positive electrode active material powder. Specifically, D minIt is the smallest particle size that appears in the volumetric cumulative distribution, D 50 It is the particle size when the cumulative volume is 50%, D max It is the maximum particle size that appears in the volumetric cumulative distribution. For example, the particle size value of the volumetric cumulative distribution can be measured by dispersing the positive electrode active material powder in a dispersion medium, then introducing the dispersion medium into a commercially available laser diffraction particle size analyzer (e.g., Microtrac MT 3000), irradiating the dispersion medium with an ultrasonic wave of approximately 28 kHz with an output power of 60 W, and obtaining the volumetric cumulative particle size distribution map.

[0051] Furthermore, in this invention, the specific surface area of ​​the positive electrode active material is measured by the Brunauer-Emmett-Teller (BET) method. Specifically, the specific surface area can be calculated using Bell Japan's BELSORP-mino II based on the amount of nitrogen adsorbed at liquid nitrogen temperature (77K).

[0052] Furthermore, X-ray photoelectron spectroscopy (hereinafter referred to as "XPS") in this specification is a method for analyzing the constituent elements and their electronic states of a sample by measuring the energy of photoelectrons generated when a sample (particularly the sample surface) is irradiated with X-rays. In particular, since XPS can analyze a region of the sample surface at a depth of approximately 2 nm to 8 nm (typically approximately 5 nm), it can perform qualitative and quantitative analysis of the elemental concentration in approximately half of the surface portion. In this invention, measurements are performed using XPS (manufactured by Rikaku; X-ray source: Cu-Kα (1486.6 eV); accelerating voltage: 10 kV, 300 W; energy resolution: approximately 1.0 eV; minimum analysis area: 10 microns; sputtering rate: 0.1 nm / min).

[0053] The invention will be described in more detail below in order to enable a clearer understanding of the invention.

[0054] The positive electrode active material of the present invention, as well as the positive electrode and lithium secondary battery including the positive electrode active material, includes at least one of the following configurations, and may include any combination of technically feasible configurations among the following configurations.

[0055] [Positive electrode active material]

[0056] In one embodiment, the present invention provides a positive electrode active material comprising: A lithium-nickel oxide having a nickel content of 70 mol% or more in all metal elements except lithium; a first coating formed on the lithium-nickel oxide; and a second coating formed on the first coating. The first coating comprises a coating element M1 (M1 is at least one selected from the group consisting of nickel (Ni), cobalt (Co) and aluminum (Al)). The second coating contains coating element M2 (M2 is titanium (Ti)), and Based on the total content of Ni, Co, lithium (Li) and oxygen (O) in the lithium nickel oxide as measured by X-ray photoelectron spectroscopy (XPS), the content of titanium in the second coating as measured by XPS is 0.7 atomic% to 3.3 atomic%.

[0057] Conventionally, secondary particle form of positive electrode active materials formed from primary particle aggregation has the following problems: particle breakage due to primary particle detachment is likely to occur during the rolling process used to prepare the positive electrode, and structural changes and cracking of the positive electrode active material are prone to occur within the particles during charge and discharge. Conversely, because the particle strength of positive electrode active materials composed of single particles of primary particles or quasi-single particles as aggregates of 30 or fewer primary particles is higher than that of conventional secondary particle form of positive electrode active materials composed of tens to hundreds of primary particles, particle breakage hardly occurs during rolling. Moreover, because the number of primary particles constituting the particles is smaller, the changes caused by the volume expansion and contraction of the primary particles during charge and discharge are also smaller, thus significantly reducing the occurrence of particle cracking.

[0058] Therefore, in order to provide a positive electrode active material with excellent thermal stability, the inventors aim to provide a positive electrode active material that uses single-particle lithium nickel oxide particles with a specific particle size range as the core part, and simultaneously forms a coating containing a specific concentration of titanium dioxide (TiO2) with excellent thermal stability on the surface of the lithium nickel oxide particles to enhance the binding with oxygen on the surface of the positive electrode active material and inhibit oxygen desorption, thereby ensuring excellent thermal stability and surface durability.

[0059] Specifically, the positive electrode active material of the present invention may contain lithium nickel oxide particles in which the nickel content of all metal elements other than lithium is 70 mol% or more, preferably 80 mol% to less than 100 mol%, and more preferably 85 mol% to less than 100 mol%.

[0060] The aforementioned high-Ni-content lithium nickel oxide particles may contain compounds represented by Formula 1 below.

[0061] [Formula 1]

[0062] Li a Ni b Co c M ' d M ''e O2

[0063] In Formula 1, M ' is manganese (Mn), aluminum (Al), or a combination thereof, M '' is at least one selected from the group consisting of Al, zirconium (Zr), tungsten (W), titanium (Ti), magnesium (Mg), calcium (Ca), and strontium (Sr), and 0.8 ≤ a ≤ 1.2, 0.7 ≤ b < 1.0, 0 < c < 0.3, 0 < d < 0.3, 0 ≤ e ≤ 0.2.

[0064] In Formula 1, a represents the molar ratio of lithium in the lithium nickel-based oxide, where a can satisfy 0.8 ≤ a ≤ 1.2, specifically can satisfy 0.85 ≤ a ≤ 1.15, and more specifically can satisfy 0.9 ≤ a ≤ 1.10. When the molar ratio of lithium in the lithium nickel-based oxide satisfies the above range, the crystal structure of the lithium nickel-based oxide can be formed stably.

[0065] b represents the molar ratio of nickel in all metals other than lithium in the lithium nickel-based oxide, where b can satisfy 0.7 ≤ b < 1.0, specifically can satisfy 0.8 ≤ b ≤ 0.95, and more specifically can satisfy 0.85 ≤ b ≤ 0.95. When the molar ratio of nickel in the lithium nickel-based oxide satisfies the above range, high energy density can be exhibited, thereby achieving high capacity.

[0066] c represents the molar ratio of cobalt in all metals other than lithium in the lithium nickel-based oxide, where c can satisfy 0 < c < 0.3, preferably can satisfy 0.001 < c < 0.20, specifically can satisfy 0.01 < c ≤ 0.二十, and more specifically can satisfy 0.01 ≤ c < 0.15. When the molar ratio of cobalt in the lithium nickel-based oxide satisfies the above range, good resistance characteristics and output characteristics can be achieved.

[0067] d represents the molar ratio of element M in all metals other than lithium in the lithium nickel-based oxide 1 where d can satisfy 0 < d < 0.3, preferably can satisfy 0.001 < d < 0.25, more preferably can satisfy 0.01 ≤ d < 0.20, more preferably can satisfy 0.01 ≤ d < 0.20, and even more specifically can satisfy 0.01 ≤ d < 0.15. When the molar ratio of element M in the lithium nickel-based oxide 1 satisfies the above range, the structural stability of the positive electrode active material is excellent.

[0068] e represents the molar ratio of element M in all metals other than lithium in the lithium nickel-based oxide 2 where e can satisfy 0 ≤ e ≤ 0.2, specifically can satisfy 0 ≤ e ≤ 0.1, and preferably can satisfy 0 ≤ e ≤ 0.05.

[0069] Specifically, to achieve high-capacity batteries, lithium nickel oxide particles may include Li(Ni) 0.8 Co 0.1 Mn 0.1 O2, Li(Ni) 0.8 Co 0.15 Al 0.05 O2, Li(Ni) 0.92 Co 0.06 Mn 0.02 O2, Li(Ni) 0.95 Co 0.03 Mn 0.02 O2, Li(Ni) 0.86 Co 0.05 Mn 0.07 Al 0.02 O2 or Li(Ni) 0.90 Co 0.05 Mn 0.05 O2, preferably Li(Ni) 0.92 Co 0.06 Mn 0.02 O2 or Li(Ni) 0.95 Co 0.03 Mn 0.02 )O2.

[0070] The lithium nickel oxide of the present invention can be in the form of a single particle consisting of a primary particle or in the form of a quasi-single particle as an aggregate of 30 or fewer primary particles.

[0071] The average particle size (D) of the lithium nickel oxide 50 It can be above 1.0 μm.

[0072] That is, the present invention uses materials with excellent structural stability and average particle size (D) 50 Lithium nickel oxides are single-particle forms with a particle size of 1.0 μm or larger. They can suppress side reactions by preventing particle breakage or cracking, and can achieve excellent fast charging characteristics because lithium ions are more easily conducted compared to polycrystalline materials.

[0073] Specifically, the average particle size (D) of the lithium nickel oxide of the present invention 50 The size can be greater than 1.0 μm, specifically from 1.0 μm to 8.0 μm, and more specifically from 4.0 μm to 8.0 μm.

[0074] Furthermore, the D of the lithium nickel oxide of the present invention min It can be above 0.5 μm, for example, from 0.5 μm to 3.0 μm, specifically within the range of 1.0 μm to 3.0 μm.

[0075] As described above, due to the average particle size (D) of the lithium nickel oxide of the present invention 50 ) and D min When the above range is met, the number of fine particles decreases, the specific surface area of ​​the positive electrode active material decreases, and therefore the contact interface with the electrolyte is reduced. As a result, side reactions are reduced, thereby improving thermal stability. Therefore, when the positive electrode active material is used in large cylindrical batteries, excellent thermal stability, reduced gas generation, and low initial resistance characteristics can be achieved.

[0076] Furthermore, the D of the lithium nickel oxide of the present invention max The diameter can be from 12 µm to 20 µm, preferably from 12 µm to 16 µm, and more preferably from 12 µm to 15 µm. When the D of lithium nickel oxides... max Meeting the above-mentioned ranges improves electrode density, thereby preventing a decrease in energy density. Furthermore, since lithium mobility can be improved by preventing an increase in lithium migration paths within the particles, an increase in resistance can be suppressed. Therefore, excellent resistance and capacity characteristics can be ensured.

[0077] Furthermore, the Brunauer-Emmett-Teller (BET) specific surface area of ​​the lithium nickel oxide of the present invention can be 2.0 m². 2 / g to 6.0 m 2 / g, preferably 2.2 m 2 / g to 4.0 m 2 / g.

[0078] When the BET specific surface area of ​​lithium nickel oxides meets the above range, the reactivity with lithium increases during sintering. As a result, the cation mixing of the synthesized single-particle positive electrode active material is reduced, and the integrity of the crystal structure of the positive electrode active material is increased. Therefore, positive electrode active materials with excellent capacity characteristics and structural stability can be prepared.

[0079] The positive electrode active material of the present invention may also contain at least one coating on the surface of a lithium nickel oxide.

[0080] Specifically, since the positive electrode active material of the present invention includes a first coating containing a coating element M1 (M1 is at least one selected from Ni, Co and Al) on a lithium nickel oxide, the structural stability and particle strength of the active material can be improved, and the effects of improving high-temperature lifetime characteristics and resistivity increase rate can be obtained.

[0081] Specifically, the first coating may be in the form of a film continuously coated on the surface of a lithium nickel oxide with a uniform thickness, or it may be distributed on a portion of the surface of the lithium nickel oxide. Preferably, the first coating may be formed in the form of a continuous coating on the lithium nickel oxide.

[0082] The first coating may contain Al(OH)3, Al2O3 or Co3O4, specifically Al2O3 and Co3O4.

[0083] Furthermore, since the positive electrode active material of the present invention contains a second coating containing a coating element M2 (M2 is Ti) with excellent thermal stability on the surface of the first coating, oxygen desorption can be suppressed by strengthening the binding with oxygen on the surface of the positive electrode active material. As a result, excellent thermal stability and surface durability can be ensured.

[0084] In other words, when conventional cathode active materials are exposed to high temperatures, the structure of the cathode active material may transform into a spinel or rock salt structure due to the continuous release of oxygen from the surface portion and the bond breakage of oxygen in the layered transition metal layer. However, in this invention, by forming a second coating containing titanium (titanium has a higher binding energy with oxygen than transition metal elements such as nickel (Ni)) on the surface of the cathode active material, the binding with oxygen is strengthened, oxygen desorption can be suppressed, and thus the structural collapse of the cathode can be suppressed, thereby ensuring thermal stability. Furthermore, since surface durability can be enhanced to prevent direct contact between the electrolyte and lithium nickel oxide particles, surface side reactions can be prevented.

[0085] The second coating is discontinuously distributed on the first coating and may include titanium dioxide (TiO2) in particulate form (see...). Figure 1 and Figure 2 ).

[0086] The average particle size (D) of titanium dioxide (TiO2) 50 The wavelength can be from 20 nm to 150 nm, specifically from 30 nm to 120 nm, preferably from 30 nm to 100 nm.

[0087] The average particle size (D) of titanium dioxide (TiO2) 50 When the above range is met, since a coating with appropriate thickness and distribution can be formed, the surface durability and thermal stability of the positive electrode active material can be improved.

[0088] Furthermore, based on the total amount of positive electrode active material, the content of titanium dioxide (TiO2) can be from 1000 ppm to 2000 ppm, or from 1500 ppm to 2000 ppm.

[0089] When the content of titanium dioxide (TiO2) is above 1000 ppm, a uniformly distributed second coating can be formed to ensure thermal stability and surface durability, while when the content of titanium dioxide (TiO2) is below 2000 ppm, it can prevent the increase in resistance and the decrease in capacity due to the formation of excessive coating.

[0090] The positive electrode active material of the present invention can have a titanium concentration gradient that decreases sequentially from the outermost surface to the core portion (i.e., to the interface with the surface of the first coating). Specifically, the titanium concentration at the interface between the first and second coatings can be reduced by more than 40%, specifically more than 50%, relative to the titanium concentration at the outermost surface of the positive electrode active material containing the second coating. Because this concentration gradient improves the surface durability of the positive electrode active material and stabilizes the internal crystal structure, it further improves thermal stability.

[0091] Based on the total content of Ni, Co, Li and oxygen (O) in lithium nickel oxides as measured by XPS photoelectron spectroscopy, the content of titanium (Ti) in the second coating of the positive electrode active material of the present invention as measured by XPS can be from 0.7 atomic% to 3.3 atomic%, specifically from 0.7 atomic% to 3.0 atomic%, more specifically from 1.0 atomic% to 2.0 atomic%.

[0092] In this invention, because a highly thermally stable titanium-containing coating is formed on the surface of single-particle lithium nickel oxide particles, and the titanium (Ti) content meets the aforementioned range, the high-temperature storage characteristics of the positive electrode active material can be further improved. Specifically, when the titanium (Ti) content is 0.7 atomic% or higher, excellent surface durability can be ensured, while when the titanium (Ti) content is 3.3 atomic% or lower, the increase in initial resistance and the decrease in capacity of the positive electrode active material due to excessive titanium (Ti) can be prevented.

[0093] In addition, in the positive electrode active material of the present invention, based on the total amount of the positive electrode active material, the content of the first coating and the second coating can be from 2.3% to 2.5% by weight, and specifically from 2.35% to 2.5% by weight.

[0094] When the total amount of the first and second coatings meets the above-mentioned range, the high thermal safety of the positive electrode active material can be ensured, and the effects of improving high-temperature life characteristics and resistance increase rate can be obtained.

[0095] Furthermore, the weight ratio of the first coating to the second coating may be from 1:0.04 to 1:0.1, specifically, the weight ratio of the first coating to the second coating may be from 1:0.04 to 1:0.09.

[0096] When the ratio of the first coating to the second coating meets the above-mentioned range, the high thermal safety of the positive electrode active material can be ensured, and the effects of improving high-temperature life characteristics and resistance increase rate can be obtained.

[0097] That is, when the weight ratio of the second coating to the first coating is 0.04 or more, the second coating can be discontinuously distributed on the surface of the first coating to ensure thermal stability, while when the weight ratio of the second coating to the first coating is 0.1 or less, the effect of increased initial resistance and reduced capacity caused by residual unreacted Ti can be prevented.

[0098] The average particle size (D) of the positive electrode active material of the present invention, including the first coating and the second coating, is... 50 The thickness can range from 5.0 μm to 7.0 μm, specifically from 5.0 μm to 6.5 μm.

[0099] Furthermore, the BET specific surface area of ​​the positive electrode active material of the present invention, including the first coating and the second coating, can be 0.3 m². 2 / g to 0.5 m 2 / g, preferably 0.35 m 2 / g to 0.50 m 2 / g.

[0100] If the average particle size (D) of the positive electrode active material of the present invention 50 When the specific surface area of ​​the positive electrode active material and the BET surface area meet the above-mentioned range, the contact interface with the electrolyte decreases as the specific surface area of ​​the positive electrode active material decreases. As a result, side reactions can be reduced and thermal stability improved. Therefore, lithium secondary batteries with excellent thermal stability, reduced gas generation, and improved capacity characteristics can be realized.

[0101] When the heat flux of the positive electrode active material of the present invention is measured by differential scanning calorimetry (DSC), the maximum heat flux peak appears in the temperature range of 220°C to 235°C, and the heat flux measured by differential scanning calorimetry (DSC) can be less than 11 W / g.

[0102] As described above, since the positive electrode active material of the present invention can ensure excellent thermal stability by reducing the heat flux, as confirmed by the heat flux peak, to below 11 W / g, the risk of explosion can be reduced even when the internal temperature of the battery rises due to overcharging or other reasons. Conversely, since most positive electrode active materials without a coating having a composition like that of the present invention have a heat flux greater than 11 W / g as measured by differential scanning calorimetry (DSC), an explosion may occur when the internal temperature of the battery rises due to overcharging or other reasons, as the heat flux may increase rapidly.

[0103] As described above, since the single-particle form of lithium nickel oxide used in the core part of the positive electrode active material of the present invention is prepared by sintering at a higher temperature than that of conventional polycrystalline lithium nickel oxide, high density improvement can be achieved. However, single-particle form of lithium nickel oxide has the disadvantage of low thermal stability due to its high Ni content. However, in the present invention, a first coating containing Al and Co is formed on the lithium nickel oxide particles, and the coating contains oxygen with a binding energy higher than that of Ni. 3+ A second coating of a heterogeneous element (i.e., Ti) with high thermal stability of about 0.6 eV is formed as a discontinuous distribution on the first coating. This can suppress oxygen desorption of the positive electrode active material, thereby improving thermal safety, and at the same time suppress side reactions with the electrolyte, thereby improving cycle characteristics and high rate performance.

[0104] [Preparation method of positive electrode active material]

[0105] This invention provides a method for preparing a positive electrode active material, which includes the following steps: Prepare transition metal precursors containing nickel (Ni), cobalt (Co), and manganese (Mn), with nickel content exceeding 70 mol% in all metal elements; A transition metal precursor is mixed with a lithium-containing raw material and sintered once to form a lithium nickel oxide. Lithium nickel oxide is mixed with aluminum and cobalt precursors and then sintered twice to form a first coating containing a coating element M1 (M1 being at least one selected from Ni, Co, and Al) on the lithium nickel oxide; and The lithium nickel oxide with the first coating is mixed with a titanium precursor and sintered three times to form a second coating containing coating element M2 (M2 is Ti) on the surface of the first coating.

[0106] The following section will describe in more detail each step of the preparation method for the positive electrode active material.

[0107] (A) Preparation of transition metal precursors

[0108] The preparation method of the positive electrode active material of the present invention may include preparing a transition metal precursor containing nickel (Ni), cobalt (Co) and manganese (Mn) with the nickel (Ni) content being more than 70 mol% of the total metal content (step (A)).

[0109] Transition metal precursors can be represented by compounds of formula 2 below.

[0110] [Equation 2]

[0111] Ni x Co y Mn zM 3 q (OH)2

[0112] In Equation 2, M 3 It can be at least one selected from the group consisting of Mn, Al, Zr, W, Ti, Mg, Ca, and Sr, and 0.7 ≤ x ≤ 1.0, 0 <y≤0.3,0<z<0.3,0≤q≤0.2。

[0113] (B) Preparation of lithium nickel oxide particles

[0114] In addition, the method for preparing the positive electrode active material of the present invention can prepare a lithium nickel oxide in the form of a single primary particle or in the form of an aggregate of 30 or fewer primary particles by mixing the transition metal precursor prepared in step (A) with a lithium-containing raw material and sintering it once (step (B)).

[0115] The molar ratio of all transition metals contained in the transition metal precursor to lithium contained in the lithium-containing raw material can be from 1:1.01 to 1:1.03, specifically from 1:1.01 to 1:1.02.

[0116] If lithium-containing raw materials are mixed within the above range, capacity reduction and separation of positive electrode active material particles after sintering (causing agglomeration of positive electrode active material) can be prevented because it can prevent capacity reduction of positive electrode active material and the large amount of unreacted lithium that may remain as by-products.

[0117] The lithium-containing raw material may include at least one selected from lithium hydroxide hydrate, lithium carbonate and lithium hydroxide, specifically, it may be lithium hydroxide hydrate, and more specifically, it may be LiOH·H2O.

[0118] When lithium hydroxide hydrate is used as a lithium-containing feedstock, the reactivity between the lithium-containing feedstock and the precursor with a high nickel atom fraction in the metal element can be improved.

[0119] A single sintering process can be carried out at a temperature of 800°C to 890°C, specifically 800°C to 850°C. Within this temperature range, a single sintering process can produce lithium-nickel oxide particles with a single-particle form and a basic layered structure.

[0120] Primary sintering can be carried out in an oxygen atmosphere. For example, primary sintering can be carried out in an oxygen atmosphere containing more than 90% by volume, specifically more than 95% by volume, of oxygen. Under these conditions, a primary sintering product with a structurally stable phase can be formed.

[0121] A single sintering process can last from 11 to 15 hours. Specifically, sintering can last from 11 to 13 hours, or more specifically, 12 hours. When the sintering time is within the above range, sintering can proceed well, with no deviation at each sintering position, that is, sintering can be carried out uniformly.

[0122] The BET specific surface area of ​​lithium-nickel oxides obtained through a single sintering process can reach 2.0 m². 2 / g to 6.0 m 2 / g, preferably 2.2 m 2 / g to 4.0 m 2 / g.

[0123] Furthermore, lithium-nickel oxides obtained through a single sintering process can have an average particle size (D... 50 The average particle size (D) of lithium nickel oxides is greater than 1.0 μm. 50 The particle size can be from 1.0 μm to 8.0 μm, more specifically, from 4.0 μm to 8.0 μm.

[0124] Furthermore, the D of the lithium nickel oxide of the present invention min It can be above 0.5 μm, for example, it can be controlled within the range of 0.5 μm to 3.0 μm, specifically 1.0 μm to 3.0 μm.

[0125] As described above, in this invention, due to the increase in the average particle size (D) of lithium nickel oxides... 50 ) and D min By reducing the amount of fine particles, the specific surface area of ​​the positive electrode active material can be reduced, thereby increasing energy density and improving thermal stability. Therefore, when this positive electrode active material is used in large cylindrical batteries, excellent thermal stability, reduced gas generation, and low initial resistance characteristics can be achieved.

[0126] The lithium nickel oxide of the present invention has D max The diameter can be from 12 μm to 20 μm, preferably from 12 μm to 16 μm, and more preferably from 12 μm to 15 μm. If the D of lithium nickel oxides... max Meeting the above ranges improves electrode density, thus preventing a decrease in energy density. Furthermore, since lithium mobility can be improved by preventing an increase in lithium migration paths within the particles, an increase in resistance can be suppressed. Therefore, excellent resistance and capacity characteristics can be ensured.

[0127] (C) Forming a first coating on the surface of nickel oxide particles

[0128] Furthermore, the method for preparing the positive electrode active material of the present invention may include the following steps: mixing lithium nickel oxide particles, which are the primary sintering products prepared in step (B), with aluminum precursor and cobalt precursor, and performing secondary sintering, thereby forming a first coating containing coating element M1 (M1 is at least one selected from the group consisting of Ni, Co and Al) on the lithium nickel oxide particles (step (C)).

[0129] Since the coating containing aluminum-rich Li-Al-Co-O solid solution, Li-Al-O solid solution and cobalt-rich Li-Co-O solid solution is formed on the surface of lithium nickel oxide particles by step (C), the surface durability is improved, and thus the side reactions between the positive electrode active material and the electrolyte can be effectively suppressed.

[0130] The aluminum precursor can be at least one selected from Al(OH)3, Al2O3, AlF3, AlBr3, AlPO4, AlCl3, Al(NO)3, Al(NO3)3·9H2O, Al2(SO4)3·H2O, Al(H2PO4)3, C2H5O4Al, Al(SO)4, NaAlO2, Al2CoO4, LaAlO3, and MgAl2O4.

[0131] In addition, the cobalt precursor may include at least one selected from Co(OH)2 and Co3O4.

[0132] The first coating can be continuously applied to the lithium nickel oxide with a uniform thickness, or it can be distributed on a portion of the surface of the lithium nickel oxide. Preferably, the first coating can be continuously applied to the lithium nickel oxide.

[0133] The first coating may include Al(OH)3, Al2O3 or Co3O4, specifically Al2O3 and Co3O4.

[0134] The lithium nickel oxide particles, aluminum precursor and cobalt precursor, which are the primary sintering products, can be mixed in a ratio of 100:0.1 mol% to 0.3 mol%:2.0 mol% to 3.0 mol%.

[0135] When lithium nickel oxide particles and aluminum / cobalt precursors are mixed within the aforementioned range, an aluminum / cobalt-containing coating capable of achieving excellent high-temperature lifetime characteristics can be formed on the lithium nickel oxide. Simultaneously, the amount of unreacted transition metal byproducts after sintering can be reduced. Consequently, the capacity reduction of the cathode active material can be prevented by suppressing the separation of cathode active material particles (cathode active material agglomeration). In other words, if the amount of aluminum precursor is 0.1 mol% or more and the amount of cobalt precursor is 2.0 mol% or more, the degradation of high-temperature lifetime characteristics can be prevented by forming a uniform and continuous first coating on the lithium nickel oxide. Furthermore, if the amount of aluminum precursor is 0.3 mol% or less and the amount of cobalt precursor is 3.0 mol% or less, the decrease in rolling density or the increase in initial resistance can be avoided by preventing the residue or increase of unreacted aluminum in the first coating.

[0136] Secondary sintering can be carried out at a temperature of 600℃ to 790℃, specifically at a temperature of 700℃ to 790℃.

[0137] During secondary sintering within the aforementioned temperature range, the primary sintering product recrystallizes to form lithium nickel oxides with good structural stability and suitable crystal size. Simultaneously, a first coating layer with uniform thickness can be continuously applied to the lithium nickel oxide.

[0138] In particular, because the aluminum precursor has a low melting point, aluminum diffuses uniformly onto the surface of the lithium nickel oxide particles during sintering within the aforementioned sintering temperature range, thereby forming a first coating of uniform thickness. Therefore, the capacity reduction of the positive electrode active material can be suppressed.

[0139] Secondary sintering can be carried out in an oxygen atmosphere. For example, secondary sintering can be carried out in an oxygen atmosphere containing more than 90% by volume, specifically more than 95% by volume, of oxygen.

[0140] Secondary sintering can be carried out for 10 to 15 hours, specifically 11 to 13 hours. In this case, secondary sintering is performed while reducing the oxygen concentration according to the sintering time. When the secondary sintering time is within the above range, sintering can proceed well without deviation at each sintering position, that is, sintering can be carried out uniformly.

[0141] (D) Formation of the second coating

[0142] The method for preparing the positive electrode active material of the present invention may include the following steps: mixing the lithium nickel oxide with a first coating prepared in step (C) with a titanium precursor and performing three sintering processes to form a second coating containing coating element M2 (M2 is Ti) on the surface of the first coating (step (D)).

[0143] The second coating containing titanium dioxide can be discontinuously distributed on the surface of the first coating through three sintering processes. Specifically, through three sintering processes, the first coating containing Li-Al-Ti-O solid solution and Li-Ti-O solid solution can be discontinuously distributed on the surface of lithium nickel oxide particles. As a result, by controlling the Ni fraction on the surface, thermal stability and surface durability can be enhanced, and the decrease in charging capacity can be suppressed.

[0144] The titanium precursor may include at least one selected from titanium dioxide (TiO2), titanium butoxide, titanium isopropoxide, titanium chloride, titanium tetraisopropoxide, and tetra-n-butyl titanate, specifically titanium dioxide.

[0145] Furthermore, the mixing ratio of the lithium nickel oxide particles with the first coating to the titanium precursor can be from 100:0.1 mol% to 100:0.3 mol%, specifically, the mixing ratio can be from 100:0.1 mol% to 100:0.2 mol%.

[0146] When lithium nickel oxide particles with a first coating and titanium precursor are mixed within the above-mentioned range, the rapid increase in the size of titanium dioxide (TiO2) crystals can be suppressed, and defects such as increased surface resistance caused by unreacted titanium remaining as a byproduct can be prevented.

[0147] In addition, the third sintering can be carried out at a temperature of 600°C to 700°C, specifically at a temperature of 650°C to 700°C.

[0148] When the sintering temperatures of the third sintering stage meet the aforementioned range, by forming a titanium-containing coating of appropriate concentration on the surface of the positive electrode active material containing the first coating, oxygen desorption can be suppressed, thereby improving the thermal stability of the positive electrode active material. In other words, when the sintering temperature of the third sintering stage is below 700°C, oxygen desorption on the surface of the positive electrode active material is suppressed by preventing the second coating from being applied to the entire surface of the positive electrode active material and controlling the discontinuous distribution of the second coating on the surface of the first coating, thus improving the thermal stability of the positive electrode active material. Furthermore, by preventing titanium doping and diffusion into the core portion, the decrease in positive electrode capacity can be prevented, and the increase in resistance can be suppressed.

[0149] The three sintering processes can last from 3 to 10 hours, specifically from 3 to 8 hours, and more specifically from 3 to 6 hours. When the three sintering times are within the above range, a second coating distribution effect can be obtained, with no deviation at each sintering position.

[0150] Since conventional single-particle lithium nickel oxide particles are sintered at higher temperatures than traditional polycrystalline lithium nickel oxides, improved density can be achieved. However, due to the high Ni concentration in single-particle lithium nickel oxides, their thermal stability is low, potentially leading to oxygen desorption and side reactions between the electrolyte and the cathode material surface, resulting in exothermic reactions. Therefore, to address these issues, this invention forms a first coating containing Al and Co on the single-particle lithium nickel oxide particles, and further forms a Ni containing a specific concentration of Ni with a binding energy ratio higher than that of oxygen on the first coating. 3+ The coating element, approximately 0.6 eV higher, acting as a second coating of the dissimilar element Ti, can suppress oxygen desorption, thereby improving the thermal safety of the positive electrode active material and inhibiting side reactions between the electrolyte and the surface of the positive electrode material. Therefore, batteries using this positive electrode active material can achieve high-temperature storage characteristics and resistance suppression.

[0151] [positive electrode]

[0152] The positive electrode of the present invention may include: a positive electrode current collector; and a layer of positive electrode material mixture disposed on at least one surface of the positive electrode current collector. In this case, the positive electrode material mixture layer may contain the aforementioned positive electrode active material.

[0153] The thickness of the positive current collector can typically range from 3 μm to 500 μm.

[0154] Fine irregularities can be formed on the surface of the positive electrode current collector to improve the adhesion of the positive electrode active material. For example, the positive electrode current collector can be used in various shapes, such as membranes, sheets, foils, meshes, porous bodies, foams, and nonwoven fabrics.

[0155] The positive electrode material mixture layer is disposed on at least one surface of the positive electrode current collector. Specifically, the positive electrode material mixture layer may be disposed on one or both surfaces of the positive electrode current collector.

[0156] To ensure sufficient capacity of the positive electrode active material, the content of the positive electrode active material in the positive electrode material mixture layer can be 80% to 90% by weight.

[0157] In addition to the aforementioned positive electrode active material, the positive electrode material mixture layer may also contain conductive agents and / or binders.

[0158] Specifically, there are no particular restrictions on the conductive agent, as long as it is conductive and does not cause chemical changes in the battery. For example, the following can be used: carbon black, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermally cracked carbon black; graphite powder, such as natural graphite, artificial graphite, or graphite with a fully developed crystal structure; conductive fibers, such as carbon fibers or metal fibers; conductive powders, such as fluorocarbon powders, aluminum powder, and nickel powder; conductive whiskers, such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides, such as titanium oxide; or polyphenylene derivatives.

[0159] Based on the total weight of solids in the cathode material mixture layer, the amount of conductive agent added is typically 1% to 30% by weight.

[0160] In addition, the adhesive improves the adhesion between positive electrode active material particles and the adhesion between the positive electrode active material and the positive electrode current collector. Specific examples of adhesives can be: fluoropolymer adhesives including polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE); rubber adhesives including styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber, or styrene-isoprene rubber; cellulose adhesives including carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, or regenerated cellulose; polyol adhesives including polyvinyl alcohol; polyolefin adhesives including polyethylene or polypropylene; polyimide adhesives; polyester adhesives; and silane adhesives.

[0161] Based on the total weight of solids in the cathode material mixture layer, the amount of binder added can be from 1% to 30% by weight.

[0162] Furthermore, the positive electrode of the present invention as described above can be prepared according to methods for preparing positive electrodes known in the art. For example, the positive electrode can be prepared by coating a positive electrode current collector with a positive electrode slurry comprising a positive electrode active material, a binder and / or a conductive agent, and a solvent, followed by drying and calendering the coated positive electrode current collector. Alternatively, the positive electrode can also be prepared by mixing the positive electrode active material with optional binders and conductive agents to prepare a film, and then laminating the film onto the positive electrode current collector.

[0163] The solvent may include, for example, at least one selected from distilled water, N-methylpyrrolidone, ethanol, methanol and isopropanol, and may preferably include N-methylpyrrolidone for the purpose of dispersing the positive electrode active material, binder and / or conductive agent.

[0164] [Lithium-ion rechargeable battery]

[0165] Furthermore, the present invention may include a lithium secondary battery containing the positive electrode.

[0166] Specifically, the lithium secondary battery can provide a lithium secondary battery comprising the positive electrode, the negative electrode, a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte of the present invention.

[0167] In this case, since the positive electrode has already been explained above, its description will be omitted, and the other components will be explained below.

[0168] (1) Negative electrode

[0169] Next, we will explain the negative electrode.

[0170] The negative electrode may contain a negative electrode active material.

[0171] Various anode active materials used in the art, such as carbon-based anode active materials, silicon-based anode active materials, or mixtures thereof, can be used as anode active materials.

[0172] According to one embodiment, the negative electrode active material may include a carbon-based negative electrode active material. Various carbon-based negative electrode active materials used in the art can be used, such as graphite materials like natural graphite, artificial graphite, and Kish graphite; pyrolytic carbon, mesophase pitch-based carbon fibers, mesophase pitch, high-temperature sintered carbon such as petroleum or coal tar pitch-derived coke, soft carbon, and hard carbon. The shape of the carbon-based negative electrode active material is not particularly limited; materials of various shapes, such as irregular shapes, planar shapes, sheet-like shapes, spherical shapes, or fibrous shapes, can be used.

[0173] Preferably, at least one carbon-based negative electrode active material, either natural graphite or artificial graphite, can be used as the negative electrode active material, and natural graphite and artificial graphite can be used together to inhibit the peeling of the active material by enhancing the adhesion to the current collector.

[0174] According to another embodiment, the negative electrode active material can be used by including silicon-based negative electrode active materials together with carbon-based negative electrode active materials.

[0175] Silicon-based anode active materials may include, for example, those selected from metallic silicon (Si) and silicon oxide (SiO2). x, where 0 < x < 2), silicon carbide (SiC), and at least one of Si-Y alloys (where Y is an element selected from the group consisting of alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, transition metals, rare earth metals, and combinations thereof, and is not Si). The element Y can be selected from the group consisting of Mg, Ca, Sr, barium (Ba), radium (Ra), scandium (Sc), yttrium (Y), Ti, Zr, hafnium (Hf), (Rf), vanadium (V), niobium (Nb), tantalum (Ta), dubnium (Db), chromium (Cr), molybdenum (Mo), W, (Sg), technetium (Tc), rhenium (Re), (Bh), iron (Fe), lead (Pb), ruthenium (Ru), osmium (Os), (Hs), rhodium (Rh), iridium (Ir), palladium (Pd), platinum (Pt), copper (Cu), silver (Ag), gold (Au), zinc (Zn), cadmium (Cd), boron (B), Al, gallium (Ga), tin (Sn), indium (In), germanium (Ge), phosphorus (P), arsenic (As), antimony (Sb), bismuth (Bi), sulfur (S), selenium (Se), tellurium (Te), polonium (Po), and combinations thereof.

[0176] The negative electrode active material of the present invention may include at least one selected from carbon-based active materials and silicon-based active materials.

[0177] Specifically, the negative electrode of the present invention may include a carbon-based active material and a silicon-based active material.

[0178] In this case, the weight ratio of the silicon-based active material to the carbon-based active material may be from 1:99 to 30:70, specifically from 3:97 to 15:8:5. When the mixing ratio of the silicon-based active material and the carbon-based active material satisfies the above range, excellent cycle performance can be ensured because the volume expansion of the silicon-based active material is suppressed while improving the capacity characteristics.

[0179] The negative electrode may include a negative electrode current collector and a negative electrode material mixture layer provided on at least one surface of the negative electrode current collector. In this case, the negative electrode active material may be included in the negative electrode material mixture layer.

[0180] There is no specific limitation on the negative electrode current collector as long as it has high conductivity and does not cause chemical changes in the battery. Specifically, copper, stainless steel, aluminum, nickel, titanium, fired carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., and aluminum cadmium alloy can be used as the negative electrode current collector.

[0181] The thickness of the negative electrode current collector can generally be 3 μm to 500 μm.

[0182] Fine irregularities can be formed on the surface of the negative electrode 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 membranes, sheets, foils, meshes, porous bodies, foams, and nonwoven fabrics.

[0183] The negative electrode material mixture layer is disposed on at least one surface of the negative electrode current collector. Specifically, the negative electrode material mixture layer may be disposed on one or both surfaces of the negative electrode current collector.

[0184] To fully realize the capacity of the secondary battery while minimizing the impact of volume expansion / contraction on the battery, the content of the negative electrode active material in the negative electrode material mixture layer can be 60% to 99% by weight.

[0185] The thickness of the negative electrode material mixture layer can be from 5 μm to 500 μm, preferably from 5 μm to 100 μm.

[0186] In addition to silicon-based active materials, the anode material mixture layer may also contain conductive agents and / or binders.

[0187] Next, conductive agents are components used to further improve the conductivity of the negative electrode active material. These can be conductive materials that do not cause chemical changes in the battery, such as: carbon black (e.g., carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermally cracked carbon black); graphite powder (e.g., natural graphite, artificial graphite, or graphite with a well-developed crystal structure); conductive fibers (e.g., carbon fibers or metal fibers); conductive powders (e.g., fluorocarbon powder, aluminum powder, and nickel powder); conductive whiskers (e.g., zinc oxide whiskers and potassium titanate whiskers); conductive metal oxides (e.g., titanium oxide); or polyphenylene derivatives.

[0188] The content of the conductive agent in the negative electrode material mixture layer can be from 1% to 20% by weight. When the content of the conductive agent is within the above range, it is ideal to form an excellent conductive network while mitigating the increase in resistance caused by the binder.

[0189] Adhesives are components that facilitate the bonding between conductive agents, active materials, and current collectors. Adhesives may include: fluoropolymer adhesives comprising polyvinylidene fluoride or polytetrafluoroethylene; rubber adhesives comprising styrene-butadiene rubber, acrylonitrile-butadiene rubber, or styrene-isoprene rubber; cellulose adhesives comprising carboxymethyl cellulose, starch, hydroxypropyl cellulose, or regenerated cellulose; polyol adhesives comprising polyvinyl alcohol; polyolefin adhesives comprising polyethylene or polypropylene; polyimide adhesives; polyester adhesives; and silane adhesives.

[0190] The content of the binder in the negative electrode material mixture layer can be from 1% to 30% by weight. When the binder content is within the above range, the binder can minimize the problem of volume expansion of the active material by better binding the active material. At the same time, it can facilitate the dispersion of the binder during the preparation of the slurry for forming the negative electrode active material layer, and can improve the coatability and phase stability of the slurry.

[0191] A negative electrode can be prepared by coating a negative electrode current collector with a negative electrode slurry, which includes a negative electrode active material and optionally a binder, a conductive agent, and a negative electrode slurry, using a solvent, followed by drying and calendering the coated negative electrode current collector. Alternatively, a negative electrode can be prepared by mixing the negative electrode active material with optional binders and conductive agents to prepare a membrane, and then laminating the membrane onto the negative electrode current collector.

[0192] The solvent for forming the negative electrode slurry may include, for example, at least one selected from distilled water, N-methylpyrrolidone, ethanol, methanol and isopropanol, and distilled water may preferably be included in order to facilitate the dispersion of the negative electrode active material, binder and / or conductive agent.

[0193] (2) Non-aqueous electrolytes

[0194] The non-aqueous electrolyte used in this invention can be any non-aqueous electrolyte that can be used in lithium secondary batteries, such as organic liquid non-aqueous electrolyte, inorganic liquid non-aqueous electrolyte, solid polymer non-aqueous electrolyte, gel polymer non-aqueous electrolyte, solid inorganic non-aqueous electrolyte or molten inorganic non-aqueous electrolyte, but there is no particular limitation on its type.

[0195] Specifically, the non-aqueous electrolyte may contain organic solvents and lithium salts.

[0196] 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, the following solvents can be used as the organic solvent: ester solvents, such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents, such as dibutyl ether or tetrahydrofuran; ketone solvents, such as cyclohexanone; aromatic 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), and propylene carbonate (PC); alcohol solvents, such as ethanol and isopropanol; nitriles, such as R-CN (wherein R is a straight-chain, branched, or cyclic C2-C20 hydrocarbon group, and may contain 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 more preferably, 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., methyl ethyl carbonate, dimethyl carbonate or diethyl carbonate) that can improve the charge / discharge performance of lithium-ion batteries are preferred.

[0197] Lithium salts can be used without particular limitation, as long as they are compounds capable of providing lithium ions for lithium secondary batteries. Specifically, LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2 can be used as lithium salts. Lithium salts can be used in concentrations ranging from 0.1 M to 5.0 M, preferably from 0.1 M to 3.0 M. If the concentration of the lithium salt is within the above range, excellent performance of the non-aqueous electrolyte can be obtained because the non-aqueous electrolyte can have suitable conductivity and viscosity, and lithium ions can move efficiently.

[0198] In order to suppress battery expansion at high temperatures, improve battery life characteristics, suppress battery capacity reduction, and improve battery discharge capacity, in addition to the above-mentioned non-aqueous electrolyte components, additives may also be included in the non-aqueous electrolyte. Examples of additives may include at least one selected from: cyclic carbonate compounds, such as vinylene carbonate (VC) and vinyl ethylene carbonate (VEC); halogenated carbonate compounds, such as fluoroethylene carbonate (FEC); at least one sulfonyl lactone compound selected from 1,3-propane sulfonyl lactone (PS), 1,4-butane sulfonyl lactone, ethylene sulfonyl lactone, 1,3-propene sulfonyl lactone (PRS), 1,4-butene sulfonyl lactone and 1-methyl-1,3-propene sulfonyl lactone; sulfate esters or salts, such as ethylene sulfate, trimethylene sulfate and methyltrimethyl sulfate; phosphate esters or salts or phosphites or salts; borate esters or salts, such as tetraphenylborate, difluorooxalate borate (LiODFB) or lithium dioxalate borate; benzene compounds; amine compounds; silane compounds, such as tetravinylsilane; and lithium salt compounds, such as LiPO2F2 or LiBF4.

[0199] Two or more compounds can be used together as additives to prevent side reactions in the battery. Based on the total weight of the non-aqueous electrolyte, the content of the additives can be from 0.01% by weight to 20% by weight, specifically from 0.05% by weight to 10% by weight.

[0200] (3) Diaphragm

[0201] The separator separates the negative and positive electrodes and provides a path for the movement of lithium ions. Any separator can be used without particular limitation, as long as it is generally used in lithium secondary batteries. In particular, separators with high moisture retention for non-aqueous electrolytes and low impedance for the transport of non-aqueous electrolyte ions can be used.

[0202] Specifically, as the separator, 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, and ethylene / methacrylate copolymers), or laminated structures of two or more layers can be used. Alternatively, typical porous nonwoven fabrics can be used, such as nonwoven fabrics formed from high-melting-point glass fibers or polyethylene terephthalate fibers. Furthermore, coated separators containing 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.

[0203] The shape of the lithium secondary battery of the present invention is not particularly limited, but cylindrical, prismatic, pouch or coin-shaped batteries made of cans can be used.

[0204] In addition, the lithium secondary battery of the present invention can be used not only as a battery cell for powering small devices such as mobile phones, laptops and digital cameras, but also as a unit cell in medium and large battery modules that include multiple battery cells, such as hybrid electric vehicles (HEVs).

[0205] Therefore, according to another embodiment of the present invention, a battery module including the lithium secondary battery as a unit cell and a battery pack including the battery module are provided.

[0206] Battery modules or battery packs can be used as a power source for at least one medium to large-sized device, including: power tools; electric vehicles, including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or energy storage systems.

[0207] The present invention will be described in detail below with reference to specific embodiments. However, the present invention may be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these exemplary embodiments are provided to make this description sufficiently complete and to fully convey the scope of this disclosure to those skilled in the art.

[0208] Example

[0209] [Preparation of positive electrode active materials]

[0210] Example 1.

[0211] (Single sintering)

[0212] Average particle size (D) 50 Its thickness is 5.6 μm and its specific surface area (BET) is 2.26 m². 2 / g of transition metal precursor (Ni 0.95 Co 0.03 Mn 0.02 LiOH)2 and lithium-containing raw material (LiOH·H2O) are mixed to make the molar ratio of Li:transition metal (Ni+Co+Mn) 1.03:1. Then, the mixture is sintered at 850°C for 12 hours in an atmosphere containing more than 90% by volume oxygen to prepare an average particle size (D). 50 Lithium-nickel oxides (Li(Ni)) with a thickness of 5.6 μm 0.95 Co 0.03 Mn 0.02 O2).

[0213] (Secondary sintering)

[0214] Subsequently, lithium nickel oxides, Al2O3, and Co3O4, which were the primary sintering products, were mixed in a ratio of 100:0.2:2.0 mol%, and subjected to a secondary sintering at 700°C for 10 hours to prepare the secondary sintering product (Li(Ni)). 0.928 Mn 0.02 Co 0.05 Al 0.002 )O2), wherein a first coating containing Al2O3 and Co3O4 is continuously coated on a lithium nickel oxide.

[0215] (Triple sintering)

[0216] Then, the secondary sintering product and titanium dioxide were mixed at a ratio of 100:0.12 mol%, and sintered three times at 600℃ for 5 hours to prepare a second coating discontinuously distributed positive electrode active material on the surface of the first coating. The surface of the prepared positive electrode active material was observed by scanning electron microscopy (SEM), and the results are as follows. Figure 1 and Figure 2 As shown.

[0217] The average particle size (D) of the obtained positive electrode active material 50 The micrometer diameter (μm) is 5.6 μm, and the specific surface area (BET) is 0.49 m². 2 / g, the total amount of the first and second coatings is 2.4% by weight, the weight ratio of the first coating to the second coating is 1:0.04, and the average particle size (D) of the titanium dioxide (TiO2) contained in the second coating is... 50 The wavelength is 50 nm, and the content of titanium dioxide (TiO2) is 1000 ppm based on the total amount of positive electrode active material.

[0218] Example 2.

[0219] (Single sintering)

[0220] Average particle size (D) 50 Its thickness is 5.0 μm and its specific surface area (BET) is 3.2 m². 2 / g of transition metal precursor (Ni 0.95 Co 0.03 Mn 0.02 LiOH)2 and lithium-containing raw material (LiOH·H2O) are mixed to make the molar ratio of Li:transition metal (Ni+Co+Mn) 1.03:1. Then, the mixture is sintered at 830°C for 12 hours in an atmosphere containing more than 90% by volume oxygen to prepare an average particle size (D). 50 Lithium-nickel oxides (Li(Ni)) with a thickness of 5.0 μm 0.95 Co 0.03 Mn 0.02 O2).

[0221] (Secondary sintering)

[0222] Subsequently, lithium nickel oxides, Al2O3, and Co3O4, which were the primary sintering products, were mixed in a ratio of 100:0.2:2.0 mol%, and subjected to a secondary sintering at 700°C for 10 hours to prepare the secondary sintering product (Li(Ni)). 0.928 Mn 0.02 Co 0.05 Al 0.002 )O2), wherein a first coating containing Al2O3 and Co3O4 is continuously coated on a lithium nickel oxide.

[0223] (Triple sintering)

[0224] Then, the secondary sintering product and titanium dioxide were mixed at a ratio of 100:0.24 mol%, and sintered three times at 600°C for 5 hours to prepare a positive electrode active material with a second coating discontinuously distributed on the surface of the first coating.

[0225] The average particle size (D) of the obtained positive electrode active material 50 The micrometer diameter (μm) is 5.8 μm, and the specific surface area (BET) is 0.41 m². 2 / g, the total amount of the first and second coatings is 2.5% by weight, the weight ratio of the first coating to the second coating is 1:0.09, and the average particle size (D) of the titanium dioxide (TiO2) contained in the second coating is... 50 The wavelength is 60 nm, and the content of titanium dioxide (TiO2) is 2000 ppm based on the total amount of positive electrode active material.

[0226] Example 3.

[0227] (Triple sintering)

[0228] The secondary sintering product prepared in Example 2 was mixed with titanium dioxide at a ratio of 100:0.24 mol%, and sintered three times at 700°C for 5 hours to prepare a positive electrode active material with a second coating discontinuously distributed on the surface of the first coating.

[0229] The average particle size (D) of the obtained positive electrode active material 50 The micrometer diameter (μm) is 5.8 μm, and the specific surface area (BET) is 0.40 m². 2 / g, the total amount of the first and second coatings is 2.5% by weight, the weight ratio of the first coating to the second coating is 1:0.10, and the average particle size (D) of the titanium dioxide (TiO2) contained in the second coating is... 50 The wavelength is 60 nm, and the content of titanium dioxide (TiO2) is 2000 ppm based on the total amount of positive electrode active material.

[0230] [Preparation of Secondary Batteries]

[0231] Example 4.

[0232] (Positive electrode preparation)

[0233] The positive electrode active material, conductive agent (carbon black), and binder (polyvinylidene fluoride) prepared in Example 1 were mixed in NMP solvent at a weight ratio of 97.5:1.15:1.35 to prepare a positive electrode slurry composition. The positive electrode slurry composition was coated onto an Al current collector with a thickness of 12 μm, dried, and then rolled to prepare the positive electrode.

[0234] (Preparation of secondary batteries)

[0235] Then, the negative electrode active material (natural graphite), conductive agent (carbon black), and binder (SBR+CMC) are mixed in water at a weight ratio of 95:1.5:3.5 to prepare a negative electrode slurry composition. The negative electrode slurry composition is then coated onto a copper current collector, dried, and rolled to prepare the negative electrode.

[0236] The prepared positive and negative electrodes are stacked together with a porous polyethylene separator, the stack is placed in a battery case, and a non-aqueous electrolyte (1 M LiPF6, with a volume ratio of ethylene carbonate (EC): dimethyl carbonate (DMC): ethyl methyl carbonate (EMC) of 3:4:3) is injected to prepare a lithium secondary battery.

[0237] Example 5.

[0238] Except that the positive electrode active material prepared in Example 2 is used instead of the positive electrode active material prepared in Example 1, the positive electrode and the lithium secondary battery containing the positive electrode are prepared in the same manner as in Example 4.

[0239] Example 6.

[0240] Except that the positive electrode active material prepared in Example 3 is used instead of the positive electrode active material prepared in Example 1, the positive electrode and the lithium secondary battery containing the positive electrode are prepared in the same manner as in Example 4.

[0241] Comparative Example 1.

[0242] (Preparation of positive electrode active materials)

[0243] (Single sintering)

[0244] Average particle size (D) 50 The transition metal precursor (Ni) has a thickness of 5.6 μm. 0.95 Co 0.03 Mn 0.02Lithium-nickel oxide (Li(Ni)2) and lithium-containing raw material (LiOH·H2O) are mixed to achieve a Li:transition metal (Ni+Co+Mn) molar ratio of 1.03:1. The mixture is then sintered at 850°C for 12 hours in an atmosphere containing more than 90% by volume oxygen to prepare lithium-nickel oxide (Li(Ni)2). 0.95 Co 0.03 Mn 0.02 O2, average particle size (D) 50 Micrometer diameter (μm): 5.6 μm, Specific surface area (BET): 2.26 m² 2 / g).

[0245] (Secondary sintering)

[0246] Subsequently, lithium nickel oxide particles, Al2O3, and Co3O4, which were the products of the first sintering, were mixed in a ratio of 100:0.2:2.0 mol%, and subjected to a second sintering at 700 °C for 10 hours to prepare the positive electrode active material (Li(Ni) 0.928 Mn 0.02 Co 0.05 Al 0.002 )O2), wherein a first coating containing Al2O3 and Co3O4 is continuously coated on a lithium nickel oxide.

[0247] (Positive electrode preparation)

[0248] The above-prepared positive electrode active material, conductive agent (carbon black), and binder (polyvinylidene fluoride) were mixed in NMP solvent at a weight ratio of 97.5:1.15:1.35 to prepare a positive electrode slurry composition. The positive electrode slurry composition was then coated onto an Al current collector with a thickness of 12 μm, dried, and then rolled to prepare the positive electrode.

[0249] (Preparation of secondary batteries)

[0250] In addition to using the positive electrode prepared above, a lithium secondary battery was prepared in the same manner as in Example 4.

[0251] Compare Example 2.

[0252] (Preparation of positive electrode active materials)

[0253] (Single sintering)

[0254] Average particle size (D) 50 The transition metal precursor (Ni) has a thickness of 5.0 μm. 0.95 Co 0.03 Mn 0.02Lithium-nickel oxide (Li(Ni)2) and lithium-containing raw material (LiOH·H2O) are mixed to achieve a Li:transition metal (Ni+Co+Mn) molar ratio of 1.03:1. The mixture is then sintered at 830°C for 12 hours in an atmosphere containing more than 90% by volume oxygen to prepare lithium-nickel oxide (Li(Ni)2). 0.95 Co 0.03 Mn 0.02 O2, average particle size (D) 50 Micrometer diameter (μm): 5.0 μm, Specific surface area (BET): 3.2 m² 2 / g).

[0255] (Secondary sintering)

[0256] Subsequently, lithium nickel oxide, Al2O3, and Co3O4, which were the products of the first sintering, were mixed in a ratio of 100:0.2:2.0 mol%, and subjected to a second sintering at 700°C for 5 hours to prepare the positive electrode active material (Li(Ni) 0.928 Mn 0.02 Co 0.05 Al 0.002 )O2), wherein a first coating containing Al2O3 and Co3O4 is continuously coated on a lithium nickel oxide.

[0257] (Positive electrode preparation)

[0258] The above-prepared positive electrode active material, conductive agent (carbon black), and binder (polyvinylidene fluoride) were mixed in NMP solvent at a weight ratio of 97.5:1.15:1.35 to prepare a positive electrode slurry composition. The positive electrode slurry composition was then coated onto an Al current collector with a thickness of 12 μm, dried, and then rolled to prepare the positive electrode.

[0259] (Preparation of secondary batteries)

[0260] In addition to using the positive electrode prepared above, a lithium secondary battery was prepared in the same manner as in Example 4.

[0261] Experimental Example

[0262] Experimental Example 1.

[0263] X-ray photoelectron spectroscopy (XPS) was performed on the second coating of the positive electrode active material prepared in Examples 1 to 3. The average titanium content in the second coating relative to the content of Ni, Co, Li, and oxygen (O) in the lithium nickel oxide and the titanium concentration reduction rate are calculated as follows: Figures 3 to 5 As shown.

[0264] XPS photoelectron spectroscopy (XPS) analysis was performed under XPS conditions (Thermo Fisher Scientific, X-ray source: Al-Kα (1486.6 eV); accelerating voltage: 1 kV, 300 W, energy resolution: approximately 1.0 eV, minimum analytical region: 400 micro, sputtering rate: 0.13 nm / min).

[0265] Figure 3 The figure shows the XPS results of the second coating of the positive electrode active material prepared in Example 1 of the present invention. Figure 4 The figure shows the XPS results of the second coating of the positive electrode active material prepared in Example 2. Figure 5 The figure shows the XPS results of the second coating of the positive electrode active material prepared in Example 3.

[0266] Specifically, refer to Figure 3 In Example 1, the outermost titanium content of the second coating of the positive electrode active material relative to the total amount of Ni, Co, Li and oxygen (O) contained in the lithium nickel oxide particles is about 3.0 atomic%. The average titanium content in the second coating is about 1.3 atomic%. Since the titanium concentration gradually decreases towards the interface between the first and second coatings, it can be considered that the titanium concentration at the interface between the first and second coatings is reduced by more than 50% compared with the titanium concentration in the second coating.

[0267] In addition, refer to Figure 4 In Example 2, the outermost titanium content of the second coating of the positive electrode active material, relative to the total amount of Ni, Co, Li, and oxygen (O) in the lithium nickel oxide particles, is approximately 3.2 atomic%. The average titanium content in the second coating is approximately 2.6 atomic%. Therefore, it can be considered that the titanium concentration at the interface between the first and second coatings is reduced by more than 50% compared to the titanium concentration in the second coating. In other words, for the positive electrode active material of Example 2 with a relatively high titanium precursor content, it can be considered that the titanium content in the second coating is slightly higher compared to the positive electrode active material of Example 1.

[0268] In addition, refer to Figure 5In Example 3, the titanium content of the outermost layer of the second coating of the positive electrode active material prepared relative to the total amount of Ni, Co, Li, and oxygen (O) contained in the lithium nickel oxide particles is approximately 2.8 atomic%. The average titanium content in the second coating is approximately 2.6 atomic%. However, it can be considered that the titanium concentration at the interface between the first and second coatings is reduced by approximately 40% compared to the titanium concentration in the second coating. In other words, for the positive electrode active material of Example 3, which was sintered three times at 700°C, it can be considered that the ratio of the titanium content in the second coating to the titanium content at the outermost layer of the second coating is slightly increased compared to the positive electrode active material of Example 2, which was sintered three times at 600°C.

[0269] Experimental Example 2. Evaluation of Fever (1)

[0270] The heat flow of the positive electrodes prepared in Examples 4 to 6 and the positive electrodes prepared in Comparative Examples 1 and 2 as a function of temperature was measured using a differential scanning calorimeter (manufactured by METTLER TOLEDO, model name: DSC3).

[0271] Specifically, the lithium secondary batteries prepared in Examples 4 to 6, as well as those prepared in Comparative Examples 1 and 2, were each charged to 4.25 V at a constant current of 0.1 C at 25°C. The positive electrodes were then separated. The separated positive electrodes were washed with dimethyl acetate and then immersed in 20 μL of electrolyte (1 M LiPF6, EC:DMC:EMC = 3:4:3 volume ratio). DSC analysis of the positive electrode active material was performed. The DSC analysis temperature range was 100°C to 400°C, with a heating rate of 10°C / min. For each positive electrode, at least three DSC measurements were performed to calculate the average value. The measurement results are shown in Table 1 below. Figure 6 As shown.

[0272] [Table 1]

[0273] Refer to Table 1 and Figure 6 It can be considered that the cathodes prepared in Examples 4 to 6 exhibit DSC exothermic peak intensities of less than 11 W / g, while the cathodes prepared in Comparative Examples 1 and 2 exhibit DSC exothermic peak intensities of greater than 11 W / g.

[0274] In other words, it can be considered that the maximum heat flux of the positive electrodes prepared in Examples 4 to 6 of the present invention is reduced by about 7% or more compared with the positive electrodes prepared in Comparative Examples 1 and 2. Based on these results, it can be concluded that by ensuring low heat flux, the positive electrode active material of the present invention exhibits excellent thermal stability even when the internal temperature of the battery rises due to overcharging or other reasons.

[0275] Experimental Example 3. Resistance Evaluation

[0276] The lithium secondary battery of Example 4 and the lithium secondary battery of Comparative Example 1 were each charged to 4.25 V at a constant current of 0.1 C at 25°C, and then each lithium secondary battery was discharged to 2.5 V at a constant current of 200 mAh / g to form a cycle, and 3 charge-discharge cycles were performed.

[0277] Subsequently, under constant current-constant voltage (CC-CV) charging conditions at 25°C, the lithium secondary battery was charged to 4.20 V at a constant current (CC) of 0.33 C. Then, pulse discharge was performed at a rate of 2.5 C at SOC levels of 95%, 80%, 50%, 20%, and 10%, and the voltage drop was measured for 10 seconds to obtain the initial resistance value. The results are as follows: Figure 7 As shown.

[0278] Reference Figure 7 For the lithium secondary battery of Example 4 of the present invention, it can be confirmed that the initial resistance is relatively lower compared with the lithium secondary battery of Comparative Example 1.

Claims

1. A positive electrode active material, comprising: A lithium-nickel oxide having a nickel content of 70 mol% or more in all metal elements except lithium; a first coating formed on the lithium-nickel oxide; and a second coating formed on the first coating. in, The first coating comprises a coating element M1, wherein M1 is at least one selected from the group consisting of nickel (Ni), cobalt (Co), and aluminum (Al). The second coating comprises a coating element M2, where M2 is titanium (Ti), and Based on the total content of Ni, Co, lithium (Li) and oxygen (O) in the lithium nickel oxide as measured by X-ray photoelectron spectroscopy (XPS), the content of titanium in the second coating as measured by XPS is from 0.7 atomic% to 3.3 atomic%.

2. The positive electrode active material according to claim 1, wherein, The lithium-nickel oxide is represented by Formula 1: [Formula 1] Li a Ni b Co c M ' d M '' e O2 In Equation 1, M ' It is manganese (Mn), aluminum (Al) or a combination thereof. M '' The element is selected from at least one element in the group consisting of Al, zirconium (Zr), tungsten (W), titanium (Ti), magnesium (Mg), calcium (Ca), and strontium (Sr), and 0.8 ≤ a ≤ 1.2, 0.7 ≤ b < 1.0, 0 <c<0.3,0<d<0.3,0≤e≤0.2。 3. The positive electrode active material according to claim 1, wherein, The lithium-nickel oxide is in the form of a single particle consisting of a primary particle, or in the form of a quasi-single particle as an aggregate of 30 or fewer primary particles.

4. The positive electrode active material according to claim 1, wherein, The average particle size (D) of the lithium nickel oxide 50 The thickness ranges from 1.0 μm to 8.0 μm.

5. The positive electrode active material according to claim 1, wherein, The first coating is continuously applied to the surface of the lithium nickel oxide.

6. The positive electrode active material according to claim 1, wherein, The first coating comprises Al2O3 and Co3O4.

7. The positive electrode active material according to claim 1, wherein, The second coating is discontinuously distributed on the surface of the first coating.

8. The positive electrode active material according to claim 1, wherein, The second coating comprises titanium dioxide (TiO2).

9. The positive electrode active material according to claim 8, wherein, The average particle size (D) of the titanium dioxide (TiO2) 50 The range is 20 nm to 150 nm.

10. The positive electrode active material according to claim 8, wherein, Based on the total amount of the positive electrode active material, the content of titanium dioxide (TiO2) is from 1000 ppm to 2000 ppm.

11. The positive electrode active material according to claim 1, wherein, Based on the total amount of the positive electrode active material, the content of the first coating and the second coating is 2.3% to 2.5% by weight.

12. The positive electrode active material according to claim 1, wherein, The weight ratio of the first coating to the second coating is from 1:0.04 to 1:0.

1.

13. The positive electrode active material according to claim 1, wherein, Based on the total content of Ni, Co, Li and oxygen (O) in the lithium nickel oxide as measured by XPS, the content of titanium in the second coating as measured by XPS is from 0.7 atomic% to 3.0 atomic%.

14. The positive electrode active material according to claim 1, wherein, The maximum heat flux of the positive electrode active material, as measured by differential scanning calorimetry (DSC), is below 11 W / g.

15. A method for preparing the positive electrode active material according to claim 1, the method comprising: Prepare transition metal precursors containing nickel (Ni), cobalt (Co), and manganese (Mn), with nickel content exceeding 70 mol% in all metal elements; The transition metal precursor is mixed with lithium-containing raw materials and sintered once to form lithium nickel oxide. The lithium nickel oxide is mixed with an aluminum precursor and a cobalt precursor and then sintered twice to form a first coating containing a coating element M1 on the lithium nickel oxide, wherein M1 is at least one selected from Ni, Co and aluminum (Al). as well as The lithium nickel oxide with the first coating is mixed with the titanium precursor and sintered three times to form a second coating containing coating element M2 on the surface of the first coating, where M2 is titanium (Ti).

16. The method according to claim 15, wherein, The transition metal precursor is represented by Equation 2: [Equation 2] Ni x What y Mn z M 3 q (OH)2 In Equation 2, M 3 The element is selected from at least one of the group consisting of manganese (Mn), aluminum (Al), zirconium (Zr), tungsten (W), titanium (Ti), magnesium (Mg), calcium (Ca), and strontium (Sr), and 0.7 ≤ x ≤ 1.0, 0 <y≤0.3,0<z<0.3,0≤q≤0.2。 17. The method according to claim 15, wherein, The first sintering is carried out at a temperature of 800°C to 890°C.

18. The method according to claim 15, wherein, The secondary sintering is carried out at a temperature of 600°C to 790°C.

19. The method according to claim 15, wherein, The three sintering processes are carried out at a temperature of 600°C to 700°C.

20. The method of claim 15, wherein, The molar ratio of the lithium nickel oxide with the first coating to the titanium precursor is from 100:0.1 to 100:0.

3.

21. A positive electrode for a lithium secondary battery, the positive electrode comprising the positive electrode active material of claim 1.

22. A lithium secondary battery comprising the positive electrode for a lithium secondary battery as described in claim 21.

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