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

Abstract

The present invention relates to: a cathode active material capable of implementing a battery with improved lifetime characteristics; and a cathode and a lithium secondary battery comprising same, the cathode active material comprising lithium nickel-based oxide particles in which the ratio of the number of moles of lithium to the total number of moles of metals excluding lithium is 0.010-0.500, wherein the ratio of the number of particles, in which crack A having lattice expansion occurring in a c-axis direction or crack B having a crystal plane pushed in an a-axis direction without lattice change in the c-axis direction is present, is 1.0%-10% on the basis of the total number of lithium nickel-based oxide particles.

Description

Cathode active material, a cathode including the same, and a lithium secondary battery

[0001] Cross-citation with related applications

[0002] This application claims the benefit of priority based on Korean Patent Application No. 10-2024-0177813 filed on December 3, 2024, and all contents disclosed in the document of said Korean Patent Application are incorporated herein as part of this specification.

[0003] Technology field

[0004] The present invention relates to a positive electrode active material for a lithium secondary battery, a positive electrode containing the same, and a lithium secondary battery.

[0005]

[0006] With the recent increase in technological development and demand for mobile devices and electric vehicles, the demand for secondary batteries as an energy source is rapidly increasing.

[0007] A lithium secondary battery generally consists of a positive electrode, a negative electrode, a separator, and an electrolyte, and the positive and negative electrodes include an active material capable of lithium ion intercalation and deintercalation.

[0008] Meanwhile, the cathode active material used in lithium secondary batteries generally has the form of spherical secondary particles formed by the aggregation of hundreds of submicron-sized fine primary particles. However, cathode active materials in the form of secondary particles have a problem in that the battery performance deteriorates as the secondary particles break down as the aggregated primary particles separate during repeated charging and discharging.

[0009] To address these issues, active development of single-particle cathode active materials is underway. Among single-particle cathode active materials, those composed solely of particles with a single-crystal structure (single-crystal cathode materials) possess a continuous crystal lattice without crystal plane boundaries within or outside the particles. This offers the advantages of reduced gas generation at crystal plane boundaries and fewer defects. However, single-crystal cathode materials have a problem with higher initial resistance compared to polycrystalline cathode materials, leading to issues with degraded capacity and lifespan characteristics in lithium-ion batteries containing them.

[0010] Meanwhile, when manufacturing electrodes and carrying out electrochemical reactions, phenomena such as gliding or cracking of crystal planes occur in an attempt to relieve stress caused by physical and chemical reactions. On the other hand, if crystal planes are gliding or cracking, they act as defects and can degrade the performance of the positive active material, so it is necessary to control the occurrence of gliding and cracking.

[0011]

[0012] The objective of the present invention is to provide a positive electrode active material capable of realizing a lithium secondary battery with improved lifespan characteristics, a positive electrode including the same, and a lithium secondary battery.

[0013]

[0014] To solve the above problem, the present invention provides a positive electrode active material, a positive electrode including the same, and a lithium secondary battery.

[0015]

[0016] (1) The present invention provides a positive electrode active material comprising lithium nickel-based oxide particles having a ratio of the number of moles of lithium to the total number of moles of metals excluding lithium of 0.010 or more and 0.500 or less, wherein the ratio of the number of particles having crack A in which lattice expansion occurs in the c-axis direction or crack B in which the crystal plane is pushed in the a-axis direction without lattice change in the c-axis direction is 1.0% or more and 10% or less relative to the total number of lithium nickel-based oxide particles.

[0017] (2) The present invention provides a positive electrode active material in which, in (1) above, the crack A is a portion in which grain expansion within the particle occurs, which is identified from the surface or cross-sectional SEM image of the positive electrode active material.

[0018] (3) The present invention provides a positive electrode active material in which, in (1) or (2), the crack A is a portion in which the interplanar distance of the (003) plane in the TEM image is greater than 1 nm and less than or equal to 100 nm.

[0019] (4) The present invention provides a positive electrode active material in any one of (1) to (3), wherein the crack B is a portion having a stepped structure with a step difference on the surface of the positive electrode active material or on the particle surface identified from a cross-sectional SEM image.

[0020] (5) The present invention provides a positive electrode active material in any one of (1) to (4), wherein the portion in which lattice expansion occurs in the c-axis direction is a portion that can be recovered.

[0021] (6) The present invention provides an anode active material in any one of (1) to (5), wherein the portion in which the crystal plane is pushed in the a-axis direction without lattice change in the c-axis direction is a portion that can be recovered.

[0022] (7) The present invention provides a positive electrode active material in which, in any one of (1) to (6), the ratio of the number of particles in which a change in the crystal plane occurs in a direction not parallel to the c-axis is 5% or less relative to the total number of lithium nickel-based oxide particles.

[0023] (8) The present invention provides a positive electrode active material in any one of (1) to (7), wherein the lithium nickel-based oxide particles have a nickel content of 60 mol% or more of the total metal excluding lithium.

[0024] (9) The present invention provides a positive electrode active material in any one of (1) to (8), wherein the lithium nickel-based oxide particles are in the form of single particles.

[0025] (10) In any one of (1) to (9) of the present invention, the lithium nickel-based oxide particles have an average particle size (D 50 Provides a positive electrode active material having a thickness of 1㎛ or more and 30㎛ or less.

[0026] (11) The present invention provides a positive electrode comprising a positive electrode active material according to any one of (1) to (10).

[0027] (12) The present invention provides a lithium secondary battery comprising a positive electrode according to (11) above.

[0028]

[0029] The positive electrode active material according to the present invention can improve the lifespan characteristics of a battery containing the same by suppressing side reaction phenomena with the electrolyte caused by the extraction of lithium ions within the positive electrode active material as a result of repeating the insertion and extraction processes of lithium ions, as well as gliding and cracking caused by repeated deformation.

[0030] The positive electrode and lithium secondary battery comprising the positive electrode active material according to the present invention have excellent lifespan characteristics.

[0031]

[0032] Figure 1 is a schematic diagram showing a clean particle without cracks, a particle with crack A, a particle with crack B, and a particle with crack C, respectively.

[0033] Figure 2 is a surface SEM image of the positive electrode active material of Example 1.

[0034] Figure 3 is a surface SEM image of the positive electrode active material of Example 2.

[0035] Figure 4 is a surface SEM image of the positive electrode active material of Example 3.

[0036] Figure 5 is a surface SEM image of the positive electrode active material of Comparative Example 1.

[0037] Figure 6 is a surface SEM image of the positive electrode active material of Comparative Example 2.

[0038] Figure 7 is a surface SEM image of the positive electrode active material of Comparative Example 3.

[0039] Figure 8 is a surface SEM image of the positive electrode active material of Comparative Example 4.

[0040] Figure 9 is a cross-sectional SEM image of the positive electrode active material of Example 1.

[0041] Figure 10 is a cross-sectional SEM image of the positive electrode active material of Example 2.

[0042] Figure 11 is a cross-sectional SEM image of the positive electrode active material of Example 3.

[0043] Figure 12 is a cross-sectional SEM image of the positive electrode active material of Comparative Example 1.

[0044] Figure 13 is a cross-sectional SEM image of the positive active material of Comparative Example 2.

[0045] Figure 14 is a cross-sectional SEM image of the positive electrode active material of Comparative Example 3.

[0046] Figure 15 is the result of TEM analysis of crack A present in the lithium nickel-based oxide particles of Example 1.

[0047]

[0048] Terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted in a meaning and concept consistent with the technical spirit of the invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe his invention.

[0049] In this specification, terms such as “comprising,” “comprising,” or “having” are intended to specify the existence of the implemented features, numbers, steps, components, or combinations thereof, and should be understood as not excluding in advance the existence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0050] In this specification, the term "on" means not only cases where one configuration is formed on the immediate upper surface of another configuration, but also cases where a third configuration is interposed between these configurations.

[0051] In this specification, "single-particle type positive active material" refers to a positive active material composed of 50 or fewer single-crystal particles, as opposed to a spherical secondary particle type positive active material formed by the aggregation of hundreds of primary particles manufactured by conventional methods. Specifically, in the present invention, the single-particle type positive active material may be a single single-crystal particle, or it may be in the form of aggregations of 2 to 50, 2 to 40, 2 to 30, 2 to 20, 2 to 15, 2 to 10, or 2 to 5 single-crystal particles. In this case, "primary particle" refers to the smallest unit of a particle recognized when the positive active material is observed through a scanning electron microscope.

[0052] In this specification, the average particle size (D 50) refers to the particle size at the 50% reference of the volume-cumulative particle size distribution of the positive electrode active material precursor, positive electrode active material, or lithium transition metal oxide powder. The above average particle size (D 50 ) can be measured using the laser diffraction method. For example, after dispersing the positive active material powder in a dispersion medium, it can be introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000), irradiated with ultrasound of about 28 kHz at an output of 60 W, obtained a volume cumulative particle size distribution graph, and then measured by determining the particle size corresponding to 50% of the volume cumulative amount.

[0053]

[0054] The present invention will be described in detail below.

[0055]

[0056] positive electrode active material

[0057] The present invention provides a positive electrode active material comprising lithium nickel-based oxide particles having a ratio of the number of moles of lithium to the number of moles of all metals excluding lithium of 0.01 or more and 0.5 or less, wherein, relative to the total number of lithium nickel-based oxide particles, the ratio of the number of particles having crack A in which lattice expansion occurs in the c-axis direction or crack B in which the crystal plane is pushed in the a-axis direction without lattice change in the c-axis direction is 1.0% or more and 10% or less.

[0058] The above lattice expansion refers to an increase in the interplanar distance between adjacent crystal planes (the size of the gap created by interlayer separation), and if the interlayer separation caused by lattice expansion is sufficiently large, grain expansion can be observed in the SEM image.

[0059] According to the present invention, the crack A is a portion where grain expansion within the particle occurs, as identified from the surface or cross-sectional SEM image of the positive electrode active material.

[0060] According to the present invention, the crack A is a portion in the TEM image where the interplanar distance of the (003) plane is greater than 1 nm and less than or equal to 100 nm. Here, the interplanar distance of the (003) plane is the size of the gap created by interlayer separation.

[0061] According to the present invention, the crack B is a portion in which a stepped structure having a step difference exists on the surface of the positive active material or on the particle surface identified from a cross-sectional SEM image. The crack B is a portion in which shear occurs on a plane perpendicular to the c-axis without lattice change in the c-axis direction.

[0062] According to the present invention, the portion in which lattice expansion occurs in the c-axis direction is a recoverable portion.

[0063] For example, the above crack A may refer to a case where the interplanar distance of the (003) plane in the TEM image has expanded to 2 to 15 nm (a case where the size of the gap caused by interlayer separation is 2 to 15 nm), and this can be recovered during the discharge process of a battery containing a positive electrode active material. That is, the part where lattice expansion occurred can be restored to its original state.

[0064] According to the present invention, the portion in which the crystal plane is pushed in the a-axis direction without lattice change in the c-axis direction is a portion that can be recovered.

[0065] For example, the above crack B may refer to a case where the crystal plane is displaced, i.e., slip occurs, without a change in the interplanar distance of the (003) plane in the TEM image, and this can be recovered during the charging and discharging process of a battery containing a positive active material. That is, the displaced crystal plane can be restored to its original state. In the present invention, a case where the change in the lattice size (d-spacing) of the (003) plane is 0.3 Å or less is considered as having no change in interplanar distance.

[0066] FIG. 1 is a schematic diagram showing a pristine particle without cracks, a particle with crack A, a particle with crack B, and a particle with crack C, respectively. In FIG. 1, crack C is an unrecoverable crack. The above crack C is a crack that interferes with the movement path of lithium ions and includes cases where a discontinuity (break) occurs in the path of lithium ion movement.

[0067]

[0068] The inventors of the present invention have discovered that when a positive electrode active material comprises lithium nickel-based oxide particles in which the ratio of the number of moles of lithium to the total number of moles of metals excluding lithium is 0.01 or more and 0.5 or less, and the ratio of the number of particles containing crack A and / or crack B satisfies a specific range, the side reaction with the electrolyte caused by the extraction of lithium ions inside the positive electrode active material and gliding and cracking caused by repeated deformation can be suppressed as the insertion and extraction process of lithium ions is repeated, thereby improving the life characteristics of a battery containing the same.

[0069] The positive electrode active material according to the present invention is a positive electrode active material in a charged state and comprises a lithium nickel-based oxide in which the ratio of the number of moles of lithium to the number of moles of all metals excluding lithium is 0.010 or more and 0.500 or less. Meanwhile, if the ratio of the number of moles of lithium to the number of moles of all metals excluding lithium is greater than 0.500, crack A or crack B does not exist, and if it is less than 0.010, there is a problem of excessive structural deformation. Specifically, the ratio of the moles of lithium to the moles of all metals excluding lithium in the above-mentioned positive electrode active material may be 0.010, 0.020, 0.030, 0.040, 0.050, 0.060, 0.070, 0.080, 0.090 or higher, and 0.210, 0.220, 0.230, 0.240, 0.250, 0.300, 0.400, 0.500 or lower.

[0070] Meanwhile, if the ratio of the number of particles containing crack A and / or crack B is less than 1% relative to the total number of lithium nickel-based oxide particles, there is a problem in that the surface area where the cathode active material and the electrolyte react is reduced, thereby decreasing the diffusion rate of lithium ions and lowering capacity and output characteristics. Furthermore, if the ratio of the number of particles containing crack A and / or crack B is greater than 10% relative to the total number of lithium nickel-based oxide particles, the occurrence rate of crack C increases, which causes discontinuity (breakage) in the path of lithium ion movement due to excessive structural deformation.

[0071] According to the present invention, the ratio of the number of particles containing crack C, in which a change in the crystal plane occurs in a direction not parallel to the c-axis, relative to the total number of lithium nickel-based oxide particles, may be 5% or less, 4% or less, 3% or less, 2.9% or less, 2.8% or less, 2.7% or less, or 2.6% or less. In this case, the structural stability of the particles may be further improved. The crack C may be a part in which a change in the crystal plane occurs in a disordered direction, rather than a stepped structure having a step on the particle surface identified from the surface SEM image of the cathode active material. The crack C is a part in which the collapse or destruction of the layered structure occurs in a direction not parallel to the c-axis, that is, in a disordered direction. The crack C is an unrecoverable crack. The crack C is a crack that obstructs the movement path of lithium ions, and includes cases where a discontinuity (break) occurs in the path of lithium ion movement.

[0072]

[0073] According to the present invention, the lithium nickel-based oxide particles may have a nickel content of 60 mol% or more among the total metals excluding lithium. Specifically, the lithium nickel-based oxide particles may have a nickel content of 60 mol% or more, 61 mol% or more, or 62 mol% or more among the total metals excluding lithium, and may have a nickel content of 93 mol% or less, 94 mol% or less, 95 mol% or less, 96 mol% or less, 97 mol% or less, 98 mol% or less, 99 mol% or less, or less than 100 mol%. In this case, the capacity characteristics of a battery including a positive electrode active material may be improved.

[0074] According to the present invention, the lithium nickel-based oxide particles may have a composition represented by the following chemical formula 1.

[0075] [Chemical Formula 1]

[0076] Li x Ni a Co b M 1 c M 2 d O2

[0077] In the above chemical formula 1,

[0078] M 1 is Mn, Al, or a combination thereof, and

[0079] M 2 is one or more selected from the group consisting of Zr, Y, Mo, B, W, Ti, V, Cr, Nb, Mg, Hf, Ta, La, Sr, Ba, Ce, Sn, Zn, F, P, and S, and

[0080] 0.010≤x≤0.500, 0.6≤a<1, 0 <b<0.4, 0<c<0.4, 0≤d≤0.2이다.

[0081] The above x may be 0.010 or more, 0.020 or more, 0.030 or more, 0.040 or more, 0.050 or more, 0.060 or more, 0.070 or more, 0.080 or more, or 0.090 or more, and may be 0.210 or less, 0.220 or less, 0.230 or less, 0.240 or less, 0.250 or less, 0.300 or less, 0.400 or less, or 0.500 or less.

[0082] The above 'a' represents the atomic fraction of nickel among all metals excluding lithium, and may be 0.60 or more, 0.61 or more, or 0.62 or more, and may be 0.93 or less, 0.94 or less, 0.95 or less, 0.96 or less, 0.97 or less, 0.98 or less, 0.99 or less, or less than 1.0. When the nickel content satisfies the above range, the capacity characteristics may be improved.

[0083] The above b represents the atomic fraction of cobalt among all metals excluding lithium, and may be greater than 0 or greater than 0.01, or less than or equal to 0.10, less than or equal to 0.20, less than or equal to 0.30, or less than or equal to 0.40. When the cobalt content satisfies the above range, the resistance characteristics may be improved.

[0084] The above c is M among all metals excluding lithium. 1 It refers to the atomic fraction of which may be greater than 0 or greater than or equal to 0.01, and less than or equal to 0.10, less than or equal to 0.20, less than or equal to 0.30, or less than or equal to 0.40. In this case, the stability of the positive electrode active material is improved, and consequently, the stability of the battery may be improved.

[0085] The above d is M among all metals excluding lithium. 2 It refers to the atomic fraction of which may be greater than 0, 0.02 or less, 0.05 or less, 0.10 or less, or 0.20 or less. In this case, life characteristics, discharge characteristics and / or stability, etc. may be improved.

[0086]

[0087] According to the present invention, the lithium nickel-based oxide particles may be in the form of single particles. When the lithium nickel-based oxide particles are in the form of single particles, there is an advantage that the gas generation rate is reduced compared to the secondary particle form, and inter-particle cracking caused by rolling and charging / discharging processes is reduced.

[0088]

[0089] According to the present invention, the lithium nickel-based oxide particles have an average particle size (D 50 ) may be 1㎛ or more and 30㎛ or less. The average particle size (D) of the lithium nickel-based oxide particles above. 50 Specifically, the thickness may be 1.0㎛ or more, 2.0㎛ or more, or 3.0㎛ or more, and may be 3.5㎛ or less, 4.0㎛ or less, 5.0㎛ or less, 6.0㎛ or less, 7.0㎛ or less, 8.0㎛ or less, 9.0㎛ or less, 10.0㎛ or less, 20.0㎛ or less, or 30.0㎛ or less. In this case, the rolling rate of the battery containing the positive electrode active material can be increased, thereby further improving the performance of the battery.

[0090]

[0091] The positive electrode active material according to the present invention may be manufactured by mixing a positive electrode active material precursor and a lithium raw material and calcining the mixture at a higher temperature than that used for manufacturing a secondary particle-shaped positive electrode active material to produce a single particle-shaped positive electrode active material (initial particle) consisting only of particles having a single crystal structure, and then electrochemically treating the initial particle. However, it is not limited thereto.

[0092]

[0093] For example, first, a lithium composite transition metal hydroxide and LiOH are mixed, then subjected to a first calcination at 850–950°C under an oxygen atmosphere, and then subjected to a second calcination at 750–850°C to produce initial particles. At this time, the cathode active material precursor and the lithium raw material can be mixed such that the molar ratio (Li / M) of lithium (Li) contained in the lithium raw material to the molar number (M) of transition metals contained in the precursor is 1.00 to 1.05. Also, the second calcination temperature may be lower than the first calcination temperature.

[0094] In addition, the process of charging and discharging the battery containing the above initial particles is repeated from once to several hundred times, and then the battery is disassembled to collect the positive active material again, thereby obtaining the positive active material according to the present invention.

[0095] When performing electrochemical treatment, specifically, the process of charging and discharging a battery containing the initial particles is repeated once to several hundred times within a range of 2.5V to 4.5V (V vs. Li+ / Li) with a current of 0.1C to 10C C-rate, and finally, the charged battery is opened to separate the positive electrode, negative electrode, and separator, and the separated positive electrode is washed with DMC and air-dried, and the dried positive electrode is peeled to collect the positive electrode active material according to the present invention in powder form.

[0096]

[0097] anode

[0098] The present invention provides a positive electrode comprising the above positive electrode active material.

[0099] According to one embodiment of the present invention, the positive electrode may comprise a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector, and the positive electrode active material layer may comprise the positive electrode active material.

[0100] According to one embodiment of the present invention, the positive current collector may include a highly conductive metal, and is not particularly limited as long as it facilitates the adhesion of the positive active material layer and is non-reactive within the voltage range of the battery. The positive current collector may be, for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface treated with carbon, nickel, titanium, silver, etc. Additionally, the positive current collector may typically have a thickness of 3 μm to 500 μm, and may form fine irregularities on the surface of the current collector to increase the adhesion of the positive active material. It may be used in various forms, such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0101] According to one embodiment of the present invention, the positive active material layer may include, together with the positive active material, a conductive material and a binder optionally as needed. In this case, the positive active material may be included in an amount of 80% to 99% by weight, more specifically 85% to 98.5% by weight, based on the total weight of the positive active material layer, and may exhibit excellent capacity characteristics within this range.

[0102] According to one embodiment of the present invention, the conductive material is used to impart conductivity to the electrode, and in the battery being constructed, it may be used without special limitations as long as it has electronic conductivity without causing chemical changes. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fibers; metal powder or metal fibers such as copper, nickel, aluminum, and silver; conductive tubes such as carbon nanotubes; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and one of these alone or a mixture of two or more may be used. The conductive material may be included in an amount of 0.1% to 15% by weight relative to the total weight of the positive electrode active material layer.

[0103] According to one embodiment of the present invention, the binder serves to improve adhesion between positive active material particles and adhesion between the positive active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, polymethyl methacrylate, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, polyacrylic acid, and polymers in which hydrogens thereof are substituted with Li, Na, or Ca, or various copolymers thereof, and one of these alone or a mixture of two or more may be used. The above binder may be included in an amount of 0.1% to 15% by weight relative to the total weight of the positive active material layer.

[0104] According to one embodiment of the present invention, the anode may be manufactured according to a conventional anode manufacturing method, except for using the anode active material described above. Specifically, the anode may be manufactured by applying a composition for forming an anode active material layer, prepared by dissolving or dispersing the anode active material and, optionally, a binder, a conductive material, and a dispersant in a solvent, onto an anode current collector, followed by drying and rolling, or by casting the composition for forming an anode active material layer onto a separate support and then laminating the film obtained by peeling from the support onto an anode current collector.

[0105] According to one embodiment of the present invention, the solvent may be a solvent generally used in the relevant technical field, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), dimethylformamide (DMF), acetone, or water, and one of these alone or a mixture of two or more may be used. The amount of solvent used is sufficient to dissolve or disperse the cathode active material, conductive material, binder, and dispersant, taking into account the coating thickness of the slurry and the manufacturing yield, and to have a viscosity that can exhibit excellent thickness uniformity when coated for cathode manufacturing thereafter.

[0106]

[0107] lithium secondary battery

[0108] The present invention provides a lithium secondary battery comprising the above positive electrode.

[0109]

[0110] According to one embodiment of the present invention, the lithium secondary battery may comprise the positive electrode; the negative electrode; a separator interposed between the positive electrode and the negative electrode; and an electrolyte. Additionally, the lithium secondary battery may optionally further comprise a battery container housing an electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member sealing the battery container.

[0111] According to one embodiment of the present invention, the cathode may comprise a cathode current collector and a cathode active material layer located on the cathode current collector.

[0112] According to one embodiment of the present invention, the negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy may be used. In addition, the negative electrode current collector may typically have a thickness of 3 μm to 500 μm, and, similar to the positive electrode current collector, fine irregularities may be formed on the surface of the current collector to strengthen the bonding strength of the negative electrode active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0113] According to one embodiment of the present invention, the negative electrode active material layer may optionally include a binder and a conductive material together with the negative electrode active material.

[0114] According to one embodiment of the present invention, the negative electrode active material may be a compound capable of reversible intercalation and deintercalation of lithium. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; and SiO₂ β(0<β<2), SnO2, 바나듐 산화물, 리튬 바나듐 산화물과 같이 리튬을 도프 및 탈도프할 수 있는 금속산화물; 또는 Si-C 복합체 또는 Sn-C 복합체과 같이 상기 금속질 화합물과 탄소질 재료를 포함하는 복합물 등을 들 수 있으며, 이들 중 어느 하나 또는 둘 이상의 혼합물이 사용될 수 있다. 또한, 상기 음극활물질로서 금속 리튬 박막이 사용될 수도 있다. 또한, 탄소재료는 저결정성 탄소 및 고결정성 탄소 등이 모두 사용될 수 있다. 저결정성 탄소로는 연화탄소 (soft carbon) 및 경화탄소 (hard carbon)가 대표적이며, 고결정성 탄소로는 무정형, 판상, 인편상, 구형 또는 섬유형의 천연 흑연 또는 인조 흑연, 키시 흑연 (Kish graphite), 열분해 탄소 (pyrolytic carbon), 액정 피치계 탄소섬유 (mesophase pitch based carbonfiber), 탄소 미소구체 (meso-carbon microbeads), 액정피치 (Mesophase pitches) 및 석유와 석탄계 코크스 (petroleum or coal tar pitch derived cokes) 등의 고온 소성탄소가 대표적이다. 상기 음극 활물질은 음극 활물질층의 전체 중량을 기준으로 80 중량% 내지 99 중량%로 포함될 수 있다.

[0115] According to one embodiment of the present invention, the binder of the negative electrode active material layer is a component that assists in the bonding between the conductive material, the active material, and the current collector, and is typically added in an amount of 0.1% to 10% by weight based on the total weight of the negative electrode active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0116] According to one embodiment of the present invention, the conductive material of the negative electrode active material layer may be added in an amount of 10% by weight or less, preferably 5% by weight or less, based on the total weight of the negative electrode active material layer, as a component for further improving the conductivity of the negative electrode active material. Such conductive material is not particularly limited as long as it is conductive without causing chemical changes in the battery, and for example, graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black; conductive fibers such as carbon fiber or metal fiber; fluorinated carbon; metal powder such as aluminum or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives may be used.

[0117] According to one embodiment of the present invention, the cathode may be manufactured by applying and drying a composition for forming a cathode active material layer, prepared by dissolving or dispersing a cathode active material and optionally a binder and a conductive material in a solvent, onto a cathode current collector, or by casting the composition for forming a cathode active material layer onto a separate support and then laminating the film obtained by peeling from the support onto a cathode current collector.

[0118] According to one embodiment of the present invention, the separator separates the negative electrode and the positive electrode and provides a pathway for the movement of lithium ions. It can be used without special limitations as long as it is typically used as a separator in a lithium secondary battery, and it is particularly desirable that it has low resistance to the movement of electrolyte ions and excellent electrolyte moisture retention capacity. Specifically, a porous polymer film, such as a porous polymer film made of a polyolefin-based polymer like an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof may be used. In addition, a conventional porous nonwoven fabric, such as a nonwoven fabric made of high-melting-point glass fibers or polyethylene terephthalate fibers, may be used. Furthermore, a coated separator containing a ceramic component or a polymer material may be used to ensure heat resistance or mechanical strength, and it may optionally be used in a single-layer or multi-layer structure.

[0119] According to one embodiment of the present invention, the electrolyte may include an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, a molten inorganic electrolyte, etc., which are usable in the manufacture of a lithium secondary battery, but is not limited thereto. As a specific example, the electrolyte may include an organic solvent and a lithium salt.

[0120] According to one embodiment of the present invention, the organic solvent may be used without special limitations as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvent may be an ester-based solvent such as methyl acetate, ethyl acetate, γ-butyrolactone, or ε-caprolactone; an ether-based solvent such as dibutyl ether or tetrahydrofuran; a ketone-based solvent such as cyclohexanone; or an aromatic hydrocarbon-based solvent such as benzene or fluorobenzene. Carbonate-based solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethylmethyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol-based solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a straight-chain, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may include a double bond, a directional ring, or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes may be used. Among these, a carbonate-based solvent is preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of the battery, and a low-viscosity linear carbonate-based compound (e.g., ethylmethyl carbonate, dimethyl carbonate or diethyl carbonate, etc.) is more preferred.

[0121] According to one embodiment of the present invention, the lithium salt may be used without special limitations as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, as the anion of the lithium salt, F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - The lithium salt may be at least one selected from the group consisting of LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. It is preferable to use the lithium salt within the range of 0.1 M to 2.0 M. When the concentration of the lithium salt falls within the above range, the electrolyte has appropriate conductivity and viscosity, so it can exhibit excellent electrolyte performance and lithium ions can move effectively.

[0122] According to one embodiment of the present invention, in addition to the electrolyte components, the electrolyte may further include one or more additives for the purpose of improving the lifespan characteristics of the battery, suppressing the decrease in battery capacity, and improving the discharge capacity of the battery, such as, for example, a haloalkylene carbonate-based compound such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, triamide hexaphosphate, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride. In this case, the additive may be included in an amount of 0.1% to 5% by weight based on the total weight of the electrolyte.

[0123]

[0124] Since the lithium secondary battery containing the positive electrode active material according to the present invention stably exhibits excellent lifespan characteristics, it is useful in fields such as portable devices like mobile phones, laptop computers, and digital cameras, and electric vehicles like hybrid electric vehicles (HEV) and electric vehicles (EV).

[0125] The external shape of the lithium secondary battery of the present invention is not particularly limited, but can be a cylindrical shape using a can, a prismatic shape, a pouch shape, or a coin shape.

[0126] The lithium secondary battery according to the present invention can be used not only as a battery cell used as a power source for a small device, but can also preferably be used as a unit cell in a medium-to-large battery module comprising a plurality of battery cells.

[0127] Accordingly, according to one embodiment of the present invention, a battery module including the lithium secondary battery as a unit cell and a battery pack including the same are provided.

[0128] According to one embodiment of the present invention, the battery module or battery pack may be used as a power source for one or more medium-to-large devices, including a power tool; an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); or a power storage system.

[0129]

[0130] Hereinafter, embodiments of the present invention are described in detail so that those skilled in the art can easily implement the invention. However, the present invention may be embodied in various different forms and is not limited to the embodiments described herein.

[0131]

[0132] Preparation Example

[0133] Preparation Example 1

[0134] Ni 0.95 Co 0.03 Mn 0.02 It has a composition represented by (OH)2, and an average particle size (D 50 A cathode active material precursor with a particle size of 3.5 μm was mixed with LiOH at a molar ratio of 1:1.05, and a calcined product was prepared by primary calcination at 870°C for 10 hours under an oxygen atmosphere. After grinding the calcined product (using a fin mill, stirring speed: 18,000 rpm), it was secondary calcined at 750°C for 10 hours under an oxygen atmosphere to produce LiNi 0.95 Co 0.03 Mn 0.02 A single-particle lithium complex transition metal oxide having a composition represented by O2 was prepared.

[0135] The above lithium composite transition metal oxide and powdered Co(OH)2 (Huayou Cobalt) were mixed in a molar ratio of 1:0.02 and heat-treated at 780°C for 5 hours under an oxygen atmosphere to produce LiNi 0.93 Co 0.05Mn 0.02 Anode active material in the form of single particles having a composition represented by O2 (average particle size (D 50 ): 3.5㎛) was manufactured.

[0136]

[0137] Preparation Example 2

[0138] Ni 0.88 Co 0.03 Mn 0.09 It has a composition represented by (OH)2, and an average particle size (D 50 A cathode active material precursor with a particle size of 3.5 μm was mixed with LiOH at a molar ratio of 1:1.03, and a calcined product was prepared by primary calcination at 880°C for 10 hours under an oxygen atmosphere. After grinding the calcined product (using a fin mill, stirring speed: 18,000 rpm), it was secondary calcined at 780°C for 9 hours under an oxygen atmosphere to produce LiNi 0.88 Co 0.03 Mn 0.09 A single-particle lithium complex transition metal oxide having a composition represented by O2 was prepared.

[0139] The above lithium composite transition metal oxide and powdered Co(OH)2 (Huayou Cobalt) were mixed in a molar ratio of 1:0.02 and heat-treated at 700°C for 5 hours under an oxygen atmosphere to produce LiNi 0.86 Co 0.05 Mn 0.09 Anode active material in the form of single particles having a composition represented by O2 (average particle size (D 50 ): 3.5㎛) was manufactured.

[0140]

[0141] Preparation Example 3

[0142] Ni 0.64 Co 0.04 Mn 0.32 It has a composition represented by (OH)2, and an average particle size (D 50A cathode active material precursor with a particle size of 3.0 μm was mixed with LiOH at a molar ratio of 1:1.05, and a calcined product was prepared by primary calcination at 900°C for 12 hours under an oxygen atmosphere. After grinding the calcined product (using a fin mill, stirring speed: 18,000 rpm), it was secondary calcined at 850°C for 12 hours under an oxygen atmosphere to produce LiNi 0.64 Co 0.04 Mn 0.32 A single-particle lithium complex transition metal oxide having a composition represented by O2 was prepared.

[0143] The above lithium composite transition metal oxide and powdered Co(OH)2 (Huayou Cobalt) were mixed in a molar ratio of 1:0.02 and heat-treated at 750°C for 5 hours under an oxygen atmosphere to produce LiNi 0.62 Co 0.06 Mn 0.32 Anode active material in the form of single particles having a composition represented by O2 (average particle size (D 50 ): 3.0㎛) was manufactured.

[0144]

[0145] Preparation Example 4

[0146] Ni 0.95 Co 0.02 Mn 0.03 It has a composition represented by (OH)2, and an average particle size (D 50 A cathode active material precursor with a thickness of 10 μm was mixed with LiOH at a molar ratio of 1:1.03, and a calcined product was prepared by primary calcination at 800°C for 12 hours under an oxygen atmosphere. After grinding the calcined product (using a fin mill, stirring speed: 18,000 rpm), it was secondary calcined at 750°C for 10 hours under an oxygen atmosphere to produce LiNi 0.95 Co 0.02 Mn 0.03 A lithium composite transition metal oxide in the form of secondary particles having a composition represented by O2 was prepared.

[0147] Powdered H3BO3 is mixed with the above lithium composite transition metal oxide at a concentration of 1000 ppm based on the total weight of the lithium composite transition metal oxide, and heat-treated at 500°C for 3 hours under an atmospheric atmosphere to obtain a cathode active material in the form of secondary particles (average particle size (D 50 ): 10㎛) was manufactured.

[0148]

[0149] Preparation Example 5

[0150] Ni 0.88 Co 0.07 Mn 0.05 It has a composition represented by (OH)2, and an average particle size (D 50 A cathode active material precursor having a particle size of 9.5 μm was mixed with LiOH at a molar ratio of 1:1.03, and a calcined product was prepared by primary calcination at 800°C for 12 hours under an oxygen atmosphere. After grinding the calcined product (using a fin mill, stirring speed: 18,000 rpm), it was secondary calcined at 750°C for 10 hours under an oxygen atmosphere to produce LiNi 0.88 Co 0.07 Mn 0.05 A lithium composite transition metal oxide in the form of secondary particles having a composition represented by O2 was prepared.

[0151] Powdered H3BO3 is mixed with the above lithium composite transition metal oxide at a concentration of 1000 ppm based on the total weight of the lithium composite transition metal oxide, and heat-treated at 500°C for 3 hours under an atmospheric atmosphere to obtain a cathode active material in the form of secondary particles (average particle size (D 50 ): 9.5㎛) was manufactured.

[0152]

[0153] Preparation Example 6

[0154] Ni 0.6 Co 0.2 Mn 0.2 It has a composition represented by (OH)2, and an average particle size (D 50A cathode active material precursor having a particle size of 9.5 μm was mixed with LiOH at a molar ratio of 1:1.03, and a calcined product was prepared by primary calcination at 850°C for 12 hours under an oxygen atmosphere. After grinding the calcined product (using a fin mill, stirring speed: 18,000 rpm), it was secondary calcined at 800°C for 10 hours under an oxygen atmosphere to produce LiNi 0.6 Co 0.2 Mn 0.2 A lithium composite transition metal oxide in the form of secondary particles having a composition represented by O2 was prepared.

[0155] Powdered H3BO3 is mixed with the above lithium composite transition metal oxide at a concentration of 500 ppm based on the total weight of the lithium composite transition metal oxide, and heat-treated at 500°C for 3 hours under an atmospheric atmosphere to obtain a cathode active material in the form of secondary particles (average particle size (D) 50 ): 9.5㎛) was manufactured.

[0156]

[0157] Examples and Comparative Examples

[0158] Example 1

[0159] A composition for forming an anode active material layer was prepared by adding the anode active material prepared in Preparation Example 1, carbon black (Denka, DenkaBlack) as a conductive material, and PVdF (Kureha, KF1300) as a binder to an N-methylpyrrolidone (NMP) (Daejeong Chemical Co.) solvent in a weight ratio of 95:3:2.

[0160] A composition for forming an anode active material layer was applied to one side of an aluminum foil current collector with a thickness of 20 μm, and dried at 135°C for 3 hours to form an anode active material layer. Subsequently, an anode was manufactured by rolling using a roll pressing method so that the porosity of the anode active material layer after rolling was 20 volume%.

[0161] A half-cell was manufactured using lithium metal as the cathode along with the above-mentioned anode.

[0162] After charging the above half cell to 4.5V in CC (0.2C)-CV (Cut-off current: 0.05C) mode at 25℃, discharging it to 2.5V at 0.2C, the charging process was carried out again.

[0163] Afterwards, the half-cell was disassembled to separate the anode, separator, and cathode, and the separated anode was washed in DMC for 60 seconds and then air-dried.

[0164] Then, the positive active material layer was scraped off to obtain a charged positive active material powder (hereinafter, the positive active material of Example 1).

[0165]

[0166] Example 2

[0167] The positive active material of Example 2 was prepared in the same manner as Example 1, except that the positive active material prepared in Example 2 was used instead of the positive active material prepared in Example 1.

[0168]

[0169] Example 3

[0170] The positive active material of Example 3 was prepared in the same manner as Example 1, except that the positive active material prepared in Example 3 was used instead of the positive active material prepared in Example 1, and that during the preparation of the positive, the porosity of the positive active material layer after rolling was 18 volume% instead of 20 volume%.

[0171]

[0172] Comparative Example 1

[0173] The positive active material of Comparative Example 1 was prepared in the same manner as Example 1, except that the positive active material prepared in Preparation Example 4 was used instead of the positive active material prepared in Preparation Example 1.

[0174]

[0175] Comparative Example 2

[0176] The positive active material of Comparative Example 2 was prepared in the same manner as Example 1, except that the positive active material prepared in Preparation Example 5 was used instead of the positive active material prepared in Preparation Example 1.

[0177]

[0178] Comparative Example 3

[0179] The positive electrode active material of Comparative Example 3 was prepared in the same manner as Example 1, except that the positive electrode active material prepared in Example 6 was used instead of the positive electrode active material prepared in Example 1, and that during the preparation of the positive electrode, the porosity of the positive electrode active material layer after rolling was 18 volume% instead of 20 volume%.

[0180]

[0181] Comparative Example 4

[0182] 2g of the positive active material prepared in Preparation Example 2 was placed into a cylindrical mold with a diameter of 13mm, and a force of 1,000kgf was applied for 50 seconds using an auto pellet press to prepare the positive active material. At this time, the pressure applied to the positive active material while applying force using the auto pellet press was 73MPa.

[0183] Subsequently, the positive active material of Comparative Example 4 was prepared in the same manner as Example 1, except that the positive active material prepared as described above was used instead of the positive active material prepared in Preparation Example 1.

[0184]

[0185] Experimental Example 1: Analysis of Cathode Active Material

[0186] Surface and cross-sectional SEM images of the cathode active materials of Examples 1 to 3 and Comparative Examples 1 to 3 were obtained using SEM (FEI, Quanta FEG 250) and TEM (FEI, Titan). SEM measurements were performed with an acceleration voltage of 10 kV and a working distance (WD) of 10 mm, while TEM measurements were performed with an acceleration voltage of 300 kV. For reference, to analyze the shape of the particle cross-section, ion milling was performed using a cross section polisher (CP) (Jeol, IB-19530CCP) or a focused ion beam (FIB) (FEI, Helios 5).

[0187] For reference, surface SEM images of the positive electrode active materials of Examples 1 to 3 and Comparative Examples 1 to 4 are shown in FIG. 2 (Example 1), FIG. 3 (Example 2), FIG. 4 (Example 3), FIG. 5 (Comparative Example 1), FIG. 6 (Comparative Example 2), FIG. 7 (Comparative Example 3), and FIG. 8 (Comparative Example 4), respectively, and cross-sectional SEM images of the positive electrode active materials of Examples 1 to 3 and Comparative Examples 1 to 3 are shown in FIG. 9 (Example 1), FIG. 10 (Example 2), FIG. 11 (Example 3), FIG. 12 (Comparative Example 1), FIG. 13 (Comparative Example 2), and FIG. 14 (Comparative Example 3), respectively.

[0188] In FIGS. 2 to 4 and 9 to 11, the solid circle (Crack A+B) indicates a particle having crack A or crack B, and the dotted circle (Crack C) indicates a particle having crack C.

[0189] In addition, the TEM analysis results of crack A present in the lithium nickel-based oxide particles of Example 1 are shown in Figure 15.

[0190] Through Fig. 15, it can be seen that crack A is a region where only the interplanar distance of the (003) plane changes, and the interplanar distance is about 15 nm, which is less than 100 nm.

[0191] Meanwhile, surface and cross-sectional SEM images of the above-mentioned cathode active material were analyzed to identify particles with crack A and particles with crack B among more than 200 total particles, and the ratio (%) of the number of particles with crack A or crack B relative to the total number of particles was calculated and is shown in Table 1 below. In addition, among more than 200 total particles, particles with crack C, in which a change in the crystal plane occurred in a disordered direction rather than a stepped structure with a step on the particle surface, were identified, and the ratio (%) of the number of particles with crack C relative to the total number of particles was calculated and is shown in Table 1 below.

[0192] Classification Ratio of particles containing crack A or B (%) Ratio of particles containing crack C (%) Example 1: 2.70 1.93 Example 2: 7.36 2.45 Example 3: 8.86 2.53 Comparative Example 1: 20.0 Comparative Example 2: 17.4 Comparative Example 3: 16.7 Comparative Example 4: 0.74 1.10

[0193]

[0194] Experimental Example 2: Li / Me Evaluation

[0195] For each of the positive electrode active materials of Examples 1 to 3 and Comparative Examples 1 to 3 above, the Li / Me ratio after charging was analyzed according to inductively coupled plasma emission analysis (ICP-OES) using an inductively coupled plasma photoluminescence spectrometer (Agilent, 5110 ICP-OES).

[0196] Classification Li / Me Example 10.093 Example 20.133 Example 30.210 Comparative Example 10.094 Comparative Example 20.127 Comparative Example 30.209 Comparative Example 40.138

[0197]

[0198] Experimental Example 3: Evaluation of Battery Life Characteristics

[0199] (Half-cell manufacturing)

[0200] A composition for forming an anode active material layer was prepared by adding carbon black (Denka, DenkaBlack) as the anode active material and PVdF (Kureha, KF1300) as the binder to an N-methylpyrrolidone (NMP) (Daejeong Chemical Co.) solvent in a weight ratio of 95:3:2, respectively, for each of Examples 1 and 2 and Comparative Examples 1 and 2.

[0201] A composition for forming an anode active material layer was applied to one side of an aluminum foil current collector with a thickness of 20 μm, and dried at 135°C for 3 hours to form an anode active material layer. Subsequently, an anode was manufactured by rolling using a roll pressing method so that the porosity of the anode active material layer after rolling was 20 volume%.

[0202] A half-cell was manufactured using lithium metal as the cathode along with the above-mentioned anode.

[0203] (Dose Retention Rate Evaluation)

[0204] The half-cells prepared above were each charged to 4.25V in CC (0.2C)-CV (Cut-off current: 0.05C) mode at 25℃, and then discharged to 2.5V at 0.2C to perform an activation process (formation). Subsequently, charging to 4.25V in CC (0.5C)-CV (Cut-off current: 0.05C) mode at 45℃ and then discharging to 2.5V at 0.5C was performed for 30 cycles, with one cycle comprising charging to 4.25V and then discharging to 2.5V at 0.5C, and the discharge capacity at each cycle was measured.

[0205] And, the percentage of the discharge capacity of the 30th cycle relative to the discharge capacity of the first cycle was expressed as the capacity retention rate (%) in Table 3 below.

[0206] Classification Capacity Retention Rate (%) Example 198.1 Example 298.3 Example 3100.0 Comparative Example 195.6 Comparative Example 297.9 Comparative Example 397.6 Comparative Example 493.4

[0207] Referring to Tables 1 to 3, it can be seen that the battery containing the positive active material of Examples 1 to 3 has a higher capacity retention rate compared to the battery containing the positive active material of Comparative Examples 1 to 3.

[0208] Accordingly, it can be seen that, as in the present invention, the positive electrode active material comprises lithium nickel-based oxide particles in which the ratio of the number of moles of lithium to the total number of moles of metals excluding lithium is 0.010 or more and 0.500 or less, and the ratio of the number of particles in which crack A, in which lattice expansion occurs in the c-axis direction, or crack B, in which the crystal plane is pushed in the a-axis direction without lattice change in the c-axis direction, exists relative to the total number of lithium nickel-based oxide particles is 1.0% or more and 10% or less, thereby improving the structural stability of the particles and improving the life characteristics of the lithium secondary battery.

Claims

1. Includes lithium nickel-based oxide particles in which the ratio of the number of moles of lithium to the number of moles of all metals excluding lithium is 0.010 or more and 0.500 or less, and A positive electrode active material having a ratio of 1.0% or more and 10% or less to the total number of lithium nickel-based oxide particles in which crack A, in which lattice expansion occurs in the c-axis direction, or crack B, in which the crystal plane is pushed in the a-axis direction without lattice change in the c-axis direction, exists.

2. In Claim 1, The above crack A is a positive active material in which grain expansion within the particle occurs, as confirmed from a surface or cross-sectional SEM image of the positive active material.

3. In Claim 1, The above crack A is a positive active material in which the interplanar distance of the (003) plane in the TEM image is greater than 1 nm and less than or equal to 100 nm.

4. In Claim 1, The above crack B is a positive active material in which a stepped structure having a step difference exists on the particle surface identified from the surface or cross-sectional SEM image of the positive active material.

5. In Claim 1, A positive active material in which the portion where lattice expansion occurs in the above c-axis direction is a recoverable portion.

6. In Claim 1, A positive active material in which the portion of the crystal plane pushed in the a-axis direction without lattice change in the c-axis direction is a recoverable portion.

7. In Claim 1, A positive electrode active material having a ratio of 5% or less of the number of particles in which a change in the crystal plane occurs in a direction not parallel to the c-axis relative to the total number of the lithium nickel-based oxide particles.

8. In Claim 1, The above lithium nickel-based oxide particles are a positive electrode active material having a nickel content of 60 mol% or more among the total metals excluding lithium.

9. In Claim 1, The above lithium nickel-based oxide particles are in the form of single particles and are a positive active material.

10. In Claim 1, The above lithium nickel-based oxide particles have an average particle size (D 50 A positive electrode active material having a thickness of 1㎛ or more and 30㎛ or less.

11. A positive electrode comprising a positive electrode active material according to any one of claims 1 to 10.

12. A lithium secondary battery comprising a positive electrode according to claim 11.

Images