Positive electrode active material for lithium secondary battery and lithium secondary battery comprising same

Abstract

The present embodiment relates to a lithium secondary battery positive electrode active material and a lithium secondary battery comprising the same. A lithium secondary battery positive electrode active material according to one embodiment comprises: a metal oxide in the form of a single particle; and a coating layer on the surface of the metal oxide, the coating layer may include a plurality of stripe shapes including protrusions with respect to a longitudinal cross-section.

Description

Technical Field

[0001] This embodiment relates to a lithium secondary battery positive electrode active material and a lithium secondary battery containing the same. Background Art

[0002] Recently, with the explosive growth in demand for electric vehicles and the requirement for increased driving mileage, secondary batteries with high capacity and high energy density that meet the requirements are being actively developed worldwide.

[0003] As a solution to these requirements, the use of high-nickel NCM (nickel-cobalt-manganese) cathode materials with high nickel content has been proposed. At the same time, in order to increase the plate density of the electrodes used as battery components, a bimodal structure with a mixture of large and small particles in a certain proportion is required.

[0004] However, for positive electrode materials in the form of secondary particles formed by the aggregation of primary particles ranging in size from tens of nanometers to several microns, since the specific surface area of the powder is large and the area in contact with the electrolyte is wide, there is a high possibility of gas generation, which leads to the problem of deterioration of life characteristics.

[0005] To address these issues, a solution has been proposed to increase the primary particle size using a sintering agent or flux. However, this method results in the formation of a rock salt structure on the particle surface, which can degrade the electrochemical performance of the positive electrode active material.

[0006] Therefore, there is a need to develop a cathode active material with increased primary particle size and excellent electrochemical performance. Summary of the Invention

[0007] Technical problems to be solved

[0008] The present embodiment aims to provide a positive electrode active material in a single particle form and excellent electrochemical performance, and a lithium secondary battery comprising the same.

[0009] Technical Solution

[0010] According to one embodiment, a positive active material for a lithium secondary battery includes: a metal oxide in a single particle form; and a coating layer on a surface of the metal oxide, the coating layer including a plurality of stripes including protrusions based on a longitudinal cross section.

[0011] A lithium secondary battery according to one embodiment may include the positive electrode; a negative electrode; and an electrolyte.

[0012] Beneficial effects

[0013] According to one embodiment, the positive active material for a lithium secondary battery is in the form of a single particle, and the surface structure is modified to include a stripe-shaped coating layer on the surface, thereby realizing a lithium secondary battery with excellent electrochemical performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a SEM image of the positive electrode active material prepared according to Example 4, which was magnified 20,000 times.

[0015] Figure 2 This is an SEM image of the positive electrode active material prepared according to Comparative Example 3, which was magnified 20,000 times.

[0016] Figure 3 This is an SEM image of the positive electrode active material prepared according to Example 4, which was magnified 120,000 times.

[0017] Figure 4 The length direction ( Figure 4 SEM image of the vertical cross section after processing (in the B direction) and magnified 60,000 times.

[0018] Figure 5 Is used to illustrate Figure 4 Schematic diagram of the distance and height between the protrusions forming the stripe shape in region A and region B.

[0019] Figure 6 This is a SEM image of the positive electrode active material prepared according to Example 8, which was magnified 5,000 times.

[0020] Figure 7 The results of measuring the HPPC resistance values of the positive electrode active materials prepared according to Example 4 and Comparative Example 3 are shown. DETAILED DESCRIPTION

[0021] The terms "first," "second," and "third" are used to describe various parts, components, regions, layers, and / or segments, but these parts, components, regions, layers, and / or segments should not be limited by these terms. These terms are only used to distinguish one part, component, region, layer, and / or segment from another part, component, region, layer, and / or segment. Therefore, a first part, component, region, layer, and / or segment described below could also be described as a second part, component, region, layer, and / or segment without departing from the scope of the present invention.

[0022] The terms used herein are for the purpose of describing specific embodiments only and are not intended to limit the present invention. Unless the context clearly indicates otherwise, the singular form used is intended to include the plural form. It should also be understood that the term "comprising" as used in this specification may specifically refer to a certain characteristic, field, integer, step, action, element and / or component, but does not exclude the presence or addition of other characteristics, fields, integers, steps, actions, elements and / or components.

[0023] If a part is described as being "on" another part, it can be directly on the other part or there can be other parts therebetween. When a part is described as being "directly on" another part, there can be no other parts therebetween.

[0024] Unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Dictionary-defined terms should be interpreted as having the same meaning as that in the relevant technical literature and disclosed herein, and should not be interpreted in an idealized or overly formal sense.

[0025] Lithium secondary battery positive electrode active materials

[0026] As mentioned above, increasing the primary particle size results in the formation of a rock salt structure on the surface, which can degrade the electrochemical performance of the positive electrode active material. However, this embodiment solves this problem by achieving a positive electrode active material with a surface structure modified to include a coating having a striped pattern of protrusions on the surface of a single metal oxide particle with an increased primary particle size.

[0027] That is, according to one embodiment, the positive active material for a lithium secondary battery includes: a metal oxide in a single particle form; and a coating layer on the surface of the metal oxide, wherein the coating layer may include a plurality of stripes including protrusions based on a longitudinal cross section.

[0028] In this case, the average length in the short-side direction of the protrusions forming the stripe shape included in the coating layer is 110 nm or more, and more specifically, may be in the range of 110 nm to 250 nm.

[0029] Furthermore, the average length of the stripes in the coating layer in the longitudinal direction is 650 nm or more, and more specifically, may be in the range of 680 nm to 1500 nm.

[0030] When the distance between protrusions and the average height of protrusions included in the stripe shape formed on the coating satisfy the ranges, the electrochemical performance of a lithium secondary battery using the positive electrode active material according to this embodiment can be greatly improved.

[0031] Secondly, the average distance between the protrusions forming the stripe shape included in the coating layer can be in the range of 10nm to 60nm or 18nm to 45nm. In addition, the average height of the protrusions can be in the range of 18nm to 75nm or 25nm to 65nm.

[0032] The stripe shape may satisfy the following formula 1.

[0033] [Formula 1]

[0034] 4

[0035] In Formula 1, A is the length in the short-side direction of the protrusion forming the stripe shape, and B is the length in the long-side direction of the protrusion forming the stripe shape.

[0036] Specifically, Formula 1 may be in the range of 5 to 10. When the width and length of the stripe-shaped protrusions satisfy the range of Formula 1, a positive electrode active material having excellent room temperature resistance and high temperature life characteristics and significantly reduced high temperature resistance increase rate can be provided.

[0037] Furthermore, the stripe shape may satisfy the following formula 2.

[0038] [Formula 2]

[0039] 0.1 <D / C<8

[0040] In Formula 2, C is the distance between the protrusions forming the stripe shape, and D is the height of the protrusions forming the stripe shape.

[0041] Specifically, Formula 2 may be in the range of 0.5 to 5 or 0.7 to 4. When the ratio of the distance between the protrusions forming the stripe shape and the protrusion height satisfies the range of Formula 2, a positive electrode active material having excellent room temperature resistance and high temperature life characteristics and a significantly reduced high temperature resistance increase rate can be provided.

[0042] On the other hand, the positive electrode active material can be a Li / Ni cation mixing ratio of 1.5% or less, further specifically 1.1 to 1.4%. If the Li / Ni cation mixing ratio is too large, the Li layer is easily disintegrated, which may cause the life characteristics of the battery to be greatly reduced. In addition, if the Li / Ni cation mixing ratio is too small, the irreversible site of the bulk portion of the positive electrode active material becomes larger, and the lithium ion mobility is reduced, which may cause the resistance characteristics and output characteristics to decline. Therefore, when the Li / Ni cation mixing ratio meets the range, a positive electrode active material with low resistance and increased life can be achieved, thus having a favorable effect.

[0043] ​In this specification, the Li / Ni cation mixing ratio refers to the amount of Li sites substituted by Ni.

[0044] In this embodiment, the coating layer may contain at least one of Co, Al, W, V, Ti, Nb, Ce, B, and P. In this case, the content of the element contained in the coating layer may be in the range of 0.5 mol % to 3.5 mol % based on the entire coating layer. Since the coating layer contains at least one of the above elements within the above range, the surface structure of the positive electrode active material of this embodiment can be modified.

[0045] The metal oxide contains nickel, cobalt and manganese, and the content of nickel in the entire metal oxide may be greater than the sum of the contents of cobalt and manganese.

[0046] More specifically, based on 1 mol of the nickel, cobalt, and manganese, the nickel content in the metal oxide particles may be greater than 0.8 mol, more specifically, the nickel content may be in the range of 0.8 to 0.99, 0.85 to 0.99, or 0.88 to 0.99.

[0047] As described in this embodiment, when the nickel content of the lithium metal oxide is 0.8 mol or greater, a positive electrode active material with high output characteristics can be achieved. The positive electrode active material of this embodiment having such a composition has a high energy density per unit volume, thereby increasing the capacity of batteries using this positive electrode active material, making it highly suitable for use in electric vehicles.

[0048] The metal oxide further includes a doping element, and the doping element may include at least one of Al, Zr, Nb, Mo, W, Ti, Ce, Mg, B, P, V, Sr and B.

[0049] The content of the doping element can be in the range of 0.0005 mol to 0.04 mol or 0.001 mol to 0.03 mol, based on 1 mol of the total of the nickel, cobalt, manganese and the doping element. In this case, the doping element refers to the doping amount of the doping element contained in the finally obtained positive electrode active material.

[0050] In the positive electrode active material, the selection of doping elements is important in order to ensure the lifespan and various electrochemical properties. In this embodiment, by using various doping elements as described above, the characteristics of the positive electrode active material can be improved.

[0051] In this embodiment, the doping element may include Zr and Al.

[0052] Because Zr ions occupy Li sites, they act as a pillar, mitigating the shrinkage of the lithium ion path during charge and discharge, thereby stabilizing the layered structure. This phenomenon reduces cation mixing and increases the lithium diffusion coefficient, thereby extending cycle life.

[0053] Furthermore, Al ions migrate to tetragonal lattice sites, thereby suppressing the degradation of the layered structure into a spinel structure in which lithium ion migration is relatively unfavorable.

[0054] The Zr content can be 0.001 to 0.01 mol, more specifically 0.0016 to 0.005 mol, based on 1 mol of the total of nickel, cobalt, manganese, and the doping element. When the Zr doping amount falls within this range, the rate of increase in high-temperature resistance can be reduced while ensuring excellent lifespan characteristics.

[0055] Based on 1 mol of the total of nickel, cobalt, manganese, and the doping element, the Al content can be 0.001 mol to 0.04 mol, more specifically 0.004 mol to 0.028 mol, 0.0045 mol to 0.027 mol, or 0.0055 mol to 0.025 mol. When the Al doping amount meets this range, high-temperature life and thermal stability can be further improved.

[0056] Secondly, the average crystallite size of the metal oxide may be greater than 200 nm.

[0057] When the average crystal grain size is within the above range, the crystal grains can be classified as single particles. In addition, if the average crystal grain size satisfies the above range, crystallization progresses well, which can reduce the residual lithium on the surface of the positive electrode active material and further improve the life characteristics of the lithium secondary battery.

[0058] In this specification, the average crystallite size is defined as the crystallite size measured by the following method.

[0059] 1. Analyze the sample structure using Rigaku smart lab equipment.

[0060] 2. To generate X-rays, 45 kV and 200 mA (9 kW) were applied to the copper anode.

[0061] 3. The optical equipment is set so that the incident slit is 1 / 2 degree and the receiving slit is 8.0 mm.

[0062] 4. XRD was performed with a scan range of 10-80°, a step rate of 0.02°, and a speed of 10° / min.

[0063] 5. Calculate the grain size using SmartLab Studio II v4.2.82.0 software.

[0064] 6. For calculation, use the whole powder pattern fitting (WPPF) in the software.

[0065] 7. When performing WPPF, the structure adopts a layered structure and the profile fitting is set to the FP method.

[0066] 8. The receiving optic is set to graphite (002) and the Soller slit is set to 3.8.

[0067] 9. Set the shape to sphere, fix the strain to 0, and calculate the grain size through refinement.

[0068] The average particle size (D50) of the positive electrode active material is 2.5 μm or more, and more specifically, it can be in the range of 3.0 μm to 5.0 μm. In this embodiment, in order to prepare a positive electrode active material in the form of a single particle having an average particle size as described above, no additional expensive disintegration equipment or multiple disintegration processes are required, that is, using a conventional disintegration device, a positive electrode active material in the form of a single particle with very little fine powder and coarse powder and a uniform particle size distribution can also be prepared. Therefore, when the average particle size of the positive electrode active material of the present embodiment meets the range, a lithium secondary battery with excellent electrochemical properties can be achieved.

[0069] On the other hand, the positive electrode active material of this embodiment may also include a positive electrode active material containing a metal oxide in the form of secondary particles formed by agglomeration of primary particles.

[0070] That is, the positive electrode active material containing the metal oxide in the form of a single particle and the positive electrode active material containing the metal oxide in the form of secondary particles having an average particle size (D50) greater than the average particle size (D50) of the positive electrode active material containing the metal oxide in the form of a single particle can be included. As described above, when the positive electrode active material containing the metal oxide in the form of a single particle and the positive electrode active material containing the metal oxide in the form of secondary particles are mixed in the bimodal form as described above, the density of the electrode mixture can be increased, which is advantageous.

[0071] As described above, in the bimodal form of the positive electrode active material, the mixing ratio of the positive electrode active material containing the metal oxide in the form of a single particle and the positive electrode active material containing the metal oxide in the form of a secondary particle can be in the range of 30:70 to 10:90 or 25:75 to 15:85 by weight ratio (single particle: secondary particle). When the positive electrode active material containing the metal oxide in the form of a single particle and the secondary particle is mixed and used in the weight ratio as described above, the density of the electrode mixture can be increased.

[0072] At this time, the positive electrode active material containing the metal oxide in the form of single particles and the secondary particles may have the same components or different components. Specifically, the positive electrode active material containing the metal oxide in the form of single particles and the secondary particles may both contain nickel, cobalt, manganese and doping elements.

[0073] For example, the positive electrode active material containing the metal oxide in the form of secondary particles contains nickel, cobalt, and manganese, and the content of the nickel in the entire metal oxide in the form of secondary particles may be greater than the sum of the contents of the cobalt and manganese.

[0074] More specifically, the nickel content in the secondary metal oxide particles may be greater than 0.8 mol, based on 1 mol of the nickel, cobalt, and manganese. More specifically, the nickel content may be in the range of 0.8 to 0.99, 0.85 to 0.99, or 0.88 to 0.99.

[0075] The metal oxide in the form of secondary particles further comprises a doping element, and the doping element may comprise at least one of Al, Zr, Nb, Mo, W, Ti, Ce, Mg, B, P, V, Sr, and B.

[0076] The specific description and content of the doping element are the same as those of the aforementioned positive electrode active material containing the metal oxide in the form of single particles, and are not repeated here.

[0077] In addition, in this embodiment, the average particle size (D50) of the positive electrode active material containing the metal oxide in the form of secondary particles can be in the range of 10 μm to 20 μm, or 12 μm to 17 μm. When the average particle size of the positive electrode active material containing the metal oxide in the form of secondary particles meets the above range, large particles and small particles can be appropriately distributed in the positive electrode active material in a bimodal form, thereby improving the energy density of the lithium secondary battery.

[0078] lithium secondary batteries

[0079] According to yet another embodiment of the present invention, a lithium secondary battery is provided, comprising: a positive electrode comprising the positive electrode active material according to one embodiment of the present invention; a negative electrode; and an electrolyte located between the positive electrode and the negative electrode.

[0080] Specifically, the positive electrode includes a current collector and a positive electrode active material layer formed on the current collector. The characteristics of the positive electrode active material constituting the positive electrode active material layer are the same as those described above. Therefore, a detailed description of the positive electrode active material is omitted.

[0081] As the current collector, for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface treated with carbon, nickel, titanium, silver, or the like can be used.

[0082] On the other hand, the positive electrode active material layer may include a binder and a conductive material.

[0083] The binder plays a role in allowing the positive electrode active material particles to be well bonded to each other and to the current collector.

[0084] The conductive material is used to impart conductivity to the electrode, and any conductive material can be used as long as it does not cause chemical changes in the constituted battery.

[0085] For the positive electrode, an active material, a conductive material, and a binder are mixed in a solvent to form an active material composition, which is then coated on a current collector. Such electrode preparation methods are well known in the art and are therefore omitted from this specification. The solvent may be, but is not limited to, N-methylpyrrolidone.

[0086] The negative electrode includes a current collector and a negative electrode active material layer formed on the current collector, wherein the negative electrode active material layer includes a negative electrode active material.

[0087] As the negative electrode active material, a substance capable of reversibly intercalating / deintercalating lithium ions, lithium metal, an alloy of lithium metal, a substance capable of doping and dedoping lithium, or a transition metal oxide may be used.

[0088] As the substance capable of reversibly intercalating and deintercalating lithium ions, any carbon-based negative electrode active material generally used as a carbon material in lithium ion secondary batteries can be used, and typical examples thereof include crystalline carbon, amorphous carbon, or a combination thereof.

[0089] As the alloy of the lithium metal, an alloy of lithium and a metal selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al and Sn can be used.

[0090] Examples of the substance capable of lithium doping and dedoping include Si, SiO x (0<x<2), Si-Y alloy (the Y is an element selected from alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, transition metals, rare earth elements and combinations thereof, but not Si), Sn, SnO2, Sn-Y (the Y is an element selected from alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, transition metals, rare earth elements and combinations thereof, but not Sn), etc.

[0091] Examples of the transition metal oxide include vanadium oxide and lithium vanadium oxide.

[0092] The negative electrode active material layer also includes a binder and may optionally further include a conductive material.

[0093] As the binder, polyvinyl alcohol, carboxymethyl cellulose / styrene-butadiene rubber, hydroxypropylene cellulose, diacetylene cellulose, polyvinyl chloride, polyvinyl pyrrolidone, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, or polypropylene can be used, but is not limited thereto. The binder can be mixed in an amount of 1% to 30% by weight relative to the total amount of the composition for forming the negative electrode active material layer.

[0094] There are no particular limitations on the conductive material, as long as it is conductive and does not cause chemical changes in the battery. Specifically, examples include graphite, such as natural graphite and artificial graphite; carbon black, such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and summer black; conductive fibers, such as carbon fibers and metal fibers; metal powders, such as carbon fluoride, aluminum, and nickel powders; conductive whiskers, such as zinc oxide and potassium titanate; conductive metal oxides, such as titanium oxide; and conductive materials, such as polyphenylene derivatives. The conductive material may be mixed in an amount of 0.1% to 30% by weight relative to the total weight of the composition used to form the negative electrode active material layer.

[0095] As the current collector, a material selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer material coated with a conductive metal, and a combination thereof can be used.

[0096] For the negative electrode, an active material, a conductive material, and a binder are mixed in a solvent to form an active material composition, which is then coated on a current collector. Such electrode preparation methods are well known in the art and are therefore omitted from this specification. The solvent may be, but is not limited to, N-methylpyrrolidone.

[0097] Examples of the electrolyte include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in preparing lithium secondary batteries, but are not limited thereto.

[0098] Specifically, the organic liquid electrolyte may include a non-aqueous organic solvent and a lithium salt.

[0099] The non-aqueous organic solvent functions as a medium through which ions participating in the electrochemical reaction of the battery can migrate.

[0100] The lithium salt is a substance that dissolves in an organic solvent and acts as a lithium ion source in the battery to ensure the basic operation of the lithium secondary battery and promote the migration of lithium ions between the positive electrode and the negative electrode.

[0101] Depending on the type of lithium secondary battery, a separator may be provided between the positive electrode and the negative electrode. Polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of at least two layers thereof may be used as the separator. Alternatively, a mixed multilayer film such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, or a polypropylene / polyethylene / polypropylene three-layer separator may be used.

[0102] Lithium secondary batteries can be categorized as lithium-ion batteries, lithium-ion polymer batteries, and lithium polymer batteries based on the type of separator and electrolyte used. They can be categorized by shape, such as cylindrical, prismatic, coin, and pouch types. They can also be categorized by size, such as block and thin-film types. The structures and preparation methods of these batteries are well known in the art and will not be detailed here.

[0103] Modes for Carrying Out the Invention

[0104] Hereinafter, embodiments of the present invention will be described in detail. However, the following embodiments are merely examples, and the present invention is not limited to the following embodiments. The scope of the present invention is subject to the claims.

[0105] Example 1 - Positive active material in single particle form, heat treated at 600°C for 6 hours

[0106] (1) Preparation of precursor

[0107] The precursor was prepared by a general co-precipitation method.

[0108] Specifically, NiSO4.6H2O was used as the nickel raw material, CoSO4.7H2O was used as the cobalt raw material, and MnSO4.H2O was used as the manganese raw material. These raw materials were dissolved in distilled water to prepare a metal salt aqueous solution.

[0109] After the coprecipitation reactor was prepared, it was purged with N2 to prevent oxidation of metal ions during the coprecipitation reaction, and the reactor temperature was maintained at 50°C.

[0110] NH4(OH) was added to the coprecipitation reactor as a chelating agent, and NaOH was used to adjust the pH. The precipitate obtained according to the coprecipitation process was filtered, washed with distilled water, and dried in an oven at 100°C for 24 hours to prepare a positive electrode active material precursor.

[0111] The components of the prepared precursor are (Ni 0.98 Co 0.01 Mn 0.01 )(OH)2, with an average particle size (D50) of about 4 μm.

[0112] (2) Preparation of positive electrode active materials

[0113] 315 g of LiOH·H2O, 2.94 g of Al(OH)3, and 1.47 g of ZrO2 were weighed and uniformly mixed with 684 g of the precursor prepared in (1). The mixture was then calcined at 830-890°C for 24 hours in a box-type calcining furnace with oxygen introduced at a rate of 1000 mL / min to synthesize a positive electrode material in the form of a metal oxide. The mixture was then disintegrated using a jet mill to prepare a positive electrode active material containing single particles of the metal oxide.

[0114] The metal oxide in the form of single particles was mixed with about 1.927 g of Co(OH) 2 per 100 μL of the metal oxide and heat-treated at 600° C. for 6 hours in an oxygen atmosphere to prepare a positive electrode active material forming a coating layer.

[0115] Example 2 to Example 7

[0116] The positive electrode active material with a coating layer was prepared by the same method as in Example 1 except that the heat treatment conditions during coating formation were adjusted as shown in Table 1 below.

[0117]

Table 1

[0118]

[0119] Example 8 (1) Preparation of precursor

[0120] In addition to the components (Ni0.92 Co 0.04 Mn 0.04 )(OH)2 and the average particle size (D50) reached about 14.5 μm, and the precursor was prepared by the same method as Example 1.

[0121] (2) Preparation of large-particle positive electrode active materials

[0122] 325 g of LiOH·H2O, 11.4 g of Al(OH)3, and 3.2 g of ZrO2 were weighed respectively, and uniformly mixed with 684 g of the precursor prepared in (1), and calcined at 830-890°C for 24 hours in a box-type calcining furnace with oxygen introduced at a rate of 1000 mL / min to synthesize a positive electrode material in the form of a metal oxide.

[0123] Then, the product was crushed using an ACM (air classifying mill), washed with water to remove residual lithium on the surface, and then dried for 12 hours.

[0124] Next, a mixture of about 0.35 g of boric acid (H 3 BO 3 ) per 100 g of the dried positive electrode material was heat-treated at 250° C. to 300° C. for 5 hours in an air atmosphere.

[0125] (3) Preparation of bimodal positive electrode active materials

[0126] The positive electrode active material prepared in (2) and the positive electrode active material prepared according to Example 4 were mixed at a weight ratio of 8:2 to prepare a bimodal positive electrode active material.

[0127] Comparative Example 1

[0128] (1) Preparation of precursor

[0129] The precursor was prepared by the same method as in Example 1.

[0130] (2) Preparation of positive electrode active materials

[0131] 315 g of LiOH·H2O, 2.94 g of Al(OH)3, and 1.47 g of ZrO2 were weighed and uniformly mixed with 684 g of the precursor prepared in (1). The mixture was then calcined at 830-890°C for 24 hours in a box-type calcining furnace with oxygen introduced at a rate of 1000 mL / min to synthesize a positive electrode material in the form of a metal oxide. The mixture was then disintegrated using a jet mill to prepare a positive electrode active material containing single particles of the metal oxide.

[0132] Comparative Example 2

[0133] The positive electrode active material prepared according to Comparative Example 1 was further heat-treated at 660° C. for 6 hours to prepare a positive electrode active material according to Comparative Example 2.

[0134] Comparative Example 3 - Co coating formed by wet method

[0135] A positive electrode active material was prepared by the same method as in Comparative Example 1.

[0136] Next, 0.03 g of LiNO3 and 11.74 g of Co(NO3)2·6H2O were dissolved in 100 g of H2O heated to 60°C, and 100 g of the positive electrode material of Comparative Example 1 was added. The resulting slurry was stirred for 30 minutes, and then the slurry was spray-dried to obtain a powder. The powder was placed in an alumina crucible, heated to about 450°C at a rate of about 5°C per minute, and maintained at about 450°C for about 1 hour. After that, the temperature was increased to about 700°C at a rate of about 2°C per minute and then maintained for about 2 hours. The sample was then cooled to room temperature to prepare the positive electrode active material according to Comparative Example 2.

[0137] Experimental Example 1: Electrochemical Performance Evaluation

[0138] (1) Preparation of coin-type half-cell

[0139] In order to perform physical and electrochemical evaluations on the positive electrode active materials prepared according to Examples 1 to 8 and Comparative Examples 1 to 2, coin-type half cells were prepared as follows.

[0140] Specifically, the positive electrode active material, polyvinylidene fluoride binder (trade name: KF1120) and carbon black conductive material were mixed in a weight ratio of 96.5:1.5:2, and the mixture was added to N-methyl-2-pyrrolidone (N-Methyl-2-pyrrolidone) solvent to achieve a solid content of about 30 weight% to prepare a positive electrode active material slurry.

[0141] The slurry was coated on an aluminum foil (thickness: 15 μm) as a positive electrode collector using a doctor blade, dried, and pressed to prepare a positive electrode. The positive electrode loading was about 15 mg / cm 2 The electrode thickness is about 65 μm and the pressing density is about 3.4 g / cm 3 above.

[0142] A 2032 coin-shaped half-cell was prepared using the aforementioned positive electrode, a lithium metal anode (300 μm thick, MTI), an electrolyte, and a polypropylene separator using conventional methods. The electrolyte was prepared by dissolving 1 M LiPF6 in a mixed solvent of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate (EMC) (EC:DMC:EMC = 3:4:3 vol%). After preparation, the half-cell was aged at room temperature for 10 hours.

[0143] (2) Detection of residual lithium and particle size

[0144] Residual lithium was measured using a T50 from METTLER TOLEDO, and particle size was measured using an S3500 from Microtrac.

[0145] (3) Evaluation capacity

[0146] The coin-type half-cell prepared according to the experimental preparation was aged at room temperature (25° C.) for 10 hours and then subjected to charge and discharge tests.

[0147] For capacity evaluation, 200 mAh / g was used as the reference capacity, and the charge and discharge conditions were CC / CV 2.5 to 4.25 V with a 1 / 20C cut-off. The initial capacity was measured using 0.2C charge / 0.2C discharge.

[0148] (4) Detection life characteristics

[0149] For life characteristics, the battery was tested 50 times under 0.5C charge / 1.0C discharge conditions at high temperature (45°C).

[0150] (5) Detection resistance characteristics

[0151] The room temperature initial resistance (DC-IR) was calculated by subjecting the battery to a 0.2C charge and a 0.2C discharge at 25°C under constant current-constant voltage conditions of 2.5V to 4.25V and a 1 / 20C cutoff. The voltage value after applying the discharge current for 60 seconds when the battery was charged to 100% at 4.25V was measured and then calculated.

[0152] For the resistance increase rate, the initial resistance (room temperature initial resistance) was measured at high temperature (45°C), and the resistance after 30 cycles was measured using the same method as the initial resistance detection method, and the increase rate was converted into percentage (%).

[0153] Experimental Example 2: X-ray diffraction evaluation

[0154] -Analyze sample structure using Rigaku smart lab equipment.

[0155] - To generate X-rays, 45 kV and 200 mA (9 kW) were applied to the copper anode.

[0156] - The optical equipment was set up with an incident slit of 1 / 2 degree and a receiving slit of 8.0 mm.

[0157] - XRD detection was performed with a scan range of 10-80°, a step of 0.02°, and a speed of 10° / min

[0158] Experimental Example 3: Cation Mixing Ratio Detection Method

[0159] 1. Analyze the sample structure using Rigaku smart lab equipment.

[0160] 2. To generate X-rays, 45 kV and 200 mA (9 kW) were applied to the copper anode.

[0161] 3. The optical equipment is set so that the incident slit is 1 / 2 degree and the receiving slit is 8.0 mm.

[0162] 4. XRD was performed with a scan range of 10-80°, a step rate of 0.02°, and a speed of 10° / min.

[0163] 5. Calculate the grain size using SmartLab Studio II v4.2.82.0 software.

[0164] 6. For calculations, the whole powder pattern fitting (WPPF) in the software was used.

[0165] 7. When performing WPPF, the structure adopts a layered structure and the profile fitting is set to the FP method.

[0166] 8. The receiving optic is set to graphite (002) and the Soller slit is set to 3.8.

[0167] 9. Set the shape to sphere, fix the strain to 0, and calculate the grain size through refinement.

[0168] 10. In the Crystal structure tap, the Ni1 occupancy is used as the cation mixing value.

[0169]

Table 2

[0170]

[0171] As shown in Table 2, Examples 1 to 8, which employed positive electrode active materials containing single-particle metal oxides and formed a Co coating, demonstrated superior electrochemical performance, including increased discharge capacity and improved lifespan, compared to Comparative Examples 1 and 2, which did not form a Co coating. In particular, the positive electrode active material of Example 4, prepared at a heat treatment temperature of 660°C during the coating formation process, exhibited the most outstanding 0.2C discharge capacity, lifespan, and high-temperature resistance increase rate.

[0172] Experimental Example 4: Structural Analysis of Positive Electrode Active Materials

[0173] Figure 1 This is a SEM image of the positive electrode active material prepared according to Example 4, magnified 20,000 times. Figure 2 This is an SEM image of the positive electrode active material prepared according to Comparative Example 3, which was magnified 20,000 times.

[0174] from Figure 1 It can be confirmed that the positive electrode active material prepared according to the embodiment has a wavy texture on the surface of a single particle. In this case, the electrochemical performance is the best.

[0175] In addition, see Figure 2 It was confirmed that when the Co coating was formed by a wet method, the surface did not include a stripe-shaped pattern.

[0176] Secondly, Figure 3 This is an SEM image of the positive electrode active material prepared according to Example 4, which was magnified 120,000 times.

[0177] Furthermore, the distances and heights between 9 protrusions in the stripe shape formed in the coating layer of the positive electrode active material formed according to Example 4 were measured and shown in Table 3 below.

[0178]

Table 3

[0179]

[0180] See also Figure 3 It can be seen that the coating layer located on the surface of the positive electrode active material prepared according to Example 4 can include multiple stripe shapes. In addition, referring to Table 4, it can be confirmed that the longitudinal length (A) of the protrusion forming the stripe shape and the width direction length (B) of the protrusion forming the stripe shape meet the range of Formula 1.

[0181] Figure 4 The length direction ( Figure 3 The SEM image of the vertical section after processing (in the B direction) is magnified 60,000 times. Figure 5 Is used to illustrate Figure 4 Schematic diagram of the distance and height between the protrusions forming the stripe shape in region A and region B.

[0182] In addition, the samples shown in Table 4 above were photographed as follows Figure 4 After analyzing the images shown, the distance (C) between the protrusions and the protrusion height (D) of the sites corresponding to region A and region B were detected and are shown in Table 4 below.

[0183]

Table 4

[0184]

[0185]

[0186] Referring to Table 4 above, the distance (C) between the protrusions in region A ranged from 20.98 nm to 62.94 nm, and the protrusion height (D) ranged from 45.56 nm to 63.45 nm. The distance (C) between the protrusions in region B ranged from 24.68 nm to 42.12 nm, and the protrusion height (D) ranged from 24.20 nm to 32.89 nm. That is, in the positive electrode active material according to one embodiment, the average distance between the protrusions forming the stripe shape formed in the coating layer was 20 nm or more, and the average height was 22 nm or more.

[0187] Furthermore, it was confirmed that the distance (C) between the protrusions forming the stripe shape and the height (D) of the protrusions forming the stripe shape satisfied the range of Formula 2.

[0188] Secondly, Figure 6 This is a SEM image of the positive electrode active material prepared according to Example 8, magnified 5,000 times. In other words, this is a positive electrode active material in a bimodal form.

[0189] See also Figure 6 It was confirmed that large particles of polycrystalline particles and small particles of single particles were uniformly mixed.

[0190] Experimental Example 5: HPPC Evaluation

[0191] The HPPC resistance was measured by the following method using the positive active materials prepared according to Example 4 and Comparative Example 3, and is shown in FIG. Figure 7 middle.

[0192] <Making a Battery>

[0193] 1. Make a 2032 coin cell (electrode density: 3.5g / cc)

[0194] 2. Place the coin cell in a 25°C chamber for 10 hours (for electrolyte infiltration and synchronization of chamber and cell temperature).

[0195] <Battery HPPC Mode>

[0196] 1. Battery activation and capacity confirmation

[0197] Charging: CC / CV {CC: 0.2C} {CV: 0.005C}

[0198] Discharge: CC {CC: 0.2C}

[0199] (Reference capacity: 200mAh / g) (Cut-off voltage: 2.5V~4.25V)

[0200] 2. Calculate the charge-discharge rate (C-rate) based on the obtained capacity (capacity: approximately 4.5mAh) (0.2C current: approximately 0.9mA)

[0201] 3. Full charge at 0.2C to 4.25V (SOC 100%) according to the calculated charge and discharge rate (C-rate)

[0202] 4.①Discharge at 0.2C for 30 minutes (target: SOC - 10%)

[0203] ②Discharge at 1C for 10 seconds (Purpose: Detect resistance at target SOC)

[0204] ③ Charge at 0.2C for 50 seconds (Purpose: To compensate for the SOC (capacity) lost when discharging at 1C for 10 seconds)

[0205] 5. Repeat the above step 4. for 9 times (SOC ~ 10%)

[0206] <Calculate HPPC value>

[0207] Calculate HPPC value for each SOC (90-10%)

[0208] (Initial voltage of ② in "4." - terminal voltage of ②) / (1C current of ②) = (10 seconds Ω for each SOC)

[0209] See also Figure 7 It can be confirmed that the positive electrode active material prepared according to Example 4 in which Co is dry-coated to form a coating layer has a lower HPPC resistance value than the positive electrode active material prepared according to Comparative Example 3 in which Co is wet-coated.

[0210] HPPC resistance refers to the resistance value detected based on the SOC of the battery. The lower the HPPC resistance, the less energy loss, which can improve the output of the battery. Figure 7 As described above, it was confirmed that HPPC has a low resistance value and is therefore excellent in charging rate and output, making it suitable for use as a battery for electric vehicles.

[0211] According to one embodiment, the positive electrode active material is in the form of a single particle, and its surface structure is modified to include a striped coating on the surface, thereby achieving a positive electrode active material with improved discharge capacity, room temperature resistance, high temperature life, and high temperature resistance characteristics. This has a very advantageous effect.

[0212] The present invention can be implemented in various ways and is not limited to the embodiments described above. Those skilled in the art will appreciate that the present invention can be implemented in other specific ways without changing the technical concept or essential features of the present invention. Therefore, it should be understood that the above embodiments are illustrative in all respects and are not intended to limit the present invention.

Claims

1. A lithium secondary battery positive electrode active material, comprising: Metal oxides in the form of single particles; a coating located on the surface of the metal oxide, The coating layer includes a plurality of stripe shapes including protrusions based on a widthwise cross-section.

2. The positive electrode active material for lithium secondary batteries according to claim 1, wherein The average length of the protrusion in the short side direction is 110 nm or more.

3. The positive electrode active material for lithium secondary batteries according to claim 1, wherein The average length of the protrusions in the longitudinal direction is 650 nm or more.

4. The positive electrode active material for lithium secondary batteries according to claim 1, wherein The average distance between the protrusions is in the range of 10 nm to 60 nm.

5. The positive electrode active material for lithium secondary batteries according to claim 1, wherein The average height of the protrusions is in the range of 18 nm to 75 nm.

6. The positive electrode active material for lithium secondary batteries according to claim 1, wherein The stripe shape satisfies the following formula 1: [Formula 1] 4 (In Formula 1, A is the length in the short-side direction of the protrusion forming the stripe shape, and B is the length in the long-side direction of the protrusion forming the stripe shape).

7. The positive electrode active material for lithium secondary batteries according to claim 1, wherein The stripe shape satisfies the following formula 2: [Formula 2] 0.1 <D / C<8 (In Formula 2, C is the distance between the protrusions forming the stripe shape, and D is the height of the protrusions forming the stripe shape).

8. The positive electrode active material for lithium secondary batteries according to claim 1, wherein The positive electrode active material has a Li / Ni cation mixing ratio of 1.5% or less.

9. The positive electrode active material for lithium secondary batteries according to claim 1, wherein The coating layer comprises at least one of Co, Al, W, V, Ti, Nb, Ce, B and P.

10. The positive electrode active material for lithium secondary batteries according to claim 9, wherein The content of the element in the coating layer is in a range of 0.5 mol % to 3.5 mol % based on the entire coating layer.

11. The positive electrode active material for lithium secondary batteries according to claim 1, wherein The metal oxides comprise nickel, cobalt and manganese, The content of nickel in the entire metal oxide is greater than the sum of the contents of cobalt and manganese.

12. The positive electrode active material for lithium secondary batteries according to claim 11, wherein The metal oxide further comprises a doping element, The doping element includes at least one of Al, Zr, Nb, Mo, W, Ti, Ce, Mg, B, P, V, Sr and B.

13. The positive electrode active material for lithium secondary batteries according to claim 1, wherein The metal oxide has a crystallite size of 200 nm or more.

14. The positive electrode active material for lithium secondary batteries according to claim 1, wherein The positive electrode active material further includes a positive electrode active material containing a metal oxide in the form of secondary particles formed by agglomeration of primary particles.

15. The positive electrode active material for lithium secondary batteries according to claim 14, wherein ​ The average particle size (D50) of the positive electrode active material containing the metal oxide in the form of secondary particles is larger than the average particle size (D50) of the positive electrode active material containing the metal oxide in the form of single particles.

16. The positive electrode active material for lithium secondary batteries according to claim 14, wherein The metal oxide in the form of secondary particles comprises nickel, cobalt and manganese, The nickel content in the entire metal oxide in the form of secondary particles is greater than the sum of the cobalt and manganese contents.

17. The positive electrode active material for lithium secondary batteries according to claim 16, wherein: The metal oxide in the form of secondary particles further comprises a doping element, The doping element includes at least one of Al, Zr, Nb, Mo, W, Ti, Ce, Mg, B, P, V, Sr and B.

18. The positive electrode active material for lithium secondary batteries according to claim 14, wherein The components of the positive electrode active material containing the metal oxide in the form of the single particle and the secondary particle are the same or different.

19. A lithium secondary battery, comprising: A positive electrode comprising the positive electrode active material according to any one of claims 1 to 18; a negative electrode; and electrolytes.

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