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

Abstract

The present embodiments relate to a positive electrode for a lithium secondary battery and a lithium secondary battery comprising same. A positive electrode for a lithium secondary battery according to an embodiment comprises a current collector and a positive electrode active material layer disposed on the current collector, wherein the positive electrode active material layer may include a boron-containing cluster.

Description

Anode for a lithium secondary battery and a lithium secondary battery including the same

[0001] The present invention relates to a positive electrode for a lithium secondary battery and a lithium secondary battery including the same.

[0002] This application claims priority to Korean Patent Application No. 10-2024-0190594, filed on December 18, 2024, the entire contents of which are incorporated herein by reference.

[0003] Driven by the recent explosive demand for electric vehicles and the need for increased driving range, the development of high-capacity, high-energy-density secondary batteries to meet these demands is actively underway worldwide. In particular, high-nickel NCM cathode materials with high nickel content are being used to satisfy these requirements.

[0004] However, as nickel content increases, particle strength decreases, leading to the occurrence of microcracks during charging and discharging. Furthermore, this results in an increased specific surface area of ​​the cathode material, which in turn increases reactivity with the electrolyte and leads to increased gas generation. Additionally, due to structural instability, unstable Ni 3+ stable Ni 2+ The phenomenon of cation mixing, in which it is reduced and converted into stable NiO, increases. Therefore, it is difficult to actually apply this as a positive electrode active material for lithium-ion batteries for electric vehicles or energy storage.

[0005] To solve this, a method was proposed to manufacture a cathode material in the form of a single particle with the size of the primary particle maximized, rather than in the form of a multi-particle secondary particle formed by the aggregation of primary particles, and then apply it.

[0006] However, generally, to manufacture a cathode material in the form of a single particle, firing must be carried out at a higher temperature compared to multi-particle materials, and consequently, more cation mixing occurs. As a result, more nickel oxide is formed on the surface of the single particle, and since this nickel oxide acts as a resistive layer, there is a problem of reduced capacity and lifespan characteristics.

[0007] In this embodiment, we aim to provide a positive electrode for a lithium secondary battery having excellent capacity and lifespan characteristics, and a lithium secondary battery including the same.

[0008] A positive electrode for a lithium secondary battery according to one embodiment comprises: a current collector; and a positive electrode active material layer located on the current collector; wherein the positive electrode active material layer may include a boron-containing cluster.

[0009] The number of boron-containing clusters observed from a 22.5 μm x 16.5 μm image at a measurement magnification of 6,000x, obtained by EDS (Energy dispersive x-ray spectroscopy) analysis of the anode cross-section, may be 1 to 10.

[0010] The above positive active material layer may further include a boron diffusion layer located on the surface of the boron-containing cluster.

[0011] In one embodiment, the positive electrode active material layer comprises a positive electrode active material including a lithium metal oxide and a surface portion located on the surface of the lithium metal oxide, and the surface portion may include boron.

[0012] In one embodiment, the boron content may be in the range of 500 ppm to 1500 ppm based on the total amount of the positive electrode active material.

[0013] The above lithium metal oxide may be in the form of a single particle.

[0014] The lithium metal oxide may contain 0.5 to 0.7 moles of nickel based on 1 mole of the total transition metal contained in the lithium metal oxide.

[0015] The above positive active material may be represented by the following chemical formula 1.

[0016] [Chemical Formula 1]

[0017] Li a [Ni x Co y Mn z M W ]O2

[0018] In the above chemical formula 1, 0.8≤a≤1.2, 0.5≤x≤0.7, 0≤y≤0.4, 0≤z≤0.4, 0≤w≤0.1, x+y+z+w=1, and M is a doping element such as Zr, Al, B, Y, Mg, Ti, Nb, W, Sc, Si, V, Fe, Mo, Ce, Hf, Ta, La, Sr, Sn, Sb, Zn, Cu, Ge, Mo, Ru, Ir, or a combination thereof.

[0019] The average particle size (D50) of the above positive active material may be 2.5㎛ to 5㎛.

[0020] The cation mixing ratio of nickel cations in the lithium layer within the lithium metal oxide may be 2.8% or less.

[0021] A lithium secondary battery according to another embodiment may include a positive electrode according to one embodiment.

[0022] According to the present embodiment, by including a boron-containing cluster in the positive electrode active material layer, a positive electrode for a lithium secondary battery with excellent capacity and lifespan characteristics can be realized.

[0023] Figure 1 shows a discharge capacity graph for the positive electrode active material prepared according to Example 1, Comparative Example 1, and Comparative Example 2.

[0024] Figure 2 shows an SEM image of the positive electrode active material prepared according to Example 1, measured at a magnification of 10,000.

[0025] Figure 3 shows an SEM image measured at 10,000x magnification for the positive electrode active material prepared according to Comparative Example 1.

[0026] Figure 4 shows an SEM image measured at 10,000x magnification for the positive electrode active material prepared according to Comparative Example 2.

[0027] Figure 5 shows an SEM image measured at 6,000x magnification for an anode cross-section prepared according to Comparative Example 2.

[0028] Figures 6 to 9 show the EDS mapping results for the SEM image of Figure 5 by element.

[0029] Figure 10 shows an SEM image measured at 6,000x magnification of the anode cross-section prepared according to Example 1.

[0030] Figures 11 to 14 show the EDS mapping results for the SEM image of Figure 10 by element.

[0031] Figure 15 shows an SEM image measured at 25,000x magnification of the anode cross-section prepared according to Example 1.

[0032] Figures 16 to 19 show the results of EDS mapping for the SEM image of Figure 15 by element.

[0033] Figure 20 shows an EDS spectrum image for the boxed portion of Figure 15.

[0034] Terms such as first, second, and third are used to describe various parts, components, regions, layers, and / or sections, but are not limited thereto. These terms are used solely to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Accordingly, the first part, component, region, layer, or section described below may be referred to as the second part, component, region, layer, or section without departing from the scope of the present invention.

[0035] The technical terms used herein are for the reference of specific embodiments only and are not intended to limit the invention. The singular forms used herein include plural forms unless phrases clearly indicate otherwise. As used in the specification, the meaning of "comprising" specifies certain characteristics, areas, integers, steps, actions, elements, and / or components, and does not exclude the presence or addition of other characteristics, areas, integers, steps, actions, elements, and / or components.

[0036] When it is stated that one part is "above" or "on" another part, it may be directly above or on the other part, or other parts may be involved in between. In contrast, when it is stated that one part is "directly above" another part, no other parts are interposed in between.

[0037] Unless otherwise defined, all terms used herein, including technical and scientific terms, have the same meaning as generally understood by those skilled in the art to which this invention pertains. Terms defined in commonly used dictionaries are further interpreted to have meanings consistent with relevant technical literature and the present disclosure, and are not interpreted in an ideal or highly formal sense unless otherwise defined.

[0038] Also, unless otherwise specified, % means weight %, and 1 ppm is 0.0001 weight %.

[0039] In this specification, the term “combination(s) of these” described in the Markush-type expression means one or more mixtures or combinations selected from the group consisting of the components described in the Markush-type expression, and means including any one or more selected from the group consisting of said components.

[0040] 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.

[0041]

[0042] cathode for lithium secondary batteries

[0043] A positive electrode for a lithium secondary battery according to one embodiment comprises: a current collector; and a positive electrode active material layer located on the current collector; wherein the positive electrode active material layer may include a boron-containing cluster.

[0044] In this embodiment, the number of boron-containing clusters observed from a 22.5 μm x 16.5 μm image at a measurement magnification of 6,000x, obtained by Energy dispersive x-ray spectroscopy (EDS) analysis of the anode cross-section, may be 1 to 10, more specifically 1 to 5, 1 to 3, or 1 to 2.

[0045] In this specification, the boron-containing cluster may exist within the positive active material included in the positive active material layer as a structure formed in which boron atoms are mainly bonded with oxygen. Such boron clusters may be, for example, in the form of boron oxide.

[0046] Due to the presence of the above boron cluster, the anode of this embodiment can secure excellent capacity and lifespan characteristics.

[0047] Meanwhile, the positive electrode active material layer may further include a boron diffusion layer located on the surface of the boron-containing cluster. This boron diffusion layer may include a lithium borate-based compound formed by the reaction of boron atoms derived from the boron-containing cluster with lithium carbonate derived from the lithium metal oxide particles of the positive electrode active material.

[0048] Next, the positive electrode active material layer comprises a lithium metal oxide and a surface portion located on the surface of the lithium metal oxide, and the surface portion may include boron.

[0049] In one embodiment, the boron content may be 500 ppm to 1500 ppm based on the total amount of the positive electrode active material, and more specifically, 750 ppm to 1250 ppm. When the boron content satisfies the above range, a lithium secondary battery with excellent electrochemical characteristics such as lifespan and capacity can be realized.

[0050] In this embodiment, the lithium metal oxide may be in the form of a single particle.

[0051] In this specification, “single particle” is a term used to distinguish it from cathode active material particles in the form of secondary particles formed by the aggregation of tens to hundreds of primary particles, which were conventionally used; it is a concept that includes a single particle consisting of one primary particle and aggregate particles of 30 or fewer primary particles. The “secondary particle” refers to an aggregate formed by the aggregation of primary particles through physical or chemical bonding between primary particles without an intentional aggregation or assembly process of the primary particles, i.e., a secondary structure.

[0052] In addition, “single particle” means a single particle composed of only one primary particle, and “quasi-single particle” means a single particle composed of multiple primary particles.

[0053] The above “primary particle” refers to a minimum particle unit that is distinguished as a single mass when the cross-section of the positive active material is observed through a scanning electron microscope (SEM), and may consist of a single crystal grain or multiple crystal grains.

[0054] As the above lithium metal oxide is composed of single particles, the particle strength is increased, which can suppress particle breakage during rolling and prevent cracks from forming between primary particles as charging and discharging are repeated. Additionally, the small specific surface area can reduce the amount of gas generated due to side reactions with the electrolyte. Furthermore, the rolling density can be increased during electrode manufacturing, thereby improving the energy density of the electrode.

[0055] In one embodiment, the average particle size (D50) of the positive active material is 2.5 μm to 5 μm, and more specifically, it may be 2.5 μm to 4.5 μm or 3.0 μm to 4.0 μm.

[0056] In this specification, the average particle size (D50) can be defined as the particle size corresponding to 50% of the volume accumulation in the particle size distribution curve. The average particle size (D50) can be measured, for example, using a laser diffraction method. The laser diffraction method generally enables the measurement of particle sizes ranging from the submicron region to several millimeters, and can obtain results with high reproducibility and high resolution.

[0057] As the average particle size of the above single-particle cathode active material is sufficiently large as within the above range, the tap density can be further improved compared to conventional small-particle single particles, and consequently, the electrode density can be significantly improved. However, if the average particle size of the cathode active material is too large, the movement path of lithium ions becomes longer, which may degrade electrochemical characteristics such as capacity and output, so an upper limit is set as above.

[0058] Next, the lithium metal oxide may contain 0.5 to 0.7 moles of nickel based on 1 mole of the total amount of transition metals contained in the lithium metal oxide, and more specifically, may contain 0.55 to 0.67 moles, 0.58 to 0.65 moles, or 0.58 to 0.62 moles of nickel. If the nickel content satisfies the above range, the production cost of the cathode active material can be reduced.

[0059] The above positive active material can be represented by the following chemical formula 1.

[0060] [Chemical Formula 1]

[0061] Li a [Ni x Co y Mn z M W ]O2

[0062] In the above chemical formula 1, 0.8≤a≤1.2, 0.5≤x≤0.7, 0≤y≤0.4, 0≤z≤0.4, 0≤w≤0.1, x+y+z+w=1, and M is a doping element such as Zr, Al, B, Y, Mg, Ti, Nb, W, Sc, Si, V, Fe, Mo, Ce, Hf, Ta, La, Sr, Sn, Sb, Zn, Cu, Ge, Mo, Ru, Ir, or a combination thereof.

[0063] In one embodiment, the cation mixing ratio of nickel cations in the lithium layer within the lithium metal oxide may be 2.8% or less, more specifically, in the range of 1.0% to 2.8%, 1.5% to 2.5%, or 2.0% to 2.5%.

[0064] If the cation mixing ratio is too high, the lithium layer within the crystal structure of the metal oxide can easily collapse, which can significantly reduce the lifespan characteristics of the battery.

[0065] Furthermore, if the cation mixing ratio is too low, irreversible sites within the metal oxide particles may enlarge, leading to a decrease in lithium ion mobility. This consequently causes a reduction in the battery's resistance and output characteristics. Therefore, satisfying the aforementioned range for the cation mixing ratio has an advantageous effect, as it enables the realization of a positive electrode active material with excellent resistance and improved lifespan.

[0066] Specifically, in this specification, the cation mixing ratio refers to the amount of nickel substituted at the lithium sites in the lithium layer.

[0067] Meanwhile, in this embodiment, the 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.

[0068] In addition, the positive active material layer may include a binder and a conductive material.

[0069] At this time, the binder serves to improve adhesion between positive active material particles and adhesion between the positive active material and the positive current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof. One of these alone or a mixture of two or more may be used, but is not limited thereto. The binder may be included in an amount of 1 to 30 weight% based on the total weight of the positive active material layer.

[0070] In addition, 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 possesses 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 powders or metal fibers such as copper, nickel, aluminum, and silver; 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, but is not limited thereto. The conductive material may typically be included in an amount of 1 to 30 weight% relative to the total weight of the positive electrode active material layer.

[0071] The above anode can be manufactured according to a conventional anode manufacturing method.

[0072] Specifically, the anode can be manufactured by applying a composition for forming an anode active material layer, comprising the aforementioned anode active material and optionally a binder, conductive material, or solvent as needed, onto an anode current collector, followed by drying and rolling. At this time, the types and contents of the anode active material, binder, and conductive material are as described above.

[0073] The above solvent may be a solvent commonly used in the relevant technical field, such as dimethylsulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and one of these alone or a mixture of two or more may be used. The amount of the above solvent used is sufficient if it has a viscosity that allows for the dissolution or dispersion of the anode active material, conductive material, and binder, taking into account the coating thickness of the slurry and the manufacturing yield, and subsequently provides excellent thickness uniformity when coated for anode manufacturing.

[0074] Alternatively, the anode may be manufactured by casting the composition for forming the anode active material layer onto a separate support, and then laminating the film obtained by peeling off from the support onto an anode current collector.

[0075]

[0076] lithium secondary battery

[0077] In another embodiment, a lithium secondary battery including the anode is provided.

[0078] Specifically, the lithium secondary battery may include a positive electrode, a negative electrode positioned opposite to the positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, wherein the positive electrode is as described above. Additionally, the lithium secondary battery may optionally further include a battery container housing an electrode assembly comprising the positive electrode, the negative electrode, and the separator, and a sealing member for sealing the battery container.

[0079] In the above lithium secondary battery, the negative electrode may include a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0080] The above-mentioned negative 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 above-mentioned negative current collector may typically have a thickness of 3 to 500 μm, and, similar to the positive current collector, fine irregularities may be formed on the surface of the current collector to strengthen the bonding strength of the negative active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0081] The above-mentioned cathode active material layer may optionally include a binder and a conductive material together with the cathode active material. The above-mentioned cathode active material layer may be manufactured, as an example, by applying a composition for forming a cathode active material layer, comprising a cathode active material and optionally a binder and a conductive material, onto a cathode current collector and drying it, or by casting the composition for forming a cathode onto a separate support and then laminating the film obtained by peeling it off from the support onto a cathode current collector.

[0082] As the above-mentioned negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. 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; metal oxides capable of doping and dedoping lithium, such as SiOβ (0 < β < 2), SnO2, vanadium oxide, and lithium vanadium oxide; or composites comprising the above-mentioned metallic compounds and carbonaceous materials, such as Si-C composites or Sn-C composites, and any one or more of these may be used. Additionally, a metallic lithium thin film may be used as the above-mentioned negative electrode active material. Furthermore, the carbon material may include both low-crystallinity carbon and high-crystallinity carbon. Representative examples of low-crystallinity carbon include soft carbon and hard carbon, while representative examples of high-crystallinity carbon include amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch-derived cokes.

[0083] The binder and conductive material mentioned above may be the same as those previously described in the anode.

[0084] Next, depending on the type of lithium secondary battery, a separator may be present between the positive and negative electrodes. As such a separator, polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more layers thereof may be used, and 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 also be used.

[0085] In addition, regarding the above lithium secondary battery, the electrolyte may include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, etc., which are usable when manufacturing a lithium secondary battery, but is not limited to these.

[0086] Specifically, the organic liquid electrolyte may include an organic solvent and a lithium salt.

[0087] The above organic solvent may be used without special restrictions as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the above organic solvent may include ester-based solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether-based solvents such as dibutyl ether or tetrahydrofuran; ketone-based solvents such as cyclohexanone; and aromatic hydrocarbon-based solvents such as benzene and fluorobenzene. Carbonate-based solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol-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 C2 to C20 structures 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.In this case, using a mixture of cyclic carbonate and chain carbonate in a volume ratio of about 1:1 to about 1:9 can result in excellent performance of the electrolyte.

[0088] The above lithium salt can be used without special restrictions as long as it is a compound capable of providing lithium ions used in lithium secondary batteries. Specifically, the lithium salt may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. The concentration of the lithium salt is preferably used within the range of 0.1 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 allow lithium ions to move effectively.

[0089]

[0090] As described above, since the lithium secondary battery containing the positive electrode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics, and capacity retention rate, it is useful in portable devices such as mobile phones, laptop computers, and digital cameras, as well as in the field of electric vehicles such as hybrid electric vehicles (HEVs).

[0091]

[0092] Hereinafter, embodiments of the present invention will be described in detail. However, these are presented as examples and are not intended to limit the present invention, and the present invention is defined only by the scope of the claims set forth below.

[0093]

[0094] Example 1

[0095] (Preparation of precursor) Ni 0.6 Co 0.2 Mn0.2 A precursor of (OH)2 composition was prepared through a conventional co-precipitation process.

[0096] (Calcination) Next, the above precursor, 20.001 mol of ZrO, and 30.005 mol of Al(OH) were added and mixed first. Then, LiOH·H2O was added to a mixer and mechanically mixed to form a mixture such that the molar ratio of lithium to the total metal in the precursor (Li / Me) became 1.02. Subsequently, the mixture was calcined for 3 hours at 950°C under an oxygen (O2) atmosphere to obtain a primary calcined product. Next, the primary calcined product was calcined for 8 hours at 650°C under an oxygen (O2) atmosphere and then naturally cooled. The composition of the obtained lithium metal oxide is Li 1.07 Ni 0.6 Co 0.2 Mn 0.2 It was O2. The doping amounts of Zr and Al were low, so it was not expressed according to the chemical formula.

[0097] (Coating) H3BO3 was dry-mixed as a coating material to the lithium metal oxide obtained above. At this time, the coating material was mixed such that the B content was 1000 ppm based on 100 moles of the total final cathode active material. Subsequently, a cathode active material with a coating layer formed was prepared by heat-treating at 350°C in an O2 atmosphere for 5 hours.

[0098] (Cathode Manufacturing) The above-prepared cathode active material, conductive material (carbon black, Denka black), and binder (PVDF, KF1100) were mixed in a ratio of 96.5 : 1.5 : 2 wt%, and NMP (N-Methyl-2-pyrrolidone) was added to adjust the viscosity so that the solid content was approximately 30%, thereby preparing a slurry for electrode plate manufacturing. The prepared slurry was coated onto a 20 µm thick Al foil using a doctor blade, and the cathode was manufactured by dry rolling. The electrode loading amount was 15.4 mg / cm². 2 It was, and the rolled density (25℃, 20kN) was 3.6 g / cm³ 3It was.

[0099]

[0100] Comparative Example 1

[0101] (Preparation of precursor) Ni 0.6 Co 0.2 Mn 0.2 A precursor of (OH)2 composition was prepared through a conventional co-precipitation process.

[0102] (Calcination) Next, the above precursor and LiOH·H2O were introduced into a mixer and mechanically mixed so that the molar ratio of lithium to the total metal in the precursor (Li / Me) was 1.02, thereby forming a mixture. Subsequently, the mixture was calcined at 950°C under an oxygen (O2) atmosphere for 3 hours and then naturally cooled to prepare the cathode active material according to Comparative Example 1. The composition of the obtained cathode active material is Li 1.07 Ni 0.6 Co 0.2 Mn 0.2 It was O2.

[0103] (Cathode manufacturing) A cathode was manufactured using the above cathode active material in the same manner as in Example 1.

[0104]

[0105] Comparative Example 2

[0106] A positive electrode active material according to Comparative Example 2 was prepared in the same manner as in Example 1, except that the coating process was not performed, and then a positive electrode was manufactured using the same.

[0107]

[0108] Experimental Example 1 - Measurement of Electrochemical Properties

[0109] CR2032 coin cells were manufactured using the anodes prepared in Example 1 and Comparative Examples 1 and 2 in the following manner, and their electrochemical characteristics were evaluated and are shown in Table 1 below.

[0110] (1) Coin cell manufacturing

[0111] A 2032 coin-type half-cell was manufactured by a conventional method using the above-mentioned positive electrode, lithium metal negative electrode (thickness 200 μm, Honzo metal), electrolyte, and polypropylene polyethylene separator. The above-mentioned electrolyte was prepared by dissolving 1M LiPF6 in a mixed solvent of ethylene carbonate, dimethyl carbonate, and diethyl carbonate (mixing ratio EC:DMC:DEC = 1:2:1 volume%) to prepare a mixed solution, and then adding 3 weight% of vinylene carbonate (VC) to it.

[0112] (2) Evaluation of initial capacity and initial efficiency

[0113] The Koen cell prepared in (1) was aged at 25°C for 10 hours, and then a charge-discharge test was performed at 25°C. To evaluate the initial capacity, 200 mAh / g was set as the reference capacity and charged to 4.25V with a constant current of 0.1C, then switched to a constant voltage and continued charging until the termination current reached 0.05C. After charging, a rest time of 10 minutes was taken, and then discharge was performed until 2.5V was reached with a constant current of 0.1C with a reference capacity of 200 mAh / g. The results are shown in Table 1 below.

[0114] In addition, FIG. 1 shows a graph of the discharge capacity for the positive electrode active materials prepared according to Example 1, Comparative Example 1, and Comparative Example 2.

[0115]

[0116] (3) Evaluation of life characteristics

[0117] After fabricating the coin cell, it was charged to 4.25V at 45℃ with a constant current of 0.5C, then switched to a constant voltage and charged until the termination current reached 0.05C. After a 10-minute rest time following charging, it was discharged with a constant current of 1.0C until it reached 2.5V. Fifty charge-discharge cycles were performed under these conditions, and the capacity retention rate of the 50th cycle relative to the first cycle was calculated. The results are shown in Table 1 below.

[0118] Classification Charging Capacity (mAh / g) Discharging Capacity (mAh / g) Efficiency (%) Capacity Retention Rate (%) (50 cycles) Example 1 210.4 190.7 90.7 97 Comparative Example 1 209.2 186.7 89.2 98.4 Comparative Example 2 209.2 188.3 90 97.7

[0119] Referring to Table 1, it can be seen that when the anode prepared according to Example 1 is applied, the lifespan characteristics are equivalent to those of the anodes prepared according to Comparative Examples 1 and 2, while the capacity is superior. Additionally, referring to Figure 1, it can be seen that the anode active material prepared according to Example 1 exhibits superior capacity characteristics compared to Comparative Examples 1 and 2. Furthermore, since Example 1 has the highest discharge capacity, it can be confirmed that it has excellent energy efficiency.

[0120]

[0121] Experimental Example 2 - Measurement of Residual Lithium

[0122] After adding distilled water to the cathode active material prepared according to the examples and comparative examples, residual lithium was extracted using a stirrer, and the cathode active material powder and extract were separated using a filtering device. Subsequently, the extract was measured by neutralization titration using a Metrohm potentiometer, and the results are shown in Table 2 below.

[0123]

[0124] Experimental Example 3 - Cation Mixing Index Ratio

[0125] After measuring the X-ray diffraction phenomenon using an XRD measuring device (X-ray diffractometer), the ratio of the (003) and (104) diffraction peak intensities was obtained from the diffraction pattern results to obtain the cation mixing index value.

[0126]

[0127] Experimental Example 4 - Measurement of Average Particle Size (D50)

[0128] The average particle size (D50) of the positive electrode active material prepared according to the examples and comparative examples was measured using the laser diffraction method, and the results are shown in Table 2 below.

[0129] Classification Residual Lithium (ppm) Li / Ni disordering D 50(㎛) LiOH Li2CO3 Total Example 1 23 44 106 245 0 2.39% 3.88 Comparative Example 1 17 05 85 425 59 3.57% 3.76 Comparative Example 2 16 11 1107 27 18 2.93% 3.09

[0130] Referring to Table 2, it can be seen that the cathode active material prepared according to Example 1 has a lower residual lithium content compared to the cathode active materials prepared according to Comparative Examples 1 and 2. That is, the cathode according to the example has excellent surface stability of the cathode active material and suppresses electrolyte decomposition reactions, so when applied to a battery, it can reduce gas generation and improve cell stability. In addition, the cation mixing ratio (Li / Ni disordering) is 2.8% or less. Therefore, since the cathode active material included in the cathode according to the example has excellent structural stability, it is possible to realize a lithium secondary battery with excellent capacity and lifespan characteristics.

[0131] It can be seen that the D50 value also satisfies the range of the example.

[0132]

[0133] Experimental Example 5 - SEM Image Analysis

[0134] Figure 2 shows an SEM image measured at magnification X10,000 of the positive electrode active material prepared according to Example 1, Figure 3 shows an SEM image measured at magnification X10,000 of the positive electrode active material prepared according to Comparative Example 1, and Figure 4 shows an SEM image measured at magnification X10,000 of the positive electrode active material prepared according to Comparative Example 2.

[0135] Referring to Figure 2, it can be seen that the positive electrode active material prepared according to Example 1, which performed first and second calcination and boron coating processes, has relatively large particle sizes, a uniform size distribution, a shape close to spherical, and some particles are bonded and clustered in a structure.

[0136] In contrast, referring to FIG. 3, it can be seen that the positive active material prepared according to Comparative Example 1, which did not undergo a secondary firing and coating process, has relatively small particle sizes, a non-uniform size distribution, and parts of the surface that appear very rough, and has less aggregation between particles and individual particles distributed independently.

[0137] Referring to Fig. 4, it can be seen that the positive active material prepared according to Comparative Example 2, in which the first and second calcination processes were performed but the coating process was not performed, has relatively large and uniform particle sizes, but has less aggregation and very distinct boundaries between individual particles.

[0138] That is, as in Example 1, a lithium secondary battery with excellent electrochemical properties such as lifespan and capacity can be realized when the aggregated particles are present in an appropriate ratio while having a large and uniform size and shape.

[0139]

[0140] Experimental Example 6 - EDS (Energy dispersive x-ray spectroscopy) analysis

[0141] The cross-section of the anode prepared according to Comparative Example 2 and Example 1 was cut using a focused ion beam (FIB), and the elements present in the anode active material were mapped by energy dispersive x-ray spectroscopy analysis.

[0142] Figure 5 shows an SEM image measured at magnification X6000 of an anode cross-section prepared according to Comparative Example 2, and Figures 6 to 9 show the EDS mapping results for the SEM image of Figure 5 by element.

[0143] Figure 10 shows an SEM image measured at magnification X6000 of an anode cross-section prepared according to Example 1, and Figures 11 to 14 show the EDS mapping results for the SEM image of Figure 10 by element.

[0144] FIG. 15 shows an SEM image measured at magnification X25000 of an anode cross-section prepared according to Example 1, and FIG. 16 to 19 show the EDS mapping results for the SEM image of FIG. 15 by element.

[0145] Figure 20 shows an EDS spectrum image for the boxed portion of Figure 15.

[0146] Referring to FIGS. 5 to 9, it can be seen that no boron-containing clusters exist in the anode cross-section prepared according to Comparative Example 2.

[0147] In contrast, referring to FIGS. 10 to 19, it can be seen that boron-containing clusters are present in the cross-section of the anode prepared according to Example 1.

[0148] That is, the present embodiment can be confirmed to contain 1 to 10 boron-containing clusters, more specifically 1 to 5 or 1 to 2, observed from a 22.5 μm x 16.5 μm image at a measurement magnification of 6,000x, obtained by EDS (Energy dispersive x-ray spectroscopy) analysis of the anode cross-section.

[0149] In addition, referring to FIGS. 15 and FIGS. 20, it can be seen that a boron diffusion layer is located on the surface of the boron-containing cluster.

[0150]

[0151] Although preferred embodiments of the present invention have been described above, the present invention is not limited thereto and can be implemented with various modifications within the scope of the claims, the detailed description of the invention, and the attached drawings, and it is obvious that such modifications also fall within the scope of the present invention.

[0152] Therefore, the substantive scope of the present invention shall be defined by the appended claims and their equivalents.

Claims

The whole house; and A positive active material layer located on the above current collector; comprising, The above positive active material layer comprises a boron-containing cluster, Cathode for lithium secondary batteries. In paragraph 1, Observed from a 22.5 μm x 16.5 μm image at a measurement magnification of 6,000x, obtained by EDS (Energy dispersive x-ray spectroscopy) analysis of the above anode cross-section, A positive electrode for a lithium secondary battery, wherein the number of boron-containing clusters is 1 to 10. In paragraph 1, A positive electrode for a lithium secondary battery, wherein the positive electrode active material layer further comprises a boron diffusion layer located on the surface of the boron-containing cluster. In paragraph 1, The above positive active material layer comprises a positive active material including a lithium metal oxide and a surface portion located on the surface of the lithium metal oxide, and The above surface portion is a positive electrode for a lithium secondary battery containing boron. In paragraph 4, The above lithium metal oxide is in the form of a single particle, a positive electrode for a lithium secondary battery. In paragraph 4, A cathode for a lithium secondary battery, wherein the boron content is in the range of 500 ppm to 1500 ppm based on the total cathode active material. In paragraph 4, The above lithium metal oxide is, A positive electrode for a lithium secondary battery comprising 0.5 to 0.7 moles of nickel based on 1 mole of the total amount of transition metals contained in the lithium metal oxide. In paragraph 4, The above positive active material is a positive electrode for a lithium secondary battery represented by the following chemical formula 1. [Chemical Formula 1] Li a [Ni x Co y Mr z M W ]O2 In the above chemical formula 1, 0.8≤a≤1.2, 0.5≤x≤0.7, 0≤y≤0.4, 0≤z≤0.4, 0≤w≤0.1, and x+y+z+w=1, M is a doping element and is Zr, Al, B, Y, Mg, Ti, Nb, W, Sc, Si, V, Fe, Mo, Ce, Hf, Ta, La, Sr, Sn, Sb, Zn, Cu, Ge, Mo, Ru, Ir, or a combination thereof. In paragraph 4, A positive electrode for a lithium secondary battery, wherein the average particle size (D50) of the positive electrode active material is 2.5㎛ to 5㎛. In paragraph 4, A positive electrode for a lithium secondary battery in which the cation mixing ratio of nickel cations in the lithium layer within the lithium metal oxide is 2.8% or less. A lithium secondary battery comprising a positive electrode for a lithium secondary battery according to claim 1.

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