KR102274717B1 - A cathode active material coated with nitrogen-doped carbon, a positive electrode and a lithium ion secondary battery comprising thereof - Google Patents

Abstract

One aspect of the present invention comprises the steps of (a) preparing lithium metal oxide particles; (b) mixing and dry grinding the particles with dopamine hydrochloride to obtain a mixture; And (c) preparing a cathode active material by calcining the mixture; provides a method for producing a cathode active material for a lithium secondary battery, including a.

Description

A cathode active material coated with nitrogen-doped carbon, and a cathode and a lithium secondary battery comprising the same

The present invention relates to a cathode active material coated with nitrogen-doped carbon, a cathode and a lithium secondary battery including the same.

As the application fields of lithium secondary batteries such as portable electronic devices and electric vehicles expand, the demand for high-power, large-capacity, long-life lithium secondary batteries is increasing. In addition, as the depletion of fossil fuels and environmental problems due to fossil fuels are emerging, interest in lithium secondary batteries, which are environmentally friendly and large-capacity energy storage devices, is increasing. However, there is a problem in that the life of the lithium secondary battery is rapidly reduced as charging and discharging are repeated. It is analyzed that this decrease in lifespan characteristics is due to a side reaction between the positive electrode and the electrolyte.

The performance of lithium secondary batteries such as energy density, power density, lifespan, safety and cost may depend on the characteristics of the anode material. Among them, LiCoO ₂ (LCO) with a layered structure has been widely used, but the LCO cathode is structurally unstable. Thus, it shows a low charge/discharge capacity of 160mAhg ^-1 _{, and the LiFePO 4} (LFP) material with an olivine structure has a charge/discharge capacity of 170mAhg ^-1 and has attracted attention for its non-toxicity and eco-friendliness. There is a problem in that the movement speed of lithium ions is lowered, and thus, intercalation/decalation behavior is limited.

Accordingly, among the recently developed positive electrode active materials, lithium metal oxide containing a high content of Ni, that is, LiNi _0.8 Co _0.1 Mn _0.1 O ₂ (NCM811), is a positive electrode active material for lithium secondary batteries due to its high theoretical capacity, low toxicity and low cost. has been proposed In general, the high Ni content of the transition metal site ensures high capacity, the Mn content contributes to structural stability, and the Co content can improve the cycle performance of NCM811. However, as the content of Ni increases, structural stability may decrease.

In this regard, conventional techniques for coating a metal oxide containing Mg, Al, Co, K, Na, Zr or Ca, etc. on the surface to stabilize the structure of the positive electrode active material have been proposed, but these are on a part of the surface. Since it is dispersed in the form of nanoparticles, there is a limitation in that the positive electrode active material cannot be protected from the front side, and furthermore, such a coating layer acts as an ion insulating layer to inhibit the movement of lithium ions.

In order to solve this problem, there is a demand for the development of a positive electrode active material for a lithium secondary battery with improved battery life characteristics and charge/discharge capacity while being suitable for a lithium secondary battery without affecting the intrinsic physical properties of lithium metal oxide.

The present invention is to solve the problems of the prior art, and an object of the present invention is to provide a method for manufacturing a cathode active material for a lithium secondary battery having excellent lifespan characteristics and charge/discharge capacity, and a lithium secondary battery having a cathode including the same will be.

One aspect of the present invention comprises the steps of (a) preparing lithium metal oxide particles; (b) mixing and dry grinding the particles with dopamine hydrochloride to obtain a mixture; And (c) preparing a cathode active material by calcining the mixture; provides a method for producing a cathode active material for a lithium secondary battery, including a.

In an embodiment, the lithium metal oxide may be LiNi _x Co _y Mn _z O ₂ , and the lithium metal oxide may satisfy 0<x<1, 0≤y<1, and 0<z<1.

In one embodiment, the average particle diameter of the lithium metal oxide may be 3 to 10㎛.

In one embodiment, the content of the dopamine hydrochloride may be 0.1 to 0.3% by weight based on the total weight of the lithium metal oxide.

In one embodiment, in the step (c), the cathode active material may have an N-doped carbon coating layer formed on at least a portion of the surface of the lithium metal oxide.

In one embodiment, the thickness of the coating layer may be 1 ~ 10㎚.

In one embodiment, the sintering in step (c) may be performed at 200 ~ 600 ℃, 2 ~ 4 hours conditions.

Another aspect of the present invention provides a cathode active material for a lithium secondary battery manufactured according to the above manufacturing method.

In addition, in order to achieve the above object, another aspect of the present invention provides a positive electrode for a lithium secondary battery prepared by applying a slurry including the positive electrode active material for a lithium secondary battery, a binder, and a conductive material to a current collector.

In one embodiment, the binder is polyvinylidene fluoride, polyvinyl fluoride, polyvinyl alcohol, carboxymethyl cellulose, starch, hydroxypropyl cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene , ethylene-propylene (EPDM) rubber, styrene-butyrene rubber, and may be at least one selected from the group consisting of fluororubber.

In one embodiment, the content of the cathode active material for a lithium secondary battery may be 60 to 95% by weight based on the total weight of the slurry.

In addition, in order to achieve the above object, another aspect of the present invention is a positive electrode comprising the positive active material; cathode; a separator interposed between the anode and the cathode; It provides a lithium secondary battery, including; and electrolyte.

In the method for manufacturing a cathode active material for a lithium secondary battery according to an aspect of the present invention, lithium metal oxide particles are mixed with dopamine hydrochloride and dry pulverized, and the cathode active material prepared by calcining is applied to the secondary battery, thereby generating in the charging and discharging process It is possible to improve the movement speed of lithium ions, thereby improving the lifespan characteristics and electrical characteristics of the battery at the same time.

It should be understood that the effects of the present invention are not limited to the above-described effects, and include all effects that can be inferred from the configuration of the invention described in the detailed description or claims of the present invention.

1 is a schematic diagram of a method of manufacturing a cathode active material for a lithium secondary battery according to an embodiment of the present invention.
2 is an XRD analysis result of a cathode active material for a lithium secondary battery according to an embodiment of the present invention.
3 is an FE-SEM image (ad) and an FE-TEM image (eh) of a cathode active material for a lithium secondary battery according to an embodiment of the present invention.
4 is an FE-TEM image (a), a distribution diagram for each element (bg), and an EDS (h) analysis result of a cathode active material for a lithium secondary battery according to an embodiment of the present invention.
5 is an XPS analysis result of a cathode active material for a lithium secondary battery according to an embodiment of the present invention.
6 is a graph of the differential capacity (dQ/dV) of a discharge curve of a secondary battery including a positive electrode for a lithium secondary battery according to an embodiment of the present invention.
7 is a performance evaluation graph of a secondary battery including a positive electrode for a lithium secondary battery according to an embodiment of the present invention.
8 is an EIS analysis result of a secondary battery including a positive electrode for a lithium secondary battery according to an embodiment of the present invention.

Hereinafter, the present invention will be described with reference to the accompanying drawings. However, the present invention may be embodied in several different forms, and thus is not limited to the embodiments described herein. And in order to clearly explain the present invention in the drawings, parts irrelevant to the description are omitted, and similar reference numerals are attached to similar parts throughout the specification.

Throughout the specification, when a part is "connected" with another part, this includes not only the case where it is "directly connected" but also the case where it is "indirectly connected" with another member interposed therebetween. . In addition, when a part "includes" a certain component, this means that other components may be further provided without excluding other components unless otherwise stated.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a schematic diagram of a method of manufacturing a cathode active material for a lithium secondary battery according to an embodiment of the present invention. Referring to FIG. 1 , a method of manufacturing a cathode active material for a lithium secondary battery according to an aspect of the present invention includes the steps of: (a) preparing lithium metal oxide particles; (b) mixing and dry grinding the particles with dopamine hydrochloride to obtain a mixture; and (c) calcining the mixture to prepare a cathode active material.

The lithium metal oxide is LiNi _x Co _y Mn _z O _{2 It} may satisfy 0<x<1, 0≤y<1, 0<z<1, preferably, the content of nickel is relatively high, yes For example, 0.6 mol or more, preferably 0.7 mol or more, and more preferably 0.8 mol or more, an example of such a lithium metal oxide may be LiNi _0.8 Co _0.1 Mn _0.1 O ₂ . The lithium metal oxide containing the high content of nickel has advantages of high theoretical capacity, low toxicity, and low cost, but there is a problem in that structural stability, particularly stability at high temperature, is deteriorated. On the other hand, if the content of nickel is excessively low, the charge and discharge capacity may be reduced, and if it is excessively high, the content of cobalt and manganese may be relatively small, and thus stability and cycle performance may not be properly implemented. In addition, the average particle diameter of the lithium metal oxide may be 3 to 10 μm, and if the average particle diameter is less than 3 μm, the reactivity with lithium ions may decrease and the performance of the battery may decrease, and if it exceeds 10 μm, during charging and discharging Volume expansion may occur.

In step (b), the lithium metal oxide particles and dopamine hydrochloride may be mixed and dry pulverized to prepare a mixture. Referring to FIG. 1 , each powder is put in a mortar and physically pulverized without a separate solvent for 0.5 to 2 hours to prepare a mixture simply compared to the prior art.

In step (c), the mixture obtained in step (b) may be fired to prepare a cathode active material, and the cathode active material may have an N-doped carbon coating layer formed on at least a portion of the surface of the lithium metal oxide, , the calcination may be performed at 200 to 600° C., for 2 to 4 hours. Since the carbon coating layer has excellent conductivity, the electrical conductivity of the positive electrode active material may be improved. In addition, when the carbon coating layer is doped with nitrogen, it acts similarly to a kind of buffer to improve the conductivity of the positive electrode active material and at the same time suppress the deterioration reaction to improve stability.

On the other hand, the content of the dopamine hydrochloride may be 0.1 to 0.3% by weight based on the total weight of the lithium metal oxide. If the content is less than 0.1% by weight, the coating layer is not properly coated on the surface of the lithium metal oxide, so stability may be reduced, and if it is more than 0.3% by weight, the coating film is thickened and electronic conductivity is lowered, thereby reducing the battery performance. have.

The thickness of the coating layer may be 1 nm or more, 2 nm or more, 3 nm or more, or 4 nm or more, and 10 nm or less, 9 nm or less, 8 nm or less, 7 nm or less, or 6 nm or less, but is not limited thereto . For example, if the content of the dopamine hydrochloride is 0.1 wt%, the thickness of the coating layer may be 2 nm, if the content of the dopamine hydrochloride is 0.2 wt%, the thickness of the coating layer may be 3 nm, the dopamine If the content of hydrochloride is 0.3% by weight, the thickness of the coating layer may be 5 nm, but is not limited thereto.

The positive electrode active material for a lithium secondary battery according to an aspect of the present invention may be manufactured according to the above-described manufacturing method.

In addition, in order to achieve the above object, the positive electrode according to another aspect of the present invention may be prepared by applying a slurry including the positive electrode active material for a lithium secondary battery, a binder, and a conductive material to a current collector.

The binder is polyvinylidene fluoride, polyvinyl fluoride, polyvinyl alcohol, carboxymethyl cellulose, starch, hydroxypropyl cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene (EPDM) ) may be at least one selected from the group consisting of rubber, styrene-butyrene rubber, and fluororubber, preferably polyvinylidene fluoride, but is not limited thereto.

The type of the conductive material is not particularly limited as long as it has conductivity without causing a chemical change in the battery. For example, the conductive material is graphite such as natural graphite or artificial graphite; carbon black, such as carbon black, 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 powder; conductive whiskeys such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; It may be a conductive material such as a polyphenylene derivative.

Based on the total weight of the slurry, the content of the cathode active material for a lithium secondary battery may be 60% by weight or more, 65% by weight or more, 70% by weight or more, or 75% by weight or more, 95% by weight or less, 90% by weight or less, or 85 weight % or less. If the weight ratio of the positive electrode active material is 60% by weight or less, the lifespan characteristics and conductivity of the battery may be deteriorated, and if it is more than 95% by weight, the content of the binder and the conductive material may be relatively decreased, thereby reducing the adhesive force.

The type of the current collector is not particularly limited as long as it has conductivity without causing a chemical change in the battery. For example, the current collector may be copper, stainless steel, aluminum, nickel, titanium, calcined carbon, a copper or stainless steel surface treated with carbon, nickel, titanium, silver, etc., or an aluminum-cadmium alloy. . In addition, the bonding strength of the positive electrode active material can be strengthened by forming fine irregularities on the surface, and it can be used in various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwovens. The current collector may have a thickness of 3 μm to 500 μm.

In addition, in order to achieve the above object, another aspect of the present invention is a positive electrode comprising a positive electrode active material; cathode; a separator interposed between the anode and the cathode; It provides a lithium secondary battery, including; and electrolyte. The lithium secondary battery may have a structure in which a lithium salt-containing electrolyte is impregnated in an electrode assembly having a structure in which a separator is interposed between a positive electrode and a negative electrode.

The separator is interposed between the anode and the cathode, and an insulating thin film having high ion permeability and mechanical strength may be used. The pore diameter of the separator is generally 0.01 μm to 10 μm, and the thickness may be 5 μm to 300 μm. For example, the separator may include an olefin-based polymer such as chemical-resistant and hydrophobic polypropylene; It may be a sheet or non-woven fabric made of glass fiber or polyethylene. In addition, when a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte may serve as a separator.

The lithium salt-containing electrolyte is composed of a lithium salt and a solvent, and may optionally further include an additive. The solvent of the electrolyte may be aqueous or non-aqueous, but is not limited thereto. The electrolyte may be an organic, inorganic liquid or solid electrolyte, but is not limited thereto.

The additive is fluoroethylene carbonate (FEC), tertiary-difluoroethylene carbonate (t-DFEC), vinyl carbonate (VC), ethylene sulfite (ethylene sulfite, ES) ), and the like, but is not limited thereto.

An example of the solvent is a non-aqueous organic solvent, and the non-aqueous organic solvent is N-methyl-2-pyrrolidone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butylo Lactone, 1,2-dimethoxyethane, tetrahydroxyfranc, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile , nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivative, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydro It may be an aprotic organic solvent such as a furan derivative, ether, methyl pyropionate, or ethyl propionate, but is not limited thereto.

An example of the electrolyte is an organic solid electrolyte, and the organic solid electrolyte is a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphate ester polymer, a poly agitation lysine, polyester sulfide, polyvinyl alcohol. , polyvinylidene fluoride, may be a polymerization agent including an ionic dissociation group, but is not limited thereto.

An example of the electrolyte is an inorganic solid electrolyte, and the inorganic solid electrolyte is Na ₂ S-SiS ₂ , Na ₂ S-GeS ₂ , NaTi ₂ (PO ₄ ) ₃ , NaFe ₂ (PO ₄ ) ₃ , Na ₂ ( SO ₄ ) ₃ , Fe ₂ (SO ₄ ) ₂ (PO ₄ ), Fe ₂ (MoO ₄ ) ₃ It may be, but is not limited thereto.

Examples of the lithium salt include LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF ₆ , SiSbF ₆ , SiAlCl ₄ , CH ₃ SO ₃ Li , (CF ₃ SO ₂ ) ₂ NLi, lithium chloroborane, lithium lower aliphatic carboxylate, lithium 4-phenylborate, imide, and the like, and a mixture of two or more thereof may be used, but is not limited thereto.

Hereinafter, embodiments of the present invention will be described in detail.

_{LiNi 0.8} Co _0.1 Mn _0.1 O ₂ /NC may be manufactured according to an embodiment of the present invention below, but the scope of the present invention is not limited thereto. /NC refers to a state in which N-doped carbon is coated on _{the LiNi 0.8} Co _0.1 Mn _0.1 O _{2 .}

Example 1

_{LiNi 0.8} Co _0.1 Mn _0.1 O ₂ (NCM811), a commercially available high content nickel (Ni), was purchased from L&F Chemical, and dopamine hydrochloride was purchased from Sigma Aldrich and used as a nitrogen and carbon precursor. All chemicals were used without further purification.

2 g of LiNi _0.8 Co _0.1 Mn _0.1 O ₂ (NCM811) powder and 0.1% by weight of dopamine hydrochloride based on the weight of the NCM811 were physically mixed and pulverized for 45 minutes. The pulverized powder was calcined at 400° C. for 3 hours under an argon atmosphere _{to prepare nitrogen-doped carbon-coated LiNi 0.8} Co _0.1 Mn _0.1 O ₂ (NCM811)/NC powder.

Example 2

_{LiNi 0.8} Co _0.1 Mn _0.1 O ₂ (NCM811)/NC powder was prepared in the same manner as in Example 1, except that the content of dopamine hydrochloride was adjusted to 0.2% by weight.

Example 3

_{LiNi 0.8} Co _0.1 Mn _0.1 O ₂ (NCM811)/NC powder was prepared in the same manner as in Example 1, except that the content of dopamine hydrochloride was adjusted to 0.3% by weight.

comparative example

_{LiNi 0.8} Co _0.1 Mn _0.1 O ₂ (NCM811) powder without coating was prepared.

Experimental Example 1: XRD analysis

2 is an XRD (X-ray diffraction, D8 Advance, Bruker) analysis result for _{LiNi 0.8} Co _0.1 Mn _0.1 O ₂ and LiNi _0.8 Co _0.1 Mn _0.1 O ₂ /NC according to Examples 1 to 3 and Comparative Examples. . Figure 2 (a) may determine the first to the third embodiments of the _{LiNi 0.8 Co 0.1 Mn 0.1 O 2} / NC and the comparative example LiNi _0.8 Co _0.1 Mn _0.1 O ₂ crystal structure and phase pure. All XRD patterns can be indexed into a layered structure based on the hexagonal α-NaFeO _{2 structure (space group R-3m).} In addition, peaks corresponding to (006)/(012) and (108)/(110) located at 2θ (38.56˚, 65.44˚) correspond to the layered structure of _{LiNi 0.8} Co _0.1 Mn _0.1 O _{2 .} indicates a peak.

In addition, in the case of LiNi _0.8 Co _0.1 Mn _0.1 O ₂ /NC of Examples 1 to 3, all diffraction patterns show a pattern consistent with _{LiNi 0.8} Co _0.1 Mn _0.1 O ₂ of Comparative Examples without additional peaks indicating the formation of a pure phase. This can be confirmed that by coating nitrogen (N) and carbon (C) on _{LiNi 0.8} Co _0.1 Mn _0.1 O _{2 no structural change occurs.} In addition, when the NC coating is 0.2 wt% and 0.3 wt% LiNi _0.8 Co _0.1 Mn _0.1 O ₂ (NCM811) / NC silver (Examples 2 and 3) when the 2θ value is 36.6˚, a minute peak change is observed and nitrogen It is analyzed that the calcination process of coating (N) and carbon (C) partially affected the crystal structure. _{On the other hand, LiNi 0.8} Co _0.1 Mn _0.1 O ₂ (NCM811)/NC (Example 1) having an NC coating content of 0.1 wt% has a diffraction pattern similar to _{that of LiNi 0.8} Co _0.1 Mn _0.1 O _{2 of Comparative Example.} Accordingly, as the amount of NC coating increases, it can be expected to give a change related to the crystal structure.

Experimental Example 2: FE-SEM, FE-TEM analysis

3 is a surface shape, particle size, and element mapping of _{LiNi 0.8} Co _0.1 Mn _0.1 O ₂ and LiNi _0.8 Co _0.1 Mn _0.1 O ₂ /NC according to Examples 1 to 3 and Comparative Examples energy dispersion spectrometer (EDS, Oxford Instruments) equipped with a high-resolution field emission scanning electron microscope (HR FE-SEM, MERLIN, Carl Zeiss) and a field emission transmission electron microscope (FE-TEM) image. Specifically, FIGS. 3(a) to 3(d) are HR FE-SEM images of _{LiNi 0.8} Co _0.1 Mn _0.1 O ₂ of Comparative Example and LiNi _0.8 Co _0.1 Mn _0.1 O _{2 /NC of Examples 1 to 3, respectively.} Referring to FIG. 3(a), _{it can be seen that LiNi 0.8} Co _0.1 Mn _0.1 O ₂ of Comparative Example has a smooth surface and is a spherical particle having an average particle size of 5 μm.

Referring to FIGS. 3 (b) to (d) of Examples 1 to 3, it can be confirmed that the spherical particles of the comparative example have a similar shape. However, Example 1 (0.1% by weight), which has the lowest content of nitrogen (N) and carbon (C), shows a rough texture compared to Examples 2 (0.2% by weight) and Example 3 (0.3% by weight), and nitrogen And it can be seen that the difference in the surface texture according to the generation of the coating layer appears as the carbon content increases, and the particle shape and size appear similarly. Therefore, it is analyzed that the nitrogen (N) and carbon (C) coatings are caused by the texture change of the particle surface, and it can be confirmed that the particle shape and size are maintained accordingly.

Referring to Figs. 3(e) to (f), which are FE-TEM images, (i and ii) of Fig. 3(e) showing _{LiNi 0.8} Co _0.1 Mn _0.1 O _{2 of Comparative Example showed high-density particles, whereas} (i and ii) of FIGS. 3(f) to (h) corresponding to Examples 1 to 3 can confirm that the coating layer is present on the surface. In detail, in (i and ii) of FIG. 3 (f), the content of nitrogen (N) and carbon (C) is small, so that the coating layer is thinner than (i and ii) of FIG. 3 (g and h). In (i and ii) of FIG. 3 (g and h), the content of nitrogen (N) and carbon (C) increased, so that the thickness of the coating layer was also increased. _{LiNi 0.8} Co _0.1 Mn _0.1 O ₂ /NC particles of Example 3 (0.3 wt %) _{were coated with a thickness of 5 nm, and LiNi 0.8} Co _0.1 of Examples 1 (0.1 wt %) and 2 (0.2 wt %) It can be seen that the Mn _0.1 O ₂ /NC particle thickness is formed to be 2 nm and 3 nm, respectively.

Experimental Example 3: EDS analysis

4 is an EDS (energy dispersive x-ray spectroscopy, energy dispersive X-ray spectroscopy) analysis image for chemical and elemental analysis of _{LiNi 0.8} Co _0.1 Mn _0.1 O ₂ /NC according to Example 2. FIG. In Example 2, the content of nitrogen (N) and carbon (C) was included in 0.2 wt % to form a coating layer, and _{the elemental analysis result of LiNi 0.8} Co _0.1 Mn _0.1 O ₂ /NC of Example 2 is shown in FIG. 4 Referring to (a) to (g), it can be confirmed that nickel (Ni), cobalt (Co), manganese (Mn), oxygen (O), nitrogen (N) and carbon (C) are present in LiNi _{It can be seen that the distribution of each element constituting 0.8} Co _0.1 Mn _0.1 O ₂ /NC is evenly distributed, and it can be expected to effectively perform the role of the coating layer. In addition, referring to FIG. 4(h), it can be confirmed that the spectral peaks of each element appear and exist.

Experimental Example 4: XPS analysis

5 shows the results of XPS (X-ray photoelectron spectroscopy, X-ray photoelectron spectroscopy, K-Alpha, Thermo Fisher) analysis for the atomic state of _{LiNi 0.8} Co _0.1 Mn _0.1 O ₂ /NC according to Example 2. Referring to FIG. 5(a), it can be seen that peaks of lithium (Li), nickel (Ni), cobalt (Co), manganese (Mn), oxygen (O), nitrogen (N) and carbon (C) appear. have. In addition, the peak of oxygen was conspicuously shown in Fig. 5(a), and it can be confirmed that this is due to the stable oxide. Referring to FIG. 5( b ), the Li1S core spectrum is shown, and it can be confirmed that the binding energy is 51.9 eV and 53.3 eV, respectively, and there are two peaks.

5(c) to (e), separate spectra of nickel (Ni), cobalt (Co), and manganese (Mn) can be confirmed, respectively, and, accordingly, the chemical state change according to the formation of the coating layer is affected. It can be confirmed that there is no Looking at FIG. 5(g), it can be seen that the C1s spectrum is shown and the binding energy is 282.7eV, 285.4eV and 288.1eV, and it can be confirmed that there are three peaks, which are carbon compounds of CC, CN, OC=O. It can be confirmed that it exists as a functional group.

5(h) shows the spectrum of N1s, and it can be confirmed that there are two peaks with binding energy of 397.3 eV and 398.7 eV, and the peak is due to pyridine-nitrogen, graphene-nitrogen functional groups. can The various peaks of the nitrogen are caused by the _{presence of an amino group (—NH 2} ) group in dopamine hydrochloride, and upon decomposition thereof, pyridine-nitrogen and graphene-nitrogen functional groups are generated. It can be seen that the pyridine-nitrogen can improve the electrochemical performance _{of LiNi 0.8} Co _0.1 Mn _0.1 O _{2 /NC.} As a result, XPS analysis is LiNi _0.8 Co _0.1 Mn _0.1 O while maintaining the inherent properties of the ₂ / NC nitrogen (N) and carbon (C) may be confirmed that the coating on the _{LiNi 0.8 Co 0.1 Mn 0.1 O 2} / NC .

Preparation Example 1

_{LiNi 0.8} Co _0.1 Mn _0.1 O ₂ /NC (positive electrode active material), polyvinylidene difluoride (PVDF, binder), and conductive carbon black (conductive material) prepared according to Example 1 were each in a weight ratio of 80: 10: 10 After dissolving the mixed material in N-methylpyrrolidone to prepare a slurry, it was applied to 10 μm aluminum foil and dried at room temperature for 12 hours, then dried in a convection oven at 120° C. for 5 hours, and 14 mm After rolling with the roll press of the die, the electrode was prepared by maintaining it at 120° C. for 5 hours in a vacuum atmosphere, and a coin-type CR2032 type cell was laminated as a working electrode using the prepared electrode disk, polished as a reference electrode, and as a separator. A positive electrode for a lithium secondary battery that was blocked from the negative electrode area by Cellgard 2340 was manufactured.

An electrode assembly was prepared using the prepared positive electrode, the negative electrode, and the separator made of Cellgard 2340. After putting the electrode assembly in a pouch and connecting a lead wire, a solution containing ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 1:1 in which _{1M LiPF 6 salt is dissolved as an additive is injected as an electrolyte,} A lithium secondary battery was assembled by sealing it in an argon glove box (Korean Kiyon) in which humidity and oxygen content were maintained at 5 ppm or less. All electrochemical measurements were performed using a battery cycler (Battery Tester 05001, HTC) and were performed at 25°C unless otherwise specified.

Preparation 2

_{A lithium secondary} battery was prepared in the same manner as in Preparation Example 1, except that _{LiNi 0.8} Co _0.1 Mn _0.1 O 2 /NC prepared according to Example 2 was applied as a cathode active material.

Preparation 3

_{A lithium secondary} battery was prepared in the same manner as in Preparation Example 1, except that _{LiNi 0.8} Co _0.1 Mn _0.1 O 2 /NC prepared according to Example 3 was applied as a cathode active material.

Comparative Preparation Example

_{A lithium secondary} battery was prepared in the same manner as in Preparation Example 1, except that _{LiNi 0.8} Co _0.1 Mn _0.1 O 2 prepared according to Comparative Example was applied as a cathode active material.

Experimental Example 5: Secondary Battery Performance Evaluation 1

6 is a graph of the differential capacity (dQ/dV) of a discharge curve of a lithium secondary battery including the positive electrodes of Preparation Examples 1 to 3 and Comparative Preparation Examples. 6(a) to (d), the charging and discharging cycle studies were conducted at a charge/discharge rate for the initial 3 cycles of 0.1C in a voltage range of 3.0 to 4.3V for ^{Li/Li + .} 6(a) shows the charge/discharge capacity of the lithium secondary battery including the positive electrode of Comparative Preparation Example converged to ^{about 209/206 mAhg −1 .} 6(b) to (d) show electrochemical behavior similar to that of the lithium secondary battery of Comparative Preparation Example as the initial charge/discharge capacity of the lithium secondary battery including the positive electrode of Preparation Examples 1 to 3; The initial discharge capacity of the lithium secondary battery prepared in Examples 1 to 3 was found to be respectively ^{171mAhg -1, 202mAhg -1, 190mAhg -1} . The difference in the initial charge/discharge capacity can be analyzed to be due to the NC content of _{LiNi 0.8} Co _0.1 Mn _0.1 O _{2 /NC applied as a positive electrode active material. Specifically, LiNi 0.8} Co _0.1 Mn _0.1 O ₂ /NC having an NC content of 0.1% by weight has a NC coating layer thickness of 2 nm ((i and ii) of FIG. 3(f)), and a coating layer according to a small content It was not uniform, so the initial charge and discharge capacity was lowered. _{On the other hand, LiNi 0.8} Co _0.1 Mn _0.1 O ₂ /NC with an NC content of 0.3% by weight has an NC coating layer thickness of 5 nm ((i and ii) in FIG. 3(h)) to form a coating layer of excessive thickness. , it was shown that the initial charge/discharge capacity was reduced compared to the Comparative Preparation Example. _{LiNi 0.8} Co _0.1 Mn _0.1 O ₂ /NC with an NC content of 0.2% by weight has an NC coating layer thickness of 3 nm ((i and ii) in FIG. 3(g)), indicating that the initial charge/discharge efficiency is the best, As for the thickness of the coating layer, it can be seen that 3 nm is the most optimal thickness and, therefore, exhibits the most excellent electrochemical behavior.

According to the differential capacity change for the initial 3 cycles, the _{lithium secondary batteries of Preparation Examples 1 to 3 and Comparative Preparation Examples maintained all characteristics of LiNi 0.8} Co _0.1 Mn _0.1 O ₂ , and the NC coating layer was oxidized in the lithium secondary battery. It can be confirmed that /reduction does not affect the behavior.

Experimental Example 6: Secondary Battery Performance Evaluation 2

7 is a performance evaluation by repeating charging and discharging cycles of charging and discharging lithium secondary batteries including positive electrodes of Preparation Examples 1 to 3 and Comparative Preparation Examples at a charge/discharge rate of 0.1C for 40 cycles in a voltage range of 3.0 to 4.3V. to be.

Referring to FIG. 7( a ), the initial charge/discharge capacity of the lithium secondary battery including the positive electrode of Comparative Preparation Example ^{converged to 170mAhg -1} , and the coulombic efficiency was maintained at about 98.7% level, whereas Preparation Example 1 The initial discharge capacity of the lithium secondary battery including the positive electrodes of to 3 ^{converges to 142mAhg -1} , 171mAhg ^{-1 , 158mAhg -1} for 40 cycles, respectively, and the coulombic efficiency is 83.6%, 87.6%, and 85.2%, respectively. Figure 7 (e) shows the charging and discharging characteristics according to the increase in the cycle of Comparative Preparation Example and Preparation Examples 1 to 3 at 1C. The discharge capacities of Comparative Preparation Examples and Preparation Examples 1 to 3 in the initial cycle were 182mAhg ^-1 , 172mAhg ^-1 , 183mAhg ^-1 , 178mAhg ^-1 , respectively, and the coulombic efficiency after 50 cycles was 63.15%, 62.14%, and 65.74%. , 58.92%. In general, LiNi _0.8 Co _0.1 Mn _0.1 O ₂ of Comparative Preparation Example may cause electrode deterioration and capacity reduction due to various factors, such as surface decomposition by HF and oxygen, which may be generated by anionic oxidation of _{PF 6} ^-. On the other hand, LiNi _0.8 Co _0.1 Mn _0.1 O ₂ /NC of Preparation Example 2 exhibits the best electrochemical performance due to smooth movement of ions and electrons when applied to a secondary battery due to the most appropriate coating amount, and It can be seen that LiNi _0.8 Co _0.1 Mn _0.1 O ₂ /NC acts as a factor that deteriorates electrochemical performance due to poor movement of ions and electrons depending on a small amount of coating and an excessive amount of coating, respectively.

7(f) shows the rate characteristics according to the current intensity of Comparative Preparation Examples and Preparation Examples 1 to 3, and experiments were conducted at 0.1C, 0.2C, 0.5C, 1C and 2C, respectively. Preparation Examples 1 to 3 in Preparation Example 2 in accordance with the current intensity ^{204.23mAhg -1, 194.09mAhg -1, 175.65mAhg -1} , 158.25mAhg -1, ^-1 exhibits a 124.31mAhg shown to be the most superior. In contrast, Comparative Preparation Example showed 199.21mAhg ^-1 , 192.14mAhg ^-1 , 171mAhg ^-1 , 157.37mAhg ^-1 , 100.01mAhg ^-1 depending on the current strength. In particular, _{it can be seen that the charge/discharge capacity of LiNi 0.8} Co _0.1 Mn _0.1 O ₂ /NC of ^{Preparation Example 2 converges to 124mAhg -1} at 2C, confirming that the charge/discharge capacity and characteristics are the most improved.

Experimental Example 7: Secondary Battery Performance Evaluation 3

Figure 8 is Comparative Preparation Example LiNi _0.8 Co _0.1 Mn _0.1 O ₂ and Preparation Examples 1 to 3 LiNi _0.8 Co _0.1 Mn _0.1 O ₂ /NC EIS (Electrochemical Impedance System) in the range of 100kHz to 10mHz to evaluate the electrochemical performance improvement ) is the result of measurement analysis. Referring to FIG. 8 , in both Comparative Preparation Examples and Preparation Examples 1 to 3, impedance plots in the form of a small semicircle were observed in the high frequency region, which is analyzed to be due to the impedance plot of the layer formed between the solid phase and the electrolyte. In addition, it can be confirmed that the small semicircle observed in the mid-frequency region is due to the resistance received during charge transfer. It can be seen that LiNi _0.8 Co _0.1 Mn _0.1 O ₂ /NC of Preparation Example 2 exhibits the smallest semicircle due to a decrease in resistance due to charge transfer as the transfer of charge is easy, and thus Comparative Preparation of Preparation Examples 1 and 3 It can be seen that the electrochemical performance is the best compared to the example.

The above description of the present invention is for illustration, and those of ordinary skill in the art to which the present invention pertains can understand that it can be easily modified into other specific forms without changing the technical spirit or essential features of the present invention. will be. Therefore, it should be understood that the embodiments described above are illustrative in all respects and not restrictive. For example, each component described as a single type may be implemented in a distributed manner, and likewise components described as distributed may be implemented in a combined form.

The scope of the present invention is indicated by the following claims, and all changes or modifications derived from the meaning and scope of the claims and their equivalents should be construed as being included in the scope of the present invention.

Claims (12)

(a) preparing lithium metal oxide particles;
(b) mixing and dry grinding the particles with dopamine hydrochloride to obtain a mixture; and
(c) preparing a cathode active material in which an N-doped carbon coating layer is formed on at least a portion of the surface of the lithium metal oxide by calcining the mixture;
The thickness of the coating layer of step (c) is 1 ~ 10㎚, a method for producing a positive electrode active material for a lithium secondary battery. According to claim 1,
The lithium metal oxide is LiNi _x Co _y Mn _z O _{2 And} ,
The lithium metal oxide satisfies 0<x<1, 0≤y<1, 0<z<1, a method of manufacturing a cathode active material for a lithium secondary battery. According to claim 1,
The average particle diameter of the lithium metal oxide is 3 to 10㎛, a method of manufacturing a positive electrode active material for a lithium secondary battery. According to claim 1,
The content of the dopamine hydrochloride is 0.1 to 0.3% by weight based on the total weight of the lithium metal oxide, a method for producing a cathode active material for a lithium secondary battery. delete delete According to claim 1,
The calcination of step (c) is carried out at 200 ~ 600 ℃, 2 ~ 4 hours conditions, a method of manufacturing a cathode active material for a lithium secondary battery. A cathode active material for a lithium secondary battery prepared by the method according to any one of claims 1 to 4 and 7. A positive electrode for a lithium secondary battery prepared by applying a slurry comprising the positive electrode active material for a lithium secondary battery according to claim 8, a binder, and a conductive material to a current collector. 10. The method of claim 9,
The binder is polyvinylidene fluoride, polyvinyl fluoride, polyvinyl alcohol, carboxymethyl cellulose, starch, hydroxypropyl cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene (EPDM) ) at least one selected from the group consisting of rubber, styrene-butyrene rubber, and fluororubber, a positive electrode for a lithium secondary battery. 10. The method of claim 9,
The content of the positive electrode active material for a lithium secondary battery is 60 to 95% by weight based on the total weight of the slurry, a positive electrode for a lithium secondary battery. The positive electrode according to claim 9;
cathode;
a separator interposed between the anode and the cathode; and
A lithium secondary battery comprising; an electrolyte.

Images