Positive electrode active material for lithium secondary battery, method for producing the same, and lithium secondary battery including a positive electrode containing the positive electrode active material

Abstract

The present invention discloses a positive electrode active material for lithium secondary batteries, which comprises a nickel-based active material having a nickel content of 60 mol % or more, the positive electrode active material comprising large crystal grains of 1 to 10 μm in size and containing a lanthanum group element inside the large crystal grains, a method for producing the same, and a lithium secondary battery comprising a positive electrode containing the positive electrode active material.

Description

[Technical Field]

[0001] The present invention relates to a positive electrode active material for a lithium secondary battery, a method for producing the same, and a lithium secondary battery including a positive electrode containing the positive electrode active material. [Background technology]

[0002] With the development of portable electronic devices and communication devices, there is a strong need for the development of high-energy density lithium secondary batteries. However, high-energy density lithium secondary batteries have the risk of reduced safety, and improvements are needed to address this.

[0003] As the positive electrode active material for lithium secondary batteries, lithium nickel manganese cobalt composite oxide, lithium cobalt oxide, etc. are used.

[0004] In order to manufacture a lithium secondary battery with improved life characteristics, a method of utilizing a positive electrode containing a single crystal positive electrode active material has been proposed.

[0005] However, the single-crystal positive electrode active materials known so far suffer from particle aggregation during the manufacturing process of the positive electrode active material, reduced productivity, increased residual lithium, and reduced capacity, lifespan, and rate-limiting performance, and improvements are required in these areas. Summary of the Invention [Problem to be solved by the invention]

[0006] One aspect of the present invention is to provide a novel positive electrode active material for a lithium secondary battery.

[0007] Another aspect of the present invention is to provide a method for producing the above-mentioned positive electrode active material for a lithium secondary battery.

[0008] In yet another aspect of the present invention, there is provided a lithium secondary battery including a positive electrode for a lithium secondary battery, the positive electrode active material being the above-described positive electrode active material. [Means for solving the problem]

[0009] In one aspect, a positive electrode active material for a lithium secondary battery is provided, the positive electrode active material including a nickel-based active material having a nickel content of 60 mol % or more, the positive electrode active material including large crystalline particles of 1 to 10 μm in size, and a lanthanum group element contained within the large crystalline particles.

[0010] In another aspect, a nickel-based active material precursor, a lithium precursor, and a lanthanum group element precursor are mixed, and a primary heat treatment is performed while controlling the mixed molar ratio of lithium to metals other than lithium to be in the range of 0.8 to 1; and adding a lithium precursor to the heat-treated product and performing a secondary heat treatment while controlling the mixed molar ratio of lithium to metals excluding lithium to be 0.95 to 1.05.

[0011] According to another aspect, a method for manufacturing a lithium-based active material, comprising: mixing a nickel-based active material precursor containing a lanthanum group element and a lithium precursor; and performing a first heat treatment while controlling the mixed molar ratio of lithium to metals other than lithium to be in the range of 0.8 to 1; and adding a lithium precursor to the product of the first heat treatment, and performing a second heat treatment while controlling the mixed molar ratio of lithium to metals excluding lithium to be 0.95 to 1.05.

[0012] The first heat treatment is carried out in an oxidizing gas atmosphere at 850 to 950°C, The secondary heat treatment is carried out at 700 to 800°C.

[0013] In yet another aspect, there is provided a lithium secondary battery including a positive electrode containing the above-described positive electrode active material. [Effects of the Invention]

[0014] In one aspect, a positive electrode active material in which grain growth is promoted has a reduced content of residual lithium and suppresses oxygen desorption from the surface, and by using the positive electrode active material, a lithium secondary battery with improved life characteristics can be manufactured. [Brief explanation of the drawings]

[0015] [Figure 1A] 1 is a scanning electron microscope photograph of the nickel-based active material precursor obtained in Production Example 1 immediately after the first heat treatment. [Figure 1B] This is an enlarged photograph of FIG. 1A. [Figure 1C] This is an enlarged photograph of FIG. 1A. [Figure 2A] 1 is a scanning electron microscope photograph of the nickel-based active material obtained in Example 1. [Figure 2B] 1 is a scanning electron microscope photograph of the nickel-based active material obtained in Example 1. [Figure 2C] 1 is a scanning electron microscope photograph of the nickel-based active material obtained in Example 1. [Figure 3A] 1 is a scanning electron microscope photograph of the nickel-based active material obtained in Example 2. [Figure 3B] 1 is a scanning electron microscope photograph of the nickel-based active material obtained in Example 2. [Figure 3C] 1 is a scanning electron microscope photograph of the nickel-based active material obtained in Example 2. [Figure 4A] 1 is a scanning electron microscope photograph of the nickel-based active material obtained in Example 3. [Figure 4B] 1 is a scanning electron microscope photograph of the nickel-based active material obtained in Example 3. [Figure 4C] 1 is a scanning electron microscope photograph of the nickel-based active material obtained in Example 3. [Figure 5] 1 is a graph showing high-temperature life characteristics of coin cells manufactured according to Manufacturing Example 1-2 and Comparative Manufacturing Example 2. [Figure 6] 1 is a schematic diagram of a lithium secondary battery according to an illustrative embodiment; [Figure 7A] 1 is an electron scanning microscope analysis image of the positive electrode active material obtained in Example 1. [Figure 7B] 1 is an electron scanning microscope analysis image of the positive electrode active material obtained in Example 2. [Figure 7C] 1 is an electron scanning microscope analysis image of the positive electrode active material obtained in Comparative Example 1. [Figure 8] 1 is a graph showing X-ray diffraction analysis spectra for the positive electrode active material of Example 1 and the positive electrode active materials of Comparative Examples 1 and 2. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, a cathode active material for a lithium secondary battery, a method for manufacturing the same, a cathode for a lithium secondary battery including the same, and a lithium secondary battery including the cathode according to an embodiment will be described in detail.

[0017] Single-crystal nickel-based active materials with nickel content of 60 mol% or more have excellent capacity characteristics, but they suffer from problems such as particle aggregation during high-temperature heat treatment for single crystallization and reduced productivity, which require improvement. To solve these problems, a method has been proposed in which an alkaline grain growth promoter is used during heat treatment.

[0018] Although the use of an alkaline grain growth promoter can somewhat reduce the aggregation between particles, the remaining grain growth promoter acts as a resistor after heat treatment, thereby reducing the life characteristics of a lithium secondary battery using a positive electrode containing a nickel-based active material.

[0019] In order to solve the above-mentioned problems, the present inventors provide a positive electrode active material containing a lanthanum group element inside a single crystal.

[0020] The cathode active material according to one embodiment has large crystalline particles, contains a lanthanum group element within the large crystalline particles, and can promote grain growth without using alkaline grain growth promoters such as NaCl and KCl, which can degrade cell performance during the preparation of the cathode active material. Furthermore, the cathode active material has a high oxygen storage capacity, which can be used to suppress oxygen desorption and thereby manufacture a lithium secondary battery with improved lifespan.

[0021] In this specification, the "interior of a large crystal particle" refers to the central region of the large crystal particle, excluding the surface of the large crystal particle.

[0022] According to an embodiment, the positive electrode active material for a lithium secondary battery includes a nickel-based active material having a nickel content of 60 mol% or more and has a large crystalline particle state containing a lanthanum group element therein. The nickel-based active material and the positive electrode active material have a single crystalline state, which can be confirmed using a high-resolution transmission electron microscope (HRTEM).

[0023] As used herein, "large crystalline particles" have a single crystal state and can be in the form of a single particle (one-body particle), a secondary particle which is an aggregate of primary particles, or a combination thereof. Large crystalline particles are single particles of 1 to 10 μm in size, secondary particles which are an aggregate of primary particles, or a combination thereof. The size of the primary particles is 1 to 10 μm.

[0024] In this specification, when the particles are spherical, the term "size" refers to the average particle diameter, and when the particles are non-spherical, the term refers to the major axis length. The average particle diameter and major axis length can be determined using a scanning electron microscope or a particle size analyzer. In the examples herein, the particle size was evaluated using a scanning electron microscope.

[0025] As used herein, the term "single particle" refers to a structure in which particles are not mutually agglomerated but exist as an independent phase in a morphological phase, separated and / or dispersed from one another. In contrast to such a single particle, a particle structure may have a structure in which small particles (primary particles) are physically and / or chemically agglomerated to form relatively large particles (secondary particles).

[0026] The size of the single particle is 2 μm to 8 μm, for example, 3 μm to 7 μm, and the size of the secondary particle is 5 μm to 30 μm, 10 μm to 25 μm, for example, 10 μm to 20 μm.

[0027] The cathode active material according to one embodiment includes large crystalline particles, which lengthens the migration path of lithium ions to the surface of the nickel-based active material. This minimizes the formation of surface impurities such as lithium carbonate and lithium hydroxide, which are formed when lithium ions migrate to the surface of the nickel-based active material react with moisture or carbon dioxide in the air and are adsorbed onto the surface of the nickel-based active material. Furthermore, the cathode active material maintains a stable crystalline structure during charge and discharge, preventing a rapid decrease in capacity due to changes in the crystalline structure.

[0028] The lanthanum group elements are La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu or combinations thereof, for example, Ce.

[0029] The positive electrode active material according to one embodiment is a compound represented by Chemical Formula 1.

[0030] [Chemical formula 1] Li a (Ni 1-w-x-y-z M3 w Co x M1 y M2 z )O 2±α1 In Chemical Formula 1, M1 is one or two elements selected from the group consisting of Mn and Al; M2 is at least one element selected from the group consisting of boron (B), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), zirconium (Zr), and aluminum (Al); M3 is at least one element selected from the group consisting of La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu; 0.95≦a≦1.1, 0.6≦(1-xyz)<1, 0 <w≦0.05、0≦x≦0.4、0≦y≦0.4、0≦z≦0.4、0≦α1≦0.1である。

[0031] In a nickel-based active material having a nickel content of 60 mol % or more, the nickel content is 60 to 95 mol % or more, or 60 to 85 mol %. By using such a nickel-based active material, a lithium secondary battery having high capacity characteristics can be manufactured.

[0032] The positive electrode active material contains a lanthanum group element in an amount of 0.1 to 5 mol %, or 0.2 to 1 mol %. The lanthanum group element in the positive electrode active material controls the particle size of the positive electrode active material and contributes to single crystallization. When the lanthanum group element content is within this range, the rate-limiting performance and life characteristics of a lithium secondary battery using the positive electrode active material are improved.

[0033] X-ray diffraction analysis of the positive electrode active material revealed that the full width at half maximum of the peak corresponding to the (003) plane was 0.1030° to 0.1052°, and the ratio of the full width at half maximum of the peak corresponding to the (003) plane to the full width at half maximum of the peak corresponding to the (104) plane (FWHM(003) / FWHM(104)) was 1.22 to 1.26. Furthermore, X-ray diffraction analysis of the positive electrode active material revealed that no CeO2-related peak was observed in the 2θ range of 28°. Here, a CeO2-related peak in the 2θ range of 27° to 29°, e.g., 28°, would be observed if cerium oxide were externally coated on the surface of a nickel-based active material. As described above, the absence of a CeO2-related peak in the positive electrode active material of an embodiment indicates that the positive electrode active material has a doped structure in which Ce is contained within large crystalline particles, rather than a surface-coated complex containing a lanthanum group element such as cerium oxide.

[0034] A method for preparing a positive electrode active material according to an embodiment is as follows.

[0035] The positive electrode active material can be produced by, for example, two production methods. The first production method is as follows.

[0036] A nickel-based active material precursor, a lithium precursor, and a lanthanum group element precursor are mixed to obtain a first mixture, in which the contents of the nickel-based active material precursor and the lithium precursor are stoichiometrically controlled so that the molar ratio of the metals excluding lithium is controlled to be in the range of 0.8 to 1.

[0037] The mixing is carried out by mechanical milling using a ball mill, a jet mill or the like.

[0038] Next, the first mixture is subjected to a primary heat treatment in an oxidizing gas atmosphere at 800 to 950° C., for example, 900 to 950° C., to obtain a nickel-based active material.

[0039] Next, a lithium precursor is added to the heat-treated product, and a secondary heat treatment is carried out at 700 to 800°C, for example, 720 to 780°C, while controlling the mixed molar ratio of lithium to metals excluding lithium to be 0.95 to 1.05.

[0040] The content of the lithium precursor is controlled so that the molar ratio of the metals excluding lithium is in the range of 0.95 to 1.05, or 0.99 to 1.03. The second heat treatment is performed at a temperature lower than that of the first heat treatment. When the first and second heat treatments are performed under the above conditions, a single crystalline positive electrode active material for a lithium secondary battery with improved life characteristics can be produced.

[0041] The contents of the nickel-based active material precursor and the lanthanum group element precursor are stoichiometrically controlled to obtain a desired positive electrode active material.

[0042] The heat treatment is carried out in an oxidizing gas atmosphere. Examples of the oxidizing gas atmosphere include an air atmosphere or an oxygen atmosphere. The oxygen atmosphere has an oxygen content of 90% by volume or more, with the remainder being an inert gas. Here, the inert gas is nitrogen, helium, argon, or a combination thereof. The oxidizing gas is composed of 10 to 20% by volume of oxygen or air and 80 to 90% by volume of an inert gas.

[0043] The lanthanum group element precursor is a compound containing a lanthanum group element, and may be a nitrate, oxide, sulfate, chloride, or the like containing one or more elements selected from La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. Examples of the lanthanum group element precursor include cerium oxide, cerium nitrate, and cerium sulfate.

[0044] The nickel-based active material precursor is, for example, a compound represented by the following chemical formula 5.

[0045] [Chemical formula 5] Ni 1-x-y-z Co x M1 y M2z (OH)2 In Chemical Formula 5, M1 is one or two elements selected from the group consisting of Mn and Al, and M2 is an element selected from the group consisting of boron (B), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), zirconium (Zr), and aluminum (Al); 0.6≦(1-xyz)<1, 0≦x≦0.4, 0≦y≦0.4, 0≦z≦0.4.

[0046] In Chemical Formula 5, 0≦z≦0.05 and 0.6≦(1−xyz)≦0.95 also apply. In Chemical Formula 5, x is 0.1 to 0.3, y is 0.05 to 0.3, and z is also 0.

[0047] Next, a second manufacturing method for manufacturing a positive electrode active material will be described.

[0048] The positive electrode active material can be prepared by a first heat treatment of a mixture of a nickel-based active material precursor containing a lanthanum group element and a lithium precursor, controlling the molar ratio of lithium to metals other than lithium to a range of 0.8 to 1, and a second heat treatment of a mixture of the heat-treated product of the mixture of the lithium and metals other than lithium to a range of 0.95 to 1.05.

[0049] A nickel-based active material precursor containing a lanthanum group element can be obtained, for example, by reacting a cobalt precursor, a manganese precursor, a nickel precursor, and a lanthanum group element precursor.

[0050] The nickel-based active material precursor containing a lanthanum group element is, for example, a compound represented by the following chemical formula 5-1.

[0051] [Chemical formula 5-1] Ni 1-w-x-y-z M3 w Co x M1y M2 z (OH)2 In Chemical Formula 5, M1 is one or two elements selected from the group consisting of Mn and Al; M2 is an element selected from the group consisting of boron (B), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), zirconium (Zr), and aluminum (Al); M3 is at least one element selected from the group consisting of La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu; 0.6≦(1-wxyz)<1, 0 <w≦0.05、0≦x≦0.4、0≦y≦0.4、0≦z≦0.4である。

[0052] The cathode active material obtained by the above-described manufacturing method can improve productivity by suppressing interparticle aggregation. Furthermore, a cathode active material with suppressed oxygen desorption from the surface can be provided, without the problem of reduced lifespan that occurs when an alkaline grain growth promoter is used in the manufacture of conventional single-crystal cathode active materials, thereby enabling the manufacture of lithium secondary batteries with improved lifespan.

[0053] In the first positive electrode active material described above, the nickel-based active material precursor is a secondary particle, which is an aggregate of primary particles, and has a size of 2 to 5 μm. An example of the nickel-based active material precursor is a compound represented by the above-mentioned Chemical Formula 5.

[0054] The nickel-based active material precursor of Chemical Formula 5 may be, for example, a compound represented by the following Chemical Formula 6, a compound represented by Chemical Formula 7, or a mixture thereof.

[0055] [Chemical formula 6] Ni 1-x1-y1-z1 Co x1 Mn y1 M z1 (OH)2 In Chemical Formula 6, M is an element selected from the group consisting of boron (B), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), and zirconium (Zr); 0.6≦(1−x1−y1−z1)<1, 0≦x1≦0.4, 0≦y1≦0.4, 0≦z1≦0.4.

[0056] [Chemical formula 7] Ni 1-x2-z2 Co x2 Al z2 (OH)2 In chemical formula 7, 0.6≦(1−x2−z2)<1, 0≦x2≦0.4, 0 <z2≦0.4である。

[0057] The nickel-based active material precursor may be, for example, Ni 0.91 Co 0.06 Mn 0.03 (OH)2), Ni 0.91 Co 0.06 Al 0.03 (OH)2, Ni 0.92 Co 0.05 Al 0.03 (OH)2, Ni 0.94 Co 0.03 Al 0.03 (OH)2, Ni 0.88 Co 0.06 Al 0.06 (OH)2, Ni 0.96 Co 0.02 Al 0.02 (OH)2, Ni 0.93 Co 0.04 Al 0.03 (OH)2, Ni 0.8 Co 0.15 Al 0.05 O2(OH) 2、 Ni 0.75 Co 0.20 Al 0.05 (OH) 2、 Ni 0.92 Co 0.05 Mn 0.03 (OH)2, Ni 0.94 Co 0.03 Mn0.03 (OH)2, Ni 0.88 Co 0.06 Mn 0.06 (OH)2, Ni 0.96 Co 0.02 Mn 0.02 (OH)2, Ni 0.93 Co 0.04 Mn 0.03 (OH)2, Ni 0.8 Co 0.15 Mn 0.05 O2(OH) 2、 Ni 0.75 Co 0.20 Mn 0.05 (OH)2, Ni 0.6 Co 0.2 Mn 0.2 (OH)2, Ni 0.7 Co 0.15 Mn 0.15 (OH)2, Ni 0.7 Co 0.1 Mn 0.2 (OH)2, Ni 0.8 Co 0.1 Mn 0.1 (OH)2 or Ni 0.85 Co 0.1 Al 0.05 It is also (OH)2.

[0058] The nickel-based active material precursor can be prepared by co-precipitation of a mixture containing metal sources such as nickel precursor, cobalt precursor, manganese precursor, and precursors of other transition metals, a complexing agent, and a pH adjuster.

[0059] The metal source may be a metal precursor corresponding to the composition of the nickel-based active material precursor, such as, but not limited to, metal carbonate, metal sulfate, metal nitrate, metal chloride, etc., as long as it is used as a metal precursor in the art.

[0060] The nickel precursor may be nickel sulfate, nickel chloride, nickel nitrate, etc. The cobalt precursor may be cobalt sulfate, cobalt chloride, cobalt nitrate, etc. The manganese precursor may be manganese sulfate, manganese chloride, manganese nitrate, etc.

[0061] The content of each metal raw material is stoichiometrically controlled so as to obtain a desired nickel-based active material precursor.

[0062] The pH adjuster reduces the solubility of metal ions in the reactor, allowing them to precipitate as hydroxides. Examples of pH adjusters include ammonium hydroxide, sodium hydroxide (NaOH), and sodium carbonate (Na2CO3). An example of a pH adjuster is sodium hydroxide (NaOH).

[0063] The complexing agent serves to regulate the reaction rate of precipitate formation in the coprecipitation reaction. Examples of the complexing agent include ammonium hydroxide (NH4OH) (aqueous ammonia), citric acid, acrylic acid, tartaric acid, glycolic acid, etc. The content of the complexing agent is used at a normal level. An example of the complexing agent is aqueous ammonia.

[0064] The product obtained by the coprecipitation reaction is washed and then dried to obtain the desired nickel-based active material precursor for lithium secondary batteries, which is dried under conventional conditions.

[0065] In the second method for preparing a positive electrode active material, a nickel-based active material precursor containing a lanthanum group element can be prepared in the same manner as in the preparation of the nickel-based active material precursor described above, except that a lanthanum group element precursor is further added to a mixture containing metal raw materials such as a nickel precursor, a cobalt precursor, a manganese precursor, and precursors of other transition metals, a complexing agent, and a pH adjuster.

[0066] A lithium secondary battery according to another embodiment includes a positive electrode including the above-described positive electrode active material, a negative electrode, and an electrolyte interposed therebetween.

[0067] By using the method for manufacturing a positive electrode active material according to an embodiment, a lithium secondary battery with improved capacity characteristics, charge / discharge efficiency, and lifespan can be obtained.

[0068] According to one embodiment, the nickel-based active material has a residual lithium content of less than 900 ppm.

[0069] Hereinafter, a method for manufacturing a lithium secondary battery having a positive electrode including a positive electrode active material, a negative electrode, a lithium salt-containing non-aqueous electrolyte, and a separator will be described according to an embodiment.

[0070] The positive electrode and negative electrode are produced by applying a positive electrode active material layer forming composition and a negative electrode active material layer forming composition to a current collector and drying them to form a positive electrode active material layer and a negative electrode active material layer, respectively.

[0071] The composition for forming the positive electrode active material is prepared by mixing a positive electrode active material, a conductive material, a binder, and a solvent. The positive electrode active material is a nickel-based active material according to an embodiment.

[0072] The positive electrode binder serves to improve adhesion between positive electrode active material particles and between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof, and these may be used alone or in combination.

[0073] The conductive material is not particularly limited as long as it is conductive and does not induce chemical changes in the battery. For example, 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, and thermal black; conductive fibers such as carbon nanotubes, carbon fibers, and metal fibers; carbon fluoride; metal powders such as aluminum and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives may be used.

[0074] The content of the conductive material is 1 to 10 parts by weight or 1 to 5 parts by weight based on 100 parts by weight of the positive electrode active material. When the content of the conductive material is within this range, the final electrode has excellent conductivity.

[0075] A non-limiting example of the solvent is N-methylpyrrolidone, and the content of the solvent is 20 to 200 parts by weight based on 100 parts by weight of the positive electrode active material. When the content of the solvent is within this range, the process of forming the positive electrode active material layer is easy.

[0076] The positive electrode current collector is not particularly limited as long as it has a thickness of 3 to 500 μm, does not induce chemical changes in the battery, and has high conductivity, and may be made of, for example, stainless steel, aluminum, nickel, titanium, heat-treated carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. The current collector may have fine irregularities on its surface to increase the adhesive strength of the positive electrode active material, and may be in various forms such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0077] Separately, a composition for forming a negative electrode active material layer is prepared by mixing a negative electrode active material, a binder, and a solvent.

[0078] The negative electrode active material may be a material capable of reversibly absorbing / desorbing lithium ions, lithium metal, a lithium metal alloy, a material capable of being doped and dedoped with lithium, a transition metal oxide, or a combination thereof.

[0079] The material capable of reversibly absorbing and releasing lithium ions may be, for example, a carbon material, i.e., a carbon-based negative electrode active material commonly used in lithium secondary batteries. Representative examples of the carbon-based negative electrode active material include crystalline carbon, amorphous carbon, or a combination of these. Examples of the crystalline carbon include graphite, such as amorphous, plate-like, flake-like, spherical, or fibrous natural graphite or artificial graphite. Examples of the amorphous carbon include soft carbon, hard carbon, mesophase pitch carbide, and calcined coke.

[0080] The lithium metal alloy may be an alloy of lithium and a metal selected from the group consisting of Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn.

[0081] The material capable of doping and dedoping lithium includes silicon-based materials such as Si and SiO x(0 < x < 2), Si-Q alloy (where Q is an element selected from the group consisting of alkali metals, alkaline earth metals, group 13 elements, group 14 elements, group 15 elements, group 16 elements, transition metals, rare earth elements, and combinations thereof, and is not Si), Si-carbon composite, Sn, SnO2, Sn-R (where R is an element selected from the group consisting of alkali metals, alkaline earth metals, group 13 elements, group 14 elements, group 15 elements, group 16 elements, transition metals, rare earth elements, and combinations thereof, and is not Sn), Sn-carbon composite, etc., and at least one of them can be mixed with SiO2 and used. As the elements Q and R, g, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ge, P, As, Sb, Bi, S, Se, Te, Po, and combinations thereof can be selected and used.

[0082] As the transition metal oxide, lithium titanate can be used.

[0083] The negative electrode binder includes, as non-limiting examples, polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM) rubber, sulfonated EPDM rubber, styrene butadiene rubber (SBR), fluorine rubber, polyacrylic acid, and polymers in which hydrogen thereof is substituted with Li, Na, Ca, etc., or various binder polymers such as various copolymers.

[0084] The negative electrode active material layer may further include a conductive material. The conductive material may be any material that does not induce chemical changes in the battery and has conductivity. Examples of the conductive material include graphite, such as natural graphite or artificial graphite; carbon black, such as carbon black, acetylene black, ketjen black, channel black, harness black, lamp black, and thermal black; conductive fibers, such as carbon fiber and metal fiber; conductive tubes, such as carbon nanotubes; metal powders, such as fluorocarbon, aluminum, and nickel powder; 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 is preferably carbon black, more specifically, carbon black having an average particle size of several tens of nanometers.

[0085] The conductive material is present in an amount of 0.01 to 10 parts by weight, 0.01 to 5 parts by weight, or 0.1 to 2 parts by weight, based on 100 parts by weight of the total weight of the negative electrode active material layer.

[0086] The composition for forming a negative electrode active material layer may further include a thickener, which may be at least one of carboxymethyl cellulose (CMC), carboxyethyl cellulose, starch, regenerated cellulose, ethyl cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, and polyvinyl alcohol, and may be, for example, CMC.

[0087] The content of the solvent is 100 to 300 parts by weight based on 100 parts by weight of the total weight of the negative electrode active material. When the content of the solvent is within this range, the process of forming the negative electrode active material layer is easy.

[0088] The thickness of the negative electrode current collector is typically 3 to 500 μm. There are no particular limitations on the material of the negative electrode current collector, as long as it does not induce chemical changes in the battery and is conductive. Examples of materials that can be used include copper, stainless steel, aluminum, nickel, titanium, heat-treated carbon, copper or stainless steel surfaces treated with carbon, nickel, titanium, silver, and the like, and aluminum-cadmium alloys. Similarly to the positive electrode current collector, fine irregularities can be formed on the surface to strengthen the binding force of the negative electrode active material, and the negative electrode current collector can be used in various forms, such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0089] A separator is interposed between the positive electrode and the negative electrode prepared by the above process.

[0090] The separator has a pore size of 0.01 to 10 μm and a thickness of usually 5 to 30 μm. Specific examples include sheets or nonwoven fabrics made of olefin polymers such as polypropylene and polyethylene, or glass fibers. When a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte can also serve as the separator.

[0091] The lithium salt-containing non-aqueous electrolyte is composed of a non-aqueous electrolyte solution and a lithium salt. The non-aqueous electrolyte may be a non-aqueous electrolyte solution, an organic solid electrolyte, or an inorganic solid electrolyte.

[0092] Examples of the non-aqueous electrolyte include, but are not limited to, aprotic organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, N,N-formamide, N,N-dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate.

[0093] Non-limiting examples of the organic solid electrolyte include polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate ester polymers, polyester sulfide, polyvinyl alcohol, and polyvinylidene fluoride.

[0094] Non-limiting examples of the inorganic solid electrolyte include nitrides, halides, and sulfates of Li, such as LiN, LiI, LiNI, LiN-LiI-LiOH, LiSiO, LiSiS, LiSiO, LiSiO-LiI-LiOH, and LiPO-LiS-SiS.

[0095] The lithium salt is a substance that is easily dissolved in the non-aqueous electrolyte, and non-limiting examples thereof include LiCl, LiBr, LiI, LiClO4, LiBF4, and LiB 10 Cl 10 , LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, CF3SO3Li, (CF3SO2)2NLi, (FSO2)2NLi, lithium chloroborate, lithium lower aliphatic carboxylate, tetraphenylborate lithium imide, etc. may be used.

[0096] FIG. 6 is a cross-sectional view schematically illustrating a representative structure of a lithium secondary battery according to an embodiment.

[0097] Referring to FIG. 6 , a lithium secondary battery 81 includes a positive electrode 83, a negative electrode 82, and a separator 84. The positive electrode 83, the negative electrode 82, and the separator 84 are wound or folded, and the resulting electrode assembly is housed in a battery case 85. Depending on the battery shape, a separator may be disposed between the positive and negative electrodes, and the electrodes may be stacked to form a battery structure. An organic electrolyte solution is then injected into the battery case 85 and sealed with a cap assembly 86 to complete the lithium secondary battery 81. The battery case 25 may be cylindrical, prismatic, thin-film, or the like. For example, the lithium secondary battery 21 may be a large-sized thin-film battery. The lithium secondary battery may also be a lithium-ion battery. The battery structure may be housed in a pouch, impregnated with an organic electrolyte solution, and sealed to form a lithium-ion polymer battery. A plurality of the battery structures may be stacked to form a battery pack, which may be used in any device requiring high capacity and high output. For example, it can be used in laptop computers, smartphones, electric vehicles, etc.

[0098] In addition, the lithium secondary battery has excellent storage stability, life characteristics, and high-rate characteristics at high temperatures, and can therefore be used in electric vehicles (EVs), for example, hybrid vehicles such as plug-in hybrid electric vehicles (PHEVs).

[0099] The present invention will be described in more detail with reference to the following examples and comparative examples, but the examples are merely illustrative and are not intended to limit the scope of the invention.

[0100] (Production of nickel-based active material precursor) Manufacturing Example 1 The nickel-based active material precursor (Ni 0.91 Co 0.06 Mn 0.03(OH)2) was synthesized.

[0101] Nickel sulfate (NiSO4 . 6H2O), cobalt sulfate (CoSO4 . 7H2O) and manganese sulfate (MnSO4 . A mixed solution was prepared by dissolving Ni:Co:Mn (H2O) in distilled water as a solvent to give a molar ratio of Ni:Co:Mn = 91:6:3. To form the complex compound, a diluted ammonia water (NH4OH) solution and sodium hydroxide (NaOH) as a precipitant were prepared. Then, the metal raw material mixed solution, ammonia water, and sodium hydroxide were each added to the reactor. Sodium hydroxide was added to maintain the pH inside the reactor. The reaction was continued with stirring for approximately 20 hours, after which the addition of the raw material solution was stopped.

[0102] The slurry solution in the reactor was filtered and washed with high-purity distilled water, and then dried in a hot air oven at 200°C for 24 hours to obtain a nickel-based active material precursor (Ni 0.91 Co 0.06 Mn 0.03 (OH)2) was obtained. The nickel-based active material precursor was in the form of secondary particles, and the average particle size of the secondary particles was about 4 μm.

[0103] (Production of positive electrode active material) Example 1 The nickel-based active material precursor (Ni 0.91 Co 0.06 Mn 0.03 Lithium hydroxide and cerium oxide (CeO2) were added to the (CuO2) (OH)2 to obtain a first mixture. In the first mixture, the molar ratio of lithium to the transition metal was approximately 0.9. The content of lithium carbonate was controlled so that the molar ratio of lithium to the metal in the nickel-based active material precursor was 0.9. Here, the metals represent Ni, Co, and Mn. The first mixture was subjected to a primary heat treatment in an oxygen atmosphere at approximately 900°C.

[0104] Lithium hydroxide was added to the product obtained by the first heat treatment to obtain a second mixture, which was then subjected to a second heat treatment in an oxygen atmosphere at approximately 800°C for 12 hours to obtain a large crystalline particle-shaped positive electrode active material (LiNi 0.908 Co 0.06 Mn 0.03 Ce 0.002 O2). The content of lithium carbonate in the second mixture was controlled so that the lithium to metal molar ratio was 1.0, where the moles of metal refer to the total moles of Ni, Co, Mn, and Ce. Ce was contained within the large crystalline particles of the positive electrode active material, and the Ce content was 0.2 mol%. The large crystalline particles had an average particle size of approximately 3 μm and were in the form of a single particle.

[0105] Example 2-3 The positive electrode active materials were obtained in the same manner as in Example 1, except that the content of cerium oxide (CeO2) was changed so that the content of Ce in the positive electrode active materials was 0.5 mol% and 1.0 mol%, respectively.

[0106] Examples 4-5 The positive electrode active material was obtained in the same manner as in Example 1, except that the manufacturing process conditions were controlled so that the average particle sizes of the large crystal particles were about 2 μm and 5 μm, respectively.

[0107] Examples 6-7 A positive electrode active material was obtained in the same manner as in Example 1, except that the mixed molar ratios of lithium and metal in the first mixture were controlled to be 0.85 and 1.0, respectively.

[0108] Examples 8-9 A positive electrode active material was obtained in the same manner as in Example 1, except that the mixed molar ratios of lithium and transition metal in the second mixture were controlled to be 0.95 and 1.05, respectively.

[0109] Example 10 A nickel-based active material precursor containing cerium was synthesized by co-immersion.

[0110] Nickel sulfate (NiSO4 . 6H2O), cobalt sulfate (CoSO4 . 7H2O) and manganese sulfate (MnSO4 . A mixed solution was prepared by dissolving Ni, Co, and Mn in distilled water as a solvent in a molar ratio of 6:2:2. Cerium nitrate was added to the mixed solution, and the content of cerium nitrate was 0.2 mol%.

[0111] To form the complex compound, a diluted solution of ammonia water (NH4OH) and sodium hydroxide (NaOH) as a precipitant were prepared. Then, the metal raw material mixed solution, ammonia water, and sodium hydroxide were each added to the reactor. Sodium hydroxide was added to maintain the pH inside the reactor. The reaction continued with stirring for approximately 20 hours, after which the addition of the raw material solution was stopped.

[0112] The slurry solution in the reactor was filtered and washed with high-purity distilled water, and then dried in a hot air oven at 200°C for 24 hours to obtain a cerium-containing nickel-based active material precursor (Ni 0.89 Co 0.06 Mn 00.03 Ce 0.02 (OH)2) was obtained. The nickel-based active material precursor was in the form of secondary particles, and the average particle size of the secondary particles was about 4 μm.

[0113] The cerium-containing nickel-based active material precursor (Ni 0.89 Co 0.06 Mn 00.03 Ce 0.02 A first mixture was obtained by adding lithium hydroxide to (OH)2). The first mixture had a lithium to transition metal molar ratio of approximately 0.9. The lithium hydroxide content was controlled so that the metal molar ratio of the nickel-based active material precursor containing lithium and cerium was 0.9, and the metal content was the total content of Ni, Co, and Mn. The first mixture was subjected to a primary heat treatment in an oxygen atmosphere at approximately 900°C.

[0114] Lithium hydroxide was added to the product obtained by the first heat treatment to obtain a second mixture, which was then subjected to a second heat treatment in an oxygen atmosphere at about 850°C for 12 hours to obtain the positive electrode active material (LiNi 0.89 Co 0.06 Mn 0.03 Ce 0.02 O2) was produced. The content of lithium hydroxide in the second mixture was controlled so that the mixed molar ratio of lithium to metal (Li / metal molar ratio) was 1.0.

[0115] Comparative Example 1 The positive electrode active material was obtained in the same manner as in Example 1, except that cerium oxide (CeO2) was not added when preparing the first mixture.

[0116] When Comparative Example 1 was carried out, it was difficult to obtain a positive electrode active material in the form of large crystal particles.

[0117] Comparative Example 2 When preparing the first mixture, cerium oxide (CeO2) was not added, but lithium hydroxide and cerium oxide (CeO2) were added to the product obtained by the first heat treatment to obtain a second mixture, and the same procedure as in Example 1 was carried out to obtain a cerium-coated positive electrode active material.

[0118] Production example 1: Coin cell manufacturing A coin cell was manufactured as follows using the positive electrode active material obtained in Example 1 as the positive electrode active material.

[0119] The nickel-based active material (LiNi 0.6 Co 0.2 Mn 0.2 A mixture of 96 g of O2), 2 g of polyvinylidene fluoride, 47 g of N-methylpyrrolidone as a solvent, and 2 g of carbon black as a conductive material was mixed using a mixer to remove air bubbles, thereby producing a uniformly dispersed slurry for forming a positive electrode active material layer.

[0120] The slurry prepared by the above process was coated on an aluminum foil using a doctor blade to form a thin electrode plate, which was then dried at 135°C for 3 hours or more, and then rolled and vacuum dried to prepare a cathode.

[0121] A 2032-type coin cell was fabricated using the positive electrode and a lithium metal counter electrode as the counter electrode. A separator (thickness: approximately 16 μm) made of a porous polyethylene (PE) film was placed between the positive electrode and the lithium metal counter electrode, and an electrolyte was injected to fabricate a 2032-type coin cell. The electrolyte was a solution containing 1.15 M LiPF6 dissolved in a solvent made by mixing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 20:40:40.

[0122] Production Example 2-10: Coin cell manufacturing Coin cells were fabricated in the same manner as in Preparation Example 1, except that the positive electrode active materials of Examples 2 to 10 were used instead of the positive electrode active material of Example 1.

[0123] Comparative production example 1: Coin cell manufacturing Lithium secondary batteries were fabricated in the same manner as in Preparation Example 1, except that the positive electrode active material prepared in Comparative Example 1 was used instead of the positive electrode active material prepared in Example 1.

[0124] Comparative production example 2: Coin cell manufacturing A lithium secondary battery was fabricated in the same manner as in Preparation Example 1, except that the positive electrode active material prepared in Preparation Example 1 was used instead of the positive electrode active material prepared in Example 1.

[0125] Evaluation example 1: Electron scanning microscope (1) Examples 1-3 and Production Example 1 Scanning electron microscope analysis was performed on the nickel-based active material precursor prepared in Preparation Example 1 and the cathode active materials prepared in Examples 1 to 3. The scanning electron microscope used was a Magellan 400L (FEI company), and the analysis results are shown in Figures 1A-1C, 2A-2C, 3A-3C, and 4A-4C. Here, the nickel-based active material precursor and cathode active materials were in a state prior to being pulverized using a jet mill.

[0126] 1A to 1C are electron scanning microscope photographs of the nickel-based active material precursor obtained in Preparation Example 1, FIGS. 2A to 2C are electron scanning microscope photographs of the positive electrode active material obtained in Example 1, FIGS. 3A to 3C are electron scanning microscope photographs of the positive electrode active material obtained in Example 2, and FIGS. 4A to 4C are electron scanning microscope photographs of the positive electrode active material obtained in Example 3.

[0127] Referring to the graphs, the particle growth of the nickel-based active material precursor of Preparation Example 1 and the cathode active materials of Examples 1-3 can be confirmed. The nickel-based active material precursor of Preparation Example 1 was found to be large crystalline (single crystal) particles with an average particle size of 3 μm, as shown in FIGS. 1A-1C, and the cathode active material of Example 1 was found to have large crystalline (single crystal) particle morphology with an average particle size of 3.2 μm, as shown in FIGS. 2A-2C. Furthermore, the cathode active material of Example 2 was found to have large crystalline (single crystal) particle morphology with an average particle size of 3.3 μm, as shown in FIGS. 3A-3C, and the cathode active material of Example 3 was found to have large crystalline particle morphology with an average particle size of 3.5 μm, as shown in FIGS. 4A-4C.

[0128] (2) Examples 1-2 and Comparative Example 1 The cathode active materials obtained in Examples 1 and 2 and Comparative Example 1 were analyzed using a scanning electron microscope, and the results are shown in Figures 7A, 7B, and 7C, respectively. Here, the cathode active materials were in a state of being pulverized by a jet mill.

[0129] As shown in FIG. 7C, in the case of Comparative Example 1, non-single-crystal particles are present, but the positive electrode active materials of Example 1 (FIG. 7A) and Example 2 (FIG. 7B) are both synthesized in a single-crystal form, and no polycrystals are observed.

[0130] Evaluation example 2: X-ray diffraction analysis (1) Examples 1-2 and Production Example 1 X-ray diffraction analysis was performed on the cathode active materials prepared in Examples 1-2 and Preparation Example 1 using X'pert pro (PANalytical) with CuKα radiation (1.54056 Å). The results of the X-ray diffraction analysis were investigated and are shown in Table 1 below.

[0131] FWHM(003) indicates the half-width of the peak corresponding to the (003) plane (peak with 2θ of approximately 18°), and FWHM(104) indicates the ratio of the half-width of the peak corresponding to the (104) plane (peak with 2θ of approximately 43°). In Table 1, Area(003 / 104) indicates the ratio of the area of ​​the peak corresponding to the (003) plane (peak with 2θ of approximately 18°) to the area of ​​the peak corresponding to the (104) plane (peak with 2θ of approximately 43°).

[0132] The peak corresponding to the (003) plane provides information about the layer structure of the positive electrode active material, and the peak corresponding to the (104) plane provides information about the crystallinity.

[0133] [Table 1]

[0134] Referring to Table 1, it was found that the positive electrode active materials of Examples 1 and 2 had a reduced half-width compared to Comparative Example 1, and had improved crystallinity.

[0135] (2) Example 1 and Comparative Examples 1-2 X-ray diffraction analysis was performed on the positive electrode active material of Example 1 and the positive electrode active materials prepared in Comparative Examples 1 and 2 using X'pert Pro (PANalytical) with CuKα radiation (1.54056 Å). The results of the X-ray diffraction analysis were investigated and are shown in Figure 8.

[0136] Referring to this, a CeO2-related peak was observed around 28° in the cerium-coated cathode active material of Comparative Example 2, but the above-mentioned peak was not observed in the cathode active materials of Example 1 and Comparative Example 1. This indicates that the cathode active material of Example 1 has a structure that is distinct from the coated cathode active material of Comparative Example 2. As a result of this analysis, it was confirmed that the cathode active material of Example 1 has a structure in which Ce is incorporated into the lattice and exists in a state of being bonded to oxygen.

[0137] Evaluation example 3: Residual lithium Residual lithium in the positive electrode active materials prepared in Examples 1 and 2 and Comparative Example 1 was investigated by the following method.

[0138] 10 g of the positive electrode active material was placed in a beaker containing 100 ml of distilled water and stirred at 200 rpm for 5 minutes to dissolve the lithium remaining on the surface. Then, the positive electrode active material was removed from the remaining lithium solution using a filter with an average pore size of 0.5 to 5 μm.

[0139] The lithium derivative remaining on the surface from which the positive electrode active material had been removed was titrated with a 1N HCl solution to measure the amount of lithium in the solution.

[0140] The amount of lithium in the solution is measured using an automatic titrator by measuring the first inflection point (EP1) where the pH suddenly changes from pH 7 to 9 and the endpoint (FP) where the pH reaches 5, and then calculating the Li2CO3 content and LiOH content using the following Equations 1 and 2.

[0141] [Formula 1] Li2CO3 content (%): (FP-EP1) Х 0.1 Х 0.001 Х (Li2CO3 Mw(73.89) / 5) Х 100

[0142] [Formula 2] LiOH content (%): (2 Х EP1-FP) Х 0.1 Х 0.001 Х (LiOH Mw(23.94) / 5) Х 100 The calculated Li2CO3 content and LiOH content were combined to measure the content of the lithium derivative remaining on the final surface, and the content of the lithium derivative remaining on the surface was converted into wt% based on the total weight of the positive electrode active material. The results are shown in Table 2 below.

[0143] [Table 2]

[0144] Referring to Table 2, it can be seen that the positive electrode active material of Example 1-2 had a reduced total residual lithium content compared to the positive electrode active material of Comparative Example 1.

[0145] Evaluation example 4: Cycle characteristics The coin cells produced in Production Examples 1-2 and Comparative Production Examples 1 and 2 were evaluated for charge / discharge characteristics using a charge / discharge machine (manufacturer: TOYO, model: TOYO-3100).

[0146] The first charge / discharge cycle consisted of a constant current charge at 0.2C at 25°C to 4.2V, followed by a constant voltage charge at 0.05C. The charged cell was allowed to rest for approximately 10 minutes, after which a constant current discharge was performed at 0.2C to a voltage of 3V. The second charge / discharge cycle consisted of a constant current charge at 0.2C to 4.2V, followed by a constant voltage charge at 0.05C. The charged cell was allowed to rest for approximately 10 minutes, followed by a constant current discharge at 0.2C to a voltage of 3V.

[0147] The battery was then charged at a constant current of 1 C for 3 hours until the battery voltage reached 4.2 V. Subsequently, the battery was discharged at a constant current of 1 C for 3 hours until the battery voltage reached 3 V. This cycle was repeated for a total of 50 cycles.

[0148] The lifespan evaluation was carried out by charging at a constant current of 1 C until the voltage reached 4.2 V, and then by charging at a constant voltage of 0.05 C until the voltage reached 3 V. After a rest period of about 10 minutes, the charged cells were discharged at a constant current of 1 C until the voltage reached 3 V, and this cycle was repeated 50 times to evaluate the lifespan.

[0149] The charge / discharge efficiency was calculated by the following formula 3, and some of the charge / discharge efficiencies were investigated and are shown in Table 3 below.

[0150] [Formula 3] Charge / discharge efficiency = [average discharge voltage of the first cycle / average charge voltage of the first cycle] x 100

[0151] [Table 3]

[0152] Referring to Table 3, it was found that the coin cells manufactured according to Manufacturing Examples 1 and 2 had improved charge-discharge efficiency compared to Comparative Manufacturing Example 2. The coin cell of Comparative Manufacturing Example 1 exhibited the same level of charge-discharge efficiency as Comparative Manufacturing Example 2. The charge-discharge efficiency of the coin cells manufactured according to Manufacturing Examples 3 to 10 was evaluated in the same manner as the coin cell of Manufacturing Example 1.

[0153] As a result of the evaluation, the coin cells manufactured according to Preparation Examples 3 to 10 exhibited the same level of charge / discharge efficiency as the coin cell of Preparation Example 1.

[0154] Evaluation example 5: High temperature life characteristics The charge / discharge characteristics of the coin cells produced in Production Example 1-2 and Comparative Production Example 2 were evaluated using a charge / discharge machine (manufacturer: TOYO, model: TOYO-3100).

[0155] The first charge / discharge cycle consisted of a constant current charge at 0.1C at 45°C to 4.3V, followed by a constant voltage charge at 0.05C. The charged cell was then rested for approximately 10 minutes, after which a constant current discharge was performed at 0.1C to a voltage of 3V. The second charge / discharge cycle consisted of a constant current charge at 0.2C to 4.3V, followed by a constant voltage charge at 0.05C. The charged cell was then rested for approximately 10 minutes, followed by a constant current discharge at 0.2C to a voltage of 3V.

[0156] The battery was then charged at a constant current of 1 C for 3 hours until the battery voltage reached 4.3 V. Subsequently, the battery was discharged at a constant current of 1 C for 3 hours until the battery voltage reached 2.5 V. This cycle was repeated for a total of 50 cycles.

[0157] The lifespan evaluation was carried out by charging at a constant current of 1 C until the voltage reached 4.2 V, and then by charging at a constant voltage of 0.05 C until the voltage reached 3 V. After a rest period of about 10 minutes, the charged cells were discharged at a constant current of 1 C until the voltage reached 3 V, and this cycle was repeated 50 times to evaluate the lifespan.

[0158] The capacity retention ratio (CRR) was calculated and the results are shown in FIG.

[0159] Referring to FIG. 5, it can be seen that the coin cell manufactured according to Manufacturing Example 1-2 has an excellent capacity retention rate, similar to the coin cell of Comparative Manufacturing Example 2.

[0160] Although one embodiment has been described above with reference to the drawings and examples, this is merely an example, and those skilled in the art will recognize that various modifications and equivalent embodiments are possible. Therefore, the scope of protection of the present invention should be determined by the following claims. [Explanation of symbols]

[0161] 81 Lithium secondary battery 82 Negative electrode 83 Positive electrode 84 Separator 85 Battery Case 86 Cap Assembly

Claims

1. A positive electrode active material including a nickel-based active material having a nickel content of 60 mol% or more, The positive electrode active material contains large crystalline particles of 1 to 10 μm in size, The large crystal particles contain cerium (Ce), the cerium content is 0.2 mol % to 1.0 mol %; According to the X-ray diffraction analysis of the positive electrode active material, CeO ２ No relevant peaks were observed, The positive electrode active material for a lithium secondary battery is a compound represented by the following Chemical Formula 1: [Chemical formula 1] Li a (Ni 1-w-x-y-z M3 w Co x M1 y M2 z)O 2±α1 In Chemical Formula 1, M1 is one or two elements selected from the group consisting of manganese (Mn) and aluminum (Al); M2 is at least one element selected from the group consisting of boron (B), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), zirconium (Zr), and aluminum (Al); M3 is Ce; 0.95≦a≦1.1, 0.6≦(1−x−y−z)<1, 0<w≦0.05, 0≦x≦0.4, 0≦y≦0.4, 0≦z≦0.4, and 0≦α1≦0.

1.

2. 2. The positive electrode active material for lithium secondary batteries according to claim 1, wherein the large crystalline particles are single particles of 1 to 10 μm in size, secondary particles which are aggregates of primary particles, or a combination thereof, and the size of the primary particles is 1 to 10 μm.

3. 3. The positive electrode active material for a lithium secondary battery according to claim 2, wherein the secondary particles have a size of 5 to 30 μm.

4. The positive electrode active material has a half-value width of 0.1030° to 0.1052° of a peak corresponding to a (003) plane determined by X-ray diffraction analysis; 2. The positive electrode active material for lithium secondary batteries according to claim 1, wherein the ratio of the full width at half maximum FWHM(003) of the peak corresponding to the (003) plane to the full width at half maximum FWHM(104) of the peak corresponding to the (104) plane (FWHM(003) / FWHM(104)) is 1.22 to 1.

26.

5. A lithium secondary battery comprising a positive electrode for a lithium secondary battery, the positive electrode active material comprising the positive electrode active material according to any one of claims 1 to 4.

6. mixing a nickel-based active material precursor, a lithium precursor, and a cerium precursor, and performing a first heat treatment while controlling the mixed molar ratio of lithium to metals other than lithium to be in the range of 0.8 to 1; and performing a second heat treatment on the product of the first heat treatment while controlling the mixture molar ratio of lithium to metals other than lithium to be 0.95 to 1.05, The positive electrode active material includes a nickel-based active material having a nickel content of 60 mol% or more, the positive electrode active material contains large crystalline particles of 1 to 10 μm in size, and cerium is contained inside the large crystalline particles; the cerium content is 0.2 mol % to 1.0 mol %; The nickel-based active material precursor is a compound represented by the following chemical formula 5: [Chemical formula 5] Ni 1-x-y-z Co x M1 y M2 z (OH) 2 In Chemical Formula 5, M1 is one or two elements selected from the group consisting of Mn and Al; M2 is an element selected from the group consisting of boron (B), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), zirconium (Zr), and aluminum (Al); 0.6≦(1−x−y−z)<1, 0≦x≦0.4, 0≦y≦0.4, and 0≦z≦0.

4.

7. 7. The method for producing a positive electrode active material for a lithium secondary battery according to claim 6, wherein the primary heat treatment is carried out in an oxidizing gas atmosphere at 800 to 950°C.

8. The method for producing a positive electrode active material for a lithium secondary battery according to claim 6, wherein the second heat treatment is performed at 700 to 800°C.

9. A method of manufacturing a semiconductor device, comprising: mixing a nickel-based active material precursor containing cerium and a lithium precursor; and performing a primary heat treatment while controlling the mixed molar ratio of lithium to metals excluding lithium to be in the range of 0.8 to 1; and performing a second heat treatment on the product of the first heat treatment while controlling the mixture molar ratio of lithium to metals other than lithium to be 0.95 to 1.05, The positive electrode active material includes a nickel-based active material having a nickel content of 60 mol% or more, the positive electrode active material contains large crystalline particles of 1 to 10 μm in size, and cerium is contained inside the large crystalline particles; the cerium content is 0.2 mol % to 1.0 mol %; The cerium-containing nickel-based active material precursor is a compound represented by the following chemical formula 5-1. [Chemical formula 5-1] Ni 1-w-x-y-z M3 w Co x M1 y M2 z (OH) 2 In Chemical Formula 5, M1 is one or two elements selected from the group consisting of Mn and Al; M2 is an element selected from the group consisting of boron (B), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), zirconium (Zr), and aluminum (Al); M3 is Ce; 0.6≦(1−w−x−y−z)<1, 0<w≦0.05, 0≦x≦0.4, 0≦y≦0.4, and 0≦z≦0.4.

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