KR102195726B1 - Lithium cobalt composite oxide for lithium secondary battery and lithium secondary battery including positive electrode comprising the same - Google Patents

Abstract

Contains magnesium (Mg), aluminum (Al) and cobalt (Co), the atomic ratio of Mg/Co is 0.0035 to 0.03, the atomic ratio of Mg/Al is 4 or less, and further contains fluorine A lithium secondary battery containing a lithium cobalt composite oxide for a lithium secondary battery and a positive electrode including the lithium cobalt composite oxide is provided.

Description

Lithium cobalt composite oxide for lithium secondary battery and lithium secondary battery including positive electrode comprising the same}

It relates to a lithium cobalt composite oxide for a lithium secondary battery and a lithium secondary battery containing a positive electrode including the same.

Lithium cobalt oxide (LiCoO ₂ ) is widely used as a positive active material for lithium secondary batteries. As the use of lithium secondary batteries expands from portable information electronic devices to power tools, automobiles, and other industries, high capacity, high power and safety are more demanded, and LiCoO ₂ performance is improved due to capacity limitations and safety issues of LiCoO ₂ Research on development for this is actively underway.

One aspect is to provide a novel lithium cobalt composite oxide for lithium secondary batteries.

Another aspect is to provide a lithium secondary battery with improved stability at high voltage and improved cell performance by using the lithium cobalt composite oxide described above.

According to one aspect,

Including magnesium (Mg) and aluminum (Al) and cobalt (Co),

The atomic ratio of Mg/Co is 0.0035 to 0.03,

The atomic ratio of Mg/Al is 4 or less,

A lithium cobalt composite oxide for a lithium secondary battery further comprising fluorine is provided.

According to another aspect, there is provided a lithium secondary battery including a positive electrode including the lithium cobalt composite oxide described above.

The lithium cobalt composite oxide according to an exemplary embodiment not only improves stability at high voltage, but also improves thermal stability, and when using this, a lithium secondary battery having improved charge/discharge and lifespan characteristics can be manufactured.

1 shows the results of differential scanning calorimeter analysis of positive active materials prepared according to Examples 1, 2, and Comparative Example 1.

Hereinafter, a lithium cobalt composite oxide according to exemplary embodiments and a lithium secondary battery including a positive electrode including the same will be described in more detail.

The lithium cobalt composite oxide for a lithium secondary battery according to an embodiment of the present invention includes magnesium and aluminum, and may further include fluorine.

In the lithium cobalt composite oxide, when aluminum is doped to the cobalt site, since the Al-O binding energy is higher than that of the Co-O binding energy, thermal stability can be improved. When the lithium cobalt composite oxide having improved thermal stability is used as described above, a lithium secondary battery having improved high temperature storage characteristics can be manufactured.

Aluminum may be doped with 5.0 mol% or less of the lithium cobalt composite oxide according to the present embodiment, specifically 0.2 mol% to 5.0 mol%, and more specifically 0.2 mol% to 3.0 mol%. When aluminum is doped in the above range, the cycle characteristics may be improved. The atomic ratio of Al/F may be greater than 0 and less than or equal to 5. In addition, the atomic ratio of Mg/Al may be greater than 0 and 4 or less. When aluminum is included in the above range, the charge/discharge capacity may be increased by suppressing the phase transition, and a battery having excellent high-temperature life characteristics may be obtained. And according to one embodiment, the atomic ratio of (Li+Mg)/(Co+Al) is 1.00 or less, for example, 0.96 to 1.00. When the above-described fluorine content, Mg/Co atomic ratio, F/Mg atomic ratio, and (Li+Mg)/(Co+Al) atomic ratio are within the above-described ranges, the effect of inhibiting phase transition at high voltage is excellent, and lifespan characteristics This improved lithium cobalt composite oxide can be obtained.

The lithium cobalt composite oxide according to the present embodiment may have an atomic ratio of Mg/Co of 0.0035 to 0.03, specifically 0.004 to 0.02, and more specifically 0.005 to 0.01.

In the lithium cobalt composite oxide, fluorine replaces some sites of oxygen to lower the average number of oxidation of cobalt ions by the number of moles of fluorine substituted at +4, and the oxidation value of Co on the surface of the lithium cobalt composite oxide is further reduced. By lowering the average oxidation number of cobalt ions in this way, the structural stability of the lithium cobalt composite oxide is improved. In addition, the generation of O ₂ gas is suppressed and the elution of Co is suppressed due to the increase in ionic bonding characteristics by Co-F bonding, thereby improving the chemical stability of the lithium cobalt composite oxide.

In the lithium cobalt composite oxide for lithium secondary batteries, fluorine is located on the surface of magnesium-doped lithium cobalt composite oxide, or in a state mixed with magnesium-doped lithium cobalt composite oxide, or fluorine is a magnesium-doped lithium cobalt composite oxide. It can be doped inside. The content of fluorine is greater than 0 and 2 mol% or less, based on the total mol of lithium cobalt composite oxide, and may be, for example, 0.2 to 2 mol%. The atomic ratio of F/Mg may be greater than 0 and less than or equal to 2, and may be, for example, 0.25 to 2, and more specifically 1 to 2. The charge/discharge capacity can be increased in the above-described range, and a battery having excellent high-temperature life characteristics can be obtained.

When lithium cobalt oxide (LiCoO ₂ ) is used as the positive electrode active material, a phase transition of O ₃ → H _1-3 → O ₁ occurs in a high voltage region. When the lithium cobalt oxide in which the phase transition has occurred is used as a positive electrode active material, the cell performance of the lithium secondary battery is deteriorated.

After many studies, the present inventors doped magnesium and aluminum into the lithium cobalt complex oxide, while controlling the atomic ratio of the doped Mg/Co, while further including fluorine in the lithium cobalt complex oxide, O ₃ occurring in the high voltage region → H _1-3 → O ₁ phase transition was effectively inhibited. As a result, when the lithium cobalt composite oxide is used, stability at high voltage is improved, thereby increasing charge/discharge capacity, and life characteristics of lithium secondary batteries at high voltage are improved. In the present application, the “high voltage region” is, for example, 4.5V (vs. vs. Li/Li+) or more, specifically in the range of 4.55V to 4.63V.

In the lithium cobalt complex oxide according to an embodiment, magnesium is doped to the lithium site, so that magnesium ions exist in the space within the lithium layer, so that even if all of the lithium ions escape from the lithium layer in the high voltage section, the magnesium acts as a pillar and the lithium cobalt complex The oxide form O ₃ further stabilizes the structure. In particular, the stability of the 0 ₃ phase increases at a high voltage of 4.5V or higher.

The lithium cobalt composite oxide according to an embodiment may be, for example, a compound represented by Formula 1 below.

[Formula 1]

Li _1-x Mg _x Co _1-y Al _y O _2-z F _z

In Formula 1, 0<x≤0.03, 0<y≤0.03, and 0<z≤0.02. In Formula 1, 0<x+y+z≤0.07, 0<z/x≤2, 0<y/z≤5, and 0<x/y≤4. When the content of magnesium in the compound of Formula 1 is 3 mol% or less, doping of magnesium to cobalt sites may be suppressed and lithium sites may be substituted.

The lithium cobalt composite oxide according to an embodiment is, for example, Li _0.995 Mg _0.005 Co _0.995 Al _0.005 O _1.99 F _0.01 , Li _{0 . 995} Mg _{0 . 005} Co _{0 . 99} Al _{0 . 01 O 1 .99 F 0.01, Li} 0.992 Mg 0.008 Co 0.98 Al 0.002 O 1.984 F 0.016, Li 0. ₉₉₂ Mg _{0 . 008} Co _{0 . 95} Al _{0 . 005 O 1 .984 F 0.016, Li} 0.992 Mg 0.008 Co 0.99 Al 0.01 O 1.984 F 0.016, Li 0. ₉₉₂ Mg _{0 . 008} Co _{0 . 985} Al _{0 . 015 O 1 .985 F 0.016, Li} 0.992 Mg 0.008 Co 0.98 Al 0.02 O 1.984 F 0.016, Li 0. ₉₉ Mg _{0 . 01} Co _{0 . 985} Al _{0 . 005 O 1 .98 F 0.02, Li} 0.99 Mg 0.01 Co 0.99 Al 0.01 O 1.98 F 0.02, Li 0.992 Mg 0.008 Co 0.995 Al 0.005 O 1.998 F 0.002, Li 0.992 Mg 0.008 Co 0.99 Al 0.01 O 1.998 F 0.002, Li 0.992 Mg _0.008 Co _0.97 Al _0.03 O _1.984 F _0.016 , Li _{0 . 99} Mg _{0 . 01} Co _{0 . 985} Al _{0 . 005 O 1 .98 F 0.02, Li} 0.99 Mg 0.01 Co 0.99 Al 0.01 O 1.98 F 0.02,, Li 0. ₉₉₂ Mg _{0 . 008} Co _{0 . 97} Al _{0 .} A ₀₃ O _{1 0.016 .984 F,} or _{Li 0.99 Mg 0.01 Co 0.985 Al 0.005} O 1.98 F 0.02.

The lithium cobalt composite oxide according to an embodiment may have a specific surface area of 0.1 to 3 m ² /g and an average particle diameter of 1 to 20 μm.

Hereinafter, a method of manufacturing a lithium cobalt composite oxide according to an embodiment will be described.

First, a lithium precursor, a cobalt precursor, a magnesium precursor, an aluminum precursor, and a fluorine precursor are mixed in a predetermined molar ratio to obtain a precursor mixture.

Specifically, a precursor mixture may be obtained by mixing a lithium precursor, a cobalt precursor, a magnesium precursor, an aluminum precursor, and a fluorine precursor while controlling stoichiometrically to obtain a desired lithium cobalt composite oxide. For example, the lithium precursor may be one or more selected from lithium hydroxide (LiOH), lithium carbonate (Li2CO3), lithium sulfate (Li2SO4), and lithium nitrate (LiNO3). The cobalt precursor may be one or more selected from cobalt carbonate, cobalt hydroxide, cobalt chloride, cobalt sulfate, and cobalt nitrate. The magnesium precursor may be one or more selected from magnesium chloride, magnesium carbonate, magnesium hydroxide, magnesium sulfate, magnesium nitrate, and magnesium fluoride. As the aluminum precursor, at least one selected from aluminum sulfate, aluminum chloride, and aluminum hydroxide may be used. The fluorine precursor may be magnesium fluoride or the like.

The mixing may be performed by dry mixing, such as mechanical mixing, using a ball mill, a bamba remixer, a homogenizer, a Hansel mixer, or the like. Dry mixing can reduce manufacturing cost compared to wet mixing.

Subsequently, the precursor mixture may be heat-treated in an air or oxygen atmosphere to obtain a lithium cobalt composite oxide.

The above-described heat treatment may be performed at 400 to 1200°C, for example 900 to 1100°C in an air or oxygen atmosphere. Here, the oxygen atmosphere can be formed by using oxygen alone or by using oxygen, nitrogen and an inert gas together. The heat treatment time varies according to the heat treatment temperature. For example, it can be carried out for 5 to 20 hours.

In addition to the above-described solid phase method, the lithium cobalt composite oxide according to an embodiment can be prepared according to a general manufacturing method such as spray pyrolysis.

According to another aspect, there is provided a lithium secondary battery including a positive electrode including the lithium cobalt composite oxide described above. The manufacturing method of the lithium secondary battery will be described as follows.

A positive electrode is prepared according to the following method.

A positive electrode active material composition in which a lithium cobalt composite oxide, a binder, and a solvent according to an exemplary embodiment are mixed is prepared. A conductive agent may be further added to the positive electrode active material composition. The positive electrode active material composition is directly coated and dried on a metal current collector to prepare a positive electrode plate. Alternatively, after the positive active material composition is cast on a separate support, a film peeled from the support may be laminated on a metal current collector to manufacture a positive electrode plate. When manufacturing the positive electrode, a first positive electrode active material, which is a positive electrode active material commonly used in lithium secondary batteries, may be further included. As the first positive electrode active material, at least one selected from the group consisting of lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, and lithium manganese oxide may be further included, but is not limited thereto. Any positive active material available in the art may be used. For _{example, Li a A 1 - b B} b D 2 ( in the above formula, 0.90≤a≤1.8, and 0≤b≤0.5); _{Li a E 1 - b B b} O 2 - c D c ( wherein, 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05 a); _{LiE 2 - b B b O 4} -c D c ( wherein, 0≤b≤0.5, 0≤c≤0.05 a); Li _a Ni _{1 -b- c} Co _b B _c D _α (in the above formula, 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, 0<α≤2); _{Li a Ni 1 -b- c Co b} B c O 2 - α F α ( wherein, 0.90≤a≤1.8, 0≤b≤0.5, is 0≤c≤0.05, 0 <α <2) ; Li _a Ni _{1 -b- c} Mn _b B _c D _α (in the above formula, 0.90≦a≦1.8, 0≦ _b ≦0.5, 0≦ _c ≦0.05, 0<α≦2); _{Li a Ni 1 -b- c Mn b} B c O 2 - α F α ( wherein, 0.90≤a≤1.8, 0≤b≤0.5, is 0≤c≤0.05, 0 <α <2) ; Li _a Ni _b E _c G _d O ₂ (In the above formula, 0.90≦a≦1.8, 0≦ _b ≦0.9, 0≦ _c ≦0.5, and 0.001≦ _d ≦0.1); Li _a Ni _b Co _c Mn _d GeO ₂ (In the above formula, 0.90≤a≤1.8, 0≤b≤0.9, 0≤c≤0.5, 0≤d≤0.5, 0.001≤e≤0.1); Li _a NiG _b O ₂ (in the above formula, 0.90≦ _a ≦1.8 and 0.001≦ _b ≦0.1); Li _a CoG _b O ₂ (In the above formula, 0.90≦a≦1.8 and 0.001≦ _b ≦0.1); Li _a MnG _b O ₂ (in the above formula, 0.90≦ _a ≦1.8 and 0.001≦ _b ≦0.1); Li _a Mn ₂ G _b O ₄ (In the above formula, 0.90≦a≦1.8 and 0.001≦ _b ≦0.1); QO ₂ ; QS ₂ ; LiQS ₂ ; V ₂ O ₅ ; LiV ₂ O ₅ ; LiIO ₂ ; LiNiVO ₄ ; Li _(3-f) J ₂ (PO ₄ ) ₃ (0≦ _f ≦2); Li _(3-f) Fe ₂ (PO ₄ ) ₃ (0≦ _f ≦ ₂ ); A compound represented by any one of the formulas of LiFePO ₄ may be used. In the above formula, A is Ni, Co, Mn, or a combination thereof; B is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, rare earth elements, or combinations thereof; D is O, F, S, P, or a combination thereof; E is Co, Mn, or a combination thereof; F is F, S, P, or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof; Q is Ti, Mo, Mn, or a combination thereof; I is Cr, V, Fe, Sc, Y, or a combination thereof; J is V, Cr, Mn, Co, Ni, Cu, or a combination thereof.

In the positive electrode active material composition, the binder is polyamideimide, polyacrylic acid (PAA), polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropyl cellulose, recycled cellulose, polyvinylpyrrolidone, tetrafluoro. Ethylene, polyethylene, polypropylene, lithium polyacrylate, lithium polymethacrylate, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene butadiene rubber, fluorine rubber, and various copolymers.

The conductive agent may include, for example, at least one carbon-based conductive agent selected from the group consisting of carbon black, carbon fiber, and graphite. The carbon black may be, for example, selected from the group consisting of acetylene black, Ketjen black, super P, channel black, furnace black, lamp black, and thermal black.

The graphite may be natural graphite or artificial graphite.

As the solvent, butanol, acetonitrile, acetone, methanol, ethanol, N-methyl-2-pyrrolidone (NMP), and the like may be used, but any other commonly used solvent may be used.

On the other hand, it is also possible to form pores inside the electrode by adding a plasticizer to the positive electrode active material composition and/or the negative electrode active material composition.

The contents of the positive electrode active material, the conductive agent, the binder, and the solvent are the levels commonly used in lithium secondary batteries. One or more of the conductive agent, the binder, and the solvent may be omitted according to the use and configuration of the lithium secondary battery.

The negative electrode can be obtained by performing almost the same method, except that a negative electrode active material is used instead of the positive electrode active material in the above-described positive electrode manufacturing process.

As the negative electrode active material, a carbon-based material, silicon, silicon oxide, silicon-based alloy, silicon-carbon-based material composite, tin, tin-based alloy, tin-carbon composite, metal oxide, or a combination thereof is used.

The carbon-based material may be crystalline carbon, amorphous carbon, or a mixture thereof. The crystalline carbon may be graphite such as amorphous, plate-like, flake, spherical or fibrous natural graphite or artificial graphite, and the amorphous carbon is soft carbon (low temperature calcined carbon) or hard carbon (hard carbon). carbon), mesophase pitch carbide, fired coke, graphene, carbon black, carbon nanotubes, carbon fibers, etc., but are not necessarily limited thereto, and any one that can be used in the art may be used. .

The negative active material may be selected from the group consisting of Si, SiOx (0<x<2, for example 0.5 to 1.5), Sn, SnO ₂ , or silicon-containing metal alloys and mixtures thereof. As a metal capable of forming the silicon alloy, one or more of Al, Sn, Ag, Fe, Bi, Mg, Zn, in, Ge, Pb, and Ti may be used.

The negative active material may include a metal/metalloid alloy capable of being alloyed with lithium, an alloy thereof, or an oxide thereof. For example, the metal/metalloid alloyable with lithium is Si, Sn, Al, Ge, Pb, Bi, Sb, Si-Y alloy (wherein Y is an alkali metal, alkaline earth metal, group 13 element, group 14 element, Transition metal, rare earth element or a combination element thereof, not Si), Sn-Y alloy (wherein Y is an alkali metal, alkaline earth metal, group 13 element, group 14 element, transition metal, rare earth element, or a combination element thereof , Not Sn), MnOx (0<x≤2), and the like. The element Y is Mg, 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, Tl, Ge, P, As, Sb, Bi, S, It may be Se, Te, Po, or a combination thereof. For example, the oxide of the metal/metalloid that can be alloyed with lithium may be lithium titanium oxide, vanadium oxide, lithium vanadium oxide, SnO ₂ , SiO _x (0<x<2), and the like.

The negative active material may include, for example, at least one element selected from the group consisting of a group 13 element, a group 14 element, and a group 15 element of the periodic table of elements, specifically at least one element selected from the group consisting of Si, Ge, and Sn. .

In the negative active material composition, the conductive agent, the binder, and the solvent may be the same as those of the positive active material composition. In addition, the contents of the negative electrode active material, the conductive agent, the binder, and the solvent are the levels commonly used in lithium secondary batteries.

The separator is interposed between the anode and the cathode, and an insulating thin film having high ion permeability and mechanical strength is used.

The pore diameter of the separator is generally 0.01 to 10 μm, and the thickness is generally 5 to 20 μm. Examples of such a separator include olefin-based polymers such as polypropylene; Sheets or non-woven fabrics made of glass fiber or polyethylene are used. When a solid polymer electrolyte is used as the electrolyte, the solid polymer electrolyte may also serve as a separator.

Among the separators, specific examples of the olefin-based polymer include polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film having two or more layers thereof, and a polyethylene/polypropylene two-layer separator, a polyethylene/polypropylene/polyethylene three-layer separator, A mixed multilayer film such as a polypropylene/polyethylene/polypropylene three-layer separator may be used.

The lithium salt-containing nonaqueous electrolyte is composed of a nonaqueous electrolyte and a lithium salt.

As the non-aqueous electrolyte, a non-aqueous electrolyte solution, an organic solid electrolyte, or an inorganic solid electrolyte is used.

The non-aqueous electrolyte solution contains an organic solvent. Any such organic solvent may be used as long as it can be used as an organic solvent in the art. For example, propylene carbonate, ethylene carbonate, fluoroethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl isopropyl carbonate, dipropyl carbonate, dibutyl carbonate , Fluoroethylene carbonate, benzonitrile, acetonitrile, tetrahydrofuran, 2-methyltetrahydrofuran, γ-butyrolactone, dioxolane, 4-methyldioxolane, N,N-dimethylformamide, N, N-dimethylacetamide, dimethyl sulfoxide, dioxane, 1,2-dimethoxyethane, sulfolane, dichloroethane, chlorobenzene, nitrobenzene, diethylene glycol, dimethyl ether, or mixtures thereof.

As the organic solid electrolyte, for example, a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphate ester polymer, polyvinyl alcohol, or the like may be used.

As the inorganic solid electrolyte, for example, Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Li ₄ SiO ₄ -LiI-LiOH, Li ₃ PO ₄ -Li ₂ S-SiS ₂ or the like may be used.

The lithium salt is a material soluble in the non-aqueous electrolyte, for example, LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , Li(CF ₃ SO ₂ ) ₂ N, Li (FSO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ , LiAlO ₂ , LiAlCl ₄ , LiN(C _x F _{2x + 1} SO ₂ )(C _y F _{2y + 1} SO ₂ ) (where x,y are natural numbers), LiCl, LiI, or mixtures thereof. And in the non-aqueous electrolyte for the purpose of improving charge/discharge characteristics and flame retardancy, for example, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexamethylphosphoamide (hexamethyl phosphoramide), nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N, N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxy ethanol, aluminum trichloride And the like may be added. In some cases, in order to impart non-flammability, a halogen-containing solvent such as carbon tetrachloride or ethylene trifluoride may be further included.

The lithium secondary battery includes a positive electrode, a negative electrode, and a separator. The above-described positive electrode, negative electrode, and separator are wound or folded to be accommodated in a battery case. Subsequently, an organic electrolyte is injected into the battery case and sealed with a cap assembly to complete a lithium secondary battery. The battery case may have a cylindrical shape, a square shape, or a thin film type.

A separator may be disposed between the positive electrode and the negative electrode to form a battery structure. After the battery structure is stacked in a bi-cell structure, it is impregnated with an organic electrolyte, and the resulting product is accommodated in a pouch and sealed to complete a lithium ion polymer battery.

In addition, a plurality of battery structures are stacked to form a battery pack, and the battery pack can be used in all devices requiring high capacity and high output. For example, it can be used for laptop computers, smart phones, electric vehicles, and the like.

The present invention will be described in more detail through the following examples and comparative examples. However, the examples are for illustrative purposes only and are not intended to limit the scope of the present invention.

Example One

Li:Mg:Co:Al:O:F by mixing Li precursor lithium carbonate, Co precursor cobalt oxide, Mg precursor magnesium carbonate, aluminum precursor aluminum sulfate, and fluorine precursor magnesium fluoride in a Hansel mixer for about 3 minutes. To obtain a mixture adjusted to have the composition of the lithium cobalt composite oxide shown in Table 1 by the atomic ratio of. The mixture was heat-treated at about 1000° C. in an air atmosphere for about 10 hours to pulverize and classify the obtained heat treated product to obtain a lithium cobalt composite oxide as a positive electrode active material.

Example 2-12 and Comparative example 1-5

A lithium cobalt composite oxide was obtained in the same manner as in Example 1, except that the mixing atomic ratio of Li:Mg:Co:Al:O:F was changed as shown in Tables 1 and 2 below. The following Mg/Co, Mg/Al, F/Mg, and Al/F all mean an atomic ratio.

division Composition of lithium cobalt complex oxide Mg/Co Mg/Al F/Mg Al/F Example 1 Li _0.995 Mg _0.005 Co _0.995 Al _0.005 O _1.99 F _0.01 0.005 One 2 0.5 Example 2 Li _0.995 Mg _0.005 Co _0.99 Al _0.01 O _1.99 F _0.01 0.005 0.5 2 One Example 3 Li _0.992 Mg _0.008 Co _0.998 Al _0.002 O _1.984 F _0.016 0.008 4 2 0.125 Example 4 Li _0.992 Mg _0.008 Co _0.995 Al _0.005 O _1.984 F _0.016 0.008 1.6 2 0.3125 Example 5 Li _0.992 Mg _0.008 Co _0.99 Al _0.01 O _1.984 F _0.016 0.008 0.8 2 0.625 Example 6 Li _0.992 Mg _0.008 Co _0.985 Al _0.015 O _1.985 F _0.016 0.008 0.53 2 0.9375 Example 7 Li _0.992 Mg _0.008 Co _0.98 Al _0.02 O _1.984 F _0.016 0.008 0.4 2 1.25 Example 8 Li _0.99 Mg _0.01 Co _0.985 Al _0.005 O _1.98 F _0.02 0.010 2 2 0.25 Example 9 Li _0.99 Mg _0.01 Co _0.99 Al _0.01 O _1.98 F _0.02 0.010 One 2 0.5 Example 10 Li _0.992 Mg _0.008 Co _0.995 Al _0.005 O _1.998 F _0.002 0.008 1.6 0.25 2.5 Example 11 Li _0.992 Mg _0.008 Co _0.99 Al _0.01 O _1.998 F _0.002 0.008 0.8 0.25 5 Example 12 Li _0.992 Mg _0.008 Co _0.97 Al _0.03 O _1.984 F _0.016 0.008 0.27 2 1.88

division Composition of lithium cobalt complex oxide Mg/Co Mg/Al F/Mg Al/F Comparative Example 1 Li _0.995 Mg _0.005 Co _1.0 O _1.99 F _0.01 0.005 - 2 0 Comparative Example 2 Li _0.992 Mg _0.008 Co _1.0 O _1.984 F _0.016 0.008 - 2 0 Comparative Example 3 Li _0.99 Mg _0.01 Co _1.0 O _1.98 F _0.02 0.01 - 2 0 Comparative Example 4 Li ₁ Co _0.99 Al _0.01 O _1.984 F _0.016 0 0 - 0.625 Comparative Example 5 Li _0.992 Mg _0.008 Co _0.99 Al _0.01 O ₂ 0.008 0.8 0 0

Evaluation example 1: Differential scanning calorimeter analysis

Differential scanning calorimeter analysis was performed on the positive electrode active materials prepared according to Example 1, Example 2, and Comparative Example 1. METTLR TOLEDO's TGA/DSC was used as an analyzer to be used when performing the differential scanning calorimeter analysis, and the analysis was performed by heat treatment at a heating rate of 5°C/min from room temperature to 400°C. Shown in. Referring to FIG. 1, it was found that the thermal stability of the positive electrode active material improved as the amount of aluminum increased.

Evaluation example 2: at 60℃ After saving Swelling Characteristics and Charge and discharge characteristic

The mixture of the positive electrode active material obtained according to Examples and Comparative Examples, polyvinylidene fluoride, and carbon black as a conductive agent was removed using a mixer to prepare a slurry for forming a positive electrode active material layer uniformly dispersed. N-methyl 2-pyrrolidone as a solvent was added to the mixture, and the mixing ratio of the composite cathode active material, polyvinylidene fluoride, and carbon black was 98:1:1 by weight. The slurry prepared according to the above process was coated on an aluminum foil using a doctor blade to form a thin electrode plate, dried at 135° C. for 3 hours or more, and then subjected to rolling and vacuum drying processes to produce a positive electrode.

The negative electrode was prepared by mixing natural graphite, carboxymethylcellulose (CMC), and styrene butadiene rubber (SBR) to obtain a composition for forming a negative electrode active material, which was coated on a copper current collector and dried to prepare a negative electrode. The weight ratio of natural graphite, CMC, and SBR was 97.5:1:1.5, and the content of distilled water was about 50 parts by weight based on 100 parts by weight of the total weight of natural graphite, CMC, and SBR.

A separator made of a porous polyethylene (PE) film (thickness: about 10 μm) was interposed between the positive electrode and the negative electrode, and an electrolyte was injected to prepare a polymer cell. The electrolyte was a solution containing 1.1M LiPF ₆ dissolved in a solvent in which ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed in a volume ratio of 3:4:3.

The polymer cell thus prepared was charged to 90% SOC at a low current at 25°C, and aging was performed for 48 hours, and then cut-off at a current of 0.05C rate while maintaining 4.45V in the constant current/constant voltage mode. off). Subsequently, at the time of discharging, it was discharged at a constant current of 0.5C rate until the voltage reached 3.0V (formation stage, 1 ^st cycle).

The polymer cell that has undergone the 1 ^st cycle of the formation phase is charged at a constant current at 25°C at a current of 0.2C until the voltage reaches 4.45V, and then cut off at a current of 0.05C while maintaining 4.45V in the constant voltage mode ( cut-off). Subsequently, at the time of discharging, it was discharged at a constant current of 0.2C rate until the voltage reached 3.0V (formation step, 2nd cycle).

The polymer cell that has undergone the chemical conversion step is charged at a constant current at 25°C at a current of 0.7C until the voltage reaches 4.45V, and then cut-off at a current of 0.025C while maintaining 4.45V in the constant voltage mode. Thus, a 4.45V full charge state was made with 100% SOC.

After storing the charged battery in an oven at 60° C. for 3 weeks, the battery was taken out and discharged for 3th cycle to 3.0V at a rate of 0.7C/discharge 0.5C.

After the charging and discharging experiment, the swelling and the change in the capacity change rate over time were investigated, respectively, and are shown in Table 3 below.

In addition, the rate of swelling change after storage at 60° C. in each polymer cell is defined by Equation 2 below.

<Equation 2>

Swelling change rate = [(thickness of battery after 3 weeks-thickness of battery before storage)/thickness of battery before storage] × 100

The capacity change rate over time after storage at 60°C is defined by Equation 3 below.

<Equation 3>

Capacity change rate = [Discharge capacity after 3 weeks/initial discharge capacity before high temperature storage] × 100

Evaluation example 3: at 45°C Life characteristics

In the polymer cell prepared in Evaluation Example 2, life evaluation was performed.

Life evaluation performed constant current charging at a current of 0.7 C until reaching 4.45 V. After charging was completed, the cell was evaluated by repeatedly performing a cycle of performing constant current discharge 500 times until the voltage reached 3 V at a current of 0.7 C after a pause of about 10 minutes.

The life evaluation results are shown in Table 3 below. In Table 3 below, the% indicating the content of magnesium, iron and aluminum indicates the mole %.

division Swelling change rate (%) Capacity change rate (%) 45℃ life (%) Example 1 6.5 89.1 86 Example 2 4.8 92.5 84 Example 3 9.8 89.3 91 Example 4 6.2 90.6 89 Example 5 4.5 93.7 88 Example 6 3.8 94.8 83 Example 7 4.0 96.1 80 Example 8 6.1 91.5 90 Example 9 4.7 94.2 89 Example 10 7.2 88.9 84 Example 11 5.3 91.2 82 Example 12 3.7 96.0 80 Comparative Example 1 18.1 84.5 87 Comparative Example 2 16.4 86.2 90 Comparative Example 3 16.1 87.5 90 Comparative Example 4 9.6 81 67 Comparative Example 5 5.6 88 75

Referring to Table 3, the polymer cells prepared using the positive electrode active material of Examples 1, 2 and 4-12 were compared with the polymer cell prepared using the positive electrode active material of Comparative Example 1-4. It was found that the shelf life characteristics were excellent and the high-temperature storage characteristics were improved because the swelling change rate was small and the capacity change rate characteristics were excellent after 3 weeks of storage at 60°C.

In addition, the polymer cell manufactured using the positive electrode active material of Example 3 has superior high-temperature (45°C) life characteristics compared to the polymer cell manufactured using the positive electrode active material of Comparative Examples 1 to 3 and stored for 3 weeks at 60°C. After that, it was found that the swelling change rate was small and the capacity change rate property was excellent, so that the high-temperature storage characteristics were improved. In addition, as shown in Table 3, the polymer cell manufactured using the positive electrode active material of Comparative Example 5 significantly reduced the lifespan at high temperature (45° C.) compared to the polymer cell manufactured using the positive electrode active material of Examples 1 to 12. Showed the result.

Although the above description has been made with reference to the preferred manufacturing examples, those skilled in the art will appreciate that various modifications and changes can be made without departing from the spirit and scope described in the following claims.

Claims (9)

Including magnesium (Mg) and aluminum (Al) and cobalt (Co),
The atomic ratio of Mg/Co is 0.0035 to 0.03,
The atomic ratio of Mg/Al is 4 or less,
A lithium cobalt composite oxide for a lithium secondary battery, further comprising fluorine, wherein the Al/F atomic ratio is greater than 0 and less than 5, and the lithium cobalt composite oxide is a compound represented by the following formula (1):
[Formula 1]
Li _1-x Mg _x Co _1-y Al _y O _2-z F _z
In Formula 1, 0<x≤0.03, 0<y≤0.03, and 0<z≤0.02. The method of claim 1,
A lithium cobalt composite oxide for a lithium secondary battery having an atomic ratio of F/Mg greater than 0 and less than or equal to 2 delete The method of claim 1,
The fluorine is a lithium cobalt composite oxide for a lithium secondary battery having greater than 0 and less than 2 mol% based on the total mole of the lithium cobalt composite oxide. The method of claim 1,
The fluorine is a lithium cobalt composite oxide for a lithium secondary battery doped inside of a magnesium-doped lithium cobalt composite oxide. The method of claim 1,
The lithium cobalt composite oxide is a lithium cobalt composite oxide for a lithium secondary battery having an atomic ratio of (Li+Mg)/(Co+Al) of 1.00 or less. delete A lithium secondary battery containing a positive electrode comprising the lithium cobalt composite oxide of claim 1, 2, 4, 5 or 6. The method of claim 8,
A lithium secondary battery having a charging voltage of 4.5V or more of the lithium secondary battery.

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