KR102385748B1 - Positive electrode active material for rechargeable lithium battery, method of preparing the same and rechargeable lithium battery including the same - Google Patents

Abstract

In one embodiment, the lithium cobalt composite oxide is doped with magnesium, and the magnesium is doped in an amount of 0.1 wt% to 0.45 wt% based on the total amount of the positive active material, and when measured by X-ray photoelectron spectroscopy, the binding energy peak of magnesium 2p The ratio (Mg1s/Mg2p) of the intensity of the magnesium 1s binding energy peak (Mg1s) to the intensity of (Mg2p) is 1.6 to 3.5, A cathode active material for a lithium secondary battery, a method for preparing the same, and a lithium secondary battery comprising the same.

Description

A cathode active material for a lithium secondary battery, a manufacturing method thereof, and a lithium secondary battery comprising the same

A cathode active material for a lithium secondary battery, a manufacturing method thereof, and a lithium secondary battery including the same.

A lithium secondary battery, which has recently been spotlighted as a power source for portable and small electronic devices, uses an organic electrolyte and exhibits a high energy density by showing a discharge voltage that is twice or more higher than that of a battery using an aqueous alkali solution.

Lithium cobalt oxide (LiCoO ₂ ) is widely used as a cathode active material for lithium secondary batteries. As the use of lithium _secondary batteries expands from portable information electronic devices to power tools and automobiles, _high capacity, high output and safety are more required. Research on the development for

One embodiment is to provide a positive active material for a lithium secondary battery having improved cell resistance.

Another embodiment is to provide a method of manufacturing the positive active material.

Another embodiment is to provide a lithium secondary battery including the positive active material.

One embodiment includes a lithium cobalt composite oxide doped with magnesium, wherein the magnesium is doped in an amount of 0.1 wt% to 0.45 wt% based on the total amount of the positive electrode active material, and when measured by X-ray photoelectron spectroscopy, the binding energy peak of magnesium 2p ( A positive active material for a lithium secondary battery is provided, wherein the ratio (Mg1s/Mg2p) of the intensity of the magnesium 1s binding energy peak (Mg1s) to the intensity of Mg2p) is 1.6 to 3.5.

A ratio (Mg1s/Mg2p) of the intensity of the magnesium 1s binding energy peak (Mg1s) to the intensity of the binding energy peak (Mg2p) of the magnesium 2p may be 1.6 to 1.9.

The binding energy peak (Mg2p) of the magnesium 2p may appear at 50±0.5 eV.

The binding energy peak (Mg1s) of the magnesium 1s may appear at 1304±0.5 eV.

The magnesium may be doped in an amount of 0.2 wt% to 0.3 wt% based on the total amount of the positive active material.

The magnesium-doped lithium cobalt composite oxide may be represented by Formula 1 below.

[Formula 1]

LiCo _1-xy Mg _x M _y O ₂

In Formula 1,

0.004 ≤ x+y ≤ 0.015,

M is at least one metal element selected from Mn, Al, Cr, Fe, V, Mg, Ti, Zr, Nb, Mo, W, Cu, Zn, Ga, In, Sn, La and Ce.

In another embodiment, a cobalt compound, a lithium salt and a magnesium compound are mixed and a first heat treatment is performed to prepare a lithium transition metal oxide powder, and after stirring the lithium transition metal oxide powder at 650° C. to 1050° C. for 6 hours to 12 hours During the second heat treatment, there is provided a method of manufacturing a cathode active material for a lithium secondary battery.

The mixing may include mixing a cobalt compound, a lithium salt, and a magnesium compound in a Co:Li:Mg molar ratio of 0.996:1.000:0.004 to 0.985:1.000:0.015.

The first heat treatment may be heat treatment at 600° C. to 1000° C. for 4 hours to 8 hours.

The second heat treatment may be heat treatment at 750° C. to 950° C. for 7 hours to 11 hours.

For the second heat treatment time, the molar ratio of magnesium to cobalt element [(Mg/Co)/(second heat treatment time)] may be adjusted to 0.0010 (hr ^-1 ) to 0.0015 (hr ^-1 ).

Another embodiment provides a lithium secondary battery including a positive electrode including the positive electrode active material for a lithium secondary battery, a negative electrode including a negative electrode active material, and an electrolyte.

Provided is a positive electrode active material for a lithium secondary battery in which cell resistance characteristics are improved by controlling the content of magnesium doped inside and on the surface of the positive electrode active material.

To provide a lithium secondary battery having improved cell performance by including the positive active material.

1 is a diagram schematically showing the structure of a lithium secondary battery according to an embodiment.
2 is a view showing the molar ratio of magnesium to cobalt element [(Mg/Co)/(second heat treatment) with respect to the second heat treatment time when the cathode active materials of Examples 1 to 6 and Comparative Examples 1 to 7 were prepared; time), hr ^-1 ].
3 is an EDS (Energy Dispersive Spectroscopy) analysis result of the positive active material prepared in Example 5;
4A and 4B show the binding energy peaks of magnesium (Mg) 1s (Mg1s) and magnesium (Mg) 2p measured by X-ray photoelectron spectroscopy for the positive active material prepared in Example 5; It is a graph showing the binding energy peak (Mg2p).
5 is a graph showing the direct current-internal resistance (DC-IR) of the coin cells prepared in Examples 1 to 6, and Comparative Examples 1 to 7;

Hereinafter, embodiments of the present invention will be described in detail. However, this is provided as an example, and the present invention is not limited thereto, and the present invention is only defined by the scope of the claims to be described later.

One embodiment includes a lithium cobalt composite oxide doped with magnesium, wherein the magnesium is doped in an amount of 0.1 wt% to 0.45 wt% based on the total amount of the positive electrode active material, and when measured by X-ray photoelectron spectroscopy, the binding energy peak of magnesium 2p ( A positive active material for a lithium secondary battery is provided, wherein the ratio (Mg1s/Mg2p) of the intensity of the magnesium 1s binding energy peak (Mg1s) to the intensity of Mg2p) is 1.6 to 3.5.

When lithium cobalt oxide (LiCoO ₂ ) is used as a positive electrode active material, a problem of O ₃ →H _1-3 → O ₁ phase transition may occur in a high voltage region, and if such a positive active material is used, the cell performance of the battery may be deteriorated . Accordingly, it is possible to dope the lithium cobalt composite oxide with magnesium (Mg) to solve the phase transition problem in the high voltage region and improve the structural stability of the positive electrode active material. However, there is a new problem that the cell resistance of the battery increases due to magnesium doping. Accordingly, the present inventors seek to solve the above-described problem by finding the optimal range of the magnesium doping amount through repeated experiments and research, and furthermore, by controlling the content ratio of magnesium doped to the inside and the surface of the positive electrode active material.

Specifically, the magnesium may be doped in an amount of 0.1 wt% to 0.45 wt%, for example, 0.2 wt% to 0.3 wt%, preferably 0.2 wt% to 0.28 wt%, based on the total amount of the positive active material. In addition, as measured by X-ray photoelectron spectroscopy, the ratio of the intensity of the magnesium 1s binding energy peak (Mg1s) to the intensity of the binding energy peak (Mg2p) of magnesium 2p is 1.6 to 3.5, preferably, 1.6 to 1.9. . When the doping amount of magnesium is within the above range and the ratio (Mg1s/Mg2p) of the strength of the binding energy peak of magnesium is within the above range, the cell resistance of the battery can be effectively improved, and as a result, the lifespan characteristics of the battery can be improved. can

Meanwhile, the binding energy peak (Mg2p) of magnesium 2p measured by X-ray photoelectron spectroscopy may appear in the range of 50±0.5 eV, and the binding energy peak (Mg1s) of magnesium 1s may appear in the range of 1304±0.5 eV.

When the surface and the inside of the positive active material according to an embodiment are analyzed by X-ray photoelectron spectroscopy, magnesium binding energy peaks Mg1s, Mg2s, and Mg2p spectrum can be obtained, in which case the binding energy of Mg1s and Mg2p By using the difference in the kinetic energy of photoelectrons due to the difference, the level of magnesium ubiquitous in the cathode active material can be known. Specifically, in the case of Mg1s, since the binding energy is larger than that of Mg2p, it is possible to measure the kinetic energy of photoelectrons on the surface of the positive electrode active material (the outermost surface of the positive electrode active material to a depth of about 10 nm), whereas in the case of Mg2p, the binding energy is relatively , so it is possible to measure the kinetic energy of photoelectrons in the inside of the positive electrode active material (the outermost surface of the positive electrode active material ~ about 15 nm deep). Therefore, through the ratio (Mg1s/Mg2p) of the intensity of the magnesium 1s binding energy peak (Mg1s) to the intensity of the magnesium 2p binding energy peak (Mg2p) measured by X-ray photoelectron spectroscopy, it is about 15 nm deep from the outermost surface of the cathode active material. Magnesium ubiquity level in the region corresponding to can be inferred. For example, when the ratio (Mg1s/Mg2p) of the intensity of the binding energy peak approaches 1, it can be inferred that magnesium is uniformly distributed in the region of the positive electrode active material, and as it is greater than 1, the surface (positive electrode) of the positive active material It can be seen that the localization level of magnesium element in the outermost surface of the active material ~ about 10 nm deep region) is high.

The magnesium-doped lithium cobalt composite oxide may be represented by Formula 1 below.

[Formula 1]

LiCo _1-xy Mg _x M _y O ₂

In Formula 1,

0.004 ≤ x+y ≤ 0.015,

M is at least one metal element selected from Mn, Al, Cr, Fe, V, Mg, Ti, Zr, Nb, Mo, W, Cu, Zn, Ga, In, Sn, La and Ce.

Hereinafter, a method of manufacturing a positive electrode active material according to an embodiment is provided.

In the method for preparing the cathode active material, a cobalt compound, a lithium salt and a magnesium compound are mixed, a first heat treatment is performed to prepare a lithium transition metal oxide powder, and the lithium transition metal oxide powder is stirred, and then at 650° C. to 1050° C. for 6 hours. and performing a second heat treatment for 12 hours to prepare a positive electrode active material.

Examples of the cobalt compound include Co(OH) ₂ , CoOOH, CoO, Co ₂ O ₃ , Co ₃ O ₄ , Co(OCOCH ₃ ) ₂ ·4H ₂ O, CoCl ₂ , Co(NO ₃ ) ₂ ·6H ₂ O , and Co(SO ₄ ) ₂ ·7H ₂ O. Among them, Co(OH) ₂ , CoOOH, CoO, Co ₂ O ₃ and Co ₃ O ₄ are preferable from the viewpoint of not generating harmful substances such as NO _x and SO _x during the calcination treatment. Co(OH) ₂ and CoOOH are industrially inexpensive and more preferable from the viewpoint of high reactivity. These cobalt compounds may be used alone or in combination of two or more.

Examples of the lithium salt include Li ₂ CO ₃ , LiNO ₃ , LiNO ₂ , LiOH, LiOH•H ₂ O, LiH, LiF, LiCl, LiBr, LiI, CH ₃ OOLi, Li ₂ O, Li ₂ SO ₄ , dicarboxyl lithium acid salt, lithium citrate, fatty acid lithium salt, and alkyl lithium. These lithium salts may be used alone or in combination of two or more.

Examples of the magnesium compound include MgCO ₃ , MgSO ₄ , MgO, MgC ₂ O ₄ , Mg ₃ (PO ₄ ) _{2 ,} Mg(OH) ₂ , MgCl ₂ , and MgNO ₃ . These magnesium compounds may be used alone or in combination of two or more.

In addition to the magnesium, an additional doping material may be optionally further mixed. As the additional doping material, a compound containing Ba, Al, Fe, Ti, W, B, Zr, or a combination thereof may be used, and specifically, a compound containing Al, Zr or a combination thereof is preferable.

The cobalt compound, lithium salt, and magnesium compound may be mixed in a Co:Li:Mg molar ratio of 0.996:1.000:0.004 to 0.985:1.000:0.015.

The first heat treatment may be performed at 600° C. to 1000° C. or 700° C. to 900° C. for 4 hours to 8 hours or 5 hours to 7 hours.

The second heat treatment may be performed at 750° C. to 950° C. for 7 hours to 11 hours or 7 hours to 9 hours. The degree to which magnesium is diffused into the cathode active material may be affected by the heat treatment temperature and heat treatment time when the cathode active material is manufactured. Specifically, when the second heat treatment time is 7 hours or more, the magnesium doping can be sufficiently diffused into the positive electrode active material, and when the second heat treatment time is 11 hours or less, excessive diffusion of the magnesium doping into the positive electrode active material can be prevented.

In addition, the cathode active material according to an exemplary embodiment may be manufactured by appropriately adjusting the second heat treatment time according to the magnesium doping amount. For example, the molar ratio of magnesium to cobalt element with respect to the second heat treatment time [(Mg/ Co) molar ratio / (second heat treatment time), hr ^-1 ] can be adjusted to 0.0010 (hr ^-1 ) to 0.0015 (hr ^-1 ). As a result, the cell resistance can be improved more effectively.

Another embodiment may include a positive electrode including the positive electrode active material; a negative electrode comprising an anode active material; And it provides a lithium secondary battery comprising an electrolyte.

The positive electrode includes a current collector and a positive electrode active material layer formed on the current collector and including a positive electrode active material.

In the positive active material layer, the positive active material is the same as described above, and the content thereof may be 90 wt% to 98 wt% based on the total weight of the cathode active material layer. In addition, the positive active material layer may further include a binder and a conductive material. The content of the binder and the conductive material may be 1 wt% to 5 wt%, respectively, based on the total weight of the positive electrode active material layer.

Examples of the binder include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, polyvinyl fluoride, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride. , polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc. may be used, but is not limited thereto.

Examples of the conductive material include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, and carbon fiber; Metal-based substances, such as metal powders, such as copper, nickel, aluminum, and silver, or a metal fiber; conductive polymers such as polyphenylene derivatives; Alternatively, a conductive material including a mixture thereof may be used.

As the current collector, an aluminum foil, a nickel foil, or a combination thereof may be used, but is not limited thereto.

The negative electrode includes a current collector and an anode active material layer including a negative active material formed on the current collector.

The negative active material includes a material capable of reversibly intercalating/deintercalating lithium ions, lithium metal, an alloy of lithium metal, a material capable of doping and dedoping lithium, or a transition metal oxide.

The material capable of reversibly intercalating/deintercalating the lithium ions is a carbon material, and any carbon-based negative active material generally used in lithium ion secondary batteries may be used, and a representative example thereof is crystalline carbon. , amorphous carbon or these may be used together. Examples of the crystalline carbon include graphite such as amorphous, plate-like, flake, spherical or fibrous natural graphite or artificial graphite, and examples of the amorphous carbon include soft carbon or hard carbon ( hard carbon), mesophase pitch carbide, and calcined coke.

The lithium metal alloy includes lithium and Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al and Sn from the group consisting of Alloys of metals of choice may be used.

Examples of materials capable of doping and dedoping lithium include Si, SiOx (0 < x < 2), Si-Q alloy (wherein Q is an alkali metal, alkaline earth metal, group 13 element, group 14 element, group 15 element, group 16 An element selected from the group consisting of elements, transition metals, rare earth elements, and combinations thereof, and not Si), Sn, SnO ₂ , Sn-R alloy (wherein R is an alkali metal, alkaline earth metal, group 13 element, group 14 element, group 15 element, group 16 element, transition metal, rare earth element, and an element selected from the group consisting of a combination thereof, not Sn), etc., and also at least one of them and SiO ₂ to be used by mixing may be The elements Q and R include 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, One selected from S, Se, Te, Po, and combinations thereof may be used.

Examples of the transition metal oxide include vanadium oxide, lithium vanadium oxide or lithium titanium oxide.

The content of the anode active material in the anode active material layer may be 95 wt% to 99 wt% based on the total weight of the anode active material layer.

In one embodiment, the negative active material layer includes a binder, and may optionally further include a conductive material. The content of the binder in the anode active material layer may be 1 wt% to 5 wt% based on the total weight of the anode active material layer. In addition, when the conductive material is further included, 90 wt% to 98 wt% of the negative active material, 1 wt% to 5 wt% of the binder, and 1 wt% to 5 wt% of the conductive material may be used.

The binder serves to well adhere the negative active material particles to each other and also to adhere the negative active material to the current collector. As the binder, a water-insoluble binder, a water-soluble binder, or a combination thereof may be used.

Examples of the water-insoluble binder include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymer, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, and polyvinylidene fluoride. , polyethylene, polypropylene, polyamideimide, polyimide, or a combination thereof.

Examples of the water-soluble binder include styrene-butadiene rubber, acrylated styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber, acrylic rubber, butyl rubber, fluororubber, ethylene propylene copolymer, polyepicrohydrin. , polyphosphazene, polyacrylonitrile, polystyrene, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, or a combination thereof can

When a water-soluble binder is used as the negative electrode binder, a cellulose-based compound capable of imparting viscosity may be further included as a thickener. As the cellulose-based compound, one or more of carboxymethyl cellulose, hydroxypropylmethyl cellulose, methyl cellulose, or alkali metal salts thereof may be mixed and used. As the alkali metal, Na, K or Li may be used. The amount of the thickener used may be 0.1 parts by weight to 3 parts by weight based on 100 parts by weight of the negative active material.

Examples of the conductive material include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, and carbon fiber; Metal-based substances, such as metal powders, such as copper, nickel, aluminum, and silver, or a metal fiber; conductive polymers such as polyphenylene derivatives; Alternatively, a conductive material including a mixture thereof may be used.

As the current collector, at least one selected from a copper foil, a nickel foil, a stainless steel foil, a titanium foil, a nickel foam, a copper foam, a polymer substrate coated with a conductive metal, and combinations thereof may be used.

The electrolyte includes a non-aqueous organic solvent and a lithium salt.

The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move.

Examples of the non-aqueous organic solvent include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methylpropionate, ethylpropionate, decanolide, mevalo mevalonolactone, caprolactone, dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, cyclohexanone, ethyl alcohol, isopropyl alcohol, R Nitriles such as -CN (R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, and may contain a double bond aromatic ring or ether bond); amides such as dimethylformamide; Dioxolanes, such as 1,3-dioxolane, sulfolanes, etc. can be used.

The organic solvents may be used alone or in a plurality of mixtures, and in the case of using a plurality of mixtures, the mixing ratio can be appropriately adjusted according to the desired battery performance, which can be widely understood by those engaged in the field. there is.

In addition, the organic solvent may further include an aromatic hydrocarbon-based organic solvent. Specific examples of the aromatic hydrocarbon-based organic solvent include benzene, fluorobenzene, 1,2-difluorobenzene, 1,3-difluorobenzene, 1,4-difluorobenzene, 1,2,3-tri Fluorobenzene, 1,2,4-trifluorobenzene, chlorobenzene, 1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene, 1,2,3-trichlorobenzene, 1 ,2,4 trichlorobenzene, iodobenzene, 1,2-diiodobenzene, 1,3-diiodobenzene, 1,4-diiodobenzene, 1,2,3-triiodobenzene, 1,2 ,4-triiodobenzene, toluene, fluorotoluene, 2,3-difluorotoluene, 2,4-difluorotoluene, 2,5-difluorotoluene, 2,3,4-trifluoro Toluene, 2,3,5-trifluorotoluene, chlorotoluene, 2,3-dichlorotoluene, 2,4-dichlorotoluene, 2,5-dichlorotoluene, 2,3,4-trichlorotoluene, 2,3 ,5-trichlorotoluene, iodotoluene, 2,3-diiodotoluene, 2,4-diiodotoluene, 2,5-diiodotoluene, 2,3,4-triiodotoluene, 2,3, At least one selected from 5-triiodotoluene, xylene, and combinations thereof may be used.

The electrolyte may further include vinylene carbonate or an ethylene carbonate-based compound as a lifespan improving additive.

Representative examples of the ethylene carbonate-based compound include difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate, fluoroethylene carbonate, and the like. can When such a life-enhancing additive is further used, its amount can be appropriately adjusted.

The lithium salt is dissolved in an organic solvent, acts as a source of lithium ions in the battery, enables basic lithium secondary battery operation, and serves to promote movement of lithium ions between the positive electrode and the negative electrode. Representative examples of such lithium salts include LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiN(SO ₂ C ₂ F ₅ ) ₂ , Li(CF ₃ SO ₂ ) ₂ N, LiN(SO ₃ C ₂ F ₅ ) ₂ , LiC ₄ F ₉ SO ₃ , LiClO ₄ , LiAlO ₂ , LiAlCl ₄ , LiN(C _x F _2x+1 SO ₂ )(C _y F _2y+1 SO ₂ ), where x and y are natural numbers, for example It is an integer from 1 to 20), LiCl, LiI and LiB(C ₂ O ₄ ) ₂ (lithium bis(oxalato) borate: LiBOB) as an electrolyte salt supporting one or more The concentration of lithium salt is preferably used within the range of 0.1 M to 2.0 M. When the concentration of lithium salt is included in the above range, the electrolyte has appropriate conductivity and viscosity, so it can exhibit excellent electrolyte performance, and lithium ions can move effectively.

A separator may exist between the positive electrode and the negative electrode depending on the type of the lithium secondary battery. As such a separator, polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more layers thereof may be used. A polyethylene/polypropylene two-layer separator, a polyethylene/polypropylene/polyethylene three-layer separator, and polypropylene/polyethylene/poly It goes without saying that a mixed multilayer film such as a propylene three-layer separator or the like can be used.

1 is a diagram schematically showing the structure of a lithium secondary battery according to an embodiment. Although the lithium secondary battery according to an embodiment is described as an example of a prismatic shape, the present invention is not limited thereto, and may be applied to various types of batteries, such as a cylindrical shape, a pouch type, and a coin type.

Referring to FIG. 1 , a lithium secondary battery 100 according to an embodiment has an electrode assembly 40 and the electrode assembly 40 wound with a separator 30 interposed between the positive electrode 10 and the negative electrode 20 . may include a case 50 in which the is built-in. The positive electrode 10 , the negative electrode 20 , and the separator 30 may be impregnated with an electrolyte solution.

Examples and comparative examples are described below. However, the following examples are only examples, and the present invention is not limited thereto.

Example

Examples 1 to 6, and Comparative Examples 1 to 7

(Production of positive electrode active material)

Co ₃ O ₄ , Li ₂ CO ₃ , and MgCO ₃ were mixed and subjected to a first heat treatment (calcination) at 800° C. for 6 hours. Then, the first heat-treated powder was well mixed, and the second heat treatment was performed at 850° C. to prepare a cathode active material.

When Co ₃ O ₄ , Li ₂ CO ₃ and MgCO ₃ are mixed, the molar ratio of Co: Li: Mg, the Mg (magnesium) doping amount (wt% relative to the total amount of the positive electrode active material), the second heat treatment time, and the second heat treatment time, The molar ratio of magnesium to the cobalt element [(Mg/Co) molar ratio/(secondary heat treatment time)] was set forth in Table 1 below.

Co:Li:Mg molar ratio second heat treatment time
(hr) [(Mg/Co) molar ratio/(second heat treatment time)]
(hr ^-1 ) Magnesium doping amount
(weight%) Example 1 0.990:1.000:0.010 9 0.001122 0.27 Example 2 0.993:1.000:0.007 7 0.001007 0.12 Example 3 0.989:1.000:0.011 9 0.001236 0.31 Example 4 0.992:1.000:0.008 8 0.001008 0.21 Example 5 0.992:1.000:0.008 7 0.001152 0.22 Example 6 0.990:1.000:0.010 7 0.001443 0.29 Comparative Example 1 0.991:1.000:0.009 11 0.000826 0.23 Comparative Example 2 0.992:1.000:0.008 10 0.000806 0.22 Comparative Example 3 0.993:1.000:0.007 10 0.000705 0.17 Comparative Example 4 0.990:1.000:0.010 6 0.001684 0.26 Comparative Example 5 0.989:1.000:0.011 6 0.001854 0.32 Comparative Example 6 0.983:1.000:0.017 7 0.002471 0.50 Comparative Example 7 0.997:1.000:0.003 7 0.00043 0.08

(Manufacture of coin cell)

Using the positive active materials prepared in Examples 1 to 6 and Comparative Examples 1 to 7, 2032 coin cells were manufactured according to the following procedure.

A composition for forming a cathode active material layer was prepared by dispersing 4.7 g of a cathode active material, 0.15 g of polyvinylidene fluoride, and 0.15 g of a carbon black conductive material (trade name: denka black, denka Korea) in 5.35 g of N-methylpyrrolidone. .

The composition for forming the positive electrode active material layer was coated on an aluminum foil to a thickness of 135 μm to form a thin electrode plate, dried at 110° C. for 20 minutes or more, and pressed to prepare a positive electrode plate having a thickness of 40 μm. Thereafter, a 2032 type coin cell was manufactured using the positive electrode and a lithium metal counter electrode as a counter electrode.

A separator (thickness: about 16 μm) made of a porous polyethylene (PE) film was interposed between the positive electrode and the lithium metal counter electrode, and electrolyte was injected, and the electrolyte was ethylene carbonate (EC), ethylmethyl carbonate (EMC) and dimethyl carbonate A solution containing 1.15M LiPF ₆ dissolved in a solvent in which (DMC) was mixed in a volume ratio of 3:3:4 was used.

evaluation example

* With respect to the second heat treatment time, the molar ratio of magnesium to the cobalt element [(Mg/Co) molar ratio/(second heat treatment time), hr ^-One ] control

When preparing the cathode active materials of Examples 1 to 6 and Comparative Examples 1 to 7, the molar ratio of magnesium to the cobalt element for the second heat treatment time [(Mg/Co) molar ratio / (second heat treatment time), hr ^-1 ] is shown in FIG. 2 .

Referring to Figure 2, the positive active material of Examples 1 to 6 is [(Mg / Co) molar ratio / (second heat treatment time), hr ^-1 ] 0.0010 (hr ^-1 ) to 0.0015 (hr ^-1 ) was prepared by adjusting the range, but it can be seen that the positive active materials of Comparative Examples 1 to 7 are not.

* EDS (Energy Dispersive Spectroscopy) analysis of cathode active material

EDS analysis of the positive active material prepared in Example 5 was performed. Specifically, the EDS was mounted on a TEM (Transmission Electron Microscopy) to analyze the components inside the positive active material in parallel, and the measurement results are shown in FIG. 3 .

Referring to FIG. 3 , it can be seen that the concentration of magnesium is relatively high in a region corresponding to a depth of 10 nm from the surface of the positive electrode active material. Therefore, it can be fully understood that a concentration gradient of magnesium may appear on the surface and inside the positive active material.

* XPS (X-ray photoelectron spectroscopy) analysis of cathode active material, magnesium doping amount measurement, and direct current resistance (DC-IR) analysis of coin cells

For XPS analysis, excitation (ESCA 250 spectrometer) was performed using nonmonochromatic Al Ka X-ray, and the chamber pressure was measured at about 5Х10 ^-7 mbar. After dispersing the positive electrode active material powder prepared in Examples 1 to 6 and Comparative Examples 1 to 7 in indium foil, it was attached to the XPS sample holder using double-sided carbon tape to perform XPS analysis on the positive electrode active material. . The binding energy peak ratio (Mg1s/Mg2p) of magnesium is shown in Table 2 below, and the magnesium (Mg) 1s binding energy peak (Mg1s) and the magnesium (Mg) 2p binding energy peak (Mg2p) measured in the positive active material of Example 5 ) are shown in FIGS. 4A and 4B, respectively.

0.1 g of the positive active materials prepared in Examples 1 to 6 and Comparative Examples 1 to 7 were mixed in a solvent in which 10 ml of pure water, 5 ml of nitric acid, and 3 ml of hydrochloric acid were mixed, and then heated to prepare a homogeneous solution. The amount of magnesium doping was quantitatively analyzed using an inductively coupled plasma atomic emission spectroscopy (ICP-AES) facility, and the results are shown in Table 2 below.

With respect to the coin cells prepared in Examples 1 to 6 and Comparative Examples 1 to 7, they were left for 6 hours at a temperature of -30°C in a state of charge (SOC) of 60%, and discharged with a 5C constant current ( The battery voltage was measured every 0.1 second while discharging pulse current value: 1A, pulse time: 2 seconds). At this time, the DC potential of the battery was 3.74 V, and the lower limit of the cut-off was 2V. The calculated DC-IR results are shown in Table 2 below, and the DC-IR results for the magnesium binding energy peak ratio (Mg1s/Mg2p) are shown in FIG. 5 .

Magnesium doping amount
(weight%) XPS Peakby
(Mg1s/Mg2p) DC-IR (ohm) Example 1 0.27 1.65 79.2 Example 2 0.12 1.7 85.2 Example 3 0.31 1.8 84.0 Example 4 0.21 1.9 60.4 Example 5 0.22 2.5 81.3 Example 6 0.29 3.2 83.2 Comparative Example 1 0.23 1.4 124.5 Comparative Example 2 0.22 1.4 122.4 Comparative Example 3 0.17 1.5 102.3 Comparative Example 4 0.26 3.7 95.2 Comparative Example 5 0.32 3.8 96.3 Comparative Example 6 0.50 4.5 138.2 Comparative Example 7 0.08 1.2 113.2

Referring to Tables 2 and 5, in the case of Examples 1 to 6, the magnesium doping amount and the XPS peak ratio (Mg1s/Mg2p) corresponded to the numerical ranges according to the embodiment, compared to Comparative Examples 1 to 7 It can be seen that the DC-IR (cell resistance) is improved. In particular, it was confirmed that the cell resistance was significantly improved in Examples 1, 4, and 5, in which the magnesium doping amount was in the preferred range among the Examples.

Although preferred embodiments of the present disclosure have been described above, the present invention is not limited thereto, and it is possible to carry out various modifications within the scope of the claims, the detailed description of the invention, and the accompanying drawings, and this also It goes without saying that it falls within the scope of the description.

10: positive electrode 20: negative electrode
30: separator 40: electrode assembly
50: battery case 100: lithium secondary battery

Claims (12)

Lithium cobalt composite oxide doped with magnesium,
The magnesium is doped in an amount of 0.1 wt% to 0.45 wt% based on the total amount of the positive active material,
When measured by X-ray photoelectron spectroscopy, the ratio (Mg1s/Mg2p) of the intensity of the magnesium 1s binding energy peak (Mg1s) to the intensity of the binding energy peak (Mg2p) of the magnesium 2p is 1.6 to 3.5, the cathode active material for a lithium secondary battery. According to claim 1,
When measured by X-ray photoelectron spectroscopy, the ratio (Mg1s/Mg2p) of the intensity of the magnesium 1s binding energy peak (Mg1s) to the intensity of the binding energy peak (Mg2p) of the magnesium 2p is 1.6 to 1.9, the positive active material for a lithium secondary battery. The method of claim 1,
The binding energy peak (Mg2p) of the magnesium 2p appears at 50 ± 0.5 eV, a cathode active material for a lithium secondary battery. According to claim 1,
The binding energy peak (Mg1s) of the magnesium 1s appears at 1304 ± 0.5 eV, a cathode active material for a lithium secondary battery. The method of claim 1,
The magnesium is doped in an amount of 0.2 wt% to 0.3 wt% based on the total amount of the cathode active material, a cathode active material for a lithium secondary battery. The method of claim 1,
The magnesium-doped lithium cobalt composite oxide is represented by the following Chemical Formula 1, a cathode active material for a lithium secondary battery:
[Formula 1]
LiCo _1-xy Mg _x M _y O ₂
In Formula 1,
0.004 ≤ x+y ≤ 0.015,
M is at least one metal element selected from Mn, Al, Cr, Fe, V, Mg, Ti, Zr, Nb, Mo, W, Cu, Zn, Ga, In, Sn, La and Ce. A lithium transition metal oxide powder is prepared by mixing a cobalt compound, a lithium salt and a magnesium compound and performing a first heat treatment,
After stirring the lithium transition metal oxide powder, a second heat treatment is performed at 650° C. to 1050° C. for 6 hours to 12 hours,
For the second heat treatment time, the molar ratio of magnesium to cobalt element [(Mg/Co) molar ratio/(second heat treatment time)] is adjusted to 0.0010 hr ^-1 to 0.0015 hr ^-1 , Preparation of a cathode active material for a lithium secondary battery Way. 8. The method of claim 7,
The mixing is to mix a cobalt compound, a lithium salt and a magnesium compound in a Co: Li: Mg molar ratio of 0.996:1.000:0.004 to 0.985:1.000:0.015,
A method of manufacturing a cathode active material for a lithium secondary battery. 8. The method of claim 7,
The first heat treatment is a method of manufacturing a positive electrode active material for a lithium secondary battery that is to be heat-treated at 600 ℃ to 1000 ℃ for 4 hours to 8 hours. 8. The method of claim 7,
The second heat treatment is a method of manufacturing a positive electrode active material for a lithium secondary battery that is to be heat-treated at 750 ° C. to 950 ° C. for 7 hours to 11 hours. delete A positive electrode comprising the positive electrode active material of any one of claims 1 to 6;
a negative electrode comprising an anode active material; and
A lithium secondary battery comprising an electrolyte.

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