KR102229622B1 - Positive electrode for rechargeable lithium battery and rechargeable lithium battery including same - Google Patents

Abstract

The present disclosure relates to a positive electrode active material for a lithium secondary battery and a lithium secondary battery including the same. The positive active material for a lithium secondary battery according to an embodiment may include a compound represented by Formula 1 below.
[Formula 1]
Li _a (Ni _x Co _y Mn _z Al _b Mg _c ) O ₂
In Formula 1,
0.96<a<1.04, 0.8≤x<1, 0<y≤0.075, 0<z≤0.025, 0.001<b≤0.02, 0<c<0.02, b>c, x+y+z+b+c = It is 1.

Description

A positive electrode active material for a lithium secondary battery and a lithium secondary battery including the same {POSITIVE ELECTRODE FOR RECHARGEABLE LITHIUM BATTERY AND RECHARGEABLE LITHIUM BATTERY INCLUDING SAME}

The present disclosure relates to a positive electrode active material for a lithium secondary battery and a lithium secondary battery including the same.

The use of portable electronic devices is increasing as it becomes possible to reduce the size and weight of electronic equipment due to the recent development of the high-tech electronic industry. As a power source for such portable electronic devices, lithium secondary batteries that have high energy density and can be used for a long time are widely used.

Core materials for lithium secondary batteries include a positive electrode including a positive electrode active material, a negative electrode including a negative electrode active material, an electrolyte, and a separator.

In recent years, as the use of lithium secondary batteries has been expanded from portable electronic devices to industries such as power tools and automobiles, studies for increasing the capacity of lithium secondary batteries are active. Specifically, various studies on improving the performance of a positive electrode active material among core materials of the lithium secondary battery have been conducted in order to secure excellent life and storage characteristics of the lithium secondary battery even in a high temperature and high voltage environment.

An object of the present disclosure is to provide a positive electrode active material for a lithium secondary battery having a high capacity and excellent thermal stability, and a lithium secondary battery including the same.

In one aspect, the present disclosure provides a positive electrode active material for a lithium secondary battery including a compound represented by the following formula (1).

[Formula 1]

Li _a (Ni _x Co _y Mn _z Al _b Mg _c ) O ₂

In Formula 1,

0.96<a<1.04, 0.8≤x<1, 0<y≤0.075, 0<z≤0.025, 0.001<b≤0.02, 0<c<0.02, b>c, x+y+z+b+c = It is 1.

In another aspect, the present disclosure provides a lithium secondary battery including a positive electrode, a negative electrode, and an electrolyte, and the positive electrode includes a positive electrode active material for a lithium secondary battery according to an exemplary embodiment.

When the positive active material for a lithium secondary battery according to an exemplary embodiment of the present disclosure is applied to a lithium secondary battery, it is possible to remarkably improve thermal stability and implement a lithium secondary battery having excellent capacity characteristics.

1 schematically shows the structure of a rechargeable lithium battery according to an exemplary embodiment of the present disclosure.

Hereinafter, various embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those of ordinary skill in the art may easily implement the present invention. The present invention may be implemented in various different forms and is not limited to the embodiments described herein.

In order to clearly describe the present invention, parts irrelevant to the description have been omitted, and the same reference numerals are attached to the same or similar components throughout the specification.

In addition, the size and thickness of each component shown in the drawings are arbitrarily shown for convenience of description, so the present invention is not necessarily limited to the illustrated bar.

In addition, throughout the specification, when a certain part "includes" a certain component, it means that other components may be further included rather than excluding other components unless otherwise stated.

The positive electrode active material for a rechargeable lithium battery according to an exemplary embodiment of the present disclosure may include a compound represented by Formula 1 below.

[Formula 1]

Li _a (Ni _x Co _y Mn _z Al _b Mg _c ) O ₂

In Formula 1, 0.96<a<1.04, 0.8≤x<1, 0<y≤0.075, 0<z≤0.025, 0.001<b≤0.02, 0<c<0.02, b>c, and x+y+ z+b+c = 1.

That is, the compound represented by Formula 1 may be, for example, a nickel-based oxide doped with Al and Mg and having a molar ratio of Ni of at least 0.8.

The role of a dopant is very important in order to improve the thermal stability of a lithium secondary battery using a nickel-based oxide having a molar ratio of Ni of at least 0.8 and to secure high capacity characteristics.

In addition, when Al is doped, the lifespan of the lithium secondary battery can be improved, and since the heat generation initiation temperature can be increased, thermal stability can also be improved. In addition, in the case of Mg, since the heating value can be lowered and the heating start temperature can be increased, the thermal stability of the secondary battery can be improved. In the case of doping Al and Mg in an appropriate amount, since the lithium secondary battery has excellent capacity and can implement the same effect as described above, Al and Mg are doped to satisfy the ranges b and c described in Formula 1 above. If it is appropriate.

On the other hand, as shown in Formula 1, two elements such as Al and Mg are doped in an amount corresponding to the range of b and c, but when Al is doped in an amount greater than Mg, nickel-based oxide Structural stability of the crystal structure of the particles may be improved, and accordingly, the thermal stability of the lithium secondary battery may be further improved.

More specifically, in Formula 1, x may be 0.9≦x<1. As the Ni content increases, it is very advantageous because a high-capacity lithium secondary battery can be implemented.

In addition, in Formula 1, b may be 0.001<b≤0.02, for example, 0.01<b≤0.02. When the molar ratio of Al satisfies the above range, the capacity of the secondary battery to which the positive active material according to the present embodiment is applied can be prevented from being reduced, and since the on-set temperature can be increased, thermal stability is excellent. Do.

In Formula 1, c may be 0<c<0.02, for example, 0.01<c<0.015. When the molar ratio of Mg satisfies the above range, the capacity of the secondary battery to which the positive active material according to the present embodiment is applied can be prevented from decreasing, and since the on-set temperature can be increased, thermal stability is excellent. Do.

In this case, b and c may be 0.2≦b/c≦3.0, for example, 0.25≦b/c≦2.0, and more specifically 0.6<b/c≦2.0. When the ratio of Al and Mg satisfies the above range, thermal stability may be improved while maximizing the specific capacity of the positive electrode active material.

More specifically, the compound represented by Formula 1 is, for example, Li _1.03 Ni _0.9 Co _0.05 Mn _0.025 Al _0.015 Mg _0.01 O ₂ , Li _{1 . 03} Ni _{0 . 9} Co _{0 . 05} Mn _{0 . 025} Al _{0 . 018} Mg _{0 . It} may be at least one of 007 O ₂ , and Li _1.03 Ni _0.9 Co _0.05 Mn _0.02 Al _0.02 Mg _0.01 O _2.

A lithium secondary battery according to an embodiment of the present disclosure includes a positive electrode, a negative electrode, and an electrolyte.

Hereinafter, a rechargeable lithium battery according to an exemplary embodiment will be described with reference to FIG. 1.

1 schematically shows a rechargeable lithium battery according to an embodiment of the present disclosure.

Referring to FIG. 1, a lithium secondary battery 100 according to an exemplary embodiment of the present disclosure includes an electrode assembly 10, an exterior material 20 accommodating the electrode assembly 10, and a positive electrode electrically connected to the electrode assembly 10. It includes a terminal 40 and a negative terminal 50.

The electrode assembly 10 includes an anode 11, a cathode 12, a separator 13 interposed between the anode 11 and the cathode 12, and an anode 11, a cathode 12, and a separator 13 ) May include an electrolyte solution (not shown) impregnated.

In the present disclosure, a positive electrode including the positive electrode active material for a lithium secondary battery according to the present disclosure described above may be used as the positive electrode 11.

That is, the positive electrode 11 includes a positive electrode active material layer positioned on the positive electrode current collector. The positive electrode active material layer may include a positive electrode active material, and may include the positive electrode active material for a lithium secondary battery according to the above-described exemplary embodiment as the positive electrode active material.

In the positive electrode active material layer, the amount of the positive electrode active material may be 90% to 98% by weight based on the total weight of the positive electrode active material layer.

In one embodiment, the positive active material layer may further include a binder and a conductive material. In this case, the content of the binder and the conductive material may be 1% to 5% by weight, respectively, based on the total weight of the positive electrode active material layer.

The binder serves to attach the positive electrode active material particles well to each other, and to attach the positive electrode active material to the current collector well. Representative examples of the binder include polyvinyl alcohol, carboxymethylcellulose, hydroxypropylcellulose, diacetylcellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymer containing ethylene oxide, polyvinylpyrroly. Don, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc. may be used, but are not limited thereto. .

The conductive material is used to impart conductivity to the electrode, and in the battery to be constructed, any material may be used as long as it does not cause chemical change and is an electron conductive 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 materials such as metal powders such as copper, nickel, aluminum, and silver, or metal fibers; Conductive polymers such as polyphenylene derivatives; Alternatively, a conductive material containing a mixture of these may be mentioned.

An aluminum foil, a nickel foil, or a combination thereof may be used as the positive electrode current collector, but the present invention is not limited thereto.

Next, the negative electrode 12 includes a negative electrode current collector and a negative electrode active material layer disposed on the current collector. The negative electrode active material layer contains a negative electrode active material.

As the negative active material, a material capable of reversibly intercalating/deintercalating lithium ions, a lithium metal, an alloy of a lithium metal, a material capable of doping and undoping lithium, or a transition metal oxide may be used.

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

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

The lithium-doped and undoped materials include silicon-based materials such as Si, SiO _x (0<x<2), and Si-Q alloys (where Q is an alkali metal, alkaline earth metal, group 13 element, group 14 An element selected from the group consisting of an element, a group 15 element, a group 16 element, a transition metal, a rare earth element, and a combination thereof, but not Si), a Si-carbon composite, Sn, SnO ₂ , Sn-R (the R is 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), Sn-carbon complex, etc. These may be mentioned, and at least one of these and SiO ₂ may be mixed and used. 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, Ge, P, As, Sb, Bi, S, What is selected from the group consisting of Se, Te, Po, and combinations thereof may be used.

Lithium titanium oxide may be used as the transition metal oxide.

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

The negative active material layer includes a negative active material and a binder, and may optionally further include a conductive material.

The content of the negative active material in the negative active material layer may be 95% to 99% by weight based on the total weight of the negative active material layer. The content of the binder in the negative active material layer may be 1% to 5% by weight based on the total weight of the negative active material layer. In addition, when a conductive material is further included, 90% to 98% by weight of the negative electrode active material, 1 to 5% by weight of the binder, and 1% to 5% by weight of the conductive material may be used.

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

As the water-insoluble binder, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymer containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride , Polyethylene, polypropylene, polyamideimide, polyimide, or combinations thereof.

Examples of the water-soluble binder include styrene-butadiene rubber, acrylated styrene-butadiene rubber, polyvinyl alcohol, sodium polyacrylate, propylene and C2-C8 olefin copolymer, (meth)acrylic acid and (meth)acrylate alkyl ester. Copolymers or combinations thereof.

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 types of carboxymethyl cellulose, hydroxypropylmethyl cellulose, methyl cellulose, or alkali metal salts thereof may be mixed and used. Na, K or Li may be used as the alkali metal. The content of the thickener may be 0.1 parts by weight to 3 parts by weight based on 100 parts by weight of the negative active material.

The conductive material is used to impart conductivity to the electrode, and in the battery to be constituted, any material may be used as long as it does not cause chemical change and is an electron conductive material. Examples of the conductive material include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, denka black, and carbon fiber; Metal-based materials such as metal powders such as copper, nickel, aluminum, and silver, or metal fibers; Conductive polymers such as polyphenylene derivatives; Alternatively, a conductive material containing a mixture of these may be mentioned.

The negative electrode current collector may be selected from the group consisting of 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 a combination thereof. .

On the other hand, the electrode assembly 10, as shown in FIG. 1, the separator 13 is interposed between the strip-shaped anode 11 and the cathode 12, the separator 13 may be wound and pressed to form a flat structure. Alternatively, although not shown, a plurality of anodes and cathodes formed in the shape of a square sheet may be alternately stacked with a separator interposed therebetween.

In addition, the anode 11, the cathode 12, and the separator 13 may be impregnated with an electrolyte.

The separator 13 separates the positive electrode 11 and the negative electrode 12 and provides a path for lithium ions to move, and any one commonly used in a lithium secondary battery may be used. That is, those having low resistance to ion movement of the electrolyte and excellent in the ability to impregnate the electrolyte may be used. The separator 13 may be selected from, for example, glass fiber, polyester, polyethylene, polypropylene, polytetrafluoroethylene, or a combination thereof, and may be in the form of a nonwoven fabric or a woven fabric. For example, a polyolefin-based polymer separator such as polyethylene, polypropylene, etc. may be mainly used for a lithium secondary battery, and a separator coated with a composition containing a ceramic component or a polymer material may be used to secure heat resistance or mechanical strength. It can be used in a single-layer or multi-layer structure.

The electrolyte solution contains 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.

As the non-aqueous organic solvent, a carbonate-based, ester-based, ether-based, ketone-based, alcohol-based, or aprotic solvent may be used. As the carbonate-based solvent, dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate ( EC), propylene carbonate (PC), butylene carbonate (BC), and the like may be used, and as the ester solvent, methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate , γ-butyrolactone, decanolide, valerolactone, mevalonolactone, caprolactone, and the like may be used. Dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, etc. may be used as the ether solvent, and cyclohexanone may be used as the ketone solvent. have. In addition, ethyl alcohol, isopropyl alcohol, etc. may be used as the alcohol-based solvent, and R-CN (R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms) as the aprotic solvent. , A double bonded aromatic ring or an ether bond), such as nitriles, amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, sulfolanes, and the like may be used. .

The non-aqueous organic solvent can be used alone or in combination of one or more, and the mixing ratio in the case of using one or more mixtures can be appropriately adjusted according to the desired battery performance, which will be widely understood by those in the field. I can.

In addition, in the case of a carbonate-based solvent, it is preferable to use a mixture of a cyclic carbonate and a chain carbonate. In this case, when the cyclic carbonate and the chain carbonate are mixed in a volume ratio of 1:1 to 1:9, the electrolyte may exhibit excellent performance.

The non-aqueous organic solvent of the present disclosure may further include an aromatic hydrocarbon-based organic solvent in the carbonate-based solvent. At this time, the carbonate-based solvent and the aromatic hydrocarbon-based organic solvent may be mixed in a volume ratio of 1:1 to 30:1.

As the aromatic hydrocarbon-based organic solvent, an aromatic hydrocarbon-based compound represented by the following formula (3) may be used.

[Formula 3]

In Formula 3, R ₁ to R ₆ are the same as or different from each other and are selected from the group consisting of hydrogen, halogen, an alkyl group having 1 to 10 carbon atoms, a haloalkyl group, and combinations thereof.

Specific examples of the aromatic hydrocarbon-based organic solvent include benzene, fluorobenzene, 1,2-difluorobenzene, 1,3-difluorobenzene, 1,4-difluorobenzene, 1,2,3-trifluoro Lobenzene, 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-diaiodobenzene, 1,4-diaiodobenzene, 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-diaiodotoluene, 2,4-diaiodotoluene, 2,5-diaiodotoluene, 2,3,4-triiodotoluene, 2,3, It is selected from the group consisting of 5-triiodotoluene, xylene, and combinations thereof.

The non-aqueous electrolyte may further include vinylene carbonate or an ethylene carbonate-based compound of Formula 4 in order to improve battery life.

[Formula 4]

In Chemical Formula 4, R ₇ and R ₈ are the same as or different from each other, and are selected from the group consisting of hydrogen, a halogen group, a cyano group (CN), a nitro group (NO ₂ ), and a fluorinated alkyl group having 1 to 5 carbon atoms, wherein At least one of R ₇ and R ₈ is selected from the group consisting of a halogen group, a cyano group (CN), a nitro group (NO ₂ ), and a fluorinated alkyl group having 1 to 5 carbon atoms, provided that both _{R 7} and R _{8 are hydrogen} no.

Representative examples of ethylene carbonate-based compounds include difluoro ethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate or fluoroethylene carbonate. have. In the case of further use of such a life-improving additive, the amount of the additive may be appropriately adjusted.

Lithium salt is a material that is dissolved in an organic solvent and acts as a source of lithium ions in the battery, enabling basic lithium secondary battery operation, and promoting the movement of lithium ions between the positive electrode and the negative electrode. Representative examples of such lithium salts are 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), LiCl, LiI and LiB(C ₂ O ₄ ) ₂ (lithium bis(oxalato) borate; LiBOB) contains one or more selected from the group consisting of as a supporting electrolytic salt. Concentration of lithium salt It is recommended to use within the range of 0.1 to 2.0 M. When the concentration of the lithium salt is included in the above range, the electrolyte has an appropriate conductivity and viscosity, so that excellent electrolyte performance can be exhibited, and lithium ions can move effectively.

Meanwhile, the separator 13 interposed between the anode 11 and the cathode 12 may be a polymer film. As the separator, for example, polyethylene, polypropylene, polyvinylidene fluoride or a multilayer film of two or more layers thereof may be used, and a polyethylene/polypropylene two-layer separator, a polyethylene/polypropylene/polyethylene three-layer separator, and polypropylene It goes without saying that a mixed multilayer film such as a /polyethylene/polypropylene three-layer separator can be used.

The casing 20 may be formed of a lower casing 22 and an upper casing 21, and the electrode assembly 10 is accommodated in the inner space 221 of the lower casing 22.

After the electrode assembly 10 is accommodated in the casing 20, the upper casing 21 and the lower casing 22 are sealed by applying a sealing material to the sealing portion 222 positioned at the edge of the lower casing 22. At this time, the positive terminal 40 and the negative terminal 50 may be wrapped around the insulating member 60 at a portion in contact with the case 20 to improve durability of the lithium secondary battery 100.

The operating voltage of the lithium secondary battery according to the present embodiment may be, for example, in the range of 4.2V to 4.55V, and more specifically, in the range of 4.25V to 4.5V. In the present specification, the operating voltage of the lithium secondary battery is based on a half coin cell.

As described above, in the present disclosure, since the positive electrode active material according to an exemplary embodiment is included, a lithium secondary battery to which the positive electrode active material is applied may have a high capacity and significantly improve thermal stability.

Meanwhile, a rechargeable lithium battery according to an exemplary embodiment may be provided to a device including one or more thereof. As such a device, for example, any one selected from the group consisting of a mobile phone, a tablet computer, a notebook computer, a power tool, a wearable electronic device, an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, and a power storage device. Can be Since devices to which the lithium secondary battery is applied are known in the art, detailed descriptions thereof will be omitted in the present specification.

Hereinafter, the present description will be described in detail through examples.

Example One

(1) Preparation of positive electrode

Lithium hydroxide, nickel hydroxide, cobalt hydroxide, manganese hydroxide, Mix aluminum hydroxide and magnesium oxide so that the molar ratio of Ni:Co:Mn:Al:Mg is 0.9:0.05:0.025:0.015:0.01, and Li is the molar ratio of Li and the remaining metals excluding Li so that Li/Me is 1.03. I did.

The mixture was heat-treated at 750° C. and oxygen (O ₂ ) atmosphere for 15 hours to prepare a positive electrode active material of _{Li (1.03)} Ni _(0.9) Co _(0.05) Mn _(0.025) Al _(0.015) Mg _(0.01) O ₂ I did.

A positive active material composition was prepared by mixing 96% by weight of the prepared positive electrode active material, 2% by weight of a polyvinylidene fluoride binder, and 2% by weight of a Ketjen Black conductive material in an N-methylpyrrolidone solvent. The positive electrode active material composition was applied to an aluminum current collector to prepare a positive electrode.

(2) Manufacture of lithium secondary battery

A coin-shaped half-cell having a nominal capacity of 190 mAh was manufactured by a conventional method using the positive electrode, lithium metal counter electrode, and electrolyte prepared according to (1). As the electrolyte, a mixed solvent (30:40:30 by volume) of ethylene carbonate (EC), ethylmethyl carbonate (EMC), and dimethyl carbonate (DMC) _{in which 1.3M LiPF 6 was dissolved was used.}

Example 2 to 3 and Comparative example 1 to 8

The positive electrode according to Examples 2 to 3 and Comparative Examples 1 to 8 in the same manner as in Example 1, except that a positive electrode was prepared by mixing so that the content of each element constituting the positive electrode active material is as shown in Table 1 below, and A lithium secondary battery was prepared.

division Ni Co Mn Al Mg Ti Fe Ga Al/Mg Example 1 90 5 2.5 1.5 One 1.5 Example 2 90 5 2.5 1.8 One 1.8 Example 3 90 5 2.5 2 One 2.0 Comparative Example 1 90 5 2.5 - - - - Comparative Example 2 90 5 2.5 One 1.5 - 0.67 Comparative Example 3 90 5 2.5 2.5 - - - Comparative Example 4 90 5 2.5 - 2.5 - - - Comparative Example 5 90 5 2.5 - - 2.5 - - Comparative Example 6 90 5 2.5 1.25 1.25 - - 1.0 Comparative Example 7 90 5 2.5 - - - 2.5 - Comparative Example 8 90 5 2.5 - - - - 2.5 -

(Unit: mol%)

Experimental example 1: thermal stability measurement

Differential scanning calorimeter (DSC) evaluation was performed to confirm thermal stability. DSC evaluation was performed by measuring the change in calorific value using the Q2000 equipment of TA Instruments.

After 100% of the lithium secondary batteries prepared according to Examples 1 to 3 and Comparative Examples 1 to 8 were charged to 4.3V at 0.1C, the battery was disassembled, and the positive electrode plate was separated. After washing the separated electrode plate with DMC (dimethylcarbonate), drying it for 10 hours or more, scrape off only the positive electrode active material from the current collector, and then add the electrolyte (mass ratio of the positive electrode active material and electrolyte = 1:2) to the scraped active material, and then DSC Evaluation proceeded. During the measurement, the scan rate was 5°C/min.

The calculated calorific value (a value obtained by integrating the calorific value curve on the DSC with respect to temperature) is shown in Table 2 below, and the maximum and maximum peak temperature values and the total calorific value are shown in Table 2 below.

division Heating start temperature
(T1)(℃) Peak temperature
(T2)(℃) Max Heat Flow
(W/g) △(T2-T1) (℃) Example 1 192.34 238.5 19.8 46.16 Example 2 192.61 237.9 19.7 45.29 Example 3 193.11 239.1 20.1 45.99 Comparative Example 1 201.13 221.2 121.3 20.07 Comparative Example 2 192.12 246.9 10.9 54.78 Comparative Example 3 172.4 220.8 113.8 48.4 Comparative Example 4 206.3 223.7 78.2 17.4 Comparative Example 5 136.5 231.5 11.47 95 Comparative Example 6 196.77 224.4 21.5 27.63 Comparative Example 7 177.67 221.2 18.5 43.53 Comparative Example 8 170.12 221.2 17.2 51.08

The lithium secondary battery manufactured according to Examples 1 to 3 is a case in which a positive active material in which the molar ratio of Al and Mg satisfies the range of Formula 1 and the molar ratio of Al is greater than Mg is applied, as in an embodiment. Referring to Table 2, it can be seen that in the lithium secondary batteries manufactured according to Examples 1 to 3, heat generation is not explosive because the difference between the maximum peak temperature and the heating start temperature is 30°C or more. In addition, the heating start temperature of 185°C or higher, the maximum peak temperature of 230°C or higher, and the Max heat flow of 30W/g or lower are all satisfied, and the thermal stability of the lithium secondary batteries manufactured according to Examples 1 to 3 is very excellent. Able to know.

On the other hand, in the lithium secondary battery manufactured according to Comparative Example 1 to which a positive electrode active material containing no Al and Mg was applied, the difference between the maximum peak temperature and the heating initiation temperature was less than 30°C. Can be seen.

In addition, the molar ratio of each component satisfies the range of Formula 1, but the lithium secondary battery manufactured according to Comparative Example 6 to which a positive electrode active material having a molar ratio of Al is less than Mg was applied, the difference between the maximum peak temperature and the heat generation initiation temperature. Since is less than 30℃, it can be confirmed that the heat generation is explosive. In addition, it can be seen that thermal stability is not good because the maximum peak temperature is less than 230°C.

In the case of a lithium secondary battery manufactured according to Comparative Example 2, charge/discharge and rate characteristics to be described later are inferior.

Prepared according to Comparative Examples 5, 7 and 8 in which a lithium secondary battery prepared according to Comparative Example 3 in which a positive electrode active material containing only Al was applied, and a positive electrode active material containing Ti, Fe, and Ga, but not including Al and Mg, respectively, was applied. In the lithium secondary battery, it can be seen that thermal stability is inferior since the heating start temperature and the maximum peak temperature are less than 185°C and 230°C.

In addition, the lithium secondary battery manufactured according to Comparative Example 4 to which a positive electrode active material containing only Mg was applied has a difference between the maximum peak temperature and the heating initiation temperature of less than 30°C, and the maximum heat flow significantly exceeds 30W/g. You can see that this is falling.

Experimental example 2: Charge and discharge characteristic

The lithium secondary batteries prepared according to Example 1 and Comparative Examples 1 to 8 were charged with a constant current and a constant voltage at 0.1C and 4.3V cut-off, and after rest for 10 minutes, a 0.1C and 2.7V cut-off was discharged at a constant current. Then, a charge/discharge cycle of rest for 10 minutes was performed once.

Next, charging and discharging were performed under a constant current-constant voltage under 1.0C, 4.3V, and 0.05C cut-off conditions and a constant current of 1.0C and 2.7V discharge condition. The results are shown in Table 3 below.

4.3V-2.7V Ch-Dch 0.1C 1C C-Rate division charge Discharge efficiency charge Discharge 0.1/1C Example 1 234.5 205.66 87.7% 194.1 185.4 90.1% Example 2 233.2 203.4 87.2% 192.2 182.8 89.9% Example 3 233.5 203.1 87.0% 192.1 182.1 89.7% Comparative Example 1 239.34 218.89 91.5% 194.3 186.5 85.2% Comparative Example 2 231.8 201.36 86.9% 188.5 180.2 89.5% Comparative Example 3 233.8 210 89.8% 192.4 183.2 87.2% Comparative Example 4 225.2 198 87.9% 170.3 163.1 82.4% Comparative Example 5 231.08 197.22 85.3% 178.77 171.56 87.0% Comparative Example 6 231.3 201.1 86.9% 181.2 174.4 86.7% Comparative Example 7 240.03 209.81 87.4% 175.48 169.28 80.7% Comparative Example 8 230.92 199.26 86.3% 173.02 165.91 83.3%

Referring to Table 3, it can be seen that the lithium secondary batteries manufactured according to Examples 1 to 3 have high charge/discharge capacity and C-Rate, and thus have excellent electrochemical properties.

On the other hand, it can be seen that the lithium secondary batteries manufactured according to Comparative Examples 1 to 8 have low charge/discharge capacity or low rate characteristics, and thus have poor electrochemical characteristics compared to the examples.

Although preferred embodiments related to the present disclosure have been described above with reference to the drawings, the present disclosure is not limited to the embodiments, and from the embodiments of the present disclosure, it is easy for those of ordinary skill in the art to which the present invention pertains. It includes all changes to the extent deemed equivalent by being changed accordingly.

100: lithium secondary battery
11: anode
12: cathode
13: separator
20: exterior material

Claims (7)

A positive electrode active material for a lithium secondary battery comprising a compound represented by the following formula (1).
[Formula 1]
Li _a (Ni _x Co _y Mn _z Al _b Mg _c ) O ₂
(In Chemical Formula 1,
a, x, y, z, b and c satisfies the following range, and satisfies x+y+z+b+c = 1, and, b and c satisfies the condition of 1.5≦b/c≦3.0 .
0.96<a<1.04, 0.8≤x<1, 0<y≤0.075, 0<z≤0.025, 0.001<b≤0.02, 0<c<0.02, b>c) The method of claim 1,
In Formula 1, x is 0.9≦x<1, a positive electrode active material for a lithium secondary battery. The method of claim 1,
In Formula 1, b is a positive electrode active material for a lithium secondary battery of 0.01<b≤0.02. The method of claim 1,
In Formula 1, c is a positive electrode active material for a lithium secondary battery of 0.01<c<0.015. delete The method of claim 1,
The compound represented by Formula 1 is Li _{1 . 03} Ni _{0 . 9} Co _{0 . 05} Mn _{0 . 025} Al _{0 . 015} Mg _{0 . 01} O ₂ , Li _1.03 Ni _0.9 Co _0.05 Mn _0.025 Al _0.018 Mg _0.007 O ₂ , and Li _{1 . 03} Ni _{0 . 9} Co _{0 . 05} Mn _{0 . 02} Al _{0 . 02} Mg _{0 . 01} O ₂ At least one of the positive electrode active material for a lithium secondary battery. anode;
cathode; And
Containing an electrolyte,
The positive electrode is a lithium secondary battery comprising the positive electrode active material for a lithium secondary battery according to any one of claims 1 to 4 and 6.

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