WO2019088807A2 - Lithium secondary battery - Google Patents

Abstract

The present invention relates to a lithium secondary battery comprising: a positive electrode comprising a first positive electrode active material with a spinel structured lithium manganese base, to which doping and coating are applied, and a second positive electrode active material with a lithium nickel manganese cobalt base; a negative electrode comprising at least one selected from the group consisting of artificial graphite having a specific surface area (BET) of 0.1-1.2 m2/g, and temper carbon and natural graphite each having a larger specific surface area than the artificial graphite; a separator interposed between the positive electrode and the negative electrode; and an electrolyte.

Description

Lithium secondary battery

[Mutual quotation with related application]

This application claims priority from Korean Patent Application No. 10-2017-0146924 filed on November 6, 2017, and Korean Patent Application No. 10-2018-0135104 filed November 6, 2018 , The contents of which are incorporated herein by reference.

[TECHNICAL FIELD]

The present invention relates to a lithium secondary battery including a cathode active material having a spinel structure and excellent in high-temperature lifetime characteristics and high-temperature storage electrochemical characteristics.

As technology development and demand for mobile devices increase, the demand for secondary batteries as energy sources is rapidly increasing. Among such secondary batteries, lithium secondary batteries having a high energy density and voltage, a long cycle life, and a low self-discharge rate are commercially available and widely used.

Various lithium transition metal oxides such as LiCoO _{2 ,} LiNiO ₂ , LiMnO ₂ , LiMn ₂ O _4, or LiFePO ₄ have been developed as a cathode active material of a lithium secondary battery. double. LiMn ₂ O ₄ lithium-manganese oxide of spinel structure is thermal stability, output characteristics and life property is excellent, but the advantage that the price is low, the structure deformed (Jahn-Teller distortion) due to the Mn ^{3 +} during the charge and discharge, such as And there is a problem that Mn elution occurs due to HF formed by reaction with an electrolytic solution at a high temperature, and performance deteriorates abruptly.

In the case of LiMn ₂ O ₄ , it can be applied to a battery requiring a high capacity because the material itself has a high working voltage but low energy density per unit mass, such as about 110 mAh / g, and low density of the material itself There was a problem that it was difficult.

In order to solve the above problems, it is an object of the present invention to provide a lithium secondary battery which has a spinel structure cathode active material and is excellent in electrochemical characteristics and high temperature lifetime characteristics after high temperature storage.

In one aspect, the present invention provides a lithium secondary battery comprising: a cathode comprising a lithium manganese-based first cathode active material having a spinel structure and a lithium-nickel-manganese-cobalt-based second cathode active material; A negative electrode comprising at least one selected from the group consisting of artificial graphite having a specific surface area (BET) of 0.1 to 1.2 m ² / g and softened carbon and natural graphite having a larger specific surface area than the artificial graphite; A separator interposed between the anode and the cathode; And a lithium secondary battery including an electrolyte.

The first cathode active material is a lithium manganese oxide represented by the following Chemical Formula 1 and a lithium manganese oxide which is located on the surface of the lithium manganese oxide and contains Al, Ti, W, B, F, P, Mg, Ni, Co, , Cu, Ca, Zn, Zr, Nb. And a coating layer containing at least one element selected from the group consisting of Mo, Sr, Sb, Bi, Si, and S.

[Chemical Formula 1]

Li _{1 + a} Mn _2-b M ¹ _b O _{4 -c} A _c

M ¹ is at least one element selected from the group consisting of Al, Li, Mg, Zn, B, W, Ni, Co, Fe, Cr, V, Ru, Cu, Cd, Ag, Y, , Pt, Au and Si, A is at least one element selected from the group consisting of F, Cl, Br, I, At and S, and 0? A? 0.2, 0 < b? 0.5, 0? c? 0.1)

The first cathode active material of the spinel structure used in the lithium secondary battery according to the present invention has excellent structural stability including a doping element and has a coating layer formed on its surface to minimize the contact with the electrolyte, This makes it possible to obtain a high-temperature characteristic superior to the conventional one.

Further, the lithium secondary battery according to the present invention can realize high energy density by using the first cathode active material having a spinel structure excellent in high temperature stability and the high nickel lithium nickel-cobalt-manganese based active material together.

Further, by using a mixture of artificial graphite having a specific specific surface area as a negative electrode active material and natural graphite and / or softened carbon having a specific surface area larger than that of the artificial graphite, the lithium secondary battery according to the present invention can exhibit resistance And it is possible to prevent degradation of the electrode due to removal of active material and the like, thereby realizing excellent electrochemical characteristics.

FIG. 1 is a graph showing the high-temperature storage characteristics of the coin cells prepared by Examples 1 and 5 and Comparative Examples 5 and 6. FIG.

Fig. 2 is a graph showing the high-temperature lifetime characteristics of the coin cell manufactured by Examples 1 and 5 and Comparative Examples 5 and 6. Fig.

Hereinafter, the present invention will be described in more detail.

The terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms and the inventor may properly define the concept of the term in order to best describe its invention It should be construed as meaning and concept consistent with the technical idea of the present invention.

In the present specification, the average particle diameter (D ₅₀ ) can be defined as the particle diameter at the 50% of the particle diameter distribution, and can be measured using a laser diffraction method. Specifically, the average particle diameter (D ₅₀ ) is measured by dispersing the target particles in a dispersion medium, introducing the particles into a commercially available laser diffraction particle size analyzer (for example, Microtrac MT 3000) After the irradiation, the average particle diameter (D ₅₀ ) of the 50% of the cumulative distribution of the particle volume according to the particle diameter in the measuring apparatus can be calculated.

In this specification, ICP analysis was conducted using an inductively coupled plasma emission spectrometer (ICP-OES; Optima 7300DV, PerkinElmer).

In the present specification, the " specific surface area " is measured by the BET method. Specifically, it can be calculated from the adsorption amount of nitrogen gas under the liquid nitrogen temperature (77K) using BELSORP-mino II manufactured by BEL Japan.

In the present specification, "%" means weight% unless otherwise specified.

As a result of intensive research to improve the high-temperature characteristics of a lithium secondary battery using a spinel-structured first cathode active material, the inventors have found that a spinel-type first cathode active material doped with a cathode active material and a lithium nickel cobalt manganese- Oxides are used in combination and one of the artificial graphite having a specific specific surface area as a negative electrode active material and one of natural graphite and softening carbon is used in combination to effectively prevent deterioration of electrochemical characteristics at high temperatures I can do it.

Specifically, the lithium manganese-based positive active material, and the first lithium nickel spinel structure in which the lithium battery of the present invention-manganese-anode including a cobalt-based second positive active material, the specific surface area (BET) is from 0.1 to 1.2m ² / g and softened carbon and natural graphite having a specific surface area (BET) larger than that of the artificial graphite; a separator interposed between the anode and the cathode; And an electrolyte, wherein the cathode active material is a lithium manganese oxide represented by the following general formula (1) and a lithium manganese oxide which is located on the surface of the lithium manganese oxide and contains Al, Ti, W, B, F, P, Mg, Ni, , V, Cu, Ca, Zn, Zr, Nb. And a coating layer containing at least one element selected from the group consisting of Mo, Sr, Sb, Bi, Si, and S.

Hereinafter, each component of the lithium secondary battery of the present invention will be described in more detail.

anode

The positive electrode according to the present invention includes a lithium manganese-based first positive electrode active material having a spinel structure and a lithium-nickel-manganese-cobalt second positive electrode active material.

(1) First cathode active material

The first cathode active material is a cathode active material having a spinel structure including a lithium manganese oxide represented by the following general formula (1) and a coating layer positioned on the surface of the lithium manganese oxide.

[Chemical Formula 1]

Li _{1 + a} Mn _2-b M ¹ _b O _{4 -c} A _c

Wherein M ¹ is a doping element substituted for a manganese site in the lithium manganese oxide and is a doping element substituted by a metal element such as Al, Li, Mg, Zn, B, W, Ni, Co, Fe, Cr, And at least one element selected from the group consisting of Cd, Ag, Y, Sc, Ga, In, As, Sb, Pt, Au and Si. Preferably, the M &lt; ¹ &gt; Al, Li, Mg, and Zn.

The A is an element substituted for an oxygen site in the lithium oxynitride, and may be at least one element selected from the group consisting of F, Cl, Br, I, At and S.

Meanwhile, 1 + a represents the molar ratio of lithium in the lithium manganese oxide, and may be 0? A? 0.2, preferably 0? A? 0.1.

B represents the molar ratio of the doping element M ^{1 in} the lithium manganese oxide, and may be 0 < b? 0.5, preferably 0.03? B? 0.25. When the molar ratio b of M ¹ satisfies the above range, a structurally stable cathode active material can be obtained while minimizing the capacity drop.

C represents the molar ratio of the element A in the lithium manganese oxide, and may be 0? C? 0.1, preferably 0.01? C? 0.05.

The lithium manganese oxide represented by Formula 1 has a relatively low average oxidation number of Mn ions including a low-oxidation doping element M ¹ , and consequently has a Jnn-Teller distortion due to Mn ³⁺ during charging and discharging, Can be minimized.

Next, the coating layer prevents contact between the lithium manganese oxide and the electrolytic solution to prevent generation of gas upon charge and discharge, and prevents manganese (Mn) from leaching at a high temperature. The coating layer is located on the surface of the lithium manganese oxide and contains Al, Ti, W, B, F, P, Mg, Ni, Co, Fe, Cr, V, Cu, Ca, Zn, (Hereinafter referred to as "coating element") selected from the group consisting of Mo, Sr, Sb, Bi, Si and S. Preferably, the coating layer may contain at least one element selected from the group consisting of Al, Ti, Zn, W and B, more preferably at least one element selected from the group consisting of B, W and Al .

According to one embodiment, the first cathode active material may be one in which the doping element M ¹ is at least one selected from Al, Li, Mg and Zn, and the coating layer contains Al ₂ O ₃ .

According to another embodiment, the first cathode active material according to the present invention may be one in which the doping element M ¹ is at least one selected from the group consisting of Al, Li, Mg and Zn, and the coating layer contains Ti.

According to another embodiment, the first cathode active material according to the present invention may be one in which the doping element M ¹ is at least one selected from Al, Li, Mg and Zn, and the coating layer contains W.

According to another embodiment, the first cathode active material according to the present invention may be one in which the doping element M ¹ is at least one selected from Al, Li, Mg and Zn, and the coating layer contains B.

According to another embodiment, the first cathode active material according to the present invention may be one in which the doping element M ¹ is at least one selected from Al, Li, Mg and Zn, and the coating layer contains B and Al.

On the other hand, the coating layer may be formed continuously or discontinuously on the surface of the lithium manganese oxide represented by the formula (1).

For example, the coating layer may be formed such that particles containing the coating elements are discontinuously attached to the surface of the lithium manganese oxide. At this time, the particles comprising the coating elements include, for _{example, ZnO, Al 2 O 3,} TiO 2, WO 3, MgO, CaO, B 2 O 3, NbO 2, SrO, CrO, Mo 2 O 5, Bi 2 O ₃ , SiO, and the like. When the oxide particles are present on the surfaces of the lithium manganese oxide particles, the oxide particles capture and decompose HF formed by the reaction with the electrolyte, as shown in the following reaction formula 1, so that the Mn elution by HF is suppressed .

[Reaction Scheme 1]

ZnO + 2HF -> ZnF ₂ + H ₂ O

Al ₂ O ₃ + 6HF? 2AlF ₃ + 3H ₂ O

Alternatively, the coating layer may be formed in the form of a film containing the coating elements on the surface of the lithium manganese oxide. When the coating layer is formed in the form of a film, the effect of preventing the contact between the electrolyte and the lithium manganese oxide and the effect of inhibiting the manganese dissolution are more excellent. Preferably, the coating comprises at least one element selected from the group consisting of B, P, F, W, S, and Al. When the above-mentioned coating is formed on the surface of the lithium manganese oxide particles, contact with the electrolytic solution is blocked by the film, and side reactions and gas generation with the electrolyte can be suppressed.

On the other hand, the coating layer may be formed in a region corresponding to 50 to 100% of the total surface area of the lithium manganese oxide, preferably in a range of 80 to 100%, more preferably 90 to 100% have. When the coating layer formation area satisfies the above range, the contact between the electrolytic solution and the lithium manganese oxide can be effectively blocked.

Further, the thickness of the coating layer may be 1 nm to 1000 nm, for example, 1 nm to 100 nm or 10 nm to 1000 nm. When the coating layer is formed in the form of a film, its thickness may be 1 nm to 100 nm, and when it is formed in the form of oxide particles, its thickness may be 10 nm to 1000 nm. When the thickness of the coating layer satisfies the above range, it is possible to effectively suppress occurrence of manganese elution and side reaction with the electrolyte while minimizing deterioration of electrical performance.

Meanwhile, in the first cathode active material of the present invention, the doping element M ¹ is used in an amount of 500 to 40000 ppm, preferably 2500 to 40000 ppm, more preferably 5000 to 40000 ppm, and most preferably 7000 to 40000 ppm based on the total weight of the first cathode active material. 20000 ppm. When the content of the doping element M ¹ satisfies the above range, the dissolution of manganese at a high temperature is effectively suppressed, thereby realizing a lithium secondary battery excellent in high-temperature storability.

According to one embodiment, the first cathode active material may include Al, Li, Mg, Zn, or a combination thereof as a doping element, wherein the Al is present in an amount of 2500 to 40000 ppm based on the total weight of the first cathode active material, May be included at 7000 to 20000 ppm, and Li may be included at 500 to 12000 ppm, preferably 1000 to 3000 ppm, based on the total weight of the first cathode active material. The Mg may be contained in an amount of 1000 to 20000 ppm, preferably 3000 to 10000 ppm, based on the total weight of the first cathode active material, and the Zn may be added in an amount of 1000 to 20000 ppm, preferably 3000 to 10000 ppm, based on the total weight of the first cathode active material .

On the other hand, the first cathode active material according to the present invention has an average particle diameter (D ₅₀ ) of 1 to 20 탆, for example, 1 to 8 탆, 7 탆 to 20 탆, 8 탆 to 20 탆, Lt; / RTI &gt;

According to one embodiment, the first cathode active material according to the present invention may have an average particle diameter (D ₅₀ ) of 1 to 8 탆. When the average particle diameter (D ₅₀ ) satisfies the above range, the content of the doping and coating elements is relatively increased as compared with the particles having a large average particle diameter, and the specific surface area is controlled by controlling the firing conditions, The first positive electrode active material having a low side reaction can be produced.

According to another embodiment, the first cathode active material according to the present invention may have an average particle diameter (D ₅₀ ) of 8 탆 to 20 탆. When the average particle diameter (D ₅₀ ) satisfies the above range, there is an advantage that the manganese dissolution is relatively small as compared with the particles having a small average particle diameter.

In addition, the lithium manganese-based first cathode active material may have a specific surface area of 0.1 to 1.5 m ² / g. The specific surface area can be adjusted according to the particle size of the lithium manganese-based first cathode active material. For example, when the lithium manganese-based first cathode active material has an average particle diameter (D ₅₀ ) of 1 to 8 μm, is 0.5 to 1.5m ² / g or 0.7 to 1.1m ² / g may be, the average particle diameter (D ₅₀₎ is not more than 20㎛ 8㎛ to have a specific surface area of 0.1 to 1m ² / g, or from 0.25 to 0.7m ² / g. &lt; / RTI &gt;

The first cathode active material may be in the form of a secondary particle formed by aggregating primary particles or a plurality of primary particles. The secondary particles may be formed, for example, by agglomerating 2 to 100 or 2 to 50 primary particles.

Meanwhile, the first cathode active material may include impurities that are not included in the manufacturing process. These impurities may include, for example, Fe, Ni, Na, Cu, Zn, Cr, Ca, K, S, Mg, Co, Si, B or combinations thereof. If such an impurity content is high, the life of the battery may be deteriorated by inducing the negative electrode dendrite, and a low voltage failure due to an internal short circuit may occur. Among these impurities, impurities such as S or the like have a problem of corroding the Al current collector. Therefore, it is preferable that the impurities are controlled to a certain degree or less.

For example, the first cathode active material according to the present invention may have an S impurity content of 20000 ppm or less, preferably 15000 ppm or less, more preferably 1000 ppm or less, and the other impurity content may be 400 ppm or less, preferably 10 ppm or less .

In the first cathode active material according to the present invention, the total amount of magnetic impurities such as Fe, Cr, Ni, Zn and the like among the above-mentioned impurities is preferably not more than 800 ppb, specifically not more than 25 ppb. If the content of the magnetic impurities exceeds the above range, the life of the battery may be deteriorated by inducing the negative electrode dendrite, or a low voltage failure due to an internal short circuit may occur.

On the other hand, the first lithium manganese-based cathode active material includes 1) a step of forming a lithium manganese oxide doped with M ¹ represented by the formula 1, and 2) a step of forming lithium manganese And mixing the oxide and the coating material to form a coating layer by heat treatment. Hereinafter, a method for producing the first cathode active material of the present invention will be described in more detail.

1) forming a lithium manganese oxide doped with M ¹

The lithium manganese oxide doped with M ¹ represented by the above formula (1) can be obtained by (i) a method of mixing a raw material for manganese, a raw material for doping including M ¹ and a raw material for lithium and then firing, or (ii) by reacting a doping raw material containing the raw material and M ^1, can be prepared by after the formation of the manganese precursor is doped with M ^1, method of sintering by mixing the manganese precursor and the lithium source material is doped with the M ¹ have. That is, in the present invention, the doping element M ¹ may be added in the step of forming the manganese precursor, or may be charged in the step of firing the manganese raw material and the lithium raw material.

The manganese raw material may be a manganese element-containing oxide, a hydroxide, an oxyhydroxide, a carbonate, a sulfate, a halide, a sulfide, an acetate, a carboxylate or a combination thereof. Specific examples thereof include MnO ₂ , MnCl ₂ , MnCO ₃ , Mn ₃ O ₄ , MnSO ₄ , Mn ₂ O ₃ , Mn (NO ₃ ) ₂ , and the like, but is not limited thereto.

Doping material source material containing the M ¹ is, M ¹ containing oxides, hydroxides, oxy-hydroxides, sulfates, carbonates, halides, sulfides, and the like acid salt, carboxylic acid salt, or a combination thereof, for example, Al ₂ ( _{SO 4) 3, AlCl 3,} Al- isopropoxide _{(Al-isopropoxide), AlNO 3} , Li (OH), LiCO 3, Li 2 O, MgO, Mg (OH) 2, MgSO 4, Mg (NO 3 ) _2, etc. However, the present invention is not limited thereto.

The lithium source material may be at least one selected from the group consisting of lithium containing carbonate (for example, lithium carbonate and the like), hydrate (for example, lithium hydroxide I hydrate (LiOH.H ₂ O) and the like), hydroxide (for example, For example, lithium nitrate (LiNO ₃ ) or the like), chloride (for example, lithium chloride (LiCl) or the like), and the like.

According to one embodiment, the lithium manganese oxide represented by the formula (1) can be produced by mixing a raw material for manganese, a raw material for doping including M ¹ , a raw material for lithium, and firing )).

The manganese raw material, the doping raw material containing M ¹ , and the lithium raw material may be mixed in an amount that satisfies the molar ratio of Mn, M ^1, and Li of Formula 1.

In addition, the mixing may be a solid-phase mixing or a liquid-phase mixing. When the components are mixed through the solid-phase mixing, the firing process can be performed without a separate drying process. In the case of mixing the components through the liquid phase mixing, the mixed components are spray dried and then subjected to the firing process. When the solid-phase mixing method is used, a lithium manganese oxide having an average particle diameter (D ₅₀ ) of less than 8 μm, preferably not more than 6 μm, and having a small specific surface area can be obtained. On the other hand, when a wet mixing method is used, a lithium manganese oxide having an average particle diameter (D ₅₀ ) of 8 μm or larger can be obtained.

On the other hand, the firing may be performed at 600 to 900 ° C, preferably 700 to 800 ° C, for 5 to 24 hours, preferably 10 to 15 hours.

For example, the calcination may be performed at 750 to 850 캜, preferably at 780 to 830 캜 for 5 to 24 hours, preferably 10 to 15 hours. When the temperature and the firing time are satisfied, undersize occurs and the primary particle size becomes large. Accordingly, the average particle size (D50) of the primary particles is 1 mu m or more, preferably 2 to 3 Mu m of lithium manganese oxide can be obtained.

According to other embodiments, the lithium manganese oxide represented by the above Formula 1 is, by reacting a doping raw material including a manganese raw material and M ^1, after the formation of the manganese precursor is doped with M ^1, wherein M ¹ By mixing the lithium source material with a doped manganese precursor (method (ii)).

Specifically, the manganese precursor doped to said M ¹ is, for example, be formed by co-precipitation reaction the doped raw material raw material containing manganese as a raw material M ^1. The manganese raw material and the doping raw material containing M &^lt; ¹ &gt; are the same as described above.

The coprecipitation reaction may be performed by a co-precipitation method well known in the art. For example, the manganese raw material and the doping element raw material are charged into the coprecipitation reactor at an appropriate ratio, and an aqueous ammonia solution as a complexing agent and an alkali And the reaction is allowed to proceed while the aqueous solution is added.

When a manganese precursor doped with M ¹ is generated through the above-mentioned coprecipitation reaction, the manganese precursor doped with M ¹ and the lithium source material are mixed and then fired to form lithium manganese oxide.

The manganese precursor doped with M ¹ and the lithium source material may be mixed in an amount that satisfies the molar ratio of Mn, M ^1, and Li of Formula 1.

On the other hand, the mixing and firing can be carried out in the same manner as described in method (i).

2) Coating layer formation step

Ti, W, B, F, P, and Mg are formed on the surface of the lithium manganese oxide of Formula 1 by preparing the lithium manganese oxide doped with M ¹ represented by Formula 1 through the above- , Ni, Co, Fe, Cr, V, Cu, Ca, Zn, Zr, Nb. A coating layer containing at least one element selected from the group consisting of Mo, Sr, Sb, Bi, Si, and S (hereinafter referred to as a coating element) is formed.

For example, a wet coating method, a dry coating method, a plasma coating method, or an ALD (Atomic Layer Deposition) method can be used for forming the coating layer.

The wet coating method may be carried out by, for example, adding lithium manganese oxide and a coating material to an appropriate solvent such as ethanol, water, methanol, acetone, etc., and mixing the mixture until the solvent disappears.

The dry coating method is a method of mixing a lithium manganese oxide and a coating raw material in a solid phase without a solvent, and for example, a grinder mixing method, a mechanofusion method, or the like can be used.

The coating material may be at least one selected from the group consisting of Al, Ti, W, B, F, P, Mg, Ni, Co, Fe, Cr, V, Cu, Ca, Zn, An oxide, a hydroxide, an oxyhydroxide, a carbonate, a sulfate, a halide, a sulfide, an acetic acid, a nitrate, a nitrate, or a salt thereof containing at least one element selected from the group consisting of Mo, Sr, Sb, Bi, Si and S Al ₂ O ₃ , Al (OH) ₃ , AlSO ₄ , AlCl ₃ , Al-isopropoxide, AlNO ₃ , Al ₂ O ₃ , TiO _2, WO _3, AlF, _{H 2 BO 3, HBO 2,} H 3 BO 3, H 2 B 4 O 7, B 2 O 3, C 6 H 5 B (OH) 2, (C 6 H 5 O) 3 B, [(CH 3 ( _{CH 2) 3 O) 3 B} , C 3 H 9 B 3 O 6, (C 3 H 7 O 3) B, Li 3 WO 4, (NH 4) 10 W 12 O 41 · 5H 2 O, NH 4 H ₂ PO ₄ , and the like.

After the coating material is adhered to the surface of the lithium manganese oxide through the above-described method, the coating layer can be formed through heat treatment. At this time, the heat treatment may be performed at 100 ° C to 700 ° C, preferably 300 ° C to 450 ° C, for 1 to 15 hours, preferably 3 to 8 hours.

(2) Second cathode active material

The anode of the present invention includes the lithium-nickel-manganese-cobalt-based second cathode active material together with the first cathode active material.

Specifically, the second cathode active material may be a lithium-titanium manganese cobalt oxide expressed by the following formula (2).

(2)

Li _{1 + x} [Ni _y Co _z Mn _w M ² _v ] O _{2 - p} B _p

M ² is a doping element substituted for a transition metal (Ni, Co, Mn) site, and W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, And at least one element selected from the group consisting of Y, In, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B and Mo. Preferably, the M ² may be at least one selected from the group consisting of Al, Zr, W, Ti, Nb and B.

B is an oxygen-site-substituted element in the lithium nickel manganese cobalt cathode active material, and may be at least one element selected from the group consisting of F, Cl, Br, I, At and S.

Meanwhile, 1 + x represents the lithium molar ratio in the lithium nickel manganese cobalt cathode active material, and may be 0? X? 0.3, preferably 0? X? 0.2, more preferably 0? X?

Y represents the molar ratio of nickel in the lithium nickel manganese cobalt based positive electrode active material and satisfies 0.5? Y <1, preferably 0.65? Y <1, more preferably 0.7? Y <1, &Lt; 1.

Z represents the molar ratio of cobalt in the lithium nickel manganese cobalt-based cathode active material, and may be 0 <z <0.35, preferably 0 <z? 0.3.

The w represents the molar ratio of manganese in the lithium nickel manganese cobalt cathode active material, and may be 0 <w <0.35, preferably 0 <w? 0.3.

When the molar ratio y, z and w of the transition metal in the lithium nickel cobalt manganese oxide satisfies the above range, a cathode active material having an excellent energy density can be obtained.

V represents the molar ratio of the doping element M ^{2 in} the lithium nickel cobalt manganese based oxide, and 0? V? 0.1, preferably 0.0005? V? 0.08, more preferably 0.001? V? 0.002? V? 0.01. When the molar ratio of the doping element M ^{2 in} the lithium nickel cobalt manganese oxide satisfies the above range, the cathode active material having excellent high-temperature stability can be obtained.

P represents the molar ratio of element B in the lithium nickel cobalt manganese-based oxide, and may be 0? P? 0.1, preferably 0? P? 0.05.

More specifically, the lithium nickel cobalt manganese oxide represented by the above formula (2) is preferably Li _{1 + x} [Ni _y Co _z Mn _w ] O _{2 ,} Li _{1 + x} [Ni _y Co _z Mn _w Al _v ] O ₂ Or the like, but is not limited thereto.

The second cathode active material may be at least one selected from the group consisting of Al, Ti, W, B, F, P, Mg, Ni, Co, Fe, Cr, V, Cu, Ca, Zn, Zr, At least one coating element selected from the group consisting of one or more elements selected from the group consisting of Si, S, and S. When the coating layer is included as described above, the contact between the second cathode active material and the electrolyte contained in the lithium secondary battery is cut off and the occurrence of side reactions is suppressed. Therefore, the life characteristics can be improved when applied to a battery, The density can be increased.

As described above, when the coating element is further included, the content of the coating element in the coating layer may be 100 ppm to 10,000 ppm, preferably 200 ppm to 5,000 ppm, based on the total weight of the second cathode active material. For example, when the coating element is contained in the above range with respect to the total weight of the second cathode active material, occurrence of side reactions with the electrolyte can be more effectively suppressed, and life characteristics can be further improved when applied to a battery.

The coating layer may be formed on the entire surface of the second cathode active material, or may be partially formed. Specifically, when the coating layer is partially formed on the surface of the second cathode active material, an area of 5% or more and less than 100%, preferably 20% or more and less than 100% of the total surface area of the second cathode active material is formed .

The average particle diameter (D ₅₀ ) of the second cathode active material may be 1 탆 to 20 탆, 2 탆 to 10 탆, or 8 to 20 탆. When the average particle diameter (D ₅₀ ) of the second cathode active material satisfies the above range, excellent electrode density and energy density can be realized.

The grain size of the second cathode active material may be 200 nm to 500 nm. When the grain size of the second cathode active material satisfies the above range, excellent electrode density and energy density can be realized.

Meanwhile, the content of the transition metal elements may be constant in the active material particle of the second cathode active material, or the content of one or more metal elements may be changed depending on the position of the transition metal element in the particles. For example, the second cathode active material may have a concentration gradient in which at least one of Ni, Mn, Co, and M ² gradually changes, and the gradually changing concentration gradient is a concentration gradient of the components Quot; means that there exists a concentration distribution continuously or stepwise changing in all or a specific region.

Meanwhile, the second cathode active material may be a commercially available lithium nickel cobalt manganese-based cathode active material purchased or used, or may be one produced by a method for producing a lithium nickel cobalt manganese-based cathode active material known in the art.

For example, the lithium nickel cobalt manganese-based cathode active material represented by Formula 2 may be prepared by mixing a nickel cobalt manganese-based precursor with a lithium source material, and optionally, a doping source material followed by sintering.

The nickel cobalt manganese precursor may be a hydroxide of nickel manganese cobalt, a hydroxide of nickel manganese cobalt, an oxide of hydroxide, a carbonate, an organic complex or a hydroxide of nickel manganese cobalt including an element M ² , an oxide, a carbonate, or an organic complex. For example, the nickel-cobalt-manganese-based precursor _{[Ni y Co z Mn w]} (OH) 2, [Ni y Co z Mn w Al v] (OH) 2, [Ni y Co z Mn w] O · OH , [Ni _y Co _z Mn _w Al _v ] O · OH, and the like, but the present invention is not limited thereto.

The lithium source material may be at least one selected from the group consisting of lithium-containing carbonate (for example, lithium carbonate and the like), hydrate (for example, lithium hydroxide I hydrate (LiOH.H ₂ O) For example, lithium nitrate (LiNO ₃ ) and the like), chlorides (e.g., lithium chloride (LiCl) and the like), and the like.

The doping material may be at least one of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, In, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, , B, and Mo, or an oxide, a hydroxide, a sulfide, an oxyhydroxide, a halide, or a mixture thereof.

On the other hand, the firing may be performed at 600 to 1000 ° C, preferably 700 to 900 ° C for 5 to 30 hours, preferably 10 to 20 hours.

If the second cathode active material includes a coating layer, the coating raw material may be further added to the cathode active material after firing, followed by heat treatment.

The coating material may be Al, Ti, W, B, F, P, Mg, Ni, Co, Fe, Cr, V, Cu, Ca, Zn, Zr, Nb. An oxide, a hydroxide, an oxyhydroxide, a carbonate, a sulfate, a halide, a sulfide, an acetic acid, a nitrate, a nitrate, or a salt thereof containing at least one element selected from the group consisting of Mo, Sr, Sb, Bi, Si and S For example, ZnO, Al ₂ O ₃ , Al (OH) ₃ , Al ₂ (SO ₄ ) ₃ , AlCl ₃ , Al-isopropoxide _{), AlNO 3, TiO 2,} WO 3, AlF, _{H 2 BO 3, HBO 2,} H 3 BO 3, H 2 B 4 O 7, B 2 O 3, C 6 H 5 B (OH) 2, (C 6 H 5 O) 3 B, [(CH 3 ( _{CH 2) 3 O) 3 B} , C 3 H 9 B 3 O 6, (C 3 H 7 O 3) B, Li 3 WO 4, (NH 4) 10 W 12 O 41 · 5H 2 O, NH 4 H ₂ PO ₄ , and the like.

For example, a wet coating method, a dry coating method, a plasma coating method, or an ALD (Atomic Layer Deposition) method can be used for forming the coating layer.

The heat treatment may be performed at 100 ° C to 700 ° C, preferably 300 ° C to 450 ° C, for 1 to 15 hours, preferably 3 to 8 hours.

The second cathode active material represented by Formula 2 is a high nickel cathode active material having a nickel ratio exceeding 50 mol%, and thus has excellent energy density characteristics. Therefore, when the second cathode active material represented by Formula 2 is mixed with the first lithium manganese-based cathode active material of the spinel structure of the present invention, the problem of capacity which is a disadvantage of the lithium manganese-based first cathode active material can be solved .

Meanwhile, in the present invention, the anode may include a cathode active material having a bimodal particle diameter distribution including large-diameter particles and small particle size particles having different average particle diameters (D ₅₀ ).

More specifically, 10% to 75% of the positive electrode is the average particle diameter (D ₅₀₎ to the 4㎛ 20㎛ the assignment particle diameter and average particle diameter (D ₅₀₎ is the assigned light particles with a mean particle size (D ₅₀₎ of, And preferably a bimodal particle size distribution including small particle diameters of 25% to 75%. When a cathode active material having a bimodal particle diameter distribution is used as described above, a cathode having a high electrode density and an energy density can be formed.

Preferably, the average particle diameter (D ₅₀ ) of the large diameter particles may be 8 탆 to 20 탆, 8 탆 to 15 탆, or 12 탆 to 20 탆, and the average particle diameter (D ₅₀ ) 1 탆 to 15 탆, 2 탆 to 13 탆, 2 탆 to 8 탆, or 4 탆 to 13 탆.

According to one embodiment, the cathode material according to the present invention may have a bimodal particle size distribution including large-diameter particles having an average particle diameter of 8 탆 to 15 탆 and small-particle particles having an average particle diameter of 1 탆 to 6 탆 .

According to another embodiment, the cathode material according to the present invention may have a bimodal particle diameter distribution including large-diameter particles having an average particle diameter of 12 to 20 μm and small-particle particles having an average particle diameter of 4 to 13 μm .

On the other hand, the kind of the active material constituting the small particle size particles and the large particle size particles is not particularly limited and may be the first positive electrode active material and / or the second positive electrode active material.

According to one embodiment, in the anode of the present invention, the first cathode active material may be a large particle and the second cathode active material may be a small particle. In this case, the average particle diameter (D50) of the first cathode active material is about 8 to 20 탆, preferably about 12 to 20 탆, and the average particle diameter (D50) of the second cathode active material is 1 to 15 탆 , Preferably about 4 탆 to 13 탆. When the large-diameter particles satisfying the above-mentioned range are used as the first cathode active material, the manganese elution in the first cathode active material can be more effectively suppressed, and as a result, the high-temperature stability of the battery can be further improved.

According to another embodiment, in the positive electrode of the present invention, the first positive electrode active material may be small particle size particles and the second positive electrode active material may be large diameter particles. In this case, the average particle diameter (D50) of the first cathode active material is about 1 탆 to 15 탆, preferably about 1 탆 to 8 탆, the average particle diameter (D50) of the second cathode active material is about 8 탆 to 20 탆, Preferably, it may be about 8 占 퐉 to 15 占 퐉. In the case of using small particle size particles satisfying the above range as the first cathode active material, the doping and / or coating amount of the first cathode active material can be applied at a high level and a low BET value can be obtained to minimize side reactions with the electrolyte .

According to another embodiment, in the anode of the present invention, at least one of the first cathode active material and the second cathode active material may have a bimodal particle diameter distribution including the large particle diameter and the small particle diameter .

Meanwhile, the anode may include the first cathode active material and the second cathode active material in a weight ratio of 10:90 to 90:10, preferably 40:60 to 60:40. When the mixing ratio of the first cathode active material and the second cathode active material is in the above range, an electrode excellent in high temperature storability and capacity characteristics can be obtained.

According to one embodiment, the positive electrode according to the present invention includes a positive electrode collector and a positive electrode active material layer formed on the positive electrode collector, wherein the positive electrode active material layer is a lithium manganese-based first positive electrode active material and lithium nickel manganese Cobalt-based second cathode active material. At this time, the cathode active material layer may further include a binder and / or a conductive material if necessary.

Since the specific contents of the first cathode active material and the second cathode active material are the same as those described above, a detailed description thereof will be omitted.

The total weight of the first cathode active material and the second cathode active material may be 80 to 99 wt%, more particularly 85 to 98.5 wt%, based on the total weight of the cathode active material layer. When the cathode active material is included in the above range, excellent capacity characteristics can be exhibited.

The positive electrode current collector is not particularly limited as long as it has conductivity without causing chemical changes in the battery. For example, carbon, nickel, titanium, , Silver or the like may be used. In addition, the cathode current collector may have a thickness of 3 to 500 탆, and fine irregularities may be formed on the surface of the current collector to increase the adhesive strength of the cathode material. For example, it can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric.

The conductive material is used for imparting conductivity to the electrode. The conductive material is not particularly limited as long as it has electron conductivity without causing chemical change. Specific examples thereof include graphite such as natural graphite and artificial graphite; Carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, summer black and carbon fiber; Metal powder or metal fibers such as copper, nickel, aluminum and silver; Conductive whiskey such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; And polyphenylene derivatives. These may be used alone or in admixture of two or more. The conductive material may include 0.1 to 15% by weight based on the total weight of the cathode active material layer.

The binder serves to improve the adhesion between the positive electrode active material particles and the adhesion between the positive electrode active material and the current collector. Specific examples of the binder include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, Polypropylene, ethylene-propylene-diene polymer (EPDM), sulphonated-EPDM, polyvinylpyrrolidone, polyvinylpyrrolidone, polyvinylpyrrolidone, Styrene-butadiene rubber (SBR), fluorine rubber, and various copolymers thereof, and one kind or a mixture of two or more kinds of them may be used. The binder may be contained in an amount of 0.1 to 15% by weight based on the total weight of the cathode active material layer.

Meanwhile, in the present invention, the cathode active material layer may have a single layer structure or a multi-layer structure in which two or more layers are stacked. For example, the anode may include a first cathode active material layer formed on the cathode current collector, and a second cathode active material layer formed on the first cathode active material layer.

Also, in the present invention, the first cathode active material and the second cathode active material may be included in the same layer or different layers.

The first cathode active material layer and the second cathode active material layer may have different compositions. Here, 'different in composition' means that the kind and / or the content of at least one of the components (for example, the cathode active material, the conductive material, the binder, etc.) contained in each layer is different.

According to one embodiment, the first cathode active material layer and the second cathode active material layer may have different mixing ratios of the first cathode active material and the second cathode active material contained in each layer.

For example, the first cathode active material layer contains the first cathode active material in an amount larger than that of the second cathode active material, and the second cathode active material layer contains a larger amount of the second cathode active material than the first cathode active material . &Lt; / RTI &gt; That is, the first cathode active material layer comprises 50 to 100% by weight, preferably 70 to 100% by weight, of the lithium manganese-based first cathode active material in the total cathode active material contained in the first cathode active material layer, The cathode active material layer may include lithium-nickel-cobalt-manganese-based second cathode active material in an amount of 50 to 100% by weight, preferably 70 to 100% by weight, of the total cathode active material contained in the second cathode active material layer. When the lithium manganese-based active material having a spinel structure is contained in a high content in the first positive electrode active material layer positioned at a lower portion of the long lithium ion migration path, the output characteristics can be further improved.

Alternatively, the first cathode active material layer contains the second cathode active material in a larger amount than the first cathode active material, and the second cathode active material layer contains the first cathode active material in a larger amount than the second cathode active material It is possible to do. That is, the first cathode active material layer comprises 50 to 100% by weight, preferably 70 to 100% by weight, of the lithium-nickel-cobalt-manganese-based second cathode active material in the total cathode active material contained in the first cathode active material layer, The second cathode active material layer may include a lithium manganese-based first cathode active material having a spinel structure in an amount of 50 to 100% by weight, preferably 70 to 100% by weight, of the total cathode active material contained in the second cathode active material layer. Since the lithium nickel-cobalt manganese-based cathode active material has a high tap density and a high rolling rate, when the lithium-nickel-cobalt manganese-based cathode active material is contained in the first active material layer located at the bottom, , The output and the lifetime improvement effect can be obtained.

According to another embodiment, the first cathode active material layer and the second cathode active material layer may have different contents of binders contained in each layer. Specifically, the first cathode active material layer contains the binder in an amount of 1 to 4 wt%, preferably 1.5 to 4 wt%, and the second cathode active material layer contains 3 wt% or less of the binder, 0.5 to 2% by weight.

The anode according to the present invention has a high loading density and a high electrode density, so that it has excellent energy density characteristics. Specifically, the anode has a loading amount of 3.0 mAh / cm &lt; ² &gt; To be 20 mAh / cm ^2, preferably from 3.6 to 6.0mAh / cm ^2, more preferably from 4.0 to 5.0 mAh / cm ^2.

The positive electrode of the present invention can be produced by a conventional positive electrode manufacturing method, except that a specific positive electrode active material according to the present invention is used. Specifically, the positive electrode active material, the binder and / or the conductive material may be dissolved or dispersed in a solvent to form a positive electrode current collector on the positive electrode current collector, followed by drying and rolling.

The solvent may be any solvent commonly used in the art and may be a solvent such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone or water . One of these may be used alone, or a mixture of two or more thereof may be used. The amount of the solvent to be used is not particularly limited as long as it can be adjusted to have an appropriate viscosity in consideration of the coating thickness of the positive electrode composite material, the production yield, workability, and the like.

Alternatively, the positive electrode may be produced by casting the positive electrode composite material on a separate support, and then peeling off the support from the support to laminate a film on the positive electrode collector.

(2) cathode

Next, the cathode will be described.

The negative electrode according to the present invention is characterized in that the negative electrode includes at least one selected from the group consisting of artificial graphite having a specific surface area (BET) of 0.1 to 1.2 m ² / g and natural graphite and softened carbon having a specific surface area larger than that of the artificial graphite .

According to research conducted by the present inventors, it has been found that a lithium secondary battery using a positive electrode comprising a lithium manganese-based first cathode active material having a spinel structure doped and coated and a lithium-nickel-manganese-cobalt-based second cathode active material has a specific surface area ) Was 0.1 to 1.2 m ² / g, the battery characteristics at high temperature were superior to those in the case of using a negative electrode containing other types of negative active materials, The effect of suppressing the increase in resistance was also excellent.

Specifically, the artificial graphite may have a specific surface area (BET) of 0.1 to 1.2 m ² / g, preferably 0.3 to 1.0 m ² / g, more preferably 0.5 to 1.0 m ² / g. When the specific surface area of the artificial graphite exceeds 0.12m ² / g or less, 1.2m ² / g, the increase in resistance appeared to be insignificant the inhibitory effect of long-term high-temperature storage.

In addition, when at least one selected from the group consisting of natural graphite and softened carbon having a specific surface area larger than that of the artificial graphite is used together with artificial graphite having a specific specific surface area as described above, the negative electrode adhesive strength is increased, It is possible to effectively prevent degradation of the electrode performance.

In this case, the soft carbon may have a specific surface area (BET) of 7 to 10 m ² / g, preferably 8 to 10 m ² / g. When the specific surface area of the softened carbon satisfies the above range, the effect of improving high-temperature storage characteristics and high-temperature lifetime characteristics is more excellent.

The natural graphite may have a specific surface area (BET) of 2 to 5 m ² / g, preferably 2.5 to 4.0 m ² / g, more preferably 2.5 to 3.5 m ² / g. When the specific surface area of natural graphite satisfies the above range, the effect of improving high-temperature storage characteristics and high-temperature lifetime characteristics is more excellent.

According to one embodiment, the negative electrode comprises a mixture of artificial graphite and softened carbon in a weight ratio of 50:50 to 95: 5, preferably 60:40 to 95: 5, more preferably 70:30 to 90:10 . When the mixing ratio of the artificial graphite and the softened carbon satisfies the above range, the life improving effect and the effect of suppressing the increase in resistance after high temperature storage are more excellent.

According to another embodiment, the cathode contains artificial graphite and natural graphite in a weight ratio of 50:50 to 95: 5, preferably 60:40 to 95: 5, more preferably 70:30 to 90:10. can do. When the mixing ratio of artificial graphite and natural graphite satisfies the above range, the life improving effect and the effect of suppressing the increase in resistance after storage at high temperature are more excellent.

The negative electrode may include a negative electrode collector and a negative electrode active material layer positioned on the negative electrode collector. The negative electrode active material layer may be a negative electrode active material, and may be a synthetic resin having a specific surface area (BET) of 0.1 to 1.2 m ² / Graphite and at least one selected from the group consisting of natural graphite and softened carbon having a larger specific surface area than the artificial graphite. In addition, the anode active material layer may further include a binder and a conductive material in addition to the artificial graphite, natural graphite, and softened carbon.

At this time, the total weight of the artificial graphite-softened carbon and the natural graphite may be about 80 to 99% by weight based on the total weight of the negative electrode active material layer. Since artificial graphite, natural graphite and softened carbon have been described above, the remaining components will be described below.

The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. For example, the negative electrode current collector may be formed on the surface of copper, stainless steel, aluminum, nickel, titanium, sintered carbon, Carbon, nickel, titanium, silver or the like, aluminum-cadmium alloy, or the like may be used. In addition, the negative electrode collector may have a thickness of 3 to 500 탆, and similarly to the positive electrode collector, fine unevenness may be formed on the surface of the collector to enhance the binding force of the negative electrode active material. For example, it can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric.

The binder is a component for assisting the bonding between the conductive material, the active material and the current collector, and is usually added in an amount of 0.1% by weight to 10% by weight based on the total weight of the negative electrode active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene Examples thereof include ethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluorine rubber and various copolymers thereof.

The conductive material may be added in an amount of 10 wt% or less, preferably 5 wt% or less, based on the total weight of the negative electrode active material layer, as a component for further improving the conductivity of the negative electrode active material. Such a conductive material is not particularly limited as long as it has electrical conductivity without causing chemical changes in the battery, for example, graphite such as natural graphite or artificial graphite; Carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskey such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used.

The negative electrode active material layer is prepared by applying and drying a negative electrode active material prepared by dissolving or dispersing a negative active material on a negative electrode current collector and optionally a binder and a conductive material in a solvent or by drying the negative electrode active material on a separate support And then laminating a film obtained by peeling from the support onto an anode current collector.

Meanwhile, the negative electrode active material layer may have a single layer structure or a multi-layer structure in which two or more layers are stacked. For example, the negative electrode may include a negative electrode collector, a first negative electrode active material layer formed on the negative electrode collector, and a second negative electrode active material layer formed on the first negative electrode active material layer, The active material layer and the second negative electrode active material layer may have different compositions. That is, the first anode active material layer and the second anode active material layer may have different kinds and / or contents of respective components in the anode active material layer. For example, the first anode active material layer and the second anode active material layer may have different contents of artificial graphite, softened carbon, natural graphite, and / or binder.

On the other hand, the loading amount of the negative electrode may be 300 to 500 mg / 25 cm ² , preferably 300 to 400 mg / 25 cm ² . When the loading amount of the negative electrode satisfies the above range, it is possible to secure a sufficient electrode bonding force, to facilitate a process, to realize a battery having excellent rapid charging performance and resistance performance, and to maximize energy density.

(3) The membrane

The separation membrane separates the cathode and the anode and provides a passage for lithium ion. The separation membrane can be used without any particular limitation as long as it is used as a separation membrane in a lithium secondary battery. Particularly, the separation membrane has low resistance against electrolyte migration, Excellent.

Specifically, a porous polymer film such as a porous polymer film made of a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer Or a laminated structure of two or more thereof may be used. Further, a nonwoven fabric made of a conventional porous nonwoven fabric, for example, glass fiber of high melting point, polyethylene terephthalate fiber, or the like may be used. In order to secure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymer material may be used, and the separator may be selectively used as a single layer or a multilayer structure.

(4) electrolyte

As the electrolyte used in the present invention, an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, a molten inorganic electrolyte, and the like, which can be used for a lithium secondary battery, are not particularly limited.

Specifically, the electrolyte may include an organic solvent and a lithium salt.

The organic solvent may be used without limitation as long as it can act as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, examples of the organic solvent include ester solvents such as methyl acetate, ethyl acetate,? -Butyrolactone and? -Caprolactone; Ether solvents such as dibutyl ether or tetrahydrofuran; Ketone solvents such as cyclohexanone; Aromatic hydrocarbon solvents such as benzene and fluorobenzene; Dimethyl carbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), propylene carbonate PC) and the like; Alcohol solvents such as ethyl alcohol and isopropyl alcohol; Ra-CN (Ra is a linear, branched or cyclic hydrocarbon group having 2 to 20 carbon atoms, which may contain a double bond aromatic ring or ether bond); Amides such as dimethylformamide; Dioxolanes such as 1,3-dioxolane; Or sulfolane may be used. Among these, a carbonate-based solvent is preferable, and a cyclic carbonate (for example, ethylene carbonate or propylene carbonate) having a high ionic conductivity and a high dielectric constant, for example, such as ethylene carbonate or propylene carbonate, For example, ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate) is more preferable.

The lithium salt may be used, without limitation, those which are commonly used in a lithium secondary battery electrolyte, such as an anion, and containing the Li ⁺ in the lithium salt cation is F ^-, Cl ^-, Br ^-, I ^-, NO _{^{3 -, N (CN) 2}} -, BF 4 -, ClO 4 -, AlO 4 -, AlCl 4 -, PF 6 -, SbF 6 -, AsF 6 -, BF 2 C 2 O 4 -, BC 4 O 8 _{^{-, PF 4 C 2 O 4}} -, PF 2 C 4 O 8 -, (CF 3) 2 PF 4 -, (CF 3) 3 PF 3 -, (CF 3) 4 PF 2 -, (CF 3) 5 _{^{PF -, (CF 3) 6}} P -, CF 3 SO 3 -, C 4 F 9 SO 3 -, CF 3 CF 2 SO 3 -, (CF 3 SO 2) 2 N -, (FSO 2) 2 N - _{, CF 3 CF 2 (CF 3} ) 2 CO -, (CF 3 SO 2) 2 CH -, (SF 5) 3 C -, (CF 3 SO 2) 3 C -, CF 3 (CF 2) 7 SO 3 ^- , CF ₃ CO ₂ ^- , CH ₃ CO ₂ ^- , SCN ^- and (CF ₃ CF ₂ SO ₂ ) ₂ N ^- . Specifically, the lithium salt may be LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCH ₃ CO ₂ , LiCF ₃ CO ₂ , LiAsF ₆ , LiSbF ₆ , LiAlCl ₄ , LiAlO ₄ , and LiCH ₃ SO ₃ , or a mixture of two or more thereof.

The lithium salt can be appropriately changed within a range that is usually usable, but it can be specifically contained in the electrolyte in an amount of 0.8 M to 3 M, specifically 0.1 M to 2.5 M.

In addition to the electrolyte components, various additives may be added to the electrolyte for the purpose of improving lifetime characteristics of the battery, suppressing the reduction of the battery capacity, and improving the discharge capacity of the battery. Such additives include, for example, haloalkylene carbonate-based compounds such as difluoroethylene carbonate and the like; N, N &lt; RTI ID = 0.0 &gt; (N, &lt; / RTI &gt; N, N'-tetramethyluronium hexafluorophosphate), pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, glyme, Substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol or aluminum trichloride, and the above additives may be used singly or in combination. The additive may be included in an amount of 0.1 wt% to 5 wt% based on the total weight of the electrolyte.

The lithium secondary battery according to the present invention can be used for portable equipment such as mobile phones, notebook computers, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEV).

According to another embodiment of the present invention, there is provided a battery module including the lithium secondary battery as a unit cell and a battery pack including the same.

The battery module or the battery pack may include a power tool; An electric vehicle including an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); Or a power storage system, as shown in FIG.

The external shape of the lithium secondary battery of the present invention is not particularly limited, but may be a cylindrical shape, a square shape, a pouch shape, a coin shape, or the like using a can.

The lithium secondary battery according to the present invention can be used not only in a battery cell used as a power source of a small device but also as a unit cell in a middle- or large-sized battery module including a plurality of battery cells.

Hereinafter, the present invention will be described in detail by way of examples with reference to the following examples. However, the embodiments according to the present invention can be modified into various other forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. The embodiments of the present invention are provided to enable those skilled in the art to more fully understand the present invention.

Example

Production Example 1

MnSO _4, Al ₂ (SO _{4) 3} and MgO to 94.2: 3.4: were mixed in a weight ratio of 2.4, MnSO containing Al ₂ (SO _{4) 3} and MgO with distilled water via a N ₂ purged ₄ and 7H ₂ &lt; / RTI &gt; MnSO ₄ .7H ₂ O was added to the continuous stirred tank reactor (CSTR, manufacturer: EMS Tech, product name: CSTR-L0) at a rate of 250 mL / h. A 40% aqueous solution of sodium hydroxide was introduced as an alkalizing agent at a rate of 10 mL / h through an aqueous solution of sodium hydroxide in the reactor, and a 25% ammonia solution was fed through the ammonia solution supply portion of the reactor at a rate of 30 mL / And the pH of the solution was maintained at 10.5. The temperature of the reactor was adjusted to 40 ° C., the residence time (RT) was adjusted to 10 hours, and the mixture was stirred at a speed of 1200 rpm to precipitate Mn ₃ O ₄ containing Al and Mg. Through the additional step of the resulting reaction solution was filtered through a filter, dried and then purified with distilled water, Al and Mg-doped manganese precursor _{(Mn 0. 94 Al 0.} 03 Mg 0. 03) was prepared in a ₃ O ₄ . The thus prepared manganese precursor doped with Al and Mg was mixed with Li ₂ CO ₃ at a molar ratio of 1: 0.75 and then calcined at 810 ° C. for 14 hours to obtain lithium manganese oxide Li (Mn _1.88 Al _0.06 Mg _0.06 ) O ₄ was obtained.

3000 parts by weight of WO ₃ was added to 100 parts by weight of the lithium manganese oxide prepared as described above, followed by dry mixing, followed by heat treatment at 600 ° C for 5 hours to obtain a first cathode active material A having a coating layer containing W formed thereon.

Production Example 2

Lithium manganese oxide Li (Mn _1.88 Al _0.06 Mg _0.06 ) O ₄ prepared according to the method of Production Example 1 1000 parts by weight of TiO ₂ was added to 100 parts by weight of WO ₃ instead of WO ₃ , and the mixture was heat-treated at 600 ° C. for 5 hours to obtain a first cathode active material B having a coating layer containing Ti.

Production Example 3

MnSO _4, Li ₂ CO ₃ (MnSO ₄ .7H ₂ O) containing Li ₂ CO ₃ and Al ₂ (SO ₄ ) ₃ was prepared by mixing Al ₂ (SO ₄ ) ₃ and Al ₂ (SO ₄ ) ₃ in a weight ratio of 95: 0.5: (Mn _0.957 Li _0.015 Al _0.028 ) ₃ O ₄ doped with Li and Al was prepared in the same manner as in Production Example 1.

The Li-doped manganese precursor thus prepared and the lithium source material Li ₂ CO ₃ were mixed at a molar ratio of 1: 0.75 and then fired at 810 ° C for 14 hours to obtain lithium manganese oxide Li (Mn _1.914 Li _0.06 Al _0.056 ) O ₄ was obtained.

5000 parts by weight of WO ₃ was added to 100 parts by weight of lithium manganese oxide prepared as described above, followed by dry mixing, followed by heat treatment at 600 ° C for 5 hours to obtain a first cathode active material C in which a coating layer containing W was formed.

Production Example 4

MnSO _4, Li ₂ CO ₃ And MgSO ₄ were mixed in a weight ratio of 98: 0.5: 1.5 to prepare (MnSO ₄ .7H ₂ O) containing Li ₂ CO ₃ and MgSO ₄ , Li And a Mg-doped manganese precursor (Mn _0.961 Li _0.021 Mg _0.018 ) ₃ O ₄ were prepared.

The Li-doped manganese precursor thus prepared and the lithium source material Li ₂ CO ₃ were mixed at a molar ratio of 1: 0.75 and then calcined at 810 ° C for 14 hours to obtain lithium manganese oxide Li (Mn _1.922 Li _0.042 Mg _0.036 ) O ₄ was obtained.

5000 parts by weight of WO ₃ was added to 100 parts by weight of lithium manganese oxide prepared as described above, followed by dry mixing and then heat treatment at 600 ° C for 5 hours to obtain a first cathode active material D having a coating layer containing W.

Production Example 5

Li (Mn _1.88 Al _0.06 Mg _0.06 ) O ₄ produced in Production Example 1 was used as the cathode active material E without forming a coating layer.

Production Example 6

(Mn _1.88 Al _0.08 Mg _0.04 ) O (2) was prepared in the same manner as in Production Example 1 except that MnSO _{4 ,} Al ₂ (SO ₄ ) ₃ and MgO were mixed at a weight ratio of 93.9: ₄ was prepared and used as the cathode active material F without forming a coating layer.

Production Example 7

5000 ppm of WO ₃ was added to 100 parts by weight of lithium manganese oxide LiMn ₂ O _4, and the mixture was heat-treated at 600 ° C for 5 hours to obtain a first cathode active material G having a coating layer containing W formed thereon.

Example 1

A positive electrode active material, a conductive material and a binder were mixed in a weight ratio of 96.25: 1.0: 1.5 in an N-methylpyrrolidone solvent to prepare a positive electrode mixture. At this time, as the cathode active material, the cathode active material A and Li [Ni _{0 . 86} Co _{0 . 07} Mn _{0 . 35} Al _{0 . 35} ] O ₂ were mixed in a weight ratio of 55:45. As the conductive material, Li435 of Denka Co. was used. KF9700 of Kureha and BM-730H of ZEON were mixed in a weight ratio of 90:10 Respectively. The prepared positive electrode material was applied to an aluminum current collector (trade name: A1100, manufactured by Sanya Aluminum Co., Ltd.) having a thickness of 12 탆, dried at 130 캜 and rolled to prepare a positive electrode.

A negative electrode active material, a binder, a CMC and a conductive material were mixed in a weight ratio of 96.1: 2.3: 1.1: 0.5 in N-methylpyrrolidone solvent to prepare a negative electrode material. At this time, the negative electrode active material as is the artificial graphite having a BET specific surface area of 0.740m ² / g (model name: GT, Manufacturer: Zichen) and a BET specific surface area of 9.5 m ² / g of carbon softening (model number: PCT-240R, Manufacturer: Power Carbon Technology) were mixed at a weight ratio of 90:10. BM-L203 of Zeon Co., Ltd., Super C65 of Imerys Co., Ltd. and Daicel of Daicel Co., Ltd. were used as the binder. The prepared negative electrode composite was applied to a copper collector (manufactured by LS Mtron) having a thickness of 82 탆, dried at 65 캜 and rolled to prepare a negative electrode.

A coin cell was prepared by interposing a separator between the positive and negative electrodes and injecting an electrolyte solution.

Example 2

Except that the cathode active material B prepared in Preparation Example 2 and Li [Ni _0.86 Co _0.07 Mn _0.35 Al _0.35 ] O ₂ were mixed in a weight ratio of 55:45 and used as the cathode active material, Coin cells were prepared.

Example 3

Except that the cathode active material C prepared in Preparation Example 3 and Li [Ni _0.86 Co _0.07 Mn _0.35 Al _0.35 ] O ₂ were mixed in a weight ratio of 55:45 and used as the cathode active material in the same manner as in Example 1 Coin cells were prepared.

Example 4

Except that the cathode active material D prepared in Preparation Example 4 and Li [Ni _0.86 Co _0.07 Mn _0.35 Al _0.35 ] O ₂ were mixed in a weight ratio of 55:45 and used as the cathode active material in the same manner as in Example 1 Coin cells were prepared.

Example 5

Natural graphite (model: PAS-C3B, manufactured by POSCO Chemtech) having a BET specific surface area of 0.740 m ² / g and a BET specific surface area of 2.680 m ² / g was used as the anode active material. Were mixed in a weight ratio of 90:10, to prepare a coin cell.

Comparative Example 1

Except that the cathode active material E prepared in Preparation Example 5 and Li [Ni _0.86 Co _0.07 Mn _0.35 Al _0.35 ] O ₂ were mixed in a weight ratio of 55:45 and used as a cathode active material in the same manner as in Example 1 Coin cells were prepared.

Comparative Example 2

Except that the cathode active material F prepared in Preparation Example 6 and Li [Ni _0.86 Co _0.07 Mn _0.35 Al _0.35 ] O ₂ 55: 45 were mixed in the weight ratio of the cathode active material to prepare a coin Cells were prepared.

Comparative Example 3

Except that the cathode active material G prepared in Preparation Example 7 and Li [Ni _0.86 Co _0.07 Mn _0.35 Al _0.35 ] O ₂ were mixed in a weight ratio of 55:45 and used as the cathode active material in the same manner as in Example 1 Coin cells were prepared.

Comparative Example 4

Except that LiMn ₂ O ₄ and Li [Ni _0.86 Co _0.07 Mn _0.35 Al _0.35 ] O ₂ , which were not doped and coated with a cathode active material, were mixed in a weight ratio of 55:45, and the same method as in Example 1 To prepare a coin cell.

Comparative Example 5

A coin cell was prepared in the same manner as in Example 1 except that natural graphite (PAS-C3B, manufactured by POSCO Chemtech) having a BET specific surface area of 2.680 m ² / g was used alone as the negative electrode active material.

Comparative Example 6

Is a BET specific surface area of 2.680m ² / g as a negative active material of natural graphite in the carbon softening (model:: PAS-C3B, manufacturer POSCO Chemtech) and the BET specific surface area of 9.5 m ² / g (model name: PCT-240R, Power Carbon Technology ) Were mixed at a weight ratio of 90:10, to prepare a coin cell.

Experimental Example 1: High-temperature storage characteristics (1)

The coin cells prepared in Examples 1 to 4 and Comparative Examples 1 to 4 were stored at 60 DEG C for 4 weeks, and the capacity retention rate and the rate of increase in resistance were measured.

Specifically, the coin cells prepared in Examples 1 to 4 and Comparative Examples 1 to 4 were fully charged to 4.2 V and stored at 60 ° C. for 4 weeks. After every one week, the coin cells were charged at a constant current of 0.33 C After discharging to 4.2 V with a constant current of 0.33 C, the discharging capacity and the resistance at that time were measured. Then, the discharging capacity and resistance after the storage for 4 weeks were compared with the initial discharging capacity and the initial resistance, Growth rate. The measurement results are shown in Table 1 below.

	Capacity retention rate (%)	Rate of resistance increase (%)
Example 1	72	185
Example 2	68	215
Example 3	67	219
Example 4	66	218
Comparative Example 1	69	221
Comparative Example 2	67	250
Comparative Example 3	63	257
Comparative Example 4	62	261

As shown in Table 1, the coin cells of Examples 1 to 4 had the same capacity retention ratios as those of the coin cells of Comparative Examples 1 to 4 after storage for 4 weeks at 60 ° C, ~ 4 coin cells.

Experimental Example  2: High Temperature Storage Characteristics (2)

The coin cells prepared in Examples 1 and 5 and Comparative Examples 5 and 6 were stored at 60 DEG C for 6 weeks, and the capacity retention rate and the rate of resistance increase were measured.

Specifically, the coin cells prepared in Examples 1 and 5 and Comparative Examples 5 and 6 were fully charged to 4.2 V, and then stored at 60 ° C. for 6 weeks. After every one week, the coin cells were subjected to a constant current of 0.1 C The battery was charged to 4.2 V, discharged to 3.0 V with a constant current of 0.1 C, and the discharge capacity and resistance at that time were measured. Then, the capacity retention rate and the rate of increase in resistance were measured by comparing the initial discharge capacity and the initial resistance.

The measurement results are shown in Fig. As shown in FIG. 1, the resistance increase rates between the coin cells of Examples 1 and 5 and Comparative Examples 5 and 6 were not significantly different up to 4 weeks storage. However, when stored for 6 weeks or more, It can be confirmed that the rate of increase in resistance is significantly smaller than that in Comparative Examples 5 and 6. [

EXPERIMENTAL EXAMPLE 3: High Temperature Life Characteristics (1)

The life characteristics of the coin cells prepared in Examples 1 to 4 and Comparative Examples 1 to 4 were measured at a high temperature.

Specifically, each of the coin cells prepared in Examples 1 to 4 and Comparative Examples 1 to 4 was charged at a constant current of 0.33 C at a temperature of 45 캜 to a voltage of 4.2 V at a cut off of 0.05C. Then, discharging was performed until the voltage reached 2.5 V at a constant current of 0.33C.

The charging and discharging behaviors were repeated one cycle, and the cycle was repeated 200 times. The discharge capacity and the resistance after 200 cycles were compared with the initial discharge capacity and the initial resistance to measure the capacity retention rate and the resistance increase rate. The measurement results are shown in Table 2 below.

	Capacity retention rate (%)	Rate of resistance increase (%)
Example 1	86	176
Example 2	82	194
Example 3	79	201
Example 4	80	198
Comparative Example 1	85	210
Comparative Example 2	84	222
Comparative Example 3	77	225
Comparative Example 4	71	232

As shown in Table 2, the coin cells of Examples 1 to 4 had the same capacity retention ratios as those of the coin cells of Comparative Examples 1 to 4 after charging and discharging for 200 cycles at 45 ° C, ~ 4 coin cells.

Experimental Example  4: High temperature lifetime characteristics (2)

The life characteristics of the coin cells prepared in Examples 1 and 5 and Comparative Examples 5 and 6 were measured at high temperature.

Specifically, the coin cells prepared in Examples 1 and 5 and Comparative Examples 5 and 6 were charged at a constant current of 0.1 C at a temperature of 45 ° C to 4.2 V at a cut off of 0.05C. Then, discharging was performed until the voltage reached 3.0 V with a constant current of 0.1C.

The charging and discharging behaviors were set as one cycle, and the cycle was repeated 300 times. Then, the discharge capacity after 300 cycles was compared with the initial discharge capacity to measure the capacity retention rate. The measurement results are shown in Fig.

As shown in FIG. 2, it can be confirmed that the capacity retention ratio is relatively higher than that of the coin cells of Comparative Example 5 and 6 of the coin cells of Examples 1 and 5.

Claims (20)

1. A cathode comprising a lithium manganese-based first cathode active material having a spinel structure and a lithium-nickel-manganese-cobalt-based second cathode active material;

   A negative electrode comprising at least one selected from the group consisting of artificial graphite having a specific surface area (BET) of 0.1 to 1.2 m ² / g and softened carbon and natural graphite having a larger specific surface area than the artificial graphite;

   A separator interposed between the anode and the cathode; And

   An electrolyte,

   Wherein the first cathode active material is a lithium manganese oxide represented by the following formula 1 and a lithium manganese oxide which is located on the surface of the lithium manganese oxide and contains Al, Ti, W, B, F, P, Mg, Ni, Co, Fe, , Ca, Zn, Zr, Nb. And a coating layer comprising at least one element selected from the group consisting of Mo, Sr, Sb, Bi, Si, and S. A lithium secondary battery comprising:

   [Chemical Formula 1]

   Li _{1 + a} Mn _2-b M ¹ _b O _{4 -c} A _c

   M ¹ is at least one element selected from the group consisting of Al, Li, Mg, Zn, B, W, Ni, Co, Fe, Cr, V, Ru, Cu, Cd, Ag, Y, , Pt, Au and Si, A is at least one element selected from the group consisting of F, Cl, Br, I, At and S, and 0? A? 0.2, 0 < b? 0.5, 0? c? 0.1)
2. The method according to claim 1,

   Wherein the doping element M ¹ comprises at least one selected from the group consisting of Al, Li, Mg, and Zn.
3. The method according to claim 1,

   Wherein the coating layer comprises at least one selected from the group consisting of Al, Ti, Zn, W and B.
4. The method according to claim 1,

   Wherein the second cathode active material is a lithium nickel manganese cobalt-based cathode active material represented by the following Formula 2:

   (2)

   Li _{1 + x} [Ni _y Co _z Mn _w M ² _v ] O _{2 - p} B _p

   In Formula 2, M ² is at least one element selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, In, La, Sr, Ga, Sc, Gd, B, at least one element selected from the group consisting of Nb, Mg, B and Mo; B is at least one element selected from the group consisting of F, Cl, Br, I, At and S; 0.50? Y <1, 0 <z <0.35, 0 <w <0.35, 0? V? 0.1, 0? P?
5. The method according to claim 1,

   Wherein the first cathode active material and the second cathode active material are contained in a weight ratio of 10:90 to 90:10.
6. The method according to claim 1,

   Wherein the positive electrode includes a positive electrode active material having a bimodal particle diameter distribution including large diameter particles and small particle diameter particles having different average particle diameters (D50).
7. The method according to claim 6,

   Wherein the first positive electrode active material is the small particle size particle and the second positive electrode active material is the large diameter particle.
8. The method according to claim 6,

   Wherein the first cathode active material is the large particle particle and the second cathode active material is the small particle particle.
9. The method according to claim 6,

   Wherein at least one of the first cathode active material and the second cathode active material has a bimodal particle size distribution including the large-diameter particles and the small particle size particles.
10. The method according to claim 1,

    Wherein the positive electrode comprises a positive electrode collector, a first positive electrode active material layer formed on the positive electrode collector, and a second positive electrode active material layer formed on the first positive electrode active material layer.
11. 11. The method of claim 10,

    Wherein the first cathode active material and the second cathode active material are contained in different layers.
12. 11. The method of claim 10,

    Wherein the first cathode active material layer and the second cathode active material layer have different compositions.
13. 11. The method of claim 10,

    Wherein the first cathode active material layer comprises the first cathode active material in an amount of 50 to 100% by weight of the total cathode active material contained in the first cathode active material layer,

    Wherein the second cathode active material layer comprises 50 to 100% by weight of the second cathode active material in the total cathode active material contained in the second cathode active material layer.
14. 11. The method of claim 10,

    Wherein the first cathode active material layer comprises 50 to 100% by weight of the second cathode active material in the total cathode active material contained in the first cathode active material layer,

    Wherein the second cathode active material layer comprises 50 to 100% by weight of the first cathode active material in the total cathode active material contained in the second cathode active material layer.
15. 11. The method of claim 10,

    Wherein the first cathode active material layer and the second cathode active material layer include a binder,

    Wherein the first cathode active material layer contains the binder in an amount of 1 to 4 wt%

    And the second cathode active material layer contains a binder in an amount of 3 wt% or less.
16. The method according to claim 1,

    Wherein the negative electrode comprises artificial graphite and softened carbon in a weight ratio of 50:50 to 95: 5.
17. The method according to claim 1,

    Wherein the negative electrode comprises artificial graphite and natural graphite in a weight ratio of 50:50 to 95: 5.
18. The method according to claim 1,

    The natural graphite has a specific surface area (BET) of 2 to 5 m ² / g.
19. The method according to claim 1,

    The softened carbon has a specific surface area (BET) of 7 to 10 m ² / g.
20. The method according to claim 1,

    Wherein the negative electrode comprises a negative electrode collector, a first negative electrode active material layer formed on the negative electrode collector, and a second negative electrode active material layer formed on the first negative electrode active material layer.

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