阅读说明：本技术 用于锂二次电池的正极、其制备方法以及包括其的锂二次电池 (Positive electrode for lithium secondary battery, method of preparing the same, and lithium secondary battery including the same ) 是由 李柱成 金浩俊 许珉智 于 2018-07-11 设计创作，主要内容包括：本发明提供一种用于锂二次电池的正极,其包括：包含锂钴基氧化物的第一正极活性材料和包含锂复合过渡金属氧化物的第二正极活性材料,所述锂复合过渡金属氧化物含有选自由镍(Ni)、钴(Co)和锰(Mn)组成的组的至少两种,其中,将所述第一正极活性材料以1C充电时达到恒定电压(CV)的充电状态(SOC)称为SOC<Sub>1</Sub>,且将所述第二正极活性材料以1C充电时达到恒定电压(CV)的充电状态(SOC)称为SOC<Sub>2</Sub>时,SOC<Sub>1</Sub>和SOC<Sub>2</Sub>之间的关系满足以下等式1：[等式1]SOC<Sub>1</Sub><SOC<Sub>2</Sub><1.1×SOC<Sub>1</Sub>。(The present invention provides a positive electrode for a lithium secondary battery, comprising: a first positive electrode active material comprising a lithium cobalt-based oxide and a second positive electrode active material comprising a lithium composite transition metal oxide containing at least two selected from the group consisting of nickel (Ni), cobalt (Co) and manganese (Mn), wherein a state of charge (SOC) at which the first positive electrode active material reaches a Constant Voltage (CV) when charged at 1C is referred to as SOC 1 And a state of charge (SOC) at which the second positive electrode active material reaches a Constant Voltage (CV) when charged at 1C is referred to as SOC 2 Time, SOC 1 And SOC 2 The relationship therebetween satisfies the following equation 1: [ equation 1]]SOC 1 <SOC 2 <1.1×SOC 1 。)

1. A positive electrode for a lithium secondary battery, comprising:

a first positive electrode active material comprising a lithium cobalt-based oxide; and

a second positive electrode active material comprising a lithium composite transition metal oxide containing at least two selected from the group consisting of nickel (Ni), cobalt (Co), and manganese (Mn), wherein,

a state of charge (SOC) that reaches a Constant Voltage (CV) when the first positive electrode active material is charged at 1C is referred to as SOC₁And a state of charge (SOC) at which the second positive electrode active material reaches a Constant Voltage (CV) when charged at 1C is referred to as SOC₂Time, SOC₁And SOC₂The relationship therebetween satisfies the following equation 1:

[ equation 1]

SOC₁<SOC₂<1.1×SOC₁。

2. The positive electrode according to claim 1, wherein the first positive electrode active material is represented by the following formula 1:

[ formula 1]

Li_a1Co_1-x1M¹ _x1O_2+β

(in formula 1, M¹Comprises a metal selected from the group consisting of Al, B, Ba, Ca, Zr, Ti, Mg, Ta, Nb,At least one of Sr, W and Mo, and 0.9<a1 is less than or equal to 1.1, x1 is less than or equal to 0.2 and beta is more than or equal to 0 and less than or equal to 0.02).

3. The positive electrode according to claim 1, wherein the second positive electrode active material is represented by the following formula 2:

[ formula 2]

Li_a2Ni_x2Mn_y2Co_z2M² _w2O_2+δ

(in formula 2, M²Including at least one selected from the group consisting of Al, B, Ba, Ca, Zr, Ti, Mg, Ta, Nb, Sr, W and Mo, and 0.9<a2≤1.1，0.3≤x2≤0.95，0<y2≤0.4，0<z2 is less than or equal to 0.5, w2 is less than or equal to 0.1, δ is less than or equal to 0.02, and x2+ y2+ z2+ w2 is 1).

4. The cathode according to claim 1, wherein the second cathode active material has a single crystal size of 180 to 800 nm.

5. The positive electrode according to claim 1, wherein the second positive electrode active material contains a coating or doping element, and the total content of the coating or doping element is 1,000ppm or more.

6. The positive electrode as claimed in claim 1, wherein the first positive electrode active material and the second positive electrode active material are mixed in a weight ratio of 90:10 to 30: 70.

7. A method of preparing a positive electrode for a lithium secondary battery, the method comprising:

preparing a first cathode active material including a lithium cobalt-based oxide, and a second cathode active material including a lithium composite transition metal oxide having at least two selected from the group consisting of nickel (Ni), cobalt (Co), and manganese (Mn); and

mixing the first positive electrode active material and the second positive electrode active material, wherein,

when the first positive electrode active material is coated with 1CThe state of charge (SOC) that reaches a Constant Voltage (CV) during charging is called SOC₁And a state of charge (SOC) at which the second positive electrode active material reaches a Constant Voltage (CV) when charged at 1C is referred to as SOC₂Time, SOC₁And SOC₂The relationship therebetween satisfies the following equation 1:

[ equation 1]

SOC₁<SOC₂<1.1×SOC₁。

8. The method according to claim 7, wherein the first positive electrode active material is represented by the following formula 1:

[ formula 1]

Li_a1Co_1-x1M¹ _x1O_2+β

(in formula 1, M¹Including at least one selected from the group consisting of Al, B, Ba, Ca, Zr, Ti, Mg, Ta, Nb, Sr, W and Mo, and 0.9<a1 is less than or equal to 1.1, x1 is less than or equal to 0.2 and beta is more than or equal to 0 and less than or equal to 0.02).

9. The method according to claim 7, wherein the second positive electrode active material is represented by the following formula 2:

[ formula 2]

Li_a2Ni_x2Mn_y2Co_z2M² _w2O_2+δ

(in formula 2, M²Including at least one selected from the group consisting of Al, B, Ba, Ca, Zr, Ti, Mg, Ta, Nb, Sr, W and Mo, and 0.9<a2≤1.1，0.3≤x2≤0.95，0<y2≤0.4，0<z2≤0.5，0≤w2≤0.1，0≤δ≤0.02，x2+y2+z2+w2＝1)。

10. The method according to claim 7, wherein the preparing of the second cathode active material includes a process of preparing the second cathode active material by using a solid phase reaction method.

11. The method according to claim 7, wherein the preparation of the second cathode active material comprises a process of preparing the second cathode active material by overburning such that the second cathode active material has a single crystal size of 180 to 800 nm.

12. The method according to claim 7, wherein the preparation of the second cathode active material includes a process of allowing the second cathode active material to contain a coating or doping element, and the total content of the coating or doping element is 1,000ppm or more.

13. The method according to claim 7, wherein the first positive electrode active material and the second positive electrode active material are mixed in a weight ratio of 90:10 to 30: 70.

14. A lithium secondary battery comprising the positive electrode for a lithium secondary battery as claimed in any one of claims 1 to 6.

Technical Field

Cross reference to related applications

This application claims the benefit of korean patent application No. 10-2017-.

Background

As the demand for mobile devices increases due to the development of mobile device technology, the demand for secondary batteries as energy sources is rapidly increasing. Among these secondary batteries, lithium secondary batteries having high energy density and voltage, long cycle life, and low self-discharge rate have been commercialized and widely used.

As a positive electrode active material of a lithium secondary battery, a lithium transition metal composite oxide has been used. Among these oxides, mainlyUse of LiCoO with high operating Voltage and Excellent Capacity Properties₂The lithium cobalt oxide of (1). However, Co is expensive, and there is a limit to using a large amount of Co as a material for a power source for applications such as electric vehicles due to its supply instability.

Therefore, a nickel-cobalt-manganese-based lithium composite metal oxide (hereinafter, simply referred to as "NCM-based lithium oxide") in which a part of Co is substituted with Ni and Mn has been developed. It is necessary to mix and apply such NCM-based lithium oxide with lithium cobalt-based oxide.

The NCM-based lithium oxide has excellent reversible capacity and thermal stability suitable for a lithium secondary battery. However, the NCM-based lithium oxide has an excessively high lithium ion desorption rate upon charging, compared to the lithium cobalt-based oxide. Therefore, when the lithium cobalt-based oxide and the currently commercialized NCM-based lithium oxide are simply mixed, the lithium ion insertion rate does not reach the lithium ion desorption rate in the negative electrode, and thus side reactions and precipitation reactions may occur on the surface of the negative electrode. Therefore, when the lithium cobalt-based oxide and the currently commercialized NCM-based lithium oxide are simply mixed, the capacity characteristics and the cycle characteristics of the battery may be deteriorated. In order to prevent such a limitation, a method of coating an anode thin film to allow high-speed charging of an anode, a method of using carbon-coated artificial graphite having improved charging characteristics, or the like has been studied. However, these methods increase the manufacturing cost and have limitations in preventing deterioration of the battery characteristics.

Disclosure of Invention

Technical problem

An aspect of the present invention provides a positive electrode for a lithium secondary battery, which is capable of suppressing the occurrence of side reactions and precipitates in a negative electrode and improving battery capacity and cycle characteristics when a lithium cobalt oxide and a lithium composite transition metal oxide are mixed for use.

Technical scheme

According to an aspect of the present invention, there is provided a positive electrode for a lithium secondary battery, the positive electrode comprising: a first positive electrode active material having a lithium cobalt-based oxide; and a second positive electrode active material having a lithium composite transition metal oxideAnd a lithium composite transition metal oxide having at least two selected from the group consisting of nickel (Ni), cobalt (Co), and manganese (Mn). The state of charge (SOC) at which the first positive electrode active material reaches a Constant Voltage (CV) when charged at 1C is referred to as SOC₁And a state of charge (SOC) at which the second positive electrode active material reaches a Constant Voltage (CV) when charged at 1C is referred to as SOC₂Time, SOC₁And SOC₂The relationship therebetween satisfies the following equation 1:

[ equation 1]

SOC₁<SOC₂<1.1×SOC₁。

In addition, according to another aspect of the present invention, there is provided a lithium secondary battery including the positive electrode.

In addition, according to another aspect of the present invention, there is provided a method of preparing a positive electrode for a lithium secondary battery, the method comprising: preparing a first cathode active material including a lithium cobalt-based oxide, and a second cathode active material including a lithium composite transition metal oxide containing at least two selected from the group consisting of nickel (Ni), cobalt (Co), and manganese (Mn); and mixing the first positive electrode active material and the second positive electrode active material. The state of charge (SOC) at which the first positive electrode active material reaches a Constant Voltage (CV) when charged at 1C is referred to as SOC₁And a state of charge (SOC) at which the second positive electrode active material reaches a Constant Voltage (CV) when charged at 1C is referred to as SOC₂Time, SOC₁And SOC₂The relationship therebetween satisfies the following equation 1:

[ equation 1]

SOC₁<SOC₂<1.1×SOC₁。

Advantageous effects

According to the present invention, when a lithium cobalt oxide and a lithium composite transition metal oxide are used in combination, side reactions and precipitation can be suppressed from occurring in the anode, and the battery capacity and cycle characteristics can be improved.

Drawings

The following drawings attached to the specification illustrate preferred embodiments of the present invention by way of examples and serve to enable further understanding of the technical concept of the invention and the detailed description of the invention given below, and the present invention should not be construed as being limited to the contents of the drawings.

Fig. 1 is an SEM photograph of the second cathode active material used in example 1;

fig. 2 is an SEM photograph of the second cathode active material used in example 2;

fig. 3 is an SEM photograph of the second cathode active material used in comparative example 2; and

fig. 4 is a graph showing the output variation according to SOC at the time of 1C charging of the lithium secondary battery using the positive electrodes of example 1 and comparative example 2.

Detailed Description

Hereinafter, the present invention will be described in more detail to facilitate understanding of the present invention. It should be understood that the words or terms used in the specification and claims should not be construed as meaning defined in commonly used dictionaries. It will be further understood that the words or terms should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and the technical idea of the present invention, based on the principle that the inventor can appropriately define the meaning of the words or terms to best explain the present invention.

The positive electrode for a lithium secondary battery of the present invention includes: a first positive electrode active material comprising a lithium cobalt-based oxide; and a second positive electrode active material including a lithium composite transition metal oxide having at least two selected from the group consisting of nickel (Ni), cobalt (Co), and manganese (Mn). The state of charge (SOC) at which the first positive electrode active material reaches a Constant Voltage (CV) when charged at 1C is referred to as SOC₁And a state of charge (SOC) at which the second positive electrode active material reaches a Constant Voltage (CV) when charged at 1C is referred to as SOC₂Time, SOC₁And SOC₂The relationship therebetween satisfies the following equation 1:

[ equation 1]

SOC₁<SOC₂<1.1×SOC₁。

When the lithium cobalt-based oxide and the NCM-based lithium oxide are simply blended, since the NCM-based lithium oxide has a higher lithium ion desorption rate than the lithium cobalt-based oxide at the time of charge, the lithium ion insertion rate does not reach the lithium ion desorption rate, so that side reactions and precipitation may occur in the anode, and the capacity characteristics and cycle characteristics of the battery may be deteriorated.

Therefore, in the present invention, the charge/discharge curve of the second cathode active material having a lithium composite transition metal oxide of at least two selected from the group consisting of nickel (Ni), cobalt (Co) and manganese (Mn) is adjusted such that the charge/discharge curves of the first cathode active material of the lithium cobalt-based oxide and the second cathode active material satisfy the above formula 1, and thus, when the first cathode active material and the second cathode active material are used in mixture, the occurrence of side reactions and precipitation in the anode is suppressed and the battery capacity and cycle characteristics are significantly improved.

The first cathode active material may be a lithium cobalt-based oxide represented by formula 1 below.

[ formula 1]

Li_a1Co_1-x1M¹ _x1O_2+β

In formula 1, M¹Including at least one selected from the group consisting of Al, B, Ba, Ca, Zr, Ti, Mg, Ta, Nb, Sr, W and Mo, and 0.9<a1 is less than or equal to 1.1, x1 is less than or equal to 0.2, and beta is more than or equal to 0 and less than or equal to 0.02.

The second cathode active material may be a lithium composite transition metal oxide represented by the following formula 2.

[ formula 2]

Li_a2Ni_x2Mn_y2Co_z2M² _w2O_2+δ

In formula 2, M²Including at least one selected from the group consisting of Al, B, Ba, Ca, Zr, Ti, Mg, Ta, Nb, Sr, W and Mo, and 0.9<a2≤1.1，0.3≤x2≤0.95，0<y2≤0.4，0<z2≤0.5，0≤w2≤0.1，0≤δ≤0.02，x2+y2+z2+w2＝1。

In order for the first cathode active material and the second cathode active material to satisfy the above equation 1, the surface resistance of the lithium composite transition metal oxide (e.g., NCM-based lithium oxide) as the second cathode active material is increased, so that the charge/discharge curves of the first cathode active material and the second cathode active material can be adjusted to be similar to each other.

The method of increasing the surface resistance of the second cathode active material may be, for example, increasing the single crystal size of the second cathode active material by overburning during firing to raise the temperature from the range of about 800 ℃ to 1000 ℃ (which is a typical cathode active material firing temperature range) by about 50 ℃, or significantly increasing the content of the doping element or coating material of the secondary cathode active material. However, the embodiments of the invention are not limited to these methods for increasing the resistance, and any method is applicable as long as it is a method capable of adjusting the charge/discharge curve such that the first positive electrode active material and the second positive electrode active material satisfy the relationship of equation 1 described above.

In one embodiment of the present invention, the second positive active material of the lithium composite transition metal oxide (e.g., NCM-based lithium oxide) may have a single crystal size of 180 to 800nm, preferably 200 to 500nm, and most preferably 220 to 400 nm. When the single crystal size of the second cathode active material satisfies the above range, the surface resistance increases and the lithium ion desorption rate decreases, so that the relationship of formula 1 may be satisfied. In addition, side reactions and precipitation in the anode can be suppressed, and the battery capacity and cycle characteristics can be improved. In addition, when the single crystal size of the second cathode active material satisfies the above range, it is possible to reduce rate characteristic deterioration during high-rate discharge while increasing resistance.

Further, in one embodiment of the present invention, the second positive electrode active material of the lithium composite transition metal oxide (e.g., NCM-based lithium oxide) may include a coating or doping element, and the total content of the coating or doping element may be 1,000ppm or more, more preferably 1,500 to 5,000ppm, and most preferably 3,000 to 5,000 ppm. When the total content of the coating or doping elements of the second cathode active material satisfies the above-described range of 1,000ppm or more, the surface resistance increases and the lithium ion desorption rate decreases, and thus the relationship of formula 1 may be satisfied. In addition, side reactions and precipitation in the anode can be suppressed, and the battery capacity and cycle characteristics can be improved. The coating or doping element may be, for example, one or more selected from the group consisting of Al, B, Ba, Ca, Zr, Ti, Mg, Ta, Nb, Sr, W and Mo.

The first positive active material of the lithium cobalt-based oxide and the second positive active material of the lithium composite transition metal oxide (e.g., NCM-based lithium oxide) may be mixed in a weight ratio of 90:10 to 30:70, more preferably 80:20 to 50: 50. By mixing the first positive electrode active material and the second positive electrode active material in the weight ratio within the above range, it is possible to reduce the manufacturing cost while increasing the battery capacity, and to improve the stability and the life characteristics.

The positive electrode for a lithium secondary battery of the present invention may be in a form in which a positive electrode mixture layer containing a first positive electrode active material and a second positive electrode active material is formed on a positive electrode collector.

The content of the first positive electrode active material and the second positive electrode active material may be 80 to 98 wt%, more specifically 85 to 98 wt%, based on the total weight of the positive electrode mixture layer. When included within the above content range, excellent capacity characteristics may be achieved.

The positive electrode current collector is not particularly limited as long as it has conductivity without causing adverse chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, fired carbon or aluminum, or stainless steel surface-treated with one of carbon, nickel, titanium, silver, and the like can be used. In addition, the cathode current collector may generally have a thickness of 3 to 500 μm, and microscopic irregularities (microscopic irregularities) may be formed on the surface of the cathode current collector to improve adhesion of the cathode active material. The positive electrode collector may be used in various shapes, for example, a film, a sheet, a foil, a mesh, a porous body, a foam, a nonwoven fabric body, or the like.

The positive electrode mixture layer includes a first positive electrode active material and a second positive electrode active material, and may further include a conductive material and a binder.

The conductive material is used to impart conductivity to the electrode, and any conductive material may be used without particular limitation so long as it has electron conductivity without causing chemical changes in the battery constituted. Specific examples of the conductive material may include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fibers; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides such as titanium oxide; or a conductive polymer such as a polyphenylene derivative, and any one thereof or a mixture of two or more thereof may be used. The content of the conductive material may be 1 wt% to 30 wt% based on the total weight of the positive electrode active material layer.

The binder is used to improve the adhesion between the positive electrode active material particles and the adhesion between the positive electrode active material and the positive electrode current collector. Specific examples of the binder may include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and any one thereof or a mixture of two or more thereof may be used. The content of the binder may be 1 to 30 wt% based on the total weight of the positive electrode mixture layer.

Hereinafter, a method of preparing a positive electrode for a lithium secondary battery according to the present invention will be described.

The method of preparing the positive electrode for a lithium secondary battery of the present invention includes: preparing a first cathode active material including a lithium cobalt-based oxide, and a second cathode active material including a lithium composite transition metal oxide containing at least two selected from the group consisting of nickel (Ni), cobalt (Co), and manganese (Mn); and mixing a first positive electrode active material and a second positive electrode active material, wherein a state of charge (SOC) at which the first positive electrode active material reaches a Constant Voltage (CV) when charged at 1C is referred to as SOC₁And a state of charge (SOC) at which the second positive electrode active material reaches a Constant Voltage (CV) when charged at 1C is referred to as SOC₂Time, SOC₁And SOC₂The relationship therebetween satisfies the following equation 1:

[ equation 1]

SOC₁<SOC₂<1.1×SOC₁。

The types, mixing weight ratios, and contents of the first positive electrode active material and the second positive electrode active material are the same as those described above.

In one embodiment of the present invention, the preparation of the second cathode active material may include a method of preparing the second cathode active material by using a solid phase reaction method. Generally, the NCM-based positive electrode active material is prepared by co-precipitation by a wet chemical method. However, in the embodiment of the invention, the second cathode active material is prepared by using the solid-phase reaction method in which the heat treatment is performed at a high temperature for a long time, so that the surface resistance can be increased.

In addition, in one embodiment of the present invention, in preparing the second cathode active material, the second cathode active material may be prepared by overburning to have a single crystal size of 180 to 800 nm. At this time, the surface resistance of the second cathode active material may be increased by overburning such that the single crystal size of the second cathode active material is 180 to 800nm, and the lithium ion desorption rate may be decreased to satisfy the relationship of the above equation 1.

Further, in one embodiment of the present invention, the preparing of the second cathode active material may include a process of allowing the second cathode active material to include a coating or doping element, and the total content of the coating or doping element is 1,000ppm or more, more preferably 1,500 to 5,000 ppm. The coating or doping process may be a process of doping the precursor by a co-precipitation reaction when forming the cathode active material precursor, adding and doping the doping raw materials together when mixing and firing the cathode active material precursor and the lithium source, or a process of coating/doping by forming the lithium composite transition metal oxide and then adding the coating/doping raw materials and then performing secondary firing. Any typical coating or doping process of the positive electrode active material may be applied without limitation. At this time, the coating or doping element may be, for example, one or more selected from the group consisting of Al, B, Ba, Ca, Zr, Ti, Mg, Ta, Nb, Sr, W and Mo.

The method of preparing the positive electrode for the lithium secondary battery may include forming a positive electrode mixture layer including a first positive electrode active material and a second positive electrode active material on a positive electrode current collector.

To form the positive electrode mixture layer, the first and second positive electrode active materials, the conductive material, and the binder may be dissolved or dispersed in a solvent to prepare a composition for forming a positive electrode. The types and contents of the first and second positive electrode active materials, the conductive material, and the binder are the same as those described above.

Meanwhile, the solvent used for preparing the composition for forming the positive electrode may be a solvent commonly used in the art. Examples of the solvent may include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and any one of them or a mixture of two or more thereof may be used. The amount of the solvent used is sufficient if the solvent can dissolve or disperse the positive electrode active material coated with the radical polymer, the conductive material, and the binder, and can allow for a viscosity that exhibits excellent thickness uniformity during subsequent use in the preparation of a positive electrode, in consideration of the coating thickness and the preparation yield of the slurry.

Next, the positive electrode may be prepared by coating the composition for forming the positive electrode on the positive electrode current collector, and then drying and rolling the coated positive electrode current collector.

In addition, as another method, the positive electrode may be prepared by casting a composition for forming a positive electrode active material on a separate support, and then laminating a membrane separated from the support on a positive electrode current collector.

According to another embodiment of the present invention, there is provided an electrochemical device including a positive electrode. The electrochemical device may be specifically a battery, a capacitor, or the like, more specifically, a lithium secondary battery.

The lithium secondary battery specifically includes a positive electrode, a negative electrode disposed to face the positive electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte. In this case, the positive electrode is as described above. In addition, the lithium secondary battery may further optionally include a battery container accommodating the electrode assembly of the positive electrode, the negative electrode and the separator, and a sealing member sealing the battery container.

In the lithium secondary battery, the anode includes an anode current collector and an anode mixture layer provided on the anode current collector.

The anode current collector is not particularly limited as long as it has high conductivity without causing chemical changes of the battery. For example, copper, stainless steel, aluminum, nickel, titanium, fired carbon, or copper or stainless steel surface-treated with one of carbon, nickel, titanium, silver, and the like, and aluminum-cadmium alloys can be used. In addition, the anode current collector may generally have a thickness of 3 μm to 500 μm, and as in the case of the cathode current collector, microscopic irregularities may be prepared on the surface of the anode current collector to improve the adhesion of the anode active material. The negative electrode collector may be used in various forms, such as a film, a sheet, a foil, a mesh, a porous body, a foam, and a nonwoven fabric body.

The negative electrode mixture layer may selectively include a binder and a conductive material, in addition to the negative electrode active material.

As the negative electrode active material, a compound capable of reversibly intercalating and deintercalating lithium may be used. Specific examples of the negative active material may include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds alloyable with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys or Al alloys; metal oxides, e.g. SiO, which may be doped and undoped with lithium_β(0<β<2)、SnO₂Vanadium oxide, lithium titanium oxide and lithium vanadium oxide; or a composite material comprising a metal compound and a carbonaceous material, such as a Si-C composite material or a Sn-C composite material, and any one of them or a mixture of two or more thereof may be used. Also, a metallic lithium thin film may be used as the negative electrode active material. In addition, both low crystalline carbon and high crystalline carbon can be used as the carbon material. Typical examples of the low crystalline carbon may include soft carbon and hard carbon, and typical examples of the high crystalline carbon may include irregular, planar, flaky, spherical or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitchCyan carbon fibers, medium carbon microspheres, mesophase pitch, and high temperature sintered carbon, such as petroleum or coal tar pitch derived coke.

Also, the binder and the conductive material may be the same as those described previously in the description of the positive electrode.

The negative electrode mixture layer may be prepared, for example, by: coating an anode active material and a composition for forming an anode prepared by selectively dissolving or dispersing a binder and a conductive material in a solvent on an anode current collector and drying the coated anode current collector; or can be prepared by: the composition for forming the negative electrode is cast on a separate support, and then a membrane separated from the support is laminated on a negative electrode current collector.

Meanwhile, in the lithium secondary battery, a separator separates a negative electrode and a positive electrode and provides a moving path of lithium ions. Any separator may be used without particular limitation so long as it is generally used as a separator in a lithium secondary battery. In particular, a separator having high moisture-retaining ability for an electrolyte and low resistance to ion transfer of the electrolyte may be used. Specifically, a porous polymer film such as a porous polymer film prepared from a polyolefin-based polymer (e.g., an ethylene homopolymer, a propylene homopolymer, an ethylene/butene copolymer, an ethylene/hexene copolymer, and an ethylene/methacrylic acid copolymer), or a laminate structure having two or more layers may be used. In addition, a typical porous nonwoven fabric, such as a nonwoven fabric formed of high-melting glass fibers or polyethylene terephthalate fibers, may be used. In addition, a coated separator including a ceramic component or a polymer material may be used to ensure heat resistance or mechanical strength, and a separator having a single-layer or multi-layer structure may be selectively used.

In addition, the electrolyte used in the present invention may include an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, or a melt-type inorganic electrolyte, which may be used in the preparation of a lithium secondary battery, but the present invention is not limited thereto.

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

Any organic solvent may be used as the organic solvent without particular limitation so long as it can be used as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, ester solvents such as methyl acetate, ethyl acetate, γ -butyrolactone, and ∈ -caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; or carbonate-based solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (MEC), Ethyl Methyl Carbonate (EMC), Ethylene Carbonate (EC), and Propylene Carbonate (PC); alcohol solvents such as ethanol and isopropanol; nitriles such as R-CN (where R is a linear, branched or cyclic C2-C20 hydrocarbon group, which may include double-bonded aromatic rings or ether linkages); amides such as dimethylformamide and the like; dioxolanes such as 1, 3-dioxolane; alternatively sulfolane may be used as the organic solvent. Among these solvents, a carbonate-based solvent, for example, a mixture of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate) having high ionic conductivity and high dielectric constant, which can increase charge/discharge properties of a battery, may be used, and a linear carbonate-based compound (e.g., ethylmethyl carbonate, dimethyl carbonate, or diethyl carbonate) having low viscosity may be used. In this case, when the cyclic carbonate and the chain carbonate are mixed in a volume ratio of about 1:1 to about 1:9, the performance of the electrolyte solution may be excellent.

A lithium salt may be used without particular limitation so long as it is a compound capable of providing lithium ions used in a lithium secondary battery. In particular, LiPF₆、LiClO₄、LiAsF₆、LiBF₄、LiSbF₆、LiAlO₄、LiAlCl₄、LiCF₃SO₃、LiC₄F₉SO₃、LiN(C₂F₅SO₃)₂、LiN(C₂F₅SO₂)₂、LiN(CF₃SO₂)₂LiCl, LiI or LiB (C)₂O₄)₂May be used as the lithium salt. The lithium salt may be at a concentration of 0.1M to 2.0MIs used within the range. In the case where the concentration of the lithium salt is included in the above range, since the electrolyte may have appropriate conductivity and viscosity, excellent performance of the electrolyte may be obtained and lithium ions may be efficiently moved.

In order to improve the life characteristics of the battery, suppress the decrease in the capacity of the battery, and improve the discharge capacity of the battery, at least one additive, such as a halogenated alkylene carbonate-based compound, e.g., ethylene difluorocarbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, N-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dye, N-substituted oxazolidinone, N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride, may be added to the electrolyte in addition to the electrolyte. In this case, the additive may be contained in an amount of 0.1 to 5 wt% based on the total weight of the electrolyte.

As described above, since the lithium secondary battery including the cathode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics, and capacity retention rate, the lithium secondary battery is suitable for portable devices, such as mobile phones, notebook computers, and digital cameras, and electric vehicles, such as Hybrid Electric Vehicles (HEVs).

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

The battery module or the battery pack may be used as a power source for at least one of the following middle-and large-sized devices: an electric tool; electric vehicles, including Electric Vehicles (EVs), Hybrid Electric Vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs); or an electrical power storage system.

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

The lithium secondary battery according to the present invention may be used not only in a battery cell used as a power source for small-sized devices, but also as a unit cell in medium-and large-sized battery modules including a plurality of battery cells.

Hereinafter, embodiments of the present invention will be described in detail in such a manner that those skilled in the art to which the present invention pertains can easily implement the embodiments of the present invention. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.