KR20140066082A - Positive active material layer for rechargeable lithium battery, separator for rechargeable lithium battery, and rechargeable lithium battery including at least one of the same - Google Patents

Abstract

Provided are a positive electrode active material layer for a lithium secondary battery, a separator for a lithium secondary battery, and a lithium secondary battery including at least one of the same. The positive electrode active material layer for a lithium secondary battery includes a positive electrode active material and a protection layer forming material. The separator for a lithium secondary battery is located on a substrate and on at least one side of the substrate and includes a porous layer including the protection layer forming material.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a positive electrode active material layer for a lithium secondary battery, a separator for a lithium secondary battery, and a lithium secondary battery including at least one of the foregoing materials. BACKGROUND OF THE INVENTION [0002] }

A positive electrode active material layer for a lithium secondary battery, a separator for a lithium secondary battery, and a lithium secondary battery including at least one of the foregoing.

Lithium secondary batteries are widely used because they have higher energy densities than lead batteries or nickel-cadmium batteries. However, lithium secondary batteries have insufficient cycle life.

Japanese Patent Application Laid-Open No. 11-171293 discloses the use of a high-permittivity solvent such as? -Butyrolactone and propylene carbonate as a solvent and a lithium compound such as lithium tetracyanoborate (LiTCB) dissolved in a high-dielectric constant solvent. That is, by using a lithium compound such as lithium tetracyanoborate (LiTCB) as the electrolyte of the electrolyte, the cycle life is improved.

However, since the lithium compound is dissolved in the high-dielectric solvent in a small amount, specifically 0.7 mol / L, the effect of improving the cycle life at a current density of 1 mA / cm ² is not sufficient. Further, since the high-k solvent is used, the current density, that is, the energy density is not sufficient. As a method for solving such a problem, a method of dissolving a high-dielectric solvent in a low-dielectric-constant solvent, for example, diethyl carbonate, is considered, but the lithium compound is not dissolved in the low-dielectric-constant solvent.

In recent years, a driving voltage of 4.3 V or more is required for the lithium secondary battery, but the driving voltage of the lithium secondary battery is low in the Japanese Patent Laid-Open Publication. As a method for raising the driving voltage of a lithium secondary battery in this document, it is considered to use an electrode having a low potential, for example, graphite as a cathode. However, in this method, the lithium compound is easily decomposed on the cathode.

As described above, since the types of solvent and cathode are limited, there is a problem that it is difficult to increase the current density and the driving voltage of the lithium secondary battery.

One embodiment is to provide a cathode active material layer for a lithium secondary battery having excellent cycle life characteristics at high current density and high voltage.

Another embodiment is to provide a separator for a lithium secondary battery excellent in cycle life characteristics at a high current density and a high voltage.

Another embodiment is to provide a lithium secondary battery comprising at least one of the positive electrode active material layer and the separator.

One embodiment includes a cathode active material; And a lithium compound represented by the following general formulas (4) to (6).

[Chemical Formula 4]

_{LiB (CN) 4- n1 (X} 1) n1

[Chemical Formula 5]

_{LiP (CN) 6- n2 (X} 2) n2

[Chemical Formula 6]

_{LiC (CN) 3- n3 (X} 3) n3

(In the above formulas 4 to 6,

n ₁ is an integer of 0 to 3, n ₂ is an integer of 0 to 5, n ₃ is an integer of 0 to 2, and X ₁ to X ₃ are ligands other than a cyano group.

The cathode active material may include at least one solid solution oxide of the compounds represented by the following general formulas (1) to (3).

[Chemical Formula 1]

Li _a Mn _x Co _y Ni _z O ₂

(In the formula 1, 1.150? A? 1.430, 0.45? X? 0.6, 0.10? Y? 0.15, and 0.20? Z?

(2)

LiMn _x Co _y Ni _z O ₂

(In the formula 2, 0.3? X? 0.85, 0.10? Y? 0.3, and 0.10? Z?

(3)

LiMn _{1 .5} Ni _{0 .5} O ₄

The protective film forming material may be included in an amount of 0.1 to 6% by weight based on the total amount of the cathode active material layer.

When the protective film forming material is a lithium compound represented by the chemical formula 4, the protective film forming material may be included in an amount of 0.5 to 6 wt% based on the total amount of the cathode active material layer, and the protective film forming material is lithium The protective film forming material may be included in an amount of 0.3 to 2% by weight based on the total amount of the positive active material layer, and when the protective film forming material is a lithium compound represented by the formula 6, By weight based on the total weight of the composition.

Another embodiment includes a substrate; And a porous layer disposed on at least one side of the substrate, wherein the porous layer comprises at least one of the lithium compound represented by Chemical Formulas 4 to 6 as a protective film forming material.

The protective film forming material may be included in an amount of 10 to 90% by weight based on the total amount of the porous layer.

Another embodiment includes a positive electrode comprising a current collector and a positive electrode active material layer disposed on the current collector and including a positive electrode active material; cathode; A separator comprising a substrate and a porous layer disposed on at least one side of the substrate; And at least one of the positive electrode active material layer and the porous layer includes at least one of a lithium compound represented by the following formulas (4) to (6).

The protective film forming material may be a material forming a protective film at an interface between the positive electrode active material layer and the porous layer and the protective film forming material may be a material forming a protective film at an interface between the positive electrode active material and the electrolyte .

The protective film may include a polymer formed by polymerizing the protective film forming material.

The electrolyte may include a lithium salt, a solvent, and an additive. The additive may be at least one selected from the group consisting of a negative electrode active compound, an anionic compound, an ester compound, a carbonate ester compound, a sulfuric acid ester compound, a phosphoric acid ester compound, Acid anhydride-based compounds, electrolyte-based compounds, or combinations thereof.

The details of other embodiments are included in the detailed description below.

A lithium secondary battery excellent in cycle life characteristics at high current density and high voltage can be realized.

1 is a cross-sectional view showing a schematic configuration of a lithium secondary battery according to one embodiment.
Fig. 2 is a graph showing the relationship between the number of cycles and the discharge capacity of the lithium secondary battery according to Examples 1 and 2 and Comparative Example 1. Fig.
3 is a graph showing the relationship between the amount of lithium compound added and the discharge capacity of a lithium secondary battery.
4 is a graph showing the relationship between the addition amount of the lithium compound and the discharge capacity retention rate of the lithium secondary battery.
5 is a graph showing the relationship between the number of cycles and the discharge capacity of the lithium secondary battery according to Examples 23 to 26 and Comparative Example 5. Fig.
6 is a graph showing the relationship between the number of cycles and the discharge capacity of the lithium secondary battery according to Examples 27 to 29 and Comparative Example 6. Fig.

Hereinafter, embodiments of the present invention will be described in detail. However, it should be understood that the present invention is not limited thereto, and the present invention is only defined by the scope of the following claims.

Unless otherwise specified herein, "substituted" means that at least one hydrogen atom in the compound is replaced by a halogen atom (F, Cl, Br, I), a hydroxy group, a C1- A thio group, an ester group, an ether group, a carboxyl group or a salt thereof, a sulfone group or a salt thereof, a phosphoric acid or a salt thereof, an amide group, an imino group, an azido group, an amidino group, a hydrazino group, a hydrazino group, a carbonyl group, a carbamoyl group, A C 1 to C 20 alkyl group, a C 2 to C 20 alkenyl group, a C 2 to C 20 alkynyl group, a C 6 to C 30 aryl group, a C 3 to C 20 cycloalkyl group, a C 3 to C 20 cycloalkenyl group, Substituted with a substituent of a C2 to C20 heterocycloalkyl group, a C2 to C20 heterocycloalkenyl group, a C2 to C20 heterocycloalkynyl group, or a combination thereof.

A lithium secondary battery according to one embodiment will be described with reference to Fig.

1 is a cross-sectional view showing a schematic configuration of a lithium secondary battery according to one embodiment.

Referring to FIG. 1, a lithium secondary battery 10 includes an anode 20, a cathode 30, and a separator layer 40. The separator layer 40 includes a separator 40a and an electrolyte 43. The anode 20 includes a current collector 21 and a cathode active material layer 22. The separator 40a includes a base 41 and a porous layer 42 disposed on at least one side of the base 41 .

In one embodiment, at least one of the cathode active material layer 22 and the porous layer 42 may include a protective film forming material. The protective film forming material will be described in detail in the cathode active material layer 22 and the porous layer 42 described later.

The voltage of the rechargeable lithium battery 10 to be charged (redox potential) may be 4.3 V or more and 5.0 V or less (vs. Li / Li +), for example, 4.5 V or more and 5.0 V or less .

The shape of the lithium secondary battery 10 is not particularly limited. In other words, the lithium secondary battery 10 may have any shape such as a cylindrical shape, a square shape, a laminate shape, a button shape, or the like.

The anode (20) includes a current collector (21) and a cathode active material layer (22).

The current collector 21 may be any conductive material, and examples thereof include aluminum, stainless steel, nickel-plated steel, and the like.

The cathode active material layer 22 includes a cathode active material, and may further include a conductive material and a binder.

The cathode active material may be, for example, a solid solution oxide containing lithium, but is not particularly limited as long as it is a material capable of occluding and releasing lithium ions electrochemically.

The solid solution oxide may be, for example, at least one of the compounds represented by the following general formulas (1) to (3).

[Chemical Formula 1]

Li _a Mn _x Co _y Ni _z O ₂

(In the formula 1, 1.150? A? 1.430, 0.45? X? 0.6, 0.10? Y? 0.15, and 0.20? Z?

(2)

LiMn _x Co _y Ni _z O ₂

(In the formula 2, 0.3? X? 0.85, 0.10? Y? 0.3, and 0.10? Z?

(3)

LiMn _{1 .5} Ni _{0 .5} O ₄

The content of the cathode active material may be 85 to 96% by weight, and more preferably 88 to 94% by weight based on the total amount of the cathode active material layer. When the content of the cathode active material is within the above range, the cycle life characteristics and the energy density of the anode can be improved. For example, the energy density of the anode can be increased to 530 Wh / l (180 Wh / kg) or more.

According to one embodiment, the cathode active material layer 22 may include the protective film forming material.

The protective film forming material is a material capable of forming a protective film upon charging the lithium secondary battery, specifically, charging the first cycle. The protective film may pass lithium ions in the electrolyte 43 and inhibit the passage of the solvent. When the protective film forming material, that is, the protective film forming material, is added, the cycle life characteristics can be improved under high current density and high voltage.

The protective film forming material may be a lithium compound including a lithium ion, an anionized central atom, and a cyano group coordinated to the central atom. In other words, the protective film forming material may be a lithium salt of lithium ion and an anion complex including a cyano group.

The central atom may be selected from boron, phosphorus, and carbon.

The protective film forming material may be at least one of the lithium compounds represented by the following formulas (4) to (6).

[Chemical Formula 4]

_{LiB (CN) 4- n1 (X} 1) n1

[Chemical Formula 5]

_{LiP (CN) 6- n2 (X} 2) n2

[Chemical Formula 6]

_{LiC (CN) 3- n3 (X} 3) n3

(In the above formulas 4 to 6,

n ₁ is an integer of 0 to 3,

n ₂ is an integer of 0 to 5,

n ₃ is an integer of 0 to 2,

X ₁ to X ₃ are ligands other than a cyano group and include, for example, a halogen atom, a substituted or unsubstituted C1 to C10 alkoxy group, a substituted or unsubstituted C1 to C4 fluoroalkyl group, A cyclic carboxy group, a sulfonyl group, etc.).

The cathode active material has a plurality of active points as having a crystal structure. The protective film forming material present in the vicinity of each active point at the time of charging supplies electrons from the isolated electrons possessed by the nitrogen atom of the cyano group to the active point. As a result, the nitrogen atom of the cyano group becomes a cation radical, and the protective film forming material is decomposed.

One of the electrons constituting the triple bond of the cyano group may also be supplied to the active site. And the cation radical may be attached to a cyano group in a protective film forming material other than the adjoining cation radical. Specifically, the cation radical can attack the isolated electron band of the cyano group and attach to the cyano group. Thus, the protective film forming materials can be polymerized with each other.

The cation radical may also attack the triple bond portion of the cyano group. When another protecting film forming material has a plurality of cyano groups, the nitrogen atom in the free cyano group may be a new cation radical. Thereafter, by repeating the same polymerization reaction, a polymer of the protective film forming material, that is, a protective film can be formed on the active point.

The decomposition and polymerization of the protective film-forming material occurs at a lower potential than the decomposition of the solvent of the electrolyte solution. In other words, the decomposition and polymerization of the protective film-forming material may occur before the decomposition of the solvent. The protective film thus formed can suppress the passage of the solvent.

Since the protective film includes an anionic complex, lithium ions can pass through the protective film by interposing the center atoms of the anionic complex.

Therefore, the protective film can pass lithium ions in the electrolytic solution and inhibit the passage of solvent. In other words, the protective film can suppress the reaction between the active site and the solvent, that is, the decomposition of the solvent, while promoting the reaction between the active site and the lithium ion upon charging after two cycles. Thus, cycle life characteristics can be improved.

As the number of cyano groups in the protective film forming material increases, the protective film having a complicated structure and having a stable structure can be formed, and the protective film forming material is difficult to dissolve in a solvent, thereby reducing the possibility of decomposition on the negative electrode.

Accordingly, in the above formulas 4 to 6, n ₁ and n ₃ may be 0, and n ₂ may be 3 in terms of the steric structure. Since a complex having a phosphorus atom as a central atom has an octahedral structure, it can be most stable on a steric structure when there are three cyano groups. In addition, when n ₁ to n ₃ have the above numerical values, the cyano group is interposed between the central atoms, so that the cyano groups are arranged at positions where they are contrasted with each other, so that the protective layer can be stabilized.

The amount of the protective film forming material to be added may be 0.1 to 6% by weight based on the total amount of the positive active material layer, and may vary depending on the composition of the protective film forming material. When the added amount of the protective film forming material is within the above range, elution into the electrolytic solution is inhibited and the thickness of the protective film is appropriate, so that lithium ions can be passed while suppressing the passage of the solvent.

Specifically, when the protective film forming material is a lithium compound represented by the chemical formula 4, the protective film forming material may be included in an amount of 0.5 to 6 wt% based on the total amount of the cathode active material layer, specifically 0.5 to 4 wt% ≪ / RTI > Specifically, as the number of cyano groups increases, the amount of the lithium compound represented by Formula 1 may be increased. The larger the number of cyano groups is, the smaller the amount of the protective film forming material dissolved in the electrolyte can be reduced even if a large amount of the protective film forming material is added to the cathode active material layer.

Specifically, w _1, which represents the upper limit of the content of the lithium compound represented by the formula (4), becomes 6 when n ₁ is 0, and can be smaller when n ₁ is larger. Specifically, when n ₁ is 1, w 1 is 4, w ₁ is 3 when n ₁ is 2, and w ₁ is 2 when n ₁ is 3. As described above, the greater the number of cyano groups, the greater the amount of the protective film forming material added. As the number of cyano groups increases, the amount of the protective film forming material dissolved in the electrolyte can be reduced even when a large amount of the protective film forming material is added to the cathode active material layer.

Specifically, when n ₁ is 0, the protective film forming material may be contained in an amount of 1 wt% or more and 5 wt% or less, specifically, 1.5 wt% or more and 4 wt% or less. When n ₁ is 1, the protective film forming material may be contained in an amount of 0.7 wt% or more and 2 wt% or less. When the protective film forming material is included in the above range, the cycle life characteristics can be improved.

When the protective film forming material is a lithium compound represented by the chemical formula 5, the protective film forming material may be included in an amount of 0.3 to 2% by weight based on the total amount of the cathode active material layer. W2 represents the upper limit of the content of the lithium compound of the formula 5 is n _2, and 3 when 3 The greater the value of n _2-│3 │ can be made small. Specifically, when │3-n has a value of ₂ │ 1 2 w2 is, if │3-n has a value of ₂ │ 2 w2 becomes 1.5, │3-n has a value of ₂ │ 3 W2 can be 1.0. The addition amount of the protective film forming material may be greatest when n ₂ is 3. The protective film forming material may be most stable on the steric structure when the number of cyano groups is three.

When the protective film forming material is a lithium compound represented by Formula 6, the protective film forming material may be included in an amount of 0.5 to 3% by weight based on the total amount of the cathode active material layer. W3 represents the upper limit of the content of the lithium compound represented by the formula (6) is the n ₃ is 0 and 3 when the larger the value of n ₃ can be made small. Specifically, when n ₃ is an w3 is the second one, w3 if n ₃ is 2, can be the first.

The greater the number of cyano groups, the greater the amount of the protective film forming material added. As the number of cyano groups increases, the amount of the protective film forming material dissolved in the electrolyte can be reduced even if a large amount of the protective film forming material is added to the cathode active material layer.

The conductive material may be, for example, carbon black such as KETJEN BLACK, acetylene black or the like; Graphite such as natural graphite and artificial graphite. However, it is not particularly limited as long as it is for increasing the conductivity of the anode.

The conductive material may be contained in an amount of 3 to 10% by weight, and more preferably 4 to 6% by weight based on the total weight of the cathode active material layer. When the conductive material is included within the above range, the cycle life characteristics and the energy density can be improved.

Examples of the binder include polyvinylidene fluoride, ethylene-propylene-diene terpolymer, styrene-butadiene rubber, acrylonitrile-butadiene rubber, fluor rubber, polyvinyl acetate, polymethyl methacrylate, polyethylene, Cellulose, and the like, but is not particularly limited as long as it can bind the positive electrode active material and the conductive material on the current collector 21.

The content of the binder may be 3 to 7% by weight, and more preferably 4 to 6% by weight based on the total weight of the cathode active material layer. When the content of the binder is within the above range, cycle life characteristics and energy density can be improved.

Although the density of the positive electrode active material layer 22 is not particularly limited, for example, 2.0 to 3.0 g / cm < ³ > Specifically, 2.5 to 3.0 g / cm < ³ > Lt; / RTI > When the density of the cathode active material layer 22 is within the above range, particles of the cathode active material are not destroyed, so there is less risk of damage due to electrical contact between the particles. As the utilization ratio of the cathode active material increases, cycle life characteristics and energy density are improved .

The density of the cathode active material layer 22 can be obtained by dividing the area density of the cathode active material layer 22 after rolling by the thickness of the cathode active material layer 22 after rolling.

The cathode active material layer 22 is obtained by, for example, dry mixing the cathode active material, the conductive material, and the binder to obtain a mixture, followed by dry mixing the mixture and the protective film forming material to obtain a dry mixture. Then, the dry mixture is dispersed in an organic solvent to form a slurry, and the slurry is applied onto the current collector 21, followed by drying and rolling. Alternatively, after the slurry in which the mixture is dispersed is formed, the protective film forming material may be dissolved in the slurry. That is, the method of adding the protective film forming material to the cathode active material layer is not limited.

The organic solvent may be a solvent capable of dissolving the protective film forming material. In this case, it can be uniformly dispersed in the positive electrode active material layer. Examples of the organic solvent include N-methyl-2-pyrrolidone and the like.

The coating method is not particularly limited, and examples thereof include a knife coater method and a gravure coater method.

The anode 20 can be manufactured by pressing the cathode active material layer 22 by a press machine and performing vacuum drying.

Carboxymethylcellulose (CMC) as a thickener may be used in an amount of 1/10 or more by weight of the total amount of the binder when the positive electrode active material layer 22 is coated on the current collector 21.

The cathode 30 includes a current collector 31 and a negative electrode active material layer 32.

As the current collector 31, for example, aluminum, stainless steel, nickel-plated steel, or the like may be used.

The negative electrode active material layer 32 may be any material as long as it is used as a negative electrode active material layer of a lithium secondary battery. For example, the negative electrode active material layer 32 includes a negative electrode active material, and may further include a binder.

The negative electrode active material is not particularly limited as long as it is a material capable of occluding and releasing lithium ions electrochemically. Natural graphite, natural graphite coated with artificial graphite, silicon, silicon-containing alloy, silicon oxide, tin, tin-containing alloy, tin oxide, silicon oxide and graphite material A mixture of tin oxide and graphite material, a mixture of Li ₄ Ti ₅ O ₁₂ , And the like.

The silicon oxide may be represented by SiOx (0? X? 2).

The content of the negative electrode active material may be 90 to 98% by weight based on the total amount of the negative electrode active material layer. When the content of the negative electrode active material is within the above range, the cycle life characteristics and the energy density can be improved.

The binder may be the same as the binder constituting the positive electrode active material layer 22.

The content of the binder containing the thickener may be 1 to 10% by weight based on the total weight of the anode active material layer. When the content of the binder containing the thickener is within the above range, the cycle life characteristics and the energy density can be improved.

The density of the negative electrode active material layer 32 is not particularly limited. For example, the density is 1.0 to 2.0 g / cm < ³ > Lt; / RTI > When the density of the negative electrode active material layer 32 is within the above range, the cycle life characteristics and the energy density can be improved.

The anode active material layer 32 is formed by dispersing, for example, an anode active material and a binder in a solvent such as N-methyl-2-pyrrolidone or water to form a slurry, ) And drying it. Subsequently, the negative electrode active material layer 32 is pressed by a press machine to produce the negative electrode 30.

The density of the negative electrode active material layer 32 can be obtained by dividing the area density of the negative electrode active material layer 32 after rolling by the thickness of the negative electrode active material layer 32 after rolling.

The separator 40a includes a substrate 41 and a porous layer 42 disposed on at least one side of the substrate 41. [

The base material 41 is made of a material such as polyethylene or polypropylene, and may include a plurality of first pores 41a.

Although the first pores 41a are spherical in FIG. 1, the first pores 41a may have various shapes.

The diameter of the first pores 41a may be, for example, 0.1 to 0.5 占 퐉. The diameter of the first pores 41a is, for example, the diameter when the first pores 41a are regarded as spherical.

The first pores 41a can be measured, for example, by an automatic porosimeterAutopore IV (Shimadzu Corporation). For example, the measurement apparatus can measure the diameter distribution of the first pores 41a, and measure the diameter with the highest distribution as a representative value.

The diameter of the first pores 41a present in the surface layer of the substrate 41 may be measured by, for example, a scanning electron microscope (JSM-6060, JEOL Ltd.). The measuring apparatus can measure the diameter of each of the first pores 41a in the surface layer, for example.

The porosity of the substrate 41 may be, for example, 38 to 44% by volume. When the porosity of the base material 41 is within the above range, the cycle life characteristics can be improved. The porosity of the substrate 41 can be obtained by dividing the total volume of the first pores 41a by the total volume of the substrate 41. [ The porosity of the substrate 41 can be measured, for example, by an automatic porosimeter Autopore IV (Shimadzu Corporation).

The thickness of the substrate 41 may be 6 to 19 [mu] m. When the thickness of the base material 41 is within the above range, the cycle life characteristics can be improved.

The porous layer 42 may be made of a material different from that of the base material 41, for example, polyvinylidene fluoride, polyamideimide, aramid (aromatic polyamide), or the like, and a plurality of second pores 42a ).

In FIG. 1, the second pores 42a are spherical, but may have various shapes.

The second pores 42a may be different from the first pores 41a.

Specifically, the diameter and the porosity of the second pores 42a may be larger than the value of the first pores 41a. In other words, the diameter of the second pore 42a may be, for example, 1 to 2 占 퐉.

The diameter of the second pore 42a is, for example, a diameter corresponding to a spherical shape of the second pore 42a, that is, a sphere equivalent diameter, for example, a scanning electron microscope (JSM-6060, Co., Ltd.).

Examples of the polyvinylidene fluoride used for the porous layer 42 include KF polymer # 1700, # 9200, and # 9300 manufactured by KUREHA CORPORATION.

The weight average molecular weight of the polyvinylidene fluoride may be about 500,000 to 1,000,000.

The porosity of the separator 40a may be, for example, 39 to 58% by volume. When the porosity of the separator 40a is within the above range, the cycle life characteristics can be improved.

The porosity of the separator 40a is determined by dividing the total volume of the first pores 41a and the second pores 42a by the total volume of the separator 40a The total volume of the pores 41a, the resin portion of the porous layer 42, and the second pores 42a).

The porosity of the separator 40a can be measured, for example, by an automatic porosimeter Autopore IV (Shimadzu Corporation).

The porosity of the porous layer 42, that is, the porosity of the second pores 42a, is higher than the porosity of the base material 41, In other words, the porosity of the first pores 41a may be higher than that of the first pores 41a.

The thickness of the porous layer 42 may be 1 to 5 탆. The total thickness of the separator 40a, that is, the total thickness of the base material 41 and the porous layer 42 may be 10 to 25 占 퐉. When the thickness of the porous layer 42 and the thickness of the separator 40a are respectively within the above ranges, the cycle life characteristics can be improved.

1, the porous layer 42 is located on both sides of the base material 41, that is, on both sides of the base material facing the positive electrode 20 and facing the negative electrode 30, but is not limited thereto. Specifically, it may be located at least on one surface of the substrate facing the cathode 30. [ In order to further improve the cycle life characteristics of the lithium secondary battery, the porous layer 42 may be formed on both sides of the base material 41. [

The air permeability (air permeability defined by JIS P8117) of the base material 41 is not particularly limited, but may be, for example, 250 to 300 sec / 100 cc. The air permeability of the separator 40a is not particularly limited, but may be, for example, 220 to 340 sec / 100 cc. When the air permeability of the base material 41 and the separator 40a are respectively within the above ranges, the cycle life characteristics can be improved.

The air permeability of the base material 41 and the separator 40a can be measured by, for example, a Gurley air permeability meter (G-B2 Toyobesq co., Ltd.) have.

The separator 40a may be manufactured as follows.

The resin constituting the porous layer 42 and the water-soluble organic solvent are mixed at a weight ratio of 5 to 10: 90 to 95 to prepare a coating liquid. Examples of the water-soluble organic solvent include N-methyl-2-pyrrolidone, dimethylacetamide (DMAc), and tripropylene glycol (TPG).

Subsequently, the coating liquid is applied on both sides or one side of the substrate 41 to a thickness of 1 to 5 mu m. Subsequently, the base material 41 coated with the coating liquid is treated with a coagulating liquid to solidify the resin in the coating liquid. Examples of the method of treating the base material 41 coated with the coating liquid with the coagulating liquid include a method of impregnating the coagulating liquid with the base material 41 coated with the coating liquid, And a method of shaking the coagulating liquid. Thus, the separator 40a can be manufactured.

The coagulating solution can be obtained, for example, by mixing water with the water-soluble organic solvent.

The mixing amount of water may be used in an amount of 40 to 80% by volume based on the total volume of the coagulating solution.

Subsequently, the separator 40a is washed with water and dried to remove water and a water-soluble organic solvent from the separator 40a.

According to another embodiment, the porous layer 42 may comprise the above-described protective film forming material.

When the protective film forming material is added to the porous layer, a protective film may be formed at the interface between the porous layer 42 and the cathode active material layer 22. Specifically, the protective film forming material may be added to the porous layer 42 facing the anode 20. A material in contact with the cathode active material layer among the protective film forming materials dispersed in the porous layer can be decomposed and polymerized at the time of charging so that a protective film is formed at the interface between the porous layer 42 and the cathode active material layer 22 . In other words, the protective film forming material may form a protective film at the interface between the cathode active material and the electrolyte.

The protective film may be a polymer formed by polymerizing the protective film forming material.

The protective film forming material may also be added to the porous layer 42 facing the cathode.

The protective film forming material may be included in an amount of 10 to 90% by weight, and more preferably 40 to 90% by weight based on the total weight of the porous layer. When the protective film forming material is contained within the above range, the amount of contact with the cathode active material can be increased, and the porosity of the porous layer can be easily controlled.

The separator may be formed by applying a coating liquid containing a resin constituting the porous layer, the protective film forming material and a water-soluble organic solvent to the substrate 41, and then performing coagulation of the resin and removal of the water-soluble organic solvent have. The water-soluble organic solvent may dissolve the protective film forming material.

According to another embodiment, both the positive electrode active material layer 22 and the porous layer 42 may include the above-mentioned protective film forming material.

When the protective film-forming material is added to an electrolyte or a cathode, it is difficult to form a protective film. When the protective film-forming material is added to a cathode, the protective film-forming material is decomposed on the cathode and the decomposition product thus formed may adversely affect the reaction on the cathode.

The electrolyte 43 may include a lithium salt, a solvent, and an additive.

The lithium salt may be an electrolyte of the electrolytic solution (43).

To the lithium salt is _{LiPF 6, LiClO 4, LiBF 4} , LiAsF 6, LiSbF 6, LiSO 3 CF 3, LiN (SO 2 CF 3), LiN (SO 2 CF 2 CF 3), LiC (SO 2 CF 2 CF _{3) 3, LiC (SO 2} CF 3) 3, LiI, LiCl, LiF, LiPF5 (SO 2 CF 3), LiPF 4 (SO 2 CF 3) _2, etc. may be mentioned. Of these, LiPF ₆ , LiClO ₄ , LiBF ₄ , LiAsF ₆ , and LiSbF ₆ can be preferably used. These lithium salts may be dissolved alone or in combination of two or more.

When the lithium salt is dissolved in the electrolyte 43, cycle life characteristics can be improved.

The concentration of the lithium salt (the sum of the concentrations of the lithium salt when the plural kinds of lithium salts are dissolved in the electrolytic solution) may be 1.15 to 1.5 mol / L, and more specifically 1.3 to 1.45 mol / L. When the concentration of the lithium salt is within the above range, the cycle life characteristics can be improved.

The solvent may comprise a fluorinated ether in which at least some of the hydrogen atoms have been replaced with fluorine atoms.

The fluorinated ether is obtained by replacing hydrogen of an ether with fluorine, and oxidation resistance can be improved.

Examples of the fluorinated ether include 2,2,2-trifluoroethyl methyl ether, 2,2,2-trifluoroethyl difluoro, and 2,2,2-trifluoroethyl methyl ether, Methyl ether, 2,2,3,3,3-pentafluoropropyl methyl ether, 2,2,3,3,3-pentafluoropropyl difluoromethyl ether, 2,2,3,3,3- Pentafluoropropyl-1,1,2,2-tetrafluoroethyl ether, 1,1,2,2-tetrafluoroethyl methyl ether, 1,1,2,2-tetrafluoroethyl ethyl ether, 1 , 1,2,2-tetrafluoroethyl propyl ether, 1,1,2,2-tetrafluoroethyl butyl ether, 1,1,2,2-tetrafluoroethyl isobutyl ether, 1,1,2 , 2-tetrafluoroethyl isopentyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, 1,1,2,2-tetrafluoroethyl- , 2,3,3-tetrafluoropropyl ether, hexafluoroisopropyl methyl ether, 1,1,3,3 , 3-pentafluoro-2-trifluoromethylpropyl methyl ether, 1,1,2,3,3,3-hexafluoropropyl methyl ether, 1,1,2,3,3,3-hexafluoro Propyl ethyl ether, 2,2,3,4,4,4-hexafluorobutyl difluoromethyl ether, and the like. These may be used alone or in combination of two or more.

The fluorinated ether may be contained in an amount of 10 to 60% by volume based on the total volume of the solvent, specifically, 30 to 50% by volume. When the content of the fluorinated ether is within the above range, the cycle life characteristics can be further improved. Since the solubility of the protective film forming material in the fluorinated ether is lower than that of the organic solvent based on ethylene carbonate, the elution of the protective film forming material into the electrolytic solution can be suppressed.

The solvent may further comprise ethylene monofluorocarbonate.

The monofluorocarbonic acid may be contained in an amount of 10 to 30% by volume based on the total volume of the solvent, and specifically 15 to 20% by volume. When the content of ethylene monofluorocarbonate is within the above range, the cycle life characteristics can be further improved.

The solvent may further include a non-aqueous solvent used in a lithium secondary battery.

Examples of the additive include an anode active compound, an anode active compound, an ester compound, a carbonate ester compound, a sulfate ester compound, a phosphate ester compound, a borate ester compound, an acid anhydride compound and an electrolyte compound. These may be used alone or in combination of two or more.

Examples of the negative-working compound include WCA-1, WCA-2 and WCA-3 of central glass.

Examples of the positive electrode active compound include bisfluorosulfonylimide lithium (LiFSI) and the like.

Examples of the ester compounds include methyl difluoroacetate, diethyl trifluoroacetate, vinyl acetate, and difluoroethyl acetate.

Examples of the carbonic ester compounds include vinylene carbonate, vinylethylene carbonate, difluoroethylene carbonate, diallyl carbonate, and 2,5-dioxahexanedimethanoic acid.

Examples of the sulfuric ester compounds include ethylene sulfite, dimethyl sulfite, dimethyl sulfate, ethylene sulfate, 3-sulfolene, 1,3-propane sultone, 1,4-butane sultone and propene sultone.

Examples of the phosphoric acid ester compound include trimethylphosphoric acid, trioctylphosphoric acid, trimethylsilylphosphoric acid, and trimethylsilylphosphine.

Examples of the boric acid ester-based compound include trimethylboric acid and trimethylsilylboric acid.

Examples of the acid anhydride-based compound include succinic anhydride, allylsuccinic anhydride, and ethane disulfonic anhydride.

Examples of the electrolyte compound include lithium bis (oxalate-O, O ') lithium borate, difluoro (oxalate-O, O') lithium borate, lithium difluorobis (oxalate- And the like.

The additive may be included in an amount of 0.01 to 5.0% by weight based on the total amount of the electrolytic solution. When the additive is included within the above range, the cycle life characteristics can be improved.

The lithium secondary battery can be manufactured as follows.

The separator 40a is disposed between the anode 20 and the cathode 30 to form an electrode structure. When the porous layer 42 is formed on only one side of the substrate 41, the cathode 30 is opposed to the porous layer 42. Next, the electrode structure is processed into a desired shape, for example, a cylindrical shape, a square shape, a laminate shape, a button shape, or the like, and inserted into the container of the above-described shape. Subsequently, the electrolytic solution of the above composition is injected into the container, and each of the pores in the separator 40a is impregnated with the electrolytic solution. Thus, a lithium secondary battery is manufactured.

Hereinafter, specific embodiments of the present invention will be described. However, the embodiments described below are only intended to illustrate or explain the present invention, and thus the present invention should not be limited thereto.

In addition, contents not described here can be inferred sufficiently technically if they are skilled in the art, and a description thereof will be omitted.

Example  One

(Preparation of positive electrode)

Solid solution oxide _{Li 1 .20 Mn 0 .55 Co 0} .10 Ni 0 .15 O 2 90 % by weight, 6% by weight of ketjen black, 4 wt% of polyvinylidene fluoride, and _{LiTCB (LiB (CN) 4)} 1 part by weight (Based on 100 parts by weight of the total amount of the solid solution oxide, the Ketjenblack and the polyvinylidene fluoride) was dispersed in N-methyl-2-pyrrolidone to prepare a slurry. The slurry was applied onto an aluminum current collecting foil as a current collector and dried to form a cathode active material layer. Subsequently, the positive electrode active material layer was pressed by a press machine to produce a positive electrode. At this time, the density of the positive electrode active material layer was pressed to be 2.3 g / cm ³ .

(Preparation of negative electrode)

96% by weight of artificial graphite and 4% by weight of styrene-butadiene rubber were dispersed in N-methyl-2-pyrrolidone to prepare a slurry. The slurry was coated on an aluminum current collecting foil as a current collector and dried to form a negative electrode active material layer. Subsequently, the negative electrode active material layer was pressed by a press machine to produce a negative electrode. At this time, the negative electrode active material layer was pressed to have a density of 1.45 g / cm ³ .

(Preparation of separator)

A coating liquid was prepared by mixing aramid (poly [N, N '- (1,3-phenylene) isophthalamide] (Sigma-Aldrich Japan K.K.) and a water-soluble organic solvent at a weight ratio of 5.5: 94.5. The water-soluble organic solvent used was a mixture of dimethylacetamide and tripropylene glycol in a weight ratio of 50:50.

As the substrate, a porous polyethylene film (thickness: 13 mu m, porosity: 42 vol%) was used.

The coating liquid was applied to both surfaces of the substrate to a thickness of 2 mu m. Subsequently, the base material coated with the coating liquid was impregnated into the coagulating solution to solidify the resin in the coating liquid, thereby preparing a separator. At this time, the coagulation solution was prepared by mixing water, dimethylacetamide and tripropylene glycol in a weight ratio of 50:25:25.

Then, the separator was washed with water and dried to remove water and a water-soluble organic solvent.

 (Preparation of electrolytic solution)

Monofluorophosphate ethylene carbonate (FEC), ethylene carbonate (EC), dimethyl carbonate (DMC) and _{HCF 2 CF 2 OCH 2 CF 2} CF a ₂ H 15: 5: 45: in a solvent mixture in a volume ratio of 35, hexafluoro And lithium phosphate was dissolved to a concentration of 1.00 mol / L to prepare an electrolytic solution.

(Production of lithium-ion battery)

The separator was disposed between the positive electrode and the negative electrode prepared above to prepare an electrode structure. The electrode structure was inserted into a test container, the electrolyte solution was injected into the test container, and each pore in the separator was impregnated with an electrolytic solution to prepare a lithium secondary battery.

Example  2

A lithium secondary battery was prepared in the same manner as in Example 1 except that 1.6 parts by weight of lithium difluoro-o, o'-oxalate borate was added to 100 parts by weight of the solvent in the preparation of the electrolytic solution in Example 1 .

Comparative Example  One

A lithium secondary battery was fabricated in the same manner as in Example 1, except that LiTCB was not used in the preparation of the positive electrode in Example 1.

Evaluation 1-1: Cycle life characteristics

The lithium secondary batteries of Examples 1 and 2 and Comparative Example 1 were charged and discharged in the following manner, and the cycle life characteristics were evaluated. The results are shown in Table 1 and FIG.

During the Mars phase, the battery was charged at a constant current of 0.2 mA / cm ^{2 up} to a voltage of 3 V, and then left for 12 hours. As a result, the LiTCB was decomposed and polymerized to form a protective film. Thereafter, constant current constant voltage charging was performed at 0.2 mA / cm < ² > until the voltage reached 4.65 V, and constant current discharge was performed at 0.2 mA / cm < ² >

Cycle step: Constant current constant voltage charging was performed at 3 mA / cm ² until a voltage of 4.55 V was reached, and a constant current discharge was performed until a voltage of 2.40 V was reached, thereby performing a charge-discharge cycle 500 times.

The discharge capacity at one cycle was taken as the initial capacity, and the discharge capacity at 500 cycles divided by the initial capacity was defined as the capacity retention rate.

All of the tests were carried out at a temperature of 25 ° C.

The discharge capacity was measured by TOSCAT 3000 (Tong Yang System Co., Ltd.).

Fig. 2 is a graph showing the relationship between the number of cycles and the discharge capacity of the lithium secondary battery according to Examples 1 and 2 and Comparative Example 1. Fig.

Discharge capacity (mAh) Capacity retention rate (%) Initial Capacity At 500 cycles Example 1 175 137 78 Example 2 175 160 91 Comparative Example 1 175 123 70

Referring to Table 1 and FIG. 2, it can be seen that a protective film is formed in the case of Example 1, and the cycle life characteristics under a high voltage and high current density are superior to those in Comparative Example 1. Also, it can be seen that the capacity retention ratio is greatly increased when the additive is added to the electrolyte through Example 2.

Example  3 to 21

A lithium secondary battery was produced in the same manner as in Example 1, except that LiTCB was used in various amounts in the following Table 2 in the preparation of the positive electrode in Example 1.

A lithium secondary battery was prepared in the same manner as in Example 1, except that LiB (CN) ₃ (OCH ₃ ) (LiMCB) was used instead of LiTCB in the preparation of the positive electrode in Example 1,

A lithium secondary battery was produced in the same manner as in Example 1, except that LiB (CN) ₃ (OCH ₂ CH ₃ ) (LiECB) was used instead of LiTCB in the preparation of the positive electrode in Example 1, .

Protective film forming material LiTCB LiMCB LiECB Addition amount 0.5 parts by weight Example 3 Example 10 Example 16 0.7 parts by weight Example 4 Example 11 Example 17 1 part by weight Example 1 Example 12 Example 18 1.5 parts by weight Example 5 Example 13 Example 19 2 parts by weight Example 6 Example 14 Example 20 3 parts by weight Example 7 Example 15 Example 21 5 parts by weight Example 8 - - 6 parts by weight Example 9 - -

- In Table 2, the parts by weight are units expressed in terms of a total amount of 100 parts by weight of the solid solution oxide, the Ketjen black and the polyvinylidene fluoride.

Evaluation 1-2: Cycle life characteristics

The cycle life characteristics of the lithium secondary batteries of Examples 3 to 21 were evaluated in the same manner as in Evaluation 1-1, and the capacity retention ratio (%) is shown in Table 3 and Figs. 3 and 4. At this time, the capacity retention rate (%) is obtained as a percentage of the discharge capacity at 500 cycles relative to the initial capacity. The initial capacity of both LiTCB, LiMCB and LiECB is 175 mAh.

3 is a graph showing the relationship between the addition amount of the lithium compound and the discharge capacity of the lithium secondary battery, and Fig. 4 is a graph showing the relationship between the addition amount of the lithium compound and the discharge capacity retention rate of the lithium secondary battery.

Discharge capacity (mAh) Capacity retention rate (%) Initial Capacity At 500 cycles Example 1 175 137 78 Example 3 175 128 73 Example 4 175 130 74 Example 5 175 140 80 Example 6 175 141 81 Example 7 175 142 81 Example 8 175 140 80 Example 9 175 127 73 Example 10 175 127 73 Example 11 175 132 75 Example 12 175 136 78 Example 13 175 137 78 Example 14 175 136 78 Example 15 175 130 74 Example 16 175 127 73 Example 17 175 130 74 Example 18 175 134 77 Example 19 175 134 77 Example 20 175 132 75 Example 21 175 128 73

Referring to Table 3 and FIGS. 3 and 4, it can be seen that the cycle life characteristics are most improved when LiTCB is used as a protective film forming material. The LiTCB has a structure in which all the ligands are composed of cyano groups, so that a stable protective film can be formed. It can also be seen that LiTCB can be used at 0.5 to 6 wt%, and LiMCB or LiECB can be used at 0.5 to 4 wt%.

Comparative Example  2

A lithium secondary battery was fabricated in the same manner as in Comparative Example 1, except that LiECB in an amount of 0.02 mol / l was added in the preparation of the electrolytic solution in Comparative Example 1.

Evaluation 1-4: Cycle life characteristics

The cycle life characteristics of the lithium secondary battery of Comparative Example 2 were evaluated in the same manner as in Evaluation 1-1, and the results are shown in Table 4 below.

Discharge capacity (mAh) Capacity retention rate (%) Initial Capacity At 500 cycles Comparative Example 2 160 80 50

Referring to Table 4, when the protective film forming material is added to the electrolyte, the cycle life characteristics are deteriorated. This shows that the protective film-forming material dissolves in the electrolyte solution to decompose on the negative electrode, and the decomposition product inhibits the reaction on the negative electrode.

On the other hand, when a cyano group of an anionic complex such as LiECB is substituted with another ligand, it is dissolved in a solvent, but LiTCB hardly dissolves.

Comparative Example  3

A lithium secondary battery was produced in the same manner as in Comparative Example 1, except that 0.5 parts by weight of LiTCB (based on 100 parts by weight of the total amount of the artificial graphite and the styrene-butadiene rubber) was added during the preparation of the negative electrode in Comparative Example 1.

Evaluation 1-5: Cycle life characteristics

The cycle life characteristics of the lithium secondary battery of Comparative Example 3 were evaluated in the same manner as in Evaluation 1-1, and the results are shown in Table 5 below.

Discharge capacity (mAh) Capacity retention rate (%) Initial Capacity At 500 cycles Comparative Example 3 159 0 0

Referring to Table 5, when the protective film forming material is added to the negative electrode active material layer, the cycle life characteristics are deteriorated. This appears to result in the protective film forming material decomposing on the negative electrode, and the decomposition products inhibiting the reaction on the negative electrode.

Example  22

A lithium secondary battery was produced in the same manner as in Example 1, except that LiTTCB was not used in preparing the positive electrode in Example 1, and polyvinylidene fluoride and LiTCB were added at a weight ratio of 40:60 in preparing the coating liquid for the separator. Respectively.

Comparative Example  4

A lithium secondary battery was fabricated in the same manner as in Example 1, except that polyvinylidene fluoride and Al ₂ O ₃ were added at a weight ratio of 40:60 in the preparation of the coating liquid for the separator in Comparative Example 1.

Evaluation 1-6: Cycle life characteristics

The cycle life characteristics of the lithium secondary batteries of Example 22 and Comparative Example 4 were evaluated in the same manner as in Evaluation 1-1, and the results are shown in Table 6 below.

Discharge capacity (mAh) Capacity retention rate (%) Initial Capacity At 500 cycles Example 22 175 130 74 Comparative Example 4 175 123 70

Referring to Table 6, it can be seen that when the protective layer forming material is included in the porous layer, the cycle life characteristics are improved by the protective layer.

Example  23 to 26

Example 1 was repeated except that LiPF ₃ (CN) ₃ was used instead of LiTCB in the preparation of the positive electrode in various amounts in Table 7, and lithium hexafluorophosphate was used in the electrolytic solution at a concentration of 1.2 mol / L. A lithium secondary battery was fabricated in the same manner.

Comparative Example  5

A lithium secondary battery was fabricated in the same manner as in Comparative Example 1, except that lithium hexafluorophosphate was used at a concentration of 1.2 mol / L in the preparation of the electrolytic solution in Comparative Example 1.

Evaluation 1-7: Cycle life characteristics

The cycle life characteristics of the lithium secondary batteries of Examples 23 to 26 and Comparative Example 5 were evaluated in the same manner as in Evaluation 1-1, and the results are shown in Table 7 and FIG.

5 is a graph showing the relationship between the number of cycles and the discharge capacity of the lithium secondary battery according to Examples 23 to 26 and Comparative Example 5. Fig.

The amount (parts by weight) of LiPF ₃ (CN) ₃ added Discharge capacity (mAh) Capacity retention rate (%) Initial Capacity At 500 cycles Example 23 0.3 180 139 77 Example 24 0.7 180 148 82 Example 25 1.0 178 143 80 Example 26 3.0 177 137 77

- In Table 7, parts by weight are units expressed in terms of a total amount of 100 parts by weight of the solid solution oxide, the Ketjen black and the polyvinylidene fluoride.

Referring to Table 7 and FIG. 5, it can be seen that even when LiPF ₃ (CN) ₃ is used as a protective film forming material, a protective film is formed by decomposition and polymerization. By this protective film, high current density and cycle life characteristics Is improved.

Example  27 to 29

The same procedure as in Example 1 was repeated except that LiC (CN) ₄ was used instead of LiTCB in the preparation of the positive electrode in Example 1 at various contents in the following Table 8 and lithium hexafluorophosphate was used at the concentration of 1.2 mol / L in the electrolytic solution preparation To prepare a lithium secondary battery.

Comparative Example  6

A lithium secondary battery was fabricated in the same manner as in Comparative Example 1, except that lithium hexafluorophosphate was used at a concentration of 1.2 mol / L in the preparation of the electrolytic solution in Comparative Example 1.

Evaluation 1-8: Cycle life characteristics

The cycle life characteristics of the lithium secondary batteries of Examples 27 to 29 and Comparative Example 6 were evaluated in the same manner as in Evaluation 1-1, and the results are shown in Table 8 and FIG.

6 is a graph showing the relationship between the number of cycles and the discharge capacity of the lithium secondary battery according to Examples 27 to 29 and Comparative Example 6. Fig.

The amount (parts by weight) of LiC (CN) ₄ added Discharge capacity (mAh) Capacity retention rate (%) Initial Capacity At 500 cycles Example 27 0.5 180 137 76.1 Example 28 1.0 180 143 79 Example 29 3.0 176 141 80

Referring to Table 8 and FIG. 6, it can be seen that even when LiC (CN) ₄ is used as a protective film-forming material, a protective film is formed by decomposition and polymerization. By this protective film, cycle life characteristics under high current density and high voltage are improved .

Example  30 to 34

A lithium secondary battery was fabricated in the same manner as in Example 1, except that LiB (CN) ₂ (OCH ₃ ) ₂ was used instead of LiTCB in the preparation of the positive electrode in Example 1 in various contents shown in Table 9 below.

In addition, a lithium secondary battery was produced in the same manner as in Example 1, except for using a variety of content to the first embodiment in manufacturing the positive electrode in place of LiTCB LiBCN (OCH _{3) 3} Table 9.

Protective film forming material _{LiB (CN) 2 (OCH 3} ) 2 LiBCN (OCH _{3) 3} Addition amount 0.5 parts by weight Example 30 Example 33 0.7 parts by weight Example 31 Example 34 1 part by weight Example 32 -

Evaluation 1-9: Cycle life characteristics

The cycle life characteristics of the lithium secondary batteries of Examples 30 to 34 were evaluated in the same manner as in Evaluation 1-1, and the results are shown in Table 10 below.

Discharge capacity (mAh) Capacity retention rate (%) Initial Capacity At 500 cycles Example 30 180 141 78 Example 31 180 140 78 Example 32 180 135 75 Example 33 180 139 77 Example 34 180 138 77

Referring to Table 10, it can be seen that even when LiB (CN) ₂ (OCH ₃ ) ₂ and LiBCN (OCH ₃ ) ₃ are used as a protective film forming material, they are decomposed and polymerized to form a protective film. And the cycle life characteristics under high voltage and high density are improved.

Example  35 to 47

A lithium secondary battery was fabricated in the same manner as in Example 1, except that LiPF ₂ (CN) ₄ was used instead of LiTCB in the preparation of the positive electrode in Example 1 in various contents shown in the following Table 11.

A lithium secondary battery was fabricated in the same manner as in Example 1, except that LiPF (CN) ₅ was used in place of LiTCB in the preparation of the positive electrode in Example 1 at various contents _shown in the following Table 11.

A lithium secondary battery was prepared in the same manner as in Example 1, except that LiP (CN) ₆ was used instead of LiTCB in the preparation of the positive electrode in Example 1 in various contents _shown in the following Table 11.

Protective film forming material LiPF ₂ (CN) ₄ LiPF (CN) ₅ LiP (CN) ₆ Addition amount 0.3 parts by weight Example 35 - - 0.5 parts by weight Example 36 Example 41 Example 45 0.7 parts by weight Example 37 Example 42 Example 46 1 part by weight Example 38 Example 43 Example 47 1.5 parts by weight Example 39 Example 44 - 2 parts by weight Example 40 - -

Evaluation 1-10: Cycle life characteristics

The cycle life characteristics of the lithium secondary batteries of Examples 35 to 47 were evaluated in the same manner as in Evaluation 1-1, and the results are shown in Table 12 below.

Discharge capacity (mAh) Capacity retention rate (%) Initial Capacity At 500 cycles Example 35 180 141 78 Example 36 180 148 82 Example 37 180 149 83 Example 38 180 153 85 Example 39 180 144 80 Example 40 180 137 77 Example 41 180 151 84 Example 42 180 157 87 Example 43 180 160 89 Example 44 180 149 83 Example 45 180 151 84 Example 46 180 166 92 Example 47 180 157 87

Referring to Table 12, it can be seen that even when LiPF ₂ (CN) ₄ , LiPF (CN) ₅ and LiP (CN) ₆ are used as a protective film forming material, they are decomposed and polymerized to form a protective film. It can be seen that the cycle life characteristics under high current density and high voltage are improved.

Example  48 to 53

A lithium secondary battery was fabricated in the same manner as in Example 1, except that LiC (CN) ₂ OCH ₃ was used instead of LiTCB in the preparation of the positive electrode in Example 1 in the various contents shown in the following Table 13.

In addition, a lithium secondary battery was produced in the same manner as in Example 1, except that the content of the various embodiments: 1 to manufacture the positive electrode in place of the LiTCB LiCCN (OCH _{3) 2} Table 13.

Protective film forming material LiC (CN) ₂ OCH ₃ LiCCN (OCH _{3) 2} Addition amount 0.5 parts by weight Example 48 Example 52 0.7 parts by weight Example 49 - 1 part by weight Example 50 Example 53 1.5 parts by weight Example 51 -

Evaluation 1-11: Cycle life characteristics

The cycle life characteristics of the lithium secondary batteries of Examples 48 to 53 were evaluated in the same manner as in Evaluation 1-1, and the results are shown in Table 14 below.

Discharge capacity (mAh) Capacity retention rate (%) Initial Capacity At 500 cycles Example 48 180 148 82 Example 49 180 142 79 Example 50 180 140 78 Example 51 180 140 78 Example 52 180 145 81 Example 53 180 141 78

Referring to Table 14 above, LiC (CN) ₂ OCH ₃ And LiCCN (OCH ₃₎ and found to be a protective film by decomposition and polymerization also in the use of _2, by such a protective film can be seen that improvement in the cycle life characteristics under a high current density and high voltage.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, And falls within the scope of the invention.

10: Lithium secondary battery
20: anode
30: cathode
40: separator layer
40a: Separator
41: substrate
41a: First groundwork
42: Porous layer
42a: Second groundwork
43: electrolyte

Claims (15)

Cathode active material; And
At least one of the lithium compounds represented by the following formulas (4) to (6)
And a positive electrode active material layer for a lithium secondary battery.
[Chemical Formula 4]
_{LiB (CN) 4- n1 (X} 1) n1
[Chemical Formula 5]
_{LiP (CN) 6- n2 (X} 2) n2
[Chemical Formula 6]
_{LiC (CN) 3- n3 (X} 3) n3
(In the above formulas 4 to 6,
n ₁ is an integer of 0 to 3, n ₂ is an integer of 0 to 5, n ₃ is an integer of 0 to 2, and X ₁ to X ₃ are ligands other than a cyano group.
The method according to claim 1,
Wherein the cathode active material comprises at least one solid solution oxide of a compound represented by the following general formulas (1) to (3).
[Chemical Formula 1]
Li _a Mn _x Co _y Ni _z O ₂
(In the formula 1, 1.150? A? 1.430, 0.45? X? 0.6, 0.10? Y? 0.15, and 0.20? Z?
(2)
LiMn _x Co _y Ni _z O ₂
(In the formula 2, 0.3? X? 0.85, 0.10? Y? 0.3, and 0.10? Z?
(3)
LiMn _{1 .5} Ni _{0 .5} O ₄
The method according to claim 1,
Wherein the protective film forming material is contained in an amount of 0.1 to 6% by weight based on the total weight of the cathode active material layer.
The method according to claim 1,
When the protective film forming material is a lithium compound represented by the general formula (4), the protective film forming material is contained in an amount of 0.5 to 6 wt% based on the total amount of the cathode active material layer,
When the protective film forming material is a lithium compound represented by the chemical formula 5, the protective film forming material is included in an amount of 0.3 to 2% by weight based on the total amount of the cathode active material layer,
When the protective film forming material is a lithium compound represented by the formula 6, the protective film forming material is included in an amount of 0.5 to 3% by weight based on the total amount of the cathode active material layer
Cathode active material layer for lithium secondary battery.
materials; And
A porous layer disposed on at least one side of the substrate,
/ RTI >
Wherein the porous layer comprises at least one protective film forming material selected from the group consisting of lithium compounds represented by the following Chemical Formulas 4 to 6
Separator for lithium secondary battery.
[Chemical Formula 4]
_{LiB (CN) 4- n1 (X} 1) n1
[Chemical Formula 5]
_{LiP (CN) 6- n2 (X} 2) n2
[Chemical Formula 6]
_{LiC (CN) 3- n3 (X} 3) n3
(In the above formulas 4 to 6,
n ₁ is an integer of 0 to 3, n ₂ is an integer of 0 to 5, n ₃ is an integer of 0 to 2, and X ₁ to X ₃ are ligands other than a cyano group.
6. The method of claim 5,
Wherein the protective film forming material is contained in an amount of 10 to 90% by weight based on the total amount of the porous layer.
A positive electrode comprising a current collector and a positive electrode active material layer disposed on the current collector and including a positive electrode active material;
cathode;
A separator comprising a substrate and a porous layer disposed on at least one side of the substrate; And
Electrolyte
/ RTI >
Wherein at least one of the positive electrode active material layer and the porous layer includes at least one of a lithium compound represented by the following Chemical Formulas 4 to 6
Lithium secondary battery.
[Chemical Formula 4]
_{LiB (CN) 4- n1 (X} 1) n1
[Chemical Formula 5]
_{LiP (CN) 6- n2 (X} 2) n2
[Chemical Formula 6]
_{LiC (CN) 3- n3 (X} 3) n3
(In the above formulas 4 to 6,
n ₁ is an integer of 0 to 3, n ₂ is an integer of 0 to 5, n ₃ is an integer of 0 to 2, and X ₁ to X ₃ are ligands other than a cyano group.
8. The method of claim 7,
Wherein the protective film forming material is a material forming a protective film at an interface between the positive electrode active material layer and the porous layer.
8. The method of claim 7,
Wherein the protective film forming material is a material forming a protective film at an interface between the cathode active material and the electrolyte.
10. The method according to claim 8 or 9,
Wherein the protective film comprises a polymer formed by polymerizing the protective film forming material.
8. The method of claim 7,
When the cathode active material layer includes the protective film forming material,
Wherein the protective film forming material is contained in an amount of 0.1 to 6 wt% based on the total amount of the positive electrode active material layer.
12. The method of claim 11,
When the protective film forming material is a lithium compound represented by the general formula (4), the protective film forming material is contained in an amount of 0.5 to 6 wt% based on the total amount of the cathode active material layer,
When the protective film forming material is a lithium compound represented by the chemical formula 5, the protective film forming material is included in an amount of 0.3 to 2% by weight based on the total amount of the cathode active material layer,
When the protective film forming material is a lithium compound represented by the formula 6, the protective film forming material is included in an amount of 0.5 to 3% by weight based on the total amount of the cathode active material layer
Lithium secondary battery.
8. The method of claim 7,
When the porous layer includes the protective film forming material,
Wherein the protective film forming material is contained in an amount of 10 to 90% by weight based on the total amount of the porous layer.
8. The method of claim 7,
Wherein the cathode active material comprises at least one of solid solution oxides of compounds represented by the following general formulas (1) to (3).
[Chemical Formula 1]
Li _a Mn _x Co _y Ni _z O ₂
(In the formula 1, 1.150? A? 1.430, 0.45? X? 0.6, 0.10? Y? 0.15, and 0.20? Z?
(2)
LiMn _x Co _y Ni _z O ₂
(In the formula 2, 0.3? X? 0.85, 0.10? Y? 0.3, and 0.10? Z?
(3)
LiMn _{1 .5} Ni _{0 .5} O ₄
8. The method of claim 7,
Wherein the electrolyte solution comprises a lithium salt, a solvent and an additive,
The additive may be at least one selected from the group consisting of a negative electrode active compound, a positive electrode active compound, an ester compound, a carbonate ester compound, a sulfuric acid ester compound, a phosphoric acid ester compound, a boric acid ester compound, an acid anhydride compound, Lithium secondary battery.

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