WO2016048094A1 - Nonaqueous electrolyte and lithium secondary battery comprising same - Google Patents

Abstract

The present invention provides a lithium secondary battery comprising: a nonaqueous electrolyte comprising lithium bis(fluorosulfonyl)imide (LiFSI) and a phosphazene-based compound additive; a positive electrode comprising a lithium-nickel-manganese-cobalt-based oxide as a positive active material; a negative electrode; and a separator. The nonaqueous electrolyte for a lithium secondary battery according to the present invention forms a strong SEI film on a negative electrode at the time of initially charging the lithium secondary battery comprising the nonaqueous electrolyte, improves the output properties of the lithium secondary battery, and further can improve output and capacity properties after high-temperature storage.

Description

Non-aqueous electrolyte solution and lithium secondary battery comprising the same

[Cross-cited with Related Applications]

This application claims the benefit of priority based on Korean Patent Application No. 10-2014-0128882 dated September 26, 2014 and Korean Patent Application No. 10-2015-0135259 dated September 24, 2015. All content disclosed in the literature is included as part of this specification.

[Technical Field]

The present invention is a non-aqueous electrolyte containing lithium bis (fluorosulfonyl) imide (LiFSI) and a phosphazene compound additive, a positive electrode comprising lithium-nickel-manganese-cobalt oxide as a positive electrode active material It relates to a lithium secondary battery comprising a negative electrode, and a separator.

As technology development and demand for mobile devices increase, the demand for secondary batteries as energy sources is rapidly increasing, and lithium secondary batteries having high energy density and voltage among these secondary batteries are commercially used and widely used.

Lithium metal oxide is used as a positive electrode active material of a lithium secondary battery, and lithium metal, a lithium alloy, crystalline or amorphous carbon or a carbon composite material is used as a negative electrode active material. The active material is applied to a current collector with a suitable thickness and length, or the active material itself is applied in a film shape to form an electrode group by winding or laminating together with a separator, which is an insulator, and then put it in a can or a similar container, and then injecting an electrolyte solution. A secondary battery is manufactured.

In such a lithium secondary battery, charging and discharging progress while repeating a process of intercalating and deintercalating lithium ions from a lithium metal oxide of a positive electrode to a graphite electrode of a negative electrode. At this time, lithium is highly reactive and reacts with the carbon electrode to generate Li ₂ CO ₃ , LiO, LiOH and the like to form a film on the surface of the negative electrode. Such a film is called a solid electrolyte interface (SEI) film, and the SEI film formed at the beginning of charging prevents the reaction between lithium ions and a carbon anode or other material during charging and discharging. It also acts as an ion tunnel, allowing only lithium ions to pass through. The ion tunnel serves to prevent the organic solvents of a large molecular weight electrolyte which solvates lithium ions and move together and are co-intercalated with the carbon anode to decay the structure of the carbon anode.

Therefore, in order to improve the high temperature cycle characteristics and the low temperature output of the lithium secondary battery, a solid SEI film must be formed on the negative electrode of the lithium secondary battery. Once formed, the SEI membrane prevents the reaction between lithium ions and the negative electrode or other materials during repeated charge / discharge cycles, and serves as an ion tunnel that passes only lithium ions between the electrolyte and the negative electrode. Will be performed.

Conventionally, in the case of an electrolyte solution containing no electrolyte additive or an electrolyte additive having poor properties, it is difficult to expect improvement in low temperature output characteristics due to the formation of a non-uniform SEI film. Furthermore, even when it contains an electrolyte additive, when the input amount cannot be adjusted to the required amount, the electrolyte additive decomposes the surface of the anode during the high temperature reaction or the electrolyte causes an oxidation reaction, ultimately increasing the irreversible capacity of the secondary battery and output characteristics. There was a problem of this deterioration.

The problem to be solved by the present invention is to provide a non-aqueous electrolyte lithium secondary battery and a lithium secondary battery comprising the same, which can not only improve the output characteristics, but also improve the life characteristics.

In order to solve the above problems, the present invention provides a non-aqueous electrolyte containing lithium bis (fluorosulfonyl) imide (LiFSI) and a phosphazene compound additive, and lithium-nickel-manganese-cobalt as a positive electrode active material. Provided is a lithium secondary battery comprising a positive electrode, a negative electrode, and a separator including an oxide.

The non-aqueous electrolyte solution may further include a lithium salt, the mixing ratio of the lithium salt and lithium bisfluoro sulfonyl imide is 1: 0.01 to 1: 1 in molar ratio, the lithium bisfluoro sulfonyl imide is The concentration of the aqueous electrolyte may be a lithium secondary battery of 0.01 mol / L to 2 mol / L.

The lithium-nickel-manganese-cobalt-based oxide may include an oxide represented by Formula 1 below.

[Formula 1]

Li _{1 + x} (Ni _a Co _b Mn _c ) O ₂

In Formula 1, 0.55 ≦ a ≦ 0.65, 0.18 ≦ b ≦ 0.22, 0.18 ≦ c ≦ 0.22, −0.2 ≦ x ≦ 0.2, and x + a + b + c + = 1.

According to the non-aqueous electrolyte solution for lithium secondary batteries of the present invention, by forming a solid SEI film in the negative electrode during the initial charging of the lithium secondary battery comprising the same, by imparting flame retardancy at high temperature environment to prevent decomposition of the positive electrode surface and oxidation reaction of the electrolyte, As well as improving the output characteristics of the lithium secondary battery, it is possible to improve the output characteristics and capacity characteristics after high temperature storage.

Hereinafter, the present invention will be described in more detail to aid in understanding the present invention. The terms or words used in this specification and claims are not to be construed as limiting in their usual or dictionary meanings, and the inventors may appropriately define the concept of terms in order to best explain their invention in the best way possible. It should be interpreted as meaning and concept corresponding to the technical idea of the present invention based on the principle that the present invention.

The non-aqueous electrolyte solution according to one embodiment of the present invention includes lithium bisfluorosulfonylimide (LiFSI).

The lithium bisfluorosulfonylimide is added to the non-aqueous electrolyte as a lithium salt to form a solid, thin SEI film on the negative electrode to improve low temperature output characteristics, as well as to decompose positive electrode surfaces that may occur during high temperature cycle operation. It can suppress and prevent the oxidation reaction of electrolyte solution. In addition, the SEI film generated on the negative electrode has a small thickness so that the movement of lithium ions in the negative electrode can be more smoothly performed, thereby improving the output of the secondary battery.

According to one embodiment of the present invention, the lithium bisfluorosulfonylimide preferably has a concentration in the non-aqueous electrolyte of 0.01 mol / L to 2 mol / L, more preferably 0.01 mol / L to 1 mol / L. Do. When the concentration of the lithium bisfluorosulfonylimide is less than 0.1 mol / L, the effect of improving the low temperature output and the high temperature cycle characteristics of the lithium secondary battery is insignificant, and the concentration of the lithium bisfluorosulfonylimide is When the amount exceeds 2 mol / l, side reactions in the electrolyte may be excessively generated during charging and discharging of the battery, and swelling may occur, and corrosion of the positive electrode or the negative electrode current collector made of metal in the electrolyte may occur.

In order to prevent such side reactions, the non-aqueous electrolyte solution of the present invention may further include a lithium salt. The lithium salt may be used a lithium salt commonly used in the art, for example LiPF ₆ , LiAsF ₆ , LiCF ₃ SO ₃ , LiBF ₆ , LiSbF ₆ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiAlO ₄ , LiAlCl ₄ , LiSO ₃ CF ₃ and LiClO ₄ may be any one selected from the group consisting of or a mixture of two or more thereof.

The mixing ratio of the lithium salt and lithium bisfluoro sulfonyl imide is preferably 1: 0.01 to 1 as molar ratio. When the mixing ratio of the lithium salt and lithium bisfluoro sulfonyl imide is greater than or equal to the molar ratio, side reactions in the electrolyte may occur excessively during charging and discharging of the battery, and a swelling phenomenon may occur. In this case, output improvement of the generated secondary battery may be reduced. Specifically, when the mixing ratio of the lithium salt and lithium bisfluoro sulfonyl imide is less than 1: 0.01, a process of forming an SEI film in a lithium ion battery, and lithium ions solvated by a carbonate solvent In the process of being inserted between the negative electrode, a large number of irreversible reactions may occur, and by the peeling of the negative electrode surface layer (for example, the carbon surface layer) and the decomposition of the electrolyte, the low temperature output of the secondary battery may be improved, the high temperature storage, the cycle characteristics and The effect of improving the dose characteristics may be insignificant. When the mixing ratio of the lithium salt and the lithium bisfluoro sulfonyl imide is a molar ratio, when the ratio is greater than 1: 1, lithium bisfluoro sulfonyl imide of excessive capacity is included in the electrolyte to prevent corrosion of the electrode current collector during charging and discharging. This may affect the stability of the secondary battery.

The positive electrode active material which is the lithium-nickel-manganese-cobalt-based oxide may include an oxide represented by Formula 1 below.

[Formula 1]

Li _{1 + x} (Ni _a Co _b Mn _c ) O ₂

In Formula 1, 0.55 ≦ a ≦ 0.65, 0.18 ≦ b ≦ 0.22, 0.18 ≦ c ≦ 0.22, −0.2 ≦ x ≦ 0.2, and x + a + b + c + = 1.

By using the positive electrode active material, which is the lithium-nickel-manganese-cobalt-based oxide, for the positive electrode, it may be combined with lithium bisfluoro sulfonyl imide to have a synergistic effect. In the lithium-nickel-manganese-cobalt-based oxide positive electrode active material, Li + 1 ions and Ni + 2 ions in the layered structure of the cathode active material change as the amount of Ni in the transition metal increases. mixing) occurs and the structure thereof collapses, and the cathode active material causes side reactions with the electrolyte, or dissolution of transition metals. This occurs because Li +1 ions and Ni +2 ions have similar sizes. As a result, the performance of the battery is easily degraded due to electrolyte depletion and structural collapse of the positive electrode active material inside the secondary battery.

Therefore, using LiFSI applied electrolyte to the positive electrode active material of Formula 1 according to an embodiment of the present invention to form a layer layer of the LiFSI-based components on the surface of the anode cation mixing of Li + 1 ions and Ni + 2 ions While suppressing the phenomenon, a range was found in which sufficient nickel transition metal amount for securing the capacity of the positive electrode active material could be secured. According to the positive electrode active material including the oxide according to Chemical Formula 1 of the present invention, when using a LiFSI-applied electrolyte, it is possible to effectively suppress the electrolyte, side reactions, metal dissolution and the like.

In particular, when the ratio of the Ni transition metal in the oxide represented by Formula 1 exceeds 0.65, since the excess Ni is included in the positive electrode active material, Li + 1 is also ionized by the layer layer formed of LiFSI on the electrode surface described above. And Ni +2 may not suppress cation mixing of ions.

In addition, when an excessive amount of Ni transition metal is included in the positive electrode active material, the nickel transition metal having a d-orbit should have an octahedral structure in coordination bond under high temperature or the like due to the variation in the oxidation number of Ni, but in order of energy level by external energy supply. Is reversed, or the oxidation number is varied (disproportionation reaction) to form a distorted octahedron. As a result, the crystal structure of the positive electrode active material including the nickel transition metal is deformed to increase the probability of eluting nickel metal in the positive electrode active material.

As a result, the present inventors have confirmed that while producing a high output when the positive electrode active material including the oxide according to the formula (1) range and the LiFSI salt combination, it shows excellent efficiency in high temperature stability and capacity characteristics.

In addition, the electrolyte additive according to an embodiment of the present invention may include a phosphazene-based compound. Specifically, at least one selected from the group of compounds represented by Formulas 2 and 3 below.

[Formula 2]

[Formula 3]

In a lithium secondary battery, oxygen released from a positive electrode in a high temperature environment promotes an exothermic decomposition reaction of an electrolyte solvent, causing a so-called swelling phenomenon in which the battery swells, thereby rapidly deteriorating battery life and charging / discharging efficiency. The battery is greatly deteriorated, such as an explosion. Accordingly, the phosphazene-based compound is added to the electrolyte as a flame retardant compound and reacts with the surface of the cathode and the anode at high temperatures in the battery and reacts with the electrolyte to suppress the gas generated by decomposition of the electrolyte, thereby suppressing the generation of oxygen in the cathode, thereby reducing the lithium secondary. It is also possible to improve the battery life characteristics. Therefore, the high temperature output characteristics and lifespan characteristics to which the phosphazene compound is added according to an embodiment of the present invention can be more effectively increased.

At this time, the content of the phosphazene-based compound may be used without limitation as long as it is an amount necessary to achieve the effects of the present invention, such as improving the high temperature output and lifespan characteristics of the battery, for example 0.1 to 15% by weight based on the total amount of the electrolyte It may be, preferably from 3.0% to 10% by weight. If the amount of the phosphazene-based compound is less than 0.1% by weight, it is difficult to sufficiently exhibit the flame retardant effect depending on the addition. If the amount of the phosphazene-based compound exceeds 15% by weight, the degree of effect increase is limited. The problem may arise that the irreversible capacity is increased or the resistance of the cathode is increased. In particular, the phosphazene-based compound can be adjusted according to the amount of lithium bis fluoro sulfonyl imide added. This is to more effectively prevent side reactions that may occur with the addition of a large amount of lithium bis fluorosulfonyl imide.

In addition, as the non-aqueous organic solvent that can be included in the non-aqueous electrolyte, decomposition by the oxidation reaction or the like during the charging and discharging process of the battery can be minimized, there is no limitation as long as it can exhibit the desired characteristics with the additive, Nitrile solvents, cyclic carbonates, linear carbonates, esters, ethers or ketones. These may be used alone, or two or more thereof may be used in combination.

Carbonate-based organic solvents of the organic solvents can be easily used, the cyclic carbonate is any one selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC) and butylene carbonate (BC) or two of them A mixture of two or more species, the linear carbonate consists of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), ethylmethyl carbonate (EMC), methylpropyl carbonate (MPC) and ethylpropyl carbonate (EPC) It may be any one selected from the group or a mixture of two or more thereof.

The nitrile solvents include acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentane carbonitrile, cyclohexane carbonitrile, 2-fluorobenzonitrile and 4-fluorobenzonitrile , Difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, 4-fluorophenylacetonitrile may be one or more selected from the group consisting of, one embodiment of the present invention Acetonitrile may be used as the non-aqueous solvent according to the example.

On the other hand, the lithium secondary battery according to an embodiment of the present invention may include a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode and the non-aqueous electrolyte. The positive electrode and the negative electrode may each include the positive electrode active material and the negative electrode active material according to an embodiment of the present invention.

On the other hand, the negative electrode active material includes amorphous carbon or crystalline carbon, specifically, carbon such as non-graphitized carbon, graphite-based carbon; LixFe ₂ O ₃ (0 ≦ x ≦ 1), LixWO ₂ (0 ≦ _x ≦ ₁ ), SnxMe _{1 - x} Me ' _y O _z (Me: Mn, Fe, Pb, Ge; Me': Al, B, P , Metal complex oxides such as Si, Group 1, 2, 3 Group elements of the periodic table, halogen, 0 <x ≦ 1, 1 ≦ y ≦ 3, 1 ≦ z ≦ 8); Lithium metal; Lithium alloys; Silicon-based alloys; Tin-based alloys; SnO, SnO ₂ , PbO, PbO ₂ , Pb ₂ O ₃ , Pb ₃ O ₄ , Sb ₂ O ₃ , Sb ₂ O ₄ , Sb ₂ O ₅ , GeO, GeO ₂ , Bi ₂ O ₃ , Bi ₂ O ₄ , And oxides such as Bi ₂ O ₅ ; Conductive polymers such as polyacetylene; Li-Co-Ni-based materials and the like can be used.

In addition, the separator is a porous polymer film, for example, a porous polymer film made of a polyolefin-based polymer such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer and ethylene / methacrylate copolymer This may be a single or two or more laminated. In addition to the above, conventional porous nonwoven fabrics such as high-melting glass fibers, polyethylene terephthalate fibers, and the like may be used, but are not limited thereto.

The secondary battery is various according to the purpose of performing the cylindrical, square, pouch type and the like, and is not limited to the configuration known in the art. Lithium secondary battery according to an embodiment of the present invention may be a pouch-type secondary battery.

Although the following Examples and Experimental Examples will be further described, the present invention is not limited to these Examples and Experimental Examples.

Example

Example 1

Preparation of Electrolyte

Ethylene carbonate (EC): Non-aqueous organic solvent and lithium salt having a composition of ethyl methyl carbonate (EMC) = 3: 7 (volume ratio) LiPF ₆ based on the total amount of the non-aqueous electrolyte solution 0.9 mol / l and 0.1 mol / l of lithium bisfluorosulfonylimide and 3 wt% of the phosphazene compound of Formula 3 as an additive were added based on the total weight of the non-aqueous electrolyte to prepare a non-aqueous electrolyte.

 [Manufacture of Lithium Secondary Battery]

92% by weight of Li (Ni _0.6 Co _0.2 Mn _0.2 ) O ₂ as a positive electrode active material, 4% by weight of carbon black as a conductive agent, and 4% by weight of polyvinylidene fluoride (PVdF) as a binder, N-methyl- A positive electrode mixture slurry was prepared by addition to 2-pyrrolidone (NMP). The positive electrode mixture slurry was applied to a thin film of aluminum (Al), which is a positive electrode current collector having a thickness of about 20 μm, dried to prepare a positive electrode, and then subjected to roll press to prepare a positive electrode.

Further, a negative electrode mixture slurry was prepared by adding carbon powder as a negative electrode active material, PVdF as a binder, and carbon black as a conductive agent at 96 wt%, 3 wt%, and 1 wt%, respectively, to NMP as a solvent. The negative electrode mixture slurry was applied to a copper (Cu) thin film, which is a negative electrode current collector having a thickness of 10 μm, dried to prepare a negative electrode, and then roll-rolled to prepare a negative electrode.

The positive electrode and the negative electrode prepared as described above were manufactured with a polymer battery by a conventional method with a separator composed of three layers of polypropylene / polyethylene / polypropylene (PP / PE / PP), followed by pouring the prepared non-aqueous electrolyte solution into a lithium secondary battery. The manufacture of the battery was completed.

Example 2

LiPF ₆ based on the total amount of the non-aqueous electrolyte A non-aqueous electrolyte solution and a lithium secondary battery were prepared in the same manner as in Example 1 except that 0.7 mol / l and 0.3 mol / l of lithium bisfluorosulfonylimide were used.

Example 3

LiPF ₆ based on the total amount of the non-aqueous electrolyte A non-aqueous electrolyte solution and a lithium secondary battery were prepared in the same manner as in Example 1 except that 0.6 mol / l and 0.4 mol / l of lithium bisfluorosulfonylimide were used.

Example 4

LiPF ₆ based on the total amount of the non-aqueous electrolyte A non-aqueous electrolyte solution and a lithium secondary battery were prepared in the same manner as in Example 1 except that 0.5 mol / l and 0.5 mol / l of lithium bisfluorosulfonylimide were used.

Example 5

A non-aqueous electrolyte solution and a lithium secondary battery were prepared in the same manner as in Example 1, except that the phosphazene compound of Formula 2 was used instead of the phosphazene compound of Formula 3 in Example 1.

Example 6

A nonaqueous electrolyte solution and a lithium secondary battery were prepared in the same manner as in Example 1, except that the phosphazene compound of Formula 4 was used instead of the phosphazene compound of Formula 3 in Example 1.

[Formula 4]

Comparative Example 1

LiPF ₆ based on the total amount of the non-aqueous electrolyte A non-aqueous electrolyte solution and a lithium secondary battery were prepared in the same manner as in Example 1 except that 0.4 mol / l and 0.6 mol / l of lithium bisfluorosulfonylimide were used.

Comparative Example 2

A non-aqueous electrolyte solution and a lithium secondary battery were prepared in the same manner as in Example 2 except that the additive was not used.

Comparative Example 3

A non-aqueous electrolyte solution and a lithium secondary battery were prepared in the same manner as in Example 2 except for Li (Ni _0.5 Co _0.3 Mn _0.2 ) O ₂ as the cathode active material.

Experimental Example

<Low Temperature Output Characteristics>

The outputs were calculated by using the voltage difference generated when the secondary batteries prepared in Examples 1 to 6 and Comparative Examples 1 to 3 were charged and discharged at −30 ° C. at 0.5C for 10 seconds. At this time, the output of Comparative Example 1 was 3.4W. Based on Comparative Example 1, the outputs of Examples 1 to 6 and Comparative Examples 2 to 3 were calculated as percentages. The results are shown in Table 1 below. The test was performed at 50% SOC (state of charge).

<Room temperature output characteristics>

The outputs were calculated using the voltage difference generated when the secondary batteries prepared in Examples 1 to 6 and Comparative Examples 1 to 3 were charged and discharged at 23 ° C. for 0.5 seconds at 0.5C. At this time, the output of Comparative Example 1 was 37.1W. Based on Comparative Example 1, the outputs of Examples 1 to 6 and Comparative Examples 2 to 3 were calculated as percentages. The results are shown in Table 1 below. The test was performed at 50% SOC (state of charge).

<Output characteristics after high temperature storage>

The secondary battery prepared in Examples 1 to 6 and Comparative Examples 1 to 3 was calculated using the voltage difference generated when charging and discharging the secondary battery prepared at 60 ° C for 20 seconds at 23 ° C after 20 weeks of storage. At this time, the output of Comparative Example 1 was 35.9W. Based on Comparative Example 1, the outputs of Examples 1 to 6 and Comparative Examples 2 to 3 were calculated as percentages. The results are shown in Table 1 below. The test was performed at 50% SOC (state of charge).

Output Characteristics (%)-Compared to Comparative Example 1 Low temperature output Room temperature output Output after high temperature storage Example 1 2.11 1.02 3.32 Example 2 4.36 2.93 8.73 Example 3 3.19 2.33 6.25 Example 4 2.31 1.61 4.01 Example 5 4.21 2.91 8.52 Example 6 1.84 0.86 1.27 Comparative Example 1 - - - Comparative Example 2 -0.75 -0.47 -2.88 Comparative Example 3 -2.99 -1.48 -7.42

As shown in Table 1, it can be seen that the secondary batteries of Examples 1 to 6 exhibited excellent outputs of up to about 5% than the secondary batteries of Comparative Examples 1 to 3 at low temperature and room temperature output. In particular, the secondary batteries of Examples 1 to 6 have an increase in stability at high temperature by using a phosphazene compound as an additive, and thus have an output characteristic of up to 14% or more than the secondary batteries of Comparative Examples 1 to 3 in the output characteristics after high temperature storage. It was found to be excellent.

<Room temperature life characteristics>

The lithium secondary batteries of Examples 1 to 6 and Comparative Examples 1 to 3 were charged at 1 C to 4.2 V / 38 mA in constant current / constant voltage (CC / CV) conditions at 23 ° C., and then to 2.5 V in constant current (CC) conditions. It discharged at 3C and the discharge capacity was measured. This was repeated 1 to 1000 cycles, the discharge capacity measured by calculating the percentage of the 1000th cycle as a percentage (1000th capacity / 1st capacity * 100 (%)) based on the first cycle is shown in Table 2.

<High temperature life characteristics>

The lithium secondary batteries of Examples 1 to 6 and Comparative Examples 1 to 3 were charged at 1 C to 4.2 V / 38 mA at constant current / constant voltage (CC / CV) conditions at 45 ° C., and then to 2.5 V at constant current (CC) conditions. It discharged at 3C and the discharge capacity was measured. This was repeated 1 to 1000 cycles, the discharge capacity measured by calculating the percentage of the 1000th cycle as a percentage (1000th capacity / 1st capacity * 100 (%)) based on the first cycle is shown in Table 2.

Life Characteristics (%) Room temperature life characteristics High temperature life characteristics Example 1 79.8 77.8 Example 2 83.9 80.8 Example 3 81.5 79.2 Example 4 80.3 77.8 Example 5 82.7 81.0 Example 6 80.4 74.8 Comparative Example 1 79.1 76.1 Comparative Example 2 79.6 74.2 Comparative Example 3 66.7 60.7

As can be seen in Table 2, the lithium secondary battery of Examples 1 to 6 was confirmed that the life characteristics at room temperature is superior to the lithium secondary batteries of Comparative Examples 1 to 3, Examples 1 to 5 It was confirmed that the lithium secondary battery of excellent in the life characteristics at high temperature than the lithium secondary batteries of Comparative Examples 1 to 3. In addition, in Comparative Example 3 using Li (Ni _0.5 Co _0.3 Mn _0.2 ) O ₂ as the cathode active material, it was found that the high temperature life characteristics and the normal temperature life characteristics were significantly lower. On the other hand, the lithium secondary battery of Example 6 did not have good high temperature life characteristics compared to the lithium secondary batteries of Examples 1 to 5.

Claims (12)

Non-aqueous electrolyte containing lithium bisfluoro sulphonyl imide (LiFSI) and phosphazene compound additives; A positive electrode comprising a lithium-nickel-manganese-cobalt-based oxide as a positive electrode active material; cathode; And a lithium secondary battery comprising a separator. The method of claim 1, The lithium-nickel-manganese-cobalt oxide is a lithium secondary battery comprising an oxide represented by the following formula (1). [Formula 1] Li _{1 + x} (Ni _a Co _b Mn _c ) O ₂ (In Formula 1, 0.55≤a≤0.65, 0.18≤b≤0.22, 0.18≤c≤0.22, -0.2≤x≤0.2, and x + a + b + c + = 1.) The method of claim 1, The non-aqueous electrolyte solution further comprises a lithium salt. The method of claim 3, wherein A mixing ratio of the lithium salt and lithium bisfluoro sulfonyl imide is 1: 0.01 to 1: 1 in molar ratio. The method of claim 1, The lithium bisfluoro sulfonyl imide has a concentration of 0.01 mol / L to 2 mol / L in the non-aqueous electrolyte. The method of claim 3, wherein The lithium salt is LiPF ₆ , LiAsF ₆ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiBF6, LiSbF ₆ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiAlO ₄ , LiAlCl ₄ , LiSO ₃ CF ₃ And LiClO ₄ Any one or a mixture of two or more selected from the group consisting of a lithium secondary battery. The method of claim 1, The phosphazene compound is at least one lithium secondary battery selected from the group consisting of compounds represented by formulas (2) to (3). [Formula 2]

[Formula 3]

The method of claim 1, The non-aqueous organic solvent is a lithium secondary battery comprising a nitrile-based solvent, linear carbonate, cyclic carbonate, ester, ether, ketone or a combination thereof. The method of claim 8, The cyclic carbonate is any one selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC) and butylene carbonate (BC) or a mixture of two or more thereof, and the linear carbonate is dimethyl carbonate (DMC) or diethyl carbonate. (DEC), dipropyl carbonate (DPC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC) and ethyl propyl carbonate (EPC) any one selected from the group consisting of or a mixture of two or more thereof. The method of claim 8, The nitrile solvents include acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentane carbonitrile, cyclohexane carbonitrile, 2-fluorobenzonitrile and 4-fluorobenzonitrile And at least one lithium secondary battery selected from the group consisting of difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile. The method of claim 1, The content of the phosphazene compound additive is a lithium secondary battery of 0.1 to 15% by weight based on the total weight of the non-aqueous electrolyte. The secondary battery according to any one of claims 1 to 11 is a pouch-type lithium secondary battery.