KR101775762B1 - Non-aqueous liquid electrolyte and lithium secondary battery comprising the same - Google Patents

Abstract

The present invention relates to a nonaqueous electrolytic solution containing lithium bis (fluorosulfonyl) imide (LiFSI) and a mixed additive, a positive electrode comprising a lithium-nickel-manganese-cobalt oxide as a positive electrode active material, And a separator. The present invention relates to a lithium secondary battery.
According to the nonaqueous electrolyte solution for a lithium secondary battery of the present invention, a solid SEI film is formed at the cathode at the time of initial charging of the lithium secondary battery including the same, and the decomposition of the surface of the anode and the oxidation reaction of the electrolyte are prevented at high- It is possible to improve not only the low-temperature output characteristics but also the high-temperature storage characteristics and the life characteristics.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolytic solution and a lithium secondary battery comprising the same.

The present invention relates to a nonaqueous electrolytic solution containing lithium bis (fluorosulfonyl) imide (LiFSI) and a mixed additive, a positive electrode comprising a lithium-nickel-manganese-cobalt oxide as a positive electrode active material, And a separator. The present invention relates to a lithium secondary battery.

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

Lithium metal oxide is used as the positive electrode active material of the lithium secondary battery, and lithium metal, lithium alloy, crystalline or amorphous carbon or carbon composite material is used as the negative electrode active material. The active material is coated on the current collector with an appropriate thickness and length, or the active material itself is coated in a film form and wrapped or laminated together with a separator as an insulator to form an electrode group. The electrode group is then placed in a can or similar container, Thereby manufacturing a secondary battery.

This lithium secondary battery is charged and discharged while repeating the process of intercalating lithium ions from the lithium metal oxide of the anode into the graphite electrode of the cathode and deintercalating the lithium ions. At this time, since lithium is highly reactive, it reacts with the carbon electrode to form Li ₂ CO ₃ , LiO, LiOH and the like to form a film on the surface of the cathode. This film is called Solid Electrolyte Interface (SEI) film. The SEI film formed at the beginning of charging prevents the reaction between lithium ion and carbon anode or other materials during charging and discharging. It also acts as an ion tunnel, allowing only lithium ions to pass through. This ion tunnel serves to prevent the collapse of the structure of the carbon anode by co-intercalating the organic solvent of the electrolyte having a large molecular weight moving together by solvation of the lithium ion together with 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 always be formed on the cathode of the lithium secondary battery. Once the SEI membrane is formed at the time of initial charging, it is used as an ion tunnel to prevent the reaction between the lithium ion and the negative electrode or other materials during repetition of charging and discharging by using the battery and passing only lithium ions between the electrolyte and the negative electrode .

It has been difficult to expect improvement in low-temperature output characteristics due to the formation of a non-uniform SEI film in the case of an electrolyte solution which does not contain an electrolyte additive or contains an electrolyte additive having poor characteristics. Further, even when the amount of the electrolyte additive is included, if the amount of the electrolyte additive can not be adjusted to the required amount, the surface of the anode may be decomposed or the oxidation reaction may occur at the high temperature due to the electrolyte additive, thereby ultimately increasing the irreversible capacity of the secondary battery, There is a problem in that it is lowered.

The present invention provides a non-aqueous electrolyte solution for a lithium secondary battery and a lithium secondary battery including the same, capable of improving high temperature storage characteristics and lifetime characteristics as well as improving low temperature output characteristics.

In order to solve the above problems, the present invention provides a non-aqueous electrolytic solution containing lithium bis (fluorosulfonyl) imide (LiFSI) and a fluorinated carbonate compound additive, a lithium-nickel-manganese- A lithium secondary battery comprising a cathode, a cathode, and a separator including a cobalt-based oxide.

The non-aqueous electrolytic solution may further include a lithium salt, wherein a mixing ratio of the lithium salt to lithium bisfluorosulfonylimide is 1: 0.01 to 1: 1 in a molar ratio, and the lithium bisfluorosulfonylimide is a non- And the concentration in the aqueous electrolytic solution is 0.01 mole / l to 2 mole / l.

The lithium-nickel-manganese-cobalt-based oxide may include an oxide represented by the following formula (1).

[Chemical Formula 1]

Li _{1 + x} (Ni _a Co _b Mn _c ) O ₂

0.55? A? 0.65, 0.18? B? 0.22, 0.18? C? 0.22, and -0.2? X? 0.2.

According to the nonaqueous electrolyte solution for a lithium secondary battery of the present invention, a solid SEI film is formed at the cathode at the time of initial charging of the lithium secondary battery including the same, and the decomposition of the surface of the anode and the oxidation reaction of the electrolyte are prevented at high- It is possible to improve not only the low-temperature output characteristics but also the high-temperature storage characteristics and the life characteristics.

FIG. 1 is a graph showing low-temperature output characteristics of Example 2 of the present invention and Comparative Examples 1 to 3. FIG.
2 is a graph showing the high-temperature lifetime characteristics of Example 2 of the present invention and Comparative Examples 1 to 3. Fig.

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

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

The lithium bisfluorosulfonylimide is added to a non-aqueous electrolyte as a lithium salt to improve the low-temperature output characteristics by forming a solid and thin SEI film on the cathode, and also to improve the decomposition of the anode surface And the oxidation reaction of the electrolytic solution can be prevented. Furthermore, since the SEI film formed on the cathode has a small thickness, it is possible to more smoothly move lithium ions in the cathode, thereby improving the output of the secondary battery.

According to an embodiment of the present invention, the concentration of the lithium bisfluorosulfonylimide in the non-aqueous electrolytic solution is preferably 0.01 mole / liter to 2 mole / liter, more preferably 0.01 mole / liter to 1 mole / liter Do. When the concentration of the lithium bisfluorosulfonylimide is less than 0.1 mole / l, the effect of improving the low-temperature power and improving the high-temperature cycle characteristics of the lithium secondary battery is insignificant, and when the lithium bisfluorosulfonylimide concentration is less than 0.1 mole / If it exceeds 2 mole / l, side reactions within the electrolyte may occur excessively during charging / discharging of the battery, causing swelling, and corrosion of the positive electrode made of metal or the negative electrode current collector in the electrolyte solution may be caused.

In order to prevent such side reactions, the non-aqueous electrolytic solution of the present invention may further include a lithium salt. Examples of the lithium salt include lithium salts such as LiPF ₆ , LiAsF ₆ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiBF ₄ , LiSbF ₆ , LiN (C _{2 F 5 SO 2) 2,} LiAlO 4, may be LiAlCl _4, LiClO _4, and any one group or a mixture of two or more of those selected from the consisting of.

The mixing ratio of the lithium salt to lithium bisfluorosulfonylimide is preferably 1: 0.01 to 1, in terms of the molar ratio. When the mixing ratio of the lithium salt and the lithium bisfluorosulfonyl imide is in the range of the above-mentioned molar ratio, a side reaction in the electrolytic solution during the charging / discharging of the battery may occur excessively and swelling may occur, , The output improvement of the generated secondary battery may be deteriorated. Specifically, when the mixing ratio of the lithium salt to the lithium bisfluorosulfonylimide is less than 1: 0.01, the process of forming the SEI film in the lithium ion battery and the process of forming the SEI film by solvating lithium ions by the carbonate solvent A large amount of irreversible reaction may occur during the process of inserting between the negative electrodes, and the deterioration of the negative electrode surface layer (for example, carbon surface layer) and the decomposition of the electrolyte may improve the low temperature output of the secondary battery, The effect of improving the capacity characteristics may be insufficient. When the mixing ratio of the lithium salt to the lithium bisfluorosulfonylimide is in a molar ratio of more than 1: 1, an excessive amount of lithium bis-fluorosulfonylimide is contained in the electrolytic solution and corrosion of the electrode current collector Thereby affecting the stability of the secondary battery.

The cathode active material, which is the lithium-nickel-manganese-cobalt oxide, may include an oxide represented by Chemical Formula 1 below.

[Chemical Formula 1]

Li _{1 + x} (Ni _a Co _b Mn _c ) O ₂

0.55? A? 0.65, 0.18? B? 0.22, 0.18? C? 0.22, and -0.2? X? 0.2.

By using the positive electrode active material, which is the lithium-nickel-manganese-cobalt oxide, as the positive electrode, it can be combined with lithium bisfluorosulfonylimide to have a synergistic effect. Lithium-nickel-manganese-cobalt oxide cathode The positive electrode active material exhibits a phenomenon in which Li + ions and Ni +2 ions in the layered structure of the cathode active material in the charge / mixing, and the structure of the cathode active material is collapsed. As a result, the cathode active material causes a side reaction with the electrolyte or elution of transition metal. This is because Li + 1 ions and Ni +2 ions are similar in size to each other. As a result, the performance of the battery is easily deteriorated due to the depletion of the electrolyte in the secondary battery and the structural collapse of the cathode active material through the side reaction.

Therefore, a LiFSI-based layer is formed on the surface of the anode using a LiFSI-based electrolyte as a positive electrode active material according to an embodiment of the present invention, and cation mixing of Li + 1 + ions and Ni + A range capable of securing a sufficient amount of nickel transition metal for ensuring the capacity of the positive electrode active material has been found. According to the cathode active material containing the oxide of Formula 1 of the present invention, when the LiFSI-applied electrolyte is used, the electrolyte solution, the side reaction, and the metal elution phenomenon can be effectively suppressed.

Particularly, when the ratio of the oxide represented by the formula (1) to the Ni transition metal exceeds 0.65, excess Ni is contained in the cathode active material, and therefore Li + And Ni +2 may not suppress the cation mixing phenomenon of ions.

In addition, when the excess Ni transition metal is included in the cathode active material, the nickel transition metal having the d orbital in an environment such as high temperature has an octahedron structure in the environment of high temperature due to the variation of oxidation number of Ni, Or the oxidation number fluctuates (non-uniformization reaction) to form a warped octahedron. As a result, the crystal structure of the positive electrode active material including the nickel transition metal is deformed, and the probability of nickel metal in the positive electrode active material is increased.

As a result, the inventors of the present invention have found that high efficiency is obtained in high temperature stability and capacity characteristics while producing high output in combination with LiFSI salt and a cathode active material containing an oxide according to the range of Formula 1 above.

Examples of the nonaqueous electrolytic solution include vinylene carbonate (VC), 1,3-propane sultone (PS), ethylene sulfate (Esa), fluorinated ethylene carbonate (FEC), lithium difluoro (bisoxalato) phosphate (LiDFOP) Two or more mixed additives selected from the group consisting of lithium difluorophosphate (LiDFP), lithium oxalyl difluoroborate (LiODFB), succinonitrile (SN) and LiBF ₄ may be included.

Although the cathode active material containing the oxide of Formula 1 and LiFSI lithium salt have high output and stability, the electrolyte can be decomposed in a high output environment and the cathode may be collapsed. When the additives are incorporated in the nonaqueous electrolyte solution, the stability of the generated secondary battery at high temperature can be ensured.

In the case of LiPF ₆ , which is a lithium salt, an electrolyte with insufficient thermal stability is easily decomposed in the cell to form LiF and PF ₅ . At this time, the LiF salt decreases the conductivity and the number of free Li ⁺ ions, thereby increasing the resistance of the battery and consequently decreasing the capacity of the battery. That is, the above decomposition of PF ₆ ^- ion on the surface of the anode which can occur in the high-temperature cycle operation leads Esa, FEC to function as an anion receptor so that PF ₆ ^- can be stably formed, and Li ⁺ and PF ₆ ^- , thereby improving the solubility of LiF in the electrolyte solution and lowering the interface resistance.

Among the above additives, VC and SN can form a stable SEI film on the surface of the negative electrode during the initial activation process of the secondary battery.

Among the additives, LiDFOP, LiDFP and LiODFB compounds are added to the electrolyte to form a solid SEI film on the cathode together with lithium bisfluorosulfonylimide to improve the low temperature output characteristics and to improve the low temperature output characteristics. The decomposition can be suppressed and the oxidation reaction of the electrolytic solution can be prevented. Therefore, the lithium secondary battery to which LiDFOP, LiDFP, and LiODFB compound according to an embodiment of the present invention is added can be improved in high temperature and low temperature output characteristics more effectively.

LiBF ₄ may be used as the additive. The LiBF ₄ may be added to a lithium secondary battery to inhibit generation of gas that may be generated due to decomposition of an electrolyte at a high temperature, thereby improving the high-temperature stability of the secondary battery.

The additive according to an embodiment of the present invention may be contained in an amount of 0.01 to 5% by weight, specifically 0.05 to 5% by weight, preferably 0.05 to 1% by weight, based on the total weight of the electrolytic solution, have. If the total content of the above-mentioned mixed additives is less than 0.05% by weight, the effect of improving the low-temperature power of the battery and improving the high-temperature storage characteristics and high-temperature lifetime characteristics are insignificant. If the total content of the above- There is a possibility that a side reaction in the electrolytic solution is excessive. In particular, when the above-mentioned mixed additives are excessively added, they can not be sufficiently decomposed at a high temperature, and may be present as unreacted materials or precipitates in an electrolyte solution at room temperature. As a result, a side reaction in which the lifetime or the resistance characteristic of the secondary battery is lowered may occur.

The mixed additive according to an embodiment of the present invention may complement each other in the non-aqueous electrolyte to produce a high output in combination with a LiFSI salt and a cathode active material containing an oxide according to the formula 1, It is possible to improve the lifetime characteristics of the generated secondary battery while complementing excellent efficiency in stability and capacity characteristics. Particularly, the additives are selected according to the results of studies conducted by the present inventors so as to perform their respective chemical and electrostatic functions in the secondary battery without reacting with each other in the secondary battery upon mixing.

In addition, the present invention can control the mixed content of the additives and the choice of additives depending on the concentration ratio of the lithium salt and the LiFSI salt. For example, when the concentration ratio of the lithium salt and LiFSI is 0.7: 0.3 or less, the output that can contain LiFSI is relatively small and can be reduced, including LiDFOP among the group of the mixed additive, can be improved, When the concentration ratio of the salt and LiFSI is 0.7: 0.3 or more, the output of the secondary battery is improved according to the addition of a large amount of LiFSI, but the battery stability such as LiBF ₄ can be improved to prevent corrosion due to the addition of a large amount of LiFSI By mixing and using the additives, it is possible to efficiently control the capacity, output and lifetime maintenance rate at a high temperature of the secondary battery within the range of the embodiment of the present invention.

As a result, by incorporating the additives into the nonaqueous electrolyte solution, the lithium secondary battery of the present invention can improve the output characteristics, can form a stable film on the surface of the negative electrode, inhibit decomposition of the electrolyte solution, and improve stability.

The non-aqueous organic solvent that can be contained in the non-aqueous electrolyte solution is not limited as long as it can minimize decomposition due to an oxidation reaction during charging and discharging of the battery and can exhibit desired properties together with additives. For example, Nitrile-based solvents, cyclic carbonates, linear carbonates, esters, ethers or ketones. These may be used alone, or two or more of them may be used in combination.

Among the above organic solvents, a carbonate-based organic solvent can be easily used. The cyclic carbonate may be any one selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC) and butylene carbonate (BC) (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC) and ethyl propyl carbonate Or a mixture of two or more thereof.

The nitrile solvent may be at least one selected from the group consisting of acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentanecarbonitrile, cyclohexanecarbonitrile, 2-fluorobenzonitrile , Difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, 4-fluorophenylacetonitrile, and may be one or more selected from the group consisting of one embodiment Examples of non-aqueous solvents include acetonitrile.

By using the cathode active material of the lithium-nickel-manganese-cobalt oxide as an anode by using an acetonitrile-based solvent, it is possible to effectively prevent the side effects due to the deterioration of the stability of a high-output battery due to combination with lithium bisfluorosulfonylimide can do.

Meanwhile, the lithium secondary battery according to an embodiment of the present invention may include 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 include the positive electrode active material and the negative electrode active material, respectively, according to an embodiment of the present invention.

On the other hand, examples of the negative electrode active material include amorphous carbon or regular carbon, specifically carbon such as non-graphitized carbon or graphite 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 , Si, Group 1, Group 2, and Group 3 elements of the periodic table, halogen, and 0 < x? 1; 1? Y? 3; 1? Z? 8); Lithium metal; Lithium alloy; Silicon-based alloys; Tin alloy; _{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 Bi ₂ O ₅ ; Conductive polymers such as polyacetylene; Li-Co-Ni-based materials and the like can be used.

The separation membrane may be a porous polymer film such as a porous polymer film made of a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer and an ethylene / methacrylate copolymer Or may be a laminate of two or more kinds. In addition, nonwoven fabrics made of conventional porous nonwoven fabrics, for example, glass fibers having a high melting point, polyethylene terephthalate fibers, or the like can be used, but the present invention is not limited thereto.

The secondary battery may have a variety of shapes depending on purposes such as a cylindrical shape, a square shape, a pouch shape, and the like, and is not limited to the structure known in the art. The lithium secondary battery according to an embodiment of the present invention may be a pouch type secondary battery.

EXAMPLES The present invention will be further illustrated by the following examples and experimental examples, but the present invention is not limited by these examples and experimental examples.

Example

Example 1

[Preparation of electrolytic solution]

Aqueous organic solvent having a composition of ethylene carbonate (EC): ethylmethyl carbonate (EMC) = 3: 7 (volume ratio) and LiPF ₆ based on the total amount of non-aqueous electrolytic solution as a lithium salt 0.9 mole / liter of lithium bisfluorosulfonylimide and 0.1 mole / liter of lithium bisfluorosulfonylimide, and 3% by weight of VC and 0.5% by weight of LiDFOP based on the total weight of the nonaqueous electrolytic solution as an additive were added to prepare a nonaqueous electrolytic solution.

 [Production of lithium secondary battery]

As a positive electrode active material Li (Ni Co _{0 .6 0 0 .2 .2} Mn) O ₂ 92% by weight, 4 wt% carbon black conductive agent (carbon black), polyvinylidene fluoride (PVdF) as a binder, 4 wt% Was added to the solvent N-methyl-2-pyrrolidone (NMP) to prepare a positive electrode mixture slurry. The positive electrode mixture slurry was applied to an aluminum (Al) thin film having a thickness of about 20 탆 and dried to produce a positive electrode, followed by a 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 to 96 wt%, 3 wt% and 1 wt%, respectively, as a solvent. The negative electrode mixture slurry was applied to a copper (Cu) thin film as an anode current collector having a thickness of 10 mu m and dried to prepare a negative electrode, followed by roll pressing to produce a negative electrode.

The thus prepared positive electrode and negative electrode were fabricated by polymerizing a polymer type cell with a separator composed of three layers of polypropylene / polyethylene / polypropylene (PP / PE / PP), and then the prepared non-aqueous electrolyte was injected, The preparation of the battery was completed.

Example 2

The lithium salt is added to LiPF ₆ based on the total amount of the non-aqueous electrolytic solution And 0.3% by mole of lithium bis-fluorosulfonylimide, and adding 3% by weight of VC and 0.5% by weight of PS based on the total weight of the non-aqueous electrolyte as an additive. In the same manner, a nonaqueous electrolytic solution and a lithium secondary battery were prepared.

Example 3

The lithium salt is added to LiPF ₆ based on the total amount of the non-aqueous electrolytic solution 0.5 mole / liter of lithium bisfluorosulfonylimide and 0.5 mole / liter of lithium bisfluorosulfonylimide were used, and 3 mass% of VC and 0.5 mass% of LiBF ₄ were added as an additive, based on the total weight of the nonaqueous electrolyte solution. , A nonaqueous electrolytic solution and a lithium secondary battery were prepared.

Example 4

The lithium salt is added to LiPF ₆ based on the total amount of the non-aqueous electrolytic solution And 0.2% by mole of lithium bis-fluorosulfonylimide and 3% by weight of VC and 0.5% by weight of LiDFOP were added as additives, based on the total weight of the nonaqueous electrolytic solution. In the same manner, a nonaqueous electrolytic solution and a lithium secondary battery were prepared.

Example 5

The lithium salt is added to LiPF ₆ based on the total amount of the non-aqueous electrolytic solution Except that 0.3 mole / liter of lithium bisfluorosulfonylimide and 0.3 weight% of VC and 0.5 weight% of LiDFP were added as an additive, based on the total weight of the nonaqueous electrolyte solution, In the same manner, a nonaqueous electrolytic solution and a lithium secondary battery were prepared.

Example 6

The lithium salt is added to LiPF ₆ based on the total amount of the non-aqueous electrolytic solution And 0.4% by mole of lithium bis-fluorosulfonylimide, and adding 3% by weight of VC and 0.5% by weight of LiBF ₄ as an additive, based on the total weight of the nonaqueous electrolyte solution, , A nonaqueous electrolytic solution and a lithium secondary battery were prepared.

Example 7

The lithium salt is added to LiPF ₆ based on the total amount of the non-aqueous electrolytic solution And 0.3 mole / liter of lithium bis-fluorosulfonylimide, and adding 3 weight% of VC and 0.5 weight% of LiODFB as an additive, based on the total weight of the nonaqueous electrolyte solution, In the same manner, a nonaqueous electrolytic solution and a lithium secondary battery were prepared.

Example 8

The lithium salt is added to LiPF ₆ based on the total amount of the non-aqueous electrolytic solution And 0.3 mole / liter of lithium bis-fluorosulfonylimide, and adding 3% by weight of VC and 0.5% by weight of Esa based on the total weight of the nonaqueous electrolytic solution as an additive. In the same manner, a nonaqueous electrolytic solution and a lithium secondary battery were prepared.

Example 9

The lithium salt is added to LiPF ₆ based on the total amount of the non-aqueous electrolytic solution Except that 0.3 weight% of VC, 0.5 weight% of LiDFOP and 0.5 weight% of PS were added as additive, based on the total weight of the nonaqueous electrolyte solution, using 0.3 mole / liter of lithium bisfluorosulfonylimide and 0.3 mole / A nonaqueous electrolytic solution and a lithium secondary battery were prepared in the same manner as in Example 1.

Example 10

The lithium salt is added to LiPF ₆ based on the total amount of the non-aqueous electrolytic solution And 0.2% by mole of lithium bis-fluorosulfonylimide, and adding 3% by weight of VC and 0.5% by weight of FEC based on the total weight of the non-aqueous electrolyte as an additive. In the same manner, a nonaqueous electrolytic solution and a lithium secondary battery were prepared.

Comparative Example 1

Wherein as a positive electrode active material Li (Ni Co _{0 .5 0 0 .2 .3} Mn) in the same manner as in Example 2 except that the O ₂ was prepared in a non-aqueous electrolyte and a lithium secondary battery.

Comparative Example 2

Wherein as a positive electrode active material Li (Ni _{0 .8} Co _{.1 0 .1 0} Mn) in the same manner as in Example 2 except that the O ₂ was prepared in a non-aqueous electrolyte and a lithium secondary battery.

Comparative Example 3

A non-aqueous electrolytic solution and a lithium secondary battery were prepared in the same manner as in Example 2 except that LiCoO ₂ was used as the cathode active material.

Comparative Example 4

As the positive electrode active material _{Li (Ni 0 .5 Co 0 .3} Mn 0 .2) LiPF 6 the use of O _2, and the lithium salt, based on the total amount of non-aqueous electrolyte solution 0.5 mole / liter of lithium bisfluorosulfonylimide and 0.5 mole / liter of lithium bisfluorosulfonylimide were used, and 3 mass% of VC and 0.5 mass% of LiBF ₄ were used as an additive, based on the total weight of the nonaqueous electrolyte solution. In the same manner, a nonaqueous electrolytic solution and a lithium secondary battery were prepared.

Comparative Example 5

As the positive electrode active material _{Li (Ni 0 .6 Co 0 .2} Mn 0 .2) LiPF 6 the use of O _2, and the lithium salt, based on the total amount of non-aqueous electrolyte solution 0.3 mole / l of lithium bisfluorosulfonylimide and 0.7 mole / l of lithium bisfluorosulfonylimide, and using 3% by weight of VC and 0.5% by weight of LiBF ₄ based on the total weight of the non-aqueous electrolyte as an additive. In the same manner, a nonaqueous electrolytic solution and a lithium secondary battery were prepared.

Comparative Example 6

A nonaqueous electrolytic solution and a lithium secondary battery were prepared in the same manner as in Example 2, except that the above additives were not used.

Experimental Example

<Output characteristics after high temperature storage>

The outputs were calculated using the voltage difference which occurs when the secondary batteries manufactured in Examples 1 to 10 and Comparative Examples 1 to 6 were charged and discharged for 10 seconds at 23 ° C and 5 ° C after storing for 16 weeks at 60 ° C. (16 watt output (W) / initial output (W) * 100 (%)) of the output amount after 16 weeks based on the initial output amount are shown in Table 1 below. The test was performed at 50% SOC (state of charge).

<Capacity characteristics after high temperature storage>

The secondary batteries manufactured in Examples 1 to 10 and Comparative Examples 1 to 6 were charged at 1 C to 4.2 V / 38 mA under constant current / constant voltage (CC / CV) conditions and discharged at 3 C to 2.5 V under constant current (CC) And the discharge capacity thereof was measured. Then, the secondary batteries prepared in Examples 1 to 10 and Comparative Examples 1 to 6 were stored at 60 DEG C for 16 weeks, and then the secondary batteries were respectively charged at a constant current / constant voltage (CC / CV) , And discharged at 3 C to 2.5 V under a constant current (CC) condition, and the discharge capacity thereof was measured. The discharge capacity after 16 weeks based on the initial discharge capacity was calculated as a percentage (discharge capacity after 16 weeks / initial discharge capacity * 100 (%)), and the results are shown in Table 1 below.

Capacity characteristics (%) Output Characteristics (%) Example 1 93.8 95.4 Example 2 95.2 97.8 Example 3 92.8 94.2 Example 4 93.1 94.2 Example 5 93.4 96.3 Example 6 92.3 93.8 Example 7 93.3 96.1 Example 8 93.8 95.6 Example 9 94.9 97.1 Example 10 92.5 96.4 Comparative Example 1 88.1 90.7 Comparative Example 2 81.5 86.3 Comparative Example 3 90.7 91.4 Comparative Example 4 89.7 88.9 Comparative Example 5 89.9 89.1 Comparative Example 6 83.6 85.9

<Low Temperature Output Characteristics>

Calculate the output according to SOC (state of charge) using the voltage difference which occurs when the secondary battery manufactured in Example 2 and Comparative Examples 1 to 3 is charged and discharged for 10 seconds at -30 ° C to 0.5 ° C Respectively. The results are shown in Fig.

As shown in FIG. 1, in the case of Example 2 using the cathode active material within the scope of the present invention, it was found that the low temperature output characteristics were the most excellent. Specifically, in the case of Comparative Examples 1 and 2 in which the content ratio of the cathode active material is out of the range of the cathode active material of the present invention, the low-temperature power differs by at least 1 W from that of Example 2 .

<High temperature life characteristics>

The lithium secondary batteries of Example 2 and Comparative Examples 1 to 3 were charged at 1 C to 4.2 V / 38 mA at a constant current / constant voltage (CC / CV) condition at 45 ° C and then discharged at 3 C And the discharge capacity thereof was measured. This was repeated 1 to 1000 cycles. The capacity was calculated as a percentage (for example, 1000 times capacity / first capacity * 100 (%)) based on the number of cycles of 1000 cycles based on the first cycle, Respectively.

In the case of Example 2 using the positive electrode active material within the scope of the present invention, it was found that the low temperature output characteristics were the most excellent. Specifically, in the case of Comparative Examples 1 and 2 in which the content ratio of the cathode active material is outside the range of the cathode active material of the present invention, the capacity is similar to that of Example 2 up to the capacity according to the 200th cycle, , The capacity retention rate rapidly decreased, and a capacity difference of at least 10% or more was confirmed at 1000th time from Example 2.

Claims (12)

A non-aqueous electrolytic solution comprising a non-aqueous organic solvent and a first lithium salt, a second lithium salt, lithium bis (fluorosulfonyl) imide (LiFSI), and a mixed additive;
A positive electrode comprising an oxide represented by the following formula (1) as a positive electrode active material;
cathode; And
Comprising a separator,
Wherein the molar ratio of the first lithium salt to the lithium bisfluorosulfonylimide as the second lithium salt is 1: 0.01 to 1: 1,
The mixed additive may be at least one selected from the group consisting of vinylene carbonate (VC), 1,3-propane sultone (PS), ethylene sulfate (Esa), fluorinated ethylene carbonate (FEC), lithium difluoro (bisoxalato) phosphate At least two members selected from the group consisting of lithium difluorophosphate (LiDFP), lithium oxalyl difluoroborate (LiODFB), succinonitrile (SN) and LiBF ₄ ,
Wherein the content of the mixed additive is 0.01 wt% to 5 wt% based on the total weight of the non-aqueous electrolyte.
&Lt; Formula 1 >
Li _{1 + x} (Ni _a Co _b Mn _c ) O ₂
0.55? A? 0.65, 0.18? B? 0.22, 0.18? C? 0.22, and -0.2? X? 0.2.
delete delete The method according to claim 1,
Wherein the concentration of the lithium bisfluorosulfonylimide in the non-aqueous electrolytic solution is 0.01 mole / l to 2 mole / l.
The method according to claim 1,
Wherein the first lithium salt is selected from the group consisting of LiPF ₆ , LiAsF ₆ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiBF ₄ , LiSbF ₆ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiAlO ₄ , LiAlCl ₄ , LiClO ₄ , or a mixture of two or more thereof.
delete The method according to claim 1,
Wherein the non-aqueous organic solvent includes a nitrile solvent, a linear carbonate, a cyclic carbonate, an ester, an ether, a ketone, or a combination thereof.
8. The method of claim 7,
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. The linear carbonate is selected from the group consisting of dimethyl carbonate (DMC) Wherein the lithium secondary carbonate is one selected from the group consisting of diphenyl carbonate (DEC), dipropyl carbonate (DPC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC) and ethyl propyl carbonate (EPC) battery.
8. The method of claim 7,
The nitrile solvent may be at least one selected from the group consisting of acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentanecarbonitrile, cyclohexanecarbonitrile, 2-fluorobenzonitrile At least one selected from the group consisting of fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile.
delete delete The method according to claim 1,
Wherein the lithium secondary battery is a pouch type lithium secondary battery.

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