KR20160081405A - An Electrolyte for a lithium ion secondary battery and a lithium ion secondary battery comprising the same - Google Patents

Abstract

The present invention relates to an electrolyte for a lithium secondary battery and a lithium secondary battery comprising the same and, more specifically, to an electrolyte which has improved lifespan properties and an inhibited resistance increase effect by stably forming an SEI thin film, and to a lithium secondary battery comprising the same. The electrolyte according to the present invention can be a secondary battery having excellent low temperature properties and high temperature properties by using LiFSI (lithium bis (fluorosulfonyl) imide) having the small influence on the temperature as lithium salts. In addition, the electrolyte according to the present invention can be a lithium secondary battery having excellent lifespan properties and an inhibited resistance increase effect when applying a structurally stable thin film to the lithium secondary battery because of forming the structurally stable thin film.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrolyte for a lithium secondary battery and a lithium secondary battery including the same,

The present invention relates to an electrolyte for a lithium secondary battery and a lithium secondary battery comprising the same. More particularly, the present invention relates to an electrolyte solution and a lithium secondary battery including the electrolyte solution.

2. Description of the Related Art As technology development and demand for mobile devices have increased, demand for secondary batteries as energy sources has been rapidly increasing. In recent years, the use of secondary batteries as a power source for electric vehicles (EVs) and hybrid electric vehicles . Accordingly, a lot of research has been conducted on a secondary battery that can meet various demands, and in particular, there is a high demand for a lithium secondary battery having a high energy density, a high discharge voltage, and an output stability.

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 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. Since lithium is highly reactive, lithium reacts with the carbon electrode to form Li ₂ CO ₃ , LiO, and LiOH to form a coating on the surface of the negative electrode. This coating is called a solid electrolyte interface (SEI). These SEI membranes exhibit negligibly low conductance and high-lithium-ion conductivity, and behave like solid electrolytes.

In addition to transferring lithium ions at the interface between the electrode and the electrolyte, the SEI film also mitigates the concentration deviation and the overvoltage, secures a uniform particle size and chemical composition, and helps to move lithium ions under a uniform current distribution. Therefore, in order to use a lithium secondary battery for a long period of time, the SEI film must have strong adhesion to electrodes and be physically and chemically stable.

On the other hand, LiFSI (lithium bis (fluorosulfonyl) imide) as a lithium salt has excellent solubility and ionic conductivity, and has little influence on temperature, and thus it is considered to use an electrolyte for electric vehicles. However, when LiSFI is applied, A problem has been reported. Accordingly, research and development of an electrolyte composition capable of forming a stable SEI film in an electrolyte containing LiFSI (lithium bis (fluorosulfonyl) imide) is in urgent need.

Disclosure of the Invention The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an electrolyte solution for a lithium secondary battery having a composition capable of forming a stable SEI film on the electrode surface in an electrolyte solution containing LiFSI (lithium bis (fluorosulfonyl) .

Other objects and advantages of the present invention will become apparent from the following description. It is also to be easily understood that the objects and advantages of the present invention can be realized by the means or method described in the claims, and the combination thereof.

The present invention provides an electrolyte for a lithium ion secondary battery comprising an additive for forming a SEI film to solve the above technical problem.

The electrolytic solution comprises 1) a non-aqueous organic solvent; 2) lithium bis (fluorosulfonyl) imide and LiPF ₆ as the lithium salt; And 3) fluoroethylene carbonate as an additive for forming a SEI film, wherein the content of the additive for forming the SEI film is 0.01 to 2% by weight based on 100% by weight of the electrolytic solution.

Here, the lithium bis (fluorosulfonyl) imide is a compound represented by the following formula (1).

[Chemical Formula 1]

In the above formula (1), Rf ₁ and Rf ₂ are each fluorine or fluoroalkyl having 1 to 4 carbon atoms, or Rf ₁ and Rf ₂ are linked to each other to form a ring having a fluoroalkylene group having 1 to 4 carbon atoms.

Here, the compound represented by Formula 1 is at least one selected from the group consisting of Formulas 1-1 to 1-7 shown below.

[Formula 1-1]

[Formula 1-2]

[Formula 1-3]

[Formula 1-4]

[Formula 1-5]

[Chemical Formula 1-6]

[Chemical Formula 1-7]

Here, the fluoroethylene carbonate may include a compound represented by the following formula (2).

 (2)

In Formula 2, at least one of R ¹ to R ⁴ is fluorine, or at least one is a C ₁ to C ₆ alkyl group, a C ₆ to C ₁₂ aryl group, a C ₂ to C ₆ alkenyl group, Sulfonate group.

Here, the electrolytic solution may be one selected from the group consisting of LiBF ₄ , LiSbF ₆ , LiAsF ₆ , lithium oxalyldifluoroborate (LiODFB), LiBOB and propensulfone (PRS) Or more.

Here, the electrolyte is _{LiBF 4, LiAsF 6, LiSbF 6} , LiAlO 4, LiAlCl 4 , and a lithium salt LiClO _4, and the like.

Here, the non-aqueous organic solvent may include at least one selected from the group consisting of cyclic carbonates, linear carbonates, esters, ethers, and ketones.

Here, the lithium bis (poulosulfonyl) imide may be mixed at a ratio of 10 mol% to 90 mol% based on the total of 100 mol% of the lithium bis (fluorosulfonyl) imide and LiPF ₆ .

The present invention also provides a method of manufacturing an electrode assembly, comprising: a) an electrode assembly including a cathode, an anode, and a separator interposed between the cathode and the anode; And b) an electrolytic solution. Here, the electrolyte b) is an electrolyte according to the present invention having the above-described characteristics.

Here, the negative electrode is a negative electrode active material, carbon material introduced, lithium titanium _{oxides, Li x Fe 2 O 3 (} 0≤x≤1), Li x WO 2 (0≤x≤1), Sn x Me 1-x Me _{y, z, and z in the} periodic table, Me, Mn, Fe, Pb, and Ge; Me ': Al, B, P, Si, 3; 1? Z? 8), a lithium metal, a lithium alloy, a silicon-based alloy, and a tin-based alloy.

Here, the positive electrode may be LiNi _1/3 Mn _1/3 Co _1/3 O ₄ , LiNi _0.5 Mn _1.5 O ₄ , And LiM _1/6 Mn _11/6 O ₄ (M is Co, Al, or Ni).

The present invention also provides a battery pack including the lithium ion secondary battery according to the present invention as a unit battery.

Since the electrolyte according to the present invention uses LiFSI (lithium bis (fluorosulfonyl) imide) having a small influence on the temperature as a lithium salt, it is possible to produce a secondary battery having excellent low temperature characteristics and high temperature characteristics.

In addition, the electrolyte according to the present invention can form a structurally stable SEI film, and can produce a lithium secondary battery having excellent lifetime characteristics and suppression of resistance increase.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. On the other hand, the shape, size, scale or ratio of the elements in the drawings incorporated herein can be exaggerated to emphasize a clearer description.
FIG. 1 is a graph showing a capacity retention rate and a rate of resistance increase with respect to a room temperature condition of a battery manufactured in a comparative example and an embodiment according to the present invention.
FIG. 2 is a graph showing the capacity retention rate and the rate of resistance increase with respect to the high temperature condition of the battery prepared in the comparative example and the example according to the present invention.

The present invention will now be described in detail with reference to the accompanying drawings. The terms or words used in the present specification and claims should not be construed to be limited to ordinary or dictionary terms and the inventor shall properly define the concept of the term in order to best explain its invention The present invention should be construed in accordance with the meaning and concept consistent with the technical idea of the present invention. Therefore, the embodiments described in this specification and the configurations shown in the drawings are merely the most preferred embodiments of the present invention and do not represent all the technical ideas of the present invention. Therefore, It is to be understood that equivalents and modifications are possible.

The present invention relates to an electrolyte solution using lithium bis (fluorosulfonyl) imide having a small influence on temperature as a lithium salt and a secondary battery comprising the electrolyte solution. The electrolyte according to the present invention is excellent in low-temperature characteristics and high-temperature characteristics and induces formation of a structurally stable SEI film, so that a lithium secondary battery having excellent lifetime characteristics and resistance increase suppression effect can be manufactured.

An electrolytic solution according to a specific embodiment of the present invention comprises a) a non-aqueous organic solvent; b) a mixed lithium salt comprising lithium bis (fluorosulfonyl) imide and LiPF ₆ ; And 3) fluoroethylene carbonate as an additive for SEI film formation.

The lithium bis (fluorosulfonyl) imide has excellent solubility and ionic conductivity, is excellent in low-temperature characteristics and high-temperature stability, and can form a stable and physico-chemically stable SEI film on a negative electrode. As a result, not only the low-temperature output characteristics of the battery are improved, but also the decomposition of the surface of the anode, which may occur in a high-temperature cycle operation, is suppressed and the oxidation reaction of the electrolyte is prevented.

According to a specific embodiment of the present invention, the lithium bis (fluorosulfonyl) imide is a compound represented by the following formula (1).

[Chemical Formula 1]

Wherein Rf ₁ and Rf ₂ are each fluorine or fluoroalkyl having 1 to 4 carbon atoms, or Rf ₁ and Rf ₂ may be connected to each other to form a ring having a fluoroalkylene group having 1 to 4 carbon atoms.

According to a specific embodiment of the present invention, the compound represented by Formula 1 may be at least one selected from the group consisting of Formulas 1-1 to 1-7 shown below, but is not limited thereto.

[Formula 1-1]

[Formula 1-2]

[Formula 1-3]

[Formula 1-4]

[Formula 1-5]

[Chemical Formula 1-6]

[Chemical Formula 1-7]

In the present invention, the mixed lithium salt includes LiPF ₆ in addition to lithium bis (fluorosulfonyl) imide. In one embodiment of the present invention, the lithium bis (fluorosulfonyl) imide in the mixed lithium salt is used in an amount of 10 mol% to 90 mol% or more based on 100 mol% of the total of lithium bis (fluorosulfonyl) imide and LiPF ₆ From 25 mol% to 90 mol%, or from 40 mol% to 90 mol%.

Although lithium bis (fluorosulfonyl) imide is chemically stable, it has a low resistance to oxidation at the cathode and may corrode aluminum, which is the current collector of the cathode, and it is preferable to lower this risk by mixing with other lithium salts . In addition, LiPF ₆ has superior solubility and ionic conductivity compared to other fluoride Lewis acids, and has excellent material compatibility with copper, which is mainly used as an anode current collector or aluminum cathode current collector. By using lithium bis (fluorosulfonyl) imide and LiPF _{6 in this way} , it is possible to complement the disadvantages of each lithium salt in the secondary battery and to expect a synergistic effect depending on the combination of them.

When the mixing ratio of lithium bis (fluorosulfonyl) imide is out of the above range of mol%, a side reaction in the electrolyte may occur excessively during charging / discharging of the battery, and swelling may occur. Specifically, when the lithium bis (fluorosulfonyl) imide does not fall within the above range, the process of forming the SEI film in the lithium ion battery and the process of inserting lithium ion solvated by propylene carbonate between the cathodes The effect of improving the low-temperature output of the secondary battery and improving the cycle characteristics and the capacity characteristics after high-temperature storage are insignificant due to peeling of the negative electrode surface layer (for example, carbon surface layer) and decomposition of the electrolytic solution .

According to a specific embodiment of the present invention, the mixed lithium salt containing lithium bis (fluorosulfonyl) imide has a concentration of 0.1M to 1.5M in the electrolytic solution. If the concentration of the mixed lithium salt is less than 0.1 M, the effect of improving the low-temperature output and improving the high-temperature cycle characteristics of the lithium secondary battery is insignificant. If the concentration of the mixed lithium salt exceeds 1.5 M, A side reaction in the electrolytic solution may occur excessively and swelling may occur.

According to a specific embodiment of the present invention, the mixed lithium salt may further include a lithium salt which is commonly used in the art. Specific examples of such auxiliary lithium salts include LiBF ₄ , LiAsF ₆ , LiSbF ₆ , LiAlO ₄ , LiAlCl ₄ , LiClO _4, and the like, and may include at least one of them. In the present invention, the content of the auxiliary lithium salt is preferably 0.1 to 1.5 mol% in 100 mol% of the mixed lithium salt.

In the present invention, the electrolyte contains fluoroethylene carbonate (FEC) as an additive for forming SEI film. In the present invention, the fluoroethylene carbonate (FEC) includes a compound represented by the following general formula (2).

 (2)

In Formula 2, at least one of R ¹ to R ⁴ is fluorine, or at least one is a C ₁ to C ₆ alkyl group, a C ₆ to C ₁₂ aryl group, a C ₂ to C ₆ alkenyl group, Sulfonate group.

SEI film is mainly in the also known to be composed of an inorganic compound such as LiF, LiCO _3, Li ₂ O, LiOH, lithium bis (sulfonyl fluorophenyl) imide in liquid electrolyte using a lithium salt, the fluorinated ethylene carbonate When the compound is added, its rapid decomposition accelerates the formation of LiF to form the SEI film.

In the present invention, the fluorethylene carbonate is 0.01 to 2% by weight, or 0.01 to 1.5% by weight, or 0.1 to 1.5% by weight, or 0.1 to 1% by weight, or 0.5 to 1% by weight, based on 100% by weight of the electrolytic solution.

If the content of the additive is too small, it may be consumed during the operation of the initial rechargeable battery, resulting in deterioration of life during charge / discharge or long-term storage. If the content of the additive is too large, adverse effects on the capacity and stability characteristics of the battery I can go crazy.

In addition to the compound of Formula 2, LiBF ₄ , One or more auxiliary additives selected from the group consisting of LiSbF ₆ , LiAsF ₆ , lithium oxalyldifluoroborate (LiODFB), LiBOB and propensulfone (PRS) may be further included.

In the present invention, it is preferable that the non-aqueous organic solvent is capable of minimizing decomposition due to an oxidation reaction or the like during charging and discharging of the battery, and capable of exhibiting desired properties together with the above-mentioned lithium salt and additives. Examples of the non-aqueous organic solvent include cyclic carbonates, linear carbonates, esters, ethers, and ketones. These may be used alone, or two or more of them may be used in combination.

Among these organic solvents, a carbonate-based organic solvent can be preferably used, and the cyclic carbonate is selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC) 1,2-butylene carbonate, Propylene carbonate, 2-pentylene carbonate, and 2,3-pentylene carbonate, or a mixture of two or more thereof, and the linear carbonate is selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate DPC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC) and ethyl propyl carbonate (EPC), or a mixture of two or more thereof.

The ester solvent is, for example, methyl acetate, ethyl acetate, propyl acetate, methyl propionate (MP), ethyl propionate (EP), gamma -butyrolactone, gamma -valerolactone, Lactone,? -Valerolactone,? -Caprolactone, and the like.

The present invention also provides a lithium ion secondary battery comprising an electrolyte solution having the above-described characteristics.

In one embodiment of the present invention, the lithium ion secondary battery includes an electrode assembly including an anode, a cathode, and a separator interposed between the anode and the cathode, and an electrolyte, wherein the electrolyte is an electrolyte solution will be.

The negative electrode may be used as the negative electrode active material without any particular limitation as long as lithium ions can be occluded and released. In the present invention, the negative electrode active material preferably includes a carbon-based material. Non-limiting examples of such carbon-based materials include low-crystalline carbon selected from the group consisting of soft carbon and hard carbon; Or natural graphite, kish graphite, pyrolytic carbon, mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches, and petroleum And at least one high crystalline carbon selected from the group consisting of petroleum or coal tar pitch derived cokes.

The negative electrode active material may be selected from the group consisting of lithium titanium oxide, Li _x Fe ₂ O ₃ (0? _X? 1), Li _x WO ₂ (0? _X? 1), Sn _x Me _1-x Me _{y y z} Mn, Fe, Pb and Ge; Me ': Al, B, P, Si, Group 1, Group 2 and Group 3 elements of the periodic table, Halogen; 0 <x? 1; 1? Y? ) Metal complex oxide; 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, Bi ₂ O ₅ and the like; Conductive polymers such as polyacetylene; Li-Co-Ni-based materials may be used singly or in combination with the carbon-based materials.

The positive electrode is made of LiMn _2-a Ni _a O ₄ (0 <a <2) _, Li _a Ni _x Mn _y Co _z O ₄ (0.8≤a <1.2, 0.2≤x <1, 0 <y <1 , 0 <z <1, x + y + z = 1), lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ); Li _{1 + x} Mn _2-x O ₄ (x is 0 to 0.33), lithium manganese oxides such as LiMnO ₃ , LiMn ₂ O ₃ and LiMnO ₂ ; Lithium copper oxide (Li ₂ CuO ₂ ); Vanadium oxides such as LiV ₃ O ₈ , LiFe ₃ O ₄ , V ₂ O ₅ and Cu ₂ V ₂ O ₇ ; LiNi _1-x M _x O ₂ (M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, x = 0.01 to 0.3); Li ₂ Mn ₃ MO ₈ (M = Fe, Co, Ni, Cu, Al, or the like) LiMn _2-x M _x O ₂ (M = Co, Ni, Fe, Cr, Zn), or LiM _1/6 Mn _11/6 O ₄ (M: Co, Al, or Ni); LiMn ₂ O _{4 in} which a part of Li in the formula is substituted with an alkaline earth metal ion; Disulfide compounds; Fe ₂ (MoO ₄ ) ₃ , and the like. However, the present invention is not limited to these. As a specific example, the cathode active material may be LiNi _1/3 Mn _1/3 Co _1/3 O ₄ , LiNi _0.5 Mn _1.5 O ₄ or LiM _1/6 Mn _11/6 O ₄ (where M is Co, Al, or Ni) will be.

The separation membrane is interposed between the anode and the cathode, and an insulating thin film having high ion permeability and mechanical strength can be used. The pore diameter of the separator is generally 0.01 to 10 mu m and the thickness is generally 5 to 300 mu m. Such separation membranes include, for example, olefinic polymers such as polypropylene, which are chemically resistant and hydrophobic; A sheet or nonwoven fabric made of glass fiber, polyethylene or the like is used. According to a specific embodiment of the present invention, the separation membrane may be a composite separation membrane in which a mixed slurry of organic binder and inorganic particles is coated on one side or both sides of the membrane. The inorganic particles are characterized by being able to complement the heat resistance and / or the mechanical strength of the separation membrane. The inorganic particles are not particularly limited as long as the oxidation and / or reduction reaction does not occur in the operating voltage range of the applied electrochemical device (for example, about 0 to about 5 V based on Li / Li + of the lithium ion battery) nitride particles such as aluminum nitride, boron nitride;-boehmite, aluminum oxide (alumina), silicon oxide, magnesium oxide (magnesia), titanium oxide (titania), BaTiO _3, ZrO, alumina, calcium oxide, oxides such as silica composite oxide particles ; Covalent crystal grains such as silicon and diamond; insoluble ionic crystal grains such as barium sulfate, calcium fluoride and barium fluoride; and fine clay particles such as talc and montmorillonite. However, the present invention is not limited thereto.

In addition, other components such as the current collector included in the electrochemical device such as the anode and / or the cathode can be easily manufactured by a process and / or a method known in the art.

In addition, the secondary battery of the present invention can be manufactured by storing and sealing the electrode assembly in which the positive electrode and the negative electrode are alternately stacked with the separator, together with an electrolytic solution, on a casing such as a battery case, and a manufacturing method thereof is generally used in this technical field The present invention can be applied without any particular limitation.

Meanwhile, the lithium ion secondary battery according to the present invention can be used not only in a battery cell used as a power source of a small device but also as a unit cell in a middle- or large-sized battery module including a plurality of battery cells used as a power source for a medium- Lt; / RTI &gt; Preferred examples of the above medium to large devices include a power tool that is powered by an electric motor and moves; An electric vehicle including an electric vehicle (EV), a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), and the like; An electric motorcycle including an electric bike (E-bike) and an electric scooter (E-scooter); An electric golf cart, and the like, but the present invention is not limited thereto.

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

Example

&Lt; Example 1 >

86% by weight of a positive electrode active material (LixN _0.4 M _0.2 C _0.2 O ₄ ), 8% by weight of Super-P (a conductive agent) and 6% by weight of PVdF (binder) were added to NMP to prepare a positive electrode mixture slurry. This was coated on one side of an aluminum foil, dried and pressed to prepare a positive electrode.

A negative electrode mixture slurry was prepared by adding 93.5 wt% of soft carbon, 2 wt% of Super-P (conductive agent), 3 wt% of SBR (binder) and 1.5 wt% of a thickener as a negative active material to H ₂ O as a solvent, Coating, drying, and pressing on one side of the cathode

.

An electrode assembly was prepared by laminating the positive electrode and the negative electrode using Celgard TM as a separator.

A mixed solvent of ethylene carbonate and ethyl methyl carbonate at a volume ratio of 4: 6 was prepared as an electrolyte, and a mixed lithium salt of lithium bis (fluorosulfonyl) imide and LiPF ₆ was added at a concentration of 0.5M. The content ratio of lithium bis (fluorosulfonyl) imide and LiPF ₆ in the mixed lithium salt was 80 mol%: 20 mol%. Further, FEC was added to the electrolytic solution so as to be 1.0 wt%. The lithium nonaqueous electrolyte solution was injected to prepare a lithium secondary battery.

&Lt; Example 2 >

A mixed solvent in which ethylene carbonate and ethyl methyl carbonate were mixed as an electrolyte at a ratio of 4: 6 by volume was prepared, and a mixed lithium salt of lithium bis (fluorosulfonyl) imide and LiPF ₆ was added at a concentration of 1.5M. The content ratio of lithium bis (fluorosulfonyl) imide and LiPF ₆ in the mixed lithium salt was 80 mol%: 20 mol%. Further, FEC was added to the electrolytic solution so as to be 1.0 wt%. A lithium ion secondary battery was produced in the same manner as in Example 1 except that the composition of the electrolytic solution was changed as described above.

<Comparative Example>

A lithium ion secondary battery was produced in the same manner as in Example 1, except that fluoroethylene carbonate was not added to the electrolytic solution.

<Life characteristics>

The lithium batteries prepared in Examples 1 and 2 and Comparative Example were charged to 1 C until the voltage reached 4.15 V (Vs. Li), and discharged again until the voltage reached 2.5 V at the same current. Subsequently, charging and discharging were repeated 1000 times in the same current and voltage section. The charge and discharge tests were carried out twice at 25 ° C and 45 ° C for each cell. The resistance increase rate and the capacity retention rate were measured and summarized as shown in the graphs shown in FIGS. 1 and 2. In FIG. 1 and FIG. 2, B is shown in Example 1, C is shown in Example 2, and A is shown in Comparative Example. The capacity retention rate is defined by the following equation (1).

<Formula 1>

Capacity retention rate (%) = [50 ^th cycle discharge capacity / 2 ^nd cycle discharge capacity] X 100

1 and 2, the batteries of Examples 1 and 2 of the present invention exhibited excellent life characteristics in terms of capacity retention rate and resistance increase rate at room temperature and high temperature, respectively, as compared with the batteries of Comparative Examples. Specifically, in the case of the capacity retention rate, the batteries of Examples 1 and 2 were effective at about 3.6%, and the batteries of Examples 1 and 2 were about 13% more effective than the batteries of Comparative Examples in terms of the resistance increase rate.

<Low-temperature output>

The cells produced in Examples 1 and 2 and Comparative Example were subjected to a constant output of 100, 110, 120, 130, 140 and 150 W for 2 seconds at -25 ° C. to measure the discharge output. According to this experiment, it was confirmed that the low-temperature output characteristics of the battery of Example 1 were superior to those of Comparative Example by about 8% or more.

Claims (12)

1) non-aqueous organic solvent;
2) lithium bis (fluorosulfonyl) imide and LiPF ₆ as the lithium salt; And
3) fluoroethylene carbonate as an additive for SEI film formation;
Wherein the content of the SEI film forming additive is 0.01 to 2% by weight based on 100% by weight of the electrolyte solution.
The method according to claim 1,
Wherein the lithium bis (fluorosulfonyl) imide is a compound represented by the following formula (1): &lt; EMI ID =
[Chemical Formula 1]

Wherein Rf ₁ and Rf ₂ are each fluorine or fluoroalkyl having 1 to 4 carbon atoms, or Rf ₁ and Rf ₂ are linked to each other to form a ring having a fluoroalkylene group having 1 to 4 carbon atoms.
3. The method of claim 2,
Wherein the compound represented by Formula 1 is at least one selected from the group consisting of Formulas 1-1 to 1-7 shown below.
[Formula 1-1]

[Formula 1-2]

[Formula 1-3]

[Formula 1-4]

[Formula 1-5]

[Chemical Formula 1-6]

[Chemical Formula 1-7]

The method according to claim 1,
Wherein the fluoroethylene carbonate comprises a compound represented by the following formula (2): &lt; EMI ID =
(2)

In Formula 2, at least one of R ¹ to R ⁴ is fluorine, or at least one is a C ₁ to C ₆ alkyl group, a C ₆ to C ₁₂ aryl group, a C ₂ to C ₆ alkenyl group, Sulfonate group.
The method according to claim 1,
The electrolyte solution may further contain at least one selected from the group consisting of LiBF ₄ , LiSbF ₆ , LiAsF ₆ , lithium oxalyldifluoroborate (LiODFB), LiBOB and propensulfone (PRS) And an electrolyte solution for a lithium ion secondary battery.
The method according to claim 1,
The electrolyte is _{LiBF 4, LiAsF 6, LiSbF 6} , LiAlO 4, LiAlCl 4 , and a lithium salt LiClO _4, and LiClO _{4. The} electrolytic solution for a lithium ion secondary battery according to claim 1, further comprising at least one selected from the group consisting of LiClO ₄ and LiClO ₄ .
The method according to claim 1,
Wherein the non-aqueous organic solvent is at least one selected from the group consisting of cyclic carbonates, linear carbonates, esters, ethers, and ketones.
The method according to claim 1,
Wherein the lithium bis (plurosulfonyl) imide is mixed at a ratio of 10 mol% to 90 mol% based on 100 mol% of the total of lithium bis (fluorosulfonyl) imide and LiPF ₆ .
a) an electrode assembly including a cathode, an anode, and a separator interposed between the cathode and the anode; And b) an electrolytic solution, wherein the electrolyte b) is according to any one of claims 1 to 7.
10. The method of claim 9,
The negative electrode is made of a carbon-based active material such as a carbon-introducing material, lithium titanium oxide, Li _x Fe ₂ O ₃ (0? _X? 1), Li _x WO ₂ (0? _X? 1), Sn _x Me _1-x Me _{y y} O _z (Me: Mn, Fe, Pb, Ge; Me ': Al, B, P, Si, Group 1, Group 2 or Group 3 elements of the periodic table, Halogen; 0? x? 1; A lithium metal, a lithium-based alloy, a silicon-based alloy, and a tin-based alloy.
10. The method of claim 9,
The positive electrode includes LiNi _1/3 Mn _1/3 Co _1/3 O ₄ , LiNi _0.5 Mn _1.5 O ₄ , And LiM _1/6 Mn _11/6 O ₄ (M is Co, Al, or Ni).
A battery pack comprising the lithium ion secondary battery according to any one of claims 9 to 11 as a unit battery.

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