KR20170038736A - Non-aqueous electrolyte solution and lithium secondary battery comprising the same - Google Patents

Abstract

The present invention relates to a non-aqueous electrolyte comprising a non-aqueous organic solvent, lithium bis(fluorosulfonyl)imide (LiFSI), and a terphenyl compound, and a lithium secondary battery comprising the same. The lithium secondary battery of the present invention, comprising the non-aqueous electrolyte of the present invention, can exhibit excellent low-temperature and room temperature output characteristics, high-temperature and room temperature cycle characteristics, capacity characteristics after storage at a high temperature, and overcharge short characteristics at a low SOC region.

Description

TECHNICAL FIELD [0001] The present invention relates to a non-aqueous electrolytic solution and a lithium secondary battery comprising the same. BACKGROUND ART < RTI ID = 0.0 >

The present invention relates to a non-aqueous electrolytic solution comprising a non-aqueous organic solvent, lithium bis (fluorosulfonyl) imide (LiFSI) and a terphenyl compound, and a lithium secondary battery comprising the same.

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 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 and deintercalating lithium ions from the lithium metal oxide of the anode into the graphite electrode of the cathode. 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. The ion tunnel serves to prevent the collapse of the structure of the carbon anode by co-intercalating the organic solvent of the electrolytic solution having a large molecular weight moving together by solvation of lithium ion together with the carbon anode do.

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 .

On the other hand, various non-aqueous organic solvents have been used for electrolytic solutions. For example, although propylene carbonate is mainly used as a non-aqueous organic solvent, it has a problem that it can cause irreversible decomposition reaction with a graphite material. In order to replace this, an ethylene / 3-component nonaqueous organic solvent including ethylene carbonate (EC) has been used. However, since ethylene carbonate has a high melting point, the use temperature is limited, and there is a problem that battery performance may be considerably deteriorated at a low temperature.

KR 2009-0030237 A

The object of the present invention is to provide a nonaqueous electrolytic solution capable of improving low temperature and room temperature output characteristics as well as improving room temperature and high temperature cycle characteristics and high temperature storage capacity characteristics and exhibiting an overcharge short circuit effect, And a lithium secondary battery comprising the same.

In order to solve the problems to be solved, the present invention provides a non-aqueous electrolytic solution comprising a non-aqueous organic solvent, lithium bis (fluorosulfonyl) imide (LiFSI) and a terphenyl compound .

The present invention also relates to a positive electrode comprising a positive electrode active material; A negative electrode comprising a negative electrode active material; A separator interposed between the anode and the cathode; And a non-aqueous electrolyte according to the present invention, wherein the cathode active material is a manganese spinel-based active material, a lithium metal oxide, or a mixture thereof.

The nonaqueous electrolyte of the present invention can improve the low temperature and room temperature output characteristics by forming a solid SEI film at the cathode at the time of initial charging of the lithium secondary battery including the lithium ion secondary battery of the present invention and can improve the high temperature and room temperature cycle characteristics, Can be improved. In the case of the lithium secondary battery including the nonaqueous electrolyte of the present invention, a film capable of protecting the positive electrode is formed near 4.45 V, whereby an overcharging short-circuiting effect in a low SOC region can be exhibited.

FIG. 1 is a graph showing the overcharge performance evaluation results of the lithium secondary batteries manufactured in Example 1 and Comparative Example 5, respectively.
2 is a graph showing the overcharging performance evaluation results of the lithium secondary batteries manufactured in Example 8 and Comparative Example 10, respectively.

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 of the present invention includes a non-aqueous organic solvent, lithium bis (fluorosulfonyl) imide (LiFSI), and terphenyl compound.

Since the non-aqueous electrolytic solution contains lithium bisfluorosulfonylimide in the non-aqueous organic solvent, a solid SEI film is formed at the cathode at the time of initial charging, thereby improving the low temperature and room temperature output characteristics and, at the same time, The capacity of the lithium secondary battery can be improved at the same time by suppressing the decomposition of the surface of the positive electrode and preventing the oxidation reaction of the electrolyte.

In addition, since the non-aqueous electrolytic solution contains a terphenyl compound, the terphenyl compound remains in the electrolytic solution, and when overcharged, the film is oxidized and decomposed at about 4.45 V to form a coating for protecting the positive electrode, And an effect of improving cycle characteristics at room temperature can be exhibited.

In one example of the present invention, the terphenyl compound is specifically selected from the group consisting of ortho-terphenyl, meta-terphenyl, and para-terphenyl Or more, and more specifically, ortho-terphenyl.

The content of the terphenyl compound may be 0.5 to 10% by weight, specifically 1 to 7% by weight, and more preferably 3 to 5% by weight based on the total weight of the nonaqueous electrolyte solution.

When the content of the terphenyl compound is 0.5 wt% or more, an appropriate effect due to the addition of the terphenyl compound can be expected. When the content of the terphenyl compound is 10 wt% or less, the anode / It is possible to improve the overcharge short-circuiting effect and the room temperature cycling characteristic in the low SOC region due to the increase of the resistance of the negative electrode, while preventing the problems such as increasing the irreversible capacity of the battery or increasing the resistance of the negative electrode.

The non-aqueous organic solvent may be any solvent which can minimize decomposition due to an oxidation reaction or the like during the charge and discharge of the battery, exhibit desired properties together with additives, and examples thereof include nitrile solvents, cyclic carbonates, Linear carbonate, ester, ether or ketone. These may be used alone, or two or more of them may be used in combination.

The cyclic carbonate may be any one selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC) Examples of the linear carbonate include 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 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 the like.

The esters may be ethyl propionate (EP), methyl propionate (MP), and mixtures thereof.

The non-aqueous electrolytic solution according to an example of the present invention may include propylene carbonate (PC) and ethylene carbonate (EC) as the non-aqueous organic solvent.

The ethylene carbonate (EC) has been used as a non-aqueous organic solvent for a non-aqueous electrolytic solution in a lithium secondary battery because of its excellent compatibility with a carbon material. However, when EC is used too much, CO ₂ gas is generated due to EC decomposition, which may adversely affect the performance of the secondary battery. In addition, low-temperature characteristics are poor due to high melting point characteristics, There is a problem that the high output characteristic is low.

On the other hand, the nonaqueous electrolytic solution containing propylene carbonate has characteristics of excellent low temperature characteristics and high output characteristics due to high conductivity. However, propylene carbonate causes irreversible decomposition reaction with the graphite material, which limits its use with graphite. In addition, there has been a problem that the capacity of the lithium secondary battery is lowered due to electrode refraction due to propylene carbonate at high temperature cycles depending on the electrode thickness.

Particularly, when propylene carbonate is used as a non-aqueous organic solvent together with a lithium salt such as LiPF ₆ , propylene carbonate is used in a process of forming a SEI film in a lithium secondary battery using a carbon electrode and a process of forming a lithium ion solvated by propylene carbonate An immense amount of irreversible reaction may occur during the insertion between the carbon layers. This may cause problems such as deterioration of battery performance such as cycle characteristics.

Further, when lithium ion solvated by propylene carbonate is inserted into the carbon layer constituting the negative electrode, exfoliation of the carbon surface layer may proceed. This exfoliation can be caused by the gas generated when the solvent is decomposed between the carbon layers causing a large distortion between the carbon layers. The peeling of the surface layer and the decomposition of the electrolyte can proceed continuously. Therefore, when the propylene carbonate electrolyte is used in combination with the carbonaceous anode material, an effective SEI film is not formed and lithium ions may not be inserted.

Therefore, when the amount of the ethylene carbonate and the propylene carbonate is mixed and used as the non-aqueous organic solvent, the conductivity characteristics of the non-aqueous electrolytic solution are improved to improve the output characteristics of the lithium secondary battery and improve the low temperature characteristics And can provide a non-aqueous electrolytic solution excellent in electrochemical affinity with the carbon layer.

In order to overcome the problems of ethylene carbonate and propylene carbonate and to make the best use of the above advantages, the non-aqueous electrolytic solution according to an example of the present invention can be prepared by mixing the propylene carbonate and ethylene carbonate (EC) Specifically in a weight ratio of 1: 0.3 to 1: 1, more specifically in a weight ratio of 1: 0.4 to 1: 0.9.

(PC) and ethylene carbonate (EC) when the non-aqueous organic solvent contains the propylene carbonate (PC) and the ethylene carbonate (EC) in the mixing ratio, The synergistic effect by mixing the non-aqueous organic solvent with the advantages of the solvent can be manifested. According to one example of the present invention, the mixing ratio of the propylene carbonate and the ethylene carbonate (EC) solvent as the non-aqueous organic solvent may have a significant effect on improving both the low temperature and room temperature output and the high temperature storage capacity characteristics.

On the other hand, the non-aqueous electrolyte of the present invention can solve the above-described problems in using lithium carbonate such as LiPF ₆ together with propylene carbonate by combining lithium bisfluorosulfonylimide with lithium bisfluorosulfonylimide.

Specifically, the lithium bisfluorosulfonylimide is added to a non-aqueous electrolytic solution as a lithium salt to improve a low temperature output characteristic by forming a stable and stable SEI film on a negative electrode, The decomposition can be suppressed and the oxidation reaction of the electrolytic solution can be prevented.

The propylene carbonate may be included in an amount of 5 to 60 parts by weight, specifically 10 to 40 parts by weight, based on 100 parts by weight of the total non-aqueous organic solvent. If the amount of the propylene carbonate is less than 5 parts by weight, the swelling phenomenon may be generated in which the thickness of the battery is increased due to the decomposition of the surface of the anode during the high-temperature cycling, It is difficult to form a solid SEI film and the high-temperature characteristics may be deteriorated.

When ethylene carbonate is appropriately adjusted to be within the range of the mixing ratio within the amount of use of the propylene carbonate, an optimal effect can be achieved not only at low temperature and normal temperature output characteristics of the lithium secondary battery of the present invention but also at high temperature storage capacity characteristics have.

The non-aqueous organic solvent may further include a non-aqueous organic solvent other than propylene carbonate (PC) and ethylene carbonate (EC). The non-aqueous organic solvent may minimize decomposition due to an oxidation reaction during charging and discharging of the battery, There is no restriction as long as it can exert the desired characteristics.

Examples of the non-aqueous organic solvent that can be further contained in the non-aqueous electrolyte include organic solvents such as ethyl propionate (EP), methyl propionate (MP), butylene carbonate (BC), 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 .

Meanwhile, the concentration of the lithium bisfluorosulfonylimide in the non-aqueous electrolytic solution may be 0.01 mol / L to 2 mol / L.

Specifically, when the non-aqueous electrolyte according to an example of the present invention comprises propylene carbonate (PC) and ethylene carbonate (EC) as the non-aqueous organic solvent, the concentration of the lithium bisfluorosulfonylimide in the non- May be from 0.1 mol / L to 2 mol / L, and more specifically from 0.5 mol / L to 1.5 mol / L. If the concentration of the lithium bisfluorosulfonylimide is less than 0.1 mol / L, the effect of improving the low-temperature power and improving the high-temperature cycle characteristics of the battery may be insignificant. If the lithium bisfluorosulfonylimide concentration is less than 2 mol / L, excessive side reactions may occur in the electrolyte during charging and 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 further prevent such side reactions, the non-aqueous electrolytic solution of the present invention may further include a lithium salt other than the lithium bisfluorosulfonylimide. Examples of the lithium salt include lithium salts such as LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN ₃ SO ₂ ) ₂ , CF ₃ SO ₃ Li, LiC (CF ₃ SO ₂ ) ₃ and LiC ₄ BO ₈ , or a mixture of two or more thereof.

The mixing ratio of the lithium salt and lithium bisfluorosulfonylimide may be 1: 0.01 to 1: 9 in a molar ratio.

Specifically, when the non-aqueous electrolyte according to an example of the present invention includes propylene carbonate (PC) and ethylene carbonate (EC) as the non-aqueous organic solvent, the mixing ratio of the lithium salt and lithium bisfluorosulfonylimide May be in a molar ratio of 1: 1 to 1: 9. When the mixing ratio of the lithium salt and the lithium bisfluorosulfonylimide is out of the range of the molar ratio, a side reaction in the electrolyte may occur excessively during charging and discharging of the battery, resulting in swelling.

More specifically, when the non-aqueous electrolyte according to an example of the present invention includes propylene carbonate (PC) and ethylene carbonate (EC) as the non-aqueous organic solvent, the mixing ratio of the lithium salt and lithium bisfluorosulfonylimide May be in a molar ratio of 1: 6 to 1: 9. For example, when the mixing ratio of the lithium salt and the lithium bisfluorosulfonylimide is 1: 6 or more, the process of forming the SEI film in the lithium ion battery and the process of forming the lithium ion solvated by propylene carbonate and ethylene carbonate It is possible to prevent a large amount of irreversible reaction from occurring in the process of inserting between the negative electrodes and to prevent the peeling of the negative electrode surface layer (for example, carbon surface layer) and the decomposition of the electrolyte solution to improve the low temperature output of the secondary battery, The cycle characteristics and the capacity characteristics can be improved.

The content of the terphenyl compound may be controlled according to the amount of lithium bisfluorosulfonylimide added, and the lithium bisfluorosulfonylimide and terphenyl compound may be used in a weight ratio of 1: 0.01 to 1:10 have.

Specifically, when the non-aqueous electrolyte according to an exemplary embodiment of the present invention includes propylene carbonate (PC) and ethylene carbonate (EC) as the non-aqueous organic solvent, the lithium bisfluorosulfonylimide and terphenyl compound have 1 : 0.01 to 1: 1, and may be used in a weight ratio of 1: 0.02 to 1: 0.95, more specifically, in a weight ratio of 1: 0.04 to 1: 0.91. When the lithium bis-fluorosulfonyl imide and the terphenyl compound are used in a weight ratio of 1: 0.01 to 1: 1, the lithium secondary battery, which can be generated by the addition of lithium bisfluorosulfonylimide, The terphenyl compound can appropriately suppress the side reaction in the electrolytic solution when the battery is charged and discharged.

The present invention also relates to a positive electrode comprising a positive electrode active material; A negative electrode comprising a negative electrode active material; A separator interposed between the anode and the cathode; And the nonaqueous electrolyte solution, wherein the cathode active material comprises a manganese spinel-based active material, a lithium metal oxide, or a mixture thereof.

The lithium metal oxide may be selected from the group consisting of a lithium-manganese-based oxide, a lithium-nickel-manganese-based oxide, a lithium-manganese-cobalt oxide and a lithium-nickel-manganese-cobalt oxide. Specifically, the cathode active material may be LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , Li _{1 + x} (Ni _a Co _b Mn _c ) O ₂ (where 0.55 a 0.65, 0.18 _b 0.22, 0.18≤c≤0.22, -0.2≤x≤0.2, x + a + b + c = 1), Li (Ni a 'Co b' Mn c ') O 2 ( where, 0 <a'<1, 0 < b '<1, 0 <c '<1, a '+ b' + c '= 1), LiNi 1 - Y Co Y O 2 ( _{where, 0≤Y <1), LiCo 1} - Y' Mn Y ' O ₂ (where, 0≤Y '<1), LiNi 1-Y "Mn Y" O 2 ( where, 0≤Y "<1), Li (Ni d Co e Mn f) O 4 (0 <d < 2, 0 <e <2, 0 <f <2, d + e + f = 2), LiMn 2 - z Ni z O 4 ( where, 0 <Z <2), LiMn 2 - z 'Co z' O ₄ (where 0 &lt; Z '&lt; 2).

In one embodiment of the present invention, the lithium metal oxide may be a lithium-nickel-manganese-cobalt oxide, and specifically, the lithium-nickel-manganese-cobalt oxide may include an oxide represented by the following formula .

[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, -0.2? X? 0.2, and x + a + b + c = 1 in Formula 1).

When the lithium-nickel-manganese-cobalt oxide is used as a cathode active material, it may be combined with lithium bisfluorosulfonylimide included in the non-aqueous electrolyte to have a synergistic effect. The positive electrode active material of lithium-nickel-manganese-cobalt oxide has a phenomenon in which Li + ions and Ni +2 ions in the layered structure of the positive electrode active material in the charge / discharge process are reversed as the content of Ni in the transition metal increases cation mixing occurs and the structure of the cathode active material is collapsed. As a result, the cathode active material undergoes side reaction with the electrolyte, or elution of transition metal occurs. 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.

Accordingly, a lithium secondary battery according to an exemplary embodiment of the present invention uses a non-aqueous electrolytic solution containing LiFSI together with the cathode active material of Formula 1 to form a layer of LiFSI- It is possible to secure a sufficient nickel transition metal amount for securing the capacity of the positive electrode active material while suppressing the phenomenon of cation mixing of negative ions and Ni +2 ions. The lithium secondary battery according to an embodiment of the present invention includes a non-aqueous electrolytic solution containing LiFSI together with the oxide represented by the formula (1), thereby effectively suppressing side reactions between the electrolyte and the anode, and dissolution of metal .

When the ratio of the oxide represented by the formula (1) to the Ni transition metal exceeds 0.65 (a > 0.65), excessive Ni is contained in the positive electrode active material, so that Li + Ion and Ni +2 may not suppress the cation mixing phenomenon of ions.

When an excessive amount of Ni transition metal is contained in the cathode active material, nickel transition metal having a d orbital in an environment of high temperature or the like must have an octahedron structure at the time of coordination according to the oxidation number variation of Ni, Or the oxidation number fluctuates (nonuniformization 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, 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.

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-power 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.

When the lithium secondary battery according to an exemplary embodiment of the present invention includes the oxide represented by Formula 1 as the cathode active material, the concentration of the lithium bisfluorosulfonylimide in the non-aqueous electrolytic solution is preferably 0.01 mol / L to 2 mol / L And may specifically be 0.01 mol / L to 1 mol / L. If the concentration of the lithium bisfluorosulfonylimide is less than 0.1 mol / L, the effect of improving the low-temperature power and improving the high-temperature cycle characteristics of the lithium secondary battery is insignificant, and if the concentration of the lithium bisfluorosulfonylimide If it exceeds 2 mol / L, side reactions within the electrolyte may occur excessively during charging and discharging of the battery, causing swelling phenomenon, and corrosion of the positive electrode made of metal or negative electrode current collector in the electrolyte may be caused.

In order to further prevent such side reactions, the non-aqueous electrolytic solution of the present invention may further include a lithium salt other than the lithium bisfluorosulfonylimide. Examples of the lithium salt include lithium salts such as LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN ₃ SO ₂ ) ₂ , CF ₃ SO ₃ Li, LiC (CF ₃ SO ₂ ) ₃ and LiC ₄ BO ₈ , or a mixture of two or more thereof.

When the lithium secondary battery according to an exemplary embodiment of the present invention includes the oxide represented by Formula 1 as the cathode active material, the mixing ratio of the lithium salt and lithium bisfluorosulfonylimide is 1: 0.01 to 1: 1 . 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.

Since the content of the terphenyl compound can be controlled according to the amount of lithium bisfluorosulfonylimide added, when the lithium secondary battery according to an embodiment of the present invention includes the oxide represented by Formula 1 as the cathode active material, The bisfluorosulfonyl imide and terphenyl compound may be used in a weight ratio of 1: 0.02 to 1:10, and may specifically be used in a weight ratio of 1: 0.03 to 1: 9, more specifically 1: 0.05 to 1 : 7.5. &Lt; / RTI &gt;

When the lithium bisfluorosulfonyl imide and the terphenyl compound are used in a weight ratio of 1: 0.02 to 1:10, the lithium secondary battery, which can be generated by the addition of lithium bisfluorosulfonyl imide, The terphenyl compound can appropriately suppress the side reaction in the electrolytic solution when the battery is charged and discharged.

When the lithium secondary battery according to an exemplary embodiment of the present invention includes the oxide represented by Formula 1 as the cathode active material, the non-aqueous solvent may minimize the decomposition due to the oxidation reaction during the charge and discharge of the battery, Any solvent capable of exhibiting the desired properties can be used without limitation. For example, nitrile solvents, cyclic carbonates, linear carbonates, esters, ethers or ketones can be used. These may be used alone, or two or more of them may be used in combination.

Specifically, when the lithium secondary battery according to an exemplary embodiment of the present invention includes the oxide represented by Formula 1 as the cathode active material, acetonitrile may be used as the non-aqueous solvent. The lithium-nickel-manganese- The use of the acetonitrile-based solvent can effectively prevent side effects due to the decrease in the stability of the high-output battery due to combination with lithium bisfluorosulfonylimide.

As the negative electrode active material, a carbonaceous anode active material such as a crystalline carbon, an amorphous carbon, or a carbon composite may be used alone or in combination of two or more. Preferably, the carbonaceous active material may be a crystalline carbon and a graphite such as natural graphite and artificial graphite (graphite) carbon.

Specifically, in the lithium secondary battery, the positive electrode or negative electrode may be prepared by mixing a mixture of a positive electrode or negative electrode active material, a conductive material and a binder with a predetermined solvent on a positive electrode or negative electrode current collector to prepare a slurry, Applying the slurry on the current collector, and then drying the slurry.

According to an embodiment of the present invention, the cathode current collector generally has a thickness of 3 to 500 mu m. Such a positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical change in the battery, and may be formed of a material such as stainless steel, aluminum, nickel, titanium, sintered carbon, or a surface of aluminum or stainless steel Treated with carbon, nickel, titanium, silver or the like may be used.

The cathode current collector may have fine irregularities on the surface thereof to increase the adhesive force of the cathode active material, and various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric are possible.

The negative electrode current collector is generally made to have a thickness of 3 [mu] m to 500 [mu] m. Such an anode current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery, and may be formed of a material such as copper, stainless steel, aluminum, nickel, titanium, fired carbon, surface of copper or stainless steel A surface treated with carbon, nickel, titanium, silver or the like, an aluminum-cadmium alloy, or the like can be used. In addition, like the positive electrode collector, fine unevenness can be formed on the surface to enhance the bonding force of the negative electrode active material, and it can be used in various forms such as films, sheets, foils, nets, porous bodies, foams and nonwoven fabrics.

The conductive material used for the positive electrode or negative electrode slurry is usually added in an amount of 1 to 20 wt% based on the total weight of the mixture including the positive electrode or the negative electrode active material. Such a conductive material is not particularly limited as long as it has electrical conductivity without causing chemical changes in the battery, for example, graphite such as natural graphite or artificial graphite; Carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and summer black; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskers such as zinc oxide and potassium titanate; Conductive oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used.

The binder is a component that assists in bonding of the positive electrode or the negative electrode active material with the conductive material and bonding to the current collector, and is usually added in an amount of 1 to 20 wt% based on the total weight of the mixture including the positive electrode or the negative electrode active material . Examples of such binders include polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HEP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate ), Polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer ), Sulfonated EPDM, styrene butylene rubber (SBR), fluorine rubber, various copolymers, and the like.

In addition, preferred examples of the solvent include dimethyl sulfoxide (DMSO), alcohol, N-methylpyrrolidone (NMP), acetone or water, and are removed during drying.

As the separator, a conventional porous polymer film conventionally used as a separator, for example, 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 The porous polymer film made of a polymer may be used alone or in a laminated form, or a nonwoven fabric made of a conventional porous nonwoven fabric such as a glass fiber having a high melting point, polyethylene terephthalate fiber or the like may be used. no.

The battery case to be used in the present invention may be of any type conventionally used in the art and is not limited in its external shape depending on the use of the battery. For example, a cylindrical case, a square type, a pouch type, coin) type.

The lithium 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. Preferable examples of the above medium and large-sized devices include, but are not limited to, electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric power storage systems, and the like.

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

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 1

[Preparation of non-aqueous electrolytic solution]

Aqueous organic solvent having a composition of propylene carbonate (PC): ethylene carbonate (EC): ethyl methyl carbonate (EMC) 3: 3: 4 (volume ratio) and LiPF ₆ based on the total amount of non- 0.1 mol / L was added, and 0.9 mol / L of lithium bis-fluorosulfonylimide and 5 wt% of ortho-terphenyl were added to prepare a non-aqueous electrolytic solution.

 [Production of lithium secondary battery]

, 96% by weight of a mixture of LiMn ₂ O ₄ and Li (Ni _0.33 Co _0.33 Mn _0.33 ) O ₂ as a positive electrode active material, ₂ % by weight of carbon black as a conductive material, 2% by weight of polyvinylidene fluoride (PVdF) % 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.

The 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 material 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 about 10 占 퐉 and dried to prepare a negative electrode, followed by roll pressing to prepare 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

LiPF ₆ Aqueous electrolyte solution and a lithium secondary battery were prepared in the same manner as in Example 1, except that the amount of lithium bisfluorosulfonylimide was changed from 0.14 mol / L and 0.86 mol / L (about 1: 6 molar ratio) .

Example 3

LiPF ₆ Aqueous electrolyte and a lithium secondary battery were prepared in the same manner as in Example 1, except that the amount of lithium bisfluorosulfonylimide was changed to 0.17 mol / L and 0.83 mol / L (about 1: 5 molar ratio) .

Example 4

A non-aqueous electrolytic solution and a lithium secondary battery were prepared in the same manner as in Example 1, except that the ortho-terphenyl was used in an amount of 3% by weight.

Example 5

A nonaqueous electrolytic solution and a lithium secondary battery were prepared in the same manner as in Example 2 except that the ortho-terphenyl was used in an amount of 3% by weight.

Example 6

A non-aqueous electrolytic solution and a lithium secondary battery were prepared in the same manner as in Example 2, except that the ortho-terphenyl was used in an amount of 10% by weight.

Example 7

A non-aqueous electrolytic solution and a lithium secondary battery were prepared in the same manner as in Example 2, except that the ortho-terphenyl was used in an amount of 0.5% by weight.

Comparative Example 1

Except that ethylene carbonate (EC) was not used and a non-aqueous organic solvent having a composition of propylene carbonate (PC): ethyl methyl carbonate (DMC) 3: 7 (volume ratio) was used instead of ethylene carbonate Aqueous electrolyte solution and a lithium secondary battery were prepared.

Comparative Example 2

Except that propylene carbonate (PC) was not used and a non-aqueous organic solvent having a composition of ethylene carbonate (EC): ethyl methyl carbonate (DMC) = 3: 7 (volume ratio) was used instead of propylene carbonate A nonaqueous electrolytic solution and a lithium secondary battery were prepared.

Comparative Example 3

A non-aqueous electrolytic solution and a lithium secondary battery were prepared in the same manner as in Example 1, except that LiFSI and ortho-terphenyl were not used.

Comparative Example 4

A non-aqueous electrolytic solution and a lithium secondary battery were prepared in the same manner as in Example 1, except that LiFSI was not used.

Comparative Example 5

A nonaqueous electrolytic solution and a lithium secondary battery were prepared in the same manner as in Example 1, except that ortho-terphenyl was not used.

Experimental Example 1

<Capacity measurement after high temperature storage>

The lithium secondary batteries of Examples 1 to 7 and Comparative Examples 1 to 5 were charged at 1 C to 4.2 V / 38 mA at a constant current / constant voltage (CC / CV) condition at room temperature, , And the discharge capacity thereof was measured to obtain the capacity of the 0th battery. Then, the lithium secondary batteries of Examples 1 to 7 and Comparative Examples 1 to 5 were stored at 60 占 폚 for 18 weeks and then charged to 1 C at 4.2 V / 38 mA under normal current / constant voltage (CC / CV) Then, the battery was discharged at 2 C to 2.5 V under a constant current (CC) condition, and its discharge capacity was measured to obtain the capacity after 18 weeks.

The capacity after high-temperature storage is calculated as (capacity after 18 weeks / capacity of 0) x 100, and is shown in Table 1 as a percentage value.

Experimental Example 2

<Output measurement after high temperature storage>

The lithium secondary batteries of Examples 1 to 7 and Comparative Examples 1 to 5 were discharged at SOC (charge depth) of 50 to 5 C for 10 seconds at room temperature to calculate a low temperature output with a voltage difference, Respectively. Then, the lithium secondary batteries of Examples 1 to 7 and Comparative Examples 1 to 5 were stored at 60 DEG C for 18 weeks, discharged at a room temperature from 50% at SOC (charge depth) to 5C for 10 seconds, And the output was set as the output after 18 weeks.

The output after high-temperature storage is calculated as (output of the output after 18 weeks / output of 0) x 100 and is shown in Table 1 as a percentage value.

Experimental Example 3

&Lt; Measurement of cell thickness increase rate &

The thicknesses of the lithium secondary batteries of Examples 1 to 7 and Comparative Examples 1 to 5 were measured and after storage at 60 ° C for 18 weeks, the cell thickness increase rate was calculated as (thickness after 18 weeks / ) -100, and the values are shown in Table 1 below.

Experimental Example 4

<Measurement at room temperature>

The lithium secondary batteries of Examples 1 to 7 and Comparative Examples 1 to 5 were charged at 1 C to 4.2 V / 38 mA at a constant current / constant voltage (CC / CV) condition at 25 ° C, V to 2 C, and the discharge capacity thereof was measured. This was repeated 1 to 1000 cycles, and the values calculated as (capacity after 1000 cycles / capacity after 1 cycle) x 100 are shown in Table 1 as normal temperature lifetime characteristics.

Experimental Example 5

<High Temperature Life Measurement>

The lithium secondary batteries of Examples 1 to 7 and Comparative Examples 1 to 5 were charged at 1 C to 4.2 V / 38 mA at a constant current / constant voltage (CC / CV) condition at 45 ° C, V to 2 C, and the discharge capacity thereof was measured. This is repeated 1 to 1000 cycles, and the value calculated by (capacity after 1000 cycles / capacity after one cycle) x 100 is shown in Table 1 as high temperature lifetime characteristics.

LiPF ₆ : LiFSI additive
(weight%) High Temperature Storage Characteristics
(%) Life characteristics
(%) Volume Print Battery Thickness
increase Room temperature High temperature Example 1 1: 9 5 88.4 92.2 9.3 86.2 86.2 Example 2 1: 6 5 88.2 91.3 10.5 85.2 85.4 Example 3 1: 5 5 86.4 90.2 10.8 86.5 84.2 Example 4 1: 9 3 90.1 92.9 8.4 90.2 88.4 Example 5 1: 6 3 98.4 90.2 8.3 91.1 88.1 Example 6 1: 6 10 82.1 91.3 14.2 83.1 80.2 Example 7 1: 6 0.5 85.3 88.1 15.1 84.2 82.6 Comparative Example 1 1: 9 5 80.2 83.6 20.3 48.5 39.2 Comparative Example 2 1: 9 5 79.1 81.4 31.7 75.3 70.2 Comparative Example 3 1: 0 0 76.2 80.1 20.3 77.1 73.2 Comparative Example 4 1: 0 5 75.1 78.3 21.5 80.1 72.3 Comparative Example 5 1: 9 0 84.4 87.3 15.5 82.2 81.5

In Table 1, the additive represents ortho-terphenyl.

As can be seen from the above Table 1, the lithium secondary batteries of Examples 1 to 7 together with the non-aqueous organic solvent containing propylene carbonate (PC) and ethylene carbonate (EC), lithium bisfluorosulfonylimide And Comparative Example 1 which does not include propylene carbonate (PC) as a non-aqueous organic solvent, and Comparative Example 2 which does not contain ethylene carbonate (EC) as a non-aqueous organic solvent. Compared to lithium secondary batteries of Comparative Example 3 which did not contain a sulfonylimide and a terphenyl compound and Comparative Example 3 which did not contain a lithium bisfluorosulfonylimide, they exhibited high capacity and output even after high temperature storage, The rate of increase is also small, indicating excellent high-temperature storage characteristics, and maintaining a high capacity even after 1000 cycles at room temperature and high temperature, The property was found to represent.

On the other hand, the effects of addition of lithium bisfluorosulfonylimide were examined. When the lithium secondary batteries of Example 1 and Comparative Example 4 in which only lithium bisfluorosulfonylimide was added were compared, It was confirmed that the lithium secondary battery of Example 1 exhibited remarkably excellent high-temperature storage characteristics and lifetime characteristics according to addition of lithium bis-fluorosulfonylimide. In addition, in the case of the lithium secondary battery of Example 1 in which LiPF ₆ : LiFSI had a ratio of 1: 9, the effect of the addition of lithium bisfluorosulfonylimide in Example 3 Which is superior to the lithium secondary battery of the present invention. In the case of the lithium secondary battery of Example 2 in which the ratio of LiPF ₆ : LiFSI was 1: 6, as compared with the lithium secondary battery of Example 3, It was confirmed that the high temperature storage characteristics and the life characteristics were excellent.

The effects of the addition of the terphenyl compound were compared with those of the lithium secondary batteries of Examples 1 and 4 and Comparative Example 5 in which only terphenyl compounds were added. The secondary battery exhibited better high-temperature storage characteristics and lifetime characteristics with the addition of ortho-terphenyl, and the rate of cell thickness increase was also remarkably low.

On the other hand, in the case of Examples 1 to 5 in which the organophosphorous compound was added in an amount of 3 to 5% by weight based on the total weight of the non-aqueous electrolytic solution, % Of Example 6 and 0.5% by weight of ortho-terphenyl. In addition, when the content of the terphenyl compound is at least 3% by weight based on the total weight of the nonaqueous electrolytic solution through comparison between Examples 1 and 3 and comparison between Examples 4 and 5, it is preferable that lithium bisfluorosulfonylimide It was confirmed that as the content ratio of terphenyl compound is decreased, the effect is generally excellent.

Experimental Example 5

&Lt; Evaluation of overcharging &

The lithium secondary batteries of Example 1 and Comparative Example 5 were overcharged to 8.3 V under a constant current / constant voltage (CC / CV) condition at 1 C (775 mAh) / 12 V from the charged state at 25 ° C, And voltage change were measured and shown in Fig.

1, the lithium secondary battery of Example 1 including a nonaqueous electrolyte containing an ortho-terphenyl additive is superior to the lithium secondary battery of Comparative Example 5 which does not contain the ortho-terphenyl additive, It was confirmed that the SOC at the time of short circuit was lower and the temperature of the battery was lower.

Example 8

[Preparation of electrolytic solution]

Aqueous organic solvent having a composition of ethylene carbonate (EC): ethyl methyl carbonate (EMC) 3: 7 (by volume) and LiPF ₆ based on the total amount of non-aqueous electrolytic solution as a lithium salt 0.9 mol / l, and 0.1 mol / l of lithium bis-fluorosulfonylimide and 3% by weight of ortho-terphenyl were added to prepare a nonaqueous electrolytic solution.

[Production of lithium secondary battery]

92% by weight of Li (Ni _0.6 Co _0.2 Mn _0.2 ) O ₂ as a cathode active material, 4% by weight of carbon black as a conductive material and 4% by weight of polyvinylidene fluoride (PVdF) -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 prepare a positive electrode, followed by roll pressing to prepare a positive electrode.

The 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 material 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 탆 and dried to prepare a negative electrode, followed by roll pressing to prepare 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 9

LiPF ₆ Aqueous electrolyte and a lithium secondary battery were prepared in the same manner as in Example 8, except that the amount of lithium bisfluorosulfonylimide was changed to 0.7 mol / L and the amount of lithium bisfluorosulfonylimide was changed to 0.3 mol / L.

Example 10

LiPF ₆ Aqueous electrolyte solution and a lithium secondary battery were prepared in the same manner as in Example 8, except that the amount of lithium bisfluorosulfonylimide was changed to 0.5 mol / L and the amount of lithium bisfluorosulfonylimide was changed to 0.5 mol / L.

Example 11

A non-aqueous electrolytic solution and a lithium secondary battery were prepared in the same manner as in Example 9 except that the ortho-terphenyl was used in an amount of 5% by weight.

Example 12

A non-aqueous electrolytic solution and a lithium secondary battery were prepared in the same manner as in Example 9, except that 10% by weight of ortho-terphenyl was used.

Example 13

A non-aqueous electrolytic solution and a lithium secondary battery were prepared in the same manner as in Example 9, except that the ortho-terphenyl was used in an amount of 1% by weight.

Comparative Example 6

A nonaqueous electrolytic solution and a lithium secondary battery were prepared in the same manner as in Example 9, except that Li (Ni _0.5 Co _0.3 Mn _0.2 ) O ₂ was used as the cathode active material.

Comparative Example 7

A nonaqueous electrolytic solution and a lithium secondary battery were prepared in the same manner as in Example 9, except that Li (Ni _0.8 Co _0.1 Mn _0.1 ) O ₂ was used as the cathode active material.

Comparative Example 8

A non-aqueous electrolytic solution and a lithium secondary battery were prepared in the same manner as in Example 9, except that LiCoO ₂ was used as the cathode active material.

Comparative Example 9

A nonaqueous electrolytic solution and a lithium secondary battery were produced in the same manner as in Example 9, except that Li (Ni _0.5 Co _0.3 Mn _0.2 ) O ₂ was used as the cathode active material and LiFSI and ortho-terphenyl were not used. Respectively.

Comparative Example 10

A non-aqueous electrolytic solution and a lithium secondary battery were prepared in the same manner as in Example 9 except that LiFSI and ortho-terphenyl were not used.

Comparative Example 11

LiPF ₆ Aqueous electrolyte solution and a lithium secondary battery were prepared in the same manner as in Example 8 except that the amount of lithium bisfluorosulfonylimide was changed to 0.3 mol / L and the amount of lithium bisfluorosulfonylimide was changed to 0.7 mol / L.

Experimental Example 6

<Capacity characteristics after high temperature storage>

The secondary batteries prepared in Examples 8 to 13 and Comparative Examples 6 to 11 were charged at 1 C to 4.2 V / 38 mA under the constant current / constant voltage (CC / CV) condition, C, and the discharge capacity thereof was measured. Then, the secondary batteries prepared in Examples 8 to 13 and Comparative Examples 6 to 11 were stored at 60 DEG C for 16 weeks, and then the secondary batteries were respectively charged at 4.2 V / 38 mA in a constant current / constant voltage (CC / And discharged at 2 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 2 below.

Experimental Example 7

<Output characteristics after high temperature storage>

The outputs of the secondary batteries prepared in Examples 8 to 13 and Comparative Examples 6 to 11 were calculated by using the voltage difference generated when charging and discharging the battery at 60 ° C. for 16 seconds at room temperature and at 5 ° C. for 10 seconds. The results are shown in Table 2 below, with 16-week output (W) / initial output (W) × 100 (%) calculated as a percentage of the output after 16 weeks based on the initial output. The test was performed at 50% SOC (state of charge).

anode
Active material LiPF ₆ : LiFSI additive
(weight%) High Temperature Storage Characteristics
(%) Volume Print Example 8 NMC622 9: 1 3 92.5 93.5 Example 9 NMC622 7: 3 3 94.2 96.1 Example 10 NMC622 5: 5 3 91.3 93.5 Example 11 NMC622 7: 3 5 91.7 92.5 Example 12 NMC622 7: 3 10 88.5 90.2 Example 13 NMC622 7: 3 One 90.3 91.2 Comparative Example 6 NMC532 7: 3 3 87.2 89.2 Comparative Example 7 NMC811 7: 3 3 80.2 85.1 Comparative Example 8 LiCoO ₂ 7: 3 3 91.2 91.5 Comparative Example 9 NMC532 7: 3 0 85.2 87.1 Comparative Example 10 NMC622 7: 3 0 87.2 91.0 Comparative Example 11 NMC622 3: 7 3 86.1 87.3

In Table 2 are NMC622 Li a _{(Ni 0.6 Co 0.2 Mn 0.2)} O 2 a, NMC532 is _{Li (Ni 0.5 Co 0.3 Mn 0.2} ) O 2 a, NMC811 is _{Li (Ni 0.8 Co 0.1 Mn 0.1} ) O 2 , And the additive represents ortho-terphenyl.

As can be seen from the above Table 2, the lithium secondary batteries of Examples 7 to 13 include a non-aqueous electrolytic solution containing both lithium bisfluorosulfonylimide and ortho-terphenyl compound, Indicating high capacity and output. In addition, since the lithium secondary batteries of Examples 8 to 11 include the non-aqueous electrolytic solution containing the lithium bisfluorosulfonylimide and the ortho-terphenyl compound, 9 and 10 lithium secondary batteries.

On the other hand, in comparison between Example 9 and Comparative Examples 6 to 8, Example 9 including Li (Ni _0.6 Co _0.2 Mn _0.2 ) O ₂ as a cathode active material was used as Li (Ni _0.5 Co _0.3 Mn _0.2 ) O ₂ , Li (Ni _0.8 Co _0.1 Mn _0.1 ) O ₂ , and LiCoO ₂ .

In addition, when comparing the Comparative Example 11 and Examples 8 to 10, lithium as the anode active material-nickel-manganese-case comprise a cobalt-based oxide, _{Li (Ni 0.6 Co 0.2 Mn 0.2} ) O 2, in case of LiPF ₆ LiFSI It was confirmed that the high temperature storage characteristics of the lithium secondary battery deteriorated.

Experimental Example 8

&Lt; Evaluation of overcharging &

The lithium secondary batteries of Example 8 and Comparative Example 10 were overcharged to 8.3 V under a constant current / constant voltage (CC / CV) condition at 1 C (775 mAh) / 12 V from the charged state at 25 ° C, And voltage change were measured and shown in Fig.

2, the lithium secondary battery of Example 8 including a non-aqueous electrolytic solution containing an ortho-terphenyl additive is superior to the lithium secondary battery of Comparative Example 10 which does not contain the ortho-terphenyl additive, It was confirmed that the SOC at the time of short circuit was lower and the temperature at the center of the battery was lower.

Claims (20)

A non-aqueous electrolytic solution comprising a non-aqueous organic solvent, lithium bis (fluorosulfonyl) imide (LiFSI) and a terphenyl compound.
The method according to claim 1,
Wherein the terphenyl compound is at least one selected from the group consisting of ortho-terphenyl, meta-terphenyl, and para-terphenyl.
The method according to claim 1,
Wherein the content of the terphenyl compound is 0.5 wt% to 10 wt% based on the total weight of the non-aqueous electrolyte.
The method according to claim 1,
The non-aqueous organic solvent includes propylene carbonate (PC) and ethylene carbonate (EC)
Wherein the mixing ratio of the propylene carbonate to the ethylene carbonate is 1: 0.1 to 2 by weight.
5. The method of claim 4,
The non-aqueous organic solvent may be at least one selected from the group consisting of ethyl propionate (EP), methyl propionate (MP), butylen carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate Wherein the electrolytic solution further comprises any one selected from the group consisting of carbonate (DPC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC) and ethyl propyl carbonate (EPC), or a mixture of two or more thereof.
5. The method of claim 4,
Wherein the non-aqueous electrolytic solution further comprises a lithium salt other than the lithium bisfluorosulfonylimide,
Wherein the mixing ratio of the lithium salt other than lithium bisfluorosulfonylimide to lithium bisfluorosulfonylimide is 1: 1 to 1: 9 in a molar ratio.
The method according to claim 6,
A lithium salt other than the sulfonyl in the lithium-bis-fluoro imide are _{LiPF 6, LiBF 4, LiSbF 6} , LiAsF 6, LiClO 4, LiN (C 2 F 5 SO 2) 2, LiN (CF 3 SO 2) 2, CF ₃ SO ₃ Li, LiC (CF ₃ SO ₂ ) ₃ and LiC ₄ BO ₈ , or a mixture of two or more thereof.
5. The method of claim 4,
Wherein the content of the propylene carbonate is 5 parts by weight to 60 parts by weight based on 100 parts by weight of the total non-aqueous organic solvent.
5. The method of claim 4,
Wherein the lithium bisfluorosulfonylimide has a concentration in the non-aqueous electrolytic solution of 0.1 mol / L to 2 mol / L.
5. The method of claim 4,
Wherein the lithium bisfluorosulfonylimide and terphenyl compound are in a weight ratio of 1: 0.02 to 1: 1.
A cathode comprising a cathode active material; A negative electrode comprising a negative electrode active material; A separator interposed between the anode and the cathode; And
A nonaqueous electrolytic solution according to claim 1,
Wherein the cathode active material comprises a manganese spinel-based active material, a lithium metal oxide, or a mixture thereof.
12. The method of claim 11,
Wherein the lithium metal oxide is selected from the group consisting of a lithium-manganese-based oxide, a lithium-nickel-manganese-based oxide, a lithium-manganese-cobalt oxide and a lithium-nickel-manganese-cobalt oxide.
12. The method of claim 11,
Wherein the lithium metal oxide is a lithium-nickel-manganese-cobalt oxide,
Wherein the lithium-nickel-manganese-cobalt-based oxide comprises 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, -0.2? X? 0.2, and x + a + b + c = 1 in Formula 1).
14. The method of claim 13,
Wherein the non-aqueous electrolytic solution further comprises a lithium salt other than the lithium bisfluorosulfonylimide,
Wherein the mixing ratio of the lithium salt other than lithium bisfluorosulfonylimide and lithium bisfluorosulfonylimide is 1: 0.01 to 1: 1 in a molar ratio.
15. The method of claim 14,
A lithium salt other than the sulfonyl in the lithium-bis-fluoro imide are _{LiPF 6, LiBF 4, LiSbF 6} , LiAsF 6, LiClO 4, LiN (C 2 F 5 SO 2) 2, LiN (CF 3 SO 2) 2, CF ₃ SO ₃ Li, LiC (CF ₃ SO ₂ ) ₃ and LiC ₄ BO ₈ , or a mixture of two or more thereof.
14. The method of claim 13,
Wherein the lithium bis-fluorosulfonylimide and terphenyl compound are in a weight ratio of 1: 0.02 to 1:10.
14. The method of claim 13,
Wherein the lithium bisfluorosulfonylimide has a concentration in the non-aqueous electrolytic solution of 0.01 mol / L to 2 mol / L.
14. The method of claim 13,
Wherein the non-aqueous organic solvent includes a nitrile-based solvent, a linear carbonate, a cyclic carbonate, an ester, an ether, a ketone, or a combination thereof.
19. The method of claim 18,
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) Which is a mixture of two or more selected from the group consisting of carbonate (DEC), dipropyl carbonate (DPC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC) and ethyl propyl carbonate (EPC) battery.
19. The method of claim 18,
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 difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile.

Images