KR20170038743A - Non-aqueous electrolyte solution and lithium secondary battery comprising the same - Google Patents

Abstract

The present invention provides a non-aqueous electrolyte solution comprising: i) a non-aqueous organic solvent including propylene carbonate (PC) and ethylene carbonate (EC); ii) lithium bis(fluorosulfonyl)imide (LiFSI); and iii) a carbodiimide-based compound represented by chemical formula 1: R_1-N=C=N-R_2, wherein R_1 and R_2 alkyl independently having 1 to 12 carbon atoms, or cycloalkyl independently having 3 to 12 carbon atoms. The present invention also provides a lithium secondary battery comprising the same. The non-aqueous electrolyte solution according to the present invention forms a robust SEI membrane on a negative electrode during the initial charging of a lithium secondary battery including the non-aqueous electrolyte solution, thereby improving low-temperature and room-temperature output characteristics, high-temperature and room-temperature cycle characteristics, and capacity characteristics after high-temperature storage. Furthermore, the non-aqueous electrolyte solution can suppress the elution of a positive electrode active material by suppressing the formation of HF, i.e., impurities which can be formed in an electrolyte solution, thereby exhibiting desirable low-temperature output characteristics, improved high-temperature storage characteristics, and improved life characteristics.

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 organic solvent comprising propylene carbonate (PC) and ethylene carbonate (EC); Lithium bis (fluorosulfonyl) imide (LiFSI); And a carbodiimide compound represented by the general formula (1), 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. This ion tunnel serves to prevent the collapse of the structure of the carbon anode by co-intercalating the organic solvent of the electrolyte with the high molecular weight, which is solvated by 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 .

Until now, a variety of non-aqueous organic solvents have been used in non-aqueous electrolytic solutions, and propylene carbonate has been used as a non-aqueous organic solvent. However, this has the problem of causing irreversible decomposition reaction with graphite materials. 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.

On the other hand, when moisture is contained in the lithium secondary battery, the performance of the battery may be deteriorated. In the lithium secondary battery, moisture may be contained in the active material during the manufacturing process, or may be contained in a minute amount in the electrolytic solution. For example, lithium-titanium oxide used as an anode active material has a very low structural change during charging and discharging, and thus has excellent life characteristics due to a zero-strain material, forms a relatively high voltage band, And it has an advantage of having a rapid charging electrode characteristic capable of charging in a few minutes. However, due to the property of absorbing moisture in the air, There is a problem that water contained therein is decomposed to generate a large amount of gas.

In addition, the moisture present in the electrolyte may react with the electrolyte due to the potential energy provided during the charging process, causing the cell to swell due to the generation of gas, which may lower the reliability of the battery. For example, LiPF ₆ lithium The salt reacts with water to form HF, which is a strong acid. The formed HF spontaneously reacts with the electrode active material exhibiting weak basicity, thereby eluting the electrode active material component, resulting in degeneration of the battery, (LiF) is formed to increase the electrical resistance in the electrode and to generate gas to cause a reduction in the life of the battery. Therefore, it is necessary to suppress the formation of HF in the electrolytic solution as much as possible.

KR 2009-0030237 A

It is an object of the present invention to improve the low temperature and room temperature output characteristics as well as to improve the room temperature and high temperature cycle characteristics and the high temperature storage capacity characteristics and to suppress the generation of HF, A nonaqueous electrolytic solution capable of reducing the side reaction and suppressing elution of the positive electrode and capable of forming a stable film, and a lithium secondary battery comprising the same.

In order to solve the problems to be solved, the present invention relates to a process for producing a polymer electrolyte membrane, comprising: i) a nonaqueous organic solvent comprising propylene carbonate (PC) and ethylene carbonate (EC); ii) lithium bis (fluorosulfonyl) imide (LiFSI); And iii) a carbodiimide compound represented by the following formula (1).

[Chemical Formula 1]

In Formula 1, R ₁ and R ₂ are each independently alkyl having 1 to 12 carbon atoms or cycloalkyl having 3 to 12 carbon atoms.

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 lithium secondary battery comprising the non-aqueous electrolyte.

The nonaqueous electrolytic solution of the present invention can improve the low temperature and room temperature output characteristics by forming a solid SEI film in the cathode at the time of initial charging of the lithium secondary battery including the same, And further suppresses the formation of HF which is an impurity that can be formed in the electrolyte solution, thereby suppressing the elution of the cathode active material. Therefore, excellent low-temperature output characteristics can be exhibited, and improved high-temperature storage characteristics and life characteristics can be exhibited.

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 comprises i) a non-aqueous organic solvent comprising propylene carbonate (PC) and ethylene carbonate (EC); ii) lithium bis (fluorosulfonyl) imide (LiFSI); And iii) a carbodiimide compound represented by the following formula (1).

[Chemical Formula 1]

In Formula 1, R ₁ and R ₂ are each independently alkyl having 1 to 12 carbon atoms or cycloalkyl having 3 to 12 carbon atoms.

The term " alkyl " as used herein, unless otherwise indicated, refers to straight, branched, or branched hydrocarbon residues.

The term " cycloalkyl ", as used herein, unless otherwise indicated, refers to cyclic alkyl including cyclopropyl and the like.

According to one example of the present invention, problems caused when propylene carbonate (PC) and ethylene carbonate (EC) are respectively used are solved by controlling the mixing ratio of propylene carbonate (PC) and ethylene carbonate (EC) , The synergistic effect by mixing the non-aqueous organic solvent can be manifested by utilizing the advantages of each of these solvents. In addition, since they contain lithium bifluorosulfonylimide in these mixed non-aqueous organic solvents, by forming a solid SEI film at the cathode at the time of initial charging, the low temperature and room temperature output characteristics as well as the anode It is possible to improve the capacity characteristics of the lithium secondary battery at the same time by inhibiting the decomposition of the surface and preventing the oxidation reaction of the electrolytic solution and further including the carbodiimide compound represented by the general formula (1), so that the carbodiimide The compound acts as a scavenger for moisture in the electrode and as a result decreases the content of HF which is an impurity that can be formed by the influence of water in the electrolyte so that the HF elutes the cathode active material Lithium fluoride (LiF) on the surface of the anode formed through the reaction between HF and the cathode active material can be prevented from contacting with the electrode By increasing the electric resistance and generates a gas can be prevented from resulting in a reduced service life of the battery. As a result, the effect of preventing deterioration of the battery as a result can be exhibited.

In general, ethylene carbonate (EC) as a non-aqueous organic solvent used in a non-aqueous electrolyte has been mainly used for a lithium secondary battery because of its excellent affinity 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 graphite material, and thus has a problem in 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, in order to overcome the problems of ethylene carbonate and propylene carbonate and to maximize the above advantages, the present invention uses a non-aqueous organic solvent and a propylene carbonate in a proper composition in combination with ethylene carbonate, It is possible to provide a nonaqueous electrolytic solution having improved conductivity characteristics and improved output characteristics of the lithium secondary battery and improved low temperature characteristics and also excellent electrochemical affinity with the carbon layer.

In addition, in the present invention, the above-mentioned problems in using a lithium salt such as propylene carbonate and LiPF ₆ together can be solved by combining them using lithium bisfluorosulfonylimide.

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, as well as to suppress decomposition of an anode surface And the oxidation reaction of the electrolytic solution can be prevented.

According to one embodiment 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 an important effect on improving both the low temperature and the room temperature output, and the high temperature storage capacity characteristics.

The mixing ratio of propylene carbonate to ethylene carbonate (EC) is, for example, in a weight ratio of 1: 0.1 to 1: 2, specifically 1: 0.3 to 1: 1, more specifically 1: 0.4 to 1: And when the mixing ratio is within the range, synergistic effects by mixing the two non-aqueous organic solvents can be exhibited.

As the non-aqueous organic solvent according to an embodiment of the present invention, 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.

According to one embodiment of the present invention, by appropriately controlling the ethylene carbonate within the mixing ratio within the amount of the propylene carbonate used, not only the low temperature and normal temperature output characteristics of the lithium secondary battery of the present invention but also the high temperature storage capacity characteristics So that an optimum effect can be achieved.

According to an embodiment of the present invention, in addition to the ethylene carbonate (EC) and the propylene carbonate, the non-aqueous organic solvent which can be further contained in the non-aqueous electrolyte solution can minimize the decomposition due to the oxidation reaction or the like during the charge- , As long as it can exhibit the desired properties together with the additives.

Examples of the non-aqueous organic solvent that can be further included in the non-aqueous electrolyte according to an embodiment of the present invention include 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 One, or a mixture of two or more thereof.

According to an embodiment of the present invention, the concentration of the lithium bisfluorosulfonylimide in the non-aqueous electrolytic solution may be from 0.1 mol / L to 2 mol / L, more specifically from 0.5 mol / L to 1.5 mol / L Lt; / RTI > 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 in the electrolyte may occur during charging and discharging of the battery, resulting in swelling.

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 other than the lithium bisfluorosulfonylimide and the lithium bisfluorosulfonylimide may be 1: 1 to 1: 9 in a molar ratio. 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.

Specifically, the mixing ratio of the lithium salt other than lithium bisfluorosulfonylimide and lithium bisfluorosulfonylimide may be 1: 6 to 1: 9 in terms of molar ratio. 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.

In one embodiment of the present invention, the carbodiimide compound represented by Formula 1 may be one wherein each of R ₁ and R ₂ is independently a cycloalkyl having 3 to 8 carbon atoms, and more specifically, And may be dicyclohexylmethane diimine to be displayed.

(2)

The content of the carbodiimide compound represented by Formula 1 may be 0.001 wt% to 3 wt%, specifically 0.005 wt% to 1 wt% based on the total weight of the non-aqueous electrolyte, more specifically 0.005 wt% By weight to 0.1% by weight.

When the content of the carbodiimide compound is 0.001% by weight or more, an appropriate effect can be expected by adding the carbodiimide compound. When the content of the carbodiimide compound is 3% by weight or less, It is possible to prevent the problem that the irreversible capacity of the battery is increased or the excessive amount of the carbodiimide compound prevents the movement of lithium ions in the electrolyte solution while the lithium salt is exerted.

The content of the carbodiimide-based compound represented by Formula 1 can be controlled depending on the amount of lithium bis-fluorosulfonylimide added, so that the lithium bis-fluorosulfonylimide and carbodiimide-based compounds are 100: 0.02 To 100: 35, and may be used in a weight ratio of 100: 0.1 to 100: 12, more specifically 100: 0.1 to 100: 1.

When the lithium bis-fluorosulfonylimide and the carbodiimide compound represented by Formula 1 are used in a weight ratio of 100: 0.02 to 100: 35, the lithium bisfluorosulfonylimide and the carbodiimide- It is possible to appropriately suppress the side reaction in the electrolytic solution when the battery is charged and discharged at room temperature, and to further improve the durability of the negative electrode.

The non-aqueous electrolytic solution according to an exemplary embodiment of the present invention may further include at least one compound selected from the group consisting of compounds represented by the following formulas (3) to (7).

(3)

[Chemical Formula 4]

[Chemical Formula 5]

[Chemical Formula 6]

(7)

In this formula,

R ₃ is an organic group having 2 to 20 carbon atoms,

R ₄ , R ₅ , R ₆ , R ₇ and X are each an organic group having 1 to 20 carbon atoms,

In Formula 5 or Formula 7, X may be the same or different from each other and may be bonded to each other to form a ring,

n is 1 or 2,

m is an integer of 1 to 3;

In the above formula, R ₃ may be alkylene having 2 to 20 carbon atoms, alkenylene having 2 to 20 carbon atoms, alkynylene having 2 to 12 carbon atoms, or arylene having 5 to 12 carbon atoms, and the alkylene, alkenylene, Alkynylene and arylene are each independently selected from the group consisting of alkyl having 2 to 8 carbons, alkenyl having 2 to 8 carbons, alkynyl having 2 to 8 carbons, aryl having 5 to 12 carbons, halogen, nitrogen, oxygen, R ₄ , R ₅ , R ₆ , R ₇ and X may contain atoms other than carbon atoms such as hydrogen, nitrogen, oxygen, sulfur, fluorine, chlorine, silicon, boron, phosphorus, For example, a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms, a substituted or unsubstituted alkenyl group having 2 to 20 carbon atoms, or a substituted or unsubstituted alkynyl group having 2 to 10 carbon atoms. Examples of the substituent include a halogen group, an ester group, a sulfuric acid ester group, a sulfonic acid group, a phosphoric acid ester group, a silyl ester group, an amide group, an ether group, a boric acid ester group or an aromatic group.

R ₃ and R ₇ are independently selected from the group consisting of -CH ₂ CH ₂ -, -CH ₂ CH (CH ₃ ) -, -CH ₂ CH (C ₂ H ₅ ) -, -CH ₂ CH (C ₃ H ₇ ) _{-CH 2 CH (C 4 H 9} ) -, -CH 2 CH (C 5 H 11) -, -CH (CH 3) CH (CH 3) -, -CH (C 2 H 5) CH (C 2 H _{5) -, -CH 2 CH (} CH = CH 2) -, -CH (CH = CH 2) CH (CH = CH 2) -, -CH 2 CH (CF 3) -, -CF 2 CF 2 -, _{-CH (Ph) CH 2 -,} -CH (Ph) CH (Ph) 2 -, -CH = CH-, -C (CH 3) = CH-, -C (CH 3) = C (CH 3) - _{, -C (C 2 H 5)} = C (C 2 H 5) -, -Ph-, -CH 2 CH 2 CH 2 -, -CH 2 CH 2 CH (CH 3) -, -CH 2 CH (CH ₃ ) CH ₂ - or -CH ₂ C (CH ₃ ) ₂ CH ₂ -, wherein R ₄ , R ₅ , R ₆ and X are CH ₃ -, CH ₃ CH ₂ -, CH ₃ CH ₂ CH _{2 -, (CH 3) 2 CH-} , CH 3 (CH 2) 2 CH 2 -, (CH 3) 2 CH 2 CH 2 -, (CH 3) 3 C-, CH 3 CH (CH 3) CH 2 - _{, CH 3 CH 2 CH (CH} 3) CH 2 - ( including the _{isomers), C 7 H 15 - -} , C 6 H 13 ( including the isomers), C ₈ H ₁₇ - (including the isomers), C ₉ H ₁₉ - (including the _{isomers), CH 2 = CH-, CH} 2 = CH-CH 2 -, CF 3 -, CF 3 CH 2 -, CF 3 CF 2 CH 2 -, (CH 3) 3 Si-, (C ₂ H ₅ ) ₃ Si-, Ph- (phenyl group), thienyl group, May be a hexyl group.

Specific examples of the compound represented by Formula 3 include ethylene glycol cyclic sulfate, propylene glycol cyclic sulfate, 1,2-butylene glycol cyclic sulfate, 1,2-pentylene glycol cyclic sulfate, 3-methyl- 1,2-pentylene glycol cyclic sulfate, 1,2-hexylene glycol cyclic sulfate, 2,3-butylene glycol cyclic sulfate, 1-vinyl-ethylene glycol cyclic sulfate, 1,2-cyclohexanediol Cyclic sulfate, 1,3-propanediol cyclic sulfate, 1,3-butanediol cyclic sulfate, 2,4-pentanediol cyclic sulfate, 2-methyl-1,3-propanediol cyclic sulfate, 2,2 -Dimethyl-1,3-propanediol cyclic sulfate, vinylene cyclic sulfate, 1-methyl-vinylene cyclic sulfate, 1-ethyl-vinylene cyclic sulfate, 1,2-dimethyl- , Catechol cyclic sulfate, or methylene disulfonic acid methylene ester The can.

Specific examples of the compound represented by the formula (4) include dimethyl sulfate, diethyl sulfate, di-n-propyl sulfate, di-i-propyl sulfate, di-n-butyl sulfate and diphenyl sulfate.

Specific examples of the compounds represented by the above Chemical Formulas 5 to 7 include phenylboronic acid, thiophene-2-boronic acid, bistrimethylsilyl ester of phenylboronic acid, bistrimethylsilyl ester of thiophene- Boronic acid diethyl ester, thiophene-2-boronic acid dibutyl ester, thiophene-2-boronic acid butyl methyl ester, thiophene-2- 2,2-trifluoroethyl) ester, thiophene-2-boronic acid diphenyl ester, thioanisole-2-boronic acid dimethyl ester, dithiophene-2,2'-boraneamer ester, dithiophen- , 2'-boronic acid butyl ester, dithiophene-2,2'-boronic acid phenyester, 2-thiophene-2-thioanisoleboric acid ester, ethyl boronic acid pinacol ester, butane boronic acid pinacol ester , 1-octene-1-boronic acid pinacol ester, vinyl boronic acid pinacol ester, vinyl boronic acid (2-methylpentane-2,4-diol) ester , Cyclopropane boronic acid pinacol ester, 1-pentene-1,2-diboronic acid pinacol ester, E-stilbene-diboronic acid pinacol ester, thiophene-2-boronic acid pinacol ester, 2-boronic acid pinacol esters, 2,2'-dithiophene-5-boronic acid pinacol esters, 5'-hexyl-2,2'-dithiophene-5-boronic acid pinacol esters, thiophene- 3-boronic acid pinacol ester, 5-chloro-thiophene-2-boronic acid pinacol ester, 5-fluoro-thiophene-2-boronic acid pinacol ester, thioanisole- , Thioanisole-4-boronic acid pinacol ester, mesyl aniline 4-boronic acid pinacol ester, phenylthiomethyl boronic acid pinacol ester, benzothiophene-5-boronic acid pinacol ester, thiazole- 3-thiophene-2-boronic acid pinacol esters, 5-cyano-benzonitrile-2-carboxylic acid esters such as 2- (methylthio) pyrimidine- 9-boronic acid (2-thienyl) benzene-4-boronic acid pinacol ester, benzonitrile-9-boronic acid neopentyl glycol ester, thiophene-2-boronic acid 1,3-propanediol ester, thiophen- - boronic acid ethylene glycol ester, thiophene-2-boronic acid neopentyl glycol ester, thiophene-2-boronic acid oxalic acid ester, thiophene-2,5-diboronic acid pinacol ester, 2,2'-bithiophene- 5,5'-diboronic acid pinacol ester, thiophene-2,3,5-tricarboinic acid pinacol ester, thioanisole-1,3,5-tribonoic acid pinacol ester, 3,5-dimethyl- (2-thiophene) borocyne, tri (5-methyl-2-thiophene) borate, furan-3-boronic acid pinacol ester, triphenylboroxine, (5-boronic acid pinacol ester-2-thiophene) borocin.

Specifically, at least one compound selected from the group consisting of the compounds represented by Chemical Formulas 3 to 7 is selected from ethylene glycol cyclic sulfate, propylene glycol cyclic sulfate, 1,2-butylene glycol cyclic sulfate, 1,2- (2-methylpentane-2, 4-diol) ester, 5- (2-methylpentane-2, 4-diol) ester, methylene disulfonic acid methylene ester, phenylboronic acid, thiophene- Methyl-thiophene-2-boronic acid pinacol ester, thiophene-3-boronic acid pinacol ester, 5-fluoro-thiophene- May be at least one kind selected from the group consisting of ginseng.

At least one compound selected from the group consisting of the compounds represented by the above formulas (3) to (7) may be contained in an amount of 0.001 to 5 parts by weight relative to 100 parts by weight of the total non-aqueous electrolytic solution, specifically 0.01 to 3 parts by weight , More specifically 0.05 part by weight to 2 parts by weight.

The non-aqueous electrolytic solution according to an exemplary embodiment of the present invention may include a compound represented by Formula 3 or a compound represented by Formula 4 and at least one compound represented by Formula 5 to 7.

When the nonaqueous electrolytic solution contains at least one compound selected from the group consisting of the compounds represented by the formulas (3) to (7), expansion of the battery during initial charging and discharging of the lithium secondary battery including the nonaqueous electrolytic solution is suppressed And the cycle characteristics can be improved.

Meanwhile, a lithium secondary battery according to an embodiment of the present invention includes a cathode including a cathode active material; A negative electrode comprising a negative electrode active material; A separator interposed between the anode and the cathode; And the non-aqueous electrolytic solution.

Here, the cathode active material may include a manganese spinel-based active material, a lithium metal oxide, or a mixture thereof. Further, the lithium metal oxide may be selected from the group consisting of lithium-manganese-based oxide, lithium-nickel-manganese-based oxide, lithium-manganese-cobalt oxide and lithium-nickel-manganese-cobalt oxide, is _{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 ( wherein, _{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).

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 the negative electrode is prepared by mixing a mixture of a positive electrode or a negative electrode active material, a conductive agent and a binder with a predetermined solvent on a positive electrode or a negative electrode current collector to prepare a slurry, Applying the slurry on a current collector, and 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 agent 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 negative electrode active material. Such a conductive agent is not particularly limited as long as it has electrical conductivity without causing a chemical change in the battery, and examples thereof include graphite such as natural graphite and 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 negative electrode active material with the conductive agent 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 containing the positive electrode or 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 used in the present invention may be of any type that is commonly 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 or the like.

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 0.1 mol / L was added, and 0.9 mol / L of lithium bis-fluorosulfonylimide and 0.02% by weight of dicyclohexylmethane diimine 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 agent, 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 prepare a positive electrode, followed by roll pressing to prepare a positive electrode.

Further, a negative electrode mixture slurry was prepared by adding carbon powder as a negative electrode active material, PVdF as a binder and carbon black as a conductive agent to 96 wt%, 3 wt% and 1 wt%, respectively, as a solvent. The negative electrode mixture slurry was applied to a copper (Cu) thin film as an anode current collector having a thickness of 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 Except that the amount of lithium bisfluorosulfonylimide was changed to 0.17 mol / L and 0.83 mol / L (molar ratio of about 1: 5) of lithium bisfluorosulfonylimide, A battery was prepared.

Example 4

A non-aqueous electrolytic solution and a lithium secondary battery were prepared in the same manner as in Example 1, except that 0.05 wt% of dicyclohexylmethanediimine was used.

Example 5

A nonaqueous electrolytic solution and a lithium secondary battery were prepared in the same manner as in Example 2 except that 0.05 wt% of dicyclohexylmethane diimine was used.

Example 6

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

Example 7

A nonaqueous electrolytic solution and a lithium secondary battery were prepared in the same manner as in Example 1, except that 1 wt% of an ethylene glycol cyclic sulfuric acid ester represented by the following general formula (8) was further used in the production of the nonaqueous electrolytic solution.

[Chemical Formula 8]

Example 8

A nonaqueous electrolytic solution and a lithium secondary battery were prepared in the same manner as in Example 1, except that 1% by weight of propylene glycol cyclic sulfuric acid ester represented by the following general formula (9) was further used in the production of the nonaqueous electrolytic solution.

[Chemical Formula 9]

Example 9

A nonaqueous electrolytic solution and a lithium secondary battery were prepared in the same manner as in Example 1, except that 0.5% by weight of phenylboronic acid represented by the following formula (10) was further used in the production of the nonaqueous electrolytic solution.

[Chemical formula 10]

Example 10

A nonaqueous electrolytic solution and a lithium secondary battery were prepared in the same manner as in Example 1, except that 0.5% by weight of thiophene-2-boronic acid represented by the following formula (11) was further used in the production of the nonaqueous electrolytic solution .

[Chemical formula 10]

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

Experimental Example 1

<High Temperature Life Measurement>

The lithium secondary batteries prepared in Examples 1 to 6 and Comparative Examples 1 to 5 were charged at 1 C to 4.2 V / 38 mA under constant current / constant voltage (CC / CV) conditions at 45 ° C, To 2.5 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 1 cycle) x 100 is shown in Table 1 as the high temperature lifetime.

Experimental Example 2

<Capacity characteristics after high temperature storage>

The secondary batteries prepared in Examples 1 to 6 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, 2 C, and the discharge capacity thereof was measured. Then, the secondary batteries prepared in Examples 1 to 6 and Comparative Examples 1 to 5 were stored at 60 DEG C for 16 weeks, and then the secondary batteries were respectively charged at a constant current / constant voltage (CC / CV) , And discharged at 2.5 C under a constant current (CC) condition to 2 C, and the discharge capacity thereof was measured. The discharge capacity after 16 weeks based on the initial discharge capacity was calculated as a percentage (discharge capacity after 16 weeks / initial discharge capacity × 100 (%)), and the results are shown in Table 1 below.

Experimental Example 3

<Output characteristics after high temperature storage>

The output was calculated using the voltage difference which occurs when the secondary batteries manufactured in Examples 1 to 6 and Comparative Examples 1 to 5 were charged and discharged for 10 seconds at 5C at room temperature after storing for 16 weeks at 60 ° C. The results are shown in Table 1 below, with 16-week output (W) / initial output (W) × 100 (%) as the percentage of output after 16 weeks based on the initial output. The test was performed at 50% SOC (state of charge).

Experimental Example 4

&Lt; Measurement of cell thickness increase rate &

The thickness of the secondary battery manufactured in Examples 1 to 6 and Comparative Examples 1 to 5 was measured and the thickness after storage at 60 占 폚 for 16 weeks was measured to determine the rate of cell thickness increase (thickness after 16 weeks / 100) -100, and the values are shown in Table 1 below.

LiPF ₆ : LiFSI additive
(weight%) Life characteristics
(%) High Temperature Storage Characteristics
(%) Volume Print Battery Thickness
increase Example 1 1: 9 DCC 0.02 81.7 84.3 86.7 5.6 Example 2 1: 6 DCC 0.02 82.1 86.9 88.6 5.3 Example 3 1: 5 DCC 0.02 80.6 82.6 80.9 8.1 Example 4 1: 9 DCC 0.05 78.6 79.5 87.1 10.3 Example 5 1: 6 DCC 0.05 86.3 87.1 90.2 5.2 Example 6 1: 6 DCC 3 64.2 70.6 60.8 13.6 Comparative Example 1 1: 9 DCC 0.02 73.6 71.2 75.4 8.3 Comparative Example 2 1: 9 DCC 0.02 76.6 73.5 79 7.9 Comparative Example 3 1: 0 0 79.8 77.4 78.5 6.1 Comparative Example 4 1: 0 DCC 0.02 80.1 80.8 81.1 5.9 Comparative Example 5 1: 9 0 79.1 81.5 83.3 5.7

In Table 1, DCC represents dicyclohexylmethane diimine.

Referring to Table 1, the lithium secondary batteries of Examples 1 to 3 were produced by mixing lithium bis-fluorosulfonylimide and dicyclohexylmethane (DME) together with a non-aqueous organic solvent containing propylene carbonate (PC) and ethylene carbonate (EC) was not contained in the non-aqueous organic solvent, Comparative Example 2 in which propylene carbonate (PC) was not contained in the non-aqueous organic solvent, and Comparative Example 2 in which lithium bisfluorosulfonylimide And Comparative Example 3 which did not contain dicyclohexylmethane diimine and Comparative Example 4 which did not contain lithium bisfluorosulfonylimide showed a high room temperature service life and a high capacity And output, and the rate of cell thickness increase was also small, indicating excellent high temperature storage characteristics.

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 showed excellent high-temperature storage characteristics and lifetime characteristics superior to those of the addition of lithium bisfluorosulfonylimide and exhibited excellent room temperature lifetime characteristics. 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 Of the lithium secondary battery of the present invention.

When the lithium secondary batteries of Examples 1 and 4 and Comparative Example 5, which differ only by the addition of dicyclohexylmethane diimine, were compared with each other, the effects of the addition of the carbodiimide compound were examined. 4 lithium secondary battery exhibited better room temperature lifetime characteristics with the addition of dicyclohexylmethane diimine, and showed better output after high temperature storage.

On the other hand, in the case of Examples 1 to 5 in which dicyclohexylmethane diimine was contained in an amount of 0.02 to 0.05 wt% based on the total weight of the non-aqueous electrolytic solution, dicyclohexylmethane dianhydride It showed an excellent effect as compared with Example 6 containing 3% by weight of imine.

Claims (18)

i) a non-aqueous organic solvent comprising propylene carbonate (PC) and ethylene carbonate (EC); And ii) a non-aqueous electrolytic solution comprising lithium bis (fluorosulfonyl) imide (LiFSI) and a carbodiimide compound represented by the following formula (1):
[Chemical Formula 1]

In Formula 1, R ₁ and R ₂ are each independently alkyl having 1 to 12 carbon atoms or cycloalkyl having 3 to 12 carbon atoms.
The method according to claim 1,
Wherein the mixing ratio of propylene carbonate to ethylene carbonate is 1: 0.1 to 1: 2 by weight.
The method according to claim 1,
Wherein the non-aqueous electrolytic solution further comprises a lithium salt other than the lithium bis-fluorosulfonylimide.
The method of claim 3,
The mixing ratio of the lithium salt to lithium bisfluorosulfonylimide is 1: 1 to 1: 9 in a molar ratio.
5. The method of claim 4,
The mixing ratio of the lithium salt to lithium bisfluorosulfonylimide is 1: 6 to 1: 9 in a molar ratio.
The method according to claim 1,
Wherein the lithium bisfluorosulfonyl imide has a concentration of 0.1 mol / L to 2 mol / L in the non-aqueous electrolytic solution.
The method according to claim 1,
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 non-aqueous organic solvent.
8. The method of claim 7,
Wherein the content of the propylene carbonate is 10 parts by weight to 40 parts by weight based on 100 parts by weight of the total non-aqueous organic solvent.
The method according to claim 1,
Wherein R ₁ and R ₂ are each independently a cycloalkyl having 3 to 8 carbon atoms.
The method according to claim 1,
Wherein the carbodiimide compound represented by Formula 1 is dicyclohexylmethane diimine.
The method according to claim 1,
The content of the carbodiimide compound represented by the formula (1) is 0.001 to 3 wt% based on the total weight of the nonaqueous electrolyte solution.
The method according to claim 1,
Wherein the lithium bisfluorosulfonylimide and the carbodiimide compound represented by Formula 1 are in a weight ratio of 100: 0.02 to 35.
The method according to claim 1,
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.
The method of claim 3,
The lithium salt is _{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.
The method according to claim 1,
Wherein the non-aqueous electrolytic solution further comprises at least one compound selected from the group consisting of compounds represented by the following Chemical Formulas 3 to 7:
(3)

[Chemical Formula 4]

[Chemical Formula 5]

[Chemical Formula 6]

(7)

In this formula,
R ₃ is an organic group having 2 to 20 carbon atoms,
R ₄ , R ₅ , R ₆ , R ₇ and X are each an organic group having 1 to 20 carbon atoms,
In Formula 5 or Formula 7, X may be the same or different from each other and may be bonded to each other to form a ring,
n is 1 or 2,
m is an integer of 1 to 3;
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 lithium secondary battery comprising the non-aqueous electrolytic solution of claim 1.
17. The method of claim 16,
Wherein the cathode active material is a manganese spinel-based active material, a lithium metal oxide, or a mixture thereof.
18. The method of claim 17,
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.