KR101018142B1 - Non-aqueous electrolyte and secondary battery comprising the same - Google Patents

Abstract

The present invention relates to an electrolyte solution containing an unsaturated sultone compound in which formation of a kinetic SEI film is more advantageous than conventional electrolyte additives, thereby minimizing battery initial capacity reduction.

Description

Non-aqueous electrolyte and secondary battery comprising same {NON-AQUEOUS ELECTROLYTE AND SECONDARY BATTERY COMPRISING THE SAME}

The present invention is a non-aqueous electrolyte; And it relates to a secondary battery comprising the same. More specifically, the present invention is a non-aqueous electrolyte containing an unsaturated sultone compound capable of improving the initial capacity, lifespan performance of the secondary battery; And it relates to a secondary battery comprising the same.

In recent years, with the trend of miniaturization and weight reduction of electronic devices, miniaturization and weight reduction of batteries serving as power sources are also required. BACKGROUND ART Secondary batteries have been put to practical use as small-sized, light-weight, high-capacitance rechargeable batteries, and are used in portable electronic and communication devices such as small video cameras, mobile phones, and notebook computers.

The secondary battery may be composed of a positive electrode, a negative electrode, a porous separator, and a non-aqueous electrolyte containing an electrolyte salt and an electrolyte solvent.

The non-aqueous electrolyte generally requires the following characteristics with respect to the operation and use of the battery. First, it must be able to sufficiently transfer ions between two electrodes during insertion and desorption of lithium ions from the cathode and anode, and second, it is electrochemically stable at the potential difference between the two electrodes, so that there is little concern about side reactions such as decomposition of electrolyte components. .

However, the potential difference between a carbon electrode and a lithium metal compound electrode, which is commonly used as a battery negative electrode and a positive electrode, is in the range of 0 to 4.3 V, and a conventional electrolyte solvent such as a carbonate-based organic solvent decomposes at the electrode surface during charge and discharge at the potential difference. May cause side reactions in the battery. In addition, an organic solvent such as propylene carbonate (PC), dimethyl carbonate (DMC), or diethyl carbonate (DEC) may be co-intercalated between graphite layers in the carbon-based negative electrode, thereby disrupting the structure of the negative electrode.

On the other hand, it is known that the problem can be solved by a solid electrolyte interface (SEI) film formed on the surface of the negative electrode by the electrical reduction of the carbonate-based organic solvent during the initial charging of the battery. However, when the SEI film is formed, lithium ions in the electrolyte are irreversibly involved, so that the initial capacity of the battery is necessarily reduced, which is particularly problematic in a carbon-based negative electrode having a small theoretical capacity.

In addition, the SEI film formed by the conventional carbonate-based organic solvent is generally not electrochemically or thermally stable, and may easily collapse due to increased electrochemical energy and thermal energy as charging and discharging proceeds. Therefore, the battery capacity can be reduced while the SEI film is continuously regenerated during charging and discharging of the battery, and the lifespan performance of the battery can be reduced. In addition, side reactions such as electrolyte decomposition may occur on the exposed surface of the negative electrode due to the collapse of the SEI film, and the gas generated at this time may cause a problem that the battery swells or the internal pressure increases.

In order to solve the above problems, 1,3-propanesultone (Japanese Patent Application No. 1999-339850), 1,3-propenesultone (1,3-propensultone; Japanese Patent Application No. 2001- 151863) has been presented. However, even in the case of the above method, as the cycle continues, the capacity gradually decreases, and the above problems still exist.

The inventors of the present invention use an unsaturated sultone compound capable of forming a more stable intermediate when forming an SEI film as an electrolyte additive, which is advantageous in terms of kinetic formation of the SEI film, thereby minimizing the amount of lithium ions consumed during initial charging of the battery. It was recognized that.

Thus, the present invention is an electrolyte containing an unsaturated sultone compound that can form a resonance structure as a reaction intermediate when forming the SEI film; And it aims to provide the secondary battery provided with the said electrolyte solution.

The present invention provides an electrolyte solution comprising an electrolyte salt and an electrolyte solvent, wherein the electrolyte solution includes an electrolyte solution containing a compound represented by Chemical Formula 1 below; And it provides a secondary battery having the electrolyte solution.

In addition, the present invention is an electrode formed on a part or all of the surface of the solid electrolyte interface (SEI) film containing the chemical reaction product of the compound of formula 1 (hereinafter, unsaturated sultone compound of the present invention); And it provides a secondary battery having the electrode.

[Formula 1]

In Formula 1, R ₁ , R ₂ , R _3, and R ₄ are each independently hydrogen, fluorine, an alkyl group having ₁ to ₆ carbon atoms, a cyclic alkyl group having 3 to 8 carbon atoms, and a C ₂ to C ₆ group. Is selected from the group consisting of an alkenyl group, a phenyl group, a benzyl group, and a halogen derivative thereof, n is an integer of 0 to 2.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

In operation of the secondary battery, a decrease in electric capacity generally occurs in the initial cycle, which is presumably because lithium ions in the electrolyte are consumed during the formation of the SEI film during the initial charging. In addition, it is estimated that the amount of lithium ions consumed above is partially influenced by the kinetics of the formation reaction of the SEI film.

Accordingly, the present invention focuses on the fact that the compound having a resonance structure can exhibit better chemical stability, using an unsaturated sultone compound capable of forming a resonance structure as a reaction intermediate when forming an SEI film as an electrolyte component. It is characterized by.

More specifically, the electrolyte solution of the present invention includes an unsaturated sultone compound of Formula 1 (hereinafter referred to as 'unsaturated sultone compound of the present invention'), and is capable of minimizing capacity reduction during initial charging of a battery. Such improvement of battery performance can be estimated as follows, but is not limited thereto.

An unsaturated sultone compound (hereinafter, 'a conventional unsaturated sultone electrolyte additive'), which is conventionally used as an electrolyte additive for forming an SEI film on a negative electrode surface during charging of a battery, is in the form of Formula 2 below, It is estimated to be reduced to 3 to form an intermediate.

[Formula 2]

In Formula 2, R ₅ to R ₈ are each independently hydrogen, halogen, C ₁ ~ C ₆ alkyl group, C ₆ ~ C ₁₂ aryl group, C ₂ ~ C ₆ alkenyl (alkenyl) group, or a halogen derivative thereof, n is an integer of 0-3.

(3)

On the other hand, the unsaturated sultone compound of the present invention is estimated to form an intermediate by reducing as shown in the following formula (4) when forming the SEI film.

[Formula 4]

That is, the unsaturated sultone compound of the present invention is a sulfur-carbon bond is broken during electrical reduction, while a resonance structure (resonance) is formed between the introduced electrons and the double bond in the compound, while the conventional unsaturated sultone electrolyte additive is a compound at the time of reduction The double bonds remain in the reducing body. Therefore, the unsaturated sultone compound of the present invention can form an intermediate of a more stable structure (intermediate) than the conventional unsaturated sultone-based electrolyte additive, which may act advantageously kinetic when forming the SEI film. For this reason, in the present invention, the amount of lithium ions consumed to form the SEI film is reduced, and as a result, the initial capacity reduction of the battery can be minimized, and the battery life performance can be improved.

Further, as the unsaturated sultone compounds of the invention are cyclic structure is ring-opened upon reduction, sulfonate anion radical (-SO ₃ ^-) to both ends of the reduced material to form a radical, and an allyl group, which as a polymerizable functionality, other electrolytic solution component Various types of polymerization reactions can be carried out together. As a result, in the present invention, a more stable SEI film can be formed as compared with the SEI film formed by the conventional carbonate organic solvent.

The unsaturated sultone compound of the present invention can be represented by the following formula (1).

[Formula 1]

In Formula 1, R ₁ , R ₂ , R _3, and R ₄ are each independently hydrogen, fluorine, an alkyl group having ₁ to ₆ carbon atoms, a cyclic alkyl group having 3 to 8 carbon atoms, and a C ₂ to C ₆ group. Is selected from the group consisting of an alkenyl group, a phenyl group, a benzyl group, and a halogen derivative thereof, n is an integer of 0 to 2.

Non-limiting examples of unsaturated sultone compounds of the present invention are 2-butenesultone, 2-methyl-2-butenesultone, 2-ethyl-2-butenesultone (2 -ethyl-2-butensultone), 2-propyl-2-butenesultone, 3-methyl-2-butenesultone, 3-ethyl-2-butensultone Butenesultone (3-ethyl-2-butensultone), 3-propyl-2-butenesultone (3-propyl-2-butensultone), 2,3-dimethyl-2-butenesultone (2,3-dimethyl-2-butensultone ), 2,3-diethyl-2-butenesultone, 2,3-dipropyl-2-butenesultone, 2- 2-fluoro-2-butenesultone, 3-fluoro-2-butenesultone, 2,3-difluoro-2-butenesultone (2 , 3-difluoro-2-butensultone), 2-phenyl-2-butenesultone, 2-benzyl-2-butenesultone, 2-allyl- 2-allyl-2-butensultone, 2-cyclopentyl-2-butensultone, 2-cyclohexyl-2-part 2-cyclohexyl-2-butensultone, 2,4-dimethyl-2-butenesultone, 2,4-dipfuoro-2-butenesultone difluoro-2-butensultone), 2,3,4-trimethyl-2-butenesultone (2,3,4-trimethyl-2-butensultone), 2,3,4,4-tetramethyl-2-butenesultone (2 , 3,4,4-tetramethyl-2-butensultone), 2,3,4-trifluoro-2-butenesultone (2,3,4-trifluoro-2-butensultone), 2,3,4,4- Tetrafluoro-2-butenesultone (2,3,4,4-tetrafluoro-2-butensultone), 2-methyl-2-pentenesultone, 2-ethyl-2-pentenesultone (2-ethyl-2-pentensultone), 2-propyl-2-pentenesultone, 2-methyl-2-pentenesultone, 3-methyl-2-pentensultone, 3-ethyl- 2-pentenesultone (3-ethyl-2-pentensultone), 3-propyl-2-pentenesultone (3-propyl-2-pentensultone), 2,3-dimethyl-2-pentenesultone (2,3-dimethyl-2 -pentensultone), 2,3-diethyl-2-pentensultone, 2,3-dipropyl-2-pentenesultone, 2-fluoro-2-pentensultone sultone), 3-fluoro-2-pentensultone, 2,3-difluoro-2-pentenesultone, 2-phenyl- 2-phenyl-2-pentensultone, 2-benzyl-2- pentensultone, 2-allyl-2-buttensultone, 2-cyclopentyl-2-pentensultone, 2-cyclohexyl-2-pentensultone, 2,4-dimethyl-2-pentenesultone , 4-dimethyl-2-pentensultone), 2,4-difluoro-2-pentensultone, 2,3,4-trimethyl-2-pentenesultone (2,3 , 4-trimethyl-2-pentensultone), 2,3,4,4-tetramethyl-2-pentenesultone (2,3,4,4-tetramethyl-2-pentensultone), 2,3,4,5-tetra Methyl-2-pentenesultone (2,3,4,5-tetramethyl-2-pentensultone), 2,3,4-trifluoro-2-pentenesultone (2,3,4-trifluoro-2-pentensultone), 2,3,4,4-tetrafluoro-2-pentenesultone (2,3,4,4-tetrafluoro-2-pentensultone), 2,3,4,5-tetrafluoro-2-pentenesultone (2 , 3,4,5-tetrafluoro-2-pentensultone )

In the electrolyte solution of the present invention, the content of the unsaturated sultone compound can be adjusted according to the goal of improving the performance of the battery, but preferably 0.1 to 20 parts by weight per 100 parts by weight of the electrolyte. If less than 0.1 part by weight, the desired cycle preservation effect is insignificant. If it exceeds 20 parts by weight, the battery resistance may increase.

In addition to the above compounds, the electrolyte of the present invention may include conventional electrolyte components known in the art, such as electrolyte salts and electrolyte solvents.

The electrolyte salt is A ⁺ B ^- A salt of the structure, such as, A ⁺ is Li ^+, Na ^+,, and comprising an alkali metal cation or an ion composed of a combination thereof, such as K ⁺ B ^- is PF ₆ ^-, BF _{^{4 -, Cl -, Br -}} , I -, ClO 4 -, AsF 6 -, CH 3 CO 2 -, CF 3 SO 3 -, N (CF 3 SO 2) 2 -, C (CF 2 SO 2) 3 ^- is a salt containing an anion ion or a combination thereof, such as. In particular, lithium salts such as LiClO ₄ , LiCF ₃ SO ₃ , LiPF ₆ , LiBF ₄ , LiN (C ₂ F ₅ SO ₂ ) ₂ , or Li (CF ₃ SO ₂ ) ₂ are preferred.

In addition, the electrolyte solvent may be used conventional organic solvents known in the art, such as cyclic carbonate and / or linear carbonate. In particular, in order to increase the dissociation and transfer ability of lithium ions in the electrolyte, it is preferable to use a cyclic carbonate having a high polarity, and to mix the cyclic carbonate and linear carbonate in order to prevent a decrease in the lithium ion conductivity due to the viscosity increase of the electrolyte. It is more preferable to improve the lifespan characteristics of the battery. Non-limiting examples of the solvent solvent is propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), dimethyl sulfoxide, acetonitrile, dimethoxy Ethane, diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethylmethyl carbonate (EMC), gamma butyrolactone (GBL), fluoroethylene carbonate (FEC), methyl formate, ethyl formate Propyl formate, methyl acetate, ethyl acetate, propyl acetate, pentyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate or halogen derivatives thereof. These electrolyte solvents can be used individually or in mixture of 2 or more types, For example, in order to solve the problem of low temperature performance of ethylene carbonate, ethylene carbonate and propylene carbonate can be mixed.

In addition, the present invention provides an electrode, preferably a cathode, on which a solid electrolyte interface (SEI) film including a chemical reaction product of the unsaturated sultone compound of Formula 1 is formed on part or all of a surface thereof.

The electrode is an electrode prepared according to a conventional method known in the art; And after assembling the battery unit using the electrolyte solution containing an unsaturated sultone compound of the present invention, it can be prepared by charging and discharging one or more times to form an SEI film on the surface of the electrode active material. In addition, before the battery unit assembly, the electrode having the SEI film preformed may be manufactured by electrically reducing the electrode containing the unsaturated sultone compound in the state of being impregnated with an electrode prepared according to a conventional method known in the art.

The electrode before the SEI film is formed may be manufactured according to a conventional method known in the art, and for example, an electrode slurry including a negative electrode active material may be prepared by applying and drying an electrode slurry on a negative current collector. . In this case, a small amount of a conductive agent and / or a binder may be optionally added.

As the negative electrode active material, a conventional negative electrode active material that can be used for a negative electrode of a conventional secondary battery can be used. Non-limiting examples thereof include lithium adsorbents such as lithium metal or lithium alloy carbon, petroleum coke, activated carbon, graphite, graphite, graphitized carbon or other carbons. It is preferable to use graphitized carbon having a crystal surface distance constant d002 of a carbonaceous material measured by X-ray diffraction method up to 0.338 nm and a specific surface area measured by BET method up to 10 m ² / g. Non-limiting examples of cathode current collectors include foils made of copper, gold, nickel or copper alloys or combinations thereof.

Furthermore, the secondary battery of the present invention is an electrolyte containing an unsaturated sultone compound of Formula 1; And / or an electrode on which a solid electrolyte interface (SEI) film comprising the chemical reaction product of the unsaturated sultone compound is formed on part or all of the surface. Preferably, the present invention is a separator; anode; A cathode in which a solid electrolyte interface (SEI) film including a chemical reaction product of the unsaturated sultone compound of Formula 1 is formed on part or all of a surface thereof; And / or It provides a secondary battery having an electrolyte solution containing the unsaturated sultone compound.

Non-limiting examples of the secondary battery includes a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery or a lithium ion polymer secondary battery.

The positive electrode to be applied to the secondary battery of the present invention is not particularly limited, and may be manufactured in a form in which a positive electrode active material is bound to a positive electrode current collector according to conventional methods known in the art. The positive electrode active material may be a conventional positive electrode active material that can be used for the positive electrode of a conventional secondary battery, non-limiting examples of lithium such as LiM _x O _y (M = Co, Ni, Mn, Co _a Ni _b Mn _c ) Transition metal composite oxides (for example, lithium manganese composite oxides such as LiMn ₂ O ₄ , lithium nickel oxides such as LiNiO ₂ , lithium cobalt oxides such as LiCoO ₂ , and some of the manganese, nickel and cobalt oxides of these oxides And the like, or a vanadium oxide containing lithium) or a chalcogen compound (for example, manganese dioxide, titanium disulfide, molybdenum disulfide, and the like). Preferably LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , Li (Ni _a Co _b Mn _c ) O ₂ (0 <a <1, 0 <b <1, 0 <c <1, a + b + c = 1), LiNi _1-Y Co _Y O ₂ , LiCo _1-Y Mn _Y O ₂ , LiNi _1-Y Mn _Y O ₂ (where 0 ≦ Y <1), Li (Ni _a Co _b Mn _c ) O ₄ (0 <a <2, 0 <b <2, 0 <c <2, a + b + c = 2), LiMn _2-z Ni _z O ₄ , LiMn _2-z Co _z O ₄ ( Here, 0 <Z <2), LiCoPO ₄ , LiFePO _4, or a mixture thereof is mentioned. Non-limiting examples of the positive electrode current collector include a foil made of aluminum, nickel, or a combination thereof.

The separator is not particularly limited, but a porous separator may be used, for example, a polypropylene-based, polyethylene-based, or polyolefin-based porous separator.

The secondary battery according to the present invention may be manufactured according to a conventional method known in the art, for example, an electrolyte prepared according to the present invention after assembling a separator between an anode and a cathode. It can be prepared by injecting.

The appearance of the secondary battery according to the present invention is not limited, but can be cylindrical, coin-shaped, square or pouch (pouch) of the can.

In the present invention, since the formation of the SEI film is advantageous in kinetic manner, the initial capacity reduction of the battery can be minimized. In addition, the present invention can improve the discharge capacity storage characteristics and the life characteristics of the battery by forming a more stable SEI film on the negative electrode surface.

Various modifications may be made without departing from the spirit and scope of the invention as set forth in the claims.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. However, the following examples are for illustrating the present invention, and the scope of the present invention is not limited thereto.

Example 1

Example 1-1. Preparation of Electrolyte

2 parts by weight of 2-methyl-2-butenesultone was added to a 1M LiPF ₆ solution of ethylene carbonate, propylene carbonate, and diethyl carbonate in a 1: 1: 2 volume ratio to prepare an electrolyte solution.

Example 1-2. Manufacture of batteries

The negative electrode was mixed with 93 parts by weight of a graphitized carbon active material and 7 parts by weight of polyvinylidene difluoride (PVDF) as a solvent, N-methyl-2-pyrrolidone, and mixed in a mixer for 2 hours. It was prepared by coating a copper foil current collector and drying at 130 ° C. The positive electrode was coated with an aluminum foil current collector after mixing for 2 hours in a mixer using N-methyl-2-pyrrolidone as a solvent with 91 parts by weight of LiCoO ₂ , 3 parts by weight of PVDF, and 6 parts by weight of conductive carbon, and at 130 ° C. Dried and prepared. The anode was cut in a circular shape, placed in a coin-shaped can, a separator (celgard 2400) was placed, and the cathode cut in a circular shape was placed. This was sufficiently impregnated with the electrolyte prepared in Example 1-1, and then a coin-type cap was prepared by covering and pressing a coin-type cap.

Example 2

Electrolyte solution in the same manner as in Example 1 except that 1 part by weight of 2-methyl-2-butenesultone was added instead of 2 parts by weight to prepare an electrolyte solution; And a secondary battery.

Example 3

Electrolyte solution in the same manner as in Example 1 except that 3 parts by weight of 2-methyl-2-butenesultone was added instead of 2 parts by weight to prepare an electrolyte solution; And a secondary battery.

Example 4

Electrolyte solution in the same manner as in Example 1 except that 5 parts by weight of 2-methyl-2-butenesultone was added instead of 2 parts by weight to prepare an electrolyte solution; And a secondary battery.

Example  5

Electrolyte solution in the same manner as in Example 1 except that 10 parts by weight of 2-methyl-2-butenesultone was added instead of 2 parts by weight to prepare an electrolyte solution; And a secondary battery.

Example 6

Electrolyte solution in the same manner as in Example 1 except that 2 parts by weight of 2,3-dimethyl-2-butenesultone was added instead of 2-methyl-2-butenesultone to prepare an electrolyte solution; And a secondary battery.

Example 7

Electrolyte solution in the same manner as in Example 1 except that 2 parts by weight of 2-fluoro-2-butenesultone was added instead of 2-methyl-2-butenesultone to prepare an electrolyte solution; And a secondary battery.

Comparative Example 1

Electrolyte solution in the same manner as in Example 1 except that no compound was added to the LiPF ₆ solution; And a secondary battery.

Comparative Example 2

An electrolyte solution in the same manner as in Example 1 except that 2 parts by weight of 1,3-propane sultone was added instead of 2-methyl-2-butenesultone to prepare an electrolyte solution; And a secondary battery.

Comparative Example 3

Electrolyte solution in the same manner as in Example 1 except that 2 parts by weight of 1,3-propene sultone was added instead of 2-methyl-2-butenesultone to prepare an electrolyte solution; And a secondary battery.

Experimental Example 1. Measurement of the reduction voltage of the electrolyte additive

The reduction potential of the unsaturated sultone compound of the present invention and the conventional sultone electrolyte additive was measured as follows.

Coin-shaped half cells were prepared in a conventional manner using the electrolyte solutions of Examples 1 and Comparative Examples 1 to 3, artificial graphite as a positive electrode, and lithium foil as a negative electrode. For each of the manufactured coin half cells, cyclic voltammetry was performed at a rate of 0.1 mV / sec between 1.5 V and 1 mV, and the reduced peak voltages measured therefrom are shown in Table 1. For reference, when the full cell is a reference, the value of the reduction potential is shown in the reverse order with the following experimental results.

TABLE 1

Electrolyte additives Reduced peak voltage (V vs Li) Example 1 2-methyl-2 butenesultone 1.2 V Comparative Example 1 - 0.6 V Comparative Example 2 1,3-propane sultone 1.0 V Comparative Example 3 1,3-propene sultone 1.1 V

As a result, the electrolyte solution of Example 1 and Comparative Examples 2 and 3 containing a sultone compound in the half cell showed a different reduction voltage from that of Comparative Example 1 in which no compound was added. From this, it can be inferred that the experimental results of Example 1 and Comparative Examples 2 and 3 are the reduction potentials of the added sultone compounds.

In particular, since the unsaturated sultone compound (2-methyl-2 butenesultone) of the present invention has a reduction voltage higher than that of a conventional electrolyte solution (Comparative Example 1), it is reduced before the electrolyte solution in a full-cell secondary battery and thus on the surface of the negative electrode. It can be predicted that an SEI film can be formed.

Experimental Example  2. Performance Evaluation of Lithium Secondary Battery

The secondary batteries prepared in Examples 1 to 7 and Comparative Examples 1 to 3 were charged at 25 ° C. to 4.2 V at a rate of 0.5 C, and charged at 4.2 V until the current became 0.05 mA or less, and 0.5 C to 3 V. Charge and discharge experiments were performed by discharging at a rate of. The discharge capacity retention rate (%) was expressed as a percentage of the ratio of the discharge capacity to the initial discharge capacity after 50 cycles. The results are shown in Table 2.

TABLE 2

Electrolyte additives Addition amount
(Parts by weight) Electrolyte composition
(Volume ratio) Initial discharge capacity
(mAh) Discharge capacity
% Retention Example 1 2-methyl-2-butenesultone 2 1M LiPF ₆
EC: PC: DEC = 1: 1: 2
4.38 84.8 Example 2 2-methyl-2-butenesultone 1.0 1M LiPF ₆
EC: PC: DEC = 1: 1: 2
4.45 82.8 Example 3 2-methyl-2-butenesultone 3.0 1M LiPF ₆
EC: PC: DEC = 1: 1: 2
4.24 84.3 Example 4 2-methyl-2-butenesultone 5.0 1M LiPF ₆
EC: PC: DEC = 1: 1: 2
4.17 83.6 Example 5 2-methyl-2-butenesultone 10 1M LiPF ₆
EC: PC: DEC = 1: 1: 2
4.43 90.5 Example 6 2,3-dimethyl-2-butenesultone 2 1M LiPF ₆
EC: PC: DEC = 1: 1: 2
4.24 85.3 Example 7 2-fluoro-2-butenesultone 2 1M LiPF ₆
EC: PC: DEC = 1: 1: 2
4.37 87.1 Comparative Example 1 - - 1M LiPF ₆
EC: PC: DEC = 1: 1: 2
4.19 57.3 Comparative Example 2 1,3-propanesultone 2 1M LiPF ₆
EC: PC: DEC = 1: 1: 2
4.04 82.2 Comparative Example 3 1,3-propenesultone 2 1M LiPF ₆
EC: PC: DEC = 1: 1: 2
3.94 83.5

As a result, the batteries of Comparative Examples 2 and 3 using the conventional sultone-based electrolyte additives showed an initial capacity of 0.15 to 0.25 mAh reduced compared to Comparative Example 1 using the electrolyte without any compound. On the other hand, the batteries of Examples 1 to 7 using the unsaturated sultone compound of the present invention as an electrolyte additive showed a similar or rather increased initial capacity value.

From this, when the unsaturated sultone compound of the present invention is used as an electrolyte additive, it was found that the initial capacity reduction of the battery is minimized than the conventional electrolyte additive, thereby exhibiting an excellent effect on securing the capacity of the battery.

In addition, in Table 2, when the unsaturated sultone compound of the present invention is used as an electrolyte additive, it showed a higher discharge capacity retention rate compared to the case of using an electrolyte solution without adding any compound or a conventional sultone-based electrolyte additive. It can be seen from the above that when the unsaturated sultone compound of the present invention is used as an electrolyte additive, a more stable SEI film is formed on the surface of the negative electrode, thereby improving discharge capacity storage characteristics and lifetime characteristics of the battery.

Experimental Example  3. Cathode surface SEI  Membrane Formation Confirmation Experiment

In order to confirm the formation of the SEI film on the surface of the negative electrode by the unsaturated sultone compound of the present invention was carried out as follows.

The batteries prepared in Example 1, Comparative Example 1, and Comparative Example 3 were charged and discharged three times at 0.2 ° C. at 25 ° C. three times, and the negative electrode was collected by disassembling the batteries in a discharged state. Then, DSC (Differential Scanning Calorimetry) analysis was performed on the collected negative electrode and the results are shown in FIG. 1. At this time, the exothermic peak temperature is generally due to the thermal collapse of the SEI film formed on the surface of the cathode.

As a result, the exothermic reaction pattern of the negative electrode was different from each other depending on the electrolyte solution used in Example 1, and Comparative Examples 1 and 3. From this, it was found that the unsaturated sultone compound of the present invention is involved in the formation of the SEI film on the surface of the negative electrode.

In addition, the negative electrode of the Example 1 battery using the electrolyte solution containing the unsaturated sultone compound of the present invention Comparative Example 1 using the electrolyte solution without adding any compound of Comparative Example 3 using the negative electrode of the battery, and the conventional unsaturated sultone electrolyte additive Compared with the negative electrode of the battery, the exothermic peak temperature was higher and the calorific value was smaller. In general, the DSC analysis results indicate that the higher the exothermic peak temperature and the smaller the calorific value, the better the thermal stability of the SEI film on the cathode surface. From this, it was found that when the electrolyte solution containing the unsaturated sultone compound of the present invention was used, a more stable SEI film was formed on the surface of the negative electrode.

1 is a graph showing the results of differential scanning calorimetry (DSC) analysis according to Experimental Example 3. FIG.

Claims (8)

An electrolyte solution comprising an electrolyte salt and an electrolyte solvent, wherein the electrolyte solution includes a compound represented by Chemical Formula 1 below. [Formula 1]

In Formula 1, R ₁ , R ₂ , R _3, and R ₄ are each independently hydrogen, fluorine, an alkyl group having ₁ to ₆ carbon atoms, a cyclic alkyl group having 3 to 8 carbon atoms, and a C ₂ to C ₆ group. Is selected from the group consisting of an alkenyl group, a phenyl group, a benzyl group, and a halogen derivative thereof, n is an integer of 0 to 2. The electrolyte of claim 1, wherein the compound is ring-opened upon electrical reduction to form a reducing body having a resonance structure. The compound of claim 1, wherein the compound is 2-butenesultone, 2-methyl-2-butenesultone, 2-ethyl-2-butenesultone 2-butensultone), 2-propyl-2-butenesultone, 3-methyl-2-butenesultone, 3-ethyl-2-butenesultone 3-ethyl-2-butensultone), 3-propyl-2-butenesultone, 2,3-dimethyl-2-butenesultone, 2,3-dimethyl-2-butensultone, 2 , 3-diethyl-2-butenesultone, 2,3-dipropyl-2-butenesultone, 2-fluoro- 2-butenesultone (2-fluoro-2-butensultone), 3-fluoro-2-butenesultone (3-fluoro-2-butensultone), 2,3-difluoro-2-butenesultone (2,3- difluoro-2-butensultone), 2-phenyl-2-butenesultone, 2-benzyl-2-butenesultone, 2-allyl-2-butene 2-allyl-2-butensultone, 2-cyclopentyl-2-butensultone, 2-cyclohexyl-2-butenesultone nsultone), 2,4-dimethyl-2-butenesultone, 2,4-difluoro-2-butenesultone, 2 , 3,4-trimethyl-2-butenesultone (2,3,4-trimethyl-2-butensultone), 2,3,4,4-tetramethyl-2-butenesultone (2,3,4,4-tetramethyl -2-butensultone), 2,3,4-trifluoro-2-butenesultone (2,3,4-trifluoro-2-butensultone), 2,3,4,4-tetrafluoro-2-butenesultone (2,3,4,4-tetrafluoro-2-butensultone), 2-methyl-2-pentenesultone, 2-ethyl-2-pentenesultone ), 2-propyl-2-pentenesultone, 3-methyl-2-pentenesultone, 3-ethyl-2-pentenesultone -2-pentensultone), 3-propyl-2-pentensultone, 2,3-dimethyl-2-pentenesultone, 2,3- 2,3-diethyl-2-pentensultone, 2,3-dipropyl-2-pentensultone, 2-fluoro-2-pentene 2-fluoro-2-pentensultone, 3-fluoro-2- 3-fluoro-2-pentensultone, 2,3-difluoro-2-pentensultone, 2-phenyl-2-pentenesultone -pentensultone, 2-benzyl-2-pentensultone, 2-allyl-2-buttensultone, 2-cyclopentyl-2-pentenesultone 2-cyclopentyl-2-pentensultone, 2-cyclohexyl-2-pentensultone, 2,4-dimethyl-2-pentenesultone, 2,4-dimethyl-2-pentensultone, 2,4-difluoro-2-pentensultone, 2,3,4-trimethyl-2-pentenesultone, 2,3,4-trimethyl-2-pentensultone, 2,3,4,4-tetramethyl-2-pentenesultone (2,3,4,4-tetramethyl-2-pentensultone), 2,3,4,5-tetramethyl-2-pentenesultone (2,3 , 4,5-tetramethyl-2-pentensultone), 2,3,4-trifluoro-2-pentenesultone (2,3,4-trifluoro-2-pentensultone), 2,3,4,4-tetrafluoro Rho-2-pentenesultone (2,3,4,4-tetrafluoro-2-pentensultone), and 2,3,4,5-tetrafluoro-2-pentenesultone (2,3,4,5-tetrafluoro- 2-pentensultone) Electrolyte solution characterized in that selected from. The electrolyte of claim 1, wherein the amount of the compound is 0.1 to 20 parts by weight per 100 parts by weight of the electrolyte. An electrode on which a solid electrolyte interface (SEI) film including a chemical reaction product of the compound of Formula 1 is formed on part or all of a surface thereof: [Formula 1]

In Formula 1, R ₁ , R ₂ , R _3, and R ₄ are each independently hydrogen, fluorine, an alkyl group having ₁ to ₆ carbon atoms, a cyclic alkyl group having 3 to 8 carbon atoms, and a C ₂ to C ₆ group. Is selected from the group consisting of an alkenyl group, a phenyl group, a benzyl group, and a halogen derivative thereof, n is an integer of 0 to 2. The compound according to claim 5, wherein the compound is 2-butenesultone, 2-methyl-2-butenesultone, 2-ethyl-2-butenesultone 2-butensultone), 2-propyl-2-butenesultone, 2-methyl-2-butenesultone, 3-methyl-2-butenesultone, 3-ethyl-2-butenesultone ( 3-ethyl-2-butensultone), 3-propyl-2-butenesultone, 2,3-dimethyl-2-butenesultone, 2,3-dimethyl-2-butensultone, 2 , 3-diethyl-2-butenesultone, 2,3-dipropyl-2-butenesultone, 2-fluoro- 2-butenesultone (2-fluoro-2-butensultone), 3-fluoro-2-butenesultone (3-fluoro-2-butensultone), 2,3-difluoro-2-butenesultone (2,3- difluoro-2-butensultone), 2-phenyl-2-butenesultone, 2-benzyl-2-butenesultone, 2-allyl-2-part 2-allyl-2-butensultone, 2-cyclopentyl-2-butensultone, 2-cyclohexyl-2-butenesultone nsultone), 2,4-dimethyl-2-butenesultone, 2,4-difluoro-2-butenesultone, 2 , 3,4-trimethyl-2-butenesultone (2,3,4-trimethyl-2-butensultone), 2,3,4,4-tetramethyl-2-butenesultone (2,3,4,4-tetramethyl -2-butensultone), 2,3,4-trifluoro-2-butenesultone (2,3,4-trifluoro-2-butensultone), 2,3,4,4-tetrafluoro-2-butenesultone (2,3,4,4-tetrafluoro-2-butensultone), 2-methyl-2-pentenesultone, 2-ethyl-2-pentenesultone ), 2-propyl-2-pentenesultone, 3-methyl-2-pentenesultone, 3-ethyl-2-pentenesultone -2-pentensultone), 3-propyl-2-pentensultone, 2,3-dimethyl-2-pentenesultone, 2,3- 2,3-diethyl-2-pentensultone, 2,3-dipropyl-2-pentensultone, 2-fluoro-2-pentene 2-fluoro-2-pentensultone, 3-fluoro-2- 3-fluoro-2-pentensultone, 2,3-difluoro-2-pentensultone, 2-phenyl-2-pentenesultone -pentensultone, 2-benzyl-2-pentensultone, 2-allyl-2-buttensultone, 2-cyclopentyl-2-pentenesultone 2-cyclopentyl-2-pentensultone, 2-cyclohexyl-2-pentensultone, 2,4-dimethyl-2-pentenesultone, 2,4-dimethyl-2-pentensultone, 2,4-difluoro-2-pentenesultone, 2,3,4-trimethyl-2-pentenesultone (2,3,4-trimethyl-2-pentensultone) , 2,3,4,4-tetramethyl-2-pentenesultone (2,3,4,4-tetramethyl-2-pentensultone), 2,3,4,5-tetramethyl-2-pentenesultone (2, 3,4,5-tetramethyl-2-pentensultone), 2,3,4-trifluoro-2-pentenesultone (2,3,4-trifluoro-2-pentensultone), 2,3,4,4-tetra Fluoro-2-pentenesultone (2,3,4,4-tetrafluoro-2-pentensultone), and 2,3,4,5-tetrafluoro-2-pentenesultone (2,3,4,5-tetrafluoro -2-pentensultone) An electrode characterized in that it is selected from. A secondary battery comprising a positive electrode, a negative electrode, and an electrolyte solution, wherein the secondary battery is characterized in that the electrolyte solution includes the electrolyte solution of any one of claims 1 to 4. A secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, wherein the secondary battery has a positive electrode or a negative electrode including the electrode of any one of claims 5 to 6.

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