KR100993391B1 - Non-aqueous electrolyte and secondary battery comprising the same - Google Patents

Abstract

The present invention provides a secondary battery electrolyte comprising an electrolyte salt and an electrolyte solvent, wherein the electrolyte further comprises an acrylate compound having at least one electron attracting group (EWG) and two or more acrylic groups at the same time; An electrode having a solid electrolyte interface (SEI) film formed on part or all of a surface thereof, the chemical reaction product of an acrylate compound having at least one electron attracting group (EWG) and at least two acrylic groups at the same time; And it relates to a secondary battery having the electrolyte and / or the electrode.

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 containing an acrylate compound capable of improving the overall performance of the secondary battery, in particular the life, high rate characteristics, and high temperature storage characteristics; And it relates to a secondary battery comprising the same.

Recently, interest in energy storage technology is increasing. As the field of application extends to the energy of mobile phones, camcorders and notebook PCs, and even electric vehicles, efforts for research and development of electrochemical devices are becoming more concrete. Electrochemical devices are the most attention in this regard, and among them, the development of secondary batteries capable of charging and discharging has become a focus of attention. Recently, in developing such a battery, research and development on the design of a new electrode and a battery have been conducted to improve capacity density and specific energy.

Among the secondary batteries currently applied, lithium secondary batteries developed in the early 1990s have a higher operating voltage and a higher energy density than conventional batteries such as Ni-MH, Ni-Cd, and sulfuric acid-lead batteries that use an aqueous electrolyte solution. I am in the spotlight.

However, the electrolyte solvent of the secondary battery may decompose on the surface of the electrode during charge and discharge and cause side reactions in the battery. In particular, an organic solvent having a large molecular weight such as ethylene carbonate (EC), dimethyl carbonate (DMC) or diethyl carbonate (DEC) may be used. Co-intercalation between graphite layers in a carbon-based negative electrode can disrupt the structure of the negative electrode. For this reason, as the charge and discharge are repeated, there is a problem in that the life performance of the secondary battery is deteriorated, and this problem becomes more serious as the capacity density of the battery is increased.

In order to solve the above problems, a vinylene carbonate (JP 1996-45545), a propane sultone compound (JP 1999-339850) or a solid electrolyte interphase (SEI) film can be formed on the negative electrode surface; By using an acrylic compound (Japanese Laid-Open Patent Publication No. 2003-168479) as an electrolyte additive for a secondary battery, a method of improving lifetime characteristics by minimizing deterioration of a negative electrode has been proposed.

In the process of using the acrylate compound as an electrolyte additive, the present inventors can improve the lifespan performance of the battery by forming the SEI film having the excellent passivation effect, but the initial capacity is largely reduced. First recognized that there was a problem.

In addition, the present inventors use an acrylate compound containing at least one electron attracting group (EWG) and at least two acrylic groups at the same time as an electrolyte additive, an SEI film having an excellent passivation effect is formed, the battery life performance At the same time, it was found that the initial capacity reduction of the battery can be minimized. In addition, the present inventors found that the introduction of the electron attracting group (EWG) reduces the electrolyte oxidative decomposition reaction at the anode, thereby ensuring thermal stability of the battery, and improving the high temperature storage characteristics of the battery. Paid.

Thus, the present invention is an electrolyte solution containing an acrylate compound containing at least one electron attracting group (EWG) and at least two acrylic groups at the same time; And it is an object to provide a secondary battery provided with the electrolyte solution to improve the overall performance.

The present invention provides a secondary battery electrolyte comprising an electrolyte salt and an electrolyte solvent, wherein the electrolyte further comprises an acrylate compound having at least one electron attracting group (EWG) and two or more acrylic groups at the same time; 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 a solid electrolyte interface (SEI) film containing a chemical reaction product of an acrylate compound having at least one electron attracting group (EWG) and at least two acrylic groups at the same time; And it provides a secondary battery having the electrode.

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

The acrylate compound used as the electrolyte additive is estimated to form a SEI film on the surface of the negative electrode by reduction and polymerization reaction at the initial charge of the battery, wherein the double bond of the polymerizable acrylic group, preferably the acrylic group in the acrylate compound It is estimated that as the number increases, more various types of polymerization reactions can be performed to form a denser SEI film.

Therefore, when using the acrylate compound which has two or more acryl groups as electrolyte additive, it can form the SEI film which has the passivation effect superior to the acrylate compound which has one acryl group, and can improve the lifetime performance of a battery. However, in actual experiments, when the acrylate compound having only two or more acryl groups was added to the electrolyte, the battery life performance was improved, but the initial capacity of the battery was revealed to be greatly reduced.

Thus, the present invention for the first time to recognize the above problems when using the acrylate compound as an electrolyte additive, to solve this problem, an acrylate compound having at least one electron attracting group (EWG) and at least two acrylic groups at the same time electrolyte additive It is characterized by using as.

The acrylate compound of the present invention improves the lifespan performance of the battery by forming an SEI film having excellent passivation effect on the surface of the negative electrode by two or more acrylic groups, and at the same time, reduces the initial capacity of the battery by the electron withdrawing group (EWG). Can be minimized. The performance improvement effect of such a battery can be estimated as follows, but is not limited thereto.

Capacity reduction during initial charging and discharging of a battery is presumably due to the consumption of a large amount of lithium ions during the SEI film formation process. The amount of irreversible lithium ions consumed at this time is partially influenced by the kinds of compounds forming the SEI film and reduction reactivity. It is assumed to receive. According to the experimental results of Table 1, the acrylate electrolyte additives (Examples 1 to 3) in which the electron attracting group (EWG) was introduced in accordance with the present invention are the acrylate electrolyte additive (EWG) in which the electron attracting group (EWG) was not introduced. Since the initial capacity is larger than that of Comparative Example 2, it can be seen that the amount of irreversible lithium ions consumed when forming the SEI film is small.

On the other hand, the amount of lithium ions consumed when forming the SEI film is estimated to affect the resistance of the formed SEI film. That is, the greater the amount of lithium ions consumed in forming the SEI film, the greater the resistance of the SEI film to the movement of lithium ions to the electrode. Therefore, the acrylate compound of the present invention can minimize the amount of irreversible lithium ions consumed when forming the SEI film by the introduction of an electron withdrawing group (EWG), thereby lowering the resistance of the SEI film to the movement of lithium ions to the electrode. have. As a result, the present invention can improve not only the life performance of the battery but also the high rate characteristic.

In addition, the present invention can improve the high temperature storage characteristics of the battery. In general, when the battery is stored at a high temperature, an electrolyte component is easily oxidized and decomposed at the anode, so that gas is generated, thereby lowering thermal stability of the battery. However, in the present invention, the oxidation potential of the acrylate compound is increased by the electron withdrawing action of the electron withdrawing group (EWG) introduced into the acrylate compound, so that the oxidative decomposition reaction at the anode can be greatly reduced.

The compound used as the electrolyte additive of the present invention may be used without limitation as long as it is an acrylate compound having at least one electron attracting group (EWG) and at least two acrylic groups, and the acrylic group may be represented by the following Chemical Formula 1. .

[Formula 1]

In Formula 1, A is C ₁ ~ C ₁₂ alkylene or C ₁ ~ C ₁₂ haloalkylene; a is an integer between 0 and 30; B is H or a methyl group.

Meanwhile, the electron attracting group (EWG) is not limited as long as it has an electron withdrawing action, and non-limiting examples thereof include halogen, cyano, nitro, trifluoromethyl, trifluoroethyl, pentafluoroethyl, and 4-fluorophenyl. , pentafluorophenyl, 4-nitrophenyl, 4-fluorobenzyl, pentafluorobenzyl, 4-nitrobenzyl, acetyl, ethylcarbonyl, propylcarbonyl, benzoyl, 4-fluorobenzoyl, 4-nitrobenzoyl, methanesulfonyl, ethanesulfonyl, propanesulfonyl, allylsulfonyl, benzylsulfonyl, 4-fluorobenzylfluorobenzylsulfonzylsulfonyl, -chlorobenzylsulfonyl, 4-fluorophenylsulfonyl, 4-trifluoromethylphenylsulfonyl, 4-nitrophenylsulfonyl and the like, but is not limited thereto.

The acrylate compound of the present invention may be a compound represented by the following Chemical Formula 2 or 3.

[Formula 2]

In Formula 2, R 1 to R 4 are each independently hydrogen, an alkyl group of C ₁ to C ₆ , an acrylic group, or an electron withdrawing group (EWG), two or more of R 1 to R 4 are acrylic groups, and one or more are EWG.

(3)

In Formula 3, R 1 to R 6 are each independently hydrogen, an alkyl group of C ₁ to C ₆ , an acrylic group, or an electron withdrawing group (EWG), and two or more of R 1 to R 6 are acrylic groups, and one or more are EWG.

The acrylate compound may be used in 0.01 to 10 parts by weight per 100 parts by weight of the electrolyte. When the amount is less than 0.01 part by weight, the overall performance improvement effect of the secondary battery according to the use of the acrylate compound is insignificant, and when the amount exceeds 10 parts by weight, the performance of the electrochemical device using the same may be reduced.

The secondary battery electrolyte to which the acrylate compound is to be added includes conventional electrolyte components known in the art, such as electrolyte salts and electrolyte solvents.

The electrolyte salt is not particularly limited as long as it is usually used as an electrolyte salt for nonaqueous electrolyte. Electrolytic salt, non-limiting example, A ⁺ B ^- A salt of the structure, such as, A ⁺ is Li ^+, Na ^+, and comprising an alkali metal cation or cations consisting 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 ) salts consisting of a combination of anions such as cations and anions, including anions such as ₃ ^- or combinations thereof. In particular, lithium salts are preferred. These electrolyte salts can be used individually or in mixture of 2 or more types.

The electrolyte solvent is not particularly limited as long as it is usually used as an organic solvent for nonaqueous electrolyte, and cyclic carbonate, linear carbonate, lactone, ether, ester, sulfoxide, acetonitrile, lactam, and / or ketone can be used.

Examples of the cyclic carbonate include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), fluoroethylene carbonate (FEC), and the like. Examples of the linear carbonate include diethyl carbonate (DEC) and dimethyl carbonate. (DMC), dipropyl carbonate (DPC), ethylmethyl carbonate (EMC), methyl propyl carbonate (MPC), and the like. Examples of the lactone include gamma butyrolactone (GBL), and examples of the ether include dibutyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, 1,2-diethoxyethane and the like. Examples of such esters include methyl formate, ethyl formate, propyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, butyl propionate, methyl pivalate and the like. The sulfoxide includes dimethyl sulfoxide, the lactam includes N-methyl-2-pyrrolidone (NMP), and the ketone includes polymethylvinyl ketone. Moreover, the halogen derivative of the said organic solvent can also be used. These organic solvents can be used individually or in mixture of 2 or more types.

In addition, the present invention is an electrode formed on a part or all of a surface of a solid electrolyte interface (SEI) film containing a chemical reaction product of an acrylate compound having at least one electron attracting group (EWG) and at least two acrylic groups at the same time, preferably Preferably provides a cathode. The electrode may be prepared by charging and discharging an electrode prepared according to a conventional method known in the art at least once in an electrolyte solution containing the acrylate-based compound to form an SEI film on the surface of the electrode active material of the electrode. In addition, before assembling the battery unit, an electrode prepared by forming an SEI film may be prepared by electrically reducing an electrode prepared according to a conventional method known in the art to an electrolyte solution containing the acrylate-based compound.

The electrode before the SEI film is formed can be prepared according to a conventional method known in the art, for example, a slurry by mixing and stirring a solvent, a binder, a conductive material, a dispersant as necessary in the electrode active material. After the preparation, it may be prepared by coating (coating), compressing and drying the current collector of a metal material. In this case, the binder may be suitably used in an amount of 1 to 10 by weight and the conductive material in an amount of 1 to 30 by weight based on the electrode active material.

The negative electrode active material may be a conventional negative electrode active material that can be used for the negative electrode of the conventional electrochemical device, non-limiting examples thereof lithium metal, lithium alloy, carbon, petroleum coke that can occlude and release lithium ions ), Activated carbon, graphite, carbon fiber, and the like. In addition, metal oxides such as TiO ₂ , SnO _2, and the like, which can occlude and release lithium, and have a potential with respect to lithium of less than 2V, can be used. In particular, carbon materials such as graphite, carbon fiber and activated carbon are preferable.

The current collector of the metal material is a metal having high conductivity, and any metal can be used as long as the slurry of the electrode active material can be easily adhered and is not reactive in the voltage range of the battery. Non-limiting examples of the negative electrode current collector include a foil made by copper, gold, nickel or a copper alloy or a combination thereof.

Examples of binders that can be used include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), and the like.

The conductive material is not particularly limited as long as it is an electronic conductive material that does not cause chemical change in the electrochemical device. In general, carbon black, graphite, carbon fiber, carbon nanotubes, metal powder, conductive metal oxide, organic conductive materials, and the like can be used, and currently commercially available products as acetylene black series (Chevron Chemical) Chevron Chemical Company or Gulf Oil Company, etc., Ketjen Black EC series (Armak Company), Vulcan XC-72 (Cabot Company) (Cabot Company) and Super P (MMM).

Examples of the solvent include organic solvents such as NMP (N-methyl pyrrolidone), DMF (dimethyl formamide), acetone, and dimethyl acetamide or water, and these solvents may be used alone or in combination of two or more thereof. . The amount of the solvent used is sufficient to dissolve and disperse the electrode active material, the binder, and the conductive material in consideration of the coating thickness of the slurry and the production yield.

Further, the secondary battery of the present invention is an electrolyte containing an acrylate compound having at least one electron attracting group (EWG) and two or more acrylic groups at the same time, and / or one or more electron attracting groups (EWG) and two or more A solid electrolyte interface (SEI) film containing a chemical reaction product of an acrylate compound having an acryl group at the same time includes an electrode formed on part or all of a surface thereof. Preferably, the present invention provides a solid electrolyte interface (SEI) membrane comprising a separator, an anode, and a chemical reaction product of an acrylate compound having at least one electron attracting group (EWG) and two or more acrylic groups simultaneously. A cathode formed in all; And / or provides a secondary battery having an electrolyte solution containing the acrylate 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 according to a conventional method known in the art, the positive electrode active material may be prepared in a form bound to the positive electrode current collector. The positive electrode active material may be _a lithium transition metal composite oxide such as LiM _x O _y (M = Co, Ni, Mn, Co _a Ni _b Mn _c ) (for example, lithium manganese composite oxide such as LiMn ₂ O ₄ , LiNiO _2, etc.). Lithium cobalt oxides such as lithium nickel oxide, LiCoO ₂ , and manganese, nickel, and cobalt in which some of these oxides are substituted with other transition metals, or lithium-containing vanadium oxide, or a chalcogenide compound (for example, manganese dioxide) , Titanium disulfide, molybdenum disulfide, etc.) may be used. 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 it is preferable to use a porous separator, and non-limiting examples include a polypropylene-based, polyethylene-based, or polyolefin-based porous separator.

The secondary battery of 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 secondary battery of the present invention is not limited in appearance, but may be cylindrical, square, pouch type or coin type using a can.

Hereinafter, the present invention will be described in detail with reference to the following Examples. However, the following examples are merely to illustrate the present invention and the present invention is not limited by the following examples.

(Example 1)

Ethylene carbonate (EC): diethyl carbonate (DEC) = 3: 7 Volume 1M LiPF ₆ solution was prepared, followed by 1 wt% of a compound of formula 4 having two methanesulfonyl (EWG) and two acrylic groups It was added to prepare an electrolyte solution.

[Formula 4]

(Example 2)

An electrolyte was prepared in the same manner as in Example 1, except that the compound of Formula 5 having one allylsulfonyl (EWG) and three acrylic groups was used instead of the compound of Formula 4.

[Chemical Formula 5]

(Example 3)

An electrolyte was prepared in the same manner as in Example 1 except for using the compound of Formula 6 having one 4-fluorobenzol (EWG) and three acrylic groups instead of the compound of Formula 4.

[Formula 6]

(Example 4)

One trifluoromethyl (CF ₃ , An electrolyte was prepared in the same manner as in Example 1, except that the compound of Formula 7 having EWG) and five acrylic groups was used.

[Formula 7]

(Comparative Example 1)

An electrolyte was prepared in the same manner as in Example 1, except that tetraethyleneglycol diacrylate (TEGDA) having only two acrylic groups introduced therein instead of the compound of Formula 4 was used.

[Formula 8]

(Comparative Example 2)

An electrolyte solution was prepared in the same manner as in Example 1, except that trimethylolpropane triacrylate (TMPTA, in which Formula 3 was introduced) into which only three acrylic groups were introduced instead of the compound of Formula 4 was used.

[Formula 9]

(Comparative Example 3)

An electrolyte solution was prepared in the same manner as in Example 4, except that only the compound of Formula 10, in which only five acrylic groups were introduced instead of the compound of Formula 7, was used.

[Formula 10]

(Comparative Example 4)

An electrolyte was prepared in the same manner as in Example 1, except that no additive was used in the electrolyte.

[Battery Test 1: Initial Capacity and Room Temperature Lifetime]

Coin-shaped half cells were manufactured in a conventional manner using artificial graphite as an electrolyte and cathode active materials prepared in Examples 1 to 4 and Comparative Examples 1 to 4, and lithium metal as a negative electrode.

The coin half cell was charged and discharged at 0.5 C at room temperature, and the initial capacity and capacity retention rate (%) are shown in Table 1 below. At this time, the dose retention rate (%) is the ratio of 50 doses to 1 dose.

TABLE 1

Electrolyte additives Initial capacity
(mAh) Capacity retention rate (%) Example 1 Formula 4 (2 acrylic groups / 2 EWG)
1 wt% 5.5 91 Example 2 Formula 5 (3 acryl groups / 1 EWG)
1 wt% 5.4 90 Example 3 Chemical Formula 6 (3 Acrylic Groups / 1 EWG)
1 wt% 5.3 92 Example 4 Formula 7 (5 acrylic groups / 1 EWG)
1 wt% 5.4 93 Comparative Example 1 Formula 8 (two acrylic groups)
1 wt% 4.6 84 Comparative Example 2 Formula 9 (3 acryl groups)
1 wt% 4.0 90 Comparative Example 3 Formula 10 (5 acrylic groups)
1 wt% 4.1 89 Comparative Example 4 - 5.6 75

As a result, the cells of Comparative Examples 1 to 3 in which the acrylate compound having only two or more acrylic groups were used as electrolyte additives showed a capacity retention of 10 to 15% higher than that of Comparative Example 4, which did not use any electrolyte additives. I, initial capacity was 1.0 ~ 1.6 mAh low. From this, when using an acrylate compound having only two or more acryl groups as the electrolyte additive, by forming a dense SEI film can have an excellent negative electrode passivation effect, it was confirmed that there is a problem that the initial capacity reduction range is very large.

On the other hand, the batteries of Examples 1 to 4 in which an acrylate compound having at least one EWG and two or more acryl groups at the same time were used as an electrolyte additive showed high capacity retention rates of 90% or more and initial capacity of 5.3 mAh or more. That is, the batteries of Examples 1 to 4 have a slightly higher level of good negative electrode passivation effect than the batteries of Comparative Examples 1 to 3 in which an acrylate compound having only two or more acrylic groups is used as an electrolyte additive, and also reduces initial capacity. The width was also significantly low, it was confirmed that the implementation of a high capacity battery.

[Cell Test 2: Oxidation Voltage of Electrolyte and High Temperature Storage Characteristics of Battery]

(2-1.Measurement of oxidation voltage of electrolyte solution)

Linear sweep voltammetry was performed on the electrolyte solutions prepared in Examples 1 to 4 and Comparative Examples 1 to 4, and the measured oxidation start voltages are shown in Table 2 below. At this time, the oxidation start voltage was defined as the voltage when the oxidation current reached 0.1 mA / cm ² . The working electrode was a Pt disc electrode, the reference electrode was lithium metal, and the auxiliary electrode was a Pt wire electrode, and the scanning speed was 20 mV / s. Measurements were carried out in a glove box in an argon (Ar) atmosphere with moisture and oxygen concentrations of 10 ppm or less.

As a result of the experiment, the batteries of Examples 1 to 4 and Comparative Examples 1 to 4 each exhibited different oxidation initiation voltages, and it was confirmed that the oxidation initiation voltage of the electrolyte differs depending on the electrolyte component, especially the electrolyte additive (see Table 2). .

In addition, the battery of Examples 1-4 using the acrylate type compound which has one or more EWG and two or more acryl groups simultaneously as an electrolyte additive is the battery of Comparative Examples 1-3 which used the acrylate compound which has two or more acryl groups only. By showing a higher oxidation initiation voltage, it was confirmed that the oxidation potential of the acrylate compound was increased by the electron withdrawing action of the electron withdrawing group (EWG) (see Table 2).

(2-2. Comparison of Gas Generation Amount at High Temperature Storage of Battery)

Coin-shaped half-cells were prepared in a conventional manner using lithium metal as an electrolyte and a cathode active material prepared in Examples 1 to 4 and Comparative Examples 1 to 4 as LiCoO ₂ anodes. After storing the coin half cell at 90 ° C. for 4 hours, the amount of gas generated in the cell was measured, and the results are shown in Table 2. In this case, the gas generated at a high temperature of generally 80 ° C. or more is presumably due to the oxidative decomposition reaction of the electrolyte at the anode.

As a result of the experiment, the gas generation amount of the battery of Examples 1 to 4 using at least one EWG and an acrylate compound having two or more acrylic groups at the same time as an electrolyte additive was Comparative Example 1 using an acrylate compound having only two or more acrylic groups. About 1/3 less than the battery of ˜3 (see Table 2). From this, in the present invention it was confirmed that the electrolyte oxidative decomposition reaction at the positive electrode is greatly reduced, it can be seen that the high temperature storage characteristics of the battery can be improved thereby.

TABLE 2

Electrolyte additives Oxidation start voltage
(V vs. Li) Gas generation amount (a.u) Example 1 Formula 4 (2 acrylic groups / 2 EWG)
1 wt% 5.7 786 Example 2 Formula 5 (3 acryl groups / 1 EWG)
1 wt% 5.6 832 Example 3 Chemical Formula 6 (3 Acrylic Groups / 1 EWG)
1 wt% 5.5 798 Example 4 Formula 7 (5 acrylic groups / 1 EWG)
1 wt% 5.3 766 Comparative Example 1 Formula 8 (two acrylic groups)
1 wt% 5.1 2974 Comparative Example 2 Formula 9 (3 acryl groups)
1 wt% 5.0 2459 Comparative Example 3 Formula 10 (5 acrylic groups)
1 wt% 4.9 2159 Comparative Example 4 - 5.9 1356

Battery test 3: negative electrode SEI  Film formation confirmation experiment]

Coin-shaped half cells were prepared in a conventional manner using the electrolyte solutions prepared in Examples 1-4 and Comparative Examples 1-4, artificial graphite as a positive electrode, and lithium metal foil as a negative electrode. After charging and discharging the manufactured coin half cell at 0.2 ° C. at 23 ° C. three times, the battery was disassembled in a discharged state to collect a negative electrode, and then subjected to differential scanning calorimetry (DSC) analysis on the negative electrode. The exothermic peak temperature measured as a result of the DSC analysis is shown in Table 3. The exothermic peak temperature in Table 3 is generally assumed to be 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 additives used in Examples 1 to 4 and Comparative Examples 1 to 4. From this, it was confirmed that the electrolyte additive of the present invention is involved in the SEI film formation on the surface of the negative electrode.

In addition, the batteries of Examples 1 to 4 using an acrylate compound having at least one EWG and two or more acrylic groups simultaneously as an electrolyte additive were compared with Comparative Examples 1 to 3 and some using an acrylate compound having only two or more acrylic groups. The exothermic peak temperature was higher than that of the battery of Comparative Example 4 in which no electrolyte additive was used (see Table 3). In general, the higher the exothermic peak temperature in the DSC analysis, the better the thermal stability of the SEI film formed on the surface of the cathode. From this, it can be seen that the SEI film formed by the acrylate compound having at least one EWG and at least two acrylic groups simultaneously according to the present invention has better thermal stability.

[Table 3]

Electrolyte additives Exothermic peak temperature (℃) Example 1 Formula 4 (2 acrylic groups / 2 EWG)
1 wt% 122 Example 2 Formula 5 (3 acryl groups / 1 EWG)
1 wt% 123 Example 3 Chemical Formula 6 (3 Acrylic Groups / 1 EWG)
1 wt% 125 Example 4 Formula 7 (5 acrylic groups / 1 EWG)
1 wt% 126 Comparative Example 1 Formula 8 (two acrylic groups)
1 wt% 117 Comparative Example 2 Formula 9 (3 acryl groups)
1 wt% 119 Comparative Example 3 Formula 10 (5 acrylic groups)
1 wt% 121 Comparative Example 4 - 113

The secondary battery electrolyte of the present invention includes an acrylate-based compound having at least one EWG and at least two acrylic groups at the same time, thereby forming a SEI film having excellent passivation effect on the surface of the negative electrode, thereby improving battery life performance and The initial dose reduction of can be minimized. On the other hand, in the present invention, an SEI film having a low resistance to the movement of lithium ions to the electrode can be formed, and smooth movement of lithium ions to the electrode can be achieved.

In addition, in the present invention, the oxidation potential of the acrylate compound is increased by the electron withdrawing action of the electron withdrawing group (EWG) introduced into the acrylate compound, and the oxidative decomposition reaction at the positive electrode is greatly reduced, whereby the high temperature storage characteristics of the battery are improved. Can be improved.

Claims (9)

An electrolyte solution for a secondary battery comprising an electrolyte salt and an electrolyte solvent, wherein the electrolyte solution further comprises an acrylate compound having at least one electron attracting group (EWG) and two or more acrylic groups at the same time. The electrolyte of claim 1, wherein the acrylic group is a compound represented by the following Chemical Formula 1: [Formula 1]

In Formula 1, A is C1 ~ C12 alkylene or C1 ~ C12 haloalkylene; a is an integer between 0 and 30; B is H or a methyl group. The method of claim 1, wherein the electron withdrawing group (EWG) is halogen, cyano, nitro, trifluoromethyl, trifluoroethyl, pentafluoroethyl, 4-fluorophenyl, pentafluorophenyl, 4-nitrophenyl, 4-fluorobenzyl, pentafluorobenzyl, 4-nitrobenzyl, acetyl, ethylcarbonyl, selected from propylcarbonyl, benzoyl, 4-fluorobenzoyl, 4-nitrobenzoyl, methanesulfonyl, ethanesulfonyl, propanesulfonyl, allylsulfonyl, benzylsulfonyl, 4-fluorobenzylsulfonyl, pentafluorobenzylsulfonyl, 4-chlorobenzylsulfonyl, 4-fluorophenylsulfonyl, 4-trifluoromethylphenylsulfonyl, and 4- Characteristic electrolyte. The method of claim 1, wherein the acrylate compound is an electrolyte solution, characterized in that the compound of formula (2): [Formula 2]

In Formula 2, R 1 to R 4 are each independently hydrogen, an acryl group, or an electron withdrawing group (EWG), at least two of R 1 to R 4 are acrylic groups, and at least one is EWG. The electrolyte of claim 1, wherein the acrylate compound is a compound of Formula 3 below: (3)

In Formula 3, R 1 to R 6 are each independently hydrogen, an acryl group, or an electron withdrawing group (EWG), at least two of R 1 to R 6 are acrylic groups, and at least one is EWG. The electrolyte of claim 1, wherein the content of the acrylate compound is 0.01 to 10 parts by weight per 100 parts by weight of the electrolyte. An electrode having a solid electrolyte interface (SEI) film formed on part or all of a surface thereof, comprising a chemical reaction product of an acrylate compound having at least one electron attracting group (EWG) and at least two acrylic groups at the same time. The secondary battery containing the electrolyte solution in any one of Claims 1-6. The secondary battery containing the electrode of Claim 7.