WO2017074027A1 - Non-aqueous electrolyte additive, non-aqueous electrolyte comprising same, and lithium secondary battery including same - Google Patents

Abstract

The present invention relates to: a non-aqueous electrolyte additive comprising, as a substituent, a cyano group and at least one fluorine element; a non-aqueous electrolyte for a lithium secondary battery, comprising the same; and a lithium secondary battery including the same.

Description

Non-aqueous electrolyte additive, non-aqueous electrolyte comprising same and lithium secondary battery having same

Cross Citation with Related Application (s)

This application claims the benefit of priority based on Korean Patent Application No. 10-2015-0150733 dated October 29, 2015 and Korean Patent Application No. 10-2016-0139012 dated October 25, 2016. All content disclosed in the literature is included as part of this specification.

Technical Field

The present invention relates to a nonaqueous electrolyte additive, a nonaqueous electrolyte including the same, and a lithium secondary battery having the same, and specifically, a nonaqueous electrolyte additive capable of improving performance while ensuring stability at high voltage, a nonaqueous electrolyte including the same, and the same It relates to a lithium secondary battery.

Recently, the interest in energy storage technology is increasing, and as the field of application to the energy of mobile phones, camcorders, notebook PCs, and even electric vehicles has been expanded, efforts for research and development of electrochemical devices are becoming more concrete.

Electrochemical devices are the most attracting field in this respect, and among them, interest in secondary batteries capable of charging and discharging has emerged. In particular, lithium secondary batteries developed in the early 1990s among the currently applied secondary batteries have been in the spotlight for their advantages of high operating voltage and high energy density.

The lithium secondary battery is composed of a negative electrode made of a carbon material or the like capable of occluding and releasing lithium ions, a positive electrode made of a lithium transition metal oxide and the like, and a nonaqueous electrolyte.

The lithium secondary battery includes a lithium ion liquid battery (LiLB) using a liquid electrolyte, a lithium ion polymer battery (LiPB) using a gel polymer electrolyte, and a LPB (lithium) using a solid polymer electrolyte according to the type of electrolyte used. polymer battery).

Recently, as the application range of lithium secondary batteries is expanded, there is a growing demand for lithium secondary batteries that can be safely charged even at high voltages while maintaining excellent cycle life characteristics even in harsh environments such as high temperature, low temperature, and high voltage charging. .

On the other hand, as the charge and discharge of the secondary battery proceeds, the cathode active material is structurally collapsed, thereby degrading the performance of the cathode. In addition, when the anode structure collapses, metal ions eluted from the surface of the anode deteriorate the cathode while electrodeposition (electrodeposition) on the cathode. Such deterioration of battery performance tends to be accelerated when the potential of the positive electrode is increased or when the battery is exposed to high temperature.

In order to solve the above problems, a method of forming a film on the positive electrode and adding a material for protecting the positive electrode to the electrolyte has been proposed.

Prior art literature

Korean Patent Publication No. 2014-0067242

Korean Patent Registration Publication No. 1249350

In order to solve the above problems, the first technical problem of the present invention is to provide a non-aqueous electrolyte additive excellent in the adsorption effect with the metal ions eluted from the anode.

Another object of the present invention is to provide a nonaqueous electrolyte solution for a lithium secondary battery that can improve overcharge safety of an electrolyte by including the nonaqueous electrolyte additive.

In addition, a third technical object of the present invention is to provide a lithium secondary battery having improved cycle characteristics and high temperature storage performance even at high voltage charging by including the nonaqueous electrolyte.

In order to achieve the above object, in one embodiment of the present invention,

It provides a nonaqueous electrolyte additive comprising a compound represented by the following formula (1):

[Formula 1]

In Chemical Formula 1,

R is an alkyl group having 1 to 3 carbon atoms substituted or unsubstituted with at least one fluorine element,

A is an alkyl group having 1 to 4 carbon atoms in which at least one fluorine element and cyano group (-CN) are substituted.

In addition, in one embodiment of the present invention

Ionizable lithium salts; Organic solvents; And it provides a non-aqueous electrolyte for lithium secondary battery comprising the non-aqueous electrolyte additive.

In addition, in one embodiment of the present invention

Provided is a negative electrode, a positive electrode, a separator interposed between the negative electrode and the positive electrode, and a lithium secondary battery having a nonaqueous electrolyte of the present invention.

The present invention provides a non-aqueous electrolyte additive that can form a more stable ionic conductive film on the surface of the anode to suppress the decomposition reaction of the electrolyte, thereby suppressing the decomposition reaction during overcharging or suppressing elution and movement of metal ions. The lithium secondary battery electrolyte which can be made, and the lithium secondary battery which improved the lifetime characteristic and high temperature safety under high voltage can be manufactured.

1 is a graph showing the life characteristics of a lithium secondary battery according to Experimental Example 1 of the present invention.

2 is a graph showing the results of measuring AC impedance according to Experimental Example 3 of the present invention.

Hereinafter, the present invention will be described in more detail.

The terms or words used in this specification and claims are not to be construed as limiting in their usual or dictionary meanings, and the inventors may appropriately define the concept of terms in order to best explain their invention in the best way possible. It should be interpreted as meaning and concept corresponding to the technical idea of the present invention based on the principle that the present invention.

In general, when overcharging occurs in a secondary battery, an excessive amount of lithium ions are released from the positive electrode, resulting in an unstable structure of the positive electrode active material. Oxygen is released from the cathode active material having such an unstable structure, causing a decomposition reaction of the electrolyte. In particular, in high temperature conditions, elution of metal ions from the positive electrode increases, and when such metal ions precipitate from the negative electrode, there is a disadvantage in that the performance of the battery is reduced.

Thus, one embodiment of the present invention to provide a non-aqueous electrolyte additive that can form a complex with the metal ions eluted from the anode.

In addition, the present invention provides a nonaqueous electrolyte solution for a lithium secondary battery that can improve the overcharge safety of the electrolyte by including the nonaqueous electrolyte additive.

In addition, the present invention provides a lithium secondary battery having improved cycle characteristics and high temperature storage performance even at high voltage charging by including the nonaqueous electrolyte.

Specifically, in one embodiment of the present invention

Provided is a nonaqueous electrolyte additive comprising a compound represented by the following Formula 1 in which a cyano group and at least one fluorine element are present as a substituent:

[Formula 1]

In Chemical Formula 1,

R is an alkyl group having 1 to 3 carbon atoms substituted or unsubstituted with at least one fluorine element,

A is an alkyl group having 1 to 4 carbon atoms in which at least one fluorine element and cyano group (-CN) are substituted.

Specific examples of the compound represented by Formula 1 include at least one compound selected from the group consisting of the following Formulas 1a to 1i.

[Formula 1a]

[Formula 1b]

[Formula 1c]

[Formula 1d]

[Formula 1e]

[Formula 1f]

[Formula 1g]

[Formula 1h]

Formula 1i]

In addition, in one embodiment of the present invention

Ionizable lithium salts; Organic solvents; And nonaqueous electrolyte additives,

It provides a non-aqueous electrolyte lithium secondary battery containing the compound represented by the formula (1) as the non-aqueous electrolyte additive.

In this case, the nonaqueous electrolyte additive may be included in about 0.5 to 5% by weight, specifically 1 to 5% by weight, based on the total weight of the nonaqueous electrolyte. If the content of the additive is less than 0.5% by weight, the stabilizing effect of the SEI film described later is insufficient, and if the content of the additive is more than 5% by weight, at least one fluorine element substituted at the terminal of the compound of Formula 1 included in the additive Or increased resistance due to cyano groups.

Among the electrochemical devices, lithium secondary battery forms a passivation film by electrochemical oxidative decomposition reaction of electrolyte at the surface of the battery's positive electrode, especially in the presence of surface bond or activation position. Increase impedance to co-intercalation. In addition, during the repetition of charging and discharging, structural dissolution of the cathode active material or chemical dissolution reaction occurs by the electrolytic solution, so that ions of Co, Mn, and Ni are eluted. These reactions lead to a decrease in the performance of the anode itself, and at the same time, eluted metal ions are electrodeposited on the surface of the cathode. The metal electrodeposited on the negative electrode generally exhibits great reactivity with the electrolyte. Therefore, the amount of reversible lithium is increased, thereby increasing the irreversible reaction according to the progress of charging and discharging, which results in deterioration of the capacity and life characteristics of the battery.

Accordingly, the present invention provides a cyano group (-CN) -containing compound having a high tendency to form a complex with metal ions such as Co, Mn, and Ni as an electrolyte additive.

That is, since the non-aqueous electrolyte additive made of the compound represented by Chemical Formula 1 of the present invention contains eluted metal ions and a cyano group of good adsorption, the non-aqueous electrolyte additive has a structural breakdown of the positive electrode active material during charge and discharge of the battery. By the chemical dissolution reaction by the electrolytic solution, the complexes may be combined with the metal ions eluted from the anode to form a stable ion conductive film on the surface of the anode. In addition, since the non-aqueous electrolyte additive composed of the compound represented by Formula 1 of the present invention includes at least one or more fluorine elements as a substituent, not only is it easier to form a film, but also the ion conductive effect of the resulting film can be enhanced. . Furthermore, the compound represented by the formula (1) of the present invention can suppress the electrodeposition of the metal ions eluted from the positive electrode to the negative electrode even in a state where no film is formed. Therefore, the lithium secondary battery of the present invention having the nonaqueous electrolyte containing such additives can significantly improve overall performance such as room temperature and high temperature life characteristics of the secondary battery by allowing the negative electrode to smoothly occlude and release lithium even at high temperatures.

On the other hand, in the non-aqueous electrolyte of the present invention, the lithium salt included as an electrolyte may be used without limitation those conventionally used in the electrolyte for lithium secondary batteries, for example, Li ⁺ as a cation of the lithium salt, an anion is ^{F -, Cl -, Br -} , I -, NO 3 -, N (CN) 2 -, BF 4 -, ClO 4 -, AlO 4 -, AlCl 4 -, PF 6 -, SbF 6 -, AsF 6 _{^{-, BF 2 C 2 O 4}} -, BC 4 O 8 -, (CF 3) 2 PF 4 -, (CF 3) 3 PF 3 -, (CF 3) 4 PF 2 -, (CF 3) 5 PF - ^{_{, (CF 3) 6 P -}} , CF 3 SO 3 -, C 4 F 9 SO 3 -, CF 3 CF 2 SO 3 -, (CF 3 SO 2) 2 N -, (FSO 2) 2 N -, CF _{3 CF 2 (CF 3) 2} CO -, (CF 3 SO 2) 2 CH -, (SF 5) 3 C -, (CF 3 SO 2) 3 C -, CF 3 (CF 2) 7 SO 3 -, _{^{CF 3 CO 2 -, CH 3}} CO 2 -, SCN - can include at least one selected from the group consisting of ^- and _{(CF 3 CF 2 SO 2)} 2 N. The said lithium salt can also be used 1 type or in mixture of 2 or more types as needed. The lithium salt may be appropriately changed within a range generally available, but may be included in an electrolyte solution at a concentration of 0.8 M to 1.5 M in order to obtain an effect of forming an anti-corrosion coating on the surface of the electrode.

In addition, the organic solvent included in the nonaqueous electrolyte of the present invention may be used without limitation those conventionally used in the lithium secondary battery electrolyte, for example, ether compounds, ester compounds, amide compounds, linear carbonate compounds, or cyclic carbonate compounds These may be used alone or in combination of two or more thereof. Representatively, it may include a cyclic carbonate compound, a linear carbonate compound, or a mixture thereof.

Specific examples of the cyclic carbonate compound include ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, vinylene carbonate and fluoroethylene carbonate (FEC) are any one selected from the group consisting of or mixtures of two or more thereof. In addition, specific examples of the linear carbonate compound include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethylmethyl carbonate (EMC), methylpropyl carbonate and ethylpropyl carbonate. Any one selected from, or a mixture of two or more thereof may be representatively used, but is not limited thereto.

In particular, ethylene carbonate and propylene carbonate, which are cyclic carbonates among the carbonate-based organic solvents, are highly viscous organic solvents, and thus may be preferably used because they dissociate lithium salts in the electrolyte well. When the same low viscosity, low dielectric constant linear carbonate is mixed and used in an appropriate ratio, an electrolyte having high electrical conductivity can be made, and thus it can be used more preferably.

In addition, as the ether compound in the organic solvent, any one selected from the group consisting of dimethyl ether, diethyl ether, dipropyl ether, methylethyl ether, methylpropyl ether and ethylpropyl ether, or a mixture of two or more thereof may be used. However, the present invention is not limited thereto.

And ester compounds in the organic solvent include linear esters such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate; And cyclic esters such as γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, and ε-caprolactone, or a mixture of two or more thereof may be used. However, the present invention is not limited thereto.

In addition, in one embodiment of the present invention,

In the secondary battery comprising a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode and a non-aqueous electrolyte, it provides a lithium secondary battery comprising the electrolyte of the present invention as the electrolyte.

Specifically, the lithium secondary battery of the present invention may be prepared by injecting the nonaqueous electrolyte of the present invention into an electrode structure consisting of a cathode, a cathode, and a separator interposed between the cathode and the anode. At this time, the positive electrode, the negative electrode, and the separator constituting the electrode structure may be used all those conventionally used in the manufacture of a lithium secondary battery.

In this case, the positive electrode may be prepared by coating a positive electrode mixture including a positive electrode active material, a binder, a conductive material and a solvent on a positive electrode current collector.

The positive electrode current collector is not particularly limited as long as it has conductivity without causing chemical changes in the battery. For example, the positive electrode current collector may be formed of stainless steel, aluminum, nickel, titanium, calcined carbon, or carbon on the surface of aluminum or stainless steel. Surface treated with nickel, titanium, silver, or the like may be used.

The positive electrode active material is a compound capable of reversible intercalation and deintercalation of lithium, and may specifically include a lithium composite metal oxide containing lithium and one or more metals such as cobalt, manganese, nickel or aluminum. have. More specifically, the lithium composite metal oxide may be lithium-manganese oxides (eg, LiMnO ₂ , LiMn ₂ O _4, etc.), lithium-cobalt oxides (eg, LiCoO _2, etc.), lithium-nickel oxides, and the like. (for example, LiNiO ₂ and the like), lithium-nickel-manganese-based oxide (for example, LiNi _1-Y Mn _Y O ₂ (where, 0 <Y <1), LiMn _2-z Ni _z O ₄ ( here, 0 <Z <2) and the like), lithium-nickel-cobalt oxide (e.g., LiNi _1-Y1 Co _Y1 O ₂ (here, 0 <Y1 <1) and the like), lithium-manganese-cobalt oxide (e. g., LiCo _1-Y2 Mn _Y2 O ₂ (here, 0 <Y2 <1), LiMn 2 - z1 Co z1 O 4 ( here, 0 <z1 <2) and the like), lithium-nickel Manganese-cobalt-based oxides (e.g., Li (Ni _p Co _q Mn _r1 ) O ₂ , where 0 <p <1, 0 <q <1, 0 <r1 <1, p + q + r1 = 1) or Li (Ni _p1 Co _q1 Mn _r2 ) O ₄ (where 0 <p1 <2, 0 <q1 <2, 0 <r2 <2, p1 + q1 + r21 = 2, etc.), or lithium- nickel-cobalt-transition metal (M) oxide (e.g., Li (Ni Co _{p2 q2} Mn _r3 M _S2) O ₂ (W Where M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg and Mo, and p2, q2, r3 and s2 are atomic fractions of the independent elements, respectively, 0 <p2 <1, 0 <Q2 <1, 0 <r3 <1, 0 <s2 <1, p2 + q2 + r3 + s2 = 1), etc.), and any one or two or more of these compounds may be included. Among the lithium composite metal oxides, LiCoO ₂ , LiMnO ₂ , LiNiO ₂ , and lithium nickel manganese cobalt oxides (eg, Li (Ni _0.6 Mn _0.2 Co _0.2 ) O ₂ may be improved in capacity and stability of the battery. , Li (Ni _0.5 Mn _0.3 Co _0.2 ) O ₂ , Li (Ni _0.7 Mn _0.15 Co _0.15 ) O ₂ or Li (Ni _0.8 Mn _0.1 Co _0.1 ) O _2, etc.), or lithium nickel cobalt aluminum oxide (eg, Li (Ni _0.8 Co _0.15 Al _0.05 ) O _2, etc.), and the lithium composite metal oxide may be Li (Ni) in consideration of the remarkable improvement effect by controlling the type and content ratio of the constituent elements forming the lithium composite metal oxide. _0.6 Mn _0.2 Co _0.2 ) O ₂ , Li (Ni _0.5 Mn _0.3 Co _0.2 ) O ₂ , Li (Ni _0.7 Mn _0.15 Co _0.15 ) O _2, or Li (Ni _0.8 Mn _0.1 Co _0.1 ) O ₂ , and the like, and any one or a mixture of two or more thereof may be used. have.

The cathode active material may be included in an amount of 80 wt% to 99 wt% based on the total weight of the cathode mixture.

The conductive material is typically added in an amount of 1 to 30% by weight based on the total weight of the positive electrode mixture.

Such a conductive material is not particularly limited as long as it has conductivity without causing chemical change in the battery, and examples thereof include graphite; Carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; Conductive fibers such as carbon fibers and metal fibers; Metal powders such as carbon fluoride powder, aluminum powder and nickel powder; Conductive whiskeys such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used. Specific examples of commercially available conductive materials include Chevron Chemical Company, Denka Singapore Private Limited, Gulf Oil Company, Ketjenblack and EC, which are acetylene black series. Family (Armak Company), Vulcan XC-72 (manufactured by Cabot Company) and Super P (manufactured by Timcal).

The binder is a component that assists in bonding the active material and the conductive material and bonding to the current collector, and is generally added in an amount of 1 to 30 wt% based on the total weight of the positive electrode mixture. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene , Polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluorine rubber, various copolymers, and the like.

In addition, the negative electrode may be prepared by, for example, coating a negative electrode mixture including a negative electrode active material, a binder, a conductive material, a solvent, and the like on a negative electrode current collector.

The negative electrode current collector generally has a thickness of 3 to 500 μm. Such a negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical change in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel Surface-treated with carbon, nickel, titanium, silver, and the like on the surface, aluminum-cadmium alloy and the like can be used. In addition, like the positive electrode current collector, fine concavities and convexities may be formed on the surface to enhance the bonding strength of the negative electrode active material, and may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric.

As the negative electrode active material, natural graphite, artificial graphite, carbonaceous material; Metals (Me) that are lithium-containing titanium composite oxide (LTO), Si, Sn, Li, Zn, Mg, Cd, Ce, Ni, or Fe; Alloys composed of the metals (Me); Oxides of the metals (Me) (MeOx); And one or two or more negative electrode active materials selected from the group consisting of a complex of the metals (Me) and carbon.

The negative active material may be included in an amount of 80 wt% to 99 wt% based on the total weight of the negative electrode mixture.

The binder is a component that assists the bonding between the conductive material, the active material and the current collector, and is usually added in an amount of 1 to 30 wt% based on the total weight of the negative electrode mixture. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoro Low ethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, fluorine rubber, various copolymers thereof, and the like.

The conductive material is a component for further improving the conductivity of the negative electrode active material, and may be added in an amount of 1 to 20 wt% based on the total weight of the negative electrode mixture. Such a conductive material is not particularly limited as long as it has conductivity without causing chemical change in the battery, and examples thereof include graphite such as natural graphite and artificial graphite; Carbon blacks such as acetylene black, Ketjen black, channel black, furnace black, lamp black and thermal black; Conductive fibers such as carbon fibers and metal fibers; Metal powders such as carbon fluoride powder, aluminum powder and nickel powder; Conductive whiskeys such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used.

The solvent may include an organic solvent such as water or NMP (N-methyl-2-pyrrolidone), and may be used in an amount that becomes a desirable viscosity when including the negative electrode active material, and optionally a binder and a conductive material. . For example, the concentration of the negative electrode active material and, optionally, the solid content including the binder and the conductive material may be 50 wt% to 95 wt%, preferably 70 wt% to 90 wt%.

In addition, as the separator, conventional porous polymer films conventionally used as separators, for example, polyolefins such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer and ethylene / methacrylate copolymer, etc. The porous polymer film made of the polymer may be used alone or by laminating them, or a conventional porous nonwoven fabric, for example, a non-woven fabric made of high melting point glass fiber, polyethylene terephthalate fiber, or the like may be used. It is not.

The external shape of the lithium secondary battery of the present invention is not particularly limited, 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 Examples. However, embodiments according to the present invention can be modified in many different forms, the scope of the present invention should not be construed as limited to the embodiments described below. The embodiments of the present invention are provided to more completely explain the present invention to those skilled in the art.

Example

Hereinafter, the present invention will be described in detail with reference to Examples. However, embodiments according to the present invention can be modified in many different forms, the scope of the present invention should not be construed as limited to the embodiments described below. The embodiments of the present invention are provided to more completely explain the present invention to those skilled in the art.

Example 1

(Non-aqueous electrolyte preparation)

Fluoroethylene carbonate (FEC), propylene carbonate (PC) and ethylene carbonate (EMC) were mixed in a ratio of 30:10:60 (vol%) to prepare an organic solvent mixture. Thereafter, 0.5 wt% of the compound of Chemical Formula 1a was further added based on the total content of the prepared organic solvent mixture, and LiPF ₆ was dissolved to a concentration of 1 M to prepare a nonaqueous electrolyte.

(Anode manufacturing)

Based on 100 parts by weight of N-methyl-2-pyrrolidone (NMP) solvent, lithium cobalt composite oxide (LiCO ₂ ) as the positive electrode active material particles, carbon black as the conductive material, and polyvinylidene fluoride (PVDF) as the binder was 90 The positive electrode mixture was prepared by adding 40 parts by weight of the positive electrode mixture mixed at a ratio of 5: 5 (wt%). The positive electrode mixture was applied to a positive electrode current collector (Al thin film) having a thickness of 100 μm, dried, and roll pressed to prepare a positive electrode.

(Cathode production)

Based on 100 parts by weight of N-methyl-2-pyrrolidone (NMP) solvent, natural graphite as a negative electrode active material, PVDF as a binder and carbon black as a conductive material at a ratio of 95: 2: 3 (wt%) 80 Part by weight was added to prepare a negative electrode mixture. The negative electrode mixture was applied to a negative electrode current collector (Cu thin film) having a thickness of 90 μm, dried, and roll pressed to prepare a negative electrode.

(Secondary Battery Manufacturing)

The positive electrode and the negative electrode prepared by the above-described method was prepared with a polyethylene porous film by a conventional method, and then the non-aqueous electrolyte was prepared by pouring the lithium secondary battery.

Example 2

In preparing the non-aqueous electrolyte, an electrolyte solution and a battery including the same were prepared in the same manner as in Example 1 except that the compound of Formula 1b was used instead of the compound of Formula 1a as an additive.

Example 3

In preparing the non-aqueous electrolyte, an electrolyte solution and a battery including the same were prepared in the same manner as in Example 1 except that the compound of Formula 1c was used instead of the compound of Formula 1a as an additive.

Example 4

In preparing the non-aqueous electrolyte, an electrolyte solution and a battery including the same were prepared in the same manner as in Example 1 except that the compound of Formula 1d was used instead of the compound of Formula 1a as an additive.

Example 5

In preparing the non-aqueous electrolyte, an electrolyte solution and a battery including the same were prepared in the same manner as in Example 1 except that the compound of Formula 1e was used instead of the compound of Formula 1a as an additive.

Example 6

In preparing the non-aqueous electrolyte, an electrolyte solution and a battery including the same were prepared in the same manner as in Example 1 except that the compound of Formula 1f was used instead of the compound of Formula 1a as an additive.

Example 7

In preparing the non-aqueous electrolyte, an electrolyte and a battery including the same were prepared in the same manner as in Example 1, except that the additive contained the compound of Formula 1g instead of the compound of Formula 1a.

Example 8

In preparing the non-aqueous electrolyte, an electrolyte solution and a battery including the same were prepared in the same manner as in Example 1, except that the compound of Formula 1h was used instead of the compound of Formula 1a as an additive.

Example 9

In preparing the non-aqueous electrolyte, an electrolyte solution and a battery including the same were prepared in the same manner as in Example 1, except that 5 wt% of the compound of Formula 1a was used as an additive.

Comparative Example 1

An electrolyte and a battery including the same were prepared in the same manner as in Example 1, except that the compound of Formula 1a was not added as an additive.

Comparative Example 2

In preparing the non-aqueous electrolyte, an electrolyte solution and a battery including the same were prepared in the same manner as in Example 1 except that the compound of Formula 2a was used instead of the compound of Formula 1a as an additive.

[Formula 2a]

Comparative Example 3

In preparing the non-aqueous electrolyte, an electrolyte solution and a battery including the same were prepared in the same manner as in Example 1 except for including the following Formula 2b as an additive instead of the compound of Formula 1a.

[Formula 2b]

Comparative Example 4

An electrolyte and a battery including the same were prepared in the same manner as in Example 1, except that 7 wt% of the compound of Formula 1a was added as an additive when preparing the non-aqueous electrolyte.

Comparative Example 5

An electrolyte and a battery including the same were prepared in the same manner as in Example 1 except for including the following Chemical Formula 2c instead of the compound of Chemical Formula 1a.

[Formula 2c]

Experimental Example

Experimental Example 1: Life Characteristics

The batteries (battery capacity 5.5 mAh) prepared in Examples 1 to 9 and Comparative Examples 1 to 5 were charged at 60 ° C. to 0.7C constant current until 4.35V, and then charged at a constant voltage of 4.35V to charge current 0.275. Charging was terminated when mA reached. Then, it was left for 10 minutes and then discharged until it became 3.0V at 0.5C constant current. After 100 cycles of charging and discharging, the battery capacity was measured and shown in FIG. 1.

Here, C represents the charge / discharge current rate and C-rate of the battery represented by ampere (A) and is usually expressed as a ratio of battery capacity. That is, 1C of the cells manufactured previously means 5.5 mA current.

As shown in FIG. 1, it can be seen that the batteries of Examples 1 to 9 are superior in cycle life characteristics to those of the secondary batteries of 1 to 5 in comparison.

Experimental Example 2: Co ion electrodeposition experiment

For the membranes of the cells subjected to the evaluation of the high temperature life characteristics in Experimental Example 1, the concentration of the eluted Co ions was measured using an ICP (Inductively Coupled Plasma) analysis method, and the comparison results are shown in Table 1 below.

	Chemical formula	usage	Co (ppm)
Example 1	1a	0.5 wt%	45
Example 2	1b	0.5 wt%	48
Example 3	1c	0.5 wt%	44
Example 4	1d	0.5 wt%	48
Example 5	1e	0.5 wt%	52
Example 6	1f	0.5 wt%	75
Example 7	1 g	0.5 wt%	63
Example 8	1h	0.5 wt%	57
Example 9	1a	5 wt%	55
Comparative Example 1	-	-	255
Comparative Example 2	2a	0.5 wt%	208
Comparative Example 3	2b	0.5 wt%	190
Comparative Example 4	1a	7 wt%	144
Comparative Example 5	2c	0.5 wt%	131

As shown in Table 1, it can be seen that the batteries of Examples 1 to 9 were all lowered to less than 75 ppm of Co concentration, whereas all of the secondary batteries of Comparative Examples 1 to 5 were higher than 190 ppm. Therefore, when using the nonaqueous electrolyte containing the additive of this invention, it can be confirmed that elution of a metal can be suppressed and a stable film can be formed.

Experimental Example 3: Measurement of AC Impedance (alternative-current impedance)

The lithium secondary batteries of Example 1, Example 9, and Comparative Example 4 were placed at 25 ° C. under SOC at 0% for 1 hour, and then the AC impedance of the battery was measured while scanning to 50 mHz-100 kHz. At this time, the amplitude of the alternating current was 10mV, and the DC potential of the battery was 3.74V. The results are shown in FIG.

At this time, the intersection point with the X-axis in the graph of Figure 2 means Ohm resistance of the battery, the half circle (half circle) at the rear means the resistance by the SEI formed on the surface of the electrode plate.

In other words, the smaller the diameter of the semicircle, the smaller the magnitude of resistance caused by SEI.

As shown in FIG. 2, it can be seen that Comparative Example 4, which has a large amount of addition compared to Examples 1 and 9, has greatly increased resistance. In addition, it can be seen that in Comparative Example 4, the amount of Co eluted is large and the life is also reduced.

Claims (8)

1. A nonaqueous electrolyte additive comprising a compound represented by the following formula (1):

   [Formula 1]

   

   In Chemical Formula 1,

   R is an alkyl group having 1 to 3 carbon atoms substituted or unsubstituted with at least one fluorine element, and A is an alkyl group having 1 to 4 carbon atoms substituted with at least one fluorine element and cyano group (-CN).
2. The method according to claim 1,

   The non-aqueous electrolyte additive is a non-aqueous electrolyte additive comprising at least one compound selected from the group consisting of compounds represented by the general formula 1a to 1i:

   [Formula 1a]

   

   [Formula 1b]

   

   [Formula 1c]

   

   [Formula 1d]

   

   [Formula 1e]

   

   [Formula 1f]

   

   [Formula 1g]

   

   [Formula 1h]

   

   Formula 1i]

   
3. Ionizable lithium salts; Organic solvents; And a nonaqueous electrolyte solution for a lithium secondary battery comprising a nonaqueous electrolyte additive,

   The non-aqueous electrolyte additive is a non-aqueous electrolyte lithium secondary battery containing a compound represented by the formula (1):

   [Formula 1]

   

   In Chemical Formula 1,

   R is an alkyl group having 1 to 3 carbon atoms substituted or unsubstituted with at least one fluorine element, and A is an alkyl group having 1 to 4 carbon atoms substituted with at least one fluorine element and cyano group (-CN).
4. The method according to claim 3,

   The non-aqueous electrolyte additive is a non-aqueous electrolyte lithium secondary battery that will be contained in 0.5% by weight to 5% by weight based on the total content of the non-aqueous electrolyte.
5. The method according to claim 4,

   The nonaqueous electrolyte additive is a non-aqueous electrolyte lithium secondary battery that will be included in 1% by weight to 5% by weight based on the total content of the nonaqueous electrolyte.
6. The method according to claim 3,

   The lithium salt includes Li ⁺ as a cation,

   Anion ^{F -, Cl -, Br -} , I -, NO 3 -, N (CN) 2 -, BF4 -, ClO 4 -, AlO 4 -, AlCl 4 -, PF 6 -, SbF 6 -, AsF 6 _{^{-, BF 2 C 2 O 4}} -, BC4O8 -, (CF 3) 2 PF 4 -, (CF 3) 3 PF 3 -, (CF 3) 4 PF 2 -, (CF 3) 5 PF-, (CF _{3) 6 P-, CF 3 SO} 3 -, C 4 F 9 SO 3 -, CF 3 CF 2 SO 3 -, (CF 3 SO 2) 2 N -, (FSO 2) 2 N -, CF 3 CF 2 ^{_{(CF 3) 2 CO -,}} (CF 3 SO 2) 2 CH -, (SF 5) 3 C -, (CF 3 SO 2) 3 C -, CF 3 (CF 2) 7 SO 3 -, CF 3 CO _{^{2 -, CH 3 CO 2 -}} , SCN- , and _{(CF 3 CF 2 SO 2)} 2 N - is the non-aqueous electrolyte lithium secondary battery comprises any one selected from the group consisting of.
7. The method according to claim 3,

   The organic solvent is any one selected from the group consisting of ether, ester, amide, linear carbonate and cyclic carbonate or a mixture of two or more thereof.
8. In a lithium secondary battery having a negative electrode, a positive electrode, a separator interposed between the negative electrode and the positive electrode, and a nonaqueous electrolyte,

   The nonaqueous electrolyte is a lithium secondary battery of the nonaqueous electrolyte for lithium secondary battery of any one of claims 3 to 7.

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