KR20200104650A - Compound for electrolyte of lithium secondary battery, electrolyte for lithium secondary battery and lithium secondary battery including the same - Google Patents

Abstract

The present invention relates to a compound represented by formula 1. The compound according to the present invention can be usefully used as an additive for an electrolyte for a lithium secondary battery.

Description

Compound for lithium secondary battery electrolyte, electrolyte for lithium secondary battery, and lithium secondary battery including the same.

The present invention relates to a compound for a lithium secondary battery electrolyte, an electrolyte for a lithium secondary battery, and a lithium secondary battery including the same.

As electronic equipment is realized in miniaturization and weight reduction and the use of portable electronic devices is generalized, research on secondary batteries having high energy density as a power source thereof has been actively conducted.

As the secondary battery, a nickel-cadmium battery, a nickel-metal hydride battery, a nickel-hydrogen battery, a lithium secondary battery, etc. may be exemplified, and among them, a discharge voltage that is twice or more higher than that of a battery using an existing alkaline aqueous solution In addition, research on lithium secondary batteries that have high energy density per unit weight and can be rapidly charged are emerging.

In general, lithium secondary batteries are manufactured by using materials capable of intercalating and desorbing lithium ions as positive and negative electrodes, and charging a non-aqueous electrolyte between the positive and negative electrodes, and oxidation when lithium ions are inserted and desorbed from the positive and negative electrodes. It generates electrical energy by reaction and reduction reaction.

Meanwhile, in order to improve the capacity of a lithium secondary battery, the internal resistance must be small, but in terms of the safety of the battery, the larger the internal resistance is, the more advantageous. The capacity and safety of a lithium secondary battery are closely related to the properties of the non-aqueous electrolyte solution, which is composed of a combination of a solute such as an electrolyte salt and a non-aqueous organic solvent.

Republic of Korea Patent Publication No. 2018-0036340 relates to an electrolyte for a lithium secondary battery and a lithium secondary battery including the same, comprising: a non-aqueous organic solvent; Lithium salt; And it discloses the content of the electrolyte for a lithium secondary battery including an additive containing the compound represented by the formula (1).

Republic of Korea Patent Publication No. 2013-0003649 relates to an electrolyte additive for a lithium secondary battery, a non-aqueous electrolyte lithium secondary battery including the same, and the non-aqueous electrolyte additive for a lithium secondary battery containing a bidentate alkoxyphosphine compound represented by Formula 1 Disclosing the information.

However, conventional lithium secondary battery electrolyte compounds are difficult to handle due to vaporization of a low molecular weight material during synthesis, have low yield and high cost, or have a problem in that reliability in the battery is deteriorated due to poor oxidation stability.

Therefore, there is a demand for the development of a compound that is easy to synthesize and can suppress a decrease in reliability in a battery when applied to an electrolyte for a lithium secondary battery.

Republic of Korea Patent Publication No. 2018-0036340 (2018.04.09) Republic of Korea Patent Publication No. 2013-0003649 (2013.01.09)

An object of the present invention is to provide a compound having excellent metal coordination and capable of imparting excellent reliability when applied to an electrolyte for a lithium secondary battery.

In addition, the present invention is to provide an electrolyte for a lithium secondary battery having excellent reliability and a lithium secondary battery including the same.

The present invention provides a compound represented by the following formula (1).

[Formula 1]

In Formula 1,

이고,X1 is

ego,

X2 is a coordination functional group,

n is an integer from 1 to 4,

* Is a binding hand,

However, X1 and X2 are different from each other.

In addition, the present invention is a compound described above; Lithium salt; And it provides an electrolyte for a lithium secondary battery comprising an organic solvent.

In addition, the present invention provides a lithium secondary battery comprising the electrolyte for a lithium secondary battery described above.

The compound according to the present invention has excellent metal coordination properties, and when applied to an electrolyte for a lithium secondary battery, there is an advantage of providing excellent reliability.

In addition, the electrolyte for a lithium secondary battery including the compound according to the present invention and the lithium secondary battery including the same have excellent life characteristics and high temperature stability, thereby increasing the reliability of the battery.

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

In the present invention, when a member is positioned "on" another member, this includes not only the case where the member is in direct contact with the other member, but also the case where another member is interposed between the two members.

In the present invention, when a part "includes" a certain component, it means that other components may be further included rather than excluding other components unless otherwise specified.

Compound for lithium secondary battery electrolyte

One aspect of the present invention relates to a compound represented by the following formula (1).

[Formula 1]

In Formula 1,

이고,X1 is

ego,

X2 is a coordination functional group,

n is an integer from 1 to 4,

* Is a binding hand,

However, X1 and X2 are different from each other.

In the present invention, the "coordinating functional group" refers to a functional group containing oxygen, sulfur, phosphorus or nitrogen capable of coordinating a metal atom and a coordination bond.

The metal atom may be, for example, a transition metal of groups 3 to 12, and specifically, the compound according to the present invention contains a coordination functional group capable of coordinating bonds with the transition metal atom.

Specifically, the coordination functional group may be a hydroxy group, a carboxyl group, an alkoxy group, an ester group, an amine group, an amide group, a cyano group, a thiol group, or a thioalkoxy group.

과 상기

과 상이한 배위 관능기를 함유하기 때문에 더 많은 종류의 금속 원자에 대한 배위 특성이 있는 이점이 있다.The compounds according to the invention are

And remind

It has the advantage of having coordination properties for more kinds of metal atoms because it contains a coordination functional group different from that.

The compound according to the present invention has an advantage of excellent coordination with respect to the eluted metal because there are two or more coordination sites capable of coordinating the compound in the compound.

In addition, when applied as an electrolyte for a lithium secondary battery, the fluoro-substituted phosphite group traps hydrogen in the electrolyte, namely, the electrolyte to suppress the generation of hydrofluoric acid (HF) and removes oxygen to suppress the expansion of the battery to improve reliability. Has the effect of being.

In one embodiment of the present invention, the compound represented by Formula 1 may be one or more selected from the group consisting of compounds represented by the following Formulas 2 to 4.

[Formula 2]

[Formula 3]

[Formula 4]

When the compound according to the present invention is at least one selected from the group consisting of the compounds represented by Chemical Formulas 2 to 4, coordination bonding with various types of metals eluted from the positive electrode is more excellent, thereby suppressing defects in lithium secondary batteries. It is particularly preferred because of its advantages.

The compound represented by Formula 1 can be synthesized using a conventional organic chemical synthesis method. For example, it can be synthesized by reacting a compound having a coordinating functional group on one side and a hydroxy group on the other side with phosphorus trichloride (PC1 ₃ ), introducing a phosphite group, and fluorinating chloride.

및 상기

와 서로 상이한 배위 관능기를 포함하기 때문에, 물질내 배위할 수 있는 사이트가 2개 이상 존재하여 용출된 여러 금속 배위성이 우수한 이점이 있다. 또한, 종래의 알콕시포스핀기를 포함하는 화합물이 산화 안정성이 떨어져 전지 내 신뢰성을 저하시키는 문제를 해결할 수 있는 이점이 있다. 구체적으로, 본 발명에 따른 화합물은 플루오로 치환 포스파이트기가 전해액 내 수소를 잡아줘 불산 생성을 억제시킬 뿐만 아니라, 산소를 제거하여 전지의 팽창을 억제시켜 신뢰성을 개선할 수 있는 효과의 부여가 가능하다.The compounds according to the invention are

And above

Since it contains coordination functional groups different from each other, there are two or more sites capable of coordination in the material, and thus there is an advantage of excellent coordination of several eluted metals. In addition, there is an advantage in that the conventional compound containing an alkoxyphosphine group has an advantage of solving the problem of lowering the reliability of the battery due to poor oxidation stability. Specifically, in the compound according to the present invention, the fluoro-substituted phosphite group traps hydrogen in the electrolyte to suppress the generation of hydrofluoric acid, and it is possible to impart the effect of improving reliability by suppressing the expansion of the battery by removing oxygen. Do.

Specifically, the compound according to the present invention has an advantage of excellent reliability such as room temperature lifetime characteristics and high temperature stability.

Electrolyte for lithium secondary battery

Another aspect of the present invention is the compound described above; Lithium salt; And it relates to an electrolyte for a lithium secondary battery comprising an organic solvent.

Specifically, another aspect of the present invention is a compound represented by the following formula (1); Lithium salt; And it relates to an electrolyte for a lithium secondary battery comprising an organic solvent.

[Formula 1]

In Formula 1,

이고,X1 is

ego,

X2 is a coordination functional group,

n is an integer from 1 to 4,

* Is a binding hand,

However, X1 and X2 are different from each other.

The above-described compounds can be applied.

In another embodiment of the present invention, the compound may be included in an amount of 0.01 to 10 parts by weight based on 100 parts by weight of the total electrolyte for the lithium secondary battery.

In another embodiment of the present invention, the compound may be included in an amount of 0.1 to 5.0 parts by weight, and more specifically, 0.2 to 5 parts by weight, based on 100 parts by weight of the total electrolyte for the lithium secondary battery.

When the compound is included within the above range, it is preferable because the effect of improving reliability, particularly, room temperature lifespan, and high temperature stability, is maximized.

The lithium salt acts as a source of lithium ions in the battery, thereby enabling basic lithium battery operation. The concentration of the lithium salt may be 0.5 to 1.5M, but is not limited thereto. However, when the concentration of the lithium salt is within the above range, it is preferable that the conductivity of the electrolyte is lowered to suppress a phenomenon in which the electrolyte performance is deteriorated, and a phenomenon that the mobility of lithium ions is decreased due to an increase in the viscosity of the electrolyte can be suppressed. In short, when the concentration of the lithium salt is within the above range, the conductivity is excellent and the electrolyte performance is excellent, and the viscosity of the electrolyte is appropriate, so that the mobility of lithium ions is excellent, but the concentration of the lithium salt is not limited to the above range, and is required. It can be used by appropriately adding or subtracting it according to.

As the lithium salt, for example, LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , LiN(SO ₂ F) ₂ , LiN(SO ₂ CF ₃ ) ₂ , LiN(SO ₂ C ₂ F ₅ ) ₂ , LiC(SO ₂ CF ₃ ) ₃ , LiN(SO ₃ CF ₃ ) ₂ , LiC ₄ F ₉ SO ₃ , LiAlO ₄ , LiAlCl ₄ , One selected from the group consisting of LiCl and LiI or Two or more types may be mixed and used, but the present invention is not limited thereto. However, in this case, lithium ion mobility is very excellent, and conductivity is excellent, so that the electrolyte solution performance is excellent, which is preferable.

The organic solvent may include one or more solvents selected from the group consisting of a high-k solvent and a low boiling point solvent.

Specifically, the high dielectric constant solvent is not particularly limited as long as it is commonly used in the art, and for example, cyclic carbonate such as fluorinated ethylene carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, 1-fluorinated ethylene carbonate, gamma-buty Lolactone and/or mixtures thereof and the like may be used.

The low boiling point solvent is, for example, dimethyl carbonate, ethylmethyl carbonate. Chain carbonates such as diethyl carbonate and dipropyl carbonate, dimethoxyethane, diethoxyethane, fatty acid ester derivatives, and/or mixtures thereof may be used, but are not limited thereto.

The organic solvent may be included as a balance so as to satisfy 100 parts by weight of the total electrolyte for the lithium secondary battery, and in this case, the lithium salt and compound described above are preferable because the desired effect is excellent.

The electrolyte for a lithium secondary battery according to the present invention may further include other additives. Specifically, the electrolyte for a lithium secondary battery according to the present invention may further include additives other than the compound represented by Formula 1 above.

In short, the compound represented by Formula 1 according to the present invention can be used as an additive for an electrolyte for a lithium secondary battery.

The other additives are, for example, from the group consisting of fluorocarbonate, vinylene carbonate, oxalyltetrafluorophosphate lithium sulfate, bis(oxalyl)difluorophosphate lithium sulfate, trisoxalylphosphate lithium sulfate, and LiPO ₂ F ₂ It may be one or more selected.

When the other additives are further included, the effect of the compound represented by Formula 1 is further maximized.

The other additives are preferably 0.5 to 10 parts by weight, specifically 1 to 3 parts by weight, based on 100 parts by weight of the total electrolyte additive for the lithium secondary battery. In this case, the reliability of the lithium secondary battery can be further increased, and thus it is preferable.

The electrolyte for a lithium secondary battery according to the present invention has excellent metal coordination, and as it plays a role of holding hydrogen in the electrolyte, suppresses the generation of hydrofluoric acid and suppresses the expansion of the battery by removing oxygen. The effect of improving reliability is excellent.

Lithium secondary battery

Another aspect of the present invention relates to a lithium secondary battery including the above-described lithium secondary battery electrolyte.

The electrolyte for a lithium secondary battery according to the present invention is injected into an electrode structure comprising a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode to form a lithium secondary battery. As for the positive electrode, negative electrode, and separator constituting the electrode structure, all those commonly used in manufacturing lithium secondary batteries may be used.

The positive and negative electrodes are prepared by applying a positive electrode active material slurry and a negative electrode active material slurry to each electrode current collector.

As the positive electrode active material, a positive electrode active material capable of intercalating and desorbing lithium ions known in the art may be used without particular limitation. For example, at least one selected from cobalt, manganese, and nickel, and one of lithium composite oxides The above are preferable, and as a representative example thereof, the lithium-containing compound described below may be preferably used.

Li _x Mn _1-y M _y A ₂ (1)

Li _x Mn _1-y M _y O _2-z X _z (2)

Li _x Mn ₂ O _4-z X _z (3)

Li _x Mn _2-y M _{y M'z} A ₄ (4)

Li _x Co _1-y M _y A ₂ (5)

Li _x Co _1-y M _y O _2-z X _z (6)

Li _x Ni _1-y M _y A ₂ (7)

Li _x Ni _1-y M _y O _2-z X _z (8)

Li _x Ni _1-y Co _y O _2-z X _z (9)

Li _x Ni _1-yz Co _y M _z A _α (10)

Li _x Ni _1-yz Co _y M _z O _2-α X _α (11)

Li _x Ni _1-yz Mn _y M _z A _α (12)

Li _x Ni _1-yz Mn _y M _z O _2-α X _α (13)

In the formula, 0.9≤x≤1.1, 0≤y≤0.5, 0≤z≤0.5, 0≤α≤2, M and M'are the same or different, and Mg, Al, Co, K, Na, Ca, Si, Ti, Sn, V, Ge, Ga, B, As, Zr, Mn, Cr, Fe, Sr, V and rare earth elements are selected from the group consisting of, A is from the group consisting of O, F, S and P Is selected, and X is selected from the group consisting of F, S and P.

As the negative electrode active material, a negative electrode active material capable of intercalating and desorbing lithium ions known in the art may be used without particular limitation, and as the negative electrode active material, a carbon material such as crystalline carbon, amorphous carbon, carbon composite, carbon fiber, etc. , Lithium metal, lithium alloy, and the like may be used. For example, amorphous carbon includes hard carbon, coke, mesocarbon microbeads (MCMB) fired at 1500° C. or lower, and mesophase pitch-based carbon fibers (MPCF). The crystalline carbon includes graphite-based materials, and specifically, natural graphite, artificial graphite, graphitized coke, graphitized MCMB, graphitized MPCF, and the like.

The carbon material is preferably a material having a d002 interplanar distance of 3.35-3.38Å Lc (crystallite size) by X-ray diffraction of at least 20 nm. As the lithium alloy, an alloy of lithium and aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, or indium may be used.

The positive electrode active material and the negative electrode active material may be mixed with a binder and a solvent, respectively, to prepare a positive electrode active material slurry and a negative electrode active material slurry.

The binder is a material that plays a role of forming a paste of the active material, bonding the active material to each other, bonding to the current collector, and buffering the expansion and contraction of the active material. For example, polyvinylidene fluoride, polyhexafluoropropylene -Polyvinylidene fluoride copolymer (P(VdF/HFP)), poly(vinyl acetate), polyvinyl alcohol, polyethylene oxide, polyvinylpyrrolidone, alkylated polyethylene oxide, polyvinyl ether, poly(methyl) Methacrylate), poly(ethylacrylate), polytetrafluoroethylene, polyvinyl chloride, polyacrylonitrile, polyvinylpyridine, styrene-butadiene rubber, acrylonitrile-butadiene rubber, and the like. The content of the binder is 0.1 to 30 parts by weight, preferably 1 to 10 parts by weight, based on 100 parts by weight of the total electrode active material. If the content of the binder is too small, the adhesion between the electrode active material and the current collector is insufficient, and if the content of the binder is too high, the adhesion is improved, but the content of the electrode active material decreases that much, which is disadvantageous in increasing the battery capacity.

As a solvent for the active material slurry, a non-aqueous solvent or an aqueous solvent may be used. As the non-aqueous solvent, for example, N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, N,N-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran, etc. can be used. , Water, isopropyl alcohol, etc. may be used as the aqueous solvent, but is not limited thereto.

If necessary, the electrode active material slurry may further include a conductive material, a thickener, and the like.

The conductive material is a material that improves electronic conductivity, and at least one selected from the group consisting of a graphite conductive material, a carbon black conductive material, and a metal or metal compound conductive material may be used. Examples of the graphite-based conductive material include artificial graphite and natural graphite, and examples of the carbon black-based conductive material include acetylene black, ketjen black, denka black, thermal black, and channel black. channel black), and examples of metal-based or metallic compound-based conductive materials include perovskite materials such as tin, tin oxide, tin phosphate (SnPO ₄ ), titanium oxide, potassium titanate, LaSrCoO ₃ , and LaSrMnO _3. have. However, it is not limited to the conductive materials listed above.

The content of the conductive material is preferably 0.1 to 10 parts by weight based on 100 parts by weight of the total electrode active material. When the content of the conductive material is less than 0.1 parts by weight, electrochemical properties may be deteriorated, and when it exceeds 10 parts by weight, the energy density per weight may decrease.

The thickener is not particularly limited as long as it can control the viscosity of the active material slurry, but for example, carboxymethyl cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, and the like may be used.

The positive and negative active material slurry prepared in this way is applied to an electrode current collector to be prepared as a positive electrode and a negative electrode. Aluminum or aluminum alloy may be used as the positive electrode current collector, and copper or copper alloy may be used as the negative electrode current collector. I can. The positive electrode current collector and the negative electrode current collector may be formed of a foil, film, sheet, punched material, porous material, foam, or the like.

The prepared positive and negative electrodes are manufactured as an electrode structure with a separator interposed therebetween, and then accommodated in a 　 battery 　 case, and an electrolyte is injected therein to make a lithium secondary battery. As a separator, a conventional porous polymer film used as a separator, for example, polyolefin-based polymers such as ethylene homopolymer, propylene homopolymer, ethylene/butene copolymer, ethylene/hexene copolymer, and ethylene/methacrylate copolymer. The porous polymer film prepared with may be used alone or by stacking them, or a conventional porous non-woven fabric, for example, a non-woven fabric made of high melting point glass fiber, polyethylene terephthalate fiber, etc., may be used, but is not limited thereto. .

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

Since the lithium secondary battery according to the present invention contains the compound represented by Chemical Formula 1, there is an advantage in that the secondary battery has excellent reliability such as life characteristics and high temperature stability.

Hereinafter, examples will be described in detail to describe the present specification in detail. However, the embodiments according to the present specification may be modified in various forms, and the scope of the present specification is not construed as being limited to the embodiments described below. The embodiments of the present specification are provided to more completely describe the present specification to those of ordinary skill in the art. In addition, "%" and "parts" indicating content hereinafter are based on weight unless otherwise noted.

Synthesis Example 1

Phosphite was introduced into ethylene cyanohydrin using phosphorus trichloride (PC1 ₃ ), and then the chloride was fluorinated to synthesize a compound represented by Chemical Formula 2.

[Formula 2]

The synthesized compound showed ¹ H NMR (299.87 MHz, acetone-d6): δ = 2.74 (t, 2H), 4.25 (t, 2H) ppm.

Synthesis Example 2

A compound represented by Chemical Formula 3 was synthesized using 2-methoxy ethanol instead of ethylene cyanohydrin.

[Formula 3]

The synthesized compound showed ¹ H NMR (299.87 MHz, acetone-d6): δ = 2.61 (S, 3H), 2.84 (t, 2H), 3.25 (t, 2H) ppm.

Synthesis Example 3

The compound represented by Formula 4 was synthesized using 2-acetaminoethanol instead of ethylene cyanohydrin.

[Formula 4]

The synthesized compound showed 1H NMR (299.87 MHz, acetone-d6): δ = 1.91 (S, 3H), 2.98 (t, 2H), 3.25 (t, 2H) ppm.

Example 1

(1) Preparation of anode and cathode

97.3 parts by weight of LiCoO ₂ as a positive electrode active material, 1.4 parts by weight of polyvinylidene fluoride as a binder, and 1.3 parts by weight of Ketjen Black as a conductive material were mixed and dispersed in N-methylpyrrolidone to prepare a positive electrode active material slurry. The positive electrode active material slurry was coated on an aluminum foil, dried, and then rolled to prepare a positive electrode.

In addition, 98 parts by weight of graphite as a negative electrode active material, 1 part by weight of binder polyvinylidene fluoride, and 1 part by weight of carbon black as a conductive material were mixed and dispersed in N-methylpyrrolidone to prepare a negative electrode active material layer composition and applied to copper foil. Then, it was dried and then rolled to prepare a negative electrode.

(2) Electrolytic solution manufacturing

A non-aqueous mixed solution was prepared as an electrolyte for a lithium secondary battery by adding 0.95M LiPF ₆ to a mixed solution in which the volume ratio of ethylene carbonate (EC):dimethyl carbonate (DMC):ethylmethyl carbonate (EMC) was 40:40:20. .

An electrolyte for a lithium secondary battery was prepared by adding 1.0 part by weight of a compound represented by the following formula 2 based on 100 parts by weight of the total non-aqueous mixed solution.

[Formula 2]

(3) Manufacture of lithium secondary battery

A secondary battery was manufactured using the positive and negative electrodes prepared according to (1) and the electrolyte prepared according to (2).

Example 2

A lithium secondary battery was manufactured in the same manner as in Example 1, except that 1.0% by weight of the compound represented by Formula 3 was added instead of the compound represented by Formula 2 when preparing the electrolyte solution.

[Formula 3]

Example 3

A lithium secondary battery was manufactured in the same manner as in Example 1, except that 1.0 part by weight of the compound represented by Formula 4 was added instead of the compound represented by Formula 2 when preparing the electrolyte solution.

[Formula 4]

Comparative Example 1

An electrolyte for a lithium secondary battery was prepared in the same manner as in Example 1, except that the compound represented by Formula 2 was not added during the preparation of the electrolyte.

Comparative Example 2

An electrolyte for a lithium secondary battery was prepared in the same manner as in Example 1, except that 1.0 part by weight of dimethylphosphinoethane was added instead of the compound represented by Formula 2 when preparing the electrolyte.

Experimental example

The secondary batteries prepared according to Examples and Comparative Examples were charged with a constant current at 25°C with a current of 0.2C until the voltage reached 4.2V, and then discharged with a constant current of 0.2C until the voltage reached 2.5V. Subsequently, constant current charging was performed with a current of 0.5C until the voltage reached 4.2V, and constant voltage charging was performed until the current reached 0.05C while maintaining 4.2V. Then, at the time of discharging, it was discharged with a constant current of 0.5C until the voltage reached 2.5V (formation step).

(1) Room temperature life characteristics

The secondary battery that had undergone the conversion step was charged at a constant current at 25°C with a current density of 1.0C until the voltage reached 4.2V, and while maintaining 4.2V, the secondary battery was charged with a constant voltage until the current density reached 0.05C. Subsequently, the cycle of discharging with a constant current of 1.0 C was repeated 300 times until the voltage reached 2.5 V during discharge.

The capacity retention ratio (%) in the 300th cycle of each secondary battery was calculated by Equation 1 below.

[Equation 1]

Capacity retention rate [%] = [Discharge capacity at the 300th cycle / Discharge capacity at the first cycle] × 100

(2) High temperature stability

The secondary battery that had undergone the formation step was charged at a constant current at 25° C. with a current of 1.0 C until the voltage reached 4.2 V, and charged at a constant voltage until the current reached 0.05 C while maintaining 4.2 V. Then, while storing the charged secondary battery at 60°C, the voltage was measured every 24 hours using a multi-meter, and the residual voltage of the charged cell was measured at a high temperature to measure the high temperature voltage storage stability.

The voltage retention ratio (%) at the time of measurement on the 15th day of each secondary battery was calculated by Equation 2 below.

[Equation 2]

Voltage retention rate[%]=[open circuit voltage on the 15th day/initial open voltage]×100

(3) Thickness increase rate

The lithium secondary batteries prepared according to Examples and Comparative Examples were charged at a constant current at a current density of 1C until the voltage reached 4.45V. After filling, the thickness was measured, and the thickness change rate (%) was measured at intervals of 7 days while storing it at 60° C. for 28 days. The thickness change rate measured on the 28th day is shown in Table 1 below.

Room temperature life characteristics High temperature stability Thickness increase rate (%) Example 1 87.1% 82.4% 13.4 Example 2 89.8% 83.2% 12.2 Example 3 89.8% 84.7% 8.0 Comparative Example 1 76.3% 70.3% 24.3 Comparative Example 2 86.3% 75.3% 18.3

Referring to Table 1, it can be seen that the examples in which the electrolyte containing the compound according to the present invention is injected as an additive exhibits excellent performance due to high room temperature life characteristics, high temperature stability, and low thickness increase rate.

Claims (6)

Compound represented by the following formula (1):
[Formula 1]

In Formula 1,
X1 is

ego,
X2 is a coordination functional group,
n is an integer from 1 to 4,
* Is a binding hand,
However, X1 and X2 are different from each other. The method of claim 1,
The compound represented by Formula 1 is one or more compounds selected from the group consisting of compounds represented by the following Formulas 2 to 4:
[Formula 2]

[Formula 3]

[Formula 4]

. A compound according to claim 1 or 2;
Lithium salt; And
An electrolyte for a lithium secondary battery containing an organic solvent. The method of claim 3,
The compound is an electrolyte for a lithium secondary battery contained in an amount of 0.01 to 10 parts by weight based on 100 parts by weight of the total electrolyte for a lithium secondary battery. The method of claim 4,
The compound is an electrolyte for a lithium secondary battery contained in an amount of 0.1 to 5.0 parts by weight based on 100 parts by weight of the total electrolyte for a lithium secondary battery. A lithium secondary battery comprising the electrolyte for a lithium secondary battery according to claim 3.