KR102451774B1 - Electrolyte for rechargeable lithium battery and rechargeable lithium battery including the same - Google Patents

Abstract

(상기 화학식 1에서, R¹ 및 R²는 각각 독립적으로 적어도 하나의 플루오린으로 치환된 C1 내지 C10 알킬기이고, R³은 치환 또는 비치환된 C1 내지 C10 알킬기이다.)It includes a lithium salt, an organic solvent, and an additive, wherein the additive is an electrolyte for a lithium secondary battery including a phosphonate-based compound represented by the following Chemical Formula 1, and a lithium secondary battery including the same.
[Formula 1]

(In Formula 1, R ¹ and R ² are each independently a C1 to C10 alkyl group substituted with at least one fluorine, and R ³ is a substituted or unsubstituted C1 to C10 alkyl group.)

Description

Electrolyte for a lithium secondary battery and a lithium secondary battery comprising the same

It relates to an electrolyte solution for a lithium secondary battery and a lithium secondary battery including the same.

Recently, as the need for a battery having a high energy density as a power source for portable electronic devices has increased, research on lithium secondary batteries has been actively conducted. In addition, as interest in environmental issues grows, research using lithium secondary batteries as a power source for electric vehicles is being conducted. A lithium secondary battery for use in such an electric vehicle is required to have high capacity and high output characteristics.

On the other hand, a lithium secondary battery comprising a positive electrode including a positive active material capable of intercalation and deintercalation of lithium and a negative electrode active material capable of intercalating and deintercalating lithium It is used by injecting an electrolyte into a battery cell including an anode. As the electrolyte, a lithium salt dissolved in an organic solvent is mainly used.

These lithium secondary batteries have limitations in battery performance, so research on this is ongoing.

One embodiment is to provide an electrolyte solution for a lithium secondary battery having improved high-temperature lifespan performance without deterioration of room-temperature lifespan performance under high voltage.

Another embodiment is to provide a lithium secondary battery including the electrolyte.

One embodiment includes a lithium salt, an organic solvent, and an additive, wherein the additive provides an electrolyte for a lithium secondary battery including a phosphonate-based compound represented by the following Chemical Formula 1.

[Formula 1]

(In Formula 1,

R ¹ and R ² are each independently a C1 to C10 alkyl group substituted with at least one fluorine,

R ³ is a substituted or unsubstituted C1 to C10 alkyl group.)

In Formula 1, R ¹ and R ² may each independently be a C1 to C5 alkyl group substituted with 1 to 5 fluorines, and R ³ may be a substituted or unsubstituted C1 to C5 alkyl group.

The phosphonate-based compound may include a compound represented by Formula 2 below.

[Formula 2]

The phosphonate-based compound may be included in an amount of 0.1 to 10 parts by weight based on 100 parts by weight of the organic solvent.

The additive may further include a phosphonoacetate-based compound represented by the following formula (3).

[Formula 3]

(In Formula 3,

R ⁴ and R ⁵ are each independently a C1 to C10 alkyl group substituted with at least one fluorine,

R ⁶ is a substituted or unsubstituted C1 to C10 alkyl group, a substituted or unsubstituted C2 to C10 alkenyl group, a substituted or unsubstituted C2 to C10 alkynyl group, a substituted or unsubstituted C3 to C20 cycloalkyl group, a substituted or unsubstituted a C3 to C20 cycloalkenyl group, a substituted or unsubstituted C3 to C20 cycloalkynyl group, or a substituted or unsubstituted C6 to C30 aryl group.)

In Formula 3, R ⁴ and R ⁵ may each independently be a C1 to C5 alkyl group substituted with 1 to 5 fluorines, and R ⁶ may be a substituted or unsubstituted C1 to C5 alkyl group.

The phosphonoacetate-based compound may include a compound represented by Formula 4 below.

[Formula 4]

The phosphonate-based compound and the phosphonoacetate-based compound may be included in a weight ratio of 1:100 to 100:1.

The additive may further include a phosphite-based compound represented by the following Chemical Formula 5.

[Formula 5]

(In Formula 5,

R ⁷ to R ⁹ are each independently a substituted or unsubstituted silyl group, a substituted or unsubstituted C1 to C10 alkyl group, a substituted or unsubstituted C2 to C10 alkenyl group, a substituted or unsubstituted C2 to C10 alkynyl group, substituted or an unsubstituted C3 to C20 cycloalkyl group, a substituted or unsubstituted C3 to C20 cycloalkenyl group, a substituted or unsubstituted C3 to C20 cycloalkynyl group, or a substituted or unsubstituted C6 to C30 aryl group, and R ⁷ to At least one of R ⁹ is the substituted or unsubstituted silyl group.)

In Formula 5, at least one of R ⁷ to R ⁹ may be a silyl group substituted with a C1 to C10 alkyl group.

The phosphite-based compound may include a compound represented by Formula 6 below.

[Formula 6]

The phosphonate-based compound and the phosphite-based compound may be included in a weight ratio of 1:100 to 100:1.

Another embodiment provides a lithium secondary battery including the electrolyte.

The lithium secondary battery may be driven at a voltage of 4.3V or higher.

The details of other implementations are included in the detailed description below.

By using the electrolyte solution according to an embodiment, a lithium secondary battery having improved high-temperature lifespan performance can be implemented without deterioration of room-temperature lifespan performance under high voltage.

1 is a cross-sectional view of a lithium secondary battery according to an embodiment.
2 is a graph showing lifespan characteristics at room temperature for lithium secondary batteries according to Examples 1 to 3 and Comparative Examples 1 to 3;
3 is a graph showing lifespan characteristics at high temperature for lithium secondary batteries according to Examples 1 to 3 and Comparative Examples 1 to 3;

Hereinafter, embodiments of the present invention will be described in detail. However, this is provided as an example, and the present invention is not limited thereto, and the present invention is only defined by the scope of the claims to be described later.

Unless otherwise defined herein, 'substituted' means that a hydrogen atom in a compound is a halogen atom (F, Br, Cl, I), a hydroxy group, an alkoxy group, a nitro group, a cyano group, an amino group, an azido group, an amidino group group, hydrazino group, hydrazono group, carbonyl group, carbamyl group, thiol group, ester group, carboxyl group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, C1 to C20 alkyl group, C2 to C20 alkenyl group, C2 to C20 alkynyl group, C6 to C30 aryl group, C7 to C30 arylalkyl group, C1 to C20 alkoxy group, C1 to C20 heteroalkyl group, C3 to C20 heteroarylalkyl group, C3 to C20 cycloalkyl group, C3 to C20 cycloalkenyl group, C4 to C20 cycloalkynyl group, C2 to C20 heterocycloalkyl group, and a combination thereof means substituted with a substituent selected from the group consisting of.

In addition, unless otherwise defined herein, 'hetero' means containing 1 to 3 heteroatoms selected from N, O, S and P.

Hereinafter, an electrolyte for a lithium secondary battery according to an embodiment will be described.

The electrolyte solution according to an embodiment may include a lithium salt, an organic solvent, and an additive.

The additive may include a phosphonate-based compound represented by Formula 1 below.

[Formula 1]

(In Formula 1,

R ¹ and R ² are each independently a C1 to C10 alkyl group substituted with at least one fluorine, and R ³ is a substituted or unsubstituted C1 to C10 alkyl group.)

The phosphonate-based compound represented by Formula 1 can form a solid electrolyte interphase (SEI) film on the surface of the anode by reductive decomposition at the cathode, and by suppressing side reactions between the cathode and the electrolyte due to the formed SEI film, room temperature life performance under high voltage and a lithium secondary battery having excellent high-temperature lifespan performance. In addition, among the phosphorus compounds, the additive according to an embodiment having a phosphonate skeleton exhibits less deterioration in room temperature life performance compared to a compound having a phosphite skeleton, and less deterioration in high temperature life performance compared to a compound having a phosphate skeleton. In addition, since the additive according to the exemplary embodiment has an alkyl group substituted with fluorine, the SEI film formed on the surface of the negative electrode may be more stably formed, and thus, the high-temperature lifespan performance of the battery may be improved under high voltage.

Specifically, in Formula 1, R ¹ and R ² may each independently be a C1 to C5 alkyl group substituted with at least one fluorine, for example, a C1 to C5 alkyl group substituted with 1 to 5 fluorine. can In addition, in Formula 1, R ³ may be a substituted or unsubstituted C1 to C5 alkyl group, for example, a C1 to C3 alkyl group.

Specific examples of the phosphonate-based compound include, but are not limited to, a compound represented by Formula 2 below.

[Formula 2]

The phosphonate-based compound may be included in an amount of 0.1 to 10 parts by weight, for example, 0.1 to 3 parts by weight based on 100 parts by weight of the organic solvent. When the phosphonate-based compound is included within the above content range, an optimal SEI film may be formed on the surface of the negative electrode, and thus, the high-temperature lifespan characteristics and high-temperature storage characteristics of the lithium secondary battery may be improved.

The additive may be used together with the above-described phosphonate-based compound and a phosphonoacetate-based compound represented by the following formula (3).

[Formula 3]

(In Formula 3,

R ⁴ and R ⁵ are each independently a C1 to C10 alkyl group substituted with at least one fluorine,

R ⁶ is a substituted or unsubstituted C1 to C10 alkyl group, a substituted or unsubstituted C2 to C10 alkenyl group, a substituted or unsubstituted C2 to C10 alkynyl group, a substituted or unsubstituted C3 to C20 cycloalkyl group, a substituted or unsubstituted a C3 to C20 cycloalkenyl group, a substituted or unsubstituted C3 to C20 cycloalkynyl group, or a substituted or unsubstituted C6 to C30 aryl group.)

When the phosphonoacetate-based compound represented by Formula 3 is mixed with the phosphonate-based compound represented by Formula 1, a stable SEI film can be formed on the surface of the negative electrode, and thus, room temperature life performance of a lithium secondary battery under high voltage and high temperature life performance can be improved at the same time.

Specifically, in the phosphonoacetate-based compound, in Formula 3, R ⁴ and R ⁵ may each independently be a C1 to C5 alkyl group substituted with at least one fluorine, for example, 1 to 5 fluorines It may be a substituted C1 to C5 alkyl group. In addition, in Formula 3, R ⁶ may be a substituted or unsubstituted C1 to C5 alkyl group, for example, a C1 to C3 alkyl group.

Specific examples of the phosphonoacetate-based compound include, but are not limited to, a compound represented by Formula 4 below.

[Formula 4]

The phosphonate-based compound and the phosphonoacetate-based compound may be used in a weight ratio of 1:100 to 100:1, for example, in a weight ratio of 1:30 to 30:1, 1:10 to 10:1 can be used in a weight ratio of When the weight ratio of the two components is used within the above range, it is possible to form a stable SEI film on the surface of the negative electrode, and thus, it is possible to improve the high temperature life performance without deterioration of the room temperature life of the lithium secondary battery under high voltage.

The additive may be used together with the above-described phosphonate-based compound and a phosphite-based compound represented by the following Chemical Formula 5.

[Formula 5]

(In Formula 5,

R ⁷ to R ⁹ are each independently a substituted or unsubstituted silyl group, a substituted or unsubstituted C1 to C10 alkyl group, a substituted or unsubstituted C2 to C10 alkenyl group, a substituted or unsubstituted C2 to C10 alkynyl group, substituted or an unsubstituted C3 to C20 cycloalkyl group, a substituted or unsubstituted C3 to C20 cycloalkenyl group, a substituted or unsubstituted C3 to C20 cycloalkynyl group, or a substituted or unsubstituted C6 to C30 aryl group, and R ⁷ to At least one of R ⁹ is the substituted or unsubstituted silyl group.)

When the phosphite-based compound represented by Formula 5 is mixed with the phosphonate-based compound represented by Formula 1, a stable SEI film can be formed on the surface of the negative electrode, and thus, room temperature life performance of a lithium secondary battery under high voltage and high temperature lifetime performance.

Specifically, in the phosphite-based compound, at least one of R ⁷ to R ⁹ in Formula 5 may be a substituted silyl group, for example, a silyl group substituted with a C1 to C10 alkyl group. Also, for example, R ⁷ to R ⁹ may each independently be a substituted silyl group, for example, a silyl group substituted with a C1 to C10 alkyl group.

Specific examples of the phosphite-based compound include, but are not limited to, a compound represented by Formula 6 below.

[Formula 6]

The phosphonate-based compound and the phosphite-based compound may be used in a weight ratio of 1:100 to 100:1, for example, in a weight ratio of 1:30 to 30:1, and 1:10 to 10:1. It can be used as a weight ratio. When the weight ratio of the two components is used within the above range, it is possible to form an optimal SEI film on the surface of the negative electrode, and thus, it is possible to simultaneously improve the room temperature life performance and high temperature life performance under high voltage of the lithium secondary battery.

The organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move.

The organic solvent may be a carbonate-based compound, an ester-based compound, an ether-based compound, a ketone-based compound, an alcohol-based compound, or a combination thereof.

Examples of the carbonate-based compound include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), ethylmethyl carbonate (EMC), etc. carbonate compounds; cyclic carbonate compounds such as ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC); Or a combination thereof may be used. When the chain carbonate compound and the cyclic carbonate compound are mixed and used, the dielectric constant may be increased and a solvent having low viscosity may be used. In this case, the cyclic carbonate compound and the chain carbonate compound may be mixed and used in a volume ratio of about 1:1 to 1:9.

Examples of the ester-based compound include methyl acetate, ethyl acetate, n-propyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone, decanolide, valerolactone, and mevalonolactone. ), caprolactone, etc. may be used.

As the ether-based compound, dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, and the like may be used. Cyclohexanone and the like may be used as the ketone-based compound. As the alcohol-based compound, ethyl alcohol, isopropyl alcohol, and the like may be used.

The lithium salt is dissolved in the organic solvent to act as a source of lithium ions in the battery to enable basic lithium secondary battery operation, and to promote movement of lithium ions between the positive electrode and the negative electrode.

The lithium salt is LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiN(SO ₃ C ₂ F ₅ ) ₂ , LiC ₄ F ₉ SO ₃ , LiClO ₄ , LiAlO ₂ , LiAlCl ₄ , LiN(C _x F _{2x + 1} SO ₂ )(C _y F _{2y +1} SO ₂ ), where x and y are natural numbers, LiCl, LiI, LiB(C ₂ O ₄ ) ₂ (lithium bisoxalatoborate, LiBOB), lithium bis( fluorosulfonyl)imide (LiFSI), or a combination thereof.

The concentration of the lithium salt may be 0.1 M to 2.0 M. When the concentration of the lithium salt is within the above range, as the electrolyte has an appropriate conductivity and viscosity, excellent electrolyte performance may be exhibited, and lithium ions may move effectively.

The lithium secondary battery including the above-described electrolyte has excellent room temperature life performance and high temperature life performance under high voltage.

Hereinafter, a lithium secondary battery according to another embodiment will be described with reference to FIG. 1 .

1 is a cross-sectional view of a lithium secondary battery according to an embodiment.

The lithium secondary battery according to the embodiment is described as an example of a coin-type battery through FIG. 1 , but the present invention is not limited thereto, and may be applied to various types of batteries such as cylindrical, prismatic, and pouch-type batteries.

Referring to FIG. 1, a lithium secondary battery according to an embodiment includes an electrode assembly including a positive electrode 10, a negative electrode 12, and a separator 16 disposed between the positive electrode 10 and the negative electrode 12, As an exterior material, a case 20 containing the electrode assembly, a bottom plate 18 , a lid 22 , and an insulating gasket 24 may be included. In addition, the electrolyte is injected into the case 20 containing the electrode assembly, and the electrolyte is as described above.

The positive electrode 10 may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector. The positive active material layer may include a positive active material, a binder, and optionally a conductive material.

Aluminum (Al), nickel (Ni), etc. may be used as the positive electrode current collector, but the present invention is not limited thereto.

As the cathode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specifically, at least one of cobalt, manganese, nickel, aluminum, iron, or a metal of a combination thereof and lithium and a complex oxide or complex phosphate may be used. More specifically, lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, or a combination thereof may be used. have.

The binder not only adheres the positive active material particles well to each other, but also serves to adhere the positive active material to the positive electrode current collector, and specific examples include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride. , carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymer, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, Acrylated styrene-butadiene rubber, epoxy resin, nylon, and the like, but is not limited thereto. These can be used individually or in mixture of 2 or more types.

The conductive material imparts conductivity to the electrode, and examples thereof include natural graphite, artificial graphite, carbon black, carbon fiber, metal powder, metal fiber, and the like, but is not limited thereto. These can be used individually or in mixture of 2 or more types. The metal powder and the metal fiber may use a metal such as copper, nickel, aluminum, silver.

The negative electrode 12 may include a negative electrode current collector and a negative electrode active material layer formed on the negative electrode current collector.

The negative electrode current collector may be made of copper (Cu), gold (Au), nickel (Ni), a copper alloy, or the like, but is not limited thereto.

The anode active material layer may include an anode active material, a binder, and optionally a conductive material.

As the negative active material, a material capable of reversibly intercalating and deintercalating lithium ions, lithium metal, an alloy of lithium metal, a material capable of doping and dedoping lithium, a transition metal oxide, or a combination thereof Can be used.

A material capable of reversibly intercalating and deintercalating lithium ions may include a carbon-based material, and examples thereof include crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon include amorphous, plate-like, flake-like, spherical or fibrous natural graphite or artificial graphite. Examples of the amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, calcined coke, and the like. The lithium metal alloy includes lithium and Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al and Sn from the group consisting of Alloys of selected metals may be used. As a material capable of doping and dedoping lithium, Si, SiO _x (0<x<2), Si-C composite, Si-Y alloy, Sn, SnO ₂ , Sn-C composite, Sn-Y, etc. In addition, at least one of these and SiO ₂ may be mixed and used. The element Y includes Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Tl, Ge, P, As, Sb, Bi, S, It may be selected from the group consisting of Se, Te, Po, and combinations thereof. Examples of the transition metal oxide include vanadium oxide and lithium vanadium oxide.

The types of the binder and the conductive material used in the negative electrode are the same as the binder and the conductive material used in the above-described positive electrode, and thus a description thereof will be omitted.

The positive electrode and the negative electrode may be prepared by mixing each active material and a binder and optionally a conductive material in a solvent to prepare each active material composition, and applying the active material composition to each current collector. In this case, as the solvent, an organic solvent such as N-methylpyrrolidone may be used, and an aqueous solvent such as water may be used depending on the type of binder, but is not limited thereto. Since such an electrode manufacturing method is widely known in the art, a detailed description thereof will be omitted herein.

The separator 16 separates the negative electrode and the positive electrode and provides a passage for lithium ions to move, and any one commonly used in a lithium secondary battery may be used. For example, polyolefin, polyester, polytetrafluoroethylene (PTFE), polyacetal, polyamide, polyimide, polycarbonate, polyetheretherketone, polyaryletherketone, polyetherimide, polyamideimide, polybenz imidazole, polyether sulfone, polyphenylene oxide, cyclic olefin copolymer, polyphenylene sulfide, polyethylene naphthalene, glass fiber, or a combination thereof, but is not limited thereto. Examples of the polyolefin include polyethylene and polypropylene, and examples of the polyester include polyethylene terephthalate and polybutylene terephthalate. It may also be in the form of a non-woven fabric or a woven fabric.

In addition, the separator may have a single-layer or multi-layer structure. For example, polyethylene single film, polypropylene single film, polyethylene/polypropylene double film, polypropylene/polyethylene/polypropylene triple film, polyethylene/polypropylene/polyethylene triple film, etc. are mentioned.

In addition, a separator coated with a ceramic component or a polymer material may be used to secure heat resistance or mechanical strength.

According to an embodiment, the lithium secondary battery including the above-described electrolyte may be driven at a high voltage. Specifically, the lithium secondary battery may be driven at a voltage of 4.3V or more, for example, 4.3V to 5.0V, or 4.6V to 5.0V. Accordingly, it is possible to realize a high-capacity lithium secondary battery while not only having no deterioration in room temperature life performance, but also having excellent high temperature life performance.

Hereinafter, specific embodiments of the present invention are presented. However, the examples described below are only for specifically illustrating or explaining the present invention, and the present invention is not limited thereto. In addition, since the contents not described herein can be technically inferred sufficiently by those skilled in the art, the description thereof will be omitted.

(Lithium secondary battery production)

Examples 1 to 2 and Comparative Examples 1 to 4

LiNi _{0.5 Mn 1.5 O 4 ,} polyvinylidene fluoride and super-P carbon were added to an N-methylpyrrolidone (NMP) solvent in a weight ratio of 86: ₄ :10 to prepare a slurry. The slurry was coated on an aluminum foil, dried, and rolled to prepare a positive electrode.

Graphite, polyvinylidene fluoride, and carbon black were added to an N-methylpyrrolidone (NMP) solvent in a weight ratio of 98:1:1 to prepare a slurry. The slurry was coated on a copper foil, dried and rolled to prepare a negative electrode.

The electrolyte solution is an organic solvent in which ethylene carbonate (EC), ethylmethyl carbonate (EMC) and diethyl carbonate (DEC) are mixed in a volume ratio of 3:5:2, 1.2M LiPF ₆ is dissolved, and an additive is added to the electrolyte solution was prepared. In this case, the types and contents of the additives used are shown in Table 1 below, and the contents (parts by weight) of the additives are shown based on 100 parts by weight of the organic solvent.

A coin-type lithium secondary battery was manufactured using the above-prepared positive electrode, negative electrode, electrolyte, and a separator made of polyethylene.

Additive type and content Comparative Example 4 FEMP 0.5 parts by weight Example 1 0.3 parts by weight of FEMP and 0.2 parts by weight of FEPA Example 2 0.3 parts by weight of FEMP and 0.2 parts by weight of TBSPi Comparative Example 1 0.5 parts by weight of TMSPi Comparative Example 2 0.5 parts by weight of PAFE Comparative Example 3 TMPa 0.5 parts by weight

- FEMP: bis(2,2,2-trifluoroethyl)methyl phosphonate, which is a compound represented by the following formula (2)

[Formula 2]

- FEPA: ethyl [bis (2,2,2-trifluoroethoxy) phosphinyl] acetate, which is a compound represented by the following formula (4)

[Formula 4]

- TBSPi: tris(t-butyldimethylsilyl)phosphite, which is a compound represented by the following formula (6)

[Formula 6]

- TMSPi: tris (trimethylsilyl) phosphite, which is a compound represented by the following formula (7)

[Formula 7]

- PAFE: bis(2,2,2-trifluoroethyl) phosphite, which is a compound represented by the following formula (8)

[Formula 8]

- TMPa: tris (trimethylsilyl) phosphate, which is a compound represented by the following formula (9)

[Formula 9]

Evaluation 1: Room temperature life performance

For lithium secondary batteries manufactured according to Examples 1 to 2 and Comparative Examples 1 to 4, after charging at a constant current/constant voltage (CC/CV) condition at 25° C. at a 1.0 C-rate to 4.9V, a cutoff at 0.1 C-rate After (cut-off), it was discharged at a C-rate of 1.0 to 3.5V. 100 cycles were performed by making 1 cycle of the said charging/discharging. After 100 cycles, the capacity retention rate was evaluated, and the results are shown in Table 2 and FIG. 2, respectively. The following capacity retention ratio (%) is calculated as a percentage of the discharge capacity at 100 cycles compared to the discharge capacity at 25°C at 1 cycle.

additive 25℃, 100cy/1cy
Capacity retention rate (%) Comparative Example 4 FEMP 83.9 Example 1 FEMP + FEPA 84.9 Example 2 FEMP + TBSPi 84.1 Comparative Example 1 TMSPi 83.4 Comparative Example 2 PAFE 79.1 Comparative Example 3 TMSPa 82.0

2 is a graph showing lifespan characteristics at room temperature for lithium secondary batteries according to Examples 1 to 2 and Comparative Examples 1 to 4;

Referring to Table 2 and FIG. 2, in the case of Examples 1 and 2, in which the phosphonate-based compound represented by Formula 1 was mixed with other additives as the electrolyte additive, room temperature life performance under high voltage was lower than that of Comparative Examples 1 to 4 can be seen to be excellent.

In addition, in Example 1 using a mixture of the phosphonate compound and the phosphonoacetate compound represented by Formula 3, and Example 2 in which the phosphonate compound and the phosphite compound represented by Formula 5 were mixed In this case, it can be seen that the room temperature life performance is more excellent than that of Comparative Example 1 in which the phosphonate-based compound is used alone.

Evaluation 2: High Temperature Life Performance

For lithium secondary batteries prepared according to Examples 1 to 2 and Comparative Examples 1 to 4, after charging at a constant current/constant voltage (CC/CV) condition at 45° C. at a C-rate of 1.0 C-rate to 4.9 V, a cut-off at a C-rate of 0.1 After (cut-off), it was discharged at a C-rate of 1.0 to 3.5V. 100 cycles were performed by making 1 cycle of the said charging/discharging. After 100 cycles, the capacity retention rate was evaluated, and the results are shown in Table 3 and FIG. 3, respectively. The following capacity retention ratio (%) is calculated as a percentage of the discharge capacity at 100 cycles compared to the discharge capacity at 45°C at 1 cycle.

additive 45℃, 100cy/1cy Capacity retention rate (%) Comparative Example 4 FEMP 64.2 Example 1 FEMP + FEPA 67.2 Example 2 FEMP + TBSPi 66.6 Comparative Example 1 TMSPi 61.4 Comparative Example 2 PAFE 58.6 Comparative Example 3 TMSPa 60.7

3 is a graph showing lifespan characteristics at high temperature for lithium secondary batteries according to Examples 1 to 2 and Comparative Examples 1 to 4;

Referring to Table 3 and FIG. 3, in the case of Examples 1 and 2, in which the phosphonate-based compound represented by Formula 1 was mixed with other additives as the electrolyte additive, the high-temperature life performance under high voltage compared to Comparative Examples 1 to 4 was higher. can be seen to be excellent.

In addition, in Example 1 using a mixture of the phosphonate compound and the phosphonoacetate compound represented by Formula 3, and Example 2 in which the phosphonate compound and the phosphite compound represented by Formula 5 were mixed In this case, it can be seen that the high temperature life performance is more excellent than that of Comparative Example 4 in which the phosphonate-based compound is used alone.

From the above evaluations, it can be seen that, when an additive according to an exemplary embodiment is added to the electrolyte solution, a lithium secondary battery having improved high-temperature lifespan performance can be implemented without deterioration of room-temperature lifespan performance under high voltage.

Although preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements by those skilled in the art using the basic concept of the present invention defined in the following claims are also present. It belongs to the scope of the right of the invention.

10: positive electrode
12: cathode
16: separator
18: bottom plate
20: case
22: lid
24: insulation gasket

Claims (14)

Lithium salts, organic solvents and additives,
The additive is a phosphonate-based compound represented by the following formula (1); And comprising a phosphonoacetate-based compound represented by the following formula (3),
Electrolyte for lithium secondary batteries.
[Formula 1]

(In Formula 1,
R ¹ and R ² are each independently a C1 to C10 alkyl group substituted with at least one fluorine,
R ³ is a substituted or unsubstituted C1 to C10 alkyl group.)
[Formula 3]

(In Formula 3,
R ⁴ and R ⁵ are each independently a C1 to C5 alkyl group substituted with 1 to 5 fluorine,
R ⁶ is a substituted or unsubstituted C1 to C5 alkyl group.) In claim 1,
In Formula 1, R ¹ and R ² are each independently a C1 to C5 alkyl group substituted with 1 to 5 fluorine, and R ³ is a substituted or unsubstituted C1 to C5 alkyl group. In claim 1,
The phosphonate-based compound is an electrolyte for a lithium secondary battery comprising a compound represented by the following formula (2).
[Formula 2]

In claim 1,
The phosphonate-based compound is an electrolyte for a lithium secondary battery contained in an amount of 0.1 to 10 parts by weight based on 100 parts by weight of the organic solvent. delete delete In claim 1,
The phosphonoacetate-based compound is an electrolyte for a lithium secondary battery comprising a compound represented by the following formula (4).
[Formula 4]

In claim 1,
The phosphonate-based compound and the phosphonoacetate-based compound are included in a weight ratio of 1:100 to 100:1 electrolyte for a rechargeable lithium battery. delete delete delete delete A lithium secondary battery comprising the electrolyte of any one of claims 1 to 4, 7, and 8. In claim 13,
The lithium secondary battery is a lithium secondary battery driven at a voltage of 4.3V or more.

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