KR102771717B1 - Additive for lithium secondary battery, electrolyte for lithium secondary battery including the same and lithium secondary batter including the same - Google Patents

Abstract

The additive for a lithium secondary battery of exemplary embodiments of the present invention may include a compound represented by Chemical Formula 1. According to exemplary embodiments of the present invention, an electrolyte for a lithium secondary battery including a lithium salt, an organic solvent, and the additive, and a lithium secondary battery including the electrolyte are provided.

Description

Additive for lithium secondary battery, electrolyte for lithium secondary battery including same, and lithium secondary battery including same {ADDITIVE FOR LITHIUM SECONDARY BATTERY, ELECTROLYTE FOR LITHIUM SECONDARY BATTERY INCLUDING THE SAME AND LITHIUM SECONDARY BATTERY INCLUDING THE SAME}

The present invention relates to an additive for a lithium secondary battery, an electrolyte for a lithium secondary battery containing the additive, and a lithium secondary battery containing the additive.

Recently, the scope of application of lithium secondary batteries has expanded from small electronic devices to large electronic devices, automobiles, etc. Accordingly, there is a demand for the development of lithium secondary batteries that can maintain excellent performance not only at room temperature but also in high or low temperature environments.

For example, a lithium secondary battery may be composed of an anode including an anode active material (e.g., carbon material, graphite) capable of inserting and releasing lithium ions; a cathode including an anode active material (e.g., lithium metal oxide) capable of inserting and deintercalating lithium ions; and a non-aqueous electrolyte including a lithium salt and an organic solvent.

For example, the non-aqueous electrolyte may include a carbonate-based organic solvent such as ethylene carbonate or dimethyl carbonate as an organic solvent, and may include LiPF ₆ , LiBF ₄ , etc. as a lithium salt.

However, carbonate-based organic solvents may decompose on the electrode surface during charging and discharging of lithium secondary batteries, causing side reactions with lithium metal oxides, and may be inserted between graphite layers to collapse the structure of the negative electrode. Accordingly, the life characteristics of lithium secondary batteries may be reduced.

To prevent the above-mentioned problems, a technology for forming a solid electrolyte interphase (SEI) on the electrode surface has been proposed. For example, a technology for including an additive (e.g., propane sultone, propene sultone, vinyl carbonate, etc.) in a non-aqueous electrolyte has been proposed for forming SEI.

In addition, Korean Patent Publication Nos. 10-2004-0115350, 10-2007-0057118, 10-2011-0029672, 10-2011-0065021, 10-2014-0012268, 10-2012-0013003, 10-2012-0132224, 10-2015-0155005, 10-2010-0086323, and 10-2016-0139011 disclose electrolytes for lithium secondary batteries containing nitrile-based additives.

However, in the case of the additives described above, there is a problem that the degree of improvement in the performance of the lithium secondary battery is insignificant, or some performances of the lithium secondary battery are improved while others are reduced. For example, vinylene carbonate can improve the room temperature performance of the lithium secondary battery by forming SEI on the electrode surface by decomposing earlier than the conventional organic solvent, but there is a problem that it easily decomposes in a high temperature environment and generates gas.

Korean Patent Publication No. 10-2004-0115350 Korean Patent Publication No. 10-2007-0057118 Korean Patent Publication No. 10-2011-0029672 Korean Patent Publication No. 10-2011-0065021 Korean Patent Publication No. 10-2014-0012268 Korean Patent Publication No. 10-2012-0013003 Korean Patent Publication No. 10-2012-0132224 Korean Patent Publication No. 10-2015-0155005 Korean Patent Publication No. 10-2010-0086323 Korean Patent Publication No. 10-2016-0139011

One object of the present invention is to provide an electrolyte for a lithium secondary battery having improved chemical stability.

One object of the present invention is to provide a lithium secondary battery having improved life characteristics.

An additive for a lithium secondary battery according to exemplary embodiments may include a compound represented by the following chemical formula 1.

[Chemical Formula 1]

In the above chemical formula 1, R ₁ may be a methylene group or an ethylene group, and R ₂ may be a C1-C6 alkylene group or a C2-C6 alkylene group including an ether group.

In one embodiment, R ₂ can be represented by chemical formula 2.

[Chemical formula 2]

In chemical formula 2, R ₃ and R ₄ can independently be a C1-C3 alkylene group.

In one embodiment, the compound represented by Chemical Formula 1 may include at least one of the compounds represented by Chemical Formulas 3 to 7 below.

[Chemical Formula 3]

[Chemical Formula 4]

[Chemical Formula 5]

[Chemical formula 6]

[Chemical formula 7]

An electrolyte for a lithium secondary battery according to exemplary embodiments may include a lithium salt; an organic solvent; and a compound represented by the chemical formula 1.

In one embodiment, an electrolyte for a lithium secondary battery, wherein the content of the compound represented by the chemical formula 1 is 0.1 to 10 wt% of the total weight of the electrolyte.

In one embodiment, the electrolyte may further include an auxiliary additive including at least one of a fluorine-containing cyclic carbonate compound, a fluorine-containing phosphate compound, a cyclic carbonate compound having a double bond, a sultone compound, a borate compound, a cyclic sulfate compound, and a phosphorus compound having a silyl group.

In one embodiment, the content of the auxiliary additive may be 0.1 to 10 wt% of the total weight of the electrolyte.

In one embodiment, the weight ratio of the auxiliary additive to the weight of the compound represented by the chemical formula 1 in the electrolyte may be 0.5 to 5.

In one embodiment, the organic solvent may comprise a carbonate-based solvent.

In one embodiment, the carbonate solvent may include a linear carbonate solvent and a cyclic carbonate solvent.

A lithium secondary battery according to exemplary embodiments may include a positive electrode; a negative electrode opposite to the positive electrode; and an electrolyte impregnating the positive electrode and the negative electrode.

The additive for a lithium secondary battery according to exemplary embodiments of the present invention can provide a lithium secondary battery having improved high-temperature storage capacity retention rate, room-temperature life retention rate, and high-temperature life retention rate.

FIG. 1 and FIG. 2 are a plan perspective view and a cross-sectional view, respectively, schematically illustrating a lithium secondary battery according to exemplary embodiments.

According to the present invention, an additive for a lithium secondary battery represented by chemical formula 1 and an electrolyte for a lithium secondary battery comprising the additive are provided. In addition, according to the present invention, a lithium secondary battery comprising the electrolyte is provided.

Hereinafter, the present invention will be described in detail.

In this specification, the term “X-based compound” may mean a compound that includes an X unit in a parent group, side group, or substituent.

In this specification, “Ca-Cb” may mean “the number of carbon atoms from a to b.”

Electrolyte for lithium secondary batteries

An electrolyte for a lithium secondary battery according to exemplary embodiments of the present invention may include a lithium salt, an organic solvent, and a compound represented by the following chemical formula 1.

[Chemical Formula 1]

In the above chemical formula 1, R ₁ is a methylene group or an ethylene group, and R ₂ can be a C1-C6 alkylene group or a C2-C6 alkylene group including an ether group.

For example, the compound of the above chemical formula 1 can be provided as an additive for an electrolyte for a lithium secondary battery.

For example, the compound of the above chemical formula 1 can form a solid electrolyte interphase (SEI) on the electrode surface of a lithium secondary battery. For example, by forming SEI at a defect point or an active point on the electrode surface, side reactions between the electrolyte and the electrode active material can be suppressed.

In addition, the compound of the above chemical formula 1 can prevent the metal ions (e.g., Ni, Co, Mn, etc.) eluted from the positive electrode active material (e.g., lithium metal oxide) from being deposited on the negative electrode by forming a complex with the metal ions.

Accordingly, a lithium secondary battery including the compound of the chemical formula 1 can have improved life characteristics. Furthermore, the compound of the chemical formula 1 can form the SEI and the complex well at high temperatures, thereby improving the high-temperature life characteristics of a lithium secondary battery.

In addition, a lithium secondary battery including the compound of the above chemical formula 1 can exhibit excellent life characteristics even when repeatedly charged and discharged at a high C-rate.

In one embodiment, R ₂ can be a methylene group or an ethylene group.

In one embodiment, R ₂ can be represented by the following formula 2 (i.e., the compound of formula 1 can include two nitrile groups, an ester group, and an ether group).

[Chemical formula 2]

In the above chemical formula 2, R ₃ and R ₄ can independently be a C1-C3 alkylene group. For example, * can represent a bond.

In some embodiments, R ₃ and R ₄ can independently be a methylene group or an ethylene group.

In one embodiment, the compound of formula 1 may include at least one of the compounds represented by formulae 3 to 7 below.

[Chemical Formula 3]

[Chemical Formula 4]

[Chemical Formula 5]

[Chemical formula 6]

[Chemical formula 7]

In one embodiment, the content of the compound of chemical formula 1 may be 0.1 to 10 wt%, preferably 0.5 to 5 wt%, and more preferably 1 to 2 wt% of the total weight of the electrolyte.

In one embodiment, the electrolyte may further include an auxiliary additive that can further improve the performance of the lithium secondary battery.

For example, the auxiliary additive may include a fluorine-containing cyclic carbonate compound, a fluorine-containing phosphate compound, a cyclic carbonate compound having a double bond, a sultone compound, a borate compound, a sulfate compound, a phosphorus compound having a silyl group, and the like.

In some embodiments, the auxiliary additive may include the fluorine-containing cyclic carbonate compound and the borate compound. In this case, the life characteristics of the lithium secondary battery may be further improved.

In some embodiments, the content of the auxiliary additive may be 0.1 to 10 wt% of the total weight of the electrolyte.

In some embodiments, the weight ratio of the auxiliary additive to the weight of the compound of formula 1 in the electrolyte may be 0.5 to 5, or 0.5 to 3.

The above fluorine-containing cyclic carbonate compound may have a 5-7 membered cyclic structure. For example, the above fluorine-containing cyclic carbonate compound may include fluoroethylene carbonate (FEC), etc.

For example, the fluorine-containing cyclic carbonate compound may be included in an amount of 0.1 to 10 wt%, preferably 0.5 to 5 wt%, and more preferably 1 to 3 wt%, relative to the total weight of the electrolyte.

For example, the fluorine-containing phosphate compound may include a compound (WCA-1) represented by the following chemical formula 8-1, a compound (WCA-2) represented by the following chemical formula 8-2, a compound (WCA-3) represented by the following chemical formula 8-3, etc.

[Chemical Formula 8-1]

[Chemical Formula 8-2]

[Chemical Formula 8-3]

For example, the fluorine-containing phosphate compound may be included in an amount of 0.1 to 10 wt%, preferably 0.5 to 5 wt%, and more preferably 1 to 3 wt%, based on the total weight of the electrolyte.

The cyclic carbonate compound having the above double bond may include a double bond within the ring structure. For example, the cyclic carbonate compound having the above double bond may include vinylene carbonate (VC), etc.

For example, the cyclic carbonate compound having the double bond may be included in an amount of 0.1 to 10 wt%, preferably 0.5 to 5 wt%, and more preferably 1 to 3 wt%, relative to the total weight of the electrolyte.

For example, the above sultone compounds may include propane sultone (PS), propene sultone (PRS), etc.

For example, the sultone compound may be included in an amount of 0.1 to 10 wt%, preferably 0.5 to 5 wt%, and more preferably 1 to 3 wt%, relative to the total weight of the electrolyte.

For example, the borate compound may include a compound represented by the following chemical formula 9-1 (LiFOB) and a compound represented by the following chemical formula 9-2 (LiBOB).

[Chemical Formula 9-1]

[Chemical Formula 9-2]

For example, the borate compound may be included in an amount of 0.1 to 10 wt%, preferably 0.5 to 5 wt%, and more preferably 1 to 3 wt%, relative to the total weight of the electrolyte.

The above cyclic sulfate compound may have a 5-7 membered cyclic structure. For example, the above cyclic sulfate compound may include ethylene sulfate (ESA), etc.

For example, the cyclic sulfate compound may be included in an amount of 0.1 to 10 wt%, preferably 0.5 to 5 wt%, and more preferably 1 to 3 wt%, relative to the total weight of the electrolyte.

For example, the phosphorus compound having the silyl group may include tris(trimethylsilyl) phosphite, tris(trimethylsilyl) phosphate, and the like.

For example, the phosphorus compound having the silyl group may be included in an amount of 0.1 to 10 wt%, preferably 0.5 to 5 wt%, and more preferably 1 to 3 wt%, relative to the total weight of the electrolyte.

For example, the lithium salt may include LiPF ₆ , LiBF ₄ , LiClO ₄ , LiCl, LiBr, LiI, LiB ₁₀ Cl ₁₀ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF ₆ , LiSbF ₆ , LiAlCl ₄ , CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, LiN(SO ₂ C ₂ F ₅ ) ₂ , Li(CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ , LiB(C ₆ H ₅ ) ₄ , Li(SO ₂ F) ₂ N(LiFSI), (CF ₃ SO ₂ ) ₂ NLi, and the like.

In one embodiment, the concentration of the lithium salt in the electrolyte may be 0.1 to 2 M.

For example, the organic solvent may have sufficient solubility for the lithium salt, the additive, and the auxiliary additive.

In one embodiment, the organic solvent may be a non-aqueous organic solvent.

For example, the organic solvent may include a carbonate solvent, an ester solvent, an ether solvent, a ketone solvent, an alcohol solvent, an aprotic solvent, etc.

In one embodiment, the organic solvent may comprise a carbonate-based solvent.

In some embodiments, the organic solvent may include a linear carbonate solvent and a cyclic carbonate solvent.

For example, the linear carbonate solvent may include dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), methyl propyl carbonate, ethyl propyl carbonate, dipropyl carbonate, and the like.

For example, the cyclic carbonate solvent may include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, etc.

Lithium secondary battery

Hereinafter, a lithium secondary battery according to exemplary embodiments will be described in more detail with reference to the drawings. FIG. 1 and FIG. 2 are schematic plan perspective views and cross-sectional views, respectively, showing a lithium secondary battery according to exemplary embodiments.

Referring to FIG. 2, a lithium secondary battery may include a positive electrode (100) and a negative electrode (130) opposite to the positive electrode (100).

The positive electrode (100) may include a positive electrode current collector (105) and a positive electrode active material layer (110) formed on the positive electrode current collector (105).

The positive electrode active material layer (110) may include a positive electrode active material, a positive electrode binder, and a conductive material, if necessary.

For example, the cathode current collector (105) may include stainless steel, nickel, aluminum, titanium, copper, or the like.

For example, the positive electrode active material may include a lithium metal oxide capable of reversible insertion and deintercalation of lithium ions.

For example, the lithium metal oxide may include lithium cobalt-based oxide, lithium manganese-based oxide, lithium copper oxide, lithium nickel-based oxide, lithium manganese composite oxide, and lithium-nickel-manganese-cobalt-based oxide.

For example, the lithium metal oxide may include LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , Li(Ni _a Co _b Mn _c )O ₂ (0<a<1, 0<b<1, 0<c<1, a+b+c=1), LiNi _1-y Co _y O ₂ (O<y<1), LiCo _1-y Mn _y O ₂ (O<y<1), LiNi _1-y Mn _y O ₂ (O≤y<1), Li(Ni _a Co _b Mn _c )O ₄ (0<a<2, 0<b<2, 0<c<2, a+b+c=2), LiMn _2-z Ni _z O ₄ (0<z<2), LiMn _2-z Co _z O ₄ (0<z<2), LiCoPO ₄ , LiFePO ₄ , etc. there is.

In one embodiment, the lithium metal oxide may include a lithium-rich metal oxide. For example, the lithium-rich metal oxide may be represented by the following chemical formula 8.

[Chemical Formula 10]

Li _x Ni _y Mn _z Co _w O ₂

In the above chemical formula 10, 1<x≤2, 0<y≤1, 0<z≤1, and 0<w≤1.

The electrolyte for a lithium secondary battery according to exemplary embodiments of the present invention can maintain electrochemically stable characteristics even at a voltage of 4.5 V, and thus can be used together with the excess lithium metal oxide particles.

For example, the binder may serve to adhere well between the positive electrode active materials, and also between the positive electrode active material and the positive electrode current collector (110). For example, the binder may include a polymer including polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, ethylene oxide, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, and the like.

For example, the conductive material may be used to impart conductivity to the positive electrode active material layer (110). For example, the conductive material may include natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, metal powder such as copper, nickel, aluminum, and silver, metal fiber, etc.

The negative electrode (130) may include a negative electrode current collector (125) and a negative electrode active material layer (120) on the negative electrode current collector (125).

The negative electrode active material layer (120) may include a negative electrode active material, a negative electrode binder, and a conductive material, if necessary.

For example, the negative electrode collector (125) may include gold, stainless steel, nickel, aluminum, titanium, copper, or the like.

For example, the negative electrode active material may be a material capable of absorbing and desorbing lithium ions. For example, the negative electrode active material may include a carbon-based material, lithium metal, an alloy of lithium metal, a silicon-based material, a transition metal oxide, etc.

The above carbonaceous material may include crystalline carbon, amorphous carbon, and the like. For example, the crystalline carbon may include graphite such as natural graphite or artificial graphite in an amorphous, plate-like, flake-like, spherical, or fiber-like form. In addition, the amorphous carbon may include soft carbon, hard carbon, mesophase pitch carbide, calcined coke, and the like.

As the above lithium metal alloy, an alloy of lithium and a metal selected from the group consisting of Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn can be used.

The above silicon-based material may include Si, SiOx (0<x<2), a combination of graphite and Si, a material in which Si is coated on the surface of graphite particles, a material in which Si and carbon are coated on the surface of graphite particles, etc.

The above transition metal oxide may include vanadium oxide, lithium vanadium oxide, and the like.

The above-described negative electrode binder and conductive material may be substantially the same as or similar to the above-described positive electrode binder and conductive material. For example, the above-described negative electrode binder may be an aqueous binder such as styrene-butadiene rubber (SBR). In addition, for example, the above-described negative electrode binder may be used together with a thickener such as carboxymethyl cellulose (CMC).

A separator (140) may be interposed between the positive electrode (100) and the negative electrode (130).

For example, the separation membrane (140) may include an ethylene homopolymer, a propylene homopolymer, or the like.

An electrode cell can be formed including a positive electrode (100), a negative electrode (130), and a separator (140). A plurality of electrode cells can be stacked to form an electrode assembly (150) (however, for convenience, only one electrode cell is illustrated in FIG. 2).

An electrode assembly (150) can be formed by winding, lamination, etc. of a separator (140).

A lithium secondary battery according to exemplary embodiments may include a positive electrode lead (107) connected to a positive electrode (100) and protruding outwardly from a case (160); and a negative electrode lead (127) connected to a negative electrode (130) and protruding outwardly from a case (160).

The anode (100) and the anode lead (107) may be electrically connected. Similarly, the cathode (130) and the cathode lead (127) may be electrically connected.

The positive electrode lead (107) may be electrically connected to the positive electrode collector (105). Additionally, the negative electrode lead (130) may be electrically connected to the negative electrode collector (125).

The positive electrode current collector (105) may include a protrusion (positive electrode tab, 106) on one side. A positive electrode active material layer (110) may not be formed on the positive electrode tab (106). The positive electrode tab (106) may be integral with the positive electrode current collector (105) or may be connected by welding or the like. The positive electrode current collector (105) and the positive electrode lead (107) may be electrically connected through the positive electrode tab (106).

The negative electrode collector (125) may include a protrusion (negative electrode tab, 126) on one side. The negative electrode active material layer (120) may not be formed on the negative electrode tab. The negative electrode tab (126) may be integral with the negative electrode collector (125) or may be connected by welding or the like. The negative electrode collector (125) and the negative electrode lead (127) may be electrically connected through the negative electrode tab (126).

For example, an electrode assembly (150) and an electrolyte for a lithium secondary battery according to exemplary embodiments of the present invention may be accommodated in a case (160) to form a lithium secondary battery.

For example, the lithium secondary battery may be cylindrical, square, pouch or coin shaped.

Hereinafter, preferred embodiments and comparative examples of the present invention will be described. However, the following examples are only preferred embodiments of the present invention, and the present invention is not limited to the following examples.

Examples and Comparative Examples

1. Preparation of electrolyte

A 1.0 M LiPF ₆ solution was prepared using an organic solvent consisting of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a 2:5:5 (v/v/v) ratio.

To the above LiPF ₆ solution, additives and auxiliary additives were added and mixed according to Table 1 below based on the total weight of the electrolyte (100 wt%), to prepare electrolytes of examples and comparative examples.

2. Manufacturing of lithium secondary batteries

LiCoO ₂ , PVDF (polyvinylidene fluoride), and carbon black were dispersed in NMP at a weight ratio of 94:3:3 to prepare a cathode slurry. The cathode slurry was coated on an aluminum foil to prepare a cathode.

Graphite, PVDF, and carbon black were dispersed in water at a weight ratio of 96:3:1 to prepare a cathode slurry. The cathode slurry was coated on a copper foil to prepare a cathode.

An electrode assembly was formed by interposing a separator (polyethylene) between the positive electrode and the negative electrode as described above.

The above electrode assembly and the electrolyte as described above were placed in a pouch and vacuum-packed to manufacture a lithium secondary battery.

Experimental Example 1: High Temperature Storage Capacity Retention Rate

The lithium secondary batteries of the examples and comparative examples were charged at 1C to 4.2 V at room temperature (25°C) and discharged at 1C to 2.75 V, and the initial discharge capacity A1 was measured.

After measuring the initial discharge capacity A1, the lithium secondary battery was recharged at 0.5 C to 4.2 V and left at high temperature (45°C) for one week.

After being stored at high temperature, the lithium secondary battery was subjected to two cycles of 1C charging to 4.2 V and 1C discharging to 2.75 V, and the discharge capacity A2 of the second cycle was measured.

The high temperature storage capacity retention rate was calculated according to the following formula.

High temperature storage capacity retention rate (%) = A2/A1 × 100

Experimental Example 2: Room Temperature Lifespan Maintenance Rate

The lithium secondary batteries of the examples and comparative examples were charged at 1C to 4.2 V at room temperature (25°C) and discharged at 2C to 2.75 V to measure the initial discharge capacity B1.

The above charging and discharging were repeated 500 times, and the discharge capacity B2 at the 500th time was measured.

The room temperature life maintenance rate was calculated according to the following formula.

Room temperature life retention rate (%) = B2/B1 × 100

Experimental Example 3: High Temperature Life Retention Rate

The lithium secondary batteries of the examples and comparative examples were charged at 1C to 4.2 V and discharged at 2C to 2.75 V at high temperature (45°C) to measure the initial discharge capacity C1.

The above charging and discharging were repeated 500 times, and the discharge capacity C2 at the 500th time was measured.

The high temperature life maintenance rate was calculated according to the following formula.

High temperature life maintenance rate (%) = C2/C1 × 100

Additives Auxiliary additives High temperature storage
Capacity retention rate
(%) Room temperature
Lifespan maintenance rate
(%) High temperature
Lifespan maintenance rate
(%) Example 1 A-1 1wt% FEC 1wt%
LiBOB 1wt% 84.2 94.5 92.2 Example 2 A-2 1wt% FEC 1wt%
LiBOB 1wt% 86.5 92.7 92.5 Example 3 A-3 1wt% FEC 1wt%
LiBOB 1wt% 86.4 93.5 93.2 Example 4 A-4 1wt% FEC 1wt%
LiBOB 1wt% 85.2 93.7 92.4 Comparative Example 1 - FEC 1wt%
LiBOB 1wt% 80.8 92.6 85.2 Comparative Example 2 B-1 1wt% FEC 1wt%
LiBOB 1wt% 82.2 91.2 89.6 A-1: Compound of chemical formula 3
[Chemical Formula 3]

A-2: Compound of chemical formula 4
[Chemical Formula 4]

A-3: Compound of chemical formula 6
[Chemical formula 6]

A-4: Compound of chemical formula 7
[Chemical formula 7]

B-1: Succinonitrile

Referring to Table 1 above, the lithium secondary batteries of the examples showed improved high-temperature storage capacity retention rate, room-temperature life retention rate, and high-temperature life retention rate compared to the lithium secondary batteries of the comparative examples.

100: Anode 105: Anode current collector
106: Positive tab 107: Positive lead
110: Cathode active material layer 120: Cathode active material layer
125: Negative current collector 126: Negative tab
127: Negative lead 130: Negative lead
140: Separator 150: Electrode assembly
160: Case

Claims (11)

An additive for a lithium secondary battery, comprising a compound represented by chemical formula 1:
[Chemical Formula 1]

(In chemical formula 1, R ₁ is a methylene group or an ethylene group,
R ₂ is represented by chemical formula 2,
[Chemical formula 2]

In chemical formula 2, R ₃ and R ₄ are independently a C1-C3 alkylene group. delete In claim 1, the compound represented by the chemical formula 1 is an additive for a lithium secondary battery, which comprises a compound represented by the chemical formula 7:
[Chemical formula 7]
. lithium salt;
organic solvent; and
An electrolyte for a lithium secondary battery, comprising a compound represented by chemical formula 1:
[Chemical Formula 1]

(In chemical formula 1, R ₁ is a methylene group or an ethylene group,
R ₂ is represented by chemical formula 2,
[Chemical formula 2]

In chemical formula 2, R ₃ and R ₄ are independently a C1-C3 alkylene group. An electrolyte for a lithium secondary battery, wherein the content of the compound represented by the chemical formula 1 in claim 4 is 0.1 to 10 wt% of the total weight of the electrolyte. An electrolyte for a lithium secondary battery according to claim 4, further comprising an auxiliary additive comprising at least one of a fluorine-containing cyclic carbonate compound, a fluorine-containing phosphate compound, a cyclic carbonate compound having a double bond, a sultone compound, a borate compound, a cyclic sulfate compound, and a phosphorus compound having a silyl group. An electrolyte for a lithium secondary battery according to claim 6, wherein the content of the auxiliary additive is 0.1 to 10 wt% of the total weight of the electrolyte. In claim 6, among the electrolytes,
An electrolyte for a lithium secondary battery, wherein the weight ratio of the auxiliary additive to the weight of the compound represented by the chemical formula 1 is 0.5 to 5. An electrolyte for a lithium secondary battery according to claim 4, wherein the organic solvent includes a carbonate solvent. In claim 9, the carbonate solvent is
An electrolyte for a lithium secondary battery, comprising a linear carbonate solvent and a cyclic carbonate solvent. anode;
a cathode opposite to the anode; and
A lithium secondary battery comprising the electrolyte for a lithium secondary battery according to claim 4, which impregnates the positive electrode and the negative electrode.