KR102452329B1 - Electrolyte for lithium secondary battery, and lithium secondary battery comprising the same - Google Patents

Abstract

The present invention relates to a non-aqueous electrolyte for a lithium secondary battery and a lithium secondary battery comprising the same, specifically, a lithium salt; organic solvents; A non-aqueous electrolyte for a lithium secondary battery comprising a first additive and a second additive, wherein the first additive is a compound represented by Formula 1, and the second additive is a compound represented by Formula 2, and a lithium secondary battery comprising the same will be.

Description

Non-aqueous electrolyte for lithium secondary battery and lithium secondary battery comprising same

The present invention relates to a non-aqueous electrolyte for a lithium secondary battery and a lithium secondary battery comprising the same.

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

Among electrochemical devices, interest in the development of rechargeable batteries capable of charging and discharging is rising. In particular, lithium secondary batteries developed in the early 1990s are in the spotlight because of their high operating voltage and extremely high energy density.

The lithium secondary battery currently applied is composed of a carbon-based negative electrode capable of occluding and discharging lithium ions, a positive electrode made of a lithium-containing transition metal oxide, and the like, and a non-aqueous electrolyte in which lithium salt is dissolved in an appropriate amount in a carbonate-based organic solvent.

In the lithium secondary battery, charging and discharging are possible by transferring energy while repeating the phenomenon in which lithium ions discharged from the positive electrode are inserted into the negative electrode, for example, carbon particles, and desorbed again during discharging.

On the other hand, during the initial charging of the lithium secondary battery, the highly reactive lithium ions emitted from the positive electrode react with the carbon-based negative electrode to form organic materials and Li ₂ CO ₃ , Li ₂ O, LiOH, etc., which are a kind of passivation on the surface of the negative electrode. A passivation layer is formed. Such a film is called a solid electrolyte interface (SEI) film.

Once the SEI film is formed during initial charging, it prevents the reaction between lithium ions and carbon-based negative electrodes or other materials during repeated charging and discharging, and serves as an ion tunnel through which only lithium ions pass between the electrolyte and the negative electrode. . By the ion tunnel effect, the SEI film prevents the organic solvents of the electrolyte having a large molecular weight from moving to the carbon-based anode, thereby preventing the carbon-based anode structure from collapsing. That is, after this film is formed, since lithium ions do not generate side reactions with the carbon-based negative electrode or other materials again, the amount of lithium ions is reversibly maintained during subsequent charging and discharging. In other words, the carbon material of the negative electrode reacts with the electrolyte during initial charging to form a passivation layer on the surface of the negative electrode, thereby preventing further decomposition of the electrolyte and maintaining stable charge and discharge. The amount of charge consumed in layer formation is an irreversible capacity, and it has a characteristic that it does not react reversibly during discharge. .

However, when a lithium ion battery is stored at a high temperature in a fully charged state (eg, stored at 60° C. after 100% charge of 4.15 V or more), there is a problem that the SEI film gradually collapses over time.

This SEI film collapse exposes the surface of the negative electrode, and the exposed surface of the negative electrode is decomposed while reacting with the carbonate-based solvent in the electrolyte, causing continuous side reactions. Moreover, these side reactions continuously generate gases. At this time, regardless of the type of gas generated, continuous gas generation at high temperature increases the internal pressure of the lithium ion battery and acts as a resistance element to lithium movement, thereby expanding the battery thickness and causing deterioration of battery performance.

Recently, as the field of application of lithium secondary batteries has been expanded, stability and long lifespan characteristics are continuously required in harsh environments such as high and low temperature environments. This performance is highly dependent on the SEI film formed by the initial reaction of the electrode and the electrolyte.

Therefore, in order to improve the high-temperature cycle characteristics and low-temperature output of the lithium secondary battery, the development of additives capable of suppressing a side reaction between the positive electrode and the electrolyte and forming a solid SEI film on the surface of the negative electrode is continuously being made.

Korean Patent Publication No. 2017-0033437

An object of the present invention is to provide a non-aqueous electrolyte for a lithium secondary battery comprising an additive capable of forming a stable film on the surface of an electrode.

In addition, an object of the present invention is to provide a lithium secondary battery having improved high temperature durability by including the non-aqueous electrolyte for a lithium secondary battery.

According to one embodiment, the present invention

lithium salt; organic solvents; a first additive and a second additive;

The first additive is a compound represented by the following formula (1),

The second additive provides a non-aqueous electrolyte for a lithium secondary battery, which is a compound represented by the following formula (2).

[Formula 1]

In Formula 1,

R ₁ and R ₂ are each independently a substituted or unsubstituted C 1 to C 5 alkylene group, and R ₃ is hydrogen or a substituted or unsubstituted C 1 to C 5 alkyl group.

[Formula 2]

In Formula 2,

Wherein A and A' are each independently O, S or N,

R ₄ is a substituted or unsubstituted C 1 to C 5 alkylene group,

R ₅ to R ₇ are each independently hydrogen or an alkyl group having 1 to 4 carbon atoms.

The weight ratio of the first additive to the second additive may be 1:0.01 to 1:10.

According to another embodiment, the present invention provides a lithium secondary battery comprising the non-aqueous electrolyte for a lithium secondary battery of the present invention.

According to the present invention, by mixing and including two types of compounds capable of forming a film on the surface of the electrode in a specific ratio, a stable passivation film is formed on the surfaces of the positive electrode and the negative electrode, and at the same time, lithium capable of stabilizing the anion of the lithium salt A non-aqueous electrolyte for a secondary battery can be prepared. In addition, by including it, it is possible to manufacture a lithium secondary battery with improved overall performance such as cycle capacity characteristics and resistance increase suppression during high-temperature storage.

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

The terms or words used in the present specification and claims should not be construed as being limited to their ordinary or dictionary meanings, and the inventor may properly define the concept of the term in order to best describe his invention. Based on the principle that there is, it should be interpreted as meaning and concept consistent with the technical idea of the present invention.

In addition, the terminology used herein is used only to describe exemplary embodiments, and is not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly dictates otherwise.

Prior to describing the present invention, in this specification, terms such as "comprises", "comprises" or "have" are not intended to designate the existence of embodied features, numbers, steps, components, or combinations thereof. , it should be understood that it does not preclude the possibility of addition or existence of one or more other features or numbers, steps, elements, or combinations thereof.

Meanwhile, in the description of "carbon number a to b" in the present specification, "a" and "b" mean the number of carbon atoms included in a specific functional group. That is, the functional group may include “a” to “b” carbon atoms. For example, an "alkylene group having 1 to 5 carbon atoms" is an alkylene group containing 1 to 5 carbon atoms, that is, -CH ₂ -, -CH ₂ CH ₂ -, -CH ₂ CH ₂ CH ₂ -, - CH ₂ (CH ₂ )CH—, —CH(CH ₂ )CH ₂ — and —CH(CH ₂ )CH ₂ CH ₂ — and the like.

The term "alkylene group" refers to a branched or unbranched divalent unsaturated hydrocarbon group. In one embodiment, the alkylene group may include a methylene group, an ethylene group, a propylene group, an isopropylene group, a butylene group, an isobutylene group, a tert-butylene group, a pentylene group, a 3-pentylene group, and the like.

In addition, in the present specification, unless otherwise defined, "substitution" means that at least one hydrogen bonded to carbon is substituted with an element other than hydrogen, for example, substituted with an alkyl group having 1 to 3 carbon atoms. means that

Non-aqueous electrolyte for lithium secondary battery

According to one embodiment, the present invention

lithium salt; organic solvents; a first additive and a second additive;

The first additive is a compound represented by the following formula (1),

The second additive provides a non-aqueous electrolyte for a lithium secondary battery, which is a compound represented by the following formula (2).

[Formula 1]

In Formula 1,

R ₁ and R ₂ are each independently a substituted or unsubstituted C 1 to C 5 alkylene group, and R ₃ is hydrogen or a substituted or unsubstituted C 1 to C 5 alkyl group.

[Formula 2]

In Formula 2,

Wherein A and A' are each independently O, S or N,

R ₄ is a substituted or unsubstituted C 1 to C 5 alkylene group,

R ₅ to R ₇ are each independently hydrogen or an alkyl group having 1 to 4 carbon atoms.

Hereinafter, each component of the non-aqueous electrolyte for a lithium secondary battery of the present invention will be described in more detail.

(1) lithium salt

In the non-aqueous electrolyte for a lithium secondary battery according to an embodiment of the present invention, the lithium salt may be used without limitation, those commonly used in the electrolyte for a lithium secondary battery, for example, Li ⁺ as a cation of the lithium salt. Anions include F ^- , Cl ^- , Br ^- , I ^- , NO ₃ ^- , N(CN) ₂ ^- , ClO ₄ ^- , BF ₄ ^- , B ₁₀ Cl ₁₀ ^- , PF ₆ ^- , CF ₃ SO ₃ ^- , CH ₃ CO ₂ ^- , CF ₃ CO ₂ ^- , AsF ₆ ^- , SbF ₆ ^- , AlCl ₄ ^- , AlO ₄ ^- , CH ₃ SO ₃ ^- , BF ₂ C ₂ O ₄ ^- , BC ₄ O ₈ ^- , PF ₄ C ₂ O ₄ ^- , PF ₂ C ₄ O ₈ ^- , (CF ₃ ) ₂ PF ₄ ^- , (CF ₃ ) ₃ PF ₃ ^- , (CF ₃ ) ₄ PF ₂ ^- , (CF ₃ ) ₅ PF ^- , C ₄ F ₉ SO ₃ ^- , CF ₃ CF ₂ SO ₃ ^- , (CF ₃ SO ₂ ) ₂ N ^- , (FSO ₂ ) ₂ N ^- , CF ₃ CF ₂ (CF ₃ ) ₂ CO ^- , (CF ₃ SO ₂ ) ) ₂ CH ^- , (SF ₅ ) ₃ C ^- , (CF ₃ SO ₂ ) ₃ C ^- , CF ₃ (CF ₂ ) ₇ SO ₃ ^- , SCN ^- and (CF ₃ CF ₂ SO ₂ ) ₂ N ^- At least one selected from the group may be mentioned.

Specifically, the lithium salt is LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCH ₃ CO ₂ , LiCF ₃ CO ₂ , LiAsF ₆ , LiSbF ₆ , LiAlCl ₄ , LiAlO ₄ , LiCH ₃ SO ₃ , LiFSI (lithium fluorosulfonyl imide, LiN(SO ₂ F) ₂ ), LiTFSI (lithium (bis)trifluoromethanesulfonimide, LiN(SO ₂ CF ₃ ) ₂ ) and LiBETI (lithium bisperfluoroethanesulfonimide, LiN(SO) ₂ C ₂ F ₅ ) ₂ ) may include a single substance or a mixture of two or more selected from the group consisting of. More specifically, the lithium salt is a single substance or two selected from the group consisting of LiPF ₆ , LiBF ₄ , LiCH ₃ CO ₂ , LiCF ₃ CO ₂ , LiCH ₃ SO ₃ , LiFSI, LiTFSI and LiN(C ₂ F ₅ SO ₂ ) ₂ . It may include a mixture of the above.

The lithium salt may be appropriately changed within the range that can be used in general, and specifically may be included in an amount of 0.1M to 3M, specifically 0.8M to 2.5M in the electrolyte. If the concentration of the lithium salt exceeds 3 M, the viscosity of the non-aqueous electrolyte increases, the lithium ion migration effect decreases, and the wettability of the non-aqueous electrolyte decreases, making it difficult to form an SEI film having a uniform thickness on the electrode surface.

(2) organic solvents

The organic solvent is not limited in its type as long as it can minimize decomposition due to oxidation reaction or the like in the charging and discharging process of the secondary battery and exhibit desired properties together with the additive. For example, a carbonate-based organic solvent, an ether-based organic solvent, or an ester-based organic solvent may be used alone or in combination of two or more.

Among the organic solvents, the carbonate-based organic solvent may include at least one of a cyclic carbonate-based organic solvent and a linear carbonate-based organic solvent. Specifically, the cyclic carbonate-based organic solvent is ethylene carbonate (ethylene carbonate, EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene It may include at least one selected from the group consisting of carbonate, 2,3-pentylene carbonate, vinylene carbonate, and fluoroethylene carbonate (FEC), and specifically ethylene carbonate and ethylene carbonate having a high dielectric constant relative to that of ethylene carbonate. as a mixed solvent of propylene carbonate having a low melting point.

In addition, the linear carbonate-based organic solvent is a solvent having a low viscosity and a low dielectric constant, dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethylmethyl carbonate (EMC), methyl It may include at least one selected from the group consisting of propyl carbonate and ethylpropyl carbonate, and more specifically, dimethyl carbonate.

The ether-based organic solvent may be any one selected from the group consisting of dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether and ethyl propyl ether, or a mixture of two or more thereof, but limited thereto it's not going to be

The ester-based organic solvent may include at least one selected from the group consisting of a linear ester-based organic solvent and a cyclic ester-based organic solvent.

In this case, the linear ester-based organic solvent is, as a specific example, any one selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, and butyl propionate or A mixture of two or more of them may be typically used, but is not limited thereto.

The cyclic ester-based organic solvent is, as a specific example, any one or two selected from the group consisting of γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone and ε-caprolactone. The above mixture may be used, but is not limited thereto.

The organic solvent may use a high-viscosity cyclic carbonate-based organic solvent capable of dissociating lithium salts in the electrolyte with high dielectric constant. In addition, in order to prepare an electrolyte having a higher electrical conductivity, the organic solvent is a low-viscosity, low-dielectric constant linear carbonate-based compound and a linear ester-based compound such as dimethyl carbonate and diethyl carbonate together with the environmental carbonate-based organic solvent. It can be used by mixing in an appropriate ratio.

More specifically, the organic solvent may be used by mixing a cyclic carbonate-based compound and a linear carbonate-based compound, and the weight ratio of the cyclic carbonate-based compound to the linear carbonate-based compound in the organic solvent may be 10:90 to 70:30.

(3) first additive

Meanwhile, the non-aqueous electrolyte for a lithium secondary battery of the present invention may include a compound represented by the following Chemical Formula 1 as a first additive.

[Formula 1]

In Formula 1,

R ₁ and R ₂ are each independently a substituted or unsubstituted C 1 to C 5 alkylene group, and R ₃ is hydrogen or a substituted or unsubstituted C 1 to C 5 alkyl group.

The compound represented by Formula 1 is electrochemically decomposed on the surfaces of the anode and cathode while the carbonate group and sulfonate group included in the compound structure are reduced during charging and discharging to form a strong SEI film that does not crack even when stored at high temperatures. have. In addition, during charging and discharging, the double bond structure included in the compound structure may undergo a reduction reaction at the negative electrode to form a more robust SEI film on the surfaces of the positive electrode and the negative electrode. The surface of the anode and the cathode may be prevented from being exposed to the electrolyte due to the firmly formed SEI film as described above. Therefore, the high temperature durability of the battery can be improved by suppressing the generation of O ₂ from the positive electrode and suppressing the side reaction between the positive electrode and the electrolyte. Moreover, even when a highly crystalline carbon material such as natural graphite or artificial graphite is used for the negative electrode as the negative electrode active material, it is possible to suppress the decomposition of the organic solvent, thereby suppressing gas generation during high-temperature storage, and improving the high-temperature storage characteristics of the battery. can

Meanwhile, in Formula 1, R ₁ and R ₂ may each independently be an unsubstituted alkylene group having 1 to 4 carbon atoms, and R ₃ may be hydrogen or an alkyl group having 1 to 3 carbon atoms. More specifically, in Formula 1, R ₁ and R ₂ may each independently represent an unsubstituted alkylene group having 1 to 3 carbon atoms, and R ₃ may be hydrogen.

More specifically, the compound represented by Formula 1 may be a compound represented by Formula 1a below.

[Formula 1a]

The compound represented by Formula 1 may be appropriately used depending on the amount of electrolyte additive generally added to the electrolyte, for example, 0.01 wt% to 5 wt%, more specifically, based on the total weight of the non-aqueous electrolyte for a lithium secondary battery As may be included in 0.1 wt% to 3 wt%.

When the compound represented by Chemical Formula 1 is included in the above ratio, a strong SEI film can be stably formed on the surfaces of the anode and the anode, and the effect thereof can be obtained.

When the content of the compound represented by Formula 1 in the non-aqueous electrolyte for a lithium secondary battery exceeds 5 wt %, an excessively thick film is formed during initial charging to increase resistance, and accordingly, the initial capacity expression of the secondary battery is lowered and output deterioration is reduced. can occur In addition, when the compound represented by Formula 1 is contained in less than 0.01 wt % in the non-aqueous electrolyte, the film forming effect is insignificant and an unstable SEI film is formed. can occur

(4) second additive

In addition, the non-aqueous electrolyte for a lithium secondary battery of the present invention may include a compound represented by the following Chemical Formula 2 as a second additive.

[Formula 2]

In Formula 2,

Wherein A and A' are each independently O, S or N,

R ₄ is a substituted or unsubstituted C 1 to C 5 alkylene group,

R ₅ to R ₇ are each independently hydrogen or an alkyl group having 1 to 4 carbon atoms.

The compound represented by Formula 2 is a compound that can give a synergistic effect to the SEI film-forming effect of the compound represented by Formula 1 included as the first additive, and the triple bond structure is converted to electricity on the surface of the anode according to the reduction reaction during battery operation. It can be chemically decomposed to form a stronger SEI film that does not crack even when stored at high temperatures. In addition, the heterocycloalkylene group structure may stabilize the lithium salt anion while reacting with the anion of the lithium salt. Accordingly, since the side reaction between the non-aqueous electrolyte and the electrode is suppressed during high temperature storage, and in particular, the side reaction of the anion at high temperature is prevented to prevent an increase in resistance, the cycle capacity characteristics of the lithium secondary battery can be improved during high temperature storage.

Meanwhile, in Formula ₂ , A and A' are both N, R ₄ is a substituted or unsubstituted C1-C3 alkylene group, and R ₅ to R7 are each independently hydrogen or a C1-C3 alkylene group. It may be an alkyl group.

Specifically, the compound represented by Formula 2 may be at least one selected from the group consisting of compounds represented by Formulas 2a and 2b below.

[Formula 2a]

[Formula 2b]

Meanwhile, the weight ratio of the first additive to the second additive may be 1:0.01 to 1:10, specifically 1:0.01 to 1:5, and more specifically 1:0.01 to 1:1.

When each component of the additive is mixed in the above ratio, a secondary battery with improved overall performance such as high temperature durability and gas generation reduction effect can be manufactured by securing a stabilizing effect and a lithium salt anion stabilizing effect when forming an SEI film. have. That is, in order for the second additive to supplement the first additive in the non-aqueous electrolyte of the present invention and to produce a synergistic effect for forming the SEI film, the weight ratio of the second additive to 1 weight of the first additive should be 10 or less.

If the ratio of the first additive to the second additive is out of the above range, initial resistance may increase and negatively affect initial capacity expression. For example, when the weight ratio of the second additive to 1 weight of the first additive exceeds 10, an excessively thick SEI film is formed to prevent absorption/desorption of lithium, and thus resistance is increased to deteriorate output characteristics and cycle life characteristics. can occur If the weight ratio of the second additive to 1 weight of the first additive is less than 0.01, the film-forming effect on the surfaces of the positive and negative electrodes is insufficient, the anion stabilization effect is lowered, and a side reaction between the electrolyte and the negative electrode is caused, thereby causing the secondary battery Performance may be degraded.

Meanwhile, the total content of the first additive and the second additive is 10 wt% or less, preferably 0.01 wt% to 9 wt% or less, specifically 0.5 wt% to 8 wt% based on the total weight of the non-aqueous electrolyte of the present invention weight % or less.

At this time, when the total content of the first and second additives exceeds 10% by weight, the coating film is formed too thickly by the excess additive, and the capacity retention rate, resistance increase rate, and thickness increase rate suppression effect are improved, whereas lithium insertion And since the resistance increases to a certain level or more during the desorption process, the initial resistance may increase and the initial capacity may decrease.

As described above, in the non-aqueous electrolyte for a lithium secondary battery of the present invention, a more stable and robust SEI film is formed on the surfaces of the positive and negative electrodes by mixing the first additive and the second additive in a specific ratio, and at the same time, additional By securing the lithium salt anion stabilization effect, it is possible to suppress side reactions of the electrolyte during storage at high temperatures, thereby suppressing gas generation. Furthermore, it is possible to improve overall performance such as improvement of capacity characteristics and suppression of resistance during high-temperature storage.

(5) additive for forming SEI film

The non-aqueous electrolyte of the present invention is used together with the mixed additive to form a stable film on the surface of the anode and the anode without significantly increasing the initial resistance along with the effect expressed by the mixed additive, or to inhibit the decomposition of the solvent in the non-aqueous electrolyte and may further include an additional additive that can serve as a complement to improve the mobility of lithium ions.

The additive is not particularly limited as long as it is an additive for forming an SEI film capable of forming a stable film on the surfaces of the anode and the cathode.

Specifically, the SEI film-forming additive is a representative example of which the non-aqueous electrolyte for a lithium secondary battery is a halogen-substituted or unsubstituted cyclic carbonate-based compound, a nitrile-based compound, a phosphate-based compound, a borate-based compound, a sulfate-based compound, and a sultone-based compound. and at least one additive for forming an SEI film selected from the group consisting of lithium salt-based compounds.

Specifically, the halogen-substituted or unsubstituted cyclic carbonate-based compound forms a stable SEI film mainly on the surface of the negative electrode during battery activation, thereby improving battery durability.

The halogen-substituted cyclic carbonate-based compound may include fluoroethylene carbonate (FEC), and the halogen-unsubstituted cyclic carbonate-based compound may include vinylene carbonate (VC) or vinylethylene carbonate.

The halogen-substituted or unsubstituted cyclic carbonate-based compound may be included in an amount of 5 wt% or less based on the total weight of the non-aqueous electrolyte. When the content of the cyclic carbonate-based compound in the non-aqueous electrolyte exceeds 5% by weight, cell swelling inhibition performance and initial resistance may be deteriorated.

When the nitrile-based compound is used together with the above-described mixed additive, effects such as improvement of high-temperature characteristics can be expected by stabilizing the anode/cathode film. That is, it can serve as a complement in forming the anode SEI film, inhibit the decomposition of the solvent in the electrolyte, and serve to improve the mobility of lithium ions. Representative examples of these nitrile-based compounds include succinonitrile, adiponitrile, acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentane carbonitrile, cyclohexane carbonitrile, 2- Fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, 4-fluorophenylacetonitrile, 1,4-dicyano at least one compound selected from the group consisting of -2-butene, glutaronitrile, 1,3,6-hexanetricarbonitrile, and pimelonitrile.

The nitrile-based compound may be included in an amount of 8 wt% or less based on the total weight of the non-aqueous electrolyte. When the total content of the nitrile-based compound in the non-aqueous electrolyte exceeds 8% by weight, resistance increases due to an increase in a film formed on the surface of the electrode, and battery performance may deteriorate.

In addition, since the phosphate-based compound stabilizes PF ₆ anions in the electrolyte and helps to form anode and cathode films, durability of the battery can be improved. These phosphate-based compounds include lithium difluoro(bisoxalato)phosphate (LiDFOP), lithium difluorophosphate (LiDFP, LiPO ₂ F ₂ ,), lithium tetramethyl trimethyl silyl phosphate, trimethyl silyl phosphite (TMSPi), Trimethyl silyl phosphate (TMSPa), ethyl di (pro-2-yn-1-yl) phosphate (ethyl di (prop-2-yn-1-yl) phosphate), allyl diphosphate (allyl diphosphate), tris (2, and at least one compound selected from the group consisting of 2,2-trifluoroethyl) phosphate (TFEPa) and tris (trifluoroethyl) phosphite, and may be included in an amount of 3 wt % or less based on the total weight of the non-aqueous electrolyte can

The borate compound promotes ion pair separation of lithium salts, can improve the mobility of lithium ions, can reduce the interfacial resistance of the SEI film, and materials such as LiF that are generated during battery reaction and are not easily separated By dissociating, problems such as generation of hydrofluoric acid gas can be solved. Such borate-based compounds may include lithium bioxalyl borate (LiBOB, LiB(C ₂ O ₄ ) ₂ ), lithium oxalyldifluoroborate, or tetramethyl trimethylsilyl borate (TMSB), based on the total weight of the non-aqueous electrolyte. It may be included in an amount of 3% by weight or less.

The sulfate-based compound is ethylene sulfate (Ethylene Sulfate; Esa), trimethylene sulfate (TMS), methyltrimethylene sulfate (MTMS), 1,3-propanediol cyclic sulfate (1,3-Propanediol cyclic sulfate), 1, 3-butylene sulfate (1,3-butylenesulfate), 2-acetoxy-1,3-propanesultone (2-acetoxy-1,3-propanesultone), methylene methanedisulfonate (methylene methanedisulfonate), or 1,4 -bis(methanesulfonyloxy)-2-butyne (,4-bis(methanesulfonyloxy)-2-butyne) may be mentioned, and may be included in an amount of 3 wt% or less based on the total weight of the non-aqueous electrolyte.

The sultone-based compound is 1,3-propane sultone (PS), 1,4-butane sultone, ethenesultone, 1,3-propene sultone (PRS), 1,4-butene sultone, and 1-methyl-1; and at least one compound selected from the group consisting of 3-propene sultone, which may be included in an amount of 0.3 wt% to 5 wt%, specifically 1 wt% to 5 wt%, based on the total weight of the non-aqueous electrolyte. When the content of the sultone-based compound in the non-aqueous electrolyte exceeds 5% by weight, an excessively thick film is formed on the electrode surface, which may cause an increase in resistance and deterioration of output. properties may be degraded.

In addition, the lithium salt-based compound is a compound different from the lithium salt included in the non-aqueous electrolyte, and includes lithium methyl sulfate, lithium ethyl sulfate, lithium 2-trifluoromethyl-4,5-dicyanoimidazole (lithium 2-trifluoromethyl- 4,5-dicyanoimidazole), lithium tetrafluorooxalatophosphate, and at least one compound selected from the group consisting of LiODFB and LiBF ₄ , and 3 wt% or less based on the total weight of the non-aqueous electrolyte may include

The SEI film-forming additive may be used in a mixture of two or more, and may be included in an amount of 15 wt% or less, specifically 0.01 wt% to 10 wt%, preferably 0.1 to 5.0 wt%, based on the total amount of the electrolyte.

When the content of the additive for forming the SEI film is less than 0.01% by weight, the high temperature storage characteristics and gas reduction effect to be realized from the additive are insignificant, and when the content of the additive for forming the SEI film exceeds 15% by weight, the battery is charged and discharged There is a possibility that side reactions in the electrolyte solution may occur excessively. In particular, when the additive for forming the SEI layer is added in excess, it may not be sufficiently decomposed and may exist as unreacted or precipitated in the electrolyte at room temperature. Accordingly, resistance may be increased, and thus lifespan characteristics of the secondary battery may be deteriorated.

lithium secondary battery

In addition, an embodiment of the present invention provides a lithium secondary battery comprising the non-aqueous electrolyte for a lithium secondary battery of the present invention.

The lithium secondary battery of the present invention can be manufactured by injecting the non-aqueous electrolyte of the present invention into an electrode assembly in which a positive electrode, a negative electrode, and a separator interposed between the positive and negative electrodes are sequentially stacked. In this case, as the positive electrode, the negative electrode, and the separator constituting the electrode assembly, those commonly used in the manufacture of a lithium secondary battery may be used.

On the other hand, the positive electrode and the negative electrode constituting the lithium secondary battery of the present invention may be manufactured and used in a conventional manner.

(1) Anode

The positive electrode may be manufactured by forming a positive electrode mixture layer on a positive electrode current collector. The positive electrode mixture layer may be formed by coating a positive electrode slurry including a positive electrode active material, a binder, a conductive material, and a solvent on a positive electrode current collector, followed by drying and rolling.

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

The positive active material is a compound capable of reversible intercalation and deintercalation of lithium, and specifically, may include one or more metals such as cobalt, manganese, nickel, or aluminum and lithium metal oxide including lithium. . More specifically, the lithium metal oxide is a lithium-nickel-manganese-cobalt-based oxide (eg, Li(Ni _p Co _q Mn _r1 )O ₂ (here, 0<p<1, 0<q<1, 0<r1<1, p+q+r1=1) or Li(Ni _p1 Co _q1 Mn _r2 )O ₄ (where 0<p1<2, 0<q1<2,0<r2<2, p1+q1+r2=2), etc.), or lithium-nickel-cobalt-transition metal (M) oxide (eg, Li(Ni _p2 Co _q2 Mn _r3 M _S2 ) O ₂ (wherein M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg and Mo, and p2, q2, r3 and s2 are the atomic fractions of each independent element, 0 < p2 <1, 0<q2<1, 0<r3<1, 0<s2<1, p2+q2+r3+s2=1), etc.) may be included.

A typical example of such a cathode active material is Li(Ni _1/3 Mn _1/3 Co _1/3 )O ₂ , Li(Ni _0.35 Mn _0.28 Co _0.37 )O ₂ , Li(Ni _0.6 Mn _0.2 Co _0.2 )O ₂ , Li(Ni _0.5 Mn _0.3 Co _0.2 )O ₂ , Li(Ni _0.7 Mn _0.15 Co _0.15 )O _{2 ,} Li(Ni _0.8 Mn _0.1 Co _0.1 )O ₂ , or Li(Ni _0.8 Co _0.15 Al _0.05 )O ₂ , etc. can

In addition to the lithium-nickel-manganese-cobalt-based oxide, the cathode active material includes a lithium-manganese-based oxide (eg, LiMnO ₂ , LiMn ₂ O ₄ , etc.), a lithium-cobalt-based oxide (eg, LiCoO ₂ , etc.), Lithium-nickel-based oxide (eg, LiNiO ₂ , etc.), lithium-nickel-manganese oxide (eg, LiNi _1-Y Mn _Y O ₂ (where 0<Y<1), LiMn _2-z Ni _z O ₄ (here, 0<Z<2), etc.), lithium-nickel-cobalt-based oxide (for example, LiNi _1-Y1 Co _Y1 O ₂ (here, 0<Y1<1), etc.), or a lithium-manganese-cobalt oxide (eg, LiCo _1-Y2 Mn _Y2 O ₂ (here, 0<Y2<1), LiMn _2-z1 Co _z1 O ₄ (here, 0<Z1<2)) etc.) and the like, and any one or two or more compounds of these may be included.

Such a positive active material may be LiCoO ₂ , LiMnO ₂ , or LiNiO ₂ .

The content of the positive active material may be 90 wt% to 99 wt%, specifically 93 wt% to 98 wt%, based on the total weight of solids in the cathode slurry.

The binder is a component that assists in bonding between the active material and the conductive material and bonding to the current collector, and is typically added in an amount of 1 to 30 wt % based on the total weight of the solid content in the positive electrode slurry. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoro roethylene, polyethylene, polypropylene, ethylene-propylene-diene ter polymer, sulfonated ethylene-propylene-diene ter polymer, styrene-butadiene rubber, fluororubber, various copolymers, and the like.

The conductive material is not particularly limited as long as it has conductivity without causing chemical change in the battery, and for example, carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal black. carbon powder; Graphite powder, such as natural graphite, artificial graphite, or graphite with a highly developed crystal structure; conductive fibers such as carbon fibers and metal fibers; conductive powders such as carbon fluoride, aluminum, and nickel powder; conductive whiskeys such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives may be used.

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

The solvent may include an organic solvent such as N-methyl-2-pyrrolidone (NMP), and may be used in an amount having a desirable viscosity when the positive active material and optionally a binder and a conductive material are included. For example, it may be included so that the solid content concentration in the slurry including the positive electrode active material, and optionally the binder and the conductive material is 10 wt% to 70 wt%, preferably 20 wt% to 60 wt%.

(2) cathode

The negative electrode may be manufactured by forming a negative electrode mixture layer on the negative electrode current collector. The negative electrode mixture layer may be formed by coating a slurry including a negative electrode active material, a binder, a conductive material and a solvent on a negative electrode current collector, drying and rolling.

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

In addition, the negative active material is lithium metal, a carbon material capable of reversibly intercalating/deintercalating lithium ions, a metal or an alloy of these metals and lithium, a metal oxide, a material capable of doping and de-doping lithium , and transition metal oxides may include at least one selected from the group consisting of transition metal oxides.

As a carbon material capable of reversibly intercalating/deintercalating lithium ions, any carbon-based negative active material generally used in lithium ion secondary batteries may be used without particular limitation, and representative examples thereof include crystalline carbon, Amorphous carbon or these may be used together. Examples of the crystalline carbon include graphite such as amorphous, plate-like, flake, spherical or fibrous natural graphite or artificial graphite, and examples of the amorphous carbon include soft carbon (low temperature calcined carbon). or hard carbon, mesophase pitch carbide, and calcined coke.

Examples of the above metals or alloys of these metals and lithium include Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al. And a metal selected from the group consisting of Sn or an alloy of these metals and lithium may be used.

Examples of the metal oxide include PbO, PbO ₂ , Pb ₂ O ₃ , Pb ₃ O ₄ , Sb ₂ O ₃ , Sb ₂ O ₄ , Sb ₂ O ₅ , GeO, GeO ₂ , Bi ₂ O ₃ , Bi ₂ O ₄ , Bi ₂ O ₅ , Li _x Fe ₂ O ₃ (0≤x≤1), Li _x WO ₂ (0≤x≤1), and Sn _x Me _1-x Me' _y O _z (Me: Mn, Fe, Pb, Ge; Me': Al, B, P, Si, elements of Groups 1, 2, and 3 of the periodic table, halogen; 0<x≤1;1≤y≤3; 1≤z≤8) One selected from may be used.

Examples of the material capable of doping and dedoping lithium include Si, SiO _x (0<x≤2), Si-Y alloy (wherein Y is an alkali metal, alkaline earth metal, group 13 element, group 14 element, transition metal, An element selected from the group consisting of rare earth elements and combinations thereof, but not Si), Sn, SnO ₂ , Sn-Y (wherein Y is an alkali metal, an alkaline earth metal, a group 13 element, a group 14 element, a transition metal, a rare earth) It is an element selected from the group consisting of elements and combinations thereof, and is not Sn) and the like. Also, 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, Ti, 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 lithium-containing titanium oxide (LTO), vanadium oxide, and lithium vanadium oxide.

The negative active material may be included in an amount of 80% to 99% by weight based on the total weight of the solid content in the negative electrode slurry.

The binder is a component that assists in bonding between the conductive material, the active material, and the current collector, and is typically added in an amount of 1 to 30% by weight based on the total weight of the solid content in the negative electrode slurry. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoro roethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer, sulfonated-ethylene-propylene-diene ter polymer, styrene-butadiene rubber, fluororubber, and various copolymers thereof.

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

The solvent may include water or an organic solvent such as NMP, alcohol, or the like, and may be used in an amount to achieve a desirable viscosity when the negative electrode active material and, optionally, a binder and a conductive material are included. For example, it may be included so that the solid content concentration in the slurry including the negative electrode active material, and optionally the binder and the conductive material is 50 wt% to 75 wt%, preferably 50 wt% to 65 wt%.

In addition, as the separation membrane, an organic separation membrane or an organic and inorganic composite separation membrane may be used.

The organic separator is a porous polymer film made of polyolefin-based polymers such as ethylene homopolymer, propylene homopolymer, ethylene/butene copolymer, ethylene/hexene copolymer, and ethylene/methacrylate copolymer alone or by laminating them. Alternatively, a conventional porous nonwoven fabric, for example, a high melting point glass fiber, a nonwoven fabric made of polyethylene terephthalate fiber, etc. may be used,

As the organic and inorganic composite separator, an organic/inorganic composite porous SRS (Safety-Reinforcing Separators) separator in which a porous coating layer including inorganic particles and a binder polymer is applied on the porous polyolefin-based separator substrate may be used.

It is preferable to use inorganic particles or a mixture thereof as the non-woven material particles, and representative examples include BaTiO ₃ , BaTiO ₃ , Pb(Zr,Ti)O ₃ (PZT), Pb _1-x La _x Zr _1-y Ti _y O ₃ (PLZT, where 0<x<1, 0<y<1), hafnia (HfO ₂ ), SrTiO ₃ , SnO ₂ , CeO ₂ , MgO, NiO, CaO, and a single substance selected from the group consisting of ZnO, ZrO ₂ , Y ₂ O ₃ , Al ₂ O ₃ , TiO ₂ , SiC, and mixtures thereof or a mixture of two or more thereof.

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 prismatic shape, a pouch type, or a coin type.

Hereinafter, examples will be given to describe the present invention in detail. However, the embodiments according to the present invention may be modified in various other forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. The embodiments of the present invention are provided to more completely explain the present invention to those of ordinary skill in the art.

Example

Example 1.

(Manufacture of non-aqueous electrolyte)

Ethylene carbonate (EC): ethyl methyl carbonate (EMC) was mixed in a volume ratio of 30:70, and LiPF ₆ was dissolved to a concentration of 1.0M to prepare a non-aqueous organic solvent. To 99.98 g of the non-aqueous organic solvent, 0.01 g of the compound represented by Formula 1a and 0.01 g of the compound represented by Formula 2a (weight ratio of the first additive: the second additive = 1:1) were added to prepare the non-aqueous electrolyte of the present invention prepared (see Table 1 below).

(electrode manufacturing)

The positive active material (Li(Ni _0.6 Mn _0.2 Co _0.2 )O ₂ ), the conductive material (carbon black), and the binder (polyvinylidene fluoride) are mixed with N-methyl-2-pyrroly as a solvent in a weight ratio of 90:5:5. It was added to Don (NMP) to prepare a positive electrode active material slurry (solid content concentration of 50% by weight). The positive electrode active material slurry was applied to a positive electrode current collector (Al thin film) having a thickness of 100 μm, dried, and roll press was performed to prepare a positive electrode.

A negative active material (artificial graphite), binder (PVDF), and conductive material (carbon black) were added to NMP as a solvent in a 95:2:3 weight ratio to prepare a negative active material slurry (solids concentration of 60% by weight). The negative electrode active material slurry was applied to a negative electrode current collector (Cu thin film) having a thickness of 90 μm, dried and rolled to prepare a negative electrode.

(Secondary battery manufacturing)

The positive electrode and the negative electrode prepared by the above method were sequentially laminated together with a polyethylene porous film to prepare an electrode assembly, then put it in a battery case, inject the non-aqueous electrolyte, and seal the lithium secondary battery (battery capacity 340 mAh) prepared.

Example 2.

Example 1, except that 0.1 g of the compound represented by Formula 1a and 0.1 g of the compound represented by Formula 2a (weight ratio of the first additive to the second additive=1:1) were added to 99.8 g of the non-aqueous organic solvent A non-aqueous electrolyte of the present invention and a secondary battery including the same were prepared in the same manner as in the above (see Table 1 below).

Example 3.

The same as in Example 1, except that 3.0 g of the compound represented by Formula 1a and 3.0 g of the compound represented by Formula 2a (weight ratio of the first additive: the second additive = 1:1) were added to 94 g of the non-aqueous organic solvent In the same manner, the non-aqueous electrolyte of the present invention and a secondary battery including the same were prepared (see Table 1 below).

Example 4.

Example 1, except that 0.5 g of the compound represented by Formula 1a and 0.005 g of the compound represented by Formula 2a (weight ratio of the first additive: the second additive = 1:0.01) were added to 99.495 g of the non-aqueous organic solvent A non-aqueous electrolyte of the present invention and a secondary battery including the same were prepared in the same manner as in the above (see Table 1 below).

Example 5.

Example 1 above except that 0.5 g of the compound represented by Formula 1a and 0.05 g of the compound represented by Formula 2a (weight ratio of the first additive: the second additive = 1:0.1) were added to 99.45 g of the non-aqueous organic solvent A non-aqueous electrolyte of the present invention and a secondary battery including the same were prepared in the same manner as in the above (see Table 1 below).

Example 6.

Except for adding 0.5 g of the compound represented by Formula 1a and 0.5 g of the compound represented by Formula 2a (weight ratio of the first additive to the second additive = 1:1) to 99 g of the non-aqueous organic solvent, the same as in Example 1 In the same manner, the non-aqueous electrolyte of the present invention and a secondary battery including the same were prepared (see Table 1 below).

Example 7.

Example 1, except that 1.0 g of the compound represented by Formula 1a and 0.5 g of the compound represented by Formula 2a (weight ratio of the first additive: the second additive = 1:0.5) were added to 98.5 g of the non-aqueous organic solvent A non-aqueous electrolyte of the present invention and a secondary battery including the same were prepared in the same manner as in the above (see Table 1 below).

Example 8.

Example 1, except that 5.0 g of the compound represented by Formula 1a and 0.5 g of the compound represented by Formula 2a (weight ratio of the first additive: the second additive = 1:0.1) were added to 94.5 g of the non-aqueous organic solvent A non-aqueous electrolyte of the present invention and a secondary battery including the same were prepared in the same manner as in the above (see Table 1 below).

Example 9.

Example 1, except that 5.0 g of the compound represented by Formula 1a and 0.25 g of the compound represented by Formula 2a (weight ratio of the first additive to the second additive = 1:0.05) were added to 94.75 g of the non-aqueous organic solvent A non-aqueous electrolyte of the present invention and a secondary battery including the same were prepared in the same manner as in the above (see Table 1 below).

Example 10.

The same as in Example 1, except that 5.0 g of the compound represented by Formula 1a and 5.0 g of the compound represented by Formula 2a (weight ratio of the first additive: the second additive = 1:1) were added to 90 g of the non-aqueous organic solvent In the same manner, the non-aqueous electrolyte of the present invention and a secondary battery including the same were prepared (see Table 1 below).

Example 11.

The same as in Example 1, except that 6.0 g of the compound represented by Formula 1a and 3.0 g of the compound represented by Formula 2a (weight ratio of the first additive: the second additive = 1:0.5) were added to 91 g of the non-aqueous organic solvent In the same manner, the non-aqueous electrolyte of the present invention and a secondary battery including the same were prepared (see Table 1 below).

Example 12.

Example 1, except that 0.1 g of the compound represented by Formula 1a and 1.1 g of the compound represented by Formula 2a (weight ratio of the first additive to the second additive = 1:11) were added to 98.8 g of the non-aqueous organic solvent A non-aqueous electrolyte of the present invention and a secondary battery including the same were prepared in the same manner as in the above (see Table 1 below).

Example 13.

Example 1, except that 5.0 g of the compound represented by Formula 1a and 0.04 g of the compound represented by Formula 2a (weight ratio of the first additive to the second additive = 1:0.008) were added to 94.96 g of the non-aqueous organic solvent A non-aqueous electrolyte of the present invention and a secondary battery including the same were prepared in the same manner as in the above (see Table 1 below).

Comparative Example 1.

A non-aqueous electrolyte and a secondary battery including the same were prepared in the same manner as in Example 1, except that 2.0 g of vinylene carbonate was added as an additive to 98 g of the non-aqueous organic solvent (see Table 1 below).

Comparative Example 2.

A non-aqueous electrolyte solution and a secondary battery including the same were prepared in the same manner as in Example 1, except that 3.0 g of the compound of Formula 1a was added without the second additive to 97 g of the non-aqueous organic solvent (Table below) see 1).

Comparative Example 3.

A non-aqueous electrolyte and a secondary battery including the same were prepared in the same manner as in Example 1, except that the first additive was not included in 95 g of the non-aqueous organic solvent and 5.0 g of the compound represented by Formula 2a was included ( See Table 1 below).

Comparative Example 4.

In the same manner as in Example 1, except that 5.0 g of the compound represented by Formula 1a and 2.0 g of vinylene carbonate were added to 93 g of the non-aqueous organic solvent without the second additive, the non-aqueous electrolyte solution and the non-aqueous electrolyte containing the same A secondary battery was prepared (see Table 1 below).

Comparative Example 5.

In the same manner as in Example 1, except that 5.0 g of the compound represented by Formula 2a and 2.0 g of vinylene carbonate were added to 93 g of the non-aqueous organic solvent without the first additive, the non-aqueous electrolyte solution and its containing A secondary battery was prepared (see Table 1 below).

Experimental example

Experimental Example 1. Initial dose evaluation

The lithium secondary batteries prepared in Examples 1 to 13 and the lithium secondary batteries prepared in Comparative Examples 3 and 5 were respectively subjected to 0.33C/4.25V constant current/constant voltage (CC/CV) 4.25V/0.05C conditions at 25°C. It was charged and discharged at a constant current of 0.33C/3.0V. At this time, the discharge capacity measured using a PNE-0506 charger/discharger (manufacturer: PNE Solution, 5V, 6A) after cell assembly and before high-temperature storage was defined as the initial discharge capacity. The measured initial doses are listed in Table 1 below.

Referring to Table 1, it can be seen that the initial capacity of the lithium secondary batteries of Examples 1 to 9 and Examples 11 to 13 having the nonaqueous electrolyte containing the mixed additive is about 1.048 mAh/g or more.

On the other hand, the initial capacity of the lithium secondary batteries of Comparative Examples 3 and 5 having the non-aqueous electrolyte solution not including the first additive and the second additive together was 1.047 mAh/g or less in Examples 1 to 9 and Examples It can be seen that the lithium secondary battery of Examples 11 to 13 was lower than that of the lithium secondary battery.

On the other hand, compared with the lithium secondary battery of Comparative Example 3, the lithium secondary battery of Example 10 having a non-aqueous electrolyte containing a large amount of additives compared to the lithium secondary battery of Comparative Example 3 formed a thick film at the initial stage of charging and discharging. Thus, it can be seen that a relatively low initial capacity is obtained.

Experimental Example 2. Evaluation of resistance increase rate after high temperature storage

Each of the lithium secondary batteries prepared in Examples 1 to 13 and Comparative Examples 1 to 5 was charged and discharged at 25° C. under the conditions of 0.33C/4.25V constant current-constant voltage 4.25V/0.05C and 0.33C to achieve SOC 50 After adjusting the state of charge of the battery by %, the voltage drop that appears when a discharge pulse is applied at 2.5C constant current for 30 seconds is measured using a PNE-0506 charger/discharger (manufacturer: PNE Solution, 5V, 6A). Thus, the initial resistance value was obtained. Thereafter, the battery was charged by SOC 100% by charging under the condition of 0.33C/4.25V constant current-constant voltage 4.25V/0.05C in the 3.0V to 4.25V voltage driving range.

Then, each secondary battery was left at 60° C. for 4 weeks.

Then, using a PNE-0506 charger/discharger (manufacturer: PNE Solution, 5V, 6A), charge at 0.33C/4.25V constant current-constant voltage 4.25V/0.05C conditions and discharge the battery by SOC 50% by 0.33C discharge. After adjusting the state of charge, the voltage drop that appeared when a discharge pulse was applied for 30 seconds at a constant current of 2.5C was measured to obtain a resistance value after storage at a high temperature.

Using Equation (1) below, the resistance increase rate (%) for each secondary battery was calculated from the ratio of the initial resistance to the increased resistance after high-temperature storage, and it is shown in Table 2 below.

Equation (1): resistance increase rate (%) = {(resistance after high temperature storage-initial resistance)/initial resistance}×100

Referring to Table 2 below, the lithium secondary batteries of Examples 1 to 13 having the nonaqueous electrolyte containing the mixed additive exhibited a resistance increase rate of 17.7% or less after high-temperature storage, whereas the first and second additives were not included. It can be seen that the resistance increase rate of the lithium secondary batteries of Comparative Examples 1 to 5 having a non-aqueous electrolyte without a non-aqueous electrolyte after high-temperature storage was mostly 18.0% or more, which was increased compared to the lithium secondary batteries of Examples 1 to 13.

Experimental Example 3. Evaluation of battery thickness increase rate after high-temperature storage

Each of the lithium secondary batteries prepared in Examples 1 to 13, Comparative Example 1 and Comparative Examples 3 to 5 was 0.33C/4.25V constant current-constant voltage 4.25V in a voltage driving range of 3.0V to 4.25V at 25°C. The thickness of each secondary battery was measured with a plate thickness measuring device (Mitsutoyo, Japan) at 100% SOC after fully charged under the /0.05C condition. The thickness measured first after cell assembly was defined as the initial thickness.

Then, the initially charged and discharged lithium secondary batteries were each charged to SOC 100% at 4.25V, and stored at 60° C. for 4 weeks.

Then, after cooling each lithium secondary battery at room temperature, the thickness after high-temperature storage is measured using a plate thickness measuring instrument (Mitsutoyo (日)), and the measured initial thickness and the thickness after high-temperature storage are substituted into the following equation (2) to calculate the thickness increase rate, and the results are shown in Table 2 below.

Equation (2): Thickness increase rate (%) = {(thickness after high temperature storage/initial thickness)×100}-100

Referring to Table 2 below, the lithium secondary batteries of Examples 1 to 13 having the non-aqueous electrolyte containing the mixed additive had a thickness increase rate of 5.0% or less after storage at a high temperature, whereas the first additive and the second additive were included together. It can be seen that the thickness increase rate of the lithium secondary batteries of Comparative Example 1 and Comparative Examples 3 to 5 having a non-aqueous electrolyte that is not used was 5.6% or more after high temperature storage, which was increased compared to the lithium secondary batteries of Examples 1 to 13. have.

Experimental Example 4. Capacity retention rate evaluation after high temperature storage

The lithium secondary batteries prepared in Examples 1 to 13 and the lithium secondary batteries prepared in Comparative Examples 1 to 5 were respectively subjected to 0.33C/4.25V constant current/constant voltage (CC/CV) 4.25V/0.05C conditions at 25°C. It was charged and discharged at a constant current of 0.33C/3.0V. At this time, the discharge capacity measured using a PNE-0506 charger/discharger (manufacturer: PNE Solution, 5V, 6A) after cell assembly and before high-temperature storage was defined as the initial discharge capacity.

Then, each secondary battery was set to SOC 100% charged state and stored at 60° C. for 4 weeks.

Then, at 25℃, charge at 0.33C/4.25V constant current/constant voltage (CC/CV) 4.25V/0.05C condition, discharge at 0.33C/3.0V constant current, and PNE-0506 charger/discharger (manufacturer: PNE Co., Ltd.) solution, 5V, 6A) was used to measure the discharge capacity. At this time, the measured capacity was defined as the discharge capacity after high-temperature storage.

Capacity retention was measured by substituting the measured initial discharge capacity and the discharge capacity after high-temperature storage into Equation (3) below, and the results are shown in Table 2 below.

Equation (3): Capacity retention rate (%) = (discharge capacity after high-temperature storage/initial discharge capacity) × 100

Referring to Table 2 below, the lithium secondary batteries of Examples 1 to 13 having the non-aqueous electrolyte containing the mixed additive had a capacity retention rate of 90.1% or more after high-temperature storage, whereas both the first additive and the second additive were included. It can be seen that the capacity retention rate of the lithium secondary batteries of Comparative Examples 1 to 5, which is not used, after high-temperature storage is 89.9% or less, which is inferior compared to the lithium secondary batteries of Examples 1 to 13.

On the other hand, Examples 12 and 13 were provided with the secondary battery of Example 11 having the non-aqueous electrolyte containing an excessive amount of the first additive, and the non-aqueous electrolyte containing the second additive in a relatively excessive or small amount compared to the first additive. In the case of the lithium secondary battery of , it can be seen that the capacity retention rate after high temperature storage is relatively inferior to that of the lithium secondary batteries of Examples 1 to 10.

Claims (10)

lithium salt; organic solvents; a first additive and a second additive;
The first additive is a compound represented by the following formula 1a,
The second additive is at least one selected from the group consisting of compounds represented by the following formulas 2a and 2b,
The weight ratio of the first additive and the second additive is 1:0.01 to 1:10 for a lithium secondary battery non-aqueous electrolyte:
[Formula 1a]

[Formula 2a]

[Formula 2b]

delete delete delete The method according to claim 1,
The content of the compound represented by Formula 1 is 0.01 wt% to 5 wt% based on the total weight of the non-aqueous electrolyte solution for a lithium secondary battery.
delete delete delete The method according to claim 1,
The non-aqueous electrolyte for a lithium secondary battery is at least one SEI selected from the group consisting of halogen-substituted or unsubstituted cyclic carbonate-based compounds, nitrile-based compounds, phosphate-based compounds, borate-based compounds, sulfate-based compounds, sultone-based compounds, and lithium salt-based compounds A non-aqueous electrolyte for a lithium secondary battery that further comprises an additive for forming a film.
A lithium secondary battery comprising the non-aqueous electrolyte for a lithium secondary battery of claim 1.