KR20220052082A - Electrolyte for lithium secondary battery, and lithium secondary battery comprising the same - Google Patents

Abstract

The present invention provides a non-aqueous electrolyte for a lithium secondary battery with improved durability at high temperature, and a lithium secondary battery comprising the same. The non-aqueous electrolyte for a lithium secondary battery comprises a lithium salt; organic solvent; and a first additive. The first additive includes compound represented by following chemical formula 1. In the chemical formula 1: R_1 and R_2 is independently selected from the group consisting of hydrogen, an alkyl group of substituted or unsubstituted carbon numbers 1 to 4, and a ring type alkyl group of substituted or unsubstituted carbon numbers 3 to 8; and R_3 is selected from the group consisting of an alkyl group of substituted or unsubstituted carbon numbers 1 to 4, and a ring type alkyl group of substituted or unsubstituted carbon numbers 3 to 8.

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, and more particularly, to a non-aqueous electrolyte for a secondary battery capable of improving the high temperature durability of the battery and a secondary battery including 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, and 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.

In the case of a lithium secondary battery system, unlike the early days when lithium metal was directly applied to the system, a transition metal oxide material containing lithium is used as a cathode material, and a carbon-based material such as graphite and an alloy-based material such as silicon are used as an anode material. It is implemented as a system in which lithium metal is not directly used inside the battery, such as applying a material as an anode.

In the case of such a lithium secondary battery, it is largely composed of a positive electrode composed of a transition metal oxide containing lithium, a negative electrode capable of storing lithium, an electrolyte as a medium for transferring lithium ions, and a separator. As it is known as a component that has a great influence on stability and safety, many studies are being conducted on it.

In the case of an electrolyte for a lithium secondary battery, it is composed of a lithium salt, an organic solvent dissolving it, and a functional additive. In order to improve the electrochemical properties of the battery, it is important to properly select these components.

In this case, the electrolyte solution for a lithium ion battery is composed of a lithium salt, an organic solvent dissolving the same, and a functional additive, and proper selection of these components is important in order to improve the electrochemical properties of the battery.

In the case of such a lithium ion battery, an increase in resistance and a decrease in capacity during charging/discharging or storage at a high temperature are suggested as problems causing performance degradation. In addition, when the side reactions caused by the deterioration of the electrolyte at high temperatures, especially the byproducts generated from the decomposition of salts at high temperatures, decompose the coatings formed on the surfaces of the positive and negative electrodes after activation, the passivation ability of the coating is lowered. There is a problem of causing further decomposition of the electrolyte and self-discharge accompanying it.

In particular, LiPF ₆ is mainly used as the lithium salt in the non-aqueous electrolyte, but the PF ₆ ^- anion is vulnerable to heat, and when the battery is exposed to high temperatures, Lewis acid such as PF ₅ is generated due to thermal decomposition, Such PF ₅ not only causes the decomposition of the carbonate-based organic solvent itself, but also generates HF to accelerate the transition metal elution of the positive electrode active material. The eluted transition metal is deposited on the positive electrode and causes an increase in the resistance of the positive electrode, or is deposited on the negative electrode, causing self-discharge of the negative electrode, destruction of the SEI film, and consumption of additional lithium ions through the regeneration phase.

Accordingly, in order to secure and maintain the passivation ability of the SEI film even during high-temperature storage, it is necessary to develop an electrolyte additive that can easily undergo reductive decomposition.

Korean Patent Publication No. 10-2014-050058

The present invention has been devised to solve the above problems, and an object of the present invention is to provide a non-aqueous electrolyte for a lithium secondary battery with improved durability at high temperature and a lithium secondary battery including the same.

The non-aqueous electrolyte for a lithium secondary battery according to the present invention includes a lithium salt; organic solvents; and a first additive, wherein the first additive includes a compound represented by the following formula (1).

[Formula 1]

(In Formula 1, R ₁ and R ₂ are each independently selected from the group consisting of hydrogen, a substituted or unsubstituted alkyl group having 1 to 4 carbon atoms, and a substituted or unsubstituted cyclic alkyl group having 3 to 8 carbon atoms, R ₃ is selected from the group consisting of a substituted or unsubstituted alkyl group having 1 to 4 carbon atoms, and a substituted or unsubstituted cyclic alkyl group having 3 to 8 carbon atoms.)

In a specific example, in Formula 1, R ₁ to R ₃ may each independently be a substituted or unsubstituted C 1 to C 4 alkyl group.

In this case, the first additive may be ethyl 2-cyano-2-methylpropionate represented by the following Chemical Formula 1a.

[Formula 1a]

In a specific example, the first additive may be included in an amount of 0.5 to 10% by weight based on the total weight of the electrolyte.

In a specific example, the first additive may be included in an amount of 1 to 7% by weight based on the total weight of the electrolyte.

In addition, the non-aqueous electrolyte for a lithium secondary battery according to the present invention is a halogen-substituted or unsubstituted cyclic carbonate-based compound, a nitrile-based compound, a phosphate-based compound, a borate-based compound, a sultone-based compound, a lithium salt-based compound, a sulfate-based compound from the group consisting of At least one selected second additive may be further included.

In a specific example, the second additive is one selected from the group consisting of vinyl ethylene carbonate, fluoroethylene carbonate, 1,3-propane sultone and lithium oxalyl difluoroborate (ODFB), or Combinations of two or more are included.

In a specific example, the lithium salt is LiPF ₆ , LiAsF ₆ , LiCF ₃ SO ₃ , LiN(CF ₃ SO ₂ ) ₂ , LiBF ₆ , LiSbF ₆ , LiN(C ₂ F ₅ SO ₂ ) ₂ , LiAlO ₄ , LiAlCl ₄ , LiSO ₃ CF ₃ And LiClO ₄ It may be at least one selected from the group consisting of.

In a specific example, the organic solvent may include a linear carbonate, a cyclic carbonate, an ester, an ether, a ketone, or a combination thereof.

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

The additive included in the non-aqueous electrolyte of the present invention not only forms a stable SEI film on the surface of the anode by adding a nitrile-based additive as shown in Formula 1, but also effectively inhibits materials such as HF/PF ₅ formed as a decomposition product of lithium salt, It is possible to manufacture a lithium secondary battery with increased durability.

Hereinafter, the present invention will be described in detail. Prior to this, the terms or words used in the present specification and claims should not be construed as being limited to conventional or dictionary meanings, and the inventor should properly understand the concept of the term in order to best describe his invention. It should be interpreted as meaning and concept consistent with the technical idea of the present invention based on the principle that it can be defined in

In the present application, terms such as "comprise" or "have" are intended to designate that a feature, number, step, operation, component, part, or a combination thereof described in the specification exists, but one or more other features It is to be understood that it does not preclude the possibility of the presence or addition of numbers, steps, operations, components, parts, or combinations thereof. Also, when a part of a layer, film, region, plate, etc. is said to be “on” another part, it includes not only the case where the other part is “directly on” but also the case where there is another part in between. Conversely, when a part of a layer, film, region, plate, etc. is said to be “under” another part, it includes not only cases where it is “directly under” another part, but also cases where another part is in between. In addition, in the present application, “on” may include the case of being disposed not only on the upper part but also on the lower part.

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, the "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.

Hereinafter, the present invention will be described in detail.

Non-aqueous electrolyte for lithium secondary battery

The non-aqueous electrolyte for a lithium secondary battery according to the present invention includes a lithium salt; organic solvents; and a first additive, wherein the first additive includes a compound represented by the following formula (1).

[Formula 1]

(In Formula 1, R ₁ and R ₂ are each independently selected from the group consisting of hydrogen, a substituted or unsubstituted alkyl group having 1 to 4 carbon atoms, and a substituted or unsubstituted cyclic alkyl group having 3 to 8 carbon atoms, R ₃ is selected from the group consisting of a substituted or unsubstituted alkyl group having 1 to 4 carbon atoms, and a substituted or unsubstituted cyclic alkyl group having 3 to 8 carbon atoms.)

(1) lithium salt

In the non-aqueous electrolyte for a lithium secondary battery according to an embodiment of the present invention, the lithium salt includes LiPF ₆ , and in addition to LiPF ₆ , those commonly used in the electrolyte for a lithium secondary battery may be used without limitation. For example, the lithium salt includes Li ⁺ as a cation, and F ^- , Cl ^- , Br ^- , I ^- , NO ₃ ^- , N(CN) ₂ ^- , ClO ₄ ^- , BF ₄ ^- , B ₁₀ as an anion. 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 consisting of.

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 types selected from the group consisting of. More specifically, the lithium salt is LiPF ₆ , LiAsF ₆ , LiCF ₃ SO ₃ , LiN(CF ₃ SO ₂ ) ₂ , LiBF ₆ , LiSbF ₆ , LiN(C ₂ F ₅ SO ₂ ) ₂ , LiAlO ₄ , LiAlCl ₄ , LiSO ₃ CF ₃ and LiClO ₄ It may be at least one selected from the group consisting of.

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 during the charging and discharging process of the secondary battery and exhibit desired properties together with the additive. for example, linear carbonates, cyclic carbonates, esters, ethers, ketones, or combinations thereof.

Specifically, the cyclic carbonate-based organic solvent is 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. It may include 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 is 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; A mixture of two or more of them may be typically used, but is not limited thereto.

The cyclic ester-based organic solvent is, for 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.

As the organic solvent, a high-viscosity cyclic carbonate-based organic solvent capable of dissociating lithium salts in the electrolyte with high dielectric constant may be used. 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 according to the present invention may include a compound represented by Formula 1 as a first additive.

[Formula 1]

(In Formula 1, R ₁ and R ₂ are each independently selected from the group consisting of hydrogen, a substituted or unsubstituted alkyl group having 1 to 4 carbon atoms, and a substituted or unsubstituted cyclic alkyl group having 3 to 8 carbon atoms, R ₃ is selected from the group consisting of a substituted or unsubstituted alkyl group having 1 to 4 carbon atoms, and a substituted or unsubstituted cyclic alkyl group having 3 to 8 carbon atoms.)

Specifically, in Formula 1, R ₁ to R ₃ may each independently be a substituted or unsubstituted alkyl group having 1 to 4 carbon atoms.

Non-limiting examples of such compounds include ethyl 2-cyano-2-methylpropionate, methyl 2-cyano-2-methylpropionate, propyl 2-cyano-2-methylpropionate, butyl 2- Cyano-2-methylpropionate, ethyl 2-cyano-2-methylbutanoate, methyl 2-cyano-2-methylbutanoate, propyl 2-cyano-2-methylbutanoate, butyl 2-cyano-2-methylbutanoate, ethyl 2-cyano-2-methylpentanoate, methyl 2-cyano-2-methylpentanoate, propyl 2-cyano-2-methylpentanoate ,Butyl 2-cyano-2-methylpentanoate, ethyl 2-cyano-2-ethylbutanoate, methyl 2-cyano-2-ethylbutanoate, propyl 2-cyano-2-ethylbuta Noate, Butyl 2-cyano-2-ethylbutanoate, ethyl 2-cyano-2-ethylpentanoate, methyl 2-cyano-2-ethylpentanoate, propyl 2-cyano-2- Ethylpentanoate, Butyl 2-cyano-2-ethylpentanoate, methyl 2-cyanoacetate, methyl 3-cyanopropionate, ethyl 3-cyanopropionate, propyl 3-cyanopropio Nate and others.

More specifically, the compound represented by Formula 1 may be ethyl 2-cyano-2-methylpropionate (ECMP) represented by Formula 1a below.

[Formula 1a]

Since the compound represented by Formula 1 contains a functional group functioning as a Lewis base including a nitrogen element in its structure, decomposition of anions such as PF ₆ ^- of lithium salts cannot be suppressed, but produced by decomposition of anions Lewis acids such as HF and PF ₅ , which are decomposition products, can be removed from the inside of the electrolyte, and thus deterioration behavior due to chemical reaction of the anode or cathode surface coating resulting from these Lewis acids can be suppressed. In particular, the compound of Formula 1 can effectively remove a Lewis acid, a decomposition product of a lithium salt, by a nitrile functional group (cyanide group, cyanide group). As a result, since deterioration of the film resulting from Lewis acid can be suppressed and further decomposition of the electrolyte solution of the battery due to the destruction of the film can be prevented, ultimately, self-discharge of the battery can be suppressed, so that the high temperature durability of the battery can be improved. .

In addition, the nitrogen atom of the nitrile functional group is directly bonded to the anode, so that it is possible to suppress the metal on the surface of the anode from directly oxidizing the organic solvent in the electrolyte. Since the oxidation reaction of the electrolyte is further accelerated in a high-temperature state of charge, this action of the nitrile functional group may show the greatest effect when the state of charge is maintained at a high temperature.

In addition, functional groups included in the structure of the compound represented by Chemical Formula 1 are easily reduced on the surface of the anode, and thus a stable SEI film having high passivation ability may be formed on the surface of the anode. Accordingly, the high temperature durability of the anode itself can be improved, and self-discharge caused by the additional reaction of the electrolyte due to the instability of the SEI film can be prevented.

On the other hand, the first additive may be included in 0.5 to 10% by weight based on the total weight of the electrolyte, or 0.5 to 7.5% by weight, or 3 to 7.5% by weight, or 3 to 5% by weight, or 5 to 7.5% by weight. may be included. When the content of the first additive is within the above range, the effect of removing by-products or inhibiting metal elution is excellent, so that the high temperature durability of the battery can be improved.

When the content of the first additive is less than the above range, it is insufficient to achieve the desired effect. Since it cannot be decomposed, it may exist as unreacted or precipitated in the electrolyte at room temperature, and thus the lifespan or resistance characteristics of the secondary battery may be reduced.

(4) second additive

In addition, the nonaqueous electrolyte for a lithium secondary battery according to the present invention is used together with the mixed additive to form a stable film on the surface of the negative electrode and the positive electrode without significantly increasing the initial resistance along with the effect expressed by the mixed additive, or A second additive capable of suppressing decomposition due to a side reaction of the solvent in the electrolyte and improving the mobility of lithium ions may be further included.

Specifically, the non-aqueous electrolyte for a lithium secondary battery according to the present invention is composed of a halogen-substituted or unsubstituted cyclic carbonate-based compound, a nitrile-based compound, a phosphate-based compound, a borate-based compound, a sultone-based compound, a lithium salt-based compound, and a sulfate-based compound It may further include at least one or more additives selected from the group.

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.

Examples of the halogen-substituted cyclic carbonate-based compound include fluoroethylene carbonate (FEC). In addition, the unsubstituted cyclic carbonate-based compound may include vinylene carbonate (VC) and vinyl ethylene carbonate (VEC).

The halogen-substituted or unsubstituted cyclic carbonate-based compound may be included in an amount of 8 wt% or less, specifically 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 8% 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 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, specifically 5 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 and the like 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 (2,2) , and at least one compound selected from the group consisting of ,2-trifluoroethyl) phosphate (TFEPa) and tris (trifluoroethyl) phosphite, 3% by weight or less based on the total weight of the non-aqueous electrolyte, specifically may be included in an amount of 1% by weight or less.

The borate compound promotes ion pair separation of lithium salts, can improve lithium ion mobility, 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, specifically 1% by weight or less.

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, at least one compound selected from the group consisting of LiODFB and LiBF4, and 3% by weight or less based on the total weight of the non-aqueous electrolyte, detailed For example, it may be included in an amount of 1 wt% or less.

In addition, the sulfate-based compound may include ethylene sulfate, trimethylene sulfate (TMS), or methyl trimethylene sulfate (MTMS), and 3 weights based on the total weight of the non-aqueous electrolyte % or less, specifically 1% by weight or less.

More specifically, the second additive is one selected from the group consisting of vinyl ethylene carbonate, fluoroethylene carbonate, 1,3-propane sultone and lithium oxalyldifluoroborate (ODFB), or a combination of two or more. may include

In this way, two or more additives that may be additionally added may be mixed and used, and may be included in an amount of 20% by weight or less, specifically 0.01% to 15% by weight, preferably 0.1 to 10% by weight based on the total amount of the electrolyte. .

When the content of the additive that can be additionally added 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 it exceeds 20% by weight, side reactions in the electrolyte during charging and discharging of the battery may excessively occur. There is a possibility. In particular, if an additive is added in excess, it may not be sufficiently decomposed and may exist as unreacted or precipitated in the electrolyte at room temperature. Accordingly, the resistance may increase and the 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 includes a positive electrode; cathode; It includes a separator and a non-aqueous electrolyte for a lithium secondary battery as described above. Specifically, the lithium secondary battery 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 lithium secondary batteries 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 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, etc. may be used.

The positive active material is a compound capable of reversible intercalation and deintercalation of lithium, and specifically, may include lithium metal oxide including lithium and one or more metals such as cobalt, manganese, nickel, or aluminum. . 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 , and the like. there is.

The content of the positive active material may be included in an amount of 90 wt% to 99 wt%, specifically 93 wt% to 98 wt%, based on the total weight of the solid content 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% by weight 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 a 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%.

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 an anode 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. A surface treated with carbon, nickel, titanium, silver, etc., an aluminum-cadmium alloy, etc. may be used on the surface. 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 dedoping 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 with 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.

Materials capable of doping and dedoping lithium include Si, SiOx (0<x≤2), Si-Y alloy (wherein Y is an alkali metal, alkaline earth metal, group 13 element, group 14 element, transition metal, rare earth) an element selected from the group consisting of elements and combinations thereof, and not Si), Sn, SnO ₂ , Sn-Y (wherein Y is an alkali metal, alkaline earth metal, group 13 element, group 14 element, transition metal, rare earth element) and an element selected from the group consisting of combinations thereof, not Sn), and the like, and also at least one of them 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 solids 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 and roethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer, sulfonated-ethylene-propylene-diene terpolymer, 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, and the like, and may be used in an amount to have 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 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 nonwoven fabric made of high melting point glass fiber, polyethylene terephthalate fiber, or the like 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, a prismatic shape, a pouch type, or a coin type using a can.

Hereinafter, examples will be given to help the understanding of the present invention be described 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 following examples. The embodiments of the present invention are provided to more completely explain the present invention to those of ordinary skill in the art.

Example 1

<Production of non-aqueous electrolyte>

Ethylene carbonate (EC), propylene carbonate (PC), ethyl propionate (EP) and propyl propionate (PP) were mixed in a volume ratio of 20:10:25:45 to prepare a non-aqueous organic solvent, and LiPF ₆ was dissolved to a concentration of 1.2M. Here, as a first additive, ethyl 2-cyano2-methylpropionate was added so as to be 3.0% by weight based on the total weight of the electrolyte.

In addition to the first additive, as a second additive, vinyl ethylene carbonate (VEC), 1,3-propane sultone (PS), fluoroethylene carbonate (FEC), and lithium oxalyl difluoroborate (ODFB) were added to the total weight of the electrolyte, respectively. 0.2% by weight, 4% by weight, 7% by weight, and 0.5% by weight were added to prepare a non-aqueous electrolyte.

<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 10 μm, dried and rolled to prepare a positive electrode.

A negative active material (artificial graphite), a binder (PVDF), and a conductive material (carbon black) were added to NMP as a solvent in a 95:2:3 weight ratio to prepare a negative electrode 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 8 μm, dried and rolled to prepare a negative electrode.

<Secondary battery manufacturing>

The positive electrode and the negative electrode prepared by the above-described method were sequentially laminated together with a polyethylene porous film to prepare an electrode assembly, which was then placed in a battery case, the non-aqueous electrolyte was injected, and sealed to prepare a lithium secondary battery.

Example 2

A non-aqueous electrolyte and a secondary battery were prepared in the same manner as in Example 1, except that ethyl 2-cyano 2-methylpropionate as the first additive was added in an amount of 5.0% by weight based on the total weight of the electrolyte.

Example 3

A non-aqueous electrolyte and a secondary battery were prepared in the same manner as in Example 1, except that ethyl 2-cyano2-methylpropionate as the first additive was added so as to be 7.0 wt% based on the total weight of the electrolyte.

Example 4

A non-aqueous electrolyte and a secondary battery were prepared in the same manner as in Example 1, except that ethyl 2-cyano 2-methylpropionate as the first additive was added so as to be 10.0 wt % based on the total weight of the electrolyte.

Comparative Example 1

A non-aqueous electrolyte and a secondary battery were prepared in the same manner as in Example 1 except that the first additive was not added.

Comparative Example 2

A non-aqueous electrolyte and a secondary battery were prepared in the same manner as in Example 1, except that ethyl 2-cyano2-methylpropionate as the first additive was added so as to be 0.1% by weight based on the total weight of the electrolyte.

Comparative Example 3

A non-aqueous electrolyte and a secondary battery were prepared in the same manner as in Example 1, except that ethyl 2-cyano 2-methylpropionate as the first additive was added so as to be 13% by weight based on the total weight of the electrolyte.

Experimental Example 1

<Evaluation of thickness increase rate after storage at 85℃>

The lithium secondary batteries prepared in Examples and Comparative Examples were fully charged (SOC 100%) at 25° C. under 0.33C/4.25V constant current/constant voltage (CC/CV) 4.25V/0.05C conditions. Then, the thickness (initial thickness) of the secondary battery was measured using a plate thickness measuring device (manufacturer: Mitsutoyo).

Thereafter, the secondary battery was stored at 85° C. for 8 hours, and the thickness (final thickness) of the secondary battery was measured. The thickness increase rate was calculated according to the following formula (1) from the measured values, and the results are shown in Table 1.

Equation (1): Thickness increase rate (%) = {(final thickness-initial thickness)/ initial thickness}Х100(%)

Experimental Example 2

<Evaluation of recovery capacity>

The lithium secondary batteries prepared in Examples and Comparative Examples were fully charged under the conditions of 0.33C/4.25V constant current/constant voltage (CC/CV) 4.25V/0.05C at 25°C, and then discharged at 0.2C until 3V was discharged. The dose (initial dose) was determined.

In addition, the lithium secondary battery was fully charged in the manner described above, stored at 85° C. for 8 hours, and then discharged in the same manner to measure the discharge capacity (capacity after storage). The recovery capacity was calculated according to the following formula (2) from the measured values, and the results are shown in Table 1.

Equation (2): Recovery capacity (%) = (initial capacity / capacity after storage) × 100 (%)

Experimental Example 3

<Evaluation of thickness increase rate after storage at 65℃>

The lithium secondary batteries prepared in Examples and Comparative Examples were fully charged (SOC 100%) at 25° C. under 0.33C/4.25V constant current/constant voltage (CC/CV) 4.25V/0.05C conditions. Then, the thickness (initial thickness) of the secondary battery was measured using a plate thickness measuring device (manufacturer: Mitsutoyo).

Thereafter, the secondary battery was stored at 65° C. for 4 weeks, and the thickness (final thickness) of the secondary battery was measured. The thickness increase rate was calculated according to the following formula (1) from the measured values, and the results are shown in Table 1.

Equation (1): Thickness increase rate (%) = {(final thickness-initial thickness)/ initial thickness}Х100(%)

Content of the first additive
(weight%) Thickness increase rate (%) after storage at 85℃ Recovery capacity (%) Thickness increase rate (%) after storage at 65℃ Example 1 3.0 4.68 92.4 6.92 Example 2 5.0 4.00 92.6 6.25 Example 3 7.5 3.85 92.1 5.87 Comparative Example 1 0 10.37 91.2 7.89 Comparative Example 2 0.1 10.03 91.2 7.98 Comparative Example 3 15 10.2 68.9 7.12

Referring to Table 1, when the compound represented by Formula 1, for example, ethyl 2-cyano2-methylpropionate (ECMP) is added within the above content range as the first additive, the secondary battery is prepared in a high-temperature environment. The thickness increase rate was low even after storage, and the recovery capacity was also excellent. This is due to the effective removal of Lewis acids such as HF and PF ₅ , which are decomposition products generated by the decomposition of anions, from the inside of the electrolyte.

In contrast, in Comparative Examples 1 and 2 in which the first additive is not added or only a small amount is added, it can be seen that the thickness increase rate is higher than in Examples, which means that the amount of the first additive may remove the Lewis acid as described above. It can be seen that this is because there are not enough of them.

In addition, it can be seen that the amount of the first additive is 15% by weight, which exceeds the numerical range according to the present invention, and the high temperature durability is lower than that of Comparative Example 3 and Example, which means that the side reaction in the electrolyte during charging and discharging of the battery is excessive. It can be seen that this is because the first additive remained and inhibited the performance of the battery even after activation.

As described above, the non-aqueous electrolyte for a lithium secondary battery according to the present invention includes the nitrile-based additive represented by Formula 1, thereby improving the high temperature durability of the lithium secondary battery.

The above description is merely illustrative of the technical spirit of the present invention, and various modifications and variations will be possible without departing from the essential characteristics of the present invention by those skilled in the art to which the present invention pertains. Accordingly, the drawings disclosed in the present invention are for explanation rather than limiting the technical spirit of the present invention, and the scope of the technical spirit of the present invention is not limited by these drawings. The protection scope of the present invention should be construed by the following claims, and all technical ideas within the scope equivalent thereto should be construed as being included in the scope of the present invention.

Claims (10)

lithium salt; organic solvents; and a first additive;
The first additive is a non-aqueous electrolyte for a lithium secondary battery comprising a compound represented by the following formula (1).
[Formula 1]

(In Formula 1, R ₁ and R ₂ are each independently selected from the group consisting of hydrogen, a substituted or unsubstituted alkyl group having 1 to 4 carbon atoms, and a substituted or unsubstituted cyclic alkyl group having 3 to 8 carbon atoms, R ₃ is selected from the group consisting of a substituted or unsubstituted alkyl group having 1 to 4 carbon atoms, and a substituted or unsubstituted cyclic alkyl group having 3 to 8 carbon atoms.)
According to claim 1,
In Formula 1, R ₁ to R ₃ are each independently a substituted or unsubstituted C 1 to C 4 alkyl group, a non-aqueous electrolyte for a lithium secondary battery.
According to claim 1,
The first additive is ethyl 2-cyano-2-methylpropionate represented by the following formula (1a), a non-aqueous electrolyte for a lithium secondary battery.
[Formula 1a]

According to claim 1,
The first additive is a non-aqueous electrolyte for a lithium secondary battery comprising 0.5 to 10% by weight based on the total weight of the electrolyte.
According to claim 1,
The first additive is a non-aqueous electrolyte for a lithium secondary battery that is included in 3 to 7% by weight based on the total weight of the electrolyte.
According to claim 1,
Lithium further comprising at least one second additive selected from the group consisting of halogen-substituted or unsubstituted cyclic carbonate-based compounds, nitrile-based compounds, phosphate-based compounds, borate-based compounds, sultone-based compounds, lithium salt-based compounds, and sulfate-based compounds Non-aqueous electrolyte for secondary batteries.
7. The method of claim 6,
The second additive is a lithium secondary including one or a combination of two or more selected from the group consisting of vinyl ethylene carbonate, fluoroethylene carbonate, 1,3-propane sultone, and lithium oxalyl difluoroborate (ODFB). Non-aqueous electrolyte for batteries.
According to claim 1,
The lithium salt is LiPF ₆ , LiAsF ₆ , LiCF ₃ SO ₃ , LiN(CF ₃ SO ₂ ) ₂ , LiBF ₆ , LiSbF ₆ , LiN(C ₂ F ₅ SO ₂ ) ₂ , LiAlO ₄ , LiAlCl ₄ , LiSO ₃ CF ₃ and LiClO ₄ A non-aqueous electrolyte for a lithium secondary battery, which is at least one selected from the group consisting of.
According to claim 1,
The organic solvent is a non-aqueous electrolyte for a lithium secondary battery comprising a linear carbonate, a cyclic carbonate, an ester, an ether, a ketone, or a combination thereof.
A lithium secondary battery comprising the non-aqueous electrolyte for a lithium secondary battery according to claim 1.