KR20200089624A - Additive for nonaqueous electrolyte, nonaqueous electrolyte for lithium secondary battery comprising the same, and lithium secondary battery - Google Patents

Abstract

The present invention relates to a non-aqueous electrolyte additive, a non-aqueous electrolyte for a lithium secondary battery containing the same, and a lithium secondary battery containing the same. Specifically, the present invention relates to a non-aqueous electrolyte additive using a Lewis base compound capable of rapidly reacting with an acid, a non-aqueous electrolyte for a lithium secondary battery containing the same, and a secondary battery having improved high-temperature storage durability by containing the same.

Description

Non-aqueous electrolyte additives, non-aqueous electrolytes for lithium secondary batteries and lithium secondary batteries containing the same

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

With the development of the information society, personal IT devices and computer networks have been developed, and as a result, the reliance on electric energy in the overall society has increased, and technology development for efficiently storing and utilizing electric energy is required.

Among these, the most suitable technology for various uses is a secondary battery-based technology. In the case of a secondary battery, it can be miniaturized to a degree that can be applied to personal IT devices, etc., and it can be applied to electric vehicles, electric power storage devices, and the like. Among these secondary battery technologies, lithium ion batteries, which are theoretically the highest energy density battery systems, are in the spotlight, and are currently applied to various devices.

In the case of a lithium ion 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 carbonaceous material such as graphite and an alloy system such as silicon are used as a cathode material. It is implemented as a system in which lithium metal is not directly used inside a battery, such as applying a material as a negative electrode.

In the case of such a lithium-ion 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 that is a medium for transferring lithium ions, and a separator. Known as a component having a great influence on stability and safety, many studies have been conducted on this.

At this time, the electrolyte for lithium ion batteries is composed of a lithium salt, an organic solvent dissolving it, and a functional additive, and it is important to properly select these components in order to improve the electrochemical properties of the battery.

LiPF ₆ , LiBF ₄ , LiFSI (lithium fluorosulfonyl imide, LiN(SO ₂ F) ₂ ), LiTFSI (lithium (bis)trifluoromethanesulfonyl imide, LiN(SO ₂ CF ₃ ) ₂ ) or LiBOB ( Lithium bis(oxalate) borate, LiB(C ₂ O ₄ ) ₂ ), etc. are used, and in the case of an organic solvent, an ester organic solvent or an ether organic solvent is used.

In the case of such a lithium ion battery, an increase in resistance during charging and discharging at a high temperature or a decrease in capacity and a decrease in capacity have been suggested as problems causing performance degradation. In addition, a side reaction caused by the deterioration of the electrolyte at high temperature, and in particular, when a by-product generated due to the decomposition of salt at high temperature decomposes a film formed on the surfaces of the positive electrode and the negative electrode after activation, a problem of lowering the passivation ability of the film Exists, and there is a problem that causes additional decomposition of the electrolyte and self-discharge accompanying it.

Particularly, in the case of a graphite-based negative electrode mainly used as a negative electrode for a lithium ion battery, since its operating potential is 0.3 V (vs. Li/Li+) or less, it is lower than the electrochemical stability window of the electrolyte used in the lithium ion battery, the electrolyte is reduced first. Decomposes. The product of the electrolytic solution that has been decomposed and decomposed permeates lithium ions, but forms a solid electrolyte interphase (SEI) film that inhibits further decomposition of the electrolyte.

However, as described above, as the film is decomposed by the decomposition products of the salt at a high temperature, the passivation ability of the film is deteriorated due to HF and PF ₅ generated by thermal decomposition of LiPF ₆ , a lithium salt widely used in lithium ion batteries, or the electrode As the surface is deteriorated, transition metal elution occurs from the anode to increase resistance, and the capacity may decrease due to loss of the redox center. Moreover, in the case of the eluted transition metal ions, electrodeposited to the cathode, the irreversible capacity increases due to the electrodeposition of the metal and the consumption of electrons due to additional electrolyte decomposition, resulting in a decrease in cell capacity as well as an increase in resistance and self-discharge of the graphite cathode. Can.

Accordingly, in order to secure and maintain the passivation ability of the SEI film even at high temperature storage, HF, which is a decomposition product such as LiPF ₆ , which is a representative lithium salt that is generated due to heat/moisture, etc. And PF ₅ and the like, and it is urgent to introduce an additive capable of removing the cause of deterioration of the battery at a high temperature.

Korea Patent Publication No. 2014-050058

In the present invention, it is intended to provide a non-aqueous electrolyte additive using a Lewis base-based compound capable of rapidly reacting with an acid.

In addition, the present invention is to provide a non-aqueous electrolyte for a lithium secondary battery containing the non-aqueous electrolyte additive.

In addition, the present invention is to provide a lithium secondary battery comprising the non-aqueous electrolyte for the lithium secondary battery.

According to one embodiment, the present invention provides a non-aqueous electrolyte additive that is a compound represented by Formula 1 below.

[Formula 1]

In Chemical Formula 1,

R ₁ to R ₄ are each independently hydrogen or a substituted or unsubstituted alkyl group having 1 to 5 carbon atoms.

According to another embodiment, the present invention provides a non-aqueous electrolyte solution for a lithium secondary battery comprising a lithium salt, an organic solvent and a non-aqueous electrolyte solution additive of the present invention as a first additive.

The non-aqueous electrolyte solution for the lithium secondary battery may further include at least one second additive among vinylene carbonate (VC), 1,3-propanesultone (PS), and ethylene sulfate (Esa).

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

According to the present invention, by including a Lewis base-based compound as a non-aqueous electrolyte additive, not only a stable SEI film is formed on the surface of the negative electrode, but also an acid such as HF/PF ₅ formed as a decomposition product of lithium salt. It is possible to provide a non-aqueous electrolyte having properties that can suppress the elution of the positive electrode, and furthermore, by including this, a lithium secondary battery with improved resistance during high temperature storage can be manufactured.

The following drawings attached to this specification are intended to illustrate preferred embodiments of the present invention, and serve to further understand the technical spirit of the present invention together with the contents of the above-described invention, so the present invention is limited to those described in those drawings. It should not be interpreted limitedly.
1 is a graph showing an initial discharge capacity evaluation result of a lithium secondary battery according to Experimental Example 1 of the present invention.
2 is a graph showing the evaluation results of the high temperature storage characteristics of the lithium secondary battery according to Experimental Example 2 of the present invention.
3 is a graph showing the result of evaluating the resistance increase rate of the lithium secondary battery according to Experimental Example 3 of the present invention.
4 is a graph showing the evaluation results of the formation of the SEI film of the lithium secondary battery according to Experimental Example 4 of the present invention.
5 is a graph showing the results of evaluating metal ion dissolution according to Experimental Example 5 of the present invention.

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

The terms or words used in the specification and claims should not be interpreted as being limited to ordinary or dictionary meanings, and the inventor can appropriately define the concept of terms in order to best describe his or her invention. Based on the principle of being present, it should be interpreted as meanings and concepts consistent with the technical spirit of the present invention.

The passivation ability of the SEI film formed by electrolytic solution decomposition on the positive/negative electrode surface is a factor influencing the high temperature storage performance. Meanwhile, acids such as HF and PF ₅ produced by thermal decomposition of LiPF ₆ , a lithium salt widely used in lithium ion batteries, are known to be one of the factors that degrade the coating. When the surface of the anode is deteriorated by the attack of the acid, transition metal elution occurs, and the surface resistance of the electrode increases due to a change in the local structure of the surface, and the theoretical capacity decreases due to the loss of the redox center, thereby reducing the expression capacity. In addition, in the case of eluted metal ions, it is electrodeposited to a cathode reacting in a strong reduction potential band, consuming electrons, destroying a film, and exposing a new surface, thereby additionally generating electrolyte decomposition to increase the resistance of the cathode. Rather, there is a problem of continuously decreasing the capacity of the cell by increasing the irreversible capacity.

Accordingly, in order to suppress the deterioration of the battery, in the present invention, by introducing a Lewis base-based additive during the production of the non-aqueous electrolyte solution, deterioration of the SEI film by PF ₅ or HF can be prevented, and the anode is removed by removing the acid from the inside of the electrolyte. Elution of transition metals from can be suppressed. In addition, in the present invention, by introducing a Lewis base-based additive in the production of a non-aqueous electrolyte solution, it is possible to form SEI different from existing additives on the surface of the cathode while undergoing reduction and decomposition, and further improve the high-temperature storage performance of the secondary battery through the modification of the SEI. You can get the characteristics you can.

Non-aqueous electrolyte additive

First, in one embodiment of the present invention provides a non-aqueous electrolyte additive that is a compound represented by Formula 1 below.

[Formula 1]

In Chemical Formula 1,

R ₁ to R ₄ are each independently hydrogen or a substituted or unsubstituted alkyl group having 1 to 5 carbon atoms.

Specifically, in Chemical Formula 1, R ₁ and R ₄ are each independently substituted or unsubstituted alkyl group having 1 to 5 carbon atoms, and R ₂ and R ₃ are each independently hydrogen or substituted or unsubstituted carbon number 1 to 5 It may be an alkyl group.

More specifically, in Chemical Formula 1, R ₁ and R ₄ are each independently substituted or unsubstituted alkyl group having 1 to 4 carbon atoms, and R ₂ and R ₃ are each independently hydrogen or substituted or unsubstituted carbon number 1 to It may be an alkyl group of 3.

More specifically, in Formula 1, R ₁ and R ₄ are substituted or unsubstituted alkyl groups having 1 to 3 carbon atoms, and R ₂ and R ₃ may be hydrogen.

* Since the compound represented by Chemical Formula 1 contains a -N-(C=S)-N- functional group that functions as a Lewis base in the structure, HF and PF ₅ , which are decomposition products generated by anionic decomposition of lithium salts, The same Lewis acid can be removed inside the electrolyte. Therefore, the deterioration behavior due to the chemical reaction of the positive or negative electrode surface coating resulting from the Lewis acid can be suppressed, thereby preventing further electrolyte decomposition of the battery due to breakage of the coating. Therefore, finally, the self-discharge of the battery and the deterioration behavior of the battery during high temperature storage can be prevented.

In addition, since the C=S functional group and -N-CO-O- functional group included in the structure of the compound represented by Chemical Formula 1 are easily reduced at the negative electrode surface, a stable SEI film with high passivation ability is formed on the negative electrode surface. can do. Therefore, it is possible to not only improve the high temperature durability of the negative electrode itself, but also reduce the amount of the transition metal electrodeposited on the negative electrode itself, and furthermore, the black due to the additional reduction and decomposition reaction of the electrolyte solution caused by the instability of the SEI film. Self-discharge reaction of the linkage or silicon-based cathode can be prevented.

Through these comprehensive effects, the non-aqueous electrolyte additive, which is a compound represented by Chemical Formula 1 of the present invention, stably forms a SEI film and can prevent the destruction of the positive/negative film by decomposition of a lithium salt, thereby causing a self-discharge reaction of the battery. It can be suppressed, and through this, it is possible to improve characteristics such as initial discharge capacity characteristics of the lithium ion battery and resistance suppression during high temperature storage.

Meanwhile, the compound represented by Chemical Formula 1 may be a compound represented by Chemical Formula 1a.

[Formula 1a]

Non-aqueous electrolyte for lithium secondary battery

According to another embodiment, the present invention provides a non-aqueous electrolyte solution for a lithium secondary battery comprising a lithium salt, an organic solvent and a non-aqueous electrolyte solution additive of the present invention as a first additive.

Hereinafter, each component of the non-aqueous electrolyte of the present invention will be described in more detail.

(1) lithium salt

The lithium salt may be used, without limitation, those which are commonly used in a lithium secondary battery electrolyte, such as an anion, and containing the Li ⁺ in the lithium salt cation is 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 there may be mentioned at least one or more selected from the group consisting of _{^{- SO 2) 3 C -,}} CF 3 (CF 2) 7 SO 3 -, SCN - , and _{(CF 3 CF 2 SO 2)} 2 N.

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 at least one selected from the group consisting of. More specifically, the lithium salt is a single 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 contain a mixture of the above.

The lithium salt may be appropriately changed within a range that can be normally used, but may be specifically included in the electrolyte in 0.1M to 3M, and specifically 0.8M to 2.5M. If, when the concentration of the lithium salt exceeds 3M, the viscosity of the non-aqueous electrolyte is increased, the lithium ion migration effect is lowered, and the wettability of the non-aqueous electrolyte is lowered, thereby making it difficult to form a uniform SEI film.

(2) Organic solvent

In the organic solvent, decomposition by an oxidation reaction or the like during charging and discharging of the secondary battery can be minimized, and the type is not limited as long as it can exhibit desired properties with additives. For example, carbonate-based organic solvents, ether-based organic solvents, or ester-based organic solvents 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 (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 is specifically compared to ethylene carbonate and ethylene carbonate having a high dielectric constant. 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 low viscosity and low dielectric constant, dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethyl methyl carbonate (EMC), methyl It may include at least one selected from the group consisting of propyl carbonate and ethylpropyl carbonate, and more specifically, may include dimethyl carbonate.

The ether-based organic solvent may be any one selected from the group consisting of dimethyl ether, diethyl ether, dipropyl ether, methylethyl ether, methylpropyl ether and ethylpropyl ether, or a mixture of two or more of them, but is not limited thereto. It does not work.

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

In this case, the linear ester-based organic solvent is specifically selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, and butyl propionate, or Mixtures of two or more of these may be representatively used, but are not limited thereto.

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

The organic solvent has a high dielectric constant and may use a high-viscosity cyclic carbonate-based organic solvent that dissociates lithium salts in the non-aqueous electrolyte well. In addition, in order to prepare a non-aqueous electrolyte having a higher electrical conductivity, the organic solvent, together with the environmental carbonate-based organic solvent, has low viscosity, low dielectric constant linear carbonate-based compound and linear ester-based compound such as dimethyl carbonate and diethyl carbonate. 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:linear carbonate-based compound in the organic solvent may be 10:90 to 70:30.

(3) First additive

The non-aqueous electrolyte solution of the present invention includes the compound represented by Chemical Formula 1 as the first additive for the non-aqueous electrolyte solution.

At this time, since the description of the non-aqueous electrolyte additive is overlapped with the above, the description is omitted.

However, with respect to the content of the non-aqueous electrolyte additive, the non-aqueous electrolyte additive may be included in an amount of 0.01% to 5% by weight, specifically 0.1% to 3% by weight based on the total weight of the non-aqueous electrolyte.

When the additive is included in the above range, it is possible to manufacture a secondary battery with improved overall performance. If the content of the additive is less than 0.01% by weight, HF or PF ₅ may be removed in a small amount, but the effect of continuously removing it may be insignificant, and when it exceeds 5% by weight, the electrode may be decomposed due to decomposition of the excess additive. Resistance may increase, or the initial capacity due to side reactions may decrease.

Thus, the additive is 0.01% by weight to 5% by weight, specifically, 0.1% to 3% by weight in the range, while suppressing the capacity decrease and increase in resistance due to side reactions as much as possible, it is possible to more effectively remove HF and PF ₅ have.

As described above, in the present invention, by including the compound represented by Chemical Formula 1, which is the Lewis salt-based compound, as an electrolyte additive, not only can a solid SEI film be formed on the surface of the negative electrode, but also a Lewis base functional group -N-( A functional group containing C=S)-N- can easily remove Lewis acids such as HF and PF ₅ formed by decomposition of a lithium salt by-product that causes deterioration of a battery at high temperature storage ( By scavenging, it is possible to improve disadvantages such as deterioration of the SEI film and elution of a transition metal at the anode.

That is, in the case of the non-aqueous electrolyte solution of the present invention containing the compound represented by the formula (1) as an additive, it is possible to remove the Lewis acid that can cause self-discharge of the battery by attacking the positive electrode surface and the negative electrode surface in the electrolyte solution. The self-discharge of the battery can be alleviated to improve the high temperature storage performance.

(4) Second additive

In addition, the non-aqueous electrolyte solution for a lithium secondary battery of the present invention forms a stable film on the surface of the negative electrode and the positive electrode in addition to the effect expressed by the electrolyte additive, improves capacity characteristics and cycle characteristics during high temperature storage, and realizes a resistance reduction effect. To this end, in addition to the compound represented by Chemical Formula 1, which is the first additive, another second additive may be further included.

As a second additive that may be additionally included, vinylene carbonate (VC), 1,3-propane sultone (PS) and ethylene, which are known to form a more stable SEI film on the cathode surface during the initial activation process of the secondary battery At least one additive of sulphate (Ethylene Sulfate; Esa) may be applied.

On the other hand, the vinylene carbonate (VC), 1,3-propane sulfone (PS) and ethylene sulfate (Ethylene Sulfate; Esa), respectively, based on the total weight of the non-aqueous electrolyte, 10% by weight or less, specifically 0.1% by weight to 7% by weight %.

When the content of each of the compounds exceeds 10% by weight, there is a possibility that a side reaction in the electrolyte is excessively generated during charging and discharging of the battery, and it is not sufficiently decomposed at a high temperature, and remains unreacted or precipitated in the electrolyte at room temperature. It may be, and accordingly, the life or resistance characteristics of the secondary battery may be deteriorated.

In particular, the total content of the second additive may be included in an amount of 15 wt% or less, specifically 0.1 wt% to 15 wt%, specifically 0.1 to 10 wt%, based on the total weight of the non-aqueous electrolyte, preferably 0.5 to 10 It may be included in weight%, more preferably 1.0 to 7.0% by weight.

That is, in order to secure the high temperature durability of the non-aqueous electrolyte, the second additive should contain at least 0.1% by weight or more, and the content of each compound exceeds 10% by weight, or the total content of the second additive exceeds 15% by weight If it does, since the content of the organic solvent and the lithium salt can be relatively reduced, there is a possibility of deteriorating the basic performance of the battery beyond the role of the additive, so it is necessary to appropriately adjust the content range within the above range. .

(5) SEI Formation Additive

In addition, the non-aqueous electrolyte solution of the present invention additionally includes additional additives that can form a stable film on the surface of the negative electrode and the positive electrode, suppress decomposition of the solvent in the non-aqueous electrolyte solution, and serve as a supplement to improve mobility of lithium ions. can do.

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

Specifically, the SEI-forming additive is a halogen-substituted or unsubstituted cyclic carbonate-based compound, nitrile-based compound, phosphate-based compound, borate-based compound, lithium salt-based compound, sulfate-based compound, sultone-based compound, fluorinated benzene-based compound It may include at least one additive for forming SEI selected from the group consisting of compounds and silane-based compounds.

Specifically, the halogen-substituted cyclic carbonate-based compound may include fluoroethylene carbonate (FEC), and the halogen-unsubstituted cyclic carbonate-based compound mainly forms a stable SEI film on the negative electrode surface upon activation of the battery. It is possible to improve the durability of the. Vinyl ethylene carbonate is mentioned as such a cyclic carbonate type compound.

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

In addition, the nitrile-based compound is succinonitrile, adiponitrile, acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentane carbonitrile, cyclohexane carbonitrile, 2-fluoro At least selected from the group consisting of robenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile One or more compounds.

When the nitrile-based compound is used together with the above-described electrolyte additive, an effect of improving high temperature characteristics can be expected by stabilizing the positive/negative film. That is, it may serve as a supplement to form the negative electrode SEI film, may serve to suppress the decomposition of the solvent in the non-aqueous electrolyte, and may serve to improve the mobility of lithium ions. The nitrile-based compound may be included in an amount of 8% by weight or less based on the total weight of the non-aqueous electrolyte. When the total weight of the nitrile-based compound in the non-aqueous electrolyte exceeds 8% by weight, resistance increases due to an increase in the film formed on the electrode surface, and battery performance may be deteriorated.

In addition, since the phosphate-based compound stabilizes PF ₆ anions and the like in the electrolyte solution and helps to form a positive electrode and a negative electrode film, durability of the battery can be improved. Such phosphate-based compounds include lithium difluoro(bisoxalato)phosphate (LiDFOP), lithium difluorophosphate (LiDFP, LiPO ₂ F ₂ ), tetramethyl trimethyl silyl phosphate (LiTFOP), and tris(2,2, 2-trifluoroethyl) phosphate (TFEPa), and one or more compounds selected from the group consisting of, and may be included in 3% by weight or less based on the total weight of the non-aqueous electrolyte.

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

In addition, the lithium salt-based compound is a compound different from the lithium salt contained in the non-aqueous electrolyte solution, and may include one or more compounds 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 solution It can contain.

The sulfate-based compound may be trimethylene sulfate (TMS), or methyl trimethylene sulfate (MTMS), and may be included in an amount of 3% by weight or less based on the total weight of the non-aqueous electrolyte.

The sultone-based compound is selected from the group consisting of 1,4-butane sultone, ethene sultone, 1,3-propene sultone (PRS), 1,4-butene sultone, and 1-methyl-1,3-propene sultone. It may include at least one compound, which may be included in an amount of 0.3% to 5% by weight, specifically 1% to 5% by weight 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 lead to an increase in resistance and output deterioration, and an increase in output characteristics due to an increase in resistance due to excessive additives in the non-aqueous electrolyte. It may deteriorate.

The fluorinated benzene-based compound may include fluorobenzene.

In addition, the silane-based compound may include a compound containing silicon, such as tetravinylsilane, and in the case of such a compound, it may include 2% by weight or less based on the total weight of the non-aqueous electrolyte.

The additive for SEI formation may be used by mixing two or more, and may be included in an amount of 10% by weight or less, specifically 0.01% by weight to 10% by weight, and preferably 0.1 to 5.0% by weight based on the total weight of the non-aqueous electrolyte. .

When the content of the additive for forming the SEI is less than 0.01% by weight, the high temperature storage property and gas reduction effect to be realized from the additive are negligible, and when the content of the additive for forming the SEI exceeds 10% by weight, the electrolyte during charging and discharging of the battery There is a possibility that side reactions within the body may occur excessively. In particular, if the additive for forming the SEI is added in an excessive amount, it may not sufficiently decompose and may remain unreacted or precipitated in the electrolyte at room temperature. Accordingly, the resistance may increase and the life characteristics of the secondary battery may deteriorate.

Lithium secondary battery

In addition, in one embodiment of the present invention, there is provided a lithium secondary battery comprising a non-aqueous electrolyte solution for a lithium secondary battery of the present invention.

Specifically, the lithium secondary battery of the present invention can be prepared by injecting the non-aqueous electrolyte solution of the present invention into an electrode assembly formed by sequentially stacking a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode. At this time, the positive electrode, the negative electrode, and the separator constituting the electrode assembly may be all those commonly used in manufacturing lithium secondary batteries.

On the other hand, the positive and negative electrodes constituting the lithium secondary battery of the present invention can be prepared and used in a conventional manner.

(1) anode

First, the positive electrode may be manufactured by forming a positive electrode mixture layer on a positive electrode current collector. The positive electrode material mixture layer may be formed by coating a positive electrode slurry containing 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. , Surface treatment with nickel, titanium, silver, or the like can be used.

The positive electrode active material is a compound capable of reversible intercalation and deintercalation of lithium, and may include a lithium transition metal oxide containing lithium and at least one metal selected from cobalt, manganese, nickel, or aluminum, Specifically, a lithium-nickel-manganese-cobalt oxide (eg Li(Ni _p Co _q Mn _r1 )O ₂ (where 0<p<1, 0<q< 1, 0<r1<1, p+q+r1=1) or lithium-manganese oxide, and more specifically lithium-manganese oxide.

The lithium-nickel-manganese-cobalt oxide is Li(Ni _1/3 Mn _1/3 Co _1/3 )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 and Li(Ni _0.8 Mn _0.1 Co _0.1 )O ₂ , and the lithium-manganese oxide is LiMn ₂ O ₄ is mentioned.

The positive electrode active material of the present invention, in addition to the lithium-manganese oxide, lithium-cobalt oxide (for example, LiCoO _2, etc.), lithium-nickel-based oxide (for example, LiNiO _2, etc.), lithium-nickel-manganese-based Oxides (eg, LiNi _1-Y Mn _Y O ₂ (here, 0<Y<1), LiMn _2-z Ni _z O ₄ (here, 0<Z<2), etc.), lithium-nickel- Cobalt oxide (for example, LiNi _1-Y1 Co _Y1 O ₂ (here, 0<Y1<1), etc.), lithium-manganese-cobalt oxide (for example, LiCo _1-Y2 Mn _Y2 O ₂ ( Here, 0<Y2<1), LiMn _2-z1 Co _z1 O ₄ (here, 0<Z1<2), etc.), lithium-nickel-manganese-cobalt oxide (for example, Li(Ni _p Co _q Mn _r1 )O ₂ (where 0<p<1, 0<q<1, 0<r1<1, p+q+r1=1) or Li(Ni _p1 Co _q1 Mn _r2 )O ₄ (here In, 0<p1<2, 0<q1<2, 0<r2<2, p1+q1+r2=2), etc.), and lithium-nickel-cobalt-transition metal (M) oxide (for example, Li (Ni _p2 Co _q2 Mn _r3 M _S2 ) O ₂ (where M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg and Mo, p2, q2, r3 and s2 are each independently Atomic fraction of phosphorus elements, at least one selected from the group consisting of 0<p2<1, 0<q2<1, 0<r3<1, 0<s2<1, p2+q2+r3+s2=1)) The above lithium transition metal oxide may be further included.

The positive electrode active material may be included in 80% to 99% by weight based on the total weight of solids in the positive electrode slurry.

The binder is a component that assists in the bonding of the active material and the conductive material and the like to the current collector, and is usually added in an amount of 1 to 30% by weight based on the total weight of solids in the positive electrode slurry. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoro Roethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer, styrene-butadiene rubber, fluorine rubber, and various copolymers.

The conductive material is usually added at 1 to 30% by weight based on the total weight of solids in the positive electrode slurry.

The conductive material is not particularly limited as long as it has conductivity without causing a chemical change in the battery. For example, graphite; Carbon-based materials such as carbon black, 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 powder, aluminum powder, and nickel powder; Conductive whiskey 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 an organic solvent such as NMP (N-methyl-2-pyrrolidone), and may be used in an amount that becomes a desirable viscosity when the positive electrode active material and optionally a binder and a conductive material are included. For example, the solid content concentration in the slurry containing the positive electrode active material, and optionally the binder and the conductive material may be included to be 50% to 95% by weight, preferably 70% to 90% by weight.

(2) Cathode

In addition, 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, followed by drying and rolling.

The negative electrode current collector generally has a thickness of 3 to 500 μm. The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel Surface-treated with carbon, nickel, titanium, silver, etc. on the surface, aluminum-cadmium alloy, or the like can be used. In addition, like the positive electrode current collector, it is also possible to form a fine unevenness on the surface to enhance the bonding force of the negative electrode active material, and may be used in various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics.

In addition, the negative electrode active material is a lithium-containing titanium composite oxide (LTO); Carbon-based materials such as non-graphitized carbon and graphite-based carbon; Li _x Fe ₂ O ₃ (0≤x≤1), Li _x WO ₂ (0≤x≤1), Sn _x Me _1-x Me' _y O _z (Me: Mn, Fe, Pb, Ge; Me' : Al, B, P, Si, group 1, group 2, group 3 elements of the periodic table, halogen; metal composite oxides such as 0<x≤1;1≤y≤3;1≤z≤8); Lithium metal; Lithium alloys; Silicon-based alloys; Tin-based alloys; SnO, SnO ₂ , 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 , And metal oxides such as Bi ₂ O ₅ ; And a single material or a mixture of two or more selected from the group consisting of conductive polymers such as polyacetylene.

The negative active material may be included in an amount of 80% to 99% by weight based on the total weight of 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 usually added in an amount of 1 to 30% by weight based on the total weight of solids in the negative electrode slurry. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoro Roethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer, styrene-butadiene rubber, fluorine rubber, 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% by weight based on the total weight of solids in the negative electrode slurry. The 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 blacks 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 powder, aluminum powder, and nickel powder; Conductive whiskey 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 and alcohol, and may be used in an amount that becomes a desirable viscosity when the negative electrode active material and optionally a binder and a conductive material are included. For example, the solid content concentration in the slurry containing the negative electrode active material, and optionally the binder and the conductive material may be included to be 50% to 95% by weight, preferably 70% to 90% by weight.

(3) separator

In addition, the separator serves to block the internal short circuit of both electrodes and impregnate the non-aqueous electrolyte, prepare a separator composition by mixing a polymer resin, a filler, and a solvent, and then coat and dry the separator composition directly on the electrode top. By forming a separator film, or after casting and drying the separator composition on a support, the separator film peeled from the support may be formed by laminating on the upper electrode.

The separator is a porous polymer film that is commonly used, such as ethylene homopolymer, propylene homopolymer, ethylene/butene copolymer, ethylene/hexene copolymer and ethylene/methacrylate copolymer. The polymer film may be used alone or by laminating them, or a conventional porous nonwoven fabric, for example, a high melting point glass fiber, a polyethylene terephthalate fiber, or the like may be used, but is not limited thereto.

At this time, the pore diameter of the porous separator is generally 0.01 to 50㎛, porosity may be 5 to 95%. In addition, the thickness of the porous separator may generally range from 5 to 300 μm.

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

Hereinafter, examples will be described in detail to specifically describe the present invention. However, the embodiments according to the present invention can be modified in many different 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 fully describe the present invention to those skilled in the art.

Example

Example 1.

(Preparation of non-aqueous electrolyte)

After mixing ethylene carbonate:ethyl methyl carbonate in a volume ratio of 30:70, LiPF ₆ was dissolved to a concentration of 0.7 M and LiFSI to a concentration of 0.3 M to prepare a non-aqueous organic solvent. 0.5 g of a compound represented by Formula 1a as a first additive to 90.7 g of the non-aqueous organic solvent, 1.0 g of ethylene sulfonate as a second additive, 0.5 g of 1,3-propane sultone, 0.1 g of tetravinylsilane as an additive for forming SEI , Lithium difluorophosphate 1.0 g and LiBF ₄ 0.2 g, fluorine benzene 6.0 g was added to prepare a non-aqueous electrolyte solution for a lithium secondary battery.

(Secondary battery manufacturing)

Cathode active material (LiNi _0.8 Co _0.1 Mn _0.1 O ₂ :LiNi _0.6 Co _0.2 Mn _0.2 O ₂ =70:30 weight ratio) and carbon black as a conductive material and polyvinylidene fluoride (PVDF) as a binder in a 97.5:1:1.5 weight ratio A positive electrode mixture slurry (solid content: 50% by weight) was prepared by adding to the furnace solvent N-methyl-2-pyrrolidone (NMP). The positive electrode mixture slurry was coated and dried on a thin film of aluminum (Al) as a positive electrode current collector having a thickness of 12 µm, and then roll press was performed to prepare a positive electrode.

Cathode mixture slurry (solid content: 60 wt. %). The negative electrode mixture slurry was coated and dried on a copper (Cu) thin film as a negative electrode current collector having a thickness of 6 μm, and then roll press was performed to prepare a negative electrode.

The prepared positive electrode, a polyolefin-based porous separator coated with inorganic particles (Al ₂ O ₃ ), and a negative electrode were sequentially stacked to prepare an electrode assembly.

Subsequently, the assembled electrode assembly was housed in a battery case, and the composition for the non-aqueous electrolyte was injected to prepare a pouch-type lithium secondary battery.

Example 2.

(Preparation of non-aqueous electrolyte)

After mixing ethylene carbonate:ethyl methyl carbonate in a volume ratio of 30:70, LiPF ₆ was dissolved to a concentration of 1.2 M to prepare a non-aqueous organic solvent. A nonaqueous electrolyte solution for a lithium secondary battery was prepared by adding 1.0 g of the compound represented by Formula 1a to 99.0 g of the nonaqueous organic solvent.

(Secondary battery manufacturing)

A pouch type lithium secondary battery was manufactured in the same manner as in Example 1, except that the nonaqueous electrolyte prepared in Example 1 was used instead of the nonaqueous electrolyte prepared in Example 1.

Example 3.

(Preparation of non-aqueous electrolyte)

After mixing ethylene carbonate:ethyl methyl carbonate:dimethyl carbonate in a volume ratio of 30:30:40, LiPF ₆ was dissolved to a concentration of 1.0M to prepare a non-aqueous organic solvent. Non-aqueous solution for lithium secondary battery by adding 0.3g of compound represented by Formula 1a as the first additive to 95.5g of the non-aqueous organic solvent, 3.0g of VC as the second additive, 1.0g of ethylene sulfonate and 0.5g of 1,3-propane sulfone. An electrolyte solution was prepared.

(Secondary battery manufacturing)

N-methyl-2-pyrrolidone (LiNi _0.7 Co _0.1 Mn _0.2 O ₂ ) as a positive electrode active material and carbon black as a conductive material and polyvinylidene fluoride (PVDF) as a binder in a weight ratio of 97.5:1:1.5 NMP) to prepare a positive electrode mixture slurry (solid content: 50% by weight). The positive electrode mixture slurry was coated and dried on a thin film of aluminum (Al) as a positive electrode current collector having a thickness of 12 µm, and then roll press was performed to prepare a positive electrode.

A negative electrode mixture slurry (solid content: 60% by weight) was prepared by adding negative electrode active material (graphite), SBR-CMC as a binder, and carbon black as a conductive material to water as a solvent in a weight ratio of 95:3.5:1.5. The negative electrode mixture slurry was coated and dried on a copper (Cu) thin film as a negative electrode current collector having a thickness of 6 μm, and then roll press was performed to prepare a negative electrode.

The prepared positive electrode, a polyolefin-based porous separator coated with inorganic particles (Al 2 O 3 ), and a negative electrode were sequentially stacked to prepare an electrode assembly.

Subsequently, the assembled electrode assembly was housed in a battery case, and the composition for the non-aqueous electrolyte was injected to prepare a pouch-type lithium secondary battery.

Comparative Example 1.

(Preparation of non-aqueous electrolyte)

After mixing ethylene carbonate:ethyl methyl carbonate in a volume ratio of 30:70, LiPF ₆ was dissolved to a concentration of 0.7 M and LiFSI to a concentration of 0.3 M to prepare a non-aqueous organic solvent. 91.2 g of the non-aqueous organic solvent, 1.0 g of ethylene sulfonate as 2 additives, 0.5 g of 1,3-propane sultone, 0.1 g of tetravinylsilane as an additive for forming SEI, 1.0 g of lithium difluorate phosphate, 0.2 g of LiBF ₄ , And 6.0 g of fluorine benzene was added to prepare a non-aqueous electrolyte solution for a lithium secondary battery.

(Secondary battery manufacturing)

A pouch type lithium secondary battery was manufactured in the same manner as in Example 1, except that the nonaqueous electrolyte prepared in Example 1 was used instead of the nonaqueous electrolyte prepared in Example 1.

Comparative Example 2.

(Preparation of non-aqueous electrolyte)

After mixing ethylene carbonate:ethyl methyl carbonate:dimethyl carbonate in a volume ratio of 30:30:40, LiPF ₆ was dissolved to a concentration of 1.0M to prepare a non-aqueous organic solvent. A non-aqueous electrolyte solution for a lithium secondary battery was prepared by adding the second additives VC 3.0 g, ethylene sulfonate 1.0 g, and 1,3-propane sultone 0.5 g to 95.8 g of the non-aqueous organic solvent.

(Secondary battery manufacturing)

A pouch-type lithium secondary battery was manufactured in the same manner as in Example 3, except that the nonaqueous electrolyte prepared in Example 3 was used instead of the nonaqueous electrolyte prepared in Example 3.

Experimental Example

Experimental Example 1. Initial discharge capacity evaluation

After activating the secondary batteries prepared in Example 1 and Comparative Example 1 to 0.1 C CC, respectively, they were charged with 0.33 C CC up to 4.20 V at a constant current-constant voltage (CC-CV) charging condition at 25° C., and then 0.05 C current. Cut was performed, and discharged to 0.3V at 2.5V under CC conditions.

After 3 cycles of the charge/discharge as 1 cycle, the initial discharge capacity was measured using a PNE-0506 charge/discharge (manufacturer: PNE solution, 5 V, 6 A), and the results are shown in FIG. 1. Did.

Referring to Figure 1, it can be seen that the secondary battery of Example 1 with the non-aqueous electrolyte containing the additive of the present invention has a higher initial capacity than the secondary battery of Comparative Example 1.

Experimental Example 2. High temperature storage property evaluation

After activating each secondary battery prepared in Example 1 and Comparative Example 1 to 0.1C CC, degassing was performed. Subsequently, it was charged with 0.33 C CC to 4.20 V under a constant current-constant voltage (CC-CV) charging condition at 25° C., and then a 0.05 C current cut was performed and discharged to 0.33 C with 2.5 V under CC conditions. The charging and discharging was performed as 1 cycle, and 3 cycles were performed.

Subsequently, the initial discharge capacity was measured using a PNE-0506 charge/discharger (manufacturer: PNE solution, 5 V, 6 A), the SOC was adjusted to 50% SOC, and then 2.5 C pulse was applied for 10 seconds. Then, the initial resistance was calculated through the difference between the voltage before and after the pulse application.

Then, after recharging to 0.3% C CC condition to 100% SOC, it was stored at a high temperature of 60°C for 4 weeks. After 2 weeks and 4 weeks after high temperature storage, CC-CV charging and discharging is performed with a current of 0.33 C CC, and then high temperature storage using PNE-0506 charging and discharging (manufacturer: PNE solution, 5 V, 6 A) After the discharge capacity was measured.

The discharge capacity retention rate was calculated by substituting the measured initial discharge capacity and the high-temperature storage discharge capacity measured at 2 and 4 weeks into the following formula (1), and the results are shown in FIG. 2.

At this time, after the 2 and 4 weeks, the discharge capacity is specified, and then the direct current internal resistance (hereinafter referred to as “DC”) is applied through a voltage drop occurring in a state where a discharge pulse is given for 10 seconds at SOC 50% to 2.5 C. -iR"), and substituted in the following formula (2) to calculate the resistance increase rate (%), and then it is shown in FIG. At this time, the voltage drop was measured using a PNE-0506 charge/discharger (manufacturer: PNE solution, 5 V, 6 A).

Equation (1): Discharge capacity retention rate (%) = (discharge capacity / initial discharge capacity after high temperature storage) x 100

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

Referring to FIG. 2, it can be seen that the discharge capacity retention rate of the secondary battery of Example 1 and the secondary battery of Comparative Example 1 is similar even after high temperature storage at 60° C. for 2 weeks and 4 weeks.

However, it can be seen that the secondary battery of Example 1 with the non-aqueous electrolyte containing the additive of the present invention has a lower resistance increase rate after two weeks of high temperature storage than the secondary battery of Comparative Example 1.

That is, in the lithium secondary battery of the present invention, the acid (HF/PF ₅ ) formed by thermal decomposition of LiPF ₆ is removed by an additive contained in the non-aqueous electrolyte solution, thereby dissolving transition metal at the positive electrode and SEI deterioration at the negative electrode surface. Since it can be suppressed, the deterioration of the SEI at a higher temperature than the existing electrolyte can be improved through the modification of the components of the SEI due to the reduction decomposition of the additive, so it can be confirmed that the resistance increase rate at a high temperature is significantly improved.

Experimental Example 3. Evaluation of resistance increase rate

After activating the lithium secondary battery prepared in Example 1 and the secondary battery prepared in Comparative Example 1 to 0.1C CC, respectively, degassing was performed.

Subsequently, it was charged with 0.33C CC to 4.20V under constant current-constant voltage (CC-CV) charging conditions at 25°C, and then 0.05 C current cut was performed, and discharged to 0.33 C up to 2.5V under CC conditions. 3 cycles were performed with the charging and discharging as one cycle.

Subsequently, the initial discharge capacity was measured using a PNE-0506 charge/discharger (manufacturer: PNE solution, 5 V, 6 A), the SOC was adjusted to 50% SOC, and then 2.5 C pulse was applied for 10 seconds. Then, the initial resistance was calculated through the difference between the voltage before and after the pulse application.

Then, it was charged with 0.33 C CC to 4.20 V under a constant current-constant voltage (CC-CV) charging condition at 45° C., followed by a 0.05 C current cut, and discharged to 0.33 C with 2.50 V under CC conditions. The charging and discharging was performed as one cycle, and charging and discharging was performed at a high temperature (45°C) for 100 cycles.

Subsequently, DC-iR is calculated through a voltage drop occurring in a state where a discharge pulse is applied for 10 seconds from SOC 50% to 2.5 C, and the increase rate of resistance (%) is calculated by substituting this into equation (3) below. , This is shown in FIG. 3. At this time, the voltage drop was measured using a PNE-0506 charge/discharger (manufacturer: PNE solution, 5 V, 6 A).

Equation (3): resistance increase rate (%) = {(resistance after 100 cycles-initial resistance)/initial resistance} x 100

Referring to Figure 3, the secondary battery of Example 1 with the non-aqueous electrolyte of the present invention has a stable film formed on the positive electrode/negative electrode surface, and when it is charged and discharged for a long time at a high temperature, the resistance increase rate compared to the secondary battery of Comparative Example 1 It can be seen that this is significantly reduced.

Experimental Example 4. Evaluation of SEI film formation

The secondary batteries prepared in Example 1 and Comparative Example 1 were charged with 0.1C CC-CV to SOC 30%, respectively, activated with 0.05C cut-off, and then degassed.

Subsequently, the discharge capacity was measured using a PNE-0506 charge/discharger (manufacturer: PNE solution, 5 V, 6 A), and the resulting capacity-voltage curve was firstly differentiated to show the differential capacity curve obtained in FIG. 4. Shown.

Looking at Figure 4, the lithium secondary battery of Example 1 with the non-aqueous electrolyte of the present invention containing the additive was confirmed that the decomposition peak (peak) occurs in the electrolyte decomposition near the 1.8V and 2.2V voltage. Through this behavior, when the additive was included, it can be confirmed that another type of SEI film was additionally formed on the surface of the cathode.

Experimental Example 5. Evaluation of metal (Mn) dissolution

A positive electrode active material (LiMn ₂ O ₄ ), carbon black as a conductive material, and polyvinylidene fluoride (PVDF) as a binder are added to the solvent N-methyl-2-pyrrolidone (NMP) in a weight ratio of 90:7.5:2.5. Thus, a positive electrode mixture slurry (solid content: 50% by weight) was prepared. The positive electrode mixture slurry was applied to a positive electrode current collector (Al foil) having a thickness of 20 μm, dried and roll-pressed to prepare a positive electrode.

Subsequently, the positive electrode was charged into the non-aqueous electrolyte solution (5 mL) prepared in Example 2 and Comparative Example 1, and the electrode was stored for 2 weeks at 0% SOC under 60° C., and then inductively coupled plasma emission spectroscopy (ICP- The concentration of the metal (Mn) eluted in the electrolytic solution was measured using an OES, inductively coupled plasma optical emission spectrophotometer. Subsequently, the amount of the metal measured using the ICP analysis is shown in FIG. 5 below.

Referring to Figure 5, when using the non-aqueous electrolyte solution of Example 2 of the present invention, because the compound containing the Lewis base contained as an additive can effectively remove the Lewis acid, which is a decomposition product of anions of lithium salts generated at high temperatures , It can be seen that, compared to the non-aqueous electrolyte solution of Comparative Example 1, which does not contain an additive, the metal elution suppression effect is significantly improved from a positive electrode containing a lithium-manganese oxide, and less Mn ions are detected.

Experimental Example 6. Evaluation of high temperature storage characteristics

After activating each secondary battery prepared in Example 3 and Comparative Example 2 to 0.1C CC, degassing was performed. Subsequently, it was charged with 0.33 C CC to 4.10 V under a constant current-constant voltage (CC-CV) charging condition at 25° C., and then a 0.05 C current cut was performed and discharged to 0.33 C with 2.5 V under CC conditions. The charging and discharging was performed as 1 cycle, and 3 cycles were performed. Subsequently, the initial discharge capacity was measured using a PNE-0506 charge/discharger (manufacturer: PNE solution, 5 V, 6 A), the SOC was adjusted to 50% SOC, and then 2.5 C pulse was applied for 10 seconds. Then, the initial resistance was calculated through the difference between the voltage before and after the pulse application.

Then, after recharging to 0.3% C CC condition to 100% SOC, it was stored at a high temperature of 45° C. for 20 weeks. After high temperature storage, after 20 weeks, CC-CV charging and discharging was performed with a current of 0.33 C CC, and then discharged after high temperature storage using PNE-0506 charging/discharging (manufacturer: PNE solution, 5 V, 6 A) Was measured.

The discharge capacity retention rate was calculated by substituting the measured initial discharge capacity and the discharge capacity after high-temperature storage measured at 20 weeks into Equation (1), and the results are shown in Table 1 below.

At this time, after 20 weeks, the discharge capacity is specified, and then the direct current internal resistance (hereinafter referred to as "DC-iR") is applied through a voltage drop occurring in a state where a discharge pulse is applied for 10 seconds at SOC 50% to 2.5 C for 10 seconds. (Referred to as &quot;), and substituted in the above formula (2) to calculate the resistance increase rate (%), and then it is shown in Table 1 below. At this time, the voltage drop was measured using a PNE-0506 charge/discharger (manufacturer: PNE solution, 5 V, 6 A).

45℃ 20 weeks storage Capacity retention rate (%) Resistance increase rate (%) Example 3 92.6 -5.03 Comparative Example 2 92.2 -0.93

Looking at Table 1, it can be seen that even after high temperature storage at 45° C. for 20 weeks, the discharge capacity retention rate and the resistance increase rate of the secondary battery of Example 3 were improved compared to the secondary battery of Comparative Example 2. That is, in the lithium secondary battery of the present invention, the acid (HF/PF ₅ ) formed by thermal decomposition of LiPF ₆ is removed by an additive contained in the non-aqueous electrolyte solution, thereby dissolving transition metal at the positive electrode and SEI deterioration at the negative electrode surface. Since it can be suppressed, the deterioration of the SEI at a higher temperature than the existing electrolyte can be improved through the modification of the components of the SEI due to the reduction decomposition of the additive, so it can be seen that the capacity retention rate and the rate of increase in resistance during storage at a high temperature are significantly improved.

Claims (11)

A non-aqueous electrolyte additive that is a compound represented by Formula 1 below:
[Formula 1]

In Chemical Formula 1,
R ₁ to R ₄ are each independently hydrogen or a substituted or unsubstituted alkyl group having 1 to 5 carbon atoms.
The method according to claim 1,
In Formula 1, R ₁ and R ₄ are each independently substituted or unsubstituted alkyl group having 1 to 5 carbon atoms, and R ₂ and R ₃ are each independently hydrogen or substituted or unsubstituted alkyl group having 1 to 5 carbon atoms. The non-aqueous electrolyte additive.
The method according to claim 1,
In Formula 1, R ₁ and R ₄ are each independently substituted or unsubstituted alkyl group having 1 to 4 carbon atoms, and R ₂ and R ₃ are each independently hydrogen or substituted or unsubstituted alkyl group having 1 to 3 carbon atoms. The non-aqueous electrolyte additive.
The method according to claim 1,
In Formula 1, R ₁ and R ₄ are each independently substituted or unsubstituted alkyl group having 1 to 3 carbon atoms, and R ₂ and R ₃ are hydrogen.
The method according to claim 1,
The compound represented by Chemical Formula 1 is a non-aqueous electrolyte additive that is a compound represented by Chemical Formula 1a:
[Formula 1a]

A non-aqueous electrolyte solution for a lithium secondary battery comprising a lithium salt, an organic solvent, and a non-aqueous electrolyte solution additive of claim 1 as a first additive.
The method according to claim 6,
The content of the non-aqueous electrolyte additive is a non-aqueous electrolyte solution for a lithium secondary battery of 0.01 to 5% by weight based on the total weight of the non-aqueous electrolyte for lithium secondary batteries.
The method according to claim 7,
The content of the non-aqueous electrolyte additive is a non-aqueous electrolyte solution for a lithium secondary battery that is 0.1 to 3% by weight based on the total weight of the non-aqueous electrolyte for the lithium secondary battery.
The method according to claim 6,
The non-aqueous electrolyte solution for the lithium secondary battery is lithium that further comprises at least one selected from the group consisting of vinylene carbonate (VC), 1,3-propanesultone (PS) and ethylene sulfate (Esa) as a second additive. Non-aqueous electrolyte for secondary batteries.
The method according to claim 6,
The non-aqueous electrolyte solution for the lithium secondary battery is a halogen-substituted or unsubstituted cyclic carbonate-based compound, nitrile-based compound, phosphate-based compound, borate-based compound, lithium salt-based compound, sulfate-based compound, sultone-based compound, fluorinated benzene-based compound and silane-based compound Non-aqueous electrolyte solution for a lithium secondary battery that further comprises at least one selected from the group consisting of as an additive for forming SEI.
A lithium secondary battery comprising the non-aqueous electrolyte solution for a lithium secondary battery of claim 6.

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