KR20220163631A - Additives for non-aqueous electrolyte, non-aqueous electrolyte comprising the same and lithium secondary battery - Google Patents

Abstract

The present invention relates to an additive for a non-aqueous electrolyte including a compound represented by chemical formula 1 capable of improving the lifespan characteristics of a lithium secondary battery by forming an electrode-electrolyte interface that is stable and has low resistance even at high temperatures, a non-aqueous electrolyte, and a lithium secondary battery including the same.

Description

Additives for non-aqueous electrolytes, non-aqueous electrolytes and lithium secondary batteries containing the same

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

Recently, personal IT devices and computer networks have been developed due to the development of the information society, and as the dependence on electrical energy in the society as a whole has increased accordingly, the development of battery technology for efficiently storing and utilizing electrical energy is required.

In particular, as interest in solving environmental problems and realizing a sustainable recycling-type society has emerged, research on electrical storage devices such as lithium ion batteries and electric double-layer capacitors has been extensively conducted.

A lithium ion battery is in the limelight as a battery system with the highest theoretical energy density among electrical storage devices.

The lithium ion battery is largely composed of a positive electrode composed of a transition metal oxide containing lithium, a negative electrode capable of storing lithium, an electrolyte serving as a medium for delivering lithium ions, and a separator, and in the case of a dual electrolyte, the stability of the battery ( As it is known as a component that greatly affects stability and safety, etc., many studies are being conducted on it.

On the other hand, as charging and discharging of the lithium secondary battery progresses, the cathode active material is structurally collapsed due to decomposition products of lithium salts contained in the electrolyte, and thus the performance of the cathode may deteriorate. In addition, when the anode structure collapses, transition metal ions from the cathode surface can be eluted. The transition metal ions thus eluted are electro-deposited on the anode or cathode, increasing the anode resistance, deteriorating the cathode, and destroying the solid electrolyte interphase (SEI), resulting in additional electrolyte decomposition and subsequent battery resistance. increase and life deterioration.

This deterioration in battery performance tends to be further accelerated when the potential of the positive electrode increases or when the battery is exposed to high temperatures.

Accordingly, there is an urgent need to research an electrolyte capable of forming a stable SEI film on the electrode surface in order to suppress the elution of transition metal ions from the anode or prevent deterioration of the cathode.

Korean Patent Publication No. 2014-0043662

An object of the present invention is to provide an additive for a non-aqueous electrolyte containing a compound capable of forming a stable and low-resistance film on the surface of an electrode even at a high temperature.

In addition, the present invention is intended to provide a non-aqueous electrolyte for a lithium secondary battery capable of forming a solid film on an electrode surface by including the additive for a non-aqueous electrolyte.

In addition, the present invention is intended to provide a lithium secondary battery having improved low-temperature capacity characteristics and high-temperature durability by including the non-aqueous electrolyte for a lithium secondary battery.

In order to achieve the above object, the present invention

Provided is an additive for a non-aqueous electrolyte comprising a compound represented by Formula 1 below.

[Formula 1]

In Formula 1,

R ₁ is hydrogen or an alkyl group having 1 to 3 carbon atoms;

n is an integer from 3 to 8;

In addition, the present invention provides a non-aqueous electrolyte for a lithium secondary battery including the additive for a non-aqueous electrolyte.

In addition, the present invention provides a lithium secondary battery including the non-aqueous electrolyte for a lithium secondary battery.

The compound represented by Formula 1 of the present invention includes an acrylate group and a fluorine-substituted alkyl group having 3 or more carbon atoms in its structure, thereby forming a strong film containing fluorine on the surface of the electrode. The non-aqueous electrolyte including the same forms an electrode-electrolyte interface with low resistance, and can effectively control the elution of the transition metal from the anode. As a result, a lithium secondary battery capable of reducing battery swelling while having excellent high-temperature storage characteristics and high-temperature cycle characteristics may be implemented. The non-aqueous electrolyte of the present invention can be particularly useful for high-output batteries used together with high-capacity active materials such as high-nickel-based cathode active materials.

The following drawings attached to this specification 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 the drawings. It should not be construed as limiting.
1 is a ¹ H-NMR graph of a compound represented by Chemical Formula 1-1.

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

The terms or words used in this specification and claims should not be construed as being limited to ordinary or dictionary meanings, and the inventors may appropriately define the concept of terms in order to explain their invention in the best way. It should be interpreted as a meaning and concept consistent with the technical idea of the present invention based on the principle that there is.

In addition, terms used in this specification are only used to describe exemplary embodiments, and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly dictates otherwise.

Prior to describing the present invention, in this specification, terms such as "comprise", "comprise" or "have" are intended to indicate that embodied features, numbers, steps, components, or combinations thereof exist. However, it should be understood that it does not preclude the presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

Meanwhile, in the description of "carbon number a to b" in the present specification, "a" and "b" mean the number of carbon atoms included in a specific functional group. That is, the functional group may include “a” to “b” carbon atoms. For example, "an alkylene group having 1 to 5 carbon atoms" refers to 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 ₃ )CH-, -CH(CH ₃ )CH ₂ - and -CH(CH ₃ )CH ₂ CH ₂ - and the like.

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

In addition, in this specification, unless otherwise defined, "substitution" means that at least one hydrogen bonded to carbon is substituted with an element other than hydrogen, for example, with an alkyl group having 1 to 6 carbon atoms or fluorine. means substituted.

Additives for non-aqueous electrolytes

An additive for a non-aqueous electrolyte according to an embodiment of the present invention includes a compound represented by Formula 1 below.

[Formula 1]

In Formula 1,

R ₁ is hydrogen or an alkyl group having 1 to 3 carbon atoms;

n is an integer from 3 to 8;

In Formula 1, R ₁ is hydrogen, n may be an integer of 4 to 8, and specifically n may be an integer of 5 to 8.

When the integer of n satisfies the above range, the thermal properties of the compound itself can be improved, and the stability of the film formed therefrom can be expected. If, in Formula 1, if n is less than 3, as the molecule becomes smaller and the content of elemental fluorine becomes smaller, the boiling point is lowered, the flame retardancy is lowered, and the high temperature durability is lowered while becoming vulnerable to electrochemical decomposition. Therefore, deterioration in gas generation and swelling characteristics may occur during high-temperature storage. In addition, in Formula 1, when n exceeds 8, the material viscosity and non-polarity increase as the fluorine element is excessively contained, and solubility in the electrolyte decreases, resulting in poor battery performance.

Preferably, the compound represented by Formula 1 may include at least one of the compounds represented by Formulas 1-1 and 1-2 below.

[Formula 1-1]

[Formula 1-2]

The compound represented by Formula 1 can form a solid SEI film containing elemental fluorine on the surface of the negative electrode while the double bond (C=C) functional group included in the molecular structure causes an electrochemical reaction during the electrochemical decomposition reaction. . In addition, an alkyl group substituted with a fluorine element having excellent flame retardancy and incombustibility included in the molecular structure can form a passivation film capable of securing excellent oxidation resistance while serving as a radical scavenger caused by elemental fluorine on the surface of the anode. As a result, side reactions between the electrode and the electrolyte are controlled, and thus a lithium secondary battery with improved lifespan characteristics at room temperature and low temperature can be provided.

In particular, since the compound represented by Formula 1 of the present invention contains an ethylene group (-CH ₂ -CH ₂ -) between the acrylate functional group and the terminal fluorine-substituted alkyl group, 2,2,3,3,4,4 Compared to compounds containing a methylene group (-CH ₂ -) between an acrylate functional group and a terminal fluorine-substituted alkyl group, such as ,4-heptafluorobutyl acrylate, the flexibility of the compound increases due to the increase in the molecular chain of the linking group. As a result, the film derived from these compounds can form a film with improved durability on the negative electrode surface.

In addition, when three or more oxygen elements are included in the molecular structure, there is a disadvantage in that the effect is limited because it causes a decrease in oxidation stability.

As described above, the compound represented by Chemical Formula 1 of the present invention includes two oxygen elements in the molecular structure, and the acrylate functional group and the terminal fluorine-substituted alkyl group are linked (bonded) through an ethylene group (-CH ₂ -CH ₂ -). ), as well as suppressing the increase in interface resistance by forming a solid SEI with low resistance on the electrode surface before side reactions occur, and preventing side reactions between the electrode and electrolyte by preventing the electrode surface from being exposed. . As a result, since the elution of transition metals from the positive electrode due to film collapse can be effectively controlled, high-temperature stability can be improved, and thus, a lithium secondary battery capable of reducing battery swelling while having excellent high-temperature storage characteristics and high-temperature cycle characteristics can be implemented. have.

Nonaqueous Electrolyte for Lithium Secondary Battery

In addition, the non-aqueous electrolyte according to an embodiment of the present invention includes an additive for non-aqueous electrolyte including the compound represented by Formula 1 above.

The non-aqueous electrolyte may further include a lithium salt, an organic solvent, and other electrolyte additives.

(1) Additives for non-aqueous electrolytes

Since the description of the compound represented by Formula 1 overlaps with the above description, the description thereof will be omitted.

Meanwhile, according to one embodiment of the present invention, the additive for the nonaqueous electrolyte may be included in an amount of 0.1 wt% to 5 wt%, more specifically, 0.5 wt% to 3 wt% based on the total weight of the nonaqueous electrolyte.

When the content of the additive for the non-aqueous electrolyte satisfies the above range, a stable film can be formed to effectively suppress the elution of transition metals from the anode at high temperatures, so that excellent high-temperature durability can be realized. That is, when the additive for the non-aqueous electrolyte is included in an amount of 0.1% by weight or more in the non-aqueous electrolyte, the film-forming effect is improved and a stable SEI film is formed even when stored at high temperature, thereby preventing an increase in resistance and a decrease in capacity even after storage at a high temperature, thereby preventing overall performance can improve In addition, when the additive for the non-aqueous electrolyte is included in an amount of 5% by weight or less, it is possible to prevent an excessively thick film from being formed during initial charging, thereby preventing an increase in resistance, thereby preventing deterioration in initial capacity and output characteristics of the secondary battery.

(2) lithium salt

As the lithium salt, those commonly used in electrolytes for lithium secondary batteries may be used without limitation, for example, including Li ⁺ as a cation and F ^- , Cl ^- , Br ^- , I ^- , NO ₃ ^- as an anion, N(CN) ₂ ^- , BF ₄ ^- , ClO ₄ ^- , B ₁₀ Cl ₁₀ ^- , AlCl ₄ ^- , AlO ₄ ^- , PF ₆ ^- , CF ₃ SO ₃ ^- , CH ₃ CO ₂ ^- , CF ₃ CO ₂ ^- , AsF ₆ ^- , SbF ₆ ^- , CH ₃ SO ₃ ^- , (CF ₃ CF ₂ SO ₂ ) ₂ N ^- , (CF ₃ SO ₂ ) ₂ N ^- , (FSO ₂ ) ₂ N ^- , 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 ^- , (CF ₃ ) ₆ P ^- , C ₄ F ₉ SO ₃ ^- , CF ₃ CF ₂ SO ₃ ^- , CF ₃ CF ₂ (CF ₃ ) ₂ CO ^- , (CF ₃ SO ₂ ) at least one selected from the group consisting of ₂ CH ^- , CF ₃ (CF ₂ ) ₇ SO ₃ ^- and SCN ^- .

Specifically, the lithium salt is LiCl, LiBr, LiI, LiBF ₄ , LiClO ₄ , LiB ₁₀ Cl ₁₀ , LiAlCl ₄ , LiAlO ₄ , LiPF ₆ , LiCF ₃ SO ₃ , LiCH ₃ CO ₂ , LiCF ₃ CO ₂ , LiAsF ₆ , LiSbF ₆ , LiCH ₃ SO ₃ , LiFSI (Lithium bis(fluorosulfonyl) imide, LiN(SO ₂ F) ₂ ), LiBETI (lithium bis(pentafluoroethanesulfonyl) imide, LiN(SO ₂ CF ₂ CF ₃ ) ₂ and LiTFSI (lithium It may include a single material or a mixture of two or more selected from the group consisting of bis(trifluoromethanesulfonyl) imide and LiN(SO ₂ CF ₃ ) ₂ ) In addition to these, lithium salts commonly used in electrolytes of lithium secondary batteries may be used without limitation. can

The lithium salt may be appropriately changed within a generally usable range, but in order to obtain an optimal effect of forming a film for preventing corrosion on the electrode surface, it is included in the electrolyte at a concentration of 0.8 M to 3.0 M, specifically 1.0 M to 3.0 M. can

If the concentration of the lithium salt is less than 0.8 M, the mobility of lithium ions is reduced, and thus capacity characteristics may be deteriorated. If the concentration of the lithium salt exceeds 3.0 M, the viscosity of the non-aqueous electrolyte may be excessively increased, and the impregnability of the electrolyte may be deteriorated, and the film-forming effect may be reduced.

(3) organic solvent

As the organic solvent, various organic solvents commonly used in lithium electrolytes can be used without limitation, and specifically, decomposition due to oxidation reactions or the like can be minimized in the charging and discharging process of a secondary battery, and desired characteristics can be exhibited together with additives. There is no limit to the type of what can be done.

For example, as the organic solvent, a high-viscosity cyclic carbonate-based organic solvent that easily dissociates lithium salts in the electrolyte due to its high permittivity may be used. In addition, the organic solvent may be used by mixing a linear carbonate-based organic solvent with the environmental carbonate-based organic solvent at an appropriate ratio in order to prepare an electrolyte having higher electrical conductivity.

The cyclic carbonate-based organic solvent is a high-viscosity organic solvent that has a high dielectric constant and can easily dissociate lithium salts in the electrolyte. Specific examples thereof include ethylene carbonate (EC), propylene carbonate (PC), and 1,2-butylene It may contain at least one organic solvent selected from the group consisting of carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate and vinylene carbonate, among which ethylene carbonate can include

In addition, the linear carbonate-based organic solvent is an organic solvent having a low viscosity and a low dielectric constant, and typical examples thereof include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, and ethylmethyl carbonate ( EMC), at least one organic solvent selected from the group consisting of methylpropyl carbonate and ethylpropyl carbonate may be used, and specifically, ethylmethyl carbonate (EMC) may be included.

The organic solvent of the present invention may be used by mixing a cyclic carbonate-based organic solvent and a linear carbonate-based organic solvent, wherein the cyclic carbonate-based organic solvent:linear carbonate-based organic solvent has a volume ratio of 10:90 to 80:20, specifically 50 :50 to 70:30 volume ratio.

In addition, the organic solvent may further include a linear ester-based organic solvent and/or a cyclic ester-based organic solvent in addition to the cyclic carbonate-based organic solvent and/or the linear carbonate-based organic solvent in order to prepare an electrolyte having high ionic conductivity. may be

Specific examples of the linear ester-based organic solvent include at least one organic solvent selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, and butyl propionate. can be heard

In addition, the cyclic ester-based organic solvent is a specific example of at least one compound selected from the group consisting of γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone and ε-caprolactone. can be used

On the other hand, other components except for the organic solvent in the non-aqueous electrolyte of the present invention, such as the additive for non-aqueous electrolyte of the present invention, lithium salt, and other additives, all may be organic solvents unless otherwise specified.

(4) Other additives

On the other hand, the nonaqueous electrolyte according to an embodiment of the present invention is used together with the additive to form a stable film on the surface of the negative electrode and the positive electrode without greatly increasing the initial resistance along with the effect of the additive, or in the nonaqueous electrolyte. Other additives capable of suppressing decomposition of the solvent and improving the mobility of lithium ions may be further included.

These other additives are not particularly limited as long as they can form stable films on the surfaces of the positive and negative electrodes.

Specifically, the other additives may include at least one additive selected from the group consisting of a cyclic carbonate-based compound, a halogen-substituted carbonate-based compound, a nitrile-based compound, a phosphate-based compound, a borate-based compound, and a lithium salt-based compound as representative examples thereof. can

Specifically, the cyclic carbonate-based compound forms a stable SEI film mainly on the surface of the negative electrode during battery activation, thereby improving battery durability. The cyclic carbonate-based compound may include vinylene carbonate (VC) or vinylethylene carbonate, and may be included in an amount of 3% by weight or less based on the total weight of the non-aqueous electrolyte. When the content of the cyclic carbonate-based compound in the nonaqueous electrolyte exceeds 3% by weight, cell swelling inhibition performance and initial resistance may be deteriorated.

The halogen-substituted carbonate-based compound may include fluoroethylene carbonate (FEC), and may be included in an amount of 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 performance may deteriorate.

In addition, the nitrile-based compound is succinonitrile, adiponitrile (Adn), acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentane carbonitrile, cyclohexane carbonitrile, In the group consisting of 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile and at least one or more selected compounds.

The nitrile-based compound may serve as a supplement to form an anode SEI film, suppress decomposition of a solvent in the electrolyte, and improve mobility of lithium ions. These nitrile-based compounds 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 content 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 surface of the electrode, and battery performance may deteriorate.

In addition, since the phosphate-based compound stabilizes PF ₆ anions in the electrolyte and helps to form positive and negative electrode films, durability of the battery can be improved. These phosphate-based compounds include lithium difluoro(bisoxalato)phosphate (LiDFOP), LiPO ₂ F ₂ , tris(trimethylsilyl) phosphate, tris(trimethylsilyl) phosphite, tris(2,2,2-trifluoro) roethyl) phosphate and at least one compound selected from the group consisting of tris (trifluoroethyl) phosphite, and may be included in an amount of 3% by weight or less based on the total weight of the non-aqueous electrolyte.

The borate-based compound promotes the separation of ion pairs of lithium salts, can improve the mobility of lithium ions, can reduce the interfacial resistance of the SEI film, and materials such as LiF, which are generated during battery reactions and are not well separated By dissociation, problems such as generation of hydrofluoric acid gas can be solved. Such a borate-based compound may include lithium bioxalylborate (LiBOB, LiB(C ₂ O ₄ ) ₂ ), lithium oxalyldifluoroborate or tetramethyl trimethylsilylborate (TMSB), based on the total weight of the non-aqueous electrolyte It may be included in 3% by weight or less.

In addition, the lithium salt-based compound is a compound different from the lithium salt included in the non-aqueous electrolyte, and may include one or more compounds selected from the group consisting of LiODFB and LiBF ₄ , and is 3% by weight or less based on the total weight of the non-aqueous electrolyte. can include

The other additives may be used in combination of two or more, and may be included in an amount of 10 wt % or less, specifically 0.01 wt % to 10 wt %, and preferably 0.1 to 5.0 wt %, based on the total amount of the electrolyte.

When the content of the other additives is less than 0.01% by weight, the high-temperature storage characteristics and gas reduction effect to be realized from the additives are insignificant, and when the content of the other additives exceeds 10% by weight, side reactions in the electrolyte during charging and discharging of the battery are excessive there is a possibility that it will happen In particular, if the other additives are added in excess, they may not be sufficiently decomposed and may exist as unreacted or precipitated in the electrolyte at room temperature. Accordingly, resistance may increase, and life characteristics of the secondary battery may be deteriorated.

lithium secondary battery

Next, the lithium secondary battery according to the present invention will be described.

The lithium secondary battery according to the present invention includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte, wherein the non-aqueous electrolyte is the non-aqueous electrolyte according to the present invention. Since the non-aqueous electrolyte has been described above, a description thereof will be omitted, and other components will be described below.

(1) anode

The cathode according to the present invention may include a cathode active material layer including a cathode active material, and if necessary, the cathode active material layer may further include a conductive material and/or a binder.

The cathode active material is a compound capable of reversible intercalation and deintercalation of lithium, and specifically, may include a lithium composite metal oxide containing lithium and at least one metal such as cobalt, manganese, nickel, or aluminum. have. More specifically, the lithium composite metal oxide may include a lithium-nickel-manganese-cobalt-based oxide represented by the following Chemical Formula 2 in that it can improve capacity characteristics and stability of a battery.

[Formula 2]

Li(Ni _x Co _y Mn _z ) O ₂

(In Formula 2, 0 <x <1, 0 <y <1, 0 <z <1, x + y + z = 1)

Specifically, the lithium composite metal oxide may be a lithium composite transition metal oxide having a nickel content of transition metal of 50 atm% or more, preferably 60 atm% or more, and a representative example thereof is Li(Ni _0.5 Mn _0.3 Co _0.2 )O ₂ , Li(Ni _0.5 Mn _0.2 Co _0.3 )O ₂ , Li(Ni _0.6 Mn _0.2 Co _0.2 )O ₂ , Li(Ni _0.7 Mn _0.15 Co _0.15 )O ₂ or and Li(Ni _0.8 Mn _0.1 Co _0.1 )O ₂ .

In addition to the lithium-nickel-manganese-cobalt-based oxide, the cathode active material may include a lithium-manganese-based oxide (eg, LiMnO ₂ , LiMn ₂ O ₄ , etc.), a lithium-cobalt-based oxide (eg, LiCoO ₂ , etc.), Lithium-nickel-based oxide (eg, LiNiO ₂ , etc.), lithium-nickel-manganese-based oxide (eg, LiNi _1-Y Mn _Y O ₂ (where 0<Y<1), LiMn _2-z Ni _z O ₄ (wherein 0<Z<2), etc.), lithium-nickel-cobalt-based oxide (for example, LiNi _1-Y1 Co _Y1 O ₂ (wherein 0<Y1<1), etc.), Lithium-manganese-cobalt-based oxides (eg, LiCo _1-Y2 Mn _Y2 O ₂ (where 0<Y2<1), LiMn _2-z1 Co _z1 O ₄ (where 0<Z1<2), etc. ), or a lithium-nickel-cobalt-transition metal (M) oxide (e.g., Li(Ni _p2 Co _q2 Mn _r3 M _S2 ) O ₂ where M is Al, Fe, V, Cr, Ti, Ta , It is selected from the group consisting of Mg and Mo, and p2, q2, r3 and s2 are atomic fractions of independent elements, respectively, 0 <p2 <1, 0 <q2 <1, 0 <r3 <1, 0 <s2 < 1, p2+q2+r3+s2=1)), and the like, and any one or two or more of these compounds may be included.

Such a cathode active material may be LiCoO ₂ , LiMnO ₂ , LiNiO ₂ , or lithium nickel cobalt aluminum oxide (eg, Li(Ni _0.8 Co _0.15 Al _0.05 ) O ₂ , etc.).

The positive electrode active material may be included in an amount of 90% to 99% by weight, specifically 93% to 98% by weight, based on the total weight of solids in the positive electrode active material layer.

The conductive material is not particularly limited as long as it has conductivity without causing a chemical change in the battery. 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 having a highly developed crystal structure; conductive fibers such as carbon fibers and metal fibers; metal powders such as carbon fluoride, aluminum, and nickel powder; conductive whiskers 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 solids in the positive electrode active material layer.

The binder is a component that serves to improve adhesion between the positive electrode active material particles and adhesion between the positive electrode 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 solids in the positive electrode active material layer. Examples of such a binder include a fluororesin-based binder including polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE); rubber-based binders including styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber, and styrene-isoprene rubber; cellulosic binders including carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, and regenerated cellulose; A polyalcohol-based binder containing polyvinyl alcohol; polyolefin binders including polyethylene and polypropylene; polyimide-based binders; polyester binders; and silane-based binders.

The positive electrode of the present invention as described above may be manufactured according to a positive electrode manufacturing method known in the art. For example, in the positive electrode, a positive electrode active material layer is formed by applying a positive electrode slurry prepared by dissolving or dispersing a positive electrode active material, a binder, and/or a conductive material in a solvent on a positive electrode current collector, followed by drying and rolling; Alternatively, it may be prepared by casting the positive electrode active material layer on a separate support and then laminating a film obtained by peeling the support on a positive electrode current collector.

The cathode current collector is not particularly limited as long as it does not cause chemical change in the battery and has conductivity. For example, stainless steel, aluminum, nickel, titanium, fired carbon, or carbon on the surface of aluminum or stainless steel. , those surface-treated with nickel, titanium, silver, etc. 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 provides a desired viscosity when the cathode active material and optionally a binder and a conductive material are included. For example, the active material slurry containing the cathode active material and, optionally, the binder and the conductive material may have a solid concentration of 10 wt% to 70 wt%, preferably 20 wt% to 60 wt%.

(2) Cathode

Next, the cathode is described.

The negative electrode according to the present invention includes a negative electrode active material layer including a negative electrode active material, and the negative electrode active material layer may further include a conductive material and/or a binder, if necessary.

The anode active material includes lithium metal, a carbon material capable of reversibly intercalating/deintercalating lithium ions, a metal or an alloy of these metals and lithium, a metal composite oxide, a material capable of doping and undoping lithium, and at least one selected from the group consisting of transition metal oxide and transition metal oxide.

As the carbon material capable of reversibly intercalating/deintercalating the lithium ion, any carbon-based negative electrode active material commonly used in lithium ion secondary batteries may be used without particular limitation, and typical examples thereof include crystalline carbon, Amorphous carbon or a combination thereof may be used. Examples of the crystalline carbon include graphite such as amorphous, plate-like, flake-like, 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, calcined coke, and the like.

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

Examples of the metal composite 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, Groups 1, 2, and 3 elements of the periodic table, halogen; 0<x≤1;1≤y≤3; 1≤z≤8) Anything selected from the group may be used.

Materials capable of doping and undoping the lithium include Si, SiO _x (0<x≤2), Si—Y alloys (Y is an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element, a transition metal, It is an element selected from the group consisting of rare earth elements and combinations thereof, but not Si), Sn, SnO ₂ , Sn—Y (Y is an alkali metal, an alkaline earth metal, a group 13 element, a group 14 element, a transition metal, and a rare earth element). It is an element selected from the group consisting of elements and combinations thereof, but not Sn), and the like, and at least one of these and SiO ₂ may be mixed and used. The element Y is Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db (dubnium), 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, Se, Te, Po, and combinations thereof.

Examples of the transition metal oxide include lithium-containing titanium composite 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 solids in the negative active material layer.

The conductive material is a component for further improving the conductivity of the negative 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 active material layer. The conductive material is not particularly limited as long as it has conductivity without causing chemical change in the battery, and examples thereof include 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; metal powders such as carbon fluoride, aluminum, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives may be used.

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 active material layer. Examples of such binders include fluororesin-based binders including polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE); rubber-based binders including styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber, and styrene-isoprene rubber; cellulosic binders including carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, and regenerated cellulose; A polyalcohol-based binder containing polyvinyl alcohol; polyolefin binders including polyethylene and polypropylene; polyimide-based binders; polyester binders; and silane-based binders.

The negative electrode may be manufactured according to a negative electrode manufacturing method known in the art. For example, the negative electrode is a method of forming a negative electrode active material layer by applying a negative electrode active material slurry prepared by dissolving or dispersing a negative electrode active material, optionally a binder and a conductive material in a solvent on a negative electrode current collector, and then rolling and drying the negative electrode active material layer. It may be manufactured by casting the negative electrode active material layer on a separate support and then laminating a film obtained by peeling the support on the negative electrode current collector.

The negative current collector generally has a thickness of 3 to 500 μm. The negative electrode current collector is not particularly limited as long as it does not cause chemical change in the battery and has high conductivity. For example, it is made of copper, stainless steel, aluminum, nickel, titanium, fired carbon, copper or stainless steel. A surface treated with carbon, nickel, titanium, silver, or the like, an aluminum-cadmium alloy, or the like may be used. In addition, like the positive electrode current collector, fine irregularities may be formed on the surface to enhance the bonding strength 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.

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

(3) Separator

The lithium secondary battery according to the present invention includes a separator between the positive electrode and the negative electrode.

The separator separates the negative electrode and the positive electrode and provides a passage for the movement of lithium ions. As long as it is used as a separator in a lithium secondary battery, it can be used without particular limitation. It is desirable that this excellent

Specifically, a porous polymer film as a separator, for example, a porous polymer film made of polyolefin polymers such as ethylene homopolymer, propylene homopolymer, ethylene/butene copolymer, ethylene/hexene copolymer, and ethylene/methacrylate copolymer. Alternatively, a laminated structure of two or more layers thereof may be used. In addition, conventional porous non-woven fabrics, for example, non-woven fabrics made of high melting point glass fibers, polyethylene terephthalate fibers, and the like may be used. In addition, a coated separator containing a ceramic component or a polymer material may be used to secure heat resistance or mechanical strength, and may be selectively used in a single-layer or multi-layer structure.

The lithium secondary battery according to the present invention as described above can be usefully used in portable devices such as mobile phones, notebook computers, digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs).

Accordingly, according to another embodiment of the present invention, a battery module including the lithium secondary battery as a unit cell and a battery pack including the same are provided.

The battery module or battery pack may include a power tool; electric vehicles, including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); Alternatively, it may be used as a power source for one or more medium or large-sized devices among power storage systems.

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

The lithium secondary battery according to the present invention can be used not only as a battery cell used as a power source for a small device, but also can be preferably used as a unit cell in a medium-large battery module including a plurality of battery cells.

Hereinafter, the present invention will be described in detail through examples.

At this time, the embodiments according to the present invention may 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 completely explain the present invention to those skilled in the art.

Example

I. Synthesis of non-aqueous electrolyte additives

Example 1. Synthesis of Compound Represented by Chemical Formula 1-1

500㎖ ethyl acetate was added to a reactor maintained at 10 ° C, and 72.84 g (0.2 mole) of tridecafluoro octanol (tridecafluoro octanol, manufactured by TCI) and 24.3 g (0.24 mole) of trimethylamine (trimethyl amine, Samcheon Chemical) ) was dissolved, and 21.7 g of acrylolyl chloride (0.24 mole, manufactured by TCI) was slowly added dropwise while stirring the mixture.

Then, the mixture was stirred at room temperature for 2 hours, and after the reaction was completed, 500 ml of the mixture was added and mixed while separating water and an organic layer.

After rinsing the organic layer with distilled water three times, the solvent was evaporated using a distillation method to obtain a compound represented by Formula 1-1 (yield: 80%). ¹ H-NMR (A500a Agilent DD2 500 MHz/solvent: Acetone-d6) spectrometer graph for the obtained compound represented by Formula 1-1 is shown in FIG.

Example 2. Synthesis of Compound Represented by Chemical Formula 1-2

Formula 1 in the same manner as in Example 1 except for using 111.4 g (0.24 mole) of 2-(perfluorononyl ethanol) (2-(perfluorononyl ethanol, manufactured by TCI) instead of tridecafluoro octanol. A compound represented by -2 (yield: 75%) was prepared.

II. Secondary battery manufacturing

Example 3.

(manufacture of non-aqueous electrolyte)

Ethylene carbonate (EC): Ethyl methyl carbonate (EMC) was dissolved in 99.5 g of a non-aqueous organic solvent mixed at a volume ratio of 30:70 so that LiPF ₆ was 1.0 M, and then 0.5 g of a compound represented by Formula 1-1 was added as an additive. was added to prepare a non-aqueous electrolyte (see Table 1 below).

(Anode manufacturing)

Cathode active material (LiCoO ₂ ), conductive material (carbon black), and binder (polyvinylidene fluoride) were added to N-methyl-2-pyrrolidone (NMP) as a solvent in a weight ratio of 97.5:1:1.5. A slurry (solids concentration 60% by weight) was prepared. The positive electrode active material slurry was applied to a positive electrode current collector (Al thin film) having a thickness of 15 μm, dried, and then subjected to a roll press to prepare a positive electrode.

(cathode manufacturing)

An anode active material slurry (solid content concentration: 50% by weight) was prepared by adding a cathode active material (graphite), a conductive material (carbon black), and a binder (polyvinylidene fluoride) to distilled water in a weight ratio of 96:0.5:3.5. 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 then rolled pressed to prepare a negative electrode.

(Secondary battery manufacturing)

An electrode assembly was prepared by laminating the positive and negative electrodes prepared by the above method together with a porous polyethylene film as a separator, and then putting it into a battery case, injecting 5 mL of the non-aqueous electrolyte, and sealing the pouch-type lithium secondary battery (battery capacity). 6.24 mAh) was produced.

Example 4.

Except for preparing a non-aqueous electrolyte by dissolving LiPF ₆ to 1.0 M in 99.5 g of a non-aqueous organic solvent and adding 0.5 g of a compound represented by Formula 1-2 as an additive (see Table 1 below), the above procedure A pouch-type lithium secondary battery was manufactured in the same manner as in Example 3.

Example 5.

Except for preparing a non-aqueous electrolyte by dissolving LiPF ₆ to 1.0 M in 99.85 g of a non-aqueous organic solvent and then adding 0.15 g of a compound represented by Formula 1-1 as an additive (see Table 1 below), the above procedure A pouch-type lithium secondary battery was manufactured in the same manner as in Example 3.

Example 6.

Except for preparing a non-aqueous electrolyte by dissolving LiPF ₆ to 1.0 M in 97 g of a non-aqueous organic solvent and then adding 3.0 g of a compound represented by Formula 1-1 as an additive (see Table 1 below), the above Example A pouch type lithium secondary battery was manufactured in the same manner as in 3.

Example 7.

Except for preparing a non-aqueous electrolyte by dissolving LiPF ₆ to 1.0 M in 99.95 g of a non-aqueous organic solvent and then adding 0.05 g of a compound represented by Formula 1-1 as an additive (see Table 1 below), the above procedure A pouch-type lithium secondary battery was manufactured in the same manner as in Example 3.

Comparative Example 1.

A lithium secondary battery was prepared in the same manner as in Example 3, except that LiPF ₆ was dissolved in 100 g of a non-aqueous organic solvent to a concentration of 1.0 M, and a non-aqueous electrolyte was prepared without adding an additive (see Table 1 below). did

Comparative Example 2.

Except for the fact that a non-aqueous electrolyte was prepared by dissolving LiPF ₆ in 99.5 g of a non-aqueous organic solvent to a concentration of 1.0 M and adding 0.5 g of a compound represented by Formula 3 as an additive (see Table 1 below), Example A lithium secondary battery was manufactured in the same manner as in 3.

[Formula 3]

Comparative Example 3.

Except for the fact that a non-aqueous electrolyte was prepared by dissolving LiPF ₆ in 99.5 g of a non-aqueous organic solvent to a concentration of 1.0 M and adding 0.5 g of a compound represented by Formula 4 as an additive (see Table 1 below), Example A lithium secondary battery was manufactured in the same manner as in 3.

[Formula 4]

Comparative Example 4.

LiPF ₆ was dissolved in 99.5 g of a non-aqueous organic solvent to be 1.0 M, and 2,2,3,3,4,4,4-heptafluorobutyl acrylate (manufactured by Merck, CAS No. 424-64- 6) A lithium secondary battery was manufactured in the same manner as in Example 3, except that a non-aqueous electrolyte was prepared by adding 0.5 g (see Table 1 below).

lithium salt organic solvent additive composition Amount added (g) type Amount added (g) Example 3 0.1M LiPF ₆ EC:EMC=30:70 99.5 Formula 1-1 0.5 Example 4 99.5 Formula 1-2 0.5 Example 5 99.85 Formula 1-1 0.15 Example 6 97 Formula 1-1 3 Example 7 99.95 Formula 1-1 0.05 Comparative Example 1 100 - - Comparative Example 2 99.5 Formula 3 0.5 Comparative Example 3 99.5 formula 4 0.5 Comparative Example 4 99.5 HFBA 0.5

In Table 1, the abbreviated names of the compounds are as follows.

HFBA: 2,2,3,3,4,4,4-heptafluoro butyl acrylate

[Experimental Example]

Experimental Example 1. Evaluation of volume change rate during storage at high temperature (80 ° C)

The secondary batteries prepared in Examples 3 to 7 and the secondary batteries prepared in Comparative Examples 1 to 4 were each activated at 0.1C CC. Subsequently, using a PESC05-0.5 charger/discharger (manufacturer: PNE Solution, 5V, 500 mA) at 25 ° C, charge with 0.33C CC up to 4.45V under constant current-constant voltage (CC-CV) charging conditions, and then 0.05 C current cut and discharged at 0.33 C up to 2.5V under CC conditions. Two cycles were performed with the charging and discharging as one cycle. Subsequently, degas was performed, and the initial thickness of the initially charged and discharged lithium secondary battery was measured using TWD-150DM equipment from Two-pls.

Then, the lithium secondary battery was fully charged at 0.33 C/4.45 V constant current-constant voltage, stored at 80° C. for 24 hours (SOC (state of charge) 100%), and then Two-pls, TWD-150DM equipment The thickness change of the lithium secondary battery was measured at room temperature using

The volume change rate (%) was calculated using the thickness ratio after high temperature storage compared to the initial thickness measured as described above, and the results are shown in Table 2 below.

Experimental Example 2. Capacity evaluation after high temperature (60 ℃) storage

The secondary batteries prepared in Examples 3 to 7 and the secondary batteries prepared in Comparative Examples 1 to 4 were each activated at 0.1C CC. Subsequently, CCV charge-CC discharge was performed three times at 0.2C at 4.45V-2.5V using a PESC05-0.5 charger and discharger (manufacturer: PNE solution, 5V, 500 mA) at 25 ° C, and the third capacity was initially capacity was set.

Then, storage at 80 ℃ for 24 hours (SOC (state of charge) 100%), then CCV charge-CC discharge at 0.2C at 4.45V-2.5V 3 times, and after storing the third capacity at high temperature It was set as the capacity.

The capacity retention rate (%) was calculated using the measured initial capacity and the capacity ratio after high temperature storage, and the results are shown in Table 2 below.

Thickness change rate (%) Capacity retention rate (%) Example 3 1.4 88.8 Example 4 3.0 90.5 Example 5 3.6 87.4 Example 6 2.0 86.4 Example 7 5.8 84.8 Comparative Example 1 6.2 84.7 Comparative Example 2 12.5 82.8 Comparative Example 3 11.8 80.2 Comparative Example 4 15.8 78.4

As shown in Table 2, looking at the high-temperature storage characteristics, in the case of the secondary batteries prepared in Examples 3 to 7, it can be confirmed that the thickness change rate and capacity retention rate are improved compared to the secondary batteries prepared in Comparative Examples 1 to 4. . In particular, in the case of using the non-aqueous electrolyte containing HFBA of Comparative Example 4, it can be seen that a relatively low safety cathode film is formed, and thermal stability is lowered, resulting in markedly deterioration in cell durability after high temperature storage.

This characteristic is believed to be due to improved battery high-temperature durability due to improved film performance on the surface of the negative electrode by the additive containing the compound represented by Formula 1.

On the other hand, in the case of the secondary battery of Example 7 having a low additive content of the present invention, it can be seen that the film formation effect is lowered and the cell performance improvement effect is not large compared to the secondary battery of Examples 3 to 6.

Experimental Example 3. Evaluation of low temperature cycle characteristics

The secondary batteries prepared in Examples 3 to 7 and the secondary batteries prepared in Comparative Examples 1 to 4 were each activated at 0.1C CC. Subsequently, at minus 10 ° C, use a PESC05-0.5 charger and discharger (manufacturer: PNE Solution Co., Ltd., 5V, 500 mA) to charge at 0.5C CC up to 4.45V under constant current-constant voltage (CC-CV) charging conditions, and then charge with 0.05 C Current Cut was performed, and discharge was performed at 0.5 C up to 2.5V under CC conditions. 50 cycles were performed with the charging and discharging as one cycle.

At this time, the low-temperature cycle capacity retention rate was calculated using the first discharge capacity and the 50th cycle discharge capacity, and the results are shown in Table 3 below.

-10℃ initial discharge capacity (mAh) 50 cycle capacity retention rate (%) Example 3 2835 90 Example 4 2842 91 Example 5 2851 90 Example 6 2800 91 Example 7 2705 82 Comparative Example 1 2604 78 Comparative Example 2 2744 80 Comparative Example 3 2700 80 Comparative Example 4 2511 76

Looking at Table 3, as the non-aqueous electrolyte of the present invention forms a fluorine-containing negative electrode film that is stable and helpful in the movement of lithium ions at low temperatures, the initial capacity of the secondary batteries of Examples 1 to 4 is about 2800 mAh Above, it can be seen that the capacity retention rate is as high as about 91% or more. At this time, in the case of the secondary battery of Example 7 containing a small amount of additives, it can be seen that the initial capacity and capacity retention rate are relatively reduced compared to the secondary batteries of Examples 3 to 6.

On the other hand, in the case of the secondary batteries of Comparative Examples 1 to 4 not including the additive of the present invention, it can be seen that the initial capacity and capacity retention rate are significantly deteriorated compared to the secondary batteries of Examples 1 to 4.

Claims (10)

An additive for a non-aqueous electrolyte comprising a compound represented by Formula 1 below:
[Formula 1]

In Formula 1,
R ₁ is hydrogen or an alkyl group having 1 to 3 carbon atoms;
n is an integer from 3 to 8;
The method of claim 1,
In Formula 1, R ₁ is hydrogen, and n is an integer of 4 to 8.
The method of claim 1,
In Formula 1, R ₁ is hydrogen, and n is an integer of 5 to 8, an additive for a non-aqueous electrolyte.
The method of claim 1,
The compound represented by Formula 1 is at least one of the compounds represented by Formulas 1-1 and 1-2 below.
[Formula 1-1]

[Formula 1-2]

A non-aqueous electrolyte for a lithium secondary battery comprising the additive for a non-aqueous electrolyte of claim 1.
The method of claim 5,
The additive for the non-aqueous electrolyte is a non-aqueous electrolyte for a lithium secondary battery, which is included in 0.1% to 5% by weight based on the total weight of the non-aqueous electrolyte for a lithium secondary battery.
The method of claim 5,
The additive for the non-aqueous electrolyte is a non-aqueous electrolyte for a lithium secondary battery, which is included in 0.5% to 3% by weight based on the total weight of the non-aqueous electrolyte for a lithium secondary battery.
The method of claim 5,
The non-aqueous electrolyte for a lithium secondary battery further comprises a lithium salt and an organic solvent.
The method of claim 5,
The nonaqueous electrolyte for a lithium secondary battery further comprises at least one other additive selected from the group consisting of a cyclic carbonate-based compound, a halogen-substituted carbonate-based compound, a nitrile-based compound, a phosphate-based compound, a borate-based compound, and a lithium salt-based compound Non-aqueous electrolyte for phosphorus lithium secondary battery.
anode; cathode; a separator interposed between the cathode and anode; and
A lithium secondary battery comprising the non-aqueous electrolyte for a lithium secondary battery of claim 5.

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