KR20240032632A - Non-aqueous electrolyte for lithium secondary battery and lithium secondary battery comprising the same - Google Patents

Abstract

The present invention provides a non-aqueous electrolyte for lithium secondary batteries and a lithium secondary battery containing the same. Specifically, the non-aqueous electrolyte for a lithium secondary battery of the present invention may include a lithium salt, an organic solvent, and a compound represented by Chemical Formula 1 as a first additive. In addition, the present invention provides a lithium secondary battery with improved high-temperature storage characteristics and high-temperature cycling characteristics by including the non-aqueous electrolyte for lithium secondary batteries.

Description

Non-aqueous electrolyte for lithium secondary batteries and lithium secondary batteries containing the same {NON-AQUEOUS ELECTROLYTE FOR LITHIUM SECONDARY BATTERY AND LITHIUM SECONDARY BATTERY COMPRISING THE SAME}

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

As dependence on electrical energy gradually increases in modern society, the development of large-capacity power storage devices that can stably supply power and increase production at the same time is emerging.

Lithium-ion batteries are devices with the highest energy density among commercially available power storage devices, and are used in various applications such as small electronic devices, electric vehicles (EVs), and power storage devices.

In particular, in the case of lithium-ion batteries applied to electric vehicles, high output characteristics are required while maintaining cycle characteristics and performance in various environments.

This lithium ion battery consists of a positive electrode made of a transition metal oxide containing lithium, a negative electrode capable of storing lithium, a non-aqueous electrolyte containing an organic solvent containing a lithium salt, and a separator.

Meanwhile, in the case of lithium hexafluorophosphate (LiPF ₆ ), which is mainly used as the lithium salt, it is easily decomposed at high temperatures to produce Lewis acid by-products such as HF and PF ₅ , and the by-products react with moisture to produce more Lewis acid by-products. (HF)

These Lewis acid by-products can erode the electrode and the passive film formed on the electrode surface, causing elution of transition metal ions from the anode. The eluted transition metal ions accelerate the decomposition of the electrolyte solvent, thereby accelerating gas generation, or by re-deposition on the anode, increasing the resistance of the anode. They also move to the cathode through the electrolyte solution and are then electrodeposited on the cathode. This causes additional consumption of lithium ions and increased resistance due to self-discharge of the cathode or destruction and regeneration of the solid electrolyte interphase (SEI) film.

Since this series of reactions reduces the amount of available lithium ions in the battery, it is a major cause of battery capacity deterioration. In addition, when metal ions electrodeposited on the cathode grow into dendrites, an internal short circuit of the battery occurs, which leads to a decrease in battery safety.

Therefore, it removes Lewis acid by-products (HF and PF ₅ , etc.) generated from thermal decomposition of lithium salt and forms a stable film on the electrode surface to suppress transition metal elution, or the eluted transition metal ions are electrodeposited on the cathode. There is a demand for the development of a non-aqueous electrolyte that can suppress this and improve battery performance such as high rate charge and discharge characteristics as well as safety.

Japanese Patent Publication No. 2012-156054

The present invention provides a non-aqueous electrolyte for lithium secondary batteries that forms a stable film on the electrode surface and includes an additive that is excellent in removing acidic materials and highly reactive Lewis acid by-products formed as decomposition products of salts in the electrolyte. We would like to provide

In addition, the present invention seeks to provide a lithium secondary battery with improved high-temperature storage characteristics and high-temperature cycling characteristics by including the non-aqueous electrolyte for lithium secondary batteries.

In one embodiment of the present invention to achieve the above object,

Contains a lithium salt, an organic solvent and a first additive,

The first additive provides a non-aqueous electrolyte solution for a lithium secondary battery containing a compound represented by the following formula (1).

[Formula 1]

In Formula 1,

Ar is a 5- or 6-membered nitrogen-containing ring,

R ₁ and R ₂ are each independently an alkyl group having 1 to 8 carbon atoms.

In another embodiment of the present invention

A positive electrode containing a positive electrode active material; A negative electrode containing a negative electrode active material; A separator interposed between the anode and the cathode; And it provides a lithium secondary battery containing the non-aqueous electrolyte for the lithium secondary battery.

The non-aqueous electrolyte solution for lithium secondary batteries of the present invention effectively removes Lewis acid by-products, which are by-products of electrolyte salts, by including a compound containing a 5- or 6-membered nitrogen-containing ring group and a phosphoryl group in the structure as an additive. By forming a solid SEI, it can suppress metal elution and reduce gases by suppressing side reactions between the electrolyte and the electrode, thereby improving battery deterioration due to electrode deterioration. Therefore, by applying this non-aqueous electrolyte for lithium secondary batteries, a lithium secondary battery with improved cycle characteristics and high-temperature storage stability can be implemented.

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

The terms and words used in the specification and claims are merely used to describe exemplary embodiments and are not intended to limit the invention.

for example, In this specification, terms such as “comprise,” “comprise,” or “have” are intended to designate the presence of implemented features, numbers, steps, components, or a combination thereof, and only’ is not used. Other parts may be added.

Additionally, in this specification, “%” means weight percent unless explicitly stated otherwise.

In this specification, unless otherwise defined, “substitution” means replacement of at least one hydrogen bonded to carbon with an element other than hydrogen, for example, substitution with an alkyl group having 1 to 5 carbon atoms or a fluorine element. It means that it has been done.

Conventional decomposition products formed by hydro/thermal decomposition of lithium salts, such as hydrogen fluoride (HF), form a film on the electrode surface, and the transition metals constituting the anode are easily eluted into the electrolyte, and the eluted transition metal ions are transferred to the anode. It causes re-deposition and increases the resistance of the anode. Alternatively, the transition metal moved to the cathode through the electrolyte is electrodeposited on the cathode, causing self-discharge of the cathode and destroying the solid electrolyte interphase (SEI) film that gives the cathode its passivation ability, thereby promoting additional electrolyte decomposition reaction and thereby causing the cathode to self-discharge. Increases interfacial resistance.

Since these series of reactions reduce the amount of available lithium ions in the battery, not only does the capacity of the battery deteriorate, but also an increase in resistance occurs due to the accompanying electrolyte decomposition reaction.

The present invention provides a non-aqueous electrolyte for lithium secondary batteries that can oxidize and decompose before the organic solvent to form a solid film on the positive electrode surface by including an additive that can effectively remove the decomposition products of electrolyte salts that cause such deterioration and poor behavior. By including this, the aim is to provide a lithium secondary battery with improved high-rate charging and discharging at high temperatures.

Non-aqueous electrolyte for lithium secondary batteries

Specifically, in one embodiment of the present invention

Contains a lithium salt, an organic solvent and a first additive,

Provided is a non-aqueous electrolyte for a lithium secondary battery containing a compound represented by the following formula (1) as the first additive.

[Formula 1]

In Formula 1,

Ar is a 5- or 6-membered nitrogen-containing ring,

R ₁ and R ₂ are each independently an alkyl group having 1 to 8 carbon atoms.

(1) Lithium salt

First, in the non-aqueous electrolyte for lithium secondary batteries of the present invention, the lithium salt may be those commonly used in electrolytes for lithium secondary batteries without limitation, and for example, includes Li ⁺ as a cation and F ^- as an anion. Cl ^- , Br ^- , I ^- , NO ₃ ^- , 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 ) ₂ CH ^- , CF ₃ (CF ₂ ) ₇ SO ₃ ^- and at least one selected from the group consisting of SCN ^- may be mentioned.

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 , LiN(SO ₂ F) ₂ (Lithium bis(fluorosulfonyl)imide, LiFSI), LiN(SO ₂ CF ₂ CF ₃ ) ₂ (lithium bis(pentafluoroethanesulfonyl)imide, LiBETI) and LiN( SO ₂ CF ₃ ) ₂ (lithium bis(trifluoromethane sulfonyl)imide, LiTFSI) may contain a single substance or a mixture of two or more types, preferably LiBF ₄ , LiPF ₆ , LiN(SO ₂ F) ₂ (LiFSI), LiN(SO ₂ CF ₂ CF ₃ ) ₂ (LiBETI), and LiN(SO ₂ CF ₃ ) ₂ (LiTFSI). It may include a single substance or a mixture of two or more types. In addition to these, lithium salts commonly used in electrolytes of lithium secondary batteries can be used without limitation.

The lithium salt can be appropriately changed within the range commonly used, but in order to obtain the optimal effect of forming an anti-corrosion film on the electrode surface, it should be included in the electrolyte solution at a concentration of 0.8M to 4.0M, specifically 1.0M to 3.0M. You can.

When the concentration of the lithium salt is within the above range, the viscosity of the non-aqueous electrolyte can be controlled to achieve optimal impregnation, and the mobility of lithium ions can be improved to improve the capacity characteristics and cycle characteristics of the lithium secondary battery. there is.

(2) Organic solvent

Additionally, a description of the organic solvent is as follows.

As the non-aqueous organic solvent, various organic solvents commonly used in non-aqueous electrolytes can be used without limitation. Decomposition due to oxidation reactions, etc. during the charging and discharging process of secondary batteries can be minimized, and the desired characteristics can be exhibited together with additives. There is no limit to the types of things that can be done.

Specifically, the non-aqueous organic solvent may include a cyclic carbonate-based organic solvent, a linear carbonate-based organic solvent, or a mixed organic solvent thereof.

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

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

In the present invention, in order to secure high ionic conductivity, a mixture of the cyclic carbonate-based organic solvent and the linear carbonate-based organic solvent can be used. In this case, the cyclic carbonate-based organic solvent and the linear carbonate-based organic solvent are used in a ratio of 10:90 to 50: 50, specifically, may be included in a volume ratio of 20:80 to 40:60.

In addition, in order to prepare an electrolyte solution with high ionic conductivity, the organic solvent is a linear ester-based organic solvent and a cyclic ester that has a lower melting point and is more stable at high temperatures than the cyclic carbonate-based organic solvent and/or the linear carbonate-based organic solvent. It may additionally include at least one organic solvent among the organic solvents.

Representative 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. It may include, specifically, at least one of ethyl propionate and propyl propionate.

The cyclic ester-based organic solvent may include at least one selected from the group consisting of γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, and ε-caprolactone.

Meanwhile, the remainder of the non-aqueous electrolyte solution of the present invention, excluding the lithium salt, the first additive, and the second additive described later, may be organic solvents unless otherwise specified.

(3) First additive

The first additive of the present invention may include a compound represented by the following formula (1).

[Formula 1]

In Formula 1,

Ar is a 5- or 6-membered nitrogen-containing ring,

R ₁ and R ₂ are each independently an alkyl group having 1 to 8 carbon atoms.

The 5- or 6-membered nitrogen-containing ring contained in the structure of the compound represented by Formula 1 is a functional group that functions as a Lewis base, and the lone pair of electrons of the nitrogen atom binds to PF ₅ and decomposes PF ₅ It can suppress the formation of Lewis acid substances such as HF. As a result, it is possible to suppress the deterioration behavior caused by the chemical reaction of the film on the surface of the anode or cathode caused by Lewis acid, thereby preventing further electrolyte decomposition of the battery due to deterioration or destruction of the film, and further preventing self-discharge of the secondary battery. By alleviating, high temperature storage characteristics can be improved.

In addition, the compound represented by Formula 1 contains a phosphoryl group in its structure that can form an inorganic film on the surface of the cathode, thereby suppressing side reactions between the electrolyte and the electrode, reducing gases and reducing battery deterioration. It can be prevented.

In particular, the compound represented by Formula 1 forms a passivation film with high passivation ability on the cathode and anode surfaces through reduction and decomposition of functional groups such as nitrogen-containing rings or phosphoryl groups, thereby preventing the formation of a passive film caused by the instability of the SEI film. It is possible to prevent the self-discharge reaction of the negative electrode caused by the additional reduction decomposition reaction of the electrolyte, and to prevent metal ions from eluting from the positive electrode or from being electrodeposited on the negative electrode, thereby improving the cycle characteristics of the lithium secondary battery and Improvements in high temperature durability, such as capacity characteristics, etc. can be realized.

Meanwhile, the compound represented by Formula 1 may be represented by the following Formula 1A.

[Formula 1A]

In Formula 1A,

R ₁ and R ₂ are each independently an alkyl group having 1 to 8 carbon atoms.

Additionally, in Formula 1A, R ₁ and R ₂ may each independently be an alkyl group having 1 to 5 carbon atoms.

Additionally, in Formula 1A, R ₁ and R ₂ may each independently be an alkyl group having 1 to 3 carbon atoms.

Preferably, the compound represented by the formula 1A may be one of the compounds represented by the following formula 1A-1 or the compound represented by the formula 1A-2.

[Formula 1A-1]

[Formula 1A-2]

Meanwhile, the compound of Formula 1 may be included in an amount of 0.5% to 3.0% by weight based on the total weight of the non-aqueous electrolyte.

When the compound represented by Formula 1 is included in the above range, side reactions caused by additives are prevented and a strong film is formed on the cathode and anode, effectively preventing deterioration of the cathode during rapid charging and discharging, thereby producing a secondary battery with improved overall performance. It can be manufactured. Specifically, if the content of the compound represented by Formula 1 is 0.5% by weight or more, the effect of removing thermal decomposition products of lithium salts such as HF or PF ₅ and forming a film on the surfaces of the cathode and anode can be more stably maintained during the battery operation time. In addition, when the content of the compound represented by Formula 1 is 3.0% by weight or less, the viscosity of the non-aqueous electrolyte solution can be controlled to achieve optimal impregnation, the increase in battery resistance due to additive decomposition can be effectively suppressed, and the electrolyte By not lowering the ionic conductivity, it is possible to prevent a decrease in rate characteristics or low-temperature lifespan characteristics.

More specifically, the compound represented by Formula 1 may be included in an amount of 0.5 wt% to 2.5 wt%, more preferably 0.5 wt% to 2.0 wt%.

(4) Second additive

In addition, the non-aqueous electrolyte for lithium secondary batteries of the present invention prevents the non-aqueous electrolyte from decomposing in a high-power environment, causing cathode collapse, and has low-temperature high-rate discharge characteristics, high-temperature stability, overcharge prevention, and battery expansion suppression effects at high temperatures. In order to improve, second additives may be additionally included in the non-aqueous electrolyte if necessary.

Representative examples of such second additives include cyclic carbonate-based compounds, halogen-substituted carbonate-based compounds, sultone-based compounds, sulfate-based compounds, phosphate-based compounds, borate-based compounds, nitrile-based compounds, benzene-based compounds, amine-based compounds, and silane-based compounds. It may include at least one second additive selected from the group consisting of a compound and a lithium salt-based compound.

The cyclic carbonate-based compound may include vinylene carbonate (VC) or vinylethylene carbonate.

The halogen-substituted carbonate-based compound may include fluoroethylene carbonate (FEC).

The sultone-based compounds include 1,3-propane sultone (PS), 1,4-butane sultone, ethenesultone, 1,3-propene sultone (PRS), 1,4-butene sultone, and 1-methyl-1,3 -At least one compound selected from the group consisting of propene sultone.

The sulfate-based compound may include ethylene sulfate (Esa), trimethylene sulfate (TMS), or methyl trimethylene sulfate (MTMS).

The phosphate-based compounds include lithium difluoro(bisoxalato)phosphate, lithium difluorophosphate, tris(trimethylsilyl)phosphate, tris(2,2,2-trifluoroethyl)phosphate, and tris(trifluorophosphate). One or more compounds selected from the group consisting of ethyl) phosphate may be mentioned.

The borate-based compounds include tetraphenyl borate and lithium oxalyldifluoroborate.

The nitrile-based compounds include succinonitrile, adiponitrile, acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentane carbonitrile, cyclohexane carbonitrile, and 2-fluorobenzo. At least one selected from the group consisting of nitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile Compounds may be mentioned.

The benzene-based compound may include fluorobenzene, and the amine-based compound may include triethanolamine or ethylene diamine.

Examples of the silane-based compound include tetravinylsilane.

The lithium salt-based compound is a compound different from the lithium salt contained in the non-aqueous electrolyte solution, and is selected from the group consisting of LiPO ₂ F ₂ , LiODFB, LiBOB (lithium bisoxalate borate (LiB(C ₂ O ₄ ) ₂ ) and LiBF ₄ One or more types of compounds may be mentioned.

Among these second additives, when at least one of vinylene carbonate, vinylethylene carbonate, and succino nitrile is included, a more robust SEI film can be formed on the surface of the negative electrode during the initial activation process of the secondary battery.

Meanwhile, the second additives may be used in combination of two or more types, and may be included in an amount of 50% by weight or less, specifically 0.01 to 10% by weight, based on the total weight of the non-aqueous electrolyte, and preferably 0.05 to 5.0% by weight. May be included. If the content of the second additive is less than 0.01% by weight, the effect of improving the low-temperature output, high-temperature storage characteristics, and high-temperature lifespan characteristics of the battery is minimal, and if the content of the second additive exceeds 50% by weight, the charging and discharging of the battery is minimal. There is a possibility that side reactions within the electrolyte may occur excessively. In particular, when the additives for forming the SEI film are added in excessive amounts, they may not be sufficiently decomposed at high temperatures and may remain unreacted or precipitated in the electrolyte solution at room temperature. As a result, side reactions that reduce the lifespan or resistance characteristics of the secondary battery may occur.

Lithium secondary battery

In addition, another embodiment of the present invention provides a lithium secondary battery containing the non-aqueous electrolyte for lithium secondary batteries of the present invention.

The lithium secondary battery of the present invention can be manufactured according to a conventional method known in the art, and specifically, an electrode assembly in which a positive electrode, a negative electrode, and a separator between the positive electrode and the negative electrode are sequentially stacked is formed and stored in a battery case. Next, it can be manufactured by adding the non-aqueous electrolyte for lithium secondary batteries of the present invention.

Next, each component of the lithium secondary battery of the present invention will be described in more detail.

(1) anode

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

The positive electrode active material is a compound capable of reversible intercalation and deintercalation of lithium, and is specifically composed of nickel (Ni), cobalt (Co), manganese (Mn), iron (Fe), and aluminum (Al). It may include a lithium composite metal oxide represented by the following formula (2) containing lithium and at least one metal selected from the group.

[Formula 2]

Li _1+a Ni _x Co _y M ¹ _z M ² _w O ₂

In Formula 2,

M ¹ is Mn, Al or a combination thereof,

M ² is at least one selected from the group consisting of Al, Zr, W, Ti, Mg, Ca and Sr, 0≤a≤0.5, 0.55<x<1.0, 0<y≤0.4, 0<z≤0.4, 0 ≤w≤0.1.

The 1+a represents the atomic fraction of lithium in the lithium transition metal oxide, and may be 0≤a≤0.5, preferably 0≤a≤0.2, and more preferably 0≤a≤0.1.

The x represents the atomic fraction of nickel among all transition metal elements in the lithium transition metal oxide, and may be 0.55<x<1.0, specifically 0.6≤x≤0.98, and more specifically 0.6≤x≤0.95.

The y represents the atomic fraction of cobalt among all transition metal elements in the lithium transition metal oxide, and may be 0<y≤0.4, specifically 0<y≤0.3, and more specifically 0.05≤y≤0.3.

The z represents the atomic fraction of the M ¹ element among all transition metal elements in the lithium transition metal oxide, and may be 0<z≤0.4, preferably 0<z≤0.3, and more preferably 0.01≤z≤0.3.

The w represents the atomic fraction of the M ² element among all transition metal elements in the lithium transition metal oxide, and is 0<w≤0.1, preferably 0<w≤0.05, and more preferably 0<w≤0.02.

Specifically, in order to implement a high-capacity battery, the positive electrode active material is Li(Ni _0.6 Mn _0.2 Co _0.2 )O ₂ with a Ni content of 0.55 atm% or more, Li(Ni _0.7 Mn _0.15 Co _0.15 )O ₂ , Li(Ni _0.7 Mn _0.2 Co _0.1 )O ₂ , Li(Ni _0.8 Mn _0.1 Co _0.1 )O ₂ , Li(Ni _0.8 Co _0.15 Al _0.05 )O ₂ , Li( It may include a lithium complex transition metal oxide such as Ni _0.86 Mn _0.07 Co _0.05 Al _0.02 )O ₂ or Li(Ni _0.90 Mn _0.05 Co _0.05 )O ₂ .

In addition, the positive electrode active material of the present invention may be selected from the lithium composite metal oxide represented by Chemical Formula 2, lithium-manganese-based oxide (e.g., LiMnO ₂ , LiMn ₂ O ₄ , etc.), lithium-cobalt-based oxide, depending on the secondary battery application. (e.g., LiCoO _2, etc.), lithium-nickel-based oxide (e.g., LiNiO ₂ , etc.), lithium-nickel-manganese oxide (e.g., LiNi _1-Y Mn _Y O ₂ (0<Y< 1), LiMn _2-z Ni _z O ₄ (0＜Z＜2), lithium-nickel-cobalt-based oxide (for example, LiNi _1-Y1 Co _Y1 O ₂ (0<Y1<1), lithium-manganese -Cobalt-based oxide (e.g., LiCo _1-Y2 Mn _Y2 O ₂ (0<Y2<1), LiMn _2-z1 Co _z1 O ₄ (0<Z1<2), or Li(Ni _p1 Co _q1 Mn _r2 )O ₄ (0＜p1＜2, 0＜q1＜2, 0＜r2＜2, p1+q1+r2=2) etc. can also be used in combination.

The positive electrode active material may be included in an amount of 80 to 98% by weight, more specifically, 85 to 98% by weight, based on the total weight of the positive electrode active material layer. When the positive electrode active material is contained within the above range, excellent capacity characteristics can be exhibited.

Next, the conductive material is used to provide conductivity to the electrode, and can be used without particular limitation as long as it does not cause chemical change and has electronic conductivity in the battery being constructed. Specific examples include carbon black, such as acetylene black (or Denka black), Ketjen black, channel black, furnace black, lamp black, or thermal black; Graphite powder such as natural graphite, artificial graphite, or graphite with a highly developed crystal structure; Conductive fibers such as carbon fiber and metal fiber; Conductive powders such as fluorinated carbon powder, aluminum powder, or nickel powder; Conductive whiskers such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Examples include polyphenylene derivatives, of which one type alone or a mixture of two or more types may be used.

The conductive material may be included in an amount of 0.1 to 10% by weight, preferably 0.1 to 5% by weight, based on the total weight of the positive electrode active material layer.

Next, the binder serves to improve adhesion between positive electrode active material particles and adhesion between the positive active material and the current collector.

Examples of such binders include fluororesin binders containing polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE); Rubber-based binders including styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber, and styrene-isoprene rubber; Cellulose-based binders including carboxymethyl cellulose (CMC), starch, hydroxypropylcellulose, and regenerated cellulose; A polyalcohol-based binder containing polyvinyl alcohol; Polyolefin-based binders including polyethylene and polypropylene; polyimide-based binder; polyester-based binder; And one type alone or a mixture of two or more types of silane-based binders may be used.

The binder may be included in an amount of 0.1 to 15% by weight, preferably 0.1 to 10% by weight, based on the total weight of the positive electrode active material layer.

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

Meanwhile, the positive electrode current collector is not particularly limited as long as it is conductive without causing chemical changes in the battery, for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or carbon or nickel on the surface of aluminum or stainless steel. , titanium, silver, etc. can be used. In addition, the positive electrode current collector may typically have a thickness of 3 to 500 μm, and fine irregularities may be formed on the surface of the current collector to increase the adhesion of the positive electrode material. For example, it can be used in various forms such as films, sheets, foils, nets, porous materials, foams, and non-woven materials.

The solvent may be a solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water. and the like, and one type of these may be used alone or a mixture of two or more types may be used. The amount of the solvent used can be adjusted so that the positive electrode mixture has an appropriate viscosity in consideration of the application thickness, manufacturing yield, workability, etc. of the positive electrode mixture, and is not particularly limited.

(2) cathode

Next, the cathode will be explained.

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

The negative electrode active material may be various types of negative electrode active materials used in the art, such as carbon-based negative electrode active materials, silicon-based negative electrode active materials, or mixtures thereof.

According to one embodiment, the negative electrode active material may include a carbon-based negative electrode active material, and the carbon-based negative electrode active material may include various carbon-based negative electrode active materials used in the industry, such as natural graphite, artificial graphite, and kishimen. Graphite-based materials such as graphite (Kish graphite); Pyrolytic carbon, mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches and petroleum or coal tar pitch derived cokes. High-temperature calcined carbon, soft carbon, hard carbon, etc. may be used. The shape of the carbon-based negative active material is not particularly limited, and materials of various shapes such as amorphous, plate-shaped, flaky, spherical, or fibrous may be used.

Preferably, the negative electrode active material may be at least one of natural graphite and artificial graphite, and natural graphite and artificial graphite may be used together to increase adhesion to the current collector and suppress detachment of the active material.

According to another embodiment, the negative electrode active material may include a silicon-based negative electrode active material together with the carbon-based negative electrode active material.

The silicon-based negative electrode active material is, for example, metallic silicon (Si ₎ , silicon oxide (SiO It is an element selected from the group consisting of elements, group 14 elements, transition metals, rare earth elements, and combinations thereof, but may include one or more types selected from the group consisting of Si. The element Y includes 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.

Since the silicon-based negative electrode active material exhibits higher capacity characteristics than the carbon-based negative electrode active material, better capacity characteristics can be obtained when the silicon-based negative electrode active material is additionally included. However, in the case of an anode containing a silicon-based anode active material, the SEI film contains more oxygen (O)-rich components than a graphite anode, and the SEI film containing O-rich components is electrolyte solution. If a Lewis acid such as HF or PF ₅ is present, it tends to decompose more easily. Therefore, in the case of a negative electrode containing a silicon-based negative electrode active material, it is necessary to suppress the generation of Lewis acids such as HF and PF ₅ in the electrolyte solution or to remove (or scavenge) the generated Lewis acids in order to maintain a stable SEI film. Since the non-aqueous electrolyte according to the present invention contains an electrolyte additive that forms a stable film on the positive and negative electrodes and has an excellent Lewis acid removal effect, it can effectively suppress SEI film decomposition when using a negative electrode containing a silicon-based active material.

Meanwhile, the mixing ratio of the silicon-based negative electrode active material and the carbon-based negative electrode active material may be 3:97 to 99:1, preferably 5:95 to 15:85, in weight ratio. When the mixing ratio of the silicon-based negative electrode active material and the carbon-based negative electrode active material satisfies the above range, capacity characteristics are improved and volume expansion of the silicon-based negative electrode active material is suppressed, thereby ensuring excellent cycle performance.

The negative electrode active material may be included in an amount of 80% to 99% by weight based on the total weight of the negative electrode active material layer. When the content of the negative electrode active material satisfies the above range, excellent capacity characteristics and electrochemical properties can be obtained.

Next, the conductive material is an ingredient to further improve the conductivity of the negative electrode active material, and may be added in an amount of 10% by weight or less, preferably 5% by weight or less, based on the total weight of the negative electrode active material layer. These conductive materials are not particularly limited as long as they are conductive without causing chemical changes in the battery. For example, carbon black, acetylene black (or Denka black), Ketjen black, channel black, furnace black, lamp black, or carbon black such as thermal black; Graphite powder such as natural graphite, artificial graphite, or graphite with a highly developed crystal structure; Conductive fibers such as carbon fiber and metal fiber; Conductive powders such as fluorinated carbon powder, aluminum powder, and nickel powder; Conductive whiskers such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Polyphenylene derivatives, etc. 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 usually added in an amount of 0.1% to 10% by weight based on the total weight of the negative electrode active material layer. Examples of binders include fluororesin binders containing polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE); Rubber-based binders including styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber, and styrene-isoprene rubber; Cellulose-based binders including carboxymethyl cellulose (CMC), starch, hydroxypropylcellulose, and regenerated cellulose; A polyalcohol-based binder containing polyvinyl alcohol; Polyolefin-based binders including polyethylene and polypropylene; polyimide-based binder; polyester-based binder; and silane-based binders.

The binder may be included in an amount of 0.1 to 15% by weight, preferably 0.1 to 10% by weight, based on the total weight of the negative electrode active material layer.

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

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, it may be used on the surface of copper, stainless steel, aluminum, nickel, titanium, fired carbon, copper or stainless steel. Surface treatment with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used. In addition, the negative electrode current collector may typically have a thickness of 3㎛ to 500㎛, and like the positive electrode current collector, fine irregularities may be formed on the surface of the current collector to strengthen the bonding force of the negative electrode active material. For example, it can be used in various forms such as films, sheets, foils, nets, porous materials, foams, and non-woven materials.

The solvent may be a solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water. and the like, and one type of these may be used alone or a mixture of two or more types may be used. The amount of the solvent used can be adjusted so that the anode slurry has an appropriate viscosity in consideration of the application thickness of the anode mixture, manufacturing yield, workability, etc., and is not particularly limited.

(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 from the positive electrode and provides a passage for lithium ions to move. It can be used without particular restrictions as long as it is normally used as a separator in lithium secondary batteries. In particular, it has low resistance to ion movement of lithium salts and moisturizes the electrolyte. It is desirable to have excellent abilities.

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, etc., may be used. Additionally, a coated separator containing a ceramic component or polymer material may be used to ensure heat resistance or mechanical strength, and may optionally be 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, laptop computers, and digital cameras, and in the field of electric vehicles such as hybrid electric vehicles (HEV).

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

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

Example

Example 1.

(Manufacture of non-aqueous electrolyte for lithium secondary battery)

LiPF ₆ was dissolved to 1.0M in a non-aqueous organic solvent mixed with ethylene carbonate (EC) and ethyl methyl carbonate (EMC) at a volume ratio of 30:70, and then 0.5% by weight of the compound represented by Chemical Formula 1A-1 and vinylene were added. A non-aqueous electrolyte for a lithium secondary battery was prepared by adding carbonate (VC) to 0.5% by weight (see Table 1 below).

(Secondary battery manufacturing)

The positive electrode active material (Li(Ni _0.9 Mn _0.03 Co _0.06 Al _0.01 )O ₂ ), conductive material (carbon black), and binder (polyvinylidene fluoride) were added to the solvent N-methyl-2-pyrrolidone (NMP) at 97.6%. :0.8:1.6 weight ratio was added to prepare a positive electrode slurry (solid content: 60.0% by weight). The positive electrode slurry was applied and dried on a positive electrode current collector (Al thin film) with a thickness of 13.5 μm, and then roll pressed to prepare a positive electrode.

The negative electrode active material (graphite:SiO = 94:6 weight ratio), binder (SBR-CMC), and conductive material (carbon black) were added to the solvent water at a weight ratio of 97.6:0.8:1.6 to create a negative electrode slurry (solid content: 60% by weight). was manufactured. The negative electrode slurry was applied and dried on a 6㎛ thick copper (Cu) thin film, which is a negative electrode current collector, and then roll pressed to produce a negative electrode.

An electrode assembly was manufactured by interposing a porous separator polypropylene between the prepared positive electrode and the negative electrode, and then stored in a battery case, and the prepared non-aqueous electrolyte for lithium secondary battery was injected to prepare a lithium secondary battery.

Example 2.

(Manufacture of non-aqueous electrolyte for lithium secondary battery)

LiPF ₆ was dissolved to 1.0M in a non-aqueous organic solvent, and then the compound represented by Formula 1A-1 was added to 1.0% by weight and vinylene carbonate (VC) was added to 0.5% by weight to prepare a non-aqueous electrolyte for a lithium secondary battery. .

(Secondary battery manufacturing)

A lithium secondary battery was manufactured in the same manner as Example 1, except that the non-aqueous electrolyte for a lithium secondary battery prepared above was injected instead of the non-aqueous electrolyte of Example 1 (see Table 1 below).

Comparative Example 1.

(Manufacture of non-aqueous electrolyte for lithium secondary battery)

LiPF ₆ was dissolved to 1.0M in a non-aqueous organic solvent, and then vinylene carbonate (VC) was added as an additive to 0.5% by weight to prepare a non-aqueous electrolyte solution.

(Secondary battery manufacturing)

A lithium secondary battery was manufactured in the same manner as Example 1, except that the non-aqueous electrolyte for a lithium secondary battery prepared above was injected instead of the non-aqueous electrolyte of Example 1 (see Table 1 below).

Comparative Example 2.

(Manufacture of non-aqueous electrolyte for lithium secondary battery)

LiPF ₆ was dissolved in a non-aqueous organic solvent to a concentration of 1.0M, and then 0.5% by weight of a compound represented by the following Chemical Formula 3 and 0.5% by weight of vinylene carbonate (VC) were added instead of the compound represented by Chemical Formula 1A-1 as additives. A non-aqueous electrolyte solution was prepared.

[Formula 3]

(Secondary battery manufacturing)

A lithium secondary battery was manufactured in the same manner as Example 1, except that the non-aqueous electrolyte for a lithium secondary battery prepared above was injected instead of the non-aqueous electrolyte of Example 1 (see Table 1 below).

Comparative Example 3.

(Manufacture of non-aqueous electrolyte for lithium secondary battery)

LiPF ₆ was dissolved in a non-aqueous organic solvent to 1.0M, and then 0.5% by weight of a compound represented by the following Chemical Formula 4 and 0.5% by weight of vinylene carbonate (VC) were added instead of the compound represented by Chemical Formula 1A-1 as additives. A non-aqueous electrolyte solution was prepared.

[Formula 4]

(Secondary battery manufacturing)

A lithium secondary battery was manufactured in the same manner as Example 1, except that the non-aqueous electrolyte for a lithium secondary battery prepared above was injected instead of the non-aqueous electrolyte of Example 1 (see Table 1 below).

Non-aqueous organic solvent additive Other additives (% by weight) type Content (% by weight) Example 1 EC:EMC=30:70 volume ratio
Formula 1A-1 0.5 VC (0.5) Example 2 Formula 1A-1 1.0 Comparative Example 1 - - Comparative Example 2 Formula 3 0.5 Comparative Example 3 Formula 4 0.5

Meanwhile, the abbreviated names of compounds in Table 1 mean the following.

EC: ethylene carbonate

EMC: Ethylmethyl Carbonate

VC: vinylene carbonate

Experiment example

Experimental Example 1. Evaluation of resistance increase rate after high temperature storage

The lithium secondary battery manufactured in the Examples and Comparative Examples was subjected to an activation process under the condition of charging at a rate of 0.1C for 3 hours, and then charged under constant current/constant voltage conditions up to 4.2V at a rate of 0.33C at 25°C (0.05 C cut-off) was performed to fully charge the SOC to 100% and stored at high temperature (60°C) for 16 weeks. Afterwards, the resistance was measured by transferring it to a charger and discharger at room temperature (25°C), the resistance increase rate was calculated using Equation 1 below, and the results are shown in Table 2 below.

[Equation 1]

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

Experimental Example 2. Evaluation of gas generation after high temperature storage

The lithium secondary battery manufactured in the Examples and Comparative Examples was subjected to an activation process under the condition of charging at a rate of 0.1C for 3 hours, and then charged under constant current/constant voltage conditions up to 4.2V at a rate of 0.33C at 25°C (0.05 C cut-off) was performed to fully charge the SOC to 100%. The fully charged battery was stored at high temperature (60°C) for 16 weeks, and then the amount of gas generated was measured using GC analysis at room temperature (25°C). When the gas generation amount measured in Comparative Example 1 was set at 100%, the relative gas generation amount of each battery was calculated as a percentage and is shown in Table 2 below.

Experimental Example 3. Evaluation of capacity retention rate after high temperature cycle

The lithium secondary battery manufactured in the Examples and Comparative Examples was subjected to an activation process under the condition of charging at a rate of 0.1C for 3 hours, and then charged under constant current/constant voltage conditions up to 4.2V at a rate of 0.33C at 25°C (0.05 C cut-off) was performed to fully charge the SOC to 100%. A fully charged battery is charged under constant current/constant voltage conditions to 4.2V at a rate of 0.33C at 45°C, and discharged under constant current conditions to 2.8V at a rate of 0.33C as one cycle, performing 300 cycles, and then using Equation 2 below: The capacity retention rate after 300 cycles was calculated using , and the results are shown in Table 2 below.

[Equation 2]

Capacity retention rate (%) = (capacity after 300 cycles/capacity after 1 cycle) × 100

Resistance increase rate (%) Gas generation amount (%) Capacity maintenance rate (%) Example 1 14.04 72.5 89.9 Example 2 13.29 70.2 90.2 Comparative Example 1 32.84 100 88.3 Comparative Example 2 28.11 94.3 88.4 Comparative Example 3 24.54 90.1 88.8

Looking at Table 2, in the case of the secondary batteries of Examples 1 and 2 of the present invention, compared to the lithium secondary batteries of Comparative Examples 1 to 3, the resistance increase rate (%) and gas generation amount (%) decreased, and the capacity retention rate (%) %) can be seen to have improved.

Claims (10)

Contains a lithium salt, an organic solvent and a first additive,
The first additive is a non-aqueous electrolyte for a lithium secondary battery comprising a compound represented by the following formula (1):
[Formula 1]

(In Formula 1 above,
Ar is a 5- or 6-membered nitrogen-containing ring,
R ₁ and R ₂ are each independently an alkyl group having 1 to 8 carbon atoms).
In claim 1,
A non-aqueous electrolyte for a lithium secondary battery, wherein the compound represented by Formula 1 is a compound represented by the following Formula 1A:
[Formula 1A]

(In Formula 1A above,
R ₁ and R ₂ are each independently an alkyl group having 1 to 8 carbon atoms).
In claim 2,
A non-aqueous electrolyte for a lithium secondary battery wherein R ₁ and R ₂ are each independently an alkyl group having 1 to 5 carbon atoms.
In claim 2,
A non-aqueous electrolyte for a lithium secondary battery wherein R ₁ and R ₂ are each independently an alkyl group having 1 to 3 carbon atoms.
In claim 2,
The compound represented by Formula 1A is a non-aqueous electrolyte for a lithium secondary battery, which is a compound represented by Formula 1A-1 or a compound represented by Formula 1A-2.
[Formula 1A-1]

[Formula 1A-2]

In claim 1,
A non-aqueous electrolyte for a lithium secondary battery, wherein the compound represented by Formula 1 is contained in an amount of 0.5% to 3.0% by weight based on the total weight of the non-aqueous electrolyte for a lithium secondary battery.
In claim 6,
A non-aqueous electrolyte for a lithium secondary battery, wherein the compound represented by Formula 1 is contained in an amount of 0.5% by weight to 2.5% by weight based on the total weight of the non-aqueous electrolyte for a lithium secondary battery.
In claim 1,
The non-aqueous electrolyte for lithium secondary batteries includes cyclic carbonate-based compounds, halogen-substituted carbonate-based compounds, sultone-based compounds, sulfate-based compounds, phosphate-based compounds, borate-based compounds, nitrile-based compounds, benzene-based compounds, amine-based compounds, and silane-based compounds. And a non-aqueous electrolyte for a lithium secondary battery, further comprising at least one second additive selected from the group consisting of lithium salt compounds.
A positive electrode containing a positive electrode active material;
A negative electrode containing a negative electrode active material;
A separator interposed between the anode and the cathode; and
A lithium secondary battery comprising the non-aqueous electrolyte for a lithium secondary battery of claim 1.
In claim 9,
The positive electrode is a lithium secondary comprising a positive electrode active material containing lithium and at least one metal selected from the group consisting of nickel (Ni), cobalt (Co), manganese (Mn), iron (Fe), and aluminum (Al). battery.