KR20230141621A - Non-aqueous electrolyte solution for lithium secondary battery and lithium secondary battery comprising the same - Google Patents

Abstract

The present invention provides a non-aqueous electrolyte for a lithium secondary battery comprising a phosphonium salt-based ionic liquid as an additive. In addition, the present invention, by applying the non-aqueous electrolyte for the lithium secondary battery, can provide the lithium secondary battery that suppresses a resistance at a low temperature and at the same time, having excellence in flame retardancy and high-temperature stability.

Description

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

The present invention relates to a non-aqueous electrolyte for a lithium secondary battery containing a phosphonium salt-based ionic liquid and a lithium secondary battery containing the same.

In modern society, dependence on electrical energy is increasing, and accordingly, the production of electrical energy is increasing further. In order to solve environmental problems that arise during this process, renewable energy generation is attracting attention as a next-generation power generation system. In the case of such renewable energy, it shows intermittent power generation characteristics, so a large-capacity power storage device is essential to stably supply power. Among these power storage devices, lithium-ion batteries are currently in the spotlight as devices with the highest energy density that are commercially available.

The lithium ion battery largely consists of a positive electrode composed of a transition metal oxide containing lithium, a negative electrode capable of storing lithium, a non-aqueous electrolyte solution that serves as a medium for transferring lithium ions, and a separator.

In particular, non-aqueous electrolytes are known to be components that have a significant impact on the stability and safety of batteries, and much research is being conducted on them.

In general, a liquid electrolyte solution in which an electrolyte salt is dissolved in an organic solvent has been mainly used as a non-aqueous electrolyte solution. However, these liquid electrolytes have the disadvantages of high volatility of the organic solvent in a high-temperature atmosphere, generation of a large amount of gas due to side reactions with the electrode, and low stability due to combustion due to an increase in the temperature of the battery itself. Moreover, in a low-temperature atmosphere, the resistance of the interface between the electrode and the non-aqueous electrolyte solution increases, resulting in deterioration of overall performance.

Accordingly, there is a demand for the development of a lithium secondary battery that has flame retardancy and improved overall performance under high and low temperature atmospheres.

Japanese Patent Publication No. 2009-054884 Japanese Patent Publication No. 2006-080488

The present invention is intended to solve the above problems and provides a non-aqueous electrolyte for lithium secondary batteries containing a phosphonium salt-based ionic liquid.

In addition, the present invention seeks to provide a lithium secondary battery that improves flame retardancy and improves output characteristics in a low-temperature atmosphere and stability and storage characteristics in a high-temperature atmosphere by including the non-aqueous electrolyte solution for a lithium secondary battery.

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

Provided is a non-aqueous electrolyte solution for a lithium secondary battery containing a lithium salt, a non-aqueous organic solvent, and an ionic liquid represented by the following formula (1):

[Formula 1]

In Formula 1,

R is an alkylene group having 1 to 5 carbon atoms,

R ₁ to R ₃ are each independently an alkyl group having 1 to 8 carbon atoms or an aryl group having 6 to 12 carbon atoms,

^X- is BF _4- ^, PF _6- , _{Clo 4-} ^, PO _{2 F 2-} ^, CF ₃ SO _3- ^, CH _{3 CO 2-} ^{, CF} ₃ CO _2- ^, SO ₃ CF _3- ^, (CF ₃ CF ₂ SO ₂ ) ₂ N ^- , (CF ₃ SO ₂ ) ₂ N ^- , (FSO ₂ ) ₂ N ^- , CF ₃ CF ₂ SO ₃ ^- , CF ₃ CF ₂ (CF ₃ ) ₂ CO ^- , B(C ₂ O ₄ ) ₂ ^- and BF ₂ (C ₂ O ₄ ) ^- It is at least one anion selected from the group consisting of.

In another embodiment of the present invention

Provided is a lithium secondary battery comprising a negative electrode, a positive electrode, a separator interposed between the negative electrode and the positive electrode, and a non-aqueous electrolyte solution, wherein the non-aqueous electrolyte solution includes the non-aqueous electrolyte solution for a lithium secondary battery of the present invention.

The phosphonium salt-based ionic liquid represented by Chemical Formula 1 included in the non-aqueous electrolyte solution of the present invention contains a propargyl group in its structure, and can form a robust film with low resistance on the electrode surface through oxidation/reduction reactions. . Therefore, by using the non-aqueous electrolyte of the present invention containing the phosphonium salt-based ionic liquid represented by Formula 1, it is possible to improve flame retardancy, minimize the increase in resistance at low temperatures, improve capacity characteristics, and provide excellent It is possible to implement a lithium secondary battery that can ensure high-temperature storage stability.

The following drawings attached to this specification illustrate preferred embodiments of the present invention, and serve to further understand the technical idea of the present invention together with the contents of the above-described invention. Therefore, the present invention is limited to the matters described in such drawings. It should not be interpreted in a limited way.
Figure 1 is a graph showing the results of evaluating the thickness increase rate of a lithium secondary battery when stored at high temperature according to Experimental Example 2.

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

Terms or words used in this specification and claims should not be construed as limited to their common or dictionary meanings, and the inventor may appropriately define the concept of terms in order to explain his or her invention in the best way. It must be interpreted with meaning and concept consistent with the technical idea of the present invention based on the principle that it is.

Non-aqueous electrolyte for lithium secondary batteries

Specifically, in one embodiment of the present invention

Provided is a non-aqueous electrolyte solution for a lithium secondary battery containing a lithium salt, a non-aqueous organic solvent, and an ionic liquid represented by the following formula (1):

[Formula 1]

In Formula 1,

R is an alkylene group having 1 to 5 carbon atoms,

R ₁ to R ₃ are each independently an alkyl group having 1 to 8 carbon atoms or an aryl group having 6 to 12 carbon atoms,

^X- is BF _4- ^, PF _6- , _{Clo 4-} ^, PO _{2 F 2-} ^, CF ₃ SO _3- ^, CH _{3 CO 2-} ^{, CF} ₃ CO _2- ^, SO ₃ CF _3- ^, (CF ₃ CF ₂ SO ₂ ) ₂ N ^- , (CF ₃ SO ₂ ) ₂ N ^- , (FSO ₂ ) ₂ N ^- , CF ₃ CF ₂ SO ₃ ^- , CF ₃ CF ₂ (CF ₃ ) ₂ CO ^- , B(C ₂ O ₄ ) ₂ ^- and BF ₂ (C ₂ O ₄ ) ^- It is at least one anion selected from the group consisting of.

(1) Lithium salt

First, the lithium salt is explained as follows.

The lithium salt may be those commonly used in non-aqueous electrolytes for lithium secondary batteries without limitation, and for example, includes 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 ) ₂ CH ^- , CF ₃ (CF ₂ ) ₇ SO ₃ ^- and SCN ^- may include at least one selected from the group consisting of.

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 contain a single substance or a mixture of two or more types selected from the group consisting of bis(trifluoromethanesulfonyl) imide, LiN(SO ₂ CF ₃ ) ₂ ), and in addition to the above-mentioned lithium salt, lithium salt commonly used in the electrolyte solution of lithium secondary batteries. It can be used without limitation. Specifically, the lithium salt may include LiPF ₆ .

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 surface of the electrode, it should be included in the electrolyte solution at a concentration of 0.8 M to 3.0 M, specifically at a concentration of 1.0 M to 3.0 M. You can. When the concentration of the lithium salt satisfies the above range, the viscosity of the non-aqueous electrolyte can be controlled to achieve optimal impregnation, and the mobility of lithium ions is improved to improve the capacity characteristics and cycle characteristics of the lithium secondary battery. You can.

(2) Non-aqueous organic solvent

Additionally, a description of the non-aqueous 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 achieved together with additives. There is no limit to the types of things that can be performed.

Specifically, the non-aqueous organic solvent may include a cyclic carbonate-based organic solvent, a linear carbonate-based organic solvent, a linear ester-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, 2, It may contain at least one organic solvent selected from the group consisting of 3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, and vinylene carbonate, and among these, it may include ethylene carbonate. there is.

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

The linear ester-based organic solvent is a solvent with relatively high stability at high temperature and high voltage operation compared to the cyclic carbonate-based organic solvent, and improves the disadvantage of the cyclic carbonate-based organic solvent that causes gas generation when operated at high voltage, while also improving the high ion Conductivity can be realized.

Specific examples of the linear ester organic solvent include at least one 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.

Additionally, the non-aqueous electrolyte solution of the present invention may further include a cyclic ester-based organic solvent, if necessary.

Additionally, 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 and the additive compound represented by Chemical Formula 1, may be non-aqueous organic solvents unless otherwise specified.

(3) Ionic liquid represented by Formula 1

The non-aqueous electrolyte solution for a lithium secondary battery of the present invention may include an ionic liquid represented by the following formula (1) as an additive.

[Formula 1]

In Formula 1,

R is an alkylene group having 1 to 5 carbon atoms,

R ₁ to R ₃ are each independently an alkyl group having 1 to 8 carbon atoms or an aryl group having 6 to 12 carbon atoms,

^X- is BF _4- ^, PF _6- , _{Clo 4-} ^, PO _{2 F 2-} ^, CF ₃ SO _3- ^, CH _{3 CO 2-} ^{, CF} ₃ CO _2- ^, SO ₃ CF _3- ^, (CF ₃ CF ₂ SO ₂ ) ₂ N ^- , (CF ₃ SO ₂ ) ₂ N ^- , (FSO ₂ ) ₂ N ^- , CF ₃ CF ₂ SO ₃ ^- , CF ₃ CF ₂ (CF ₃ ) ₂ CO ^- , B(C ₂ O ₄ ) ₂ ^- and BF ₂ (C ₂ O ₄ ) ^- is at least one anion selected from the group consisting of

The phosphonium salt-based ionic liquid represented by Formula 1 contains a propargyl group in its structure, and has stable oxidation/reduction reactivity compared to phosphonium salt-based ionic liquids containing double bonds, such as ethylene carbonate (EC), It can further promote the reaction of film-forming additives such as vinylene carbonate (VC) or vinylethylene carbonate (VEC), forming a strong copolymerized film with low resistance on the electrode surface, thereby enhancing film durability. You can. In addition, the phosphonium salt-based ionic liquid represented by Formula 1 is a non-volatile compound and has higher flame retardancy than organic solvents such as ethylene carbonate (EC), which are included as the main component of conventional non-aqueous electrolytes, and thus lithium secondary ion liquid under high temperature atmosphere. By improving the flame retardancy of the battery, the possibility of ignition can be reduced. Therefore, when applying the non-aqueous electrolyte of the present invention containing the phosphonium salt-based ionic liquid represented by Formula 1, flame retardancy is improved and the increase in resistance in a low-temperature atmosphere is minimized to improve low-temperature output characteristics and high-temperature It is possible to implement a lithium secondary battery with improved stability and storage characteristics in an atmosphere.

Specifically, in Formula 1, R is an alkylene group having 1 to 3 carbon atoms, R ₁ to R ₃ are each independently an alkyl group or phenyl group having 1 to 5 carbon atoms, and X ^- is BF ₄ ^- , PF ₆ ^- , ClO ₄ ^- , PO ₂ F ₂ ^- , CF ₃ SO ₃ ^- , SO ₃ CF ₃ ^- , (CF ₃ CF ₂ SO ₂ ) ₂ N ^- , (CF ₃ SO ₂ ) ₂ N ^- , (FSO ₂ ) ₂ N ^- , CF ₃ CF ₂ SO ₃ ^- , CF ₃ CF ₂ (CF ₃ ) ₂ CO ^- and BF ₂ (C ₂ O ₄ ) ^- It may be at least one anion.

Additionally, in Formula 1, R ₁ to R ₃ may each independently be a methyl group, an ethyl group, or a phenyl group.

More specifically, the ionic liquid represented by Formula 1 may be at least one of the compounds represented by Formulas 1-1 to 1-4 below.

[Formula 1-1]

[Formula 1-2]

[Formula 1-3]

[Formula 1-4]

Additionally, the ionic liquid represented by Formula 1 may be included in an amount of 0.3% to 50% by weight based on the total weight of the non-aqueous electrolyte solution.

When the content of the ionic liquid represented by Formula 1 satisfies the above range, a stable passive film with low resistance is formed on the anode and cathode surfaces, thereby securing safe high and low temperature capacity characteristics and implementing a flame retardant strengthening effect. Therefore, the overall performance of the lithium secondary battery can be further improved under high and low temperature atmospheres.

Specifically, the ionic liquid represented by Formula 1 may be included in an amount of 0.5% to 30% by weight, preferably 0.5% to 20% by weight, based on the total weight of the non-aqueous electrolyte solution.

(4) Other additives

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, battery expansion suppression effects at high temperatures, etc. In order to further improve, other additives may be additionally included in the non-aqueous electrolyte solution as needed.

Representative examples of these other 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. and at least one selected from the group consisting of lithium salt compounds.

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, the amine-based compound may include triethanolamine or ethylene diamine, and the silane-based compound may 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 selected compounds may be included.

Among these other additives, when vinylene carbonate, vinylethylene carbonate, or 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 above other 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 other additives 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 other additives exceeds 50% by weight, the electrolyte during charging and discharging of the battery There is a possibility that excessive internal side reactions may occur. 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, in another embodiment of the present invention, an anode; cathode; a separator interposed between the anode and the cathode; And it provides a lithium secondary battery including the non-aqueous electrolyte solution of the present invention described above.

The lithium secondary battery of the present invention can be manufactured by forming an electrode assembly in which a positive electrode, a negative electrode, and a separator are sequentially stacked between the positive electrode and the negative electrode, storing it in a battery case, and then adding the non-aqueous electrolyte solution of the present invention.

The method of manufacturing the lithium secondary battery of the present invention can be manufactured and applied according to a common method known in the art, and will be described in detail later.

(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<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 in this case, it 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 lithium transition metal oxide, 0<x≤1.0, specifically 0.55<x<1.0, more specifically 0.6≤x≤0.98, and even more specifically 0.6. It may be ≤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 includes the lithium composite metal oxide represented by Chemical Formula 2, lithium-manganese-based oxides (e.g., LiMnO ₂ , LiMn ₂ O ₄ , etc.), and lithium-cobalt-based oxides (e.g., LiCoO _2, etc.), lithium-nickel-based oxide (for example, LiNiO ₂ , etc.), lithium-nickel-manganese-based oxide (for example, 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 ( For example, 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) can also be used in combination.

The positive electrode active material may be included in an amount of 80% to 99% by weight, specifically 90% to 99% by weight, based on the total weight of solids in the positive electrode slurry. At this time, if the content of the positive electrode active material is 80% by weight or less, the energy density may be lowered and the capacity may be reduced.

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 powders such as carbon black, 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; Conductive materials such as polyphenylene derivatives may be used, and one type of these may be used 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 5.0% 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 the positive electrode active material, binder, and/or conductive material in a solvent, applying a positive electrode slurry onto the positive electrode current collector, followed by drying and rolling to form an active material layer, or It can be manufactured by casting the positive electrode slurry on a separate support and then laminating the film obtained by peeling off the support on the positive electrode current collector.

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, nickel, titanium on the surface of aluminum or stainless steel. , surface treated with silver, etc. may 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 be used in combination with the carbon-based negative electrode active material and the silicon-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 solution according to the present invention contains an electrolyte additive capable of forming a stable film on the positive and negative electrodes, 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 may be included to further improve the conductivity of the negative electrode active material layer, and is not particularly limited as long as it has conductivity without causing chemical changes in the battery. For example, the conductive material may be carbon powder such as carbon black, 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, 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 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.

The binder is a component that assists in bonding between the conductive material, the active material, and the current collector. For example, a fluororesin binder 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 typically 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 the negative electrode slurry It can be manufactured by casting on a separate support and then peeling off the support and laminating the film obtained on 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 separator included in the lithium secondary battery of the present invention is a commonly used porous polymer film, such as ethylene homopolymer, propylene homopolymer, ethylene/butene copolymer, ethylene/hexene copolymer, and ethylene/methacrylate. Porous polymer films made of polyolefin-based polymers such as copolymers can be used alone or by laminating them, or conventional porous non-woven fabrics, such as high-melting point glass fibers, polyethylene terephthalate fibers, etc., can be used. However, it is not limited to this.

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.

[Example]

Example 1.

(Production of non-aqueous electrolyte solution)

LiPF ₆ was dissolved to 1.0M in a non-aqueous organic solvent mixed with ethylene carbonate (EC) and ethylmethyl carbonate (EMC) at a volume ratio of 30:70, and then 0.5% by weight of the compound represented by Formula 1-1 and other A non-aqueous electrolyte solution was prepared by adding 1.0 wt% of vinylene carbonate, 1.0 wt% of 1,3-propane sultone, and 1.0 wt% of ethylene sulfate as additives.

(Secondary battery manufacturing)

N-methyl-2-pyrrolidone (NMP) was mixed with the positive electrode active material (Li(Ni _0.86 Mn _0.07 Co _0.05 Al _0.02 )O ₂ ), conductive material (carbon black), and binder (polyvinylidene fluoride) at a ratio of 97.5:1. :1.5 weight ratio was added to prepare a positive electrode slurry (solid content: 50% by weight). The positive electrode slurry was applied and dried on a 12㎛ thick aluminum (Al) thin film, which is a positive electrode current collector, and then roll pressed to produce a positive electrode.

A negative electrode slurry (solid content: 60% by weight) was prepared by adding the negative electrode active material (graphite), binder (SBR-CMC), and conductive material (carbon black) to water as a solvent at a weight ratio of 95:3.5:1.5. 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 sequentially stacking the positive electrode, the polyolefin-based porous separator coated with inorganic particles (Al ₂ O ₃ ), and the negative electrode, and then stored in a pouch-type battery case, and injected with the non-aqueous electrolyte for a lithium secondary battery. A pouch-type lithium secondary battery with a driving voltage of 4.45 V or more was manufactured.

Example 2.

(Production of non-aqueous electrolyte solution)

LiPF ₆ was dissolved to 1.0M in a non-aqueous organic solvent mixed with ethylene carbonate (EC) and ethylmethyl carbonate (EMC) at a volume ratio of 30:70, and then 2.0% by weight of the compound represented by Formula 1-1 and other A non-aqueous electrolyte solution was prepared by adding 1.0 wt% of vinylene carbonate, 1.0 wt% of 1,3-propane sultone, and 1.0 wt% of ethylene sulfate as additives.

(Secondary battery manufacturing)

A pouch-type lithium secondary battery was manufactured in the same manner as Example 1, except that the prepared non-aqueous electrolyte solution was injected.

Example 3.

(Production of non-aqueous electrolyte solution)

LiPF ₆ was dissolved to 1.0M in a non-aqueous organic solvent mixed with ethylene carbonate (EC) and ethylmethyl carbonate (EMC) at a volume ratio of 30:70, and then mixed with 30.0% by weight of the compound represented by Formula 1 and other additives. A non-aqueous electrolyte solution was prepared by adding 1.0% by weight of vinylene carbonate, 1.0% by weight of 1,3-propanesultone, and 1.0% by weight of ethylene sulfate.

(Secondary battery manufacturing)

A pouch-type lithium secondary battery was manufactured in the same manner as Example 1, except that the prepared non-aqueous electrolyte solution was injected.

Comparative example.

Dissolve LiPF ₆ to 1.0M in a non-aqueous organic solvent mixed with ethylene carbonate (EC) and ethylmethyl carbonate (EMC) at a volume ratio of 30:70, 1.0% by weight of vinylene carbonate, and 1.0% by weight of 1,3-propane sultone. A non-aqueous electrolyte solution for a lithium secondary battery and a pouch-type lithium secondary battery containing the same were prepared in the same manner as Example 1, except that the non-aqueous electrolyte solution was prepared by adding 1.0% by weight of ethylene sulfate.

[Experimental example]

Experimental Example 1. Evaluation of low temperature output characteristics

The lithium secondary battery prepared in Examples 1 and 2 and the lithium secondary battery prepared in Comparative Example were stored at room temperature. After performing 0.04C constant current charging to 4.2V each at (25°C), 3 cycles were performed with 1 cycle of charging and discharging process of discharging to 3.0V under constant current (CC) conditions, and then the initial discharge capacity was measured and shown in Table 1 below. shown in

Next, charge to SOC (state of charge) 10% with 0.04C constant current, store at low temperature (-10℃) for 1 hour, and then calculate the discharge capacity after 1 hour as a percentage based on the initial discharge capacity. The calculated and measured results are shown in Table 1 below.

At room temperature (25℃)
Initial capacity (mAh) After storage at low temperature (-10℃)
Volume (%) Example 1 2,000 79.06 Example 2 1,999 84.10 Comparative Example 1 2004 71.82

Looking at Table 1, in the case of the lithium secondary batteries of Examples 1 and 2 of the present invention, the initial capacity at room temperature is somewhat lower than that of the lithium secondary battery of the comparative example, but the capacity retention rate after storage at low temperature is similar to that of the lithium secondary battery of the comparative example. You can see the improvement compared to the previous version.

Experimental Example 2. Evaluation of high temperature storage characteristics

The lithium secondary battery prepared in Examples 1 and 2 and the lithium secondary battery prepared in Comparative Example were stored at room temperature. The initial discharge capacity was measured by performing 0.04C constant current charging to 4.2V at (25°C) and then performing 3 cycles with 1 cycle of charging and discharging to 3.0V under constant current (CC) conditions.

Subsequently, it was charged to 100% SOC (state of charge) at a constant current of 0.04C, and then stored at high temperature (60℃) for 20 weeks, measuring the thickness increase rate every 4 weeks, and the results are shown in Figure 1. It was.

Looking at Figure 1, it can be seen that in the case of the lithium secondary batteries of Examples 1 and 2 of the present invention, as the amount of gas generated decreases when stored at high temperature, the thickness increase rate is relatively reduced compared to the comparative example.

Experimental Example 3. Evaluation of high temperature stability characteristics

The lithium secondary battery prepared in Example 3 and the lithium secondary battery prepared in Comparative Example were stored at room temperature. (25°C) 0.04C constant current charging was performed up to 4.2V, respectively, and then 3 cycles were performed with 1 cycle of the charging/discharging process of discharging to 3.0V under constant current (CC) conditions, and then the initial discharge capacity was measured.

Next, the battery was charged to 100% SOC (state of charge) at a constant current of 0.04C, and then the heat generated inside the battery was measured while the temperature was raised to a high temperature (300°C), and the results are shown in Table 2 below.

Calorific value (J) Example 3 264 Comparative example 499

Looking at Table 2, it can be seen that the lithium secondary battery of Example 3 of the present invention has improved high-temperature stability due to a decrease in calorific value at high temperatures compared to the lithium secondary battery of the comparative example.

Claims (8)

A non-aqueous electrolyte solution for a lithium secondary battery containing a lithium salt, a non-aqueous organic solvent, and an ionic liquid represented by the following formula (1):
[Formula 1]

In Formula 1,
R is an alkylene group having 1 to 5 carbon atoms,
R ₁ to R ₃ are each independently an alkyl group having 1 to 8 carbon atoms or an aryl group having 6 to 12 carbon atoms,
^X- is BF _4- ^, PF _6- , _{Clo 4-} ^, PO _{2 F 2-} ^, CF ₃ SO _3- ^, CH _{3 CO 2-} ^{, CF} ₃ CO _2- ^, SO ₃ CF _3- ^, (CF ₃ CF ₂ SO ₂ ) ₂ N ^- , (CF ₃ SO ₂ ) ₂ N ^- , (FSO ₂ ) ₂ N ^- , CF ₃ CF ₂ SO ₃ ^- , CF ₃ CF ₂ (CF ₃ ) ₂ CO ^- , B(C ₂ O ₄ ) ₂ ^- and BF ₂ (C ₂ O ₄ ) ^- It is at least one anion selected from the group consisting of.
In claim 1,
Wherein R is an alkylene group having 1 to 3 carbon atoms,
R ₁ to R ₃ are each independently an alkyl group or phenyl group having 1 to 5 carbon atoms,
^X- is BF _4- ^, PF _{6- , Clo 4-} ^, PO ₂ F ^2- , CF _{3 SO 3-} ^, SO ₃ CF ^{3- ,} ( _{CF 3 CF 2} So ₂ ) ₂ n- ^, (CF ₃ SO ₂ ) ₂ N ^- , (FSO ₂ ) ₂ N ^- , CF ₃ CF ₂ SO ₃ ^- , CF ₃ CF ₂ (CF ₃ ) ₂ CO ^- and BF ₂ (C ₂ O ₄ ) ^- At least one selected from the group consisting of A non-aqueous electrolyte for lithium secondary batteries that is an anion.
In claim 1,
The non-aqueous electrolyte solution for a lithium secondary battery wherein R ₁ to R ₃ are each independently a methyl group, an ethyl group, or a phenyl group.
In claim 1,
A non-aqueous electrolyte solution for a lithium secondary battery, wherein the ionic liquid represented by Formula 1 is at least one of the compounds represented by Formulas 1-1 to 1-4:
[Formula 1-1]

[Formula 1-2]

[Formula 1-3]

[Formula 1-4]

In claim 1,
The ionic liquid represented by Formula 1 is a non-aqueous electrolyte solution for a lithium secondary battery that is contained in an amount of 0.3% to 50% by weight based on the total weight of the non-aqueous electrolyte solution for a lithium secondary battery.
In claim 5,
The ionic liquid represented by Formula 1 is a non-aqueous electrolyte solution for a lithium secondary battery that is contained in an amount of 0.5% to 30% by weight based on the total weight of the non-aqueous electrolyte solution 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 or phosphite-based compounds, borate-based compounds, benzene-based compounds, amine-based compounds, and silane-based compounds. A non-aqueous electrolyte solution for a lithium secondary battery, further comprising at least one other additive selected from the group consisting of a compound and a lithium salt-based compound.
It includes a cathode, an anode, a separator interposed between the cathode and the anode, and a non-aqueous electrolyte solution,
The non-aqueous electrolyte solution is a lithium secondary battery comprising the non-aqueous electrolyte solution for a lithium secondary battery of claim 1.