KR102347979B1 - Non-aqueous electrolyte and lithium secondary battery comprising the same - Google Patents

Abstract

The present invention relates to a non-aqueous electrolyte for a lithium secondary battery and a lithium secondary battery comprising the same, and specifically, to a non-aqueous electrolyte for a lithium secondary battery comprising a lithium salt, a solvent and an additive, wherein the lithium salt is lithium bisfluorosulfonyl imide ( Lithium bis(fluorosulfonyl)imide; LiFSI), an ionic liquid containing a bis(fluorosulfonyl)imide anion as an anion component as the solvent, and a Si-O unit in the main chain as the additive It relates to a non-aqueous electrolyte for a lithium secondary battery comprising an oligomer and a lithium secondary battery comprising the same.

Description

Non-aqueous electrolyte and lithium secondary battery containing same

The present invention relates to a non-aqueous electrolyte having improved flame retardancy and to a lithium secondary battery having improved output characteristics and safety by including the same.

As technology development and demand for mobile devices increase, the demand for secondary batteries as an energy source is rapidly increasing, and among these secondary batteries, lithium secondary batteries having high energy density and voltage are commercialized and widely used.

Lithium secondary batteries are produced by applying a positive electrode active material and a negative electrode active material to a current collector to an appropriate thickness, or forming the active material itself in a film shape of an appropriate length, and then winding or laminating it together with a separator, which is an insulator, to manufacture an electrode assembly, can or After putting the electrode assembly in a container similar to this, it is manufactured by a process of injecting an electrolyte.

Lithium metal oxide is used as the positive electrode active material, and lithium metal, lithium alloy, crystalline or amorphous carbon or carbon composite is used as the negative electrode active material. In addition, as the electrolyte, a liquid electrolyte in which an appropriate amount of salt is dissolved in a non-aqueous organic solvent has been mainly used.

Currently, examples of the organic solvent widely used in the electrolyte include ethylene carbonate, propylene carbonate, dimethoxyethane, gamma-butyrolactone, N,N-dimethylformamide, tetrahydrofuran or acetonitrile.

However, when these organic solvents are stored at high temperatures for a long time, the stable structure of the battery is deformed due to gas generation due to the oxidation of the electrolyte, or internal heat generated by overcharging or overdischarging can lead to internal short circuit in severe cases, causing the battery to ignite and explode. can cause

In order to solve this problem, (1) using a porous polyolphine-based separator having a high melting point that does not easily melt in a high-temperature environment, or (2) mixing a flame-retardant solvent or additive in the electrolyte solution to improve high-temperature safety. has been proposed

In the case of the method (1), since the film thickness must be increased in order to realize the high melting point of the polyolefin-based separator, the loading amount of the negative electrode and the positive electrode is relatively low, and thus the capacity reduction of the battery is unavoidable. In addition, due to the characteristics of polyolefin films made of polyethylene or polypropylene, the melting point is before/after 150℃, so if rapid internal heat generation occurs due to oxidation of the electrolyte during overcharging, the separator melts and causes the battery to ignite and explode due to a short circuit inside the battery. hard to avoid

In the case of method (2), ethylene carbonate was mixed with dimethyl carbonate or diethyl carbonate, which is a linear carbonate-based organic solvent, or an organic solvent was added with additives such as vinyl acetate, ethyl sulfite, vinyl carbonate, etc., There is still a limit to sufficiently improving the initial charge/discharge efficiency and lifespan characteristics, and furthermore, the problem of ignition of the battery during overcharge and misuse has not been solved.

Accordingly, in order to put a lithium secondary battery into practical use, there is a need for a method capable of solving the problem of ignition of the battery.

Republic of Korea Patent Publication No. 2014-0129872

In order to solve the above problems,

A first technical object of the present invention is to provide a non-aqueous electrolyte for a lithium secondary battery with improved flame retardancy.

A second technical object of the present invention is to provide a lithium secondary battery with improved safety by including the non-aqueous electrolyte for a lithium secondary battery, thereby suppressing initial output characteristics and ignition of the secondary battery during overcharging.

Specifically, in one embodiment of the present invention

A non-aqueous electrolyte for a lithium secondary battery comprising a solvent, a lithium salt and an additive,

The solvent comprises an ionic liquid comprising a bis (fluorosulfonyl) imide anion as an anion component,

The lithium salt includes lithium bis(fluorosulfonyl)imide (LiFSI),

It provides a non-aqueous electrolyte for a lithium secondary battery comprising an oligomer represented by the following formula (1) as the additive.

[Formula 1]

In Formula 1,

R ₀ is a substituted or unsubstituted C 1 to C 5 alkylene group,

R _a and R _b are a substituted or unsubstituted C 1 to C 3 alkyl group,

R' and R" are each independently hydrogen or an alkyl group having 1 to 3 carbon atoms,

R is an aliphatic, alicyclic or aromatic hydrocarbon group,

a is an integer of any one of 1 to 3,

b is an integer of any one of 0 to 2,

n, m and x are the number of repeating units,

n is an integer of any one of 1 to 10,

m is an integer of any one of 1 to 5,

x is an integer of any one of 1 to 15.

In this case, in the oligomer represented by Formula 1,

The aliphatic hydrocarbon group is an alkylene group having 1 to 20 carbon atoms; an alkylene group having 1 to 20 carbon atoms containing an isocyanate group (NCO); an alkoxyylene group having 1 to 20 carbon atoms; an alkenylene group having 2 to 20 carbon atoms; or an alkynylene group having 2 to 20 carbon atoms;

The alicyclic hydrocarbon group is a cycloalkylene group having 4 to 20 carbon atoms; a cycloalkylene group having 4 to 20 carbon atoms containing an isocyanate group (NCO); a cycloalkenylene group having 4 to 20 carbon atoms; Or a heterocycloalkylene group having 2 to 20 carbon atoms;

The aromatic hydrocarbon group is an arylene group having 6 to 20 carbon atoms; Or it may include a heteroarylene group having 2 to 20 carbon atoms.

Specifically, the ionic liquid may include at least one cation selected from the group consisting of compounds represented by the following Chemical Formulas 2 to 6 as a cation component.

[Formula 2]

In Formula 2,

R ₁ , R ₂ , R ₃ and R ₄ are each independently hydrogen or an alkyl group having 1 to 5 carbon atoms.

[Formula 3]

In Formula 3,

R ₅ and R ₆ are each independently an alkyl group having 1 to 5 carbon atoms.

[Formula 4]

In Formula 4,

R ₇ and R ₈ are each independently an alkyl group having 1 to 5 carbon atoms.

[Formula 5]

In Formula 5,

R ₉ , R ₁₀ , R ₁₁ and R ₁₂ are each independently hydrogen or an alkyl group having 1 to 5 carbon atoms.

[Formula 6]

In Formula 6,

R ₁₃ , R ₁₄ , R ₁₅ and R ₁₆ are each independently an alkyl group having 1 to 5 carbon atoms.

The cation represented by Formula 2 may be at least one selected from the group consisting of compounds represented by Formulas 2a and 2b below.

[Formula 2a]

[Formula 2b]

In addition, the cation represented by Formula 3 may be at least one selected from the group consisting of compounds represented by Formulas 3a and 3b below.

[Formula 3a]

[Formula 3b]

In addition, the cation represented by Formula 4 may be at least one selected from the group consisting of compounds represented by Formulas 4a and 4b below.

[Formula 4a]

[Formula 4b]

In addition, the cation represented by the formula (6) may be a compound represented by the following formula (6a).

[Formula 6a]

In addition, the concentration of the lithium salt may be 1M to 4M, specifically 1.2M to 4M, more specifically 1.2M to 3M.

In addition, the oligomer represented by Formula 1 may be an oligomer represented by Formula 1a.

[Formula 1a]

In Formula 1a,

n1 and x1 are the number of repeating units,

n1 is an integer of any one of 1 to 10,

x1 is an integer in any one of 1 to 15.

The oligomer represented by Formula 1 may be included in an amount of 0.01 wt% to 10 wt%, specifically 0.5 wt% to 10 wt%, based on the total weight of the non-aqueous electrolyte for a lithium secondary battery.

In addition, in one embodiment of the present invention

A positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and

Contains non-aqueous electrolyte,

The non-aqueous electrolyte provides a lithium secondary battery, which is a non-aqueous electrolyte for a lithium secondary battery of the present invention.

As described above, according to the present invention, an ionic liquid having excellent electrochemical safety and nonflammable is used as a solvent for a non-aqueous electrolyte, and lithium bisfluorosulfonyl imide and an oligomer having a specific structure are simultaneously included as a lithium salt. , it is possible to prepare a non-aqueous electrolyte for a lithium secondary battery with improved flame retardancy. Furthermore, by providing such a non-aqueous electrolyte, it is possible to manufacture a lithium secondary battery having improved initial output characteristics and improved safety by suppressing ignition due to external short circuit, mechanical shock, and overcharging.

The following drawings attached to the present specification illustrate preferred embodiments of the present invention, and serve to further understand the technical spirit of the present invention together with the above-described content of the present invention, so the present invention is limited to the matters described in those drawings It should not be construed as being limited.
1 to 3 are graphs showing the corrosion evaluation results of the aluminum current collector with respect to the non-aqueous electrolyte according to Experimental Example 2 of the present invention.
4 and 5 are graphs showing the evaluation results of oxidation stability of the non-aqueous electrolyte according to Experimental Example 3 of the present invention.
6 is a photograph showing the flame retardancy evaluation result of the non-aqueous electrolyte according to Experimental Example 4 of the present invention.

Hereinafter, the present invention will be described in more detail to help the understanding of the present invention. At this time, the terms or words used in the present specification and claims should not be construed as being limited to conventional or dictionary meanings, and the inventor appropriately defines the concept of the term in order to describe his invention in the best way. Based on the principle that it can be done, it should be interpreted as meaning and concept consistent with the technical idea of the present invention.

Specifically, in one embodiment of the present invention

A non-aqueous electrolyte for a lithium secondary battery comprising a solvent, a lithium salt and an additive,

The solvent comprises an ionic liquid comprising a bis (fluorosulfonyl) imide anion as an anion component,

The lithium salt includes lithium bis(fluorosulfonyl)imide (LiFSI),

It provides a non-aqueous electrolyte for a lithium secondary battery comprising an oligomer represented by the following formula (1) as the additive.

[Formula 1]

In Formula 1,

R ₀ is a substituted or unsubstituted C 1 to C 5 alkylene group,

R _a and R _b are a substituted or unsubstituted C 1 to C 3 alkyl group,

R' and R" are each independently hydrogen or an alkyl group having 1 to 3 carbon atoms,

R is an aliphatic, alicyclic or aromatic hydrocarbon group,

a is an integer of any one of 1 to 3,

b is an integer of any one of 0 to 2,

n, m and x are the number of repeating units,

n is an integer of any one of 1 to 10,

m is an integer of any one of 1 to 5,

x is an integer of any one of 1 to 15.

In this case, in R of the oligomer represented by Formula 2, the aliphatic hydrocarbon group is an alkylene group having 1 to 20 carbon atoms; an alkylene group having 1 to 20 carbon atoms containing an isocyanate group (NCO); an alkoxyylene group having 1 to 20 carbon atoms; an alkenylene group having 2 to 20 carbon atoms; or an alkynylene group having 2 to 20 carbon atoms, wherein the alicyclic hydrocarbon group is a cycloalkylene group having 4 to 20 carbon atoms; a cycloalkylene group having 4 to 20 carbon atoms containing an isocyanate group (NCO); a cycloalkenylene group having 4 to 20 carbon atoms; or a heterocycloalkylene group having 2 to 20 carbon atoms, wherein the aromatic hydrocarbon group is an arylene group having 6 to 20 carbon atoms; Or it may be a heteroarylene group having 2 to 20 carbon atoms.

Currently, in most secondary batteries, the heat of reaction generated by an electrochemical (ex. overcharge) or chemical (ex. hot box) reaction raises the internal temperature of the battery, and when the temperature reaches a temperature above the ignition point, it is combined with surrounding oxygen There is a problem in that the secondary battery is ignited as it leads to a thermal-runaway phenomenon. Accordingly, it is very important to secure the flame retardancy by lowering the calorific value of the electrolyte in order to increase the high temperature stability of the secondary battery.

Accordingly, in the present invention, in order to secure flame retardancy and excellent electrochemical performance, an ionic liquid having excellent electrochemical safety and nonflammability may be included as a solvent.

Specifically, in the non-aqueous electrolyte for a lithium secondary battery according to an embodiment of the present invention, the ionic liquid includes a bis (fluorosulfonyl) imide anion as an anion component, and is represented by the following Chemical Formulas 2 to 6 as a cation component It may contain at least one or more cations selected from the group consisting of compounds.

[Formula 2]

In Formula 2,

R ₁ , R ₂ , R ₃ and R ₄ are each independently hydrogen or an alkyl group having 1 to 5 carbon atoms.

[Formula 3]

In Formula 3,

R ₅ and R ₆ are each independently an alkyl group having 1 to 5 carbon atoms.

[Formula 4]

In Formula 4,

R ₇ and R ₈ are each independently an alkyl group having 1 to 5 carbon atoms.

[Formula 5]

In Formula 5,

R ₉ , R ₁₀ , R ₁₁ and R ₁₂ are each independently hydrogen or an alkyl group having 1 to 5 carbon atoms.

[Formula 6]

In Formula 6,

R ₁₃ , R ₁₄ , R ₁₅ and R ₁₆ are each independently an alkyl group having 1 to 5 carbon atoms.

In this case, the cation represented by Formula 2 may be at least one selected from the group consisting of compounds represented by Formulas 2a and 2b below.

[Formula 2a]

[Formula 2b]

In addition, the cation represented by Formula 3 may be at least one selected from the group consisting of compounds represented by Formulas 3a and 3b below.

[Formula 3a]

[Formula 3b]

In addition, the cation represented by Formula 4 may be at least one selected from the group consisting of compounds represented by Formulas 4a and 4b below.

[Formula 4a]

[Formula 4b]

In addition, the cation represented by the formula (6) may be a compound represented by the following formula (6a).

[Formula 6a]

In addition, in the non-aqueous electrolyte for a lithium secondary battery according to an embodiment of the present invention, the lithium salt is a lithium salt containing the same anion as the anion of the ionic liquid, for example, has excellent solubility and conductivity, It is preferable to use lithium bisfluorosulfonyl imide (LiFSI) alone, which is known as a lithium salt with excellent durability and high electrochemical safety without generating a side reaction of a Lewis acid such as hydrofluoric acid (HF).

At this time, when the lithium salt includes a lithium salt including an anion different from the anion of the ionic liquid, an interaction between the anions in the electrolyte solution occurs, and the movement of lithium cations is reduced, so that the output characteristics of the secondary battery, etc. can be lowered Accordingly, in the non-aqueous electrolyte of the present invention, lithium bisfluorosulfonyl imide is included as the lithium salt, which is the same as the anion of the ionic liquid. can do.

In addition, in the nonaqueous electrolyte for a lithium secondary battery according to an embodiment of the present invention, the concentration of the lithium salt may be 1M or more, specifically 1M to 4M, specifically 1.2M to 4M, more specifically 1.2M to 3M.

When the concentration of the lithium salt in the non-aqueous electrolyte of the present invention satisfies the above range, ^{ion transport properties of high lithium cations (Li +} ) due to an increase in the amount of lithium cations present in the non-aqueous electrolyte (that is, cation transport rate (transference number)) ), it is possible to improve the problem that the reduction stability of the ionic liquid used as a solvent is lowered. Therefore, it is possible to implement the effect of improving the output characteristics of the lithium secondary battery. In addition, it is possible to prevent the occurrence of an exothermic reaction at a high temperature in the initial stage of the reaction by adding the effect of improving the flame retardancy. At this time, when the concentration of the electrolyte salt is 4M or more, since the viscosity of the electrolyte is greatly increased, it is difficult to secure the movement speed of lithium ions, the wetting property of the electrolyte is deteriorated, and the battery performance may be rather deteriorated.

In addition, in the non-aqueous electrolyte for a lithium secondary battery according to an embodiment of the present invention, the oligomer represented by Formula 1 may be an oligomer represented by Formula 1a below.

[Formula 1a]

In Formula 1a,

n1 and x1 are the number of repeating units,

n1 is an integer of any one of 1 to 10,

x1 is an integer in any one of 1 to 15.

In this case, the oligomer represented by Formula 1 may be included in an amount of 0.01 wt% to 10 wt%, specifically 0.5 wt% to 10 wt%, based on the total weight of the non-aqueous electrolyte for a lithium secondary battery.

When the content of the oligomer represented by Formula 1 is 0.01 wt% or more, the effect of lowering the surface tension of the electrolyte to which the ionic liquid is applied can be improved, and when the content of the oligomer is 10 wt% or less, resistance increase due to the addition of an excess of oligomer and lithium It is possible to prevent the restriction of the movement of ions and the consequent decrease in ionic conductivity.

The weight average molecular weight (MW) of the oligomer represented by Formula 1 may be controlled by the number of repeating units, and is about 1,000 g/mol to 100,000 g/mol, specifically 1,000 g/mol to 50,000 g/mol, more specifically As a result, it may be 1,000 g/mol to 10,000 g/mol. When the weight average molecular weight of the oligomer is within the above range, it is possible to effectively improve the wetting phenomenon of the electrolyte by reducing the surface tension of the electrolyte.

If the weight average molecular weight of the oligomer is less than 1,000 g/mol, it may not be possible to reduce the surface tension of the electrolyte. On the other hand, when the weight average molecular weight exceeds 100,000 g/mol, the oligomer properties themselves become rigid, and the affinity with the electrolyte solvent is lowered to make dissolution difficult, so that the viscosity of the electrolyte increases, which can rather reduce wettability.

The weight average molecular weight may mean a value converted to standard polystyrene measured by gel permeation chromatography (GPC), and unless otherwise specified, the molecular weight may mean a weight average molecular weight. For example, in the present invention, measurement is performed using Agilent's 1200 series under GPC conditions, and the column used at this time may be Agilent's PL mixed B column, and the solvent may be THF.

In this case, since the oligomer represented by Formula 1 includes a siloxane group (-Si-O) unit and a urethane group (-NC(O)O-) in the main chain, it has excellent solubility in an ionic liquid, It can be given the role of a surfactant in the Accordingly, the non-aqueous electrolyte for a lithium secondary battery including the oligomer represented by Chemical Formula 1 has a reduced surface tension with the electrode, thereby further improving the wetting of the electrolyte. In addition, the oligomer represented by Formula 1 is electrochemically very stable and includes a siloxane group (-Si-O) having low reactivity with Li in the main chain, thereby causing ^{side reactions of lithium ions (Li +} ) and lithium salts (salt). ), it is possible to control the decomposition reaction and the like, so that it is possible to reduce the generation of gases such as _{CO or CO 2 during overcharging.} Accordingly, it is possible to further improve the safety of the secondary battery by suppressing ignition during overcharging.

In addition, the non-aqueous electrolyte for a lithium secondary battery according to an embodiment of the present invention includes at least one additive selected from the group consisting of N,N'-dichlorohexylcarbodiimide (DCC), vinylene carbonate, saturated sultone, and cyclic sulfite. may further include.

The additive may be included in an amount of 10 wt% or less, specifically 0.1 wt% to 7 wt%, and more specifically 0.5 wt% to 5 wt%, based on the total weight of the non-aqueous electrolyte for a lithium secondary battery.

The additive is a compound capable of inhibiting the occurrence of side reactions in the anode and cathode coatings. When the additive is included in an amount of 10% by weight or less, the oxidation stability of the electrolyte and the amount of heat generated by the electrolyte decomposition reaction are not affected, and the initial During activation, it is mostly consumed to protect the surface of the anode and does not remain decomposed.

Among the additives, the dichlorohexylcarbodiimide (DCC) does not directly form the negative passivation layer, but suppresses HF production and suppresses the generation of byproducts caused by salt anions, and ultimately prevents side reactions in the positive and negative electrode films By suppressing it, the effect of improving resistance can be expected.

Representative examples of the saturated sultone include 1,3-propane sultone (PS) and 1,4-butane sultone, and examples of the unsaturated sultone include ethensultone, 1,3-propene sultone, and 1,4-butene sultone. , or 1-methyl-1,3-propene sultone.

Representative examples of the cyclic sulfite include ethylene sulfite (Esa), methyl ethylene sulfite, ethyl ethylene sulfite, 4,5-dimethyl ethylene sulfite, 4,5-diethyl ethylene sulfite, propylene sulfite, 4, 5-dimethyl propylene sulfite, 4,5-diethyl propylene sulfite, 4,6-dimethyl propylene sulfite, 4,6-diethyl propylene sulfite, or 1,3-butylene glycol sulfite; have.

The non-aqueous electrolyte for a lithium secondary battery of the present invention according to an embodiment may further include at least one additive for forming an SEI film selected from the group consisting of acyclic sulfones, alkylsilyl compounds, and inorganic compounds, if necessary.

Representative examples of the acyclic sulfone include divinyl sulfone, dimethyl sulfone, diethyl sulfone, methylethyl sulfone, or methylvinyl sulfone.

Representative examples of the alkylsilyl compound include tri (trimethylsilyl) phosphate, tri (trimethylsilyl) phosphite, tri (triethylsilyl) phosphate, tri (triethylsilyl) phosphite, tri (trimethylsilyl) borate, or tri ( triethylsilyl) borate; and the like.

Representative examples of the inorganic compound include lithium difluoro(bisoxalate) phosphate, lithium difluorophosphate, lithium tetrafluorooxalatophosphate, lithium bis(fluorosulfonyl) imide, lithium bis(trifluoro methyl sulfonyl) imide and the like.

Most of these additives are preferably included in an amount of 10% by weight or less based on the total weight of the non-aqueous electrolyte for lithium secondary batteries so as not to induce side reactions.

In addition, in one embodiment of the present invention

positive, negative,

a separator interposed between the positive electrode and the negative electrode, and

Contains non-aqueous electrolyte,

The non-aqueous electrolyte provides a lithium secondary battery, which is a non-aqueous electrolyte for a lithium secondary battery of the present invention.

Specifically, the lithium secondary battery of the present invention can be prepared by injecting the non-aqueous electrolyte for a lithium secondary battery of the present invention into an electrode assembly in which a positive electrode, a negative electrode, and a separator selectively interposed between the positive and negative electrodes are sequentially stacked.

In this case, the positive electrode, the negative electrode, and the separator constituting the electrode assembly may be all those manufactured and used in a conventional manner when manufacturing a lithium secondary battery.

First, the positive electrode may be manufactured by forming a positive electrode mixture layer on a positive electrode current collector. The positive electrode mixture layer may be formed by coating a positive electrode slurry including a positive electrode active material, a binder, a conductive material, and a solvent on a positive electrode current collector, followed by drying and rolling.

The positive electrode current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or carbon on the surface of aluminum or stainless steel. , nickel, titanium, silver, etc. may be used.

In addition, the positive active material is a compound capable of reversible intercalation and deintercalation of lithium, and specifically includes a lithium composite metal oxide containing lithium and one or more metals such as cobalt, manganese, nickel or aluminum. can do. More specifically, the lithium composite metal oxide is a lithium-manganese-based oxide (eg, LiMnO ₂ , LiMn ₂ O _{4 ,} etc.), a lithium-cobalt-based oxide (eg, LiCoO ₂ etc.), lithium-nickel-based oxide (for example, LiNiO ₂ and the like), lithium-nickel-manganese-based oxide (for example, LiNi _1-Y Mn _Y O ₂ (where, 0 <Y <1), LiMn _2-z Ni _z O ₄ ( here, 0 <Z <2) and the like), lithium-nickel-cobalt oxide (e.g., LiNi _1-Y1 Co _Y1 O ₂ (here, 0 <Y1 <1) and the like), lithium-manganese-cobalt oxide (e. g., LiCo _1-Y2 Mn _Y2 O ₂ (here, 0 <Y2 <1), LiMn 2 - z1 Co z1 O 4 ( here, 0 <Z1 <2) and the like), lithium-nickel -Manganese-cobalt oxide (for example, Li(Ni _p Co _q Mn _r1 )O ₂ (here, 0<p<1, 0<q<1, 0<r1<1, p+q+r1= 1) or Li(Ni _p1 Co _q1 Mn _r2 )O ₄ (where 0<p1<2, 0<q1<2, 0<r2<2, p1+q1+r2=2), etc.), or lithium- Nickel-cobalt-transition metal (M) oxide (eg, Li(Ni _p2 Co _q2 Mn _r3 M _S2 )O ₂ , where M is Al, Fe, V, Cr, Ti, Ta, Mg and Mo is selected from the group consisting of, and p2, q2, r3 and s2 are atomic fractions of independent elements, respectively, 0<p2<1, 0<q2<1, 0<r3<1, 0<s2<1, p2+q2 +r3+s2=1), etc.), and any one or two or more compounds of these may be included.

_{Among them, the lithium composite metal oxide is LiCoO 2} , LiMnO ₂ , LiNiO ₂ , lithium nickel manganese cobalt oxide (for example, Li(Ni _1/3 Mn _1/3 Co _{1 )} in that the capacity characteristics and stability of the battery can be improved. _/3 )O ₂ , Li(Ni _0.6 Mn _0.2 Co _0.2 )O ₂ , Li(Ni _0.5 Mn _0.3 Co _0.2 )O ₂ , Li(Ni _0.7 Mn _0.15 Co _0.15 )O _{2 ,} and Li(Ni _0.8 Mn _0.1 Co _{0.1 )} )O ₂ and the like), or lithium nickel cobalt aluminum oxide (eg, Li(Ni _0.8 Co _0.15 Al _0.05 )O _{2 ,} etc.).

The positive active material may be included in an amount of 40 wt% to 90 wt%, specifically 40 wt% to 75 wt%, based on the total weight of the solid content in the cathode slurry.

The binder is a component that assists in bonding between the active material and the conductive material and bonding to the current collector, and is typically added in an amount of 1 to 30% by weight based on the total weight of the solid content in the positive electrode slurry. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoro roethylene, polyethylene, polypropylene, ethylene-propylene-diene ter polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, various copolymers, and the like.

In addition, the conductive material is not particularly limited as long as it has conductivity without causing chemical change in the battery. For example, carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal black carbon powder, such as; Graphite powder, such as natural graphite, artificial graphite, or graphite with a highly developed crystal structure; conductive fibers such as carbon fibers and metal fibers; metal powders such as carbon fluoride, aluminum, and nickel powder; conductive whiskeys such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives may be used.

In this case, the average particle diameter (D ₅₀ ) of the conductive material may be 10 μm or less, specifically 0.01 μm to 10 μm, and more specifically 0.01 μm to 1 μm. At this time, when the average particle diameter of the conductive material exceeds 10 μm, dispersibility is poor, and the effect of improving conductivity by adding graphite powder is insignificant, which is not preferable.

In the present invention, the average particle diameter (D ₅₀ ) of the conductive material may be defined as a particle diameter corresponding to 50% of the accumulated number in the particle size distribution curve of the particles. The average particle diameter (D ₅₀ ) may be measured using, for example, a laser diffraction method. In general, the laser diffraction method can measure a particle diameter of several mm from a submicron region, and can obtain high reproducibility and high resolution results.

In addition, the specific surface area of the conductive material may be 10m ² /g to 1000m ² /g. For example, specifically, the specific surface area of the carbon powder is 40 to 80 m 2 /g, and the specific surface area of the graphite powder is 10 to 40 m 2 /g, and the specific surface area is small compared to the carbon powder, but the conductivity is the carbon powder better than

In this case, as the specific surface area of the conductive material increases, the contact area with the positive electrode active material increases, and as a result, it is easy to form a conductive path between the positive electrode active material particles. However, when the specific surface area is too large, specifically, when ^{it exceeds 1000 m 2} /g, there is a fear that the energy density of the positive electrode may be lowered due to the bulky structural characteristics. On the other hand, when the specific surface area of the conductive material is too small, specifically, ^{if it is less than 100 m 2} /g, there is a risk of a decrease in the contact area with the positive electrode active material and aggregation between the conductive materials. In the present invention, the specific surface area of the conductive material can be defined as a value (BET specific surface area) measured by a nitrogen adsorption method.

The conductive material may be added in an amount of 1 to 30% by weight based on the total weight of the solid content in the positive electrode slurry.

Specific examples of such commercially available conductive materials include acetylene black-based Chevron Chemical Company, Denka Singapore Private Limited, Gulf Oil Company, etc.), Ketjenblack, EC series (products of the Armak Company), the Vulcan XC-72 (products of the Cabot Company) and the Super P (products of the Timcal Company).

In addition, the solvent may include an organic solvent such as N-methyl-2-pyrrolidone (NMP), and may be used in an amount having a desirable viscosity when the positive active material and optionally a binder and a conductive material are included. For example, it may be included so that the solid content concentration in the slurry including the positive electrode active material and, optionally, the binder and the conductive material is 10 wt% to 60 wt%, preferably 20 wt% to 50 wt%.

In addition, the negative electrode may be manufactured by forming a negative electrode mixture layer on the negative electrode current collector. The negative electrode mixture layer may be formed by coating a negative electrode slurry including a negative electrode active material, a binder, a conductive material and a solvent on a negative electrode current collector, drying and rolling.

The negative electrode current collector generally has a thickness of 3 to 500 μm. Such a negative current collector is not particularly limited as long as it has high conductivity without causing a chemical change in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel. A surface treated with carbon, nickel, titanium, silver, etc., an aluminum-cadmium alloy, etc. may be used on the surface. In addition, like the positive electrode current collector, the bonding strength of the negative electrode active material may be strengthened by forming fine irregularities on the surface, and may be used in various forms such as a film, sheet, foil, net, porous body, foam, non-woven body, and the like.

The negative active material includes lithium metal, a carbon-based material capable of reversibly intercalating/deintercalating lithium ions, an alloy of lithium metal, a metal composite oxide, a material capable of doping and dedoping lithium, and a transition metal It may include at least one selected from the group consisting of oxides.

As the carbon-based material capable of reversibly intercalating/deintercalating lithium ions, any carbon-based negative active material generally used in lithium ion secondary batteries may be used without particular limitation, and representative examples thereof include crystalline carbon, Amorphous carbon or these may be used together. Examples of the crystalline carbon include graphite such as amorphous, plate-like, flake, spherical or fibrous natural graphite or artificial graphite, and examples of the amorphous carbon include soft carbon (low-temperature calcined carbon). or hard carbon, mesophase pitch carbide, and calcined coke.

The lithium metal alloy includes lithium and Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al and Sn from the group consisting of Alloys of metals of choice may be used.

Examples of the metal composite oxide include PbO, PbO ₂ , Pb ₂ O ₃ , Pb ₃ O ₄ , Sb ₂ O ₃ , Sb ₂ O ₄ , Sb ₂ O ₅ , GeO, GeO ₂ , Bi ₂ O ₃ , Bi ₂ O _{4 .} , Bi ₂ O ₅ , Li _x Fe ₂ O ₃ (0≤≤x≤≤1), Li _x WO ₂ (0≤≤x≤≤1), and Sn _x Me _1-x Me' _y O _z (Me : Mn, Fe, Pb, Ge; Me': Al, B, P, Si, elements of groups 1, 2, and 3 of the periodic table, halogen; 0<x≤≤1;1≤≤y≤≤3; 1 ≤z≤≤8) may be used.

Materials capable of doping and dedoping lithium include Si, SiO _x (0 < x < 2), Si-Y alloy (where Y is an alkali metal, alkaline earth metal, group 13 element, group 14 element, transition metal, An element selected from the group consisting of rare earth elements and combinations thereof, but not Si), Sn, SnO ₂ , Sn-Y (wherein Y is an alkali metal, an alkaline earth metal, a group 13 element, a group 14 element, a transition metal, a rare earth) It is an element selected from the group consisting of elements and combinations thereof, and is not Sn), and at least one of these and SiO ₂ may be mixed and used. The element Y includes Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ti, Ge, P, As, Sb, Bi, S, It may be selected from the group consisting of Se, Te, Po, and combinations thereof.

Examples of the transition metal oxide include lithium-containing titanium composite oxide (LTO), vanadium oxide, and lithium vanadium oxide.

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

The binder is a component that assists in bonding between the conductive material, the active material, and the current collector, and is typically added in an amount of 1 to 30% by weight based on the total weight of the solid content in the negative electrode slurry. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoro and roethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, fluororubber, and various copolymers thereof.

The conductive material is a component for further improving the conductivity of the negative electrode active material, and may be added in an amount of 1 to 20 wt % based on the total weight of the solid content in the negative electrode slurry. Such a conductive material is not particularly limited as long as it has conductivity without causing a chemical change in the battery. For example, graphite such as natural graphite or artificial graphite used in the manufacture of a positive electrode; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; metal powders such as carbon fluoride, aluminum, and nickel powder; conductive whiskeys such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives may be used.

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

In addition, the separator serves to block the internal short circuit of both electrodes and impregnate the electrolyte. A separator composition is prepared by mixing a polymer resin, a filler, and a solvent, and then the separator composition is directly coated on the electrode and dried. A separator film may be formed, or the separator composition may be cast and dried on a support, and then formed by laminating a separator film peeled off from the support on an electrode.

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

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

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

Hereinafter, examples will be given to describe the present invention in detail. However, the embodiments according to the present invention may be modified in various other forms, and the scope of the present invention should not be construed as being limited to the embodiments described in detail below. The embodiments of the present invention are provided to more completely explain the present invention to those of ordinary skill in the art.

Example

Example One.

To 99 g of ethylmethylimidazolium-bis(fluorosulfonyl)imide (EMI-FIS) in which 1.2M LiFSI was dissolved, 1 g of the oligomer represented by Formula 1a (weight average molecular weight (Mw): 3,000) was added, followed by lithium secondary A non-aqueous electrolyte for batteries was prepared.

Example 2.

A non-aqueous electrolyte for a lithium secondary battery was prepared in the same manner as in Example 1, except that 3M LiFSI was dissolved in the preparation of the non-aqueous electrolyte for a lithium secondary battery in Example 1.

Example 3.

Except for using methylpropylpyrrolidinium-bis(fluorosulfonyl)imide (Pyr13-FSI) instead of EMI-FIS as an ionic liquid in the preparation of the non-aqueous electrolyte for a lithium secondary battery in Example 1, A non-aqueous electrolyte for a lithium secondary battery was prepared in the same manner as in Example 1.

Example 4.

In Example 1, when preparing the non-aqueous electrolyte for a lithium secondary battery, 0.01 g of the oligomer represented by Formula 1a (weight average molecular weight (Mw): 3,000) was dissolved in 99.99 g of a solvent. A non-aqueous electrolyte for a lithium secondary battery was prepared by this method.

Example 5.

To 99.5 g of ethylmethylimidazolium-bis(fluorosulfonyl)imide (EMI-FIS) dissolved in 4M LiFSI, 0.5 g of the oligomer represented by Formula 1a (weight average molecular weight (Mw): 3,000) was added to lithium A non-aqueous electrolyte for secondary batteries was prepared.

Example 6.

A non-aqueous electrolyte for a lithium secondary battery was prepared in the same manner as in Example 2, except that 11 g of the oligomer represented by Formula 1a was added to 89 g of the solvent when preparing the non-aqueous electrolyte for a lithium secondary battery in Example 2.

comparative example One.

A non-aqueous electrolyte for a lithium secondary battery was prepared by dissolving 1.2 M LiFSI in 100 g of ethylene carbonate:ethylmethyl carbonate (3:7% by volume).

comparative example 2.

A non-aqueous electrolyte for a lithium secondary battery was prepared by dissolving 3M LiFSI in 100 g of ethylene carbonate:ethylmethyl carbonate (3:7% by volume).

comparative example 3.

A non-aqueous electrolyte for a lithium secondary battery was prepared by dissolving 1.2 M LiFSI in 100 g of ethylmethylimidazolium-bis(fluorosulfonyl)imide (EMI-FIS).

comparative example 4.

A non-aqueous electrolyte for a lithium secondary battery was prepared in the same manner as in Example 1, except that the oligomer represented by the following Chemical Formula 7 was used instead of the oligomer represented by Chemical Formula 1a when preparing the non-aqueous electrolyte for a lithium secondary battery in Example 1 prepared.

[Formula 7]

electrolyte oligomer lithium salt menstruum content (g) additive content (g) Example 1 1.2M LiFSI EMI-FIS 99 Formula 1a One Example 2 3M LiFSI EMI-FIS 99 Formula 1a One Example 3 1.2M LiFSI Pyr13-FSI 99 Formula 1a One Example 4 1.2M LiFSI EMI-FIS 99.99 Formula 1a 0.01 Example 5 4M LiFSI EMI-FIS 99.5 Formula 1a 0.5 Example 6 3M LiFSI EMI-FIS 89 Formula 1a 11 Comparative Example 1 1.2M LiFSI EC:EMC=3:7 100 - - Comparative Example 2 3M LiFSI EC:EMC=3:7 100 - - Comparative Example 3 1.2M LiFSI EMI-FIS 100 - - Comparative Example 4 1.2M LiFSI EMI-FIS 99 Formula 7 One

Experimental example

Experimental example 1: Evaluation of solubility of oligomers in ionic liquids

The non-aqueous electrolyte prepared in Examples 1 and 3 and the non-aqueous electrolyte prepared in Comparative Example 4 were stored with stirring at room temperature (25° C.) for 1 day, and then the solubility of the oligomer in the ionic liquid was evaluated, and the The results are shown in Table 2 below.

Example 1
non-aqueous electrolyte Example 3
non-aqueous electrolyte Comparative Example 5
non-aqueous electrolyte Dissolution result O O X

In Table 2 above,

O: When the oligomer is completely dissolved in the ionic liquid

X: When the oligomer does not dissolve in the ionic liquid and remains partially

As shown in Table 2, in the case of the non-aqueous electrolyte of Comparative Example 4 containing the oligomer of Formula 7, the affinity between the ionic liquid and the oligomer is low, so that the oligomer of Formula 7 is not completely dissolved in the ionic liquid, It can be seen that the low wettability effect of the electrolyte is not suitable for use as a non-aqueous electrolyte for lithium secondary batteries.

On the other hand, in the case of the non-aqueous electrolytes of Examples 1 and 3 of the present invention containing the oligomer represented by Formula 1a including a Si-O unit in the main chain, since the affinity between the ionic liquid and the oligomer is high, the formula 1a It was confirmed that all of the displayed oligomers were dissolved in the ionic liquid. Therefore, it is expected that the wettability of the electrolyte can be improved during the manufacture of the lithium secondary battery.

Experimental example 2: aluminum current collector Corrosion Characterization Test

Corrosion characteristics of the aluminum current collector as the positive electrode current collector were evaluated using the non-aqueous electrolytes prepared in Examples 1 to 6 and the non-aqueous electrolytes prepared in Comparative Examples 1 to 3.

At this time, using the aluminum foil used for the positive electrode current collector as the working electrode, using the lithium metal as the reference electrode, and using the lithium metal electrode as the auxiliary electrode, the non-water prepared in Examples 1 to 6 and Comparative Examples 1 to 3 After immersion in the electrolyte, the 4.5V potential is maintained for 2h using the cyclic voltammetry method under a glove box in an argon (Ar) atmosphere with moisture and oxygen concentrations of 10 ppm or less, while maintaining the By measuring the current, it was measured whether the aluminum foil was corroded.

The results are shown in Table 3 below.

Whether aluminum corrosion
(whether oxidation current is generated) Example 1 X Example 2 X Example 3 X Example 4 X Example 5 X Example 6 X Comparative Example 1 O Comparative Example 2 O Comparative Example 3 X

Oxidative corrosion of the aluminum current collector during the manufacture of conventional secondary batteries is caused by FSI anions, and FSI dissociated in carbonate-based solvents in an oxidizing atmosphere. It is caused by negative ions taking electrons from the aluminum current collector.

However, in the case of the non-aqueous electrolyte of Examples 1 to 6 and the non-aqueous electrolyte of Comparative Example 3 of the present invention, they consist only of an ionic liquid and a lithium salt instead of a carbonate-based solvent, so that the FSI anion is not in a dissociated state, Since it is difficult to obtain electrons from the aluminum current collector, oxidative corrosion of the aluminum current collector does not occur as shown in Table 3 above.

On the other hand, in the case of the non-aqueous electrolytes of Comparative Examples 1 and 2, it can be seen that oxidative corrosion of the aluminum current collector occurs.

As such, it is known that, moreover, when oxidative corrosion of the aluminum current collector occurs, an electric current is generated.

Specifically, referring to FIGS. 1 to 3 , when the non-aqueous electrolyte of Example 1 of the present invention containing an ionic liquid (EMI-FIS) as a main solvent is used, an ultra-fine current of ^{2.0 X 10 -6 A or less is} (see FIG. 1) and, as shown in FIG. 2, when using the non-aqueous electrolyte of Example 3 of the present invention containing an ionic liquid (Pyr13-FSI) as a main solvent, 4.0 X 10 ^-6 A or less ultrafine It can be seen that a current appears (see FIG. 2).

From these results, it can be seen that, when an ionic liquid is included as a main solvent like the non-aqueous electrolyte of the present invention, corrosion of the aluminum current collector is not caused.

On the other hand, in the case of using the non-aqueous electrolyte of Comparative Example 1 using a carbonate-based solution as the main solvent as shown in FIG. 3 , in the point that a current ^{of about 2.5 X 10 -3 A or less appears initially, oxidation of the aluminum current collector} It can be seen that corrosion has occurred.

Experimental example 3. Oxidative Stability Evaluation Experiment

A platinum (Pt) disk electrode as a working electrode, lithium metal as a reference electrode, and a platinum (Pt) wire electrode as an auxiliary electrode, the nonaqueous electrolyte prepared in Examples 1 to 5 and Comparative Example 1 were used. After each immersion in one non-aqueous electrolyte, a linear sweep voltammetry method was used at a scan rate of 20 mV/s under a glove box in an argon (Ar) atmosphere with a moisture and oxygen concentration of 10 ppm or less. Thus, the electrochemical oxidation stability of the aluminum current collector was evaluated.

The results are shown in FIGS. 4 and 5, respectively.

First, looking at FIG. 5, when the non-aqueous electrolytes of Examples 1 to 5 containing an ionic liquid are used, the ionic liquid itself used as the main solvent has excellent oxidation resistance compared to the general carbonate-based organic solvent. It can be seen that oxidation is caused in a high voltage region of 5.0 V or higher (see FIG. 5 ).

On the other hand, referring to FIG. 4, when the non-aqueous electrolyte of Comparative Example 1 containing a carbonate-based solvent is used, it is confirmed that oxidation is caused before 4.0V, and oxidation occurs several times or more in the 4.0V region. can

Therefore, when the nonaqueous electrolytes of Examples 1 to 5 are used in the high voltage region, it is determined that the oxidation stability of the secondary battery can be remarkably improved compared to the case of using the nonaqueous electrolyte of Comparative Example 1.

Experimental example 4. Flame Retardant Evaluation Experiment

The flame retardancy was evaluated by dropping 2 ml of each of the non-aqueous electrolyte prepared in Examples 1 to 6 and the non-aqueous electrolyte prepared in Comparative Examples 1 to 3 on an aluminum plate, and then applying a flame. The results are shown in Table 4 and FIG. 6 . Among them, the results of using the non-aqueous electrolyte prepared in Examples 2, 4, and 5 and the non-aqueous electrolyte prepared in Comparative Example 1 are shown in FIG. 6 below.

ignition or not Example 1 X Example 2 X Example 3 X Example 4 X Example 5 X Example 6 X Comparative Example 1 O Comparative Example 2 Δ Comparative Example 3 X

In Table 4 above,

X: If the flame does not stick when touched, or goes out within 2 seconds after sticking

△: When the flame is put on and goes out within 2 to 4 seconds after the flame is attached

O: If the flame stays on for more than 5 seconds when the flame is touched

Referring to Tables 4 and 6, in the case of the nonaqueous electrolytes prepared in Examples 1 to 6 using an ionic liquid as a solvent and the nonaqueous electrolytes prepared in Comparative Example 3, ignition does not occur, whereas a carbonate-based solvent is used as the main solvent. It can be seen that ignition occurs in the non-aqueous electrolytes prepared in Comparative Examples 1 and 2 containing

At this time, in the case of the non-aqueous electrolyte of Comparative Example 2, since the salt concentration (3M) is high and the flame retardancy is improved, the flame is extinguished within 3 seconds after being attached, but it was confirmed that the non-aqueous electrolyte did not express as perfect incombustibility as in the Example.

Accordingly, it can be seen that the flame retardancy of the non-aqueous electrolyte for a lithium secondary battery of the present invention is improved.

Experimental example 5. Ionic Conductivity Assessment

The ionic conductivity of each of the nonaqueous electrolytes prepared in Examples 1, 2, 4 and 6 and the nonaqueous electrolytes prepared in Comparative Examples 1 to 3 was measured at room temperature using a probe-type ion conductivity measuring instrument. Table 5 below shows the ionic conductivity results for different lithium salt concentrations.

Ion Conductivity (mS/cm, 25℃) Contains 1.2M LiFSI
non-aqueous electrolyte Example 1 11 Example 4 11.2 Comparative Example 1 9.4 Comparative Example 3 11.5 Contains 3M LiFSI
non-aqueous electrolyte Example 2 8.0 Example 6 7.2 Comparative Example 2 3.1

As shown in Table 5, the ionic conductivity of the non-aqueous electrolyte of Example 1, the non-aqueous electrolyte of Example 4, the non-aqueous electrolyte of Comparative Example 1, and the non-aqueous electrolyte of Comparative Example 3 with a lithium salt concentration of 1.2 M. The ionic conductivity (11.5 mS/cm) of the non-aqueous electrolyte of Example 1 (11 mS/cm), the non-aqueous electrolyte of Example 4 (11.2 mS/cm) and Comparative Example 3 using a liquid (11.5 mS/cm) was It can be seen that the ionic conductivity (9.4 mS/cm) of the non-aqueous electrolyte of Comparative Example 1 is higher than that of the non-aqueous electrolyte.

On the other hand, in the case of the non-aqueous electrolytes of Examples 2 and 6 and Comparative Example 2 having a lithium salt concentration of 3M, the viscosity increased as the salt concentration increased, and the ionic conductivity decreased compared to the non-aqueous electrolyte solution having a lithium salt concentration of 1.2M. it can be seen that

At this time, looking at the ionic conductivity of the non-aqueous electrolytes of Examples 2 and 6 and Comparative Example 2 in which the lithium salt concentration is 3M, the non-aqueous electrolyte of Example 2 containing the ionic liquid and the oligomer of Formula 1a in a specific range It can be seen that the ionic conductivity (8.0 mS/cm) is superior to that of the non-aqueous electrolyte solution (3.1 mS/cm) of Comparative Example 2 containing a carbonate-based solvent.

On the other hand, it can be seen that the ionic conductivity of the non-aqueous electrolyte of Comparative Example 4 (7.2 mS/cm ) containing an excess of the oligomer of Formula 1a is deteriorated compared to the ionic conductivity of Example 2.

Experimental example 6: Output Characteristics Evaluation Experiment

( Electrode manufacturing)

_{LiNi 0} , the cathode active material _{. 6} Co _{0 . 2} Mn _{0 . After mixing 2} O ₂ (NCM), carbon black as a conductive material, and polyvinylidene fluoride (PVDF) as a binder in a weight ratio of 85:6:9, N-methyl-2-pyrrolidone (NMP) ) to prepare a cathode active material slurry having a solid content of 60 wt%. The positive electrode active material slurry was coated on an aluminum (Al) thin film as a positive electrode current collector having a thickness of about 20 μm, dried to prepare a positive electrode, and then a positive electrode was manufactured by performing a roll press.

Carbon powder as an anode active material, PVDF as a binder, and carbon black as a conductive material were mixed at 96 wt%, 3 wt% and 1 wt%, respectively, and then added to NMP as a solvent to have a solid content of 80 wt%. A slurry was prepared. The negative electrode active material slurry was applied to a 10 μm-thick copper (Cu) thin film as a negative electrode current collector, dried to prepare a negative electrode, and then roll press was performed to prepare a negative electrode.

(Secondary battery manufacturing)

A separator consisting of three layers of polypropylene/polyethylene/polypropylene (PP/PE/PP) was interposed between the prepared positive electrode and the negative electrode, and sequentially stacked to prepare an electrode assembly.

The assembled electrode assembly was housed in a battery case, and the non-aqueous electrolytes for lithium secondary batteries prepared in Examples 1 to 6 and Comparative Examples 1 to 3 were respectively injected and stored at room temperature for 2 days to prepare a lithium secondary battery. .

After formation at 100mA current (0.1 C rate) for each secondary battery, 4.2 V 333mA (0.3 C, 0.05 C cut-off) CC/CV charge and 3 V 333 mA (0.3 C) CC discharge were performed. Repeated times . After that, the capacity is measured by discharging the cells in a fully charged state at current densities of 0.3C, 1C, 2C, and 5C rates, respectively, and the output retention rate (%) at 1C, 2C, and 5C based on 0.3C (100) It was calculated and shown in Table 6 below (unit is % in the table below) .

0.3C 1C 2C 5C Non-aqueous electrolyte containing 1.2M LiFSI Example 1 100 99.5 98 90 Example 3 100 98.4 94.1 80.5 Example 4 100 97.5 92.7 79.9 Comparative Example 1 100 99.1 90.1 78.4 Comparative Example 3 100 88.1 42.2 21.5 Non-aqueous electrolyte containing 3M LiFSI Example 2 100 99 97.1 84.1 Example 6 100 89 75 42 Comparative Example 2 100 90.1 86.4 74.1 Non-aqueous electrolyte containing 4M LiFSI Example 5 100 97.2 96 81.6

Looking at Table 6, the secondary batteries including the non-aqueous electrolytes of Examples 1 to 5 including the ionic liquid and the oligomer of Formula 1a in a specific range had the output retention rate (%) at 5C mostly maintained at 79.9% or more. Able to know.

Specifically, a secondary battery containing the non-aqueous electrolyte of Example 1 having a lithium salt concentration of 1.2 M, a secondary battery containing the non-aqueous electrolyte of Example 3, a secondary battery containing the non-aqueous electrolyte of Example 4, Comparative Example 1 Looking at the output characteristics of the secondary battery containing the non-aqueous electrolyte and the secondary battery containing the non-aqueous electrolyte of Comparative Example 3, the secondary containing the non-aqueous electrolyte of Example 1 including the ionic liquid and the oligomer of Formula 1a in a specific range The output retention rate (%) of the battery (90%), the secondary battery containing the nonaqueous electrolyte of Example 3 (80.5%), and the secondary battery containing the nonaqueous electrolyte of Example 4 (79.9%) was the nonaqueous electrolyte of Comparative Example 1 It can be seen that the improvement compared to the secondary battery (78.4%) containing

In this case, in the case of the secondary battery using the non-aqueous electrolyte of Example 4 containing a small amount of oligomer, the effect of improving electrolyte wettability is low due to the low oligomer content, and thus it can be seen that the output characteristics are lower than in Examples 1 to 3.

In addition, in the case of the lithium secondary battery containing the non-aqueous electrolyte of Comparative Example 3 containing only the ionic liquid without including the oligomer, the electrolyte wettability was very low, and it was found that the output characteristics were significantly deteriorated compared to the non-aqueous electrolyte of Comparative Example 1. .

On the other hand, in the case of the secondary battery containing the non-aqueous electrolyte of Example 2 having a lithium salt concentration of 3M, the secondary battery containing the non-aqueous electrolyte of Example 6, and the secondary battery containing the non-aqueous electrolyte of Comparative Example 2, the lithium salt concentration was As the viscosity increases, it can be seen that the output retention rate (%) is decreased by a small amount compared to the secondary batteries including the non-aqueous electrolyte having the lithium salt concentration of 1.2M.

At this time, the secondary battery containing the non-aqueous electrolyte of Example 2 and the secondary battery containing the non-aqueous electrolyte of Example 6 and the secondary battery containing the non-aqueous electrolyte of Comparative Example 2 having a lithium salt concentration of 3M (%) Looking at it, the output retention rate of the secondary battery (84.1%) including the non-aqueous electrolyte of Example 1 containing the ionic liquid and the oligomer of Formula 1a in a specific range contains the non-aqueous electrolyte of Comparative Example 2 containing a carbonate-based solvent It can be seen that it is superior to that of the secondary battery (74.1%).

In addition, in the case of the secondary battery (42%) containing the non-aqueous electrolyte of Example 6 containing an excess of oligomer, the movement of lithium ions was prevented due to the rather high content of oligomer, so that the output characteristics of Example 2 and Comparative Example 2 It can be seen that the secondary battery is deteriorated compared to the secondary battery.

Claims (14)

A non-aqueous electrolyte for a lithium secondary battery comprising a solvent, a lithium salt and an additive,
The solvent comprises an ionic liquid comprising a bis (fluorosulfonyl) imide anion as an anion component,
The lithium salt includes lithium bis(fluorosulfonyl)imide (LiFSI),
The additive includes an oligomer represented by the following formula (1),
The oligomer represented by Formula 1 is a non-aqueous electrolyte for a lithium secondary battery that is included in an amount of 0.01 wt % to 10 wt % based on the total weight of the non-aqueous electrolyte for a lithium secondary battery.
[Formula 1]

In Formula 1,
R ₀ is a substituted or unsubstituted C 1 to C 5 alkylene group,
R _a and R _b are a substituted or unsubstituted C 1 to C 3 alkyl group,
R' and R" are each independently hydrogen or an alkyl group having 1 to 3 carbon atoms,
R is an aliphatic, alicyclic or aromatic hydrocarbon group,
a is an integer of any one of 1 to 3,
b is an integer of any one of 0 to 2,
n, m and x are the number of repeating units,
n is an integer of any one of 1 to 10,
m is an integer of any one of 1 to 5,
x is an integer of any one of 1 to 15.
The method according to claim 1,
In the oligomer represented by Formula 1,
The aliphatic hydrocarbon group is an alkylene group having 1 to 20 carbon atoms; an alkylene group having 1 to 20 carbon atoms containing an isocyanate group (NCO); an alkoxyylene group having 1 to 20 carbon atoms; an alkenylene group having 2 to 20 carbon atoms; or an alkynylene group having 2 to 20 carbon atoms;
The alicyclic hydrocarbon group is a cycloalkylene group having 4 to 20 carbon atoms; a cycloalkylene group having 4 to 20 carbon atoms containing an isocyanate group (NCO); a cycloalkenylene group having 4 to 20 carbon atoms; Or a heterocycloalkylene group having 2 to 20 carbon atoms;
The aromatic hydrocarbon group is an arylene group having 6 to 20 carbon atoms; Or a non-aqueous electrolyte for a lithium secondary battery that is a heteroarylene group having 2 to 20 carbon atoms.
The method according to claim 1,
The ionic liquid is a non-aqueous electrolyte for a lithium secondary battery comprising at least one selected from the group consisting of compounds represented by the following Chemical Formulas 2 to 6 as a cation.
[Formula 2]

In Formula 2,
R ₁ , R ₂ , R ₃ and R ₄ are each independently hydrogen or an alkyl group having 1 to 5 carbon atoms.

[Formula 3]

In Formula 3,
R ₅ and R ₆ are each independently an alkyl group having 1 to 5 carbon atoms.

[Formula 4]

In Formula 4,
R ₇ and R ₈ are each independently an alkyl group having 1 to 5 carbon atoms.

[Formula 5]

In Formula 5,
R ₉ , R ₁₀ , R ₁₁ and R ₁₂ are each independently hydrogen or an alkyl group having 1 to 5 carbon atoms.

[Formula 6]

In Formula 6,
R ₁₃ , R ₁₄ , R ₁₅ and R ₁₆ are each independently an alkyl group having 1 to 5 carbon atoms.
4. The method according to claim 3,
The cation represented by Formula 2 is at least one selected from the group consisting of compounds represented by Formulas 2a and 2b below.
[Formula 2a]

[Formula 2b]

4. The method according to claim 3,
The cation represented by Formula 3 is at least one or more selected from the group consisting of compounds represented by Formulas 3a and 3b.
[Formula 3a]

[Formula 3b]

4. The method according to claim 3,
The cation represented by Formula 4 is at least one or more selected from the group consisting of compounds represented by Formulas 4a and 4b.
[Formula 4a]

[Formula 4b]

4. The method according to claim 3,
The cation represented by the formula (6) is a non-aqueous electrolyte for a lithium secondary battery that is a compound represented by the following formula (6a).
[Formula 6a]

The method according to claim 1,
The concentration of the lithium salt is 1M to 4M non-aqueous electrolyte for a lithium secondary battery.
The method according to claim 1,
The concentration of the lithium salt is 1.2M to 4M non-aqueous electrolyte for a lithium secondary battery.
The method according to claim 1,
The lithium salt concentration is 1.2M to 3M non-aqueous electrolyte for a lithium secondary battery.
The method according to claim 1,
The oligomer represented by Formula 1 is an oligomer represented by Formula 1a below.
[Formula 1a]

In Formula 1a,
n1 and x1 are the number of repeating units,
n1 is an integer of any one of 1 to 10,
x1 is an integer in any one of 1 to 15.
delete The method according to claim 1,
The oligomer represented by Formula 1 is a non-aqueous electrolyte for a lithium secondary battery that is included in an amount of 0.5 wt % to 10 wt % based on the total weight of the non-aqueous electrolyte for a lithium secondary battery.
positive, negative,
a separator interposed between the positive electrode and the negative electrode, and
Contains non-aqueous electrolyte,
The non-aqueous electrolyte is a lithium secondary battery that is the non-aqueous electrolyte for a lithium secondary battery of claim 1.

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