KR102455341B1 - Electrolyte for lithium secondary battery and lithium secondary battery comprising the same - Google Patents

Abstract

The present invention provides an additive comprising a compound represented by Formula 1; an oligomer including a unit represented by Formula 2 and including an acrylate group at the terminal; lithium salt; and an organic solvent; and an electrolyte for a lithium secondary battery comprising the same, and a lithium secondary battery including the same.

Description

Electrolyte for a lithium secondary battery and a lithium secondary battery comprising the same

The present invention relates to an electrolyte for a lithium secondary battery and a lithium secondary battery including the same, and more particularly, to an electrolyte for a lithium secondary battery having improved battery performance at high voltage or high temperature.

As personal IT devices and computer networks are developed due to the development of the information society, and the overall society's dependence on electric energy increases accordingly, technology development for efficiently storing and utilizing electric energy is required.

Among the technologies developed for this purpose, the most suitable technology for various uses is a secondary battery-based technology. In the case of secondary batteries, interest in this is emerging because they can be miniaturized enough to be applied to personal IT devices, and can be applied to electric vehicles and power storage devices. Among such secondary batteries, lithium ion batteries, which are battery systems with high energy density, are in the spotlight and are currently being applied to various devices.

In the case of lithium ion battery systems, unlike the early days when lithium metal was directly applied to the system, a transition metal oxide material containing lithium was used as a cathode material, and a carbon-based material such as graphite and an alloy-based material such as silicon were used as an anode material. It is implemented as a system in which lithium metal is not directly used inside the battery, such as applying a material as an anode.

In the case of such a lithium ion battery, it is largely composed of a positive electrode composed of a transition metal oxide containing lithium, a negative electrode capable of storing lithium, an electrolyte as a medium for transferring lithium ions, and a separator. As it is known as a component that has a great influence on stability and safety, many studies are being conducted on it.

In the case of an electrolyte for a lithium ion battery, it is composed of a lithium salt, an organic solvent dissolving the same, and a functional additive, and proper selection of these components is important in order to improve the electrochemical properties of the battery. Representative lithium salts currently used include LiPF ₆ , LiBF ₄ , LiFSI (lithium fluorosulfonyl imide, LiN(SO ₂ F) ₂ ), LiTFSI (lithium (bis)trifluoromethanesulfonyl imide, LiN(SO ₂ CF ₃ ) ₂ ) or LiBOB ( lithium bis(oxalate) borate, LiB(C ₂ O ₄ ) ₂ ), etc. are used, and in the case of an organic solvent, a carbonate-based organic solvent, an ester-based organic solvent, or an ether-based organic solvent is used.

In the case of such a lithium ion battery, an increase in resistance and a decrease in capacity during charging/discharging or storage at high temperature are suggested as major problems in performance degradation, and one of the causes of this problem is degradation of electrolyte at high temperature. It is a side reaction that occurs due to decomposition of salts at high temperature, among others. When the by-products of these salts decompose the coatings formed on the surfaces of the positive and negative electrodes after activation, there is a problem of lowering the passivation ability of the coating, which causes additional decomposition of the electrolyte and accompanying self-discharge. there is

Among the electrode materials of lithium ion batteries, especially in the case of negative electrodes, graphite-based negative electrodes are most often used. In the case of graphite, its operating potential is 0.3 V (vs. Li/Li+) or less. It is lower than the stable window, and the electrolyte currently used is reduced and decomposed. This reductive decomposition product forms a solid electrolyte interphase (SEI) film that transmits lithium ions but inhibits further decomposition of the electrolyte.

However, if the SEI film does not have sufficient passivation ability to suppress the further decomposition of the electrolyte, the electrolyte is additionally decomposed during storage and the charged graphite is self-discharged, and consequently, the potential of the entire battery is lowered. Therefore, in order to maintain the passivation ability of SEI at high temperature, HF, PF ₅ , etc., which are decomposition products such as LiPF ₆ , which are representative lithium salts generated due to heat/moisture, etc., are removed to suppress damage to the SEI film, or There is an urgent need to propose and introduce an additive that can further form an additional stable film on the SEI film formed in the

Japanese Laid-Open Patent Publication No. 2003-217655

The present invention is to solve the above problems, and the electrolyte for a lithium secondary battery having improved high-temperature characteristics of a lithium secondary battery by suppressing side reactions caused by by-products generated when lithium salts are decomposed at high voltage or high temperature, and including the same The invention relates to a lithium secondary battery.

According to one embodiment, the present invention is an additive comprising a compound represented by the following formula (1); an oligomer including a unit represented by the following formula (2) and including an acrylate group at the terminal; lithium salt; and an organic solvent; provides an electrolyte for a lithium secondary battery comprising.

[Formula 1]

In Formula 1, R ₁ is an alkyl group having 1 to 5 carbon atoms in which a halogen element is substituted or unsubstituted, an alkoxy group having 1 to 5 carbon atoms in which a halogen element is substituted or unsubstituted, or an alkyl group having 1 to 3 carbon atoms is substituted or An unsubstituted phenyl group and an alkyl group having 1 to 5 carbon atoms are selected from the group consisting of a substituted or unsubstituted amine group.

[Formula 2]

In Formula 2, Ra, Rb, Rc and Rd are each independently a fluorine element or an alkyl group having 1 to 3 carbon atoms substituted or unsubstituted with an element fluorine, and p is an integer of 1 to 50.

According to another embodiment, the present invention provides a positive electrode; cathode; And it provides a lithium secondary battery comprising the electrolyte for a lithium secondary battery of the present invention.

Since the electrolyte for a lithium secondary battery according to the present invention contains a specific oligomer and additives, it has excellent high-temperature performance and can minimize deterioration of battery performance even when the voltage is increased.

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

The terms or words used in the present specification and claims are not to be construed as being limited to their ordinary or dictionary meanings, and the inventor may properly define the concept of the term in order to best describe his invention. Based on the principle that there is, it should be interpreted as meaning and concept consistent with the technical idea of the present invention.

The terminology used herein is used to describe exemplary embodiments only, and is not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly dictates otherwise.

In the present specification, terms such as "comprise", "comprising" or "having" are intended to designate the presence of an embodied feature, number, step, element, or a combination thereof, but one or more other features or It should be understood that the existence or addition of numbers, steps, elements, or combinations thereof is not precluded in advance.

In the present specification, 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. can 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.

Electrolyte for Lithium Secondary Battery

The electrolyte for a lithium secondary battery according to the present invention includes an additive comprising a compound represented by Formula 1; an oligomer including a unit represented by Formula 2 and including an acrylate group at the terminal; lithium salt; and organic solvents.

Hereinafter, each component of the electrolyte for a lithium secondary battery of the present invention will be described in more detail.

(1) additives

First, the additive will be described. The additive includes a compound represented by the following Chemical Formula 1, and other additives may be further added depending on the type of electrode used or the use of the battery.

[Formula 1]

In Formula 1, R ₁ is an alkyl group having 1 to 5 carbon atoms in which a halogen element is substituted or unsubstituted, an alkoxy group having 1 to 5 carbon atoms in which a halogen element is substituted or unsubstituted, or an alkyl group having 1 to 3 carbon atoms is substituted or An unsubstituted phenyl group and an alkyl group having 1 to 5 carbon atoms may be selected from the group consisting of a substituted or unsubstituted amine group.

When the driving voltage of a lithium secondary battery increases or the battery is exposed to high temperatures, transition metals are eluted from the positive electrode, and an unstable SEI (Solid Electrolyte Interphase) film is formed on the surface of the negative electrode. There is a problem that this cannot be suppressed.

In the present invention, in order to solve the above problems, a compound represented by Formula 1 is further formed on the positive/negative interface to prevent the electrolyte decomposition reaction and the SEI membrane from being decomposed. was added to the electrolyte and used. The compound represented by Formula 1 may form a Solid Electrolyte Interphase (SEI) film on the positive electrode interface, thereby preventing transition metal ions eluted from the positive electrode active material from adhering to the negative electrode, thereby improving battery performance. In addition, by forming a passive layer on the interface between the anode and the cathode, it is possible to suppress the further decomposition reaction of the electrolyte.

As a specific example, the compound represented by Chemical Formula 1 may be at least one selected from the group consisting of compounds represented by the following Chemical Formulas 1A to 1E.

[Formula 1A]

In Formula 1A, n is an integer of 0 to 4.

[Formula 1B]

In Formula 1B, m is an integer of 0 to 4, wherein X, X' and X" are each independently one of hydrogen or a halogen element, and at least one is a halogen element.

[Formula 1C]

In Formula 1C, k is an integer of 0 to 4, Y, Y' and Y" are each independently one of hydrogen or a halogen element, and at least one is a halogen element.

[Formula 1D]

In Formula 1D, s is an integer of 0 to 2.

[Formula 1E]

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

More specifically, the compound represented by Chemical Formula 1A may be a compound represented by the following Chemical Formulas 1A-1 to 1A-3.

[Formula 1A-1]

[Formula 1A-2]

[Formula 1A-3]

In addition, the compound represented by Formula 1B may be a compound represented by Formula 1B-1 below.

[Formula 1B-1]

In addition, the compound represented by Formula 1C may be at least one selected from the group consisting of compounds represented by the following Formulas 1C-1 to 1C-5.

[Formula 1C-1]

[Formula 1C-2]

[Formula 1C-3]

[Formula 1C-4]

[Formula 1C-5]

In addition, the compound represented by Formula 1D may be a compound represented by Formula 1D-1 below.

[Formula 1D-1]

In addition, the compound represented by Formula 1E may be a compound represented by Formula 1E-1 below.

[Formula 1E-1]

On the other hand, the compound represented by the formula (1) is 0.1 parts by weight to 5 parts by weight, preferably 0.1 parts by weight to 3 parts by weight, more preferably 0.1 parts by weight to 1 parts by weight based on 100 parts by weight of the electrolyte for a lithium secondary battery. may be included. When the compound represented by Formula 1 is included within the above range, it is possible to effectively remove lithium salt byproducts such as PF ₅ while controlling the increase in internal resistance.

On the other hand, the additive according to the present invention, in addition to the above-described components, according to the use of the battery, the internal configuration of the battery, etc., in order to give the effect of reducing the resistance in the battery, other additives that can implement these properties known in the art, etc. may contain more. The other additives include, for example, vinylene carbonate (VC), vinyl ethylene carbonate (VEC), propane sultone (PS), succinonitrile (SN), Adiponitrile (AdN), ethylene sulfate (ESa), propene sultone (PRS), fluoroethylene carbonate (FEC), lithium difluorophosphate (LiPO ₂ F ₂ ), lithium difluoro (oxalate) borate (LiODFB), lithium bis- (oxalato) borate (LiBOB), 3-trimethoxysila Other additives such as nyl-propyl-N-aniline (3-trimethoxysilanyl-propyl-N-aniline), TMSPa) and tris(trimethylsilyl)phosphate ((Tris(trimethylsilyl) Phosphite), TMSPi) may be used.

(2) oligomers

Next, an oligomer including a unit represented by the following formula (2) and including an acrylate at the terminal will be described.

[Formula 2]

In Formula 2, Ra, Rb, Rc and Rd are each independently a fluorine element or an alkyl group having 1 to 3 carbon atoms substituted or unsubstituted with an element fluorine, and p is an integer of 1 to 50.

Since the oligomer including the unit represented by Formula 2 and having an acrylate group at the terminal contains an ethylene group substituted with a fluorine element having low reactivity with lithium ions, a side reaction of lithium ions and a lithium salt (salt) It is possible to control the decomposition reaction and the like, and it is possible to suppress side reactions occurring when a high concentration of lithium salt is used. In addition, since the oligomer contains elemental fluorine having excellent flame retardancy, when an electrolyte including the oligomer is used, heat generation and ignition of a lithium secondary battery are suppressed, and high temperature safety can be improved.

On the other hand, since the oligomer includes a unit containing a fluorine element having hydrophobicity and at the same time a hydrophilic acrylate group at the terminal, it serves as a surfactant to lower the surface resistance with the electrode interface, and a lithium secondary battery of the wetting effect (wetting) can be improved.

Specifically, the oligomer may be an oligomer represented by the following Chemical Formula 2A.

[Formula 2A]

In Formula 2A,

Wherein R _a ', R _b ', R _c ' and R _d ' are each independently a fluorine element or an alkyl group having 1 to 3 carbon atoms unsubstituted or substituted with an element fluorine,

Wherein R _e is an aliphatic hydrocarbon group or an aromatic hydrocarbon group,

Wherein R _f is an alkylene group having 1 to 5 carbon atoms substituted or unsubstituted with a fluorine element,

Wherein R' is hydrogen or an alkyl group having 1 to 3 carbon atoms,

Wherein o is an integer from 1 to 3,

Wherein p is an integer from 1 to 50,

Wherein q is an integer of 1 to 15.

In this case, p may be an integer of preferably 1 to 45, more preferably an integer of 1 to 40.

In the oligomer represented by Formula 2A, the aliphatic hydrocarbon group includes an alicyclic hydrocarbon group or a linear hydrocarbon group.

The alicyclic hydrocarbon group is a substituted or unsubstituted cycloalkylene group having 4 to 20 carbon atoms; a substituted or unsubstituted C4-C20 cycloalkylene group containing an isocyanate group (NCO); a substituted or unsubstituted C4 to C20 cycloalkenylene group; And it may include at least one selected from the group consisting of a substituted or unsubstituted heterocycloalkylene group having 2 to 20 carbon atoms.

The linear hydrocarbon group is a substituted or unsubstituted alkylene group having 1 to 20 carbon atoms; A substituted or unsubstituted C1-C20 alkylene group containing an isocyanate group (NCO); a substituted or unsubstituted C1-C20 alkoxyl group; a substituted or unsubstituted alkenylene group having 2 to 20 carbon atoms; and at least one selected from the group consisting of a substituted or unsubstituted alkynylene group having 2 to 20 carbon atoms.

In addition, in the oligomer represented by Formula 2A, the aromatic hydrocarbon group may include a substituted or unsubstituted arylene group having 6 to 20 carbon atoms; Or it may include a substituted or unsubstituted heteroarylene group having 2 to 20 carbon atoms.

As a specific example, the oligomer represented by Formula 2A may be an oligomer represented by Formula 2A-1 below.

[Formula 2A-1]

In Formula 2A-1, p' is an integer from 1 to 50, and q is an integer from 1 to 15. The p' may be an integer of preferably 1 to 45, more preferably an integer of 1 to 40.

Alternatively, the oligomer may be an oligomer represented by the following Chemical Formula 2B.

[Formula 2B]

In Formula 2B, R _a ", R _b ", R _c ", and R _d " are each independently a fluorine element or an alkyl group having 1 to 3 carbon atoms unsubstituted or substituted with an elemental fluorine element, and R _e ' is an aliphatic a hydrocarbon group or an aromatic hydrocarbon group, wherein R _f ' is an alkylene group having 1 to 5 carbon atoms substituted or unsubstituted with a fluorine element, r is an integer of 1 to 2, and r' is an integer of 1 to 3, Wherein p' is an integer from 1 to 50, and q' is an integer from 1 to 15. The p may be an integer of preferably 1 to 45, more preferably an integer of 1 to 40.

As a specific example, the oligomer represented by Formula 2B may be an oligomer represented by Formula 2B-1 below.

[Formula 2B-1]

In Formula 2B-1, p is an integer from 1 to 50, and q is an integer from 1 to 15. In this case, p is preferably an integer of 1 to 45, more preferably an integer of 1 to 40.

Meanwhile, the weight average molecular weight (MW) of the oligomer may be controlled by the number of repeating units, and may be about 500 to 200,000, specifically 1,000 to 150,000, and more specifically 2,000 to 100,000. When the weight average molecular weight of the oligomer is within the above range, it has a high affinity with an organic solvent and can be well dispersed, and the wettability of the electrolyte can be improved by lowering the surface tension to a certain level or less, and the decomposition reaction of the lithium salt is suppressed. and lithium ions can be prevented from causing side reactions.

In this case, the oligomer may be included in an amount of 0.1 part by weight to 5 parts by weight, preferably 0.1 part by weight to 3 parts by weight, more preferably 0.1 part by weight to 1 part by weight based on 100 parts by weight of the lithium secondary electrolyte. When the oligomer is included within the above range, it is possible to minimize the interfacial resistance in the battery by maintaining the mobility and ionic conductivity of lithium ions at a certain level or more, thereby suppressing side reactions and acting as a surfactant.

(3) lithium salt

The lithium salt may be included in the electrolyte for a lithium secondary battery in a molar concentration of 1M to 3M, preferably 1M to 2M, more preferably 1M to 1.5M. When the lithium salt is included within the molar concentration range, lithium ions may be sufficiently supplied, so that a lithium ion yield (Li+ transference number) and a degree of dissociation of lithium ions may be improved, thereby improving output characteristics of the battery.

Typically, the lithium salt is LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiN(C ₂ F ₅ SO ₂ ) ₂ , LiN(CF ₃ SO ₂ ) ₂ , CF ₃ SO ₃ Li, LiC(CF) ₃ SO ₂ ) ₃ , LiC ₄ BO ₈ , LiTFSI, LiFSI and LiClO ₄ It may include at least one compound selected from the group consisting of, preferably LiPF ₆ and/or LiBF ₄ It may include, but It is not limited.

Among lithium salts, LiPF ₆ and/or LiBF ₄ are generally used because of their high ionic conductivity. However, when the organic solvent is decomposed at a high temperature, the decomposition product of the organic solvent reacts with PF ₆ ⁻ , which is an anion of the lithium salt, and a Lewis acid by-product such as PF ₅ may be generated. In the case of a Lewis acid by-product, it promotes a spontaneous decomposition reaction of the organic solvent and causes a side reaction that collapses the SEI film formed on the electrode interface. If the side reaction is not suppressed, the resistance in the battery may rapidly increase, and the capacity characteristics of the battery may be deteriorated.

More specifically, when LiPF ₆ is used as the lithium salt, PF ₆ ⁻ , which is an anion, loses electrons from the negative electrode side, and PF ₅ may be generated. At this time, the following chemical reaction may proceed in a chain.

When the chain reaction proceeds, decomposition of an organic solvent or a side reaction with the SEI film may occur due to other by-products including HF generated, thereby continuously decreasing battery performance. Therefore, in the case of the present invention, in order to solve the above problems, an oligomer including an additive including a compound represented by Formula 1 and a unit represented by Formula 2 and having an acrylate group at the terminal as described above is used as a lithium secondary oligomer. It is used in addition to the electrolyte for batteries.

(4) organic solvents

In the non-aqueous electrolyte for a lithium secondary battery according to the present specification, the organic solvent may include a cyclic carbonate-based organic solvent, a linear carbonate-based organic solvent, or a mixed organic solvent thereof.

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

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

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

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

In addition, the cyclic ester-based organic solvent includes at least one organic solvent selected from the group consisting of γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone and ε-caprolactone. can

Meanwhile, as the organic solvent, an organic solvent commonly used in an electrolyte solution for a lithium secondary battery may be added without limitation, if necessary. For example, at least one organic solvent of an ether-based organic solvent, an amide-based organic solvent, and a nitrile-based organic solvent may be further included.

lithium secondary battery

Next, a lithium secondary battery according to the present invention will be described. A lithium secondary battery according to an embodiment of the present invention includes a positive electrode, a negative electrode, and the electrolyte for the lithium secondary battery, and optionally further includes a separator. Meanwhile, since the electrolyte for a lithium secondary battery is the same as that described above, a detailed description thereof will be omitted.

(1) Anode

The positive electrode may be prepared by coating a positive electrode active material slurry including a positive electrode active material, a binder, a conductive material, and a solvent on a positive electrode current collector.

The positive electrode may be prepared by coating a positive electrode active material slurry including a positive electrode active material, a binder, a conductive material, and a solvent on a positive electrode current collector.

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

The positive active material is a compound capable of reversible intercalation and deintercalation of lithium, and specifically may include a lithium composite metal oxide including lithium and one or more metals such as cobalt, manganese, nickel, or aluminum. have. More specifically, the lithium composite metal oxide is a lithium-manganese oxide (eg, LiMnO ₂ , LiMn ₂ O ₄ , etc.), a lithium-cobalt-based oxide (eg, LiCoO ₂ , etc.), lithium-nickel-based oxide (eg, LiNiO ₂ , etc.), lithium-nickel-manganese oxide (eg, LiNi _1-Y1 Mn _Y1 O ₂ (here, 0<Y1<1), LiMn _2-z1 Ni _z1 O ₄ ( Here, 0<Z1<2, etc.), lithium-nickel-cobalt-based oxide (eg, LiNi _1-Y2 Co _Y2 O ₂ (here, 0<Y2<1), etc.), lithium-manganese-cobalt based oxides (eg, LiCo _1-Y3 Mn _Y3 O ₂ (here, 0<Y3<1), LiMn _2-z2 Co _z2 O ₄ (here, 0<Z2<2), etc.), lithium-nickel -Manganese-cobalt oxide (for example, Li(Ni _p1 Co _q1 Mn _r1 )O ₂ (here, 0<p1<1, 0<q1<1, 0<r1<1, p1+q1+r1= 1) or Li(Ni _p2 Co _q2 Mn _r2 )O ₄ (where 0<p2<2, 0<q2<2, 0<r2<2, p2+q2+r2=2), etc.), or lithium- Nickel-cobalt-transition metal (M) oxide (eg, Li(Ni _p3 Co _q3 Mn _r3 M _S1 )O ₂ , where M is Al, Fe, V, Cr, Ti, Ta, Mg and Mo is selected from the group consisting of, and p3, q3, r3 and s1 are atomic fractions of each independent element, 0<p3<1, 0<q3<1, 0<r3<1, 0<s1<1, p3+q3 +r3+s1=1), etc.) and the like, and any one or two or more compounds may be included.

Among them, the lithium composite metal oxide is LiCoO ₂ , LiMnO ₂ , LiNiO ₂ , lithium nickel manganese cobalt oxide (eg, Li(Ni _0.6 Mn _0.2 Co _0.2 )O ₂ , in that it is possible to increase the capacity characteristics and stability of the battery. , Li(Ni _0.5 Mn _0.3 Co _0.2 )O ₂ , or Li(Ni _0.8 Mn _0.1 Co _0.1 )O ₂ , etc.), or lithium nickel cobalt aluminum oxide (eg, LiNi _0.8 Co _0.15 Al _0.05 O ₂ , etc.), etc. In consideration of the significant improvement effect by controlling the type and content ratio of the element forming the lithium composite metal oxide, the lithium composite metal oxide is 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 , or Li(Ni _0.8 Mn _0.1 Co _0.1 )O ₂ , and the like, and any one or a mixture of two or more thereof may be used. have.

The binder is a component that assists in bonding between the active material and the conductive material and bonding to the current collector, and examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxy Propylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene (PE), polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluorine rubber, various copolymers, and the like.

The conductive material is a component for further improving the conductivity of the positive electrode active material, and is not particularly limited as long as it has conductivity without causing a chemical change in the battery. For example, graphite; carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; 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; A conductive material such as a polyphenylene derivative may be used.

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.

(2) cathode

The negative electrode may be prepared by, for example, coating a negative electrode active material slurry including a negative electrode active material, a binder, a conductive material and a solvent on a negative electrode current collector.

The negative electrode current collector generally has a thickness of 3 μm 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. The surface treated with carbon, nickel, titanium, silver, etc., an aluminum-cadmium alloy, etc. may be used. 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.

Examples of the negative active material include natural graphite, artificial graphite, carbonaceous material; lithium-containing titanium composite oxide (LTO), Si, Sn, Li, Zn, Mg, Cd, Ce, Ni or Fe metals (Me); alloys composed of the metals (Me); oxides of the metals (Me); and one or more negative active materials selected from the group consisting of a composite of the metal (Me) and carbon.

The binder is a component that assists in bonding between the conductive material, the active material, and the current collector. Examples of the binder include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxy Propylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, fluororubber, these and various copolymers of

The conductive material is a component for further improving the conductivity of the negative active material, and the conductive material is not particularly limited as long as it has conductivity without causing a chemical change in the battery. For example, graphite such as natural graphite or artificial graphite ; carbon 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; A conductive material such as a polyphenylene derivative may be used.

The solvent may include water or an organic solvent such as N-methyl-2-pyrrolidone (NMP), and may be used in an amount to achieve a desirable viscosity when the negative electrode active material, and, optionally, a binder and a conductive material are included. .

(3) separator

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

Hereinafter, the present invention will be described in more detail through specific examples. However, the following examples are only examples to help the understanding of the present invention, and do not limit the scope of the present invention. It is obvious to those skilled in the art that various changes and modifications can be made within the scope and spirit of the present disclosure, and it is natural that such variations and modifications fall within the scope of the appended claims.

[Example]

1. Example 1

(1) Preparation of electrolyte for lithium secondary battery

As an organic solvent, ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed in a volume ratio of 30:70, and LiPF ₆ was added to a concentration of 1M to prepare a non-aqueous organic solvent. 0.5 g of the compound represented by Formula 1E-1 and the oligomer represented by Formula 2A-1 in 99.3 g of the non-aqueous organic solvent (weight average molecular weight (Mw)=7,400 g/mol, p'=5, q=10) 0.2 g was added to prepare an electrolyte for a lithium secondary battery.

(2) Lithium secondary battery manufacturing

A cathode active material (LiNi _0.8 Co _0.1 Mn _0.1 O ₂ ; NCM), a conductive material carbon black, and a binder PVDF were mixed in N-methyl-2-pyrrolidone (NMP) as a solvent in a weight ratio of 97:1.5:1.5. was added to prepare a cathode active material slurry. The positive electrode active material slurry was coated on an aluminum (Al) thin film, which is a positive electrode current collector, having a thickness of about 20 μm, dried, and then a roll press was performed to prepare a positive electrode.

The negative active material (carbon powder:SiO=90:5 weight ratio), styrene-butadiene rubber (SBR) as a binder, carboxymethylcellulose (CMC) as a thickener, and carbon black as a conductive material were mixed with 95:3:1:1. A negative active material slurry was prepared by adding it to N-methyl-2-pyrrolidone (NMP) as a solvent in a weight ratio. The negative electrode active material slurry was applied to a 10 μm-thick copper (Cu) thin film as an anode current collector, dried, and then roll press was performed to prepare a negative electrode.

An electrode assembly was prepared using the positive electrode, the negative electrode, and a separator consisting of three layers of polypropylene/polyethylene/polypropylene (PP/PE/PP), and then stored in a pouch-type secondary battery case, and then the pouch-type secondary battery A lithium secondary battery was manufactured by injecting the electrolyte for a lithium secondary battery into the case.

2. Example 2

5.0 g of the compound represented by Formula 1E-1 and 0.2 g of the oligomer represented by Formula 2A-1 (weight average molecular weight (Mw)=7,400 g/mol, p'=5, q=10) in 94.8 g of a non-aqueous organic solvent A liquid electrolyte for a lithium secondary battery and a lithium secondary battery were prepared in the same manner as in Example 1, except that .

3. Example 3

chemical formula A liquid electrolyte for a lithium secondary battery and a lithium secondary battery were prepared in the same manner as in Example 1, except that 0.5 g of the compound represented by Formula 1B-1 was added instead of 0.5 g of the compound represented by 1E-1.

4. Example 4

chemical formula A liquid electrolyte for a lithium secondary battery and a lithium secondary battery were prepared in the same manner as in Example 2, except that 5.0 g of the compound represented by Formula 1B-1 was added instead of 5.0 g of the compound represented by 1E-1.

5. Example 5

oligomeric Except for adding 0.2 g of the oligomer represented by Formula 2B-1 (weight average molecular weight (Mw)=7,570 g/mol, p'=5, q=10) instead of 0.2 g of the oligomer represented by Formula 2A-1 A liquid electrolyte for a lithium secondary battery and a lithium secondary battery were prepared in the same manner as in Example 3.

6. Example 6

0.5 g of the compound represented by Formula 1B-1 was added to 94.5 g of a non-aqueous organic solvent, and the oligomer represented by Formula 2A-1 (weight average molecular weight (Mw)=7,400 g/mol, p'=5, q=10 ) A liquid electrolyte for a lithium secondary battery and a lithium secondary battery were prepared in the same manner as in Example 1, except that 5.0 g was added.

7. Example 7

Carried out except that 5 g of the oligomer represented by Formula 2B-1 (weight average molecular weight (Mw)=7,570 g/mol, p'=5, q=10) was added instead of the oligomer represented by Formula 2A-1, which is an oligomer. A liquid electrolyte for a lithium secondary battery and a lithium secondary battery were prepared in the same manner as in Example 6.

[Comparative example]

1. Comparative Example 1

An electrolyte for a lithium secondary battery and a lithium secondary battery were prepared in the same manner as in Example 1, except that the compound represented by Formula 1E-1 was not added when preparing the electrolyte for a lithium secondary battery.

2. Comparative Example 2

An electrolyte for a lithium secondary battery and a lithium secondary battery were prepared in the same manner as in Example 1, except that the oligomer represented by Formula 2A-1 was not added when preparing the electrolyte for a lithium secondary battery.

3. Comparative Example 3

The electrolyte and lithium secondary battery for a lithium secondary battery were prepared in the same manner as in Example 1, except that neither the compound represented by Formula 1E-1 nor the oligomer represented by Formula 2A-1 was added when preparing the electrolyte for a lithium secondary battery. was prepared.

[Experimental example]

1. Experimental Example 1: Measurement of high temperature (45°C) capacity retention rate and resistance increase rate

After the formation of the lithium secondary batteries prepared according to Examples 1 to 7 and Comparative Examples 1 to 3 at 200 mA current (0.1 C rate), the discharge capacity at this time is set as the initial capacity, at this time The measured resistance was set as the initial resistance. After that, 4.2 V, 660 mA (0.33 C, 0.05 C cut-off) CC/CV charge and 2.5 V, 660 mA (0.33 C) CC discharge were performed 200 times at high temperature (45℃), respectively, and then the discharge capacity and resistance was measured. At this time, the capacity retention rate was calculated by comparing the measured 200th discharge capacity with the initial capacity. At this time, the resistance increase rate was calculated by comparing the measured resistance with the initial resistance, and the results are shown in Table 1.

Capacity retention rate (%) Resistance increase rate (%) Example 1 98.0 1.5 Example 2 89.2 10.2 Example 3 98.5 1.2 Example 4 95.2 5.4 Example 5 96.5 3.5 Example 6 92.1 9.5 Example 7 90.2 12.7 Comparative Example 1 82.4 25.4 Comparative Example 2 85.3 22.9 Comparative Example 3 74.5 35.7

Referring to Table 1, it can be seen that the capacity retention rate of the lithium secondary battery prepared according to the example is all higher than that of the secondary battery prepared according to the comparative example, while the resistance increase rate is all low.

2. Experimental Example 2: Measurement of high temperature (60° C.) storage characteristics

For the lithium secondary batteries prepared according to Examples 1 to 7 and Comparative Examples 1 to 3, charging and 0.05C cut-off charging were performed under constant current/constant voltage conditions up to 4.2V at 0.33C rate, and discharged at 0.33C 2.5V. The subsequent discharge capacity was set as the initial capacity, and the resistance at this time was set as the initial resistance. Then, charging under constant current/constant voltage conditions up to 4.2V at 0.33C rate and 0.05C cut-off charging were performed, and residual capacity and resistance after storage at 60°C for 10 weeks (10 weeks) were measured. At this time, the capacity retention rate was calculated by comparing the measured discharge capacity and the initial capacity. At this time, the resistance increase rate was calculated by comparing the measured resistance and the initial resistance and is shown in Table 2.

Capacity retention rate (%) Resistance increase rate (%) Example 1 95.4 5.4 Example 2 80.3 21.2 Example 3 97.5 3.5 Example 4 91.2 10.5 Example 5 92.5 8.1 Example 6 84.7 5.4 Example 7 81.5 25.8 Comparative Example 1 72.9 36.5 Comparative Example 2 75.2 32.4 Comparative Example 3 67.5 49.2

Referring to Table 2, it can be seen that the lithium secondary battery prepared according to the example has a high residual capacity retention rate and a low resistance increase rate during high temperature storage compared to the lithium secondary battery prepared according to the comparative example.

3. Experimental Example 3: High-temperature safety test

For the lithium secondary batteries prepared according to Examples 1 to 7 and Comparative Examples 1 to 3, it was stored at a high temperature for 10 weeks (10weeks) in a SOC 100% state (4.15 V) at a temperature of 60°C. Then, after 10 weeks, the volume increase rate was measured based on the volume of the battery measured at the initial stage (1 week). The results are shown in Table 3 below.

Volume increase rate (%) after 10 weeks of storage at 60°C Example 1 7.5 Example 2 25.4 Example 3 5.1 Example 4 12.4 Example 5 10.5 Example 6 18.4 Example 7 28.5 Comparative Example 1 39.5 Comparative Example 2 38.4 Comparative Example 3 50.6

Referring to Table 3, the lithium secondary battery prepared according to the example has a lower volume increase rate even when stored at a high temperature compared to the lithium secondary battery prepared according to the comparative example, so that even when stored for a long time at high temperature, the safety of the battery is better that can be checked

4. Experimental Example 4: Anion stabilization evaluation

After storing the electrolyte for lithium secondary batteries prepared in Examples 1, 2, 3 and 6 and the electrolytes for lithium secondary batteries prepared in Comparative Examples 1 to 3 at 60° C. for 2 weeks, NMR analyzer (1H Bruker 700 MHz NMR, solvent tetra Anion stabilization was evaluated by checking the integration value of the PO ₂ F ₂ peak in the electrolyte using methylsilane (TMS)). The results are shown in Table 4 below. In this case, the integration value of the PO ₂ F ₂ peak means that the higher the value, the more unstable the PF ₆ ⁻ anion is decomposed.

Integration value of PO ₂ F ₂ peak Example 1 0.95 Example 2 0.71 Example 3 1.02 Example 6 0.75 Comparative Example 1 2.54 Comparative Example 2 1.01 Comparative Example 3 3.12

In the case of the electrolyte for a lithium secondary battery prepared according to Examples 1, 2, 3, and 6, it can be seen that the anion stabilization degree is higher than that of the electrolyte for a lithium secondary battery prepared in Comparative Examples 1 to 3.

Claims (13)

An additive comprising a compound represented by the following formula (1);
an oligomer represented by Formula 2A or Formula 2B;
lithium salt; And an organic solvent; Lithium secondary battery electrolyte comprising:
[Formula 1]

(In Formula 1,
R ₁ is an alkyl group having 1 to 5 carbon atoms in which a halogen element is substituted or unsubstituted, an alkoxy group having 1 to 5 carbon atoms in which a halogen element is substituted or unsubstituted, a phenyl group in which an alkyl group having 1 to 3 carbon atoms is substituted or unsubstituted, and an alkyl group having 1 to 5 carbon atoms is selected from the group consisting of a substituted or unsubstituted amine group);

[Formula 2A]

(In Formula 2A,
Wherein R _a ', R _b ', R _c ' and R _d ' are each independently a fluorine element or an alkyl group having 1 to 3 carbon atoms unsubstituted or substituted with an element fluorine,
Wherein R _e is an aliphatic hydrocarbon group or an aromatic hydrocarbon group,
Wherein R _f is an alkylene group having 1 to 5 carbon atoms substituted or unsubstituted with a fluorine element,
Wherein R' is hydrogen or an alkyl group having 1 to 3 carbon atoms,
Wherein o is an integer from 1 to 3,
Wherein p' is an integer from 1 to 50,
wherein q is an integer from 1 to 15);

[Formula 2B]

(In Formula 2B,
Wherein R _a ", R _b ", R _c " and R _d " are each independently a fluorine element or an alkyl group having 1 to 3 carbon atoms unsubstituted or substituted with an element fluorine,
Wherein R _e 'is an aliphatic hydrocarbon group or an aromatic hydrocarbon group,
Wherein R _f ' is an alkylene group having 1 to 5 carbon atoms that is unsubstituted or substituted with a fluorine element,
Wherein r is an integer of 1 to 2,
Wherein r' is an integer of 1 to 3,
Wherein p '' is an integer from 1 to 50,
wherein q' is an integer from 1 to 15).
According to claim 1,
The compound represented by Formula 1 is at least one selected from the group consisting of compounds represented by the following Formulas 1A to 1E, electrolyte for a lithium secondary battery:
[Formula 1A]

In Formula 1A, n is an integer of 0 to 4.

[Formula 1B]

In Formula 1B, m is an integer of 0 to 4, wherein X, X' and X" are each independently one of hydrogen or a halogen element, and at least one is a halogen element.

[Formula 1C]

In Formula 1C, k is an integer of 0 to 4, Y, Y' and Y" are each independently one of hydrogen or a halogen element, and at least one is a halogen element.

[Formula 1D]

In Formula 1D, s is an integer of 0 to 2.

[Formula 1E]

In Formula 1E, R ₂ and R ₃ are each independently hydrogen or an alkyl group having 1 to 5 carbon atoms.
3. The method of claim 2,
The compound represented by the formula 1A is at least one selected from the group consisting of compounds represented by the following formulas 1A-1 to 1A-3, an electrolyte for a lithium secondary battery.
[Formula 1A-1]

[Formula 1A-2]

[Formula 1A-3]

3. The method of claim 2,
The compound represented by Formula 1B is an electrolyte for a lithium secondary battery that is a compound represented by Formula 1B-1.
[Formula 1B-1]

3. The method of claim 2,
The compound represented by Formula 1C is at least one selected from the group consisting of compounds represented by the following Formulas 1C-1 to 1C-5, an electrolyte for a lithium secondary battery.
[Formula 1C-1]

[Formula 1C-2]

[Formula 1C-3]

[Formula 1C-4]

[Formula 1C-5]

3. The method of claim 2,
The compound represented by Formula 1D is an electrolyte for a lithium secondary battery that is a compound represented by the following Formula 1D-1.
[Formula 1D-1]

3. The method of claim 2,
The compound represented by the formula 1E is an electrolyte for a lithium secondary battery that is a compound represented by the following formula 1E-1.
[Formula 1E-1]

According to claim 1,
The compound represented by Formula 1 is an electrolyte for a lithium secondary battery that is included in an amount of 0.1 parts by weight to 5 parts by weight based on 100 parts by weight of the electrolyte for a lithium secondary battery.
According to claim 1,
The compound represented by Formula 1 is an electrolyte for a lithium secondary battery that is included in an amount of 0.1 parts by weight to 3 parts by weight based on 100 parts by weight of the electrolyte for a lithium secondary battery.
delete According to claim 1,
The oligomer is an electrolyte for a lithium secondary battery that is included in an amount of 0.1 parts by weight to 5 parts by weight based on 100 parts by weight of the electrolyte for a lithium secondary battery.
According to claim 1,
The lithium salt is an electrolyte for a lithium secondary battery comprising at least one selected from the group consisting of LiPF ₆ and LiBF ₄ .
anode; cathode; separator; And a lithium secondary battery comprising the electrolyte for a lithium secondary battery according to claim 1.