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

Abstract

The present invention relates to an electrolyte solution for a lithium secondary battery and a lithium secondary battery including the same. More particularly, the electrolyte solution includes a polymer compound represented by Formula 1, and thus is capable of improving high-temperature durability, stability, and life characteristics of the lithium secondary battery.

Description

Technical Field

[0001] This application claims priority based on Korean Patent Application No. 2020-0143242, filed on October 30, 2020; Korean Patent Application No. 2020-0143254, filed on October 30, 2020; and Korean Patent Application No. 2020-0143269, filed on October 30, 2020, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to an electrolyte solution for lithium secondary batteries and a lithium secondary battery comprising the electrolyte solution. Background Technology

[0003] Recently, with the rapid development of industries such as electrical, electronics, communications, and computers, the demand for high-performance and high-safety rechargeable batteries has been gradually increasing. Furthermore, the trend towards miniaturization and weight reduction in these electronic communication devices necessitates the thinning and miniaturization of lithium rechargeable batteries, a key component in this field.

[0004] Lithium-ion batteries offer high performance, but suffer from poor discharge characteristics under harsh environments such as low or high temperatures, or when high output power is required for short periods. Furthermore, in traditional lithium-ion batteries containing non-aqueous electrolyte solutions, the use of solvents such as ethylene carbonate as the main component can lead to side reactions at high voltages, posing a risk of thermal runaway or fire.

[0005] Therefore, research is emerging on developing electrolyte solutions that can improve high-rate life characteristics and high-output characteristics by enhancing the high-temperature durability and safety of lithium secondary batteries.

[0006] Korean Patent Publication No. 10-2019-0017477 discloses a non-aqueous electrolyte solution for lithium secondary batteries. This solution contains a high concentration of lithium salt and oligomers, which can reduce resistance caused by lithium-ion depletion during high-rate charging and discharging, thereby improving the high-temperature and low-temperature stability of the lithium secondary battery. However, due to the rapid reactivity of the numerous acrylic acid structures formed at the ends of the oligomers, a pre-gel phenomenon may occur during wetting after injection into the electrolyte solution, making it difficult to uniformly wet and form a uniform solid electrolyte interphase (SEI) for the negative electrode.

[0007] Furthermore, Korean Patent Publication No. 10-2018-0083272, pending examination, relates to a non-aqueous electrolyte solution for lithium secondary batteries, which contains oligomers and can improve the output characteristics and safety of lithium secondary batteries. However, due to the rapid reactivity of the acrylic structure formed at the ends of the oligomers, a pre-gel phenomenon may occur during the wetting process after injection, making it difficult to form a uniform negative electrode SEI.

[0008] Therefore, there is a need to develop an electrolyte solution for lithium secondary batteries that improves the high-rate life and high-output characteristics of the battery by solving the problems of existing technologies, thereby improving high-temperature durability and safety, and forming a uniform SEI on the positive and negative electrodes.

[0009] [Existing technical documents]

[0010] [Patent Literature]

[0011] (Patent Document 1) Korean Patent Publication No. 10-2019-0017477

[0012] (Patent Document 2) Korean Patent Publication No. 10-2018-0083272 Summary of the Invention

[0013] Technical issues

[0014] One object of the present invention is to provide an electrolyte solution for a lithium secondary battery comprising a polymer compound and a lithium secondary battery comprising said electrolyte solution, which can exhibit high rate life characteristics and high output characteristics by improving the high temperature durability and safety of the lithium secondary battery, and form a uniform solid electrolyte interface (SEI) on the positive or negative electrode.

[0015] Technical solution

[0016] To achieve the above objectives, the present invention provides an electrolyte solution for lithium secondary batteries, comprising a polymer compound represented by Formula 1, a lithium salt, and an organic solvent:

[0017] <Formula 1>

[0018]

[0019] Where n is an integer from 1 to 300, and R is hydrogen, halogen, alkyl group having 1 to 6 carbon atoms, halogen-substituted alkyl group having 1 to 6 carbon atoms, alkoxy group having 1 to 6 carbon atoms, or halogen-substituted alkoxy group having 1 to 6 carbon atoms, and X is a functional group represented by the following formula 2:

[0020] <Formula 2>

[0021]

[0022] Where m is an integer from 0 to 4, l is an integer from 1 to 3, R1 and R2 are each hydrogen, halogen, saturated or unsaturated alkyl with 1 to 6 carbon atoms, or halogen-substituted saturated or unsaturated alkyl with 1 to 6 carbon atoms, and R1 and R2 are each the same or different from each other.

[0023] The present invention also provides a lithium secondary battery, comprising: a positive electrode; a negative electrode; a separator inserted between the positive electrode and the negative electrode; and an electrolyte solution.

[0024] Beneficial effects

[0025] Lithium secondary batteries including the electrolyte solution for lithium secondary batteries according to the present invention have improved high-temperature durability, thereby producing improved high-rate life characteristics and high output characteristics.

[0026] Furthermore, lithium secondary batteries including the electrolyte solution for lithium secondary batteries exhibit improved safety by controlling their heating characteristics.

[0027] Furthermore, in a lithium secondary battery including the electrolyte solution for a lithium secondary battery, when the battery is in operation, a uniform SEI is formed on the positive or negative electrode, thereby exhibiting the effect of preventing the increase of resistance and improving capacity expression characteristics and lifetime characteristics. Detailed Implementation

[0028] The invention will be described in more detail below to aid in understanding it.

[0029] The terms and words used in this specification and claims should not be construed as limited to ordinary or dictionary terms, but should be interpreted based on the inventor's principle of appropriately defining the concepts of terms to describe the invention in the best possible way, in a meaning and concept consistent with the technical concept of the invention.

[0030] Electrolyte solution for lithium secondary batteries

[0031] This invention relates to an electrolyte solution for lithium secondary batteries.

[0032] The electrolyte solution for lithium secondary batteries according to the present invention comprises a polymer compound represented by Formula 1 (hereinafter referred to as the compound of Formula 1), a lithium salt, and an organic solvent. Furthermore, the electrolyte solution may further comprise additives:

[0033] <Formula 1>

[0034]

[0035] Where n is an integer from 1 to 300, and R is hydrogen, halogen, alkyl group having 1 to 6 carbon atoms, halogen-substituted alkyl group having 1 to 6 carbon atoms, alkoxy group having 1 to 6 carbon atoms, or halogen-substituted alkoxy group having 1 to 6 carbon atoms, and X is a functional group represented by the following formula 2:

[0036] <Formula 2>

[0037]

[0038] Where m is an integer from 0 to 4, l is an integer from 1 to 3, R1 and R2 are each hydrogen, halogen, saturated or unsaturated alkyl group having 1 to 6 carbon atoms, or halogen-substituted saturated or unsaturated alkyl group having 1 to 6 carbon atoms. When there are two or more R1 and R2, R1 and R2 are each the same or different from each other. In addition, each of m and l can be an integer.

[0039] The electrolyte solution used in lithium secondary batteries can be a non-aqueous electrolyte solution.

[0040] In addition, unsaturated alkyl groups can refer to unsaturated hydrocarbons.

[0041] In this invention, the compound of Formula 1 above can improve the high-temperature durability, stability and high-rate life characteristics of lithium secondary batteries.

[0042] Based on the total weight of the electrolyte solution, the content of the compound of Formula 1 can be 0.1-5% by weight. Specifically, the content of the compound of Formula 1 can be 0.1% or more by weight, 0.5% or more by weight, or 1% or more by weight, and 3% or less by weight, 4% or less by weight, or 5% or less by weight. If the content of the compound of Formula 1 is less than 0.1% by weight, the high-temperature durability, stability, and high-rate life characteristics of the lithium secondary battery may deteriorate. If the content of the compound of Formula 1 exceeds 5% by weight, the viscosity may increase and wetting problems may occur.

[0043] Furthermore, the weight-average molecular weight (Mw) of the compound of Formula 1 can be from 1,000 g / mol to 35,000 g / mol. Specifically, the weight-average molecular weight (Mw) of the compound of Formula 1 can be 1,000 g / mol or greater, 1,500 g / mol or greater, 3,000 g / mol or greater, or 4,000 g / mol or greater, and 8,000 g / mol or less, 10,000 g / mol or less, 20,000 g / mol or less, or 35,000 g / mol or less. If the weight-average molecular weight (Mw) of the compound of Formula 1 is less than 1,000 g / mol, there is a problem that the uniformity of the compound in the battery is reduced due to intermolecular interactions. If the weight-average molecular weight (Mw) of the compound of Formula 1 is greater than 35,000 g / mol, due to the bulky molecular characteristics, it is difficult to wet the micropores of the electrode, and therefore there may be wettability problems.

[0044] Furthermore, in the compound of Formula 2, R1 and R2 can each be an unsaturated alkenyl group, and the unsaturated alkenyl group can be a vinyl group. If the unsaturated alkenyl group is bonded to R1 and / or R2, due to its reactivity, a protective layer can be formed on the electrode surface by physical and / or chemical bonding, and with the increase of the number of vinyl groups, a faster and stronger protective layer can be formed.

[0045] In this invention, the additive may include one or two additives. These two additives are referred to as the first additive and the second additive, respectively.

[0046] The first additive can be a salt additive, a nitrile compound, or a ethylene carbonate compound.

[0047] Salt additives can act as ion transporters between the positive and negative electrodes, and can form free radicals based on the charging / discharging behavior in the battery.

[0048] Salt additives may include at least one selected from the group consisting of LiBF4, lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LiODFB), lithium difluorophosphate (LiDFP), and lithium difluorobis(oxalato)phosphate (LiDFOP).

[0049] Based on the total weight of the electrolyte solution, the content of the salt additive can range from 0.1 wt% to 5 wt%. Specifically, the content of the salt additive can be 0.1 wt% or more, 0.2 wt% or more, or 0.3 wt% or more, and 3 wt% or less, 4 wt% or less, or 5 wt% or less. The salt additive can form free radicals depending on the charging / discharging behavior in the battery. If the content is less than 0.1 wt%, the reactivity of the compound may decrease due to the small number of free radicals formed, thereby increasing the amount of unreacted compounds, and thus the formation of the protective layer in the battery may be uneven. If the content exceeds 5 wt%, there is a problem of excessive free radical formation; therefore, the molecular weight of the protective layer (polymer) formed by the compound on the electrode surface decreases, resulting in poor battery durability.

[0050] In addition, nitrile compounds act as a protective layer on the positive and negative electrodes, while also capturing metals leached from the positive electrode.

[0051] Nitrile compounds include at least one selected from the group consisting of succinonitrile (SN), dicyanobutene (DCB), ethylene glycol bis(propionitrile) ether (ASA3), hexane tricyanide (HTCN), and adiponitrile (ADN).

[0052] Furthermore, based on the total weight of the electrolyte solution, the content of nitrile compounds can range from 0.05 wt% to 10 wt%. Specifically, the content of nitrile compounds can be 0.05 wt% or more, 1 wt% or more, or 3 wt% or more, and 6 wt% or less, 8 wt% or less, or 10 wt% or less. If the content of nitrile compounds is less than 0.05 wt%, the protective layer formed on the positive and negative electrodes may be incomplete. If the content exceeds 10 wt%, the resistance of the protective layer formed on the positive and negative electrodes will become very high, and the migration rate of lithium ions between excess unreacted additives will decrease. If the content exceeds 10 wt%, side effects may occur.

[0053] In addition, ethylene carbonate compounds include ethylene ethylene carbonate (VEC) and fluoroethylene carbonate (FEC).

[0054] Based on the total weight of the electrolyte solution, the content of ethylene carbonate compounds can range from 0.02 wt% to 15 wt%. Specifically, the content of ethylene carbonate compounds can be 0.02 wt% or more, 1 wt% or more, or 3 wt% or more, and 10 wt% or less, 12 wt% or less, or 15 wt% or less. If the content of ethylene carbonate compounds is less than 0.02 wt%, the protective layer formed on the negative electrode may be incomplete, and therefore the battery performance may deteriorate. If the content exceeds 15 wt%, the resistance may increase due to the excessive additives used to form the protective layer on the negative electrode, and therefore side effects may occur. The content of VEC can range from 0.01 wt% to 5 wt%, and the content of FEC can range from 0.01 wt% to 10 wt%.

[0055] If only VEC or FEC is included as a ethylene carbonate compound, the battery performance may be degraded due to the inhomogeneity of the negative electrode protective layer composition.

[0056] Furthermore, in ethylene carbonate compounds, the content of VEC can be less than that of FEC. Specifically, the weight ratio of VEC to FEC can be from 1:2 to 1:30, specifically 1:5 or less, 1:10 or less, or 1:13 or less, and 1:18 or more, 1:20 or more, or 1:25 or more. If the content is within the above weight ratio range, the effect of improving the high-temperature durability and high-rate life characteristics of the battery will be very good.

[0057] In addition, the second additive can form a protective layer on the surfaces of the positive and negative electrodes, and includes compounds that can be used with the first additive to suppress side reactions at the positive and negative electrodes.

[0058] The type of the second additive can vary depending on the type of the first additive.

[0059] If the first additive is a salt additive, the second additive may include at least one selected from the group consisting of ethylene ethylene carbonate (VEC), vinylene carbonate (VC), fluoroethylene carbonate (FEC), polysiloxane (PS), vinyl sulfate (ESa), succinic acid nitrile (SN), oxaloyl difluoroborate (ODFB), dicyclohexylcarbodiimide (DCC), 1,3-propenylsulfonyl lactone (PRS), ethylene glycol bis(propionitrile) ether (ASA3), adiponitrile (ADN), tricyanohexane (HTCN), dicyanobutylene (DCB), fluorobenzene (FB), and 1H-imidazolium-1-carboxylic acid propargyl ester (PIC). In the second additive, DCC does not directly form a protective layer on the negative electrode, but rather inhibits the generation of HF and the formation of byproducts induced by salt anions, ultimately potentially improving resistance by suppressing side reactions in the films of both the positive and negative electrodes.

[0060] Furthermore, if the first additive is a nitrile compound, the second additive may include at least one selected from the group consisting of ethylene ethylene carbonate (VEC), vinylene carbonate (VC), fluoroethylene carbonate (FEC), polysiloxane (PS), vinyl sulfate (ESa), oxaloyl difluoroborate (ODFB), dicyclohexylcarbodiimide (DCC), 1,3-propenylsulfonate (PRS), fluorobenzene (FB), and 1H-imidazolium-1-carboxylic acid propargyl ester (PIC). In the second additive, DCC does not directly form a protective layer on the negative electrode, but rather inhibits the generation of HF and suppresses the generation of byproducts induced by salt anions, ultimately potentially improving resistance by suppressing side reactions in the films of both the positive and negative electrodes.

[0061] Furthermore, if the first additive is a vinyl carbonate compound, the second additive may include at least one selected from the group consisting of vinylene carbonate (VC), polysiloxane (PS), vinyl sulfate (ESa), succinate (SN), oxaloyl difluoroborate (ODFB), dicyclohexylcarbodiimide (DCC), 1,3-propenylsulfonyl lactone (PRS), ethylene glycol bis(propionitrile) ether (ASA3), adiponitrile (ADN), tricyanohexane (HTCN), dicyanobutene (DCB), fluorobenzene (FB), and 1H-imidazolium-1-carboxylic acid propargyl ester (PIC). In the second additive, dicyclohexylcarbodiimide (DCC) does not directly form the negative electrode passivation layer, but it inhibits the generation of HF and suppresses the generation of byproducts caused by salt anions, ultimately potentially improving resistance by suppressing side reactions at the positive and negative electrode protective layers.

[0062] Furthermore, based on the total weight of the electrolyte solution, the content of the second additive can range from 5% to 30% by weight. Specifically, the content of the second additive can be 5% or more by weight, 10% or more by weight, or 15% or more by weight, and 20% or less by weight, 25% or less by weight, or 30% or less by weight. If the content of the second additive is within the above range, it will not affect the oxidative safety of the electrolyte solution or the calorific value generated by the decomposition reaction of the electrolyte solution (including Faraday and non-Faraday reactions), and, in order to protect the negative electrode surface during initial activation, sometimes a large portion of the second additive is consumed and decomposed without leaving any residue.

[0063] In this invention, lithium salts are used to provide lithium ions, and there are no particular limitations, as long as they are compounds capable of providing lithium ions in lithium secondary batteries.

[0064] If the lithium salt according to the present invention is used in conjunction with the first additive and / or the second additive described above, an SEI film can be stably formed on the negative electrode, and a stable film can also be formed on the positive electrode surface, thus controlling the side reactions caused by the decomposition of the electrolyte solution at high temperatures.

[0065] In this invention, the lithium salt may include at least one selected from the group consisting of LiPF6, lithium bis(fluorosulfonyl)imide (LiFSI), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

[0066] Furthermore, the concentration of lithium salt in the electrolyte solution can range from 0.8M to 2M. Specifically, the concentration can be 0.8M or greater, 1.0M or greater, or 1.2M or greater, and 1.5M or less, 1.8M or less, or 2.0M or less. If the lithium salt concentration is below 0.8M, kinetic problems may arise in the electrolyte solution due to insufficient lithium ion supply and decreased ionic conductivity. If the lithium salt concentration exceeds 2.0M, battery performance may deteriorate due to increased viscosity leading to physical property degradation.

[0067] Furthermore, based on the total weight of the electrolyte solution used in the lithium secondary battery, the lithium salt content can be from 10% to 30% by weight, specifically 10% or more by weight, or 13% or more by weight, and 20% or less by weight, or 30% or less by weight.

[0068] In this invention, there are no particular limitations on the organic solvent, as long as it is a solvent commonly used in the electrolyte solution of lithium secondary batteries.

[0069] In this invention, the organic solvent may be a non-aqueous organic solvent, including at least one selected from the group consisting of carbonate-based organic solvents, ester-based organic solvents, ether-based organic solvents, propionate-based organic solvents, and fluorine-based organic solvents.

[0070] The non-aqueous organic solvent may include at least one selected from the group consisting of propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, dipropyl carbonate, fluoroethylene carbonate, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, sulfolane, γ-butyrolactone, propylene sulfite, tetrahydrofuran, methyl formate, methyl acetate, ethyl acetate, isopropyl acetate, isoamyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, methyl butyrate, and ethyl butyrate, or a mixture of two or more thereof. Preferably, the non-aqueous organic solvent may include at least one selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), ethyl propionate (EP), and propyl propionate (PP).

[0071] In addition, based on the total weight of the electrolyte solution used in the lithium secondary battery, the content of organic solvent is 40% to 90% by weight, specifically 40% or more, 50% or more, or 60% or more, and 70% or less, 75% or less, or 80% or less, 85% or less, or 90% or less.

[0072] Lithium secondary batteries

[0073] The present invention also relates to a lithium secondary battery, which includes a positive electrode, a negative electrode, a separator inserted between the positive electrode and the negative electrode, and an electrolyte solution.

[0074] The lithium secondary battery of the present invention can be prepared by injecting the above-described electrolyte solution into an electrode assembly, which is formed by sequentially stacking a positive electrode, a negative electrode, and a separator selectively placed between the positive and negative electrodes. In this case, the positive electrode, negative electrode, and separator constituting the electrode assembly can be those commonly used in the manufacture of lithium secondary batteries.

[0075] The positive and negative electrodes constituting the lithium secondary battery of the present invention can be manufactured and used in a conventional manner.

[0076] First, the positive electrode can be manufactured by forming a hybrid layer for the positive electrode on the positive current collector. The hybrid layer for the positive electrode can be formed by coating the positive current collector with a slurry for the positive electrode, which includes a positive electrode active material, a binder, a conductive material, and a solvent, and then drying and rolling it.

[0077] The positive electrode current collector is not particularly limited as long as it has conductivity and does not cause chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, sintered carbon; or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver or the like can be used as the positive electrode current collector.

[0078] The positive electrode active material is a compound capable of reversibly inserting and extracting lithium, and specifically, may include lithium composite metal oxides, and the lithium composite metal oxides include lithium and at least one metal such as cobalt, manganese, nickel or aluminum. More specifically, the lithium composite metal oxide may be a lithium manganese-based oxide (e.g., LiMnO2, LiMn2O4, etc.), a lithium cobalt-based oxide (e.g., LiCoO2, etc.), a lithium nickel-based oxide (e.g., LiNiO2, etc.), a lithium nickel manganese-based oxide (e.g., LiNi 1-Y Mn Y O2 (where 0 < Y < 1), LiMn 2-z1 Ni z O4 (where 0 < Z < 2), etc.), a lithium nickel cobalt-based oxide (e.g., LiNi 1-Y1 Co Y1 O2 (where 0 < Y1 < 1), etc.), a lithium manganese cobalt-based oxide (e.g., LiCo 1-Y2 Mn Y2 O2 (where 0 < Y2 < 1), LiMn 2-z1 Co z1 O4 (where 0 < Z1 < 2), etc.), a lithium nickel manganese cobalt-based oxide (e.g., Li(Ni p Co q Mn r1 )O2 (where 0 < p < 1, 0 < q < 1, 0 < r1 < 1, p + q + r1 = 1), or Li(Ni p1 Co q1 Mn r2 )O4 (0 < p1 < 2, 0 < q1 < 2, 0 < r2 < 2, p1 + q1 + r2 = 2), etc.), or a lithium-nickel-cobalt-transition metal (M) oxide (e.g., Li(Ni p2 Co q2 Mn r3 M S2 )O2 (where M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg and Mo, and p2, q2, r3 and s2 are the atomic fractions of each independent element, where 0 < p2 < 1, 0 < q2 < 1, 0 < r3 < 1, 0 < s2 < 1, and p2 + q2 + r3 + s2 = 1), etc.), and may include any one or two or more of these compounds.

[0079] Among these, considering the potential to improve battery capacity characteristics and stability, lithium composite metal oxides can be LiCoO2, LiMnO2, LiNiO2, or lithium nickel manganese cobalt oxides (e.g., Li(Ni)O2). 1 / 3 Mn 1 / 3 Co 1 / 3 O2, Li(Ni) 0.6 Mn 0.2 Co 0.2 O2, Li(Ni) 0.5 Mn 0.3 Co 0.2 O2, Li(Ni) 0.7 Mn0.15Co 0.15 )O2, and Li(Ni 0.8 Mn 0.1 Co 0.1 (e.g., O2), or lithium nickel cobalt aluminum oxides (e.g., Li(Ni) 0.8 Co 0.15 Al 0.05 (O2, etc.)

[0080] Based on the total weight of solids in the slurry used for the positive electrode, the content of the positive electrode active material can be from 80% to 99% by weight.

[0081] Binders are components that facilitate the bonding of active and conductive materials, as well as their bonding with current collectors, and are typically added in an amount from 1% to 30% by weight based on the total weight of solids in the slurry used for the positive electrode. Examples of such binders may include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, and various copolymers.

[0082] Conductive materials can typically be added in amounts ranging from 1% to 30% by weight based on the total weight of solids in the slurry used for the positive electrode.

[0083] There are no particular limitations on conductive materials, as long as they are conductive and do not cause chemical changes in the battery. Examples include: graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lampblack, and thermal black; conductive fibers such as carbon fibers and metal fibers; metal powders such as fluorinated carbon powder, aluminum powder, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives. Specific examples of commercially available conductive materials may include acetylene black series products from Chevron Chemical Company or Denka black (Denka Singapore Private Limited), products from Gulf Oil Company, Ketjen black, EC series (products from Armak Company), Vulcan XC-72 (products from Cabot Company), and Super P (products from Timcal Company).

[0084] Solvents may include organic solvents such as N-methyl-2-pyrrolidone (NMP) and may be used in amounts to achieve the desired viscosity when including the positive electrode active material and optional binders, conductive materials, and the like. For example, the solvent content may be such that the solids concentration in the slurry containing the positive electrode active material and optional binders and conductive materials is 50-95% by weight, preferably 70-95% by weight.

[0085] Furthermore, the negative electrode can be manufactured by forming a hybrid layer for the negative electrode on the negative electrode current collector. This hybrid layer can be formed by coating the negative electrode current collector with a slurry containing a negative electrode active material, a binder, a conductive material, and a solvent, followed by drying and rolling.

[0086] Negative electrode current collectors typically have a thickness of 3-500 μm. There are no particular limitations on the negative electrode current collector, as long as it has high conductivity and does not cause chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, sintered carbon; copper or stainless steel with a surface treated with carbon, nickel, titanium, silver, or the like; aluminum-cadmium alloys, or the like, can be used as negative electrode current collectors. Furthermore, similar to positive electrode current collectors, negative electrode current collectors can enhance their adhesion to the negative electrode active material by forming fine irregularities on their surface, and can be used in various forms such as films, sheets, foils, meshes, porous bodies, foams, nonwoven fabrics, and the like.

[0087] In addition, negative electrode active materials may also include a single material selected from the group consisting of: lithium-titanium composite oxides (LTO); carbon-based materials, such as non-graphitized carbon, graphitized carbon, etc.; metal composite oxides, such as Li xFe2O3 (0 ≤ x ≤ 1), Li x WO2 (0 ≤ x ≤ 1), 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, halogens; 0 < x ≤ 1; 1 ≤ y ≤ 3; 1 ≤ z ≤ 8); lithium metal; lithium alloy; silicon-based alloy; tin-based alloy; metal oxides such as SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, and Bi2O5; and conductive polymers such as polyacetylene, or mixtures of two or more of them.

[0088] Based on the total weight of the solids in the slurry for the negative electrode, the content of the negative electrode active material can be 80 wt% to 99 wt%.

[0089] The binder is a component that helps the binding between the conductive material, the active material, and the current collector, and is usually added in an amount of 1 wt% to 30 wt% based on the total weight of the solids in the slurry for the negative electrode. Examples of such binders can include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, and various copolymers thereof.

[0090] The conductive material is a component for further improving the conductivity of the negative electrode active material, and can be added in an amount of 1 wt% to 20 wt% based on the total weight of the solids in the slurry for the negative electrode. The conductive material is not particularly limited as long as it has conductivity and does not cause chemical changes in the relevant battery. For example, the following can be used: graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal carbon black; conductive fibers such as carbon fibers and metal fibers; metal powders such as carbon fluoride powder, aluminum powder, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; polyphenylene derivatives.

[0091] The solvent can include water or an organic solvent such as NMP or alcohol, and can be used in an amount to achieve the desired viscosity when including the negative electrode active material and optionally a binder, a conductive material, and the like. For example, the content of the solvent can be such that the solid concentration in the slurry containing the negative electrode active material and optionally a binder and a conductive material is 50 - 95 wt%, preferably 70 - 90 wt%.

[0092] In addition, the separator serves to block internal short circuits between the two electrodes and to impregnate the electrolyte solution. Alternatively, the separator can be formed as a separating membrane by mixing a polymer resin, filler, and solvent to prepare a composition for the separator, then directly coating the composition onto the upper part of the electrode and drying it; or the separator can be formed by casting the composition onto a support and drying it, and then laminating the separating membrane peeled off from the support onto the upper part of the electrode.

[0093] As a separator, it can be used alone or in conjunction with its laminate using commonly used porous polymer membranes, such as porous polymer membranes made of polyolefin polymers such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer and ethylene / methacrylate copolymer, or conventional porous nonwoven fabrics can be used, such as nonwoven fabrics made of high melting point glass fiber, polyethylene terephthalate fiber, etc., but not limited thereto.

[0094] In this case, the pore size of the porous separator is typically 0.01-50 μm, and the porosity can be 5%-95%. In addition, the thickness of the porous separator can usually be in the range of 5-300 μm.

[0095] The shape of the lithium secondary battery of the present invention is not particularly limited, and it can be cylindrical, rectangular, bag-shaped, coin-shaped or similar in shape.

[0096] Preferred embodiments are presented below to aid in understanding the invention. However, it will be apparent to those skilled in the art that the following embodiments are merely illustrative of the invention, and various changes and modifications can be made within the scope and spirit of the invention, and it is self-evident that such changes and modifications fall within the scope of the appended claims.

[0097] Electrolyte solutions for lithium secondary batteries of Examples 1 to 3 and Comparative Examples 1 to 2 were prepared according to the compositions shown in Table 1 below.

[0098] Table 1:

[0099]

[0100]

[0101] Example 1

[0102] (1-1) Preparation of non-aqueous electrolyte solutions

[0103] Based on the composition shown in Table 1, prepare the non-aqueous electrolyte solution as follows.

[0104] As an organic solvent, ethylene carbonate (EC), polypropylene carbonate (PC), ethyl propionate (EP), and propyl propionate (PP) are mixed in a weight ratio of 2:1:2:5 (EC:PC:EP:PP) to prepare a mixed organic solvent.

[0105] A mixed solution was prepared by dissolving 1.2 M LiPF6, which is a lithium salt, in a mixed organic solvent.

[0106] A non-aqueous electrolyte solution was prepared by adding a compound of formula 1 (n = 3, R: CF3CF2CF2-, X: compound of formula 2 (m = 0, l = 3, R1: CH2CH=CH2)), a first additive, and a second additive to a mixed solution.

[0107] Lithium bis(oxalate)borate (LiBOB) is added as the first additive.

[0108] As a second additive, ethylene ethylene carbonate (VEC), polysiloxane (PS), fluoroethylene carbonate (FEC), succinic acid nitrile (SN), tricyanohexane (HTCN), oxaloyl difluoroborate (ODFB), and dicyclohexylcarbodiimide (DCC) are added to prepare an electrolyte solution.

[0109] (1-2) Preparation of lithium secondary batteries

[0110] To 100 parts by weight of N-methyl-2-pyrrolidone (NMP), a ternary active material (Li(Ni)) is added as the positive electrode active material. 0.5 Mn 0.3 Co 0.2 40 parts by weight of solids were obtained by mixing O2, carbon black as a conductive material, and polyvinylidene fluoride (PVDF) as a binder in a ratio of 90:5:5 (wt%) to prepare a slurry for a positive electrode active material. The slurry for the positive electrode active material was applied to a positive electrode current collector (Al film) with a thickness of 100 μm, and then dried and rolled to prepare the positive electrode.

[0111] To 100 parts by weight of NMP, 100 parts by weight of solids obtained by mixing graphene as the negative electrode active material, PVDF as the binder, and carbon black as the conductive material in a ratio of 90:5:2:3 (wt%) were added to prepare a slurry for the negative electrode active material. The slurry for the negative electrode active material was applied to a negative electrode current collector (Cu film) with a thickness of 90 μm, then dried and rolled to prepare the negative electrode.

[0112] The positive and negative electrodes prepared by the above method are then combined with a safety-enhancing separator. LG Chem) laminates together to prepare an electrode assembly, then places the electrode assembly into a pouch battery casing, injects the prepared non-aqueous electrolyte solution into each and seals it to prepare a 4.45V, 4,500mAh lithium secondary battery.

[0113] Example 2

[0114] The non-aqueous electrolyte solution and lithium secondary battery were prepared in the same manner as in Example 1, except that lithium difluorobis(oxalate)phosphate (LiDFOP) was used instead of LiBOB as the first additive.

[0115] Example 3

[0116] The non-aqueous electrolyte solution and lithium secondary battery were prepared in the same manner as in Example 1, except that lithium tetrafluoroborate (LiBF4) was used instead of LiBOB as the first additive.

[0117] Comparative Example 1

[0118] The non-aqueous electrolyte solution and lithium secondary battery were prepared in the same manner as in Example 1, except that the compound of Formula 1 was not used.

[0119] Comparative Example 2

[0120] The non-aqueous electrolyte solution and lithium secondary battery were prepared in the same manner as in Example 1, except that LiBOB was not used as the first additive.

[0121] Test Example 1: Measurement of High-Temperature Performance and Lifespan Characteristics

[0122] The lithium secondary batteries prepared in the examples and comparative examples were operated under voltage conditions from 3V to 4.45V, and the recovery capacity, low-temperature life, calorific value and thermal box improvement were measured as follows. The results are then shown in Table 2 below.

[0123] (1) Recovery capacity

[0124] The lithium secondary batteries prepared in the examples and comparative examples were fully charged to 100% SOC (4356mAh) at 4.45V. Then, they were heated from 25°C to 60°C at a heating rate of 0.7°C / min, and then stored at high temperature (60°C, 90% humidity) for 7 days. The recovery capacity was then measured under 1C charging and 1C discharging (1C = 4356mA).

[0125] (2) Lifetime characteristics

[0126] The life characteristics of lithium secondary batteries at low temperature (15℃), room temperature (25℃), and high temperature (60℃) were measured by charging at 2C and discharging at 15℃, 25℃, and 60℃, respectively.

[0127] (3) Heat value

[0128] The heat value is measured by measuring the internal heat value of the lithium secondary battery using an MMC device (Multiple Module Calorimeter, NETZSCH company, MMC274 MMC 274). Using Equation 1 below, the relative heat value (%) compared to the lithium secondary battery of Comparative Example 1 containing a non-aqueous electrolyte solution is calculated.

[0129] <Equation 1>

[0130] (Heat value of the secondary battery after storage at 150 °C for 100 minutes / Heat value of the lithium secondary battery of Comparative Example 1 after storage at 150 °C for 100 minutes) × 100

[0131] (4) Hot box test

[0132] The lithium secondary battery is placed in a high-temperature oven at 135 °C and 140 °C at a heating rate of 5 °C / min for 1 hour to evaluate the state of the battery. The case where no fire or explosion occurs is judged as qualified, and the case where fire or explosion occurs is judged as unqualified.

[0133] Table 2:

[0134]

[0135] The results confirmed that the recovery capacity was improved in the cases of Examples 1 to 3 compared to Comparative Examples 1 and 2.

[0136] In addition, it was confirmed that the low-temperature and room-temperature life characteristics were improved and the high-temperature life characteristics were equivalent or superior in the cases of Examples 1 to 3 compared to Comparative Examples 1 and 2.

[0137] In addition, it was confirmed that the heat value was reduced in the cases of Examples 1 to 3 compared to Comparative Examples 1 and 2.

[0138] According to the compositions shown in Table 3 below, electrolyte solutions for lithium secondary batteries of Examples 4 to 6 and Comparative Examples 3 to 4 were prepared.

[0139] Table 3

[0140]

[0141] Example 4

[0142] (1-1) Preparation of non-aqueous electrolyte solution

[0143] As an organic solvent, ethylene carbonate (EC), polypropylene carbonate (PC), ethyl propionate (EP), and propyl propionate (PP) are mixed in a weight ratio of 2:1:2:5 (EC:PC:EP:PP) to prepare a mixed organic solvent.

[0144] A mixed solution was prepared by dissolving 1.2 M LiPF6, which is a lithium salt, in a mixed organic solvent.

[0145] A non-aqueous electrolyte solution was prepared by adding a compound of formula 1 (n = 3, R: CF3CF2CF2-, X: compound of formula 2 (m = 0, l = 3, R1: CH2CH=CH2)), a first additive, and a second additive to a mixed solution.

[0146] As the first additive, succinic anionyl (SN) and tricyanohexane (HTCN) are added.

[0147] As a second additive, ethylene ethylene carbonate (VEC), polysiloxane (PS), fluoroethylene carbonate (FEC), oxaloyl difluoroborate (ODFB), and dicyclohexylcarbodiimide are added to prepare an electrolyte solution.

[0148] (1-2) Preparation of lithium secondary batteries

[0149] To 100 parts by weight of N-methyl-2-pyrrolidone (NMP), a ternary active material (Li(Ni)) is added as the positive electrode active material. 0.5 Mn 0.3 Co 0.2 40 parts by weight of solids were obtained by mixing O2, carbon black as a conductive material, and polyvinylidene fluoride (PVDF) as a binder in a ratio of 90:5:5 (wt%) to prepare a slurry for a positive electrode active material. The slurry for the positive electrode active material was applied to a positive electrode current collector (Al film) with a thickness of 100 μm, and then dried and rolled to prepare the positive electrode.

[0150] To 100 parts by weight of NMP, 100 parts by weight of solids obtained by mixing graphene as the negative electrode active material, PVDF as the binder, and carbon black as the conductive material in a ratio of 90:5:2:3 (wt%) were added to prepare a slurry for the negative electrode active material. The slurry for the negative electrode active material was applied to a negative electrode current collector (Cu film) with a thickness of 90 μm, then dried and rolled to prepare the negative electrode.

[0151] The positive and negative electrodes prepared by the above method are then combined with a safety-enhancing separator. LG Chem) laminates together to prepare an electrode assembly, then places the electrode assembly into a pouch battery casing, injects the prepared non-aqueous electrolyte solution into each and seals it to prepare a 4.45V, 4,500mAh lithium secondary battery.

[0152] Example 5

[0153] The non-aqueous electrolyte solution and lithium secondary battery were prepared in the same manner as in Example 4, except that 1.5% by weight of HTCN and 1% by weight of dicyanobutylene (DCB) were used instead of SN and HTCN as the first additives.

[0154] Example 6

[0155] The non-aqueous electrolyte solution and lithium secondary battery were prepared in the same manner as in Example 4, except that 2% by weight of SN and 3% by weight of DCB were used instead of SN and HTCN as the first additives.

[0156] Comparative Example 3

[0157] The non-aqueous electrolyte solution and lithium secondary battery were prepared in the same manner as in Example 4, except that the compound of Formula 1 was not used.

[0158] Comparative Example 4

[0159] The non-aqueous electrolyte solution and lithium secondary battery were prepared in the same manner as in Example 4, except that SN and HTCN were not used as the first additives.

[0160] Test Example 2: Measurement of High-Temperature Performance and Lifespan Characteristics

[0161] The lithium secondary batteries prepared in Examples 4 to 6, as well as Comparative Examples 3 and 4, were operated under voltage conditions ranging from 3V to 4.45V. Recovery capacity, low-temperature lifetime, calorific value, and thermal box improvement were measured in the same manner as in Test Example 1, and the results are shown in Table 4 below. In this case, the relative calorific value (%) in Equation 1 above is calculated as a relative calorific value compared to the lithium secondary battery of Comparative Example 3, but not Comparative Example 1.

[0162] Table 4:

[0163]

[0164] As a result, it was confirmed that the recovery capacity was improved in Examples 4 to 6 compared to Comparative Examples 3 and 4. Furthermore, it was confirmed that the low-temperature, room-temperature, and high-temperature lifetime characteristics were improved in Examples 4 to 6 compared to Comparative Examples 3 and 4, and the high-temperature lifetime characteristics were equal to or better than those in Examples 4 to 6.

[0165] Furthermore, it was confirmed that the calorific value was reduced in Examples 4 to 6 compared to Comparative Examples 3 and 4.

[0166] The electrolyte solutions of Examples 7 to 9 and Comparative Examples 5 to 7 were prepared according to the compositions shown in Table 5 below.

[0167] Table 5:

[0168]

[0169] Example 7

[0170] (1-1) Preparation of non-aqueous electrolyte solutions

[0171] Based on the composition shown in Table 5 above, prepare the non-aqueous electrolyte solution as follows.

[0172] As an organic solvent, ethylene carbonate (EC), polypropylene carbonate (PC), ethyl propionate (EP), and propyl propionate (PP) are mixed in a weight ratio of 2:1:2:5 (EC:PC:EP:PP) to prepare a mixed organic solvent.

[0173] A mixed solution was prepared by dissolving 1.2 M LiPF6, which is a lithium salt, in a mixed organic solvent.

[0174] A non-aqueous electrolyte solution was prepared by adding a compound of formula 1 (n = 3, R: CF3CF2CF2-, X: compound of formula 2 (m = 0, l = 3, R1: CH2CH=CH2)), a first additive, and a second additive to a mixed solution.

[0175] As the first additive, ethylene ethylene carbonate (VEC) and fluoroethylene carbonate (FEC) are added.

[0176] As a second additive, polysiloxane (PS), succinate (SN), tricyanohexane (HTCN), oxaloyl difluoroborate (ODFB), and dicyclohexylcarbodiimide (DCC) are added to prepare an electrolyte solution.

[0177] (1-2) Preparation of lithium secondary batteries

[0178] To 100 parts by weight of N-methyl-2-pyrrolidone (NMP), a ternary active material (Li(Ni)) is added as the positive electrode active material. 0.5 Mn 0.3 Co 0.240 parts by weight of solids were obtained by mixing O2, carbon black as a conductive material, and polyvinylidene fluoride (PVDF) as a binder in a ratio of 90:5:5 (wt%) to prepare a slurry for a positive electrode active material. The slurry for the positive electrode active material was applied to a positive electrode current collector (Al film) with a thickness of 100 μm, and then dried and rolled to prepare the positive electrode.

[0179] To 100 parts by weight of NMP, 100 parts by weight of solids obtained by mixing graphene as the negative electrode active material, PVDF as the binder, and carbon black as the conductive material in a ratio of 90:5:2:3 (wt%) were added to prepare a slurry for the negative electrode active material. The slurry for the negative electrode active material was applied to a negative electrode current collector (Cu film) with a thickness of 90 μm, then dried and rolled to prepare the negative electrode.

[0180] The positive and negative electrodes prepared by the above method are then combined with a safety-enhancing separator. LG Chem) laminates together to prepare an electrode assembly, then places the electrode assembly into a pouch battery casing, injects the prepared non-aqueous electrolyte solution into each and seals it to prepare a 4.45V, 4,500mAh lithium secondary battery.

[0181] Example 8

[0182] The non-aqueous electrolyte solution and lithium secondary battery were prepared in the same manner as in Example 7, except that 1.5% by weight of VEC and 7% by weight of FEC were used as the first additives.

[0183] Example 9

[0184] The non-aqueous electrolyte solution and lithium secondary battery were prepared in the same manner as in Example 7, except that 0.5% by weight of VEC and 5% by weight of FEC were used as the first additives.

[0185] Comparative Example 5

[0186] The non-aqueous electrolyte solution and lithium secondary battery were prepared in the same manner as in Example 7, except that the compound of Formula 1 was not used.

[0187] Comparative Example 6

[0188] The non-aqueous electrolyte solution and lithium secondary battery were prepared in the same manner as in Example 7, except that only VEC was used as the first additive.

[0189] Comparative Example 7

[0190] The non-aqueous electrolyte solution and lithium secondary battery were prepared in the same manner as in Example 7, except that only FEC was used as the first additive.

[0191] Test Example 3: Measurement of High-Temperature Performance and Lifespan Characteristics

[0192] The lithium secondary batteries prepared in Examples 7 to 9 and Comparative Examples 5 to 7 were operated under voltage conditions ranging from 3V to 4.45V, and their recovery capacity, low-temperature life, calorific value, and thermal box improvement were measured as follows. The results are then shown in Table 6 below. In this case, the relative calorific value (%) in Equation 1 above is calculated as the relative calorific value compared to the lithium secondary battery of Comparative Example 5, but not Comparative Example 1.

[0193] Table 6:

[0194]

[0195] The results confirmed that the recovery capacity was improved in Examples 7 to 9 compared with Comparative Examples 5 to 7.

[0196] Furthermore, it was confirmed that the low-temperature, room-temperature, and high-temperature life characteristics were improved in Examples 7 to 9 compared to Comparative Examples 5 to 7.

[0197] Furthermore, it was confirmed that the calorific value was reduced in Examples 7 to 9 compared to Comparative Examples 5 to 7.

[0198] In the foregoing, although the invention has been described with reference to limited embodiments and accompanying drawings, the invention is not limited thereto. Of course, those skilled in the art can make various modifications and variations within the technical spirit of the invention and the equivalent scope of the claims described below.

Claims

1. An electrolyte solution for lithium secondary batteries, comprising a polymer compound represented by Formula 1, a lithium salt, and an organic solvent: <Formula 1> Where n is an integer from 1 to 300, R is hydrogen, halogen, alkyl group having 1 to 6 carbon atoms, halogen-substituted alkyl group having 1 to 6 carbon atoms, alkoxy group having 1 to 6 carbon atoms, or halogen-substituted alkoxy group having 1 to 6 carbon atoms, and X is a functional group represented by the following formula 2: <Formula 2> Where m is an integer from 0 to 4, l is an integer from 1 to 3, R1 and R2 are each hydrogen, halogen, saturated or unsaturated alkyl group having 1 to 6 carbon atoms, or halogen-substituted saturated or unsaturated alkyl group having 1 to 6 carbon atoms, and R1 and R2 may be the same as or different from each other. The electrolyte solution further includes a first additive and a second additive. The first additive is a salt additive, and the second additive comprises at least one selected from the group consisting of ethylene ethylene carbonate (VEC), ethylene carbonate (VC), fluoroethylene carbonate (FEC), polysiloxane (PS), ethylene sulfate (ESa), succinic acid nitrile (SN), oxaloyl difluoroborate (ODFB), dicyclohexylcarbodiimide (DCC), 1,3-propenyl sulpholol (PRS), ethylene glycol bis(propionitrile) ether (ASA3), adiponitrile (ADN), tricyanohexane (HTCN), dicyanobutylene (DCB), fluorobenzene (FB), and 1H-imidazolium-1-carboxylic acid propargyl ester (PIC). The content of the second additive is from 5% to 30% by weight, based on the total weight of the electrolyte solution.

2. The electrolyte solution for lithium secondary batteries according to claim 1, wherein the salt additive comprises at least one selected from the group consisting of LiBF4, lithium bis(oxalate)borate (LiBOB), lithium difluoro(oxalate)borate (LiODFB), lithium difluorophosphate (LiDFP), and lithium difluorobis(oxalate)phosphate (LiDFOP).

3. The electrolyte solution for lithium secondary batteries according to claim 1, wherein the content of the salt additive is from 0.1% to 5% by weight based on the total weight of the electrolyte solution.

4. An electrolyte solution for a lithium secondary battery, comprising a polymer compound represented by Formula 1, a lithium salt, and an organic solvent: <Formula 1> Where n is an integer from 1 to 300, R is hydrogen, halogen, alkyl group having 1 to 6 carbon atoms, halogen-substituted alkyl group having 1 to 6 carbon atoms, alkoxy group having 1 to 6 carbon atoms, or halogen-substituted alkoxy group having 1 to 6 carbon atoms, and X is a functional group represented by the following formula 2: <Formula 2> Where m is an integer from 0 to 4, l is an integer from 1 to 3, R1 and R2 are each hydrogen, halogen, saturated or unsaturated alkyl group having 1 to 6 carbon atoms, or halogen-substituted saturated or unsaturated alkyl group having 1 to 6 carbon atoms, and R1 and R2 may be the same as or different from each other. The electrolyte solution further includes a first additive and a second additive. The first additive is a nitrile compound, and the second additive comprises at least one selected from the group consisting of ethylene ethylene carbonate (VEC), ethylene carbonate (VC), fluoroethylene carbonate (FEC), polysiloxane (PS), ethylene sulfate (ESa), succinic anionyl (SN), oxaloyl difluoroborate (ODFB), dicyclohexylcarbodiimide (DCC), 1,3-propenyl sulfonyl lactone (PRS), fluorobenzene (FB), and 1H-imidazolium-1-carboxylic acid propargyl ester (PIC). The content of the second additive is from 5% to 30% by weight, based on the total weight of the electrolyte solution.

5. The electrolyte solution for a lithium secondary battery according to claim 4, wherein the nitrile compound comprises at least one selected from the group consisting of succinic anionyl (SN), dicyanobutylene (DCB), ethylene glycol bis(propionitrile) ether (ASA3), tricyanohexane (HTCN), and adiponitrile (ADN).

6. The electrolyte solution for a lithium secondary battery according to claim 4, wherein the content of the nitrile compound is from 0.05% by weight to 10% by weight based on the total weight of the electrolyte solution.

7. An electrolyte solution for a lithium secondary battery, comprising a polymer compound represented by Formula 1, a lithium salt, and an organic solvent: <Formula 1> Where n is an integer from 1 to 300, R is hydrogen, halogen, alkyl group having 1 to 6 carbon atoms, halogen-substituted alkyl group having 1 to 6 carbon atoms, alkoxy group having 1 to 6 carbon atoms, or halogen-substituted alkoxy group having 1 to 6 carbon atoms, and X is a functional group represented by the following formula 2: <Formula 2> Where m is an integer from 0 to 4, l is an integer from 1 to 3, R1 and R2 are each hydrogen, halogen, saturated or unsaturated alkyl group having 1 to 6 carbon atoms, or halogen-substituted saturated or unsaturated alkyl group having 1 to 6 carbon atoms, and R1 and R2 may be the same as or different from each other. The electrolyte solution further includes a first additive and a second additive. The first additive is a vinyl carbonate compound, and the second additive comprises at least one selected from the group consisting of vinylene carbonate (VC), polysiloxane (PS), vinyl sulfate (ESa), succinate (SN), oxaloyl difluoroborate (ODFB), dicyclohexylcarbodiimide (DCC), 1,3-propenylsulfonyl lactone (PRS), ethylene glycol bis(propionitrile) ether (ASA3), adiponitrile (ADN), tricyanohexane (HTCN), dicyanobutene (DCB), fluorobenzene (FB), and 1H-imidazolium-1-carboxylic acid propargyl ester (PIC). The content of the second additive is from 5% to 30% by weight, based on the total weight of the electrolyte solution.

8. The electrolyte solution for a lithium secondary battery according to claim 7, wherein the ethylene carbonate compound includes ethylene ethylene carbonate (VEC) and fluoroethylene carbonate (FEC).

9. The electrolyte solution for a lithium secondary battery according to claim 7, wherein the content of the ethylene carbonate compound is from 0.02% to 15% by weight based on the total weight of the electrolyte solution.

10. The electrolyte solution for a lithium secondary battery according to any one of claims 1, 4 and 7, wherein the content of the polymer compound represented by Formula 1 is from 0.1% to 5% by weight based on the total weight of the electrolyte solution.

11. The electrolyte solution for a lithium secondary battery according to any one of claims 1, 4 and 7, wherein the unsaturated alkenyl groups are respectively bonded to the R1 and R2 ends in Formula 2.

12. The electrolyte solution for a lithium secondary battery according to claim 11, wherein the unsaturated alkenyl group is a vinyl group.

13. The electrolyte solution for a lithium secondary battery according to any one of claims 1, 4 and 7, wherein the organic solvent comprises at least one selected from the group consisting of ester-based organic solvents, ether-based organic solvents and fluorine-based organic solvents.

14. The electrolyte solution for a lithium secondary battery according to any one of claims 1, 4 and 7, wherein the organic solvent comprises at least one selected from the group consisting of carbonate-based organic solvents, ether-based organic solvents, propionate-based organic solvents and fluorine-based organic solvents.

15. The electrolyte solution for a lithium secondary battery according to any one of claims 1, 4 and 7, wherein the lithium salt comprises at least one selected from the group consisting of LiPF6, lithium bis(fluorosulfonyl)imide (LiFSI) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

16. A lithium secondary battery, comprising: positive electrode; negative electrode; A separator inserted between the positive electrode and the negative electrode; and The electrolyte solution according to any one of claims 1 to 15.

Images