Nonaqueous electrolyte for lithium secondary battery and lithium secondary battery containing same

Abstract

The present invention provides a non-aqueous electrolyte for a lithium secondary battery and a lithium secondary battery including the same. The non-aqueous electrolyte for a lithium secondary battery of the present invention may include a lithium salt, an organic solvent, and a compound represented by Chemical Formula 1 as an additive.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2021-0169690 filed December 1, 2021 and Korean Patent Application No. 10-2022-0161914 filed November 28, 2022, and all contents disclosed in the documents of said Korean patent applications are incorporated herein by reference.

[0002] The present invention relates to a non-aqueous electrolyte for a lithium secondary battery and a lithium secondary battery containing the same. [Background technology]

[0003] 2. Description of the Related Art As modern society becomes increasingly dependent on electrical energy, renewable energy power generation systems that can produce electrical energy without causing environmental problems are gaining attention.

[0004] Among currently commercially available power storage devices, lithium-ion batteries are known to provide a stable supply of power and exhibit the highest energy density. A lithium-ion battery is composed of a positive electrode made of a lithium-containing transition metal oxide, a negative electrode capable of storing lithium, an electrolyte solution containing an organic solvent containing lithium salt, and a separator. Of these, the positive electrode stores energy through the oxidation-reduction reaction of the transition metal, which means that the positive electrode material must contain a transition metal.

[0005] On the other hand, when lithium-ion batteries are repeatedly charged and discharged and exposed to high-temperature environments, electrolyte decomposition increases, inducing gas generation within the cell. In particular, in the case of high-voltage positive electrodes used in recent lithium-ion batteries, reactive oxygen compounds are formed above a certain voltage. These reactive oxygen compounds cause decomposition of carbonate-based solvents, which are the main solvents in the electrolyte, further increasing gas generation.

[0006] When the electrolyte is depleted due to these various side reactions, a sudden death phenomenon occurs in which the battery capacity suddenly drops, and the battery performance may be significantly reduced.

[0007] Furthermore, lithium salts used as electrolyte salts are vulnerable to moisture and react with moisture present in the cell to generate Lewis acids such as HF. These Lewis acids can corrode the passive film formed at the electrode-electrolyte interface, inducing the elution of transition metal ions from the positive electrode. The eluted transition metal ions are then electro-deposited on the surface of the negative electrode, accelerating the decomposition of the electrolyte and causing the desorption of lithium ions inserted into the negative electrode, resulting in a significant decrease in the battery capacity retention rate. Therefore, in order to prevent such various side reactions, there is a need to develop a new electrolyte that can form a stable coating on the surface of the electrode. Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention has been made to solve the above-mentioned problems, and has an object to provide a nonaqueous electrolyte for a lithium secondary battery that forms a stable coating on the surface of an electrode and contains an additive that is excellent in removing highly reactive Lewis acids, acidic materials, and reactive oxygen species in the electrolyte.

[0009] Another object of the present invention is to provide a lithium secondary battery containing the nonaqueous electrolyte solution for lithium secondary batteries, and thereby having improved high-rate charge-discharge characteristics. [Means for solving the problem]

[0010] In order to achieve the above object, in one embodiment of the present invention, The present invention provides a non-aqueous electrolyte solution for a lithium secondary battery, which comprises a lithium salt, an organic solvent, and a compound represented by the following chemical formula 1 as an additive:

[0011] [ka]

[0012] In the above Chemical Formula 1, R1 to R6 are each independently a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, -SiR7R8R9 (R7 to R9 are each independently an alkyl group having 1 to 10 carbon atoms), or -O-SiR 10 R 11 R 12 (R 10 ~R 12 are each independently an alkyl group having 1 to 10 carbon atoms, At least one of R1 to R5 is -SiR7R8R9 (R7 to R9 are each independently an alkyl group having 1 to 10 carbon atoms), or -O-SiR 10 R 11 R 12 (R 10 ~R 12 are each independently an alkyl group having 1 to 10 carbon atoms.

[0013] On the other hand, in another embodiment of the present invention, The present invention provides a lithium secondary battery comprising a negative electrode, a positive electrode, a separator interposed between the negative electrode and the positive electrode, and a non-aqueous electrolyte solution, wherein the non-aqueous electrolyte solution comprises the non-aqueous electrolyte solution for lithium secondary batteries of the present invention. [Effects of the Invention]

[0014] The nonaqueous electrolyte of the present invention contains a coumarin derivative substituted with a trialkylsilyl group or a trialkylsilyl ether group as an additive, which not only effectively removes Lewis acids generated as decomposition products of the electrolyte but also forms a stable coating on the electrode surface, suppressing the sustained decomposition reaction between the positive electrode and the organic solvent. Therefore, by including such a nonaqueous electrolyte, a lithium secondary battery with improved high-rate charge-discharge characteristics can be realized. DETAILED DESCRIPTION OF THE INVENTION

[0015] The present invention will now be described in more detail. The terms and words used in this specification and claims should not be interpreted in a limited way to their ordinary or dictionary meanings, but should be interpreted in a way that is consistent with the technical idea of the present invention, based on the principle that the inventor can appropriately define the concept of the term in order to best explain his / her invention.

[0016] Conventionally, decomposition products formed by the hydration or thermal decomposition of lithium salts, such as hydrogen fluoride (HF), form a film on the electrode surface, but the transition metals that make up the positive electrode are easily dissolved into the electrolyte, and the dissolved transition metal ions are re-deposited on the positive electrode, causing an increase in the positive electrode resistance. Alternatively, transition metals that migrate to the negative electrode via the electrolyte are electrodeposited on the negative electrode, causing self-discharge of the negative electrode and destroying the solid electrolyte interphase (SEI) film that provides passivation to the negative electrode, accelerating the decomposition reaction of additional electrolytes and increasing the interfacial resistance of the negative electrode.

[0017] This series of reactions not only reduces the amount of available lithium ions in the battery, resulting in a decrease in battery capacity, but also increases resistance due to the accompanying decomposition reaction of the electrolyte.

[0018] The present invention aims to provide a nonaqueous electrolyte solution for lithium secondary batteries that contains an additive capable of effectively removing decomposition products of the electrolyte salt that cause such deterioration and poor behavior, and that is capable of being oxidatively decomposed prior to organic solvents to form a robust coating on the surface of the positive electrode, and a lithium secondary battery that contains the same and thereby has improved high-rate charge / discharge performance at high temperatures.

[0019] Nonaqueous electrolyte for lithium secondary batteries Specifically, in one embodiment of the present invention, The present invention provides a non-aqueous electrolyte solution for a lithium secondary battery, which comprises a lithium salt, an organic solvent, and a compound represented by the following chemical formula 1 as an additive:

[0020] [ka]

[0021] In the above Chemical Formula 1, R1 to R6 are each independently a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, -SiR7R8R9 (R7 to R9 are each independently an alkyl group having 1 to 10 carbon atoms), or -O-SiR 10 R 11 R 12 (R 10 ~R 12 are each independently an alkyl group having 1 to 10 carbon atoms, At least one of R1 to R5 is -SiR7R8R9 (R7 to R9 are each independently an alkyl group having 1 to 10 carbon atoms), or -O-SiR 10 R 11 R 12 (R 10 ~R 12 are each independently an alkyl group having 1 to 10 carbon atoms.

[0022] (1) Lithium salt First, the lithium salt will be described as follows. The lithium salt may be any one that is commonly used in non-aqueous electrolytes for lithium secondary batteries without any limitation. For example, the cation may be Li + and the anion is F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , B 10 Cl 10 - , AlCl4 - , AlO4 - , PF6 - , CF3SO3 - , CH3CO2 - , CF3CO2 - , AsF6 - , SbF6- , CH3SO3 - , (CF3CF2SO2)2N - , (CF3SO2)2N - , (FSO2)2N - , BF2C2O4 - , BC4O8 - , PF4C2O4 - , PF2C4O8 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , C4F9SO3 - , CF3CF2SO3 - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , CF3(CF2)7SO3 - , and SCN - The composition may include at least one selected from the group consisting of:

[0023] Specifically, the lithium salts include LiCl, LiBr, LiI, LiBF4, LiClO4, LiB 10 Cl 10 The lithium salt may include a single material or a mixture of two or more materials selected from the group consisting of LiAlCl, LiAlO, LiPF, LiCF, SO, LiCH, CO, LiCF, CO, LiAsF, LiSbF, LiCH, SO, LiN(SO, F) (Lithium bis(fluorosulfonyl)imide, LiFSI), LiN(SOCF, CF) (Lithium bis(pentafluoroethanesulfonyl)imide, LiBETI), and LiN(SOCF) (Lithium bis(trifluoromethanesulfonyl)imide, LiTFSI). In addition to the lithium salts listed above, any lithium salt commonly used in electrolytes for lithium secondary batteries may be used without limitation. Specifically, the lithium salt may include at least one selected from LiPF, LiBF, and LiN(SOF).

[0024] The lithium salt may be varied as appropriate within a generally usable range, but in order to obtain an optimal effect of forming a coating for preventing corrosion on the electrode surface, it may be contained in the electrolyte at a concentration of 0.8 M to 3.0 M, specifically 1.0 M to 3.0 M. When the concentration of the lithium salt satisfies this range, the viscosity of the nonaqueous electrolyte can be controlled to achieve optimal impregnation, and the mobility of lithium ions can be improved, resulting in improved capacity characteristics and cycle characteristics of the lithium secondary battery.

[0025] (2) Non-aqueous organic solvent The non-aqueous organic solvent is described below. The non-aqueous organic solvent may be any of various organic solvents commonly used in non-aqueous electrolytes, and the type of organic solvent is not limited as long as it can minimize decomposition due to oxidation reactions during the charge / discharge process of the secondary battery and can exhibit desired properties together with the additives.

[0026] Specifically, the non-aqueous organic solvent may include a cyclic carbonate organic solvent, a linear carbonate organic solvent, a linear ester organic solvent, or a mixed organic solvent thereof.

[0027] The cyclic carbonate organic solvent is a high-viscosity organic solvent that has a high dielectric constant and effectively dissociates the lithium salt in the non-aqueous electrolyte solution. Specific examples thereof include at least one organic solvent selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, and vinylene carbonate, and among these, ethylene carbonate may be included.

[0028] The linear carbonate organic solvent is an organic solvent having low viscosity and low dielectric constant, and specific examples thereof may include at least one organic solvent selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethyl methyl carbonate (EMC), methyl propyl carbonate, and ethyl propyl carbonate, and specifically may include ethyl methyl carbonate (EMC).

[0029] The linear ester organic solvent is a solvent that is relatively more stable at high temperatures and high voltages than cyclic carbonate organic solvents, and can overcome the drawback of cyclic carbonate organic solvents, such as gas generation during high voltage operation, while achieving high ionic conductivity. Specific examples of the linear ester organic solvent include at least one selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, and butyl propionate, and more specifically, at least one selected from ethyl propionate and propyl propionate.

[0030] In the present invention, in order to ensure high ionic conductivity of the nonaqueous electrolyte solution, a cyclic carbonate organic solvent, a linear carbonate organic solvent, and / or a linear ester organic solvent may be mixed in a volume ratio of 10:90 to 50:50, specifically 20:80 to 40:60.

[0031] The nonaqueous electrolyte solution of the present invention may further contain a cyclic ester organic solvent, if necessary, which may include at least one selected from the group consisting of γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, and ε-caprolactone.

[0032] Meanwhile, the remainder of the non-aqueous electrolyte solution of the present invention, excluding the lithium salt and the compound represented by Chemical Formula 1 as an additive, may be a non-aqueous organic solvent unless otherwise specified.

[0033] (3) Additives The non-aqueous electrolyte for a lithium secondary battery of the present invention may contain a compound represented by the following chemical formula 1 as an additive.

[0034] [ka]

[0035] In the above Chemical Formula 1, R1 to R6 are each independently a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, -SiR7R8R9 (R7 to R9 are each independently an alkyl group having 1 to 10 carbon atoms), or -O-SiR 10 R 11 R 12 (R 10 ~R 12 are each independently an alkyl group having 1 to 10 carbon atoms, At least one of R1 to R5 is -SiR7R8R9 (R7 to R9 are each independently an alkyl group having 1 to 10 carbon atoms), or -O-SiR 10 R 11 R 12 (R 10 ~R 12 are each independently an alkyl group having 1 to 10 carbon atoms.

[0036] Specifically, in the above-mentioned chemical formula 1, R7 to R 12 may each independently contain a primary, secondary, or tertiary alkyl group having 1 to 10 carbon atoms, which may be substituted or unsubstituted with an alkyl group, and may be the same or different from each other.

[0037] The compound represented by Chemical Formula 1, which is an additive of the present invention, as an aromatic coumarin derivative, can remove reactive oxygen compounds (Singlet oxygen, Superoxide radical anion) that can occur in high-voltage / high-capacity cathodes such as Mn-rich cathodes, overlithiated layered oxides, or ternary cathodes (LiNi x Co y Mn z O2 (0.6 < x ≤ 0.92, 0 < y ≤ 1.0, 0 < z ≤ 1.0)), and can effectively suppress the generation of CO2, CO, or H2O that has an adverse effect in the battery. In addition, functional groups such as trialkylsilyl groups and trialkylsilyl ether groups substituted in the aromatic coumarin derivative of the present invention react with HF generated as a decomposition product of the electrolyte to form fluorotrialkylsilylsilane, thereby effectively removing HF or acidic substances. In particular, in the case of the trialkylsilyl ether group, by stabilizing a Lewis acid such as PF5 through the interaction of Lewis acid-base and effectively suppressing chemical decomposition and hydrolysis, the generation of HF and reactive acid compounds that may occur due to the decomposition of the Lewis acid can be suppressed. Therefore, compared with a compound in which a halogen group is directly substituted in an aromatic coumarin compound or a compound in which a hydrocarbon-based halogen functional group is substituted, reactive acid compounds such as Lewis acid can be effectively removed, so side reactions generated by reactive acid compounds and deterioration reactions at the electrode-electrolyte interface can be effectively controlled.

[0038] Furthermore, such an additive is oxidatively decomposed prior to the organic solvent to form a firm film on the surfaces of the positive and negative electrodes, and such a film can suppress the continuous decomposition reaction between the positive electrode and the organic solvent. Therefore, by providing a non-aqueous electrolyte containing the additive, a lithium secondary battery with improved high-rate charge and discharge can be realized.

[0039] Specifically, in the above Chemical Formula 1, R1 to R6 are each independently hydrogen, -SiR7R8R9 (R7 to R9 are each independently an alkyl group having 1 to 7 carbon atoms), or -O-SiR 10 R 11 R 12 (R 10 ~R 12 are each independently an alkyl group having 1 to 7 carbon atoms), and at least one of R1 or R5 is -SiR7R8R9 (R7 to R9 are each independently an alkyl group having 1 to 7 carbon atoms), or -O-SiR 10 R 11 R 12 (R 10 ~R 12 are each independently an alkyl group having 1 to 7 carbon atoms), and R2 to R4 and R6 may each independently be hydrogen or an alkyl group having 1 to 7 carbon atoms.

[0040] In addition, in the above Chemical Formula 1, R1 to R6 are each independently hydrogen, -SiR7R8R9 (R7 to R9 are each independently an alkyl group having 1 to 5 carbon atoms), or -O-SiR 10 R 11 R 12 (R 10 ~R 12 are each independently an alkyl group having 1 to 5 carbon atoms), and at least one of R1 or R5 is -SiR7R8R9 (R7 to R9 are each independently an alkyl group having 1 to 5 carbon atoms), or -O-SiR 10 R 11 R 12 (R 10 ~R 12 are each independently an alkyl group having 1 to 5 carbon atoms), and R2 to R4 and R6 may each independently be hydrogen or an alkyl group having 1 to 5 carbon atoms.

[0041] Specifically, the compound represented by Chemical Formula 1 may include at least one selected from compounds represented by the following Chemical Formulas 1a and 1b.

[0042] [ka] 7-[tert-butyl(dimethyl)silyl]oxychromen-2-one (CAS No. 918314-89-3)

[0043] [ka] 3-(Trimethylsilyl)coumarin (CAS No. 647836-33-7)

[0044] The compound represented by Chemical Formula 1 may be included in an amount of 0.01 wt % to 5.0 wt % based on the total weight of the non-aqueous electrolyte solution. When the compound represented by Formula 1 is contained within the above range, it is possible to effectively remove decomposition products of the electrolyte salt and form a strong passivation film on the surface of the electrode while minimizing disadvantages such as additive-induced side reactions, a decrease in initial capacity, and an increase in resistance, thereby enabling the manufacture of a secondary battery with improved performance.

[0045] Specifically, when the content of the compound represented by Chemical Formula 1 is 0.01 wt % or more, a stable coating is formed and the effect of removing Lewis acid generated as a decomposition product of the electrolyte during battery operation is more stably maintained. Also, when the content of the compound represented by Chemical Formula 1 is 5.0 wt % or less, an increase in the viscosity of the electrolyte due to excess compound is prevented, ion mobility within the battery is improved, and excessive coating formation is suppressed, effectively preventing an increase in battery resistance, thereby preventing a decrease in capacity and cycle characteristics.

[0046] Specifically, the compound represented by Chemical Formula 1 may be included in an amount of 0.01 wt % to 3.0 wt %, more specifically 0.1 wt % to 3.0 wt %, based on the total weight of the non-aqueous electrolyte solution.

[0047] (4) Other additives In addition, the non-aqueous electrolyte of the present invention may further contain other additives to prevent the breakdown of the negative electrode due to decomposition of the non-aqueous electrolyte in a high-power environment, and to further improve low-temperature high-rate discharge characteristics, high-temperature stability, overcharge prevention, and the effect of suppressing battery expansion at high temperatures.

[0048] Examples of such other additives include at least one selected from the group consisting of cyclic carbonate-based compounds, halogen-substituted carbonate-based compounds, sultone-based compounds, sulfate-based compounds, sulfite-based compounds, phosphate-based compounds, phosphite-based compounds, borate-based compounds, benzene-based compounds, amine-based compounds, silane-based compounds, and lithium salt-based compounds.

[0049] Examples of the cyclic carbonate compounds include vinylene carbonate (VC) and vinyl ethylene carbonate (VEC). Examples of the halogen-substituted carbonate compounds include fluoroethylene carbonate (FEC).

[0050] The sultone compound may be, for example, at least one compound selected from the group consisting of 1,3-propane sultone (PS), 1,4-butane sultone, ethene sultone, 1,3-propene sultone (PRS), 1,4-butene sultone, and 1-methyl-1,3-propene sultone.

[0051] The sulfate-based compound may be, for example, ethylene sulfate (Esa), trimethylene sulfate (TMS), methyl trimethylene sulfate (MTMS), or the like.

[0052] Examples of the sulfite-based compound include ethylene sulfite and trimethylene sulfite. The phosphate-based or phosphite-based compound may be, for example, one or more compounds selected from the group consisting of lithium difluoro(bisoxalato)phosphate, lithium difluorophosphate, tris(trimethylsilyl)phosphate, tris(trimethylsilyl)phosphite, tris(2,2,2-trifluoroethyl)phosphate, and tris(trifluoroethyl)phosphite.

[0053] Examples of the borate-based compounds include tetraphenylborate, lithium oxalyldifluoroborate (LiODFB) which can form a coating on the surface of the negative electrode, and lithium bisoxalateborate (LiB(C2O4)2, LiBOB).

[0054] The benzene-based compound may be fluorobenzene or the like, the amine-based compound may be triethanolamine, ethylenediamine or the like, and the silane-based compound may be tetravinylsilane or the like. The lithium salt compound is a compound different from the lithium salt contained in the non-aqueous electrolyte, and examples thereof include LiPO2F2 and LiBF4.

[0055] Among these other additives, in order to form a stronger SEI coating on the surface of the negative electrode during the initial activation step, other additives having an excellent coating formation effect on the surface of the negative electrode, specifically at least one selected from the group consisting of vinylene carbonate, vinylethylene carbonate, fluoroethylene carbonate (FEC), and lithium oxalyl difluoroborate (LiODFB), may be included.

[0056] The other additives may be used as a mixture of two or more compounds, and may be included in an amount of 0.01 wt % to 50 wt %, specifically 0.01 wt % to 10 wt %, and preferably 0.05 wt % to 5 wt %, based on the total weight of the non-aqueous electrolyte. When the content of the other additives is within the above range, cycle characteristics are improved, side reactions in the battery caused by excessive addition are prevented, and the remaining or precipitation of unreacted materials can be prevented, which is preferable.

[0057] Lithium secondary battery In another embodiment of the present invention, there is provided a lithium secondary battery including a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and the nonaqueous electrolyte solution of the present invention.

[0058] The lithium secondary battery of the present invention can be manufactured by forming an electrode assembly in which a positive electrode, a negative electrode, and a separator between the positive electrode and the negative electrode are sequentially stacked, housing the electrode assembly in a battery case, and then adding the nonaqueous electrolyte of the present invention.

[0059] The method for manufacturing the lithium secondary battery of the present invention may be carried out by a conventional method well known in the art, and will be described in detail below.

[0060] (1) Positive electrode The positive electrode according to the present invention may include a positive electrode active material layer containing a positive electrode active material, and if necessary, the positive electrode active material layer may further include a conductive material and / or a binder.

[0061] The positive electrode active material is a compound capable of reversible intercalation and deintercalation of lithium, and specifically may include a lithium composite metal oxide containing lithium and one or more metals such as cobalt, manganese, nickel, or aluminum.

[0062] Specifically, the positive electrode active material may include lithium-cobalt-based oxides (e.g., LiCoO2, etc.), lithium-manganese-based oxides (e.g., LiMnO2, LiMn2O4, etc.), lithium-nickel-based oxides (e.g., LiNiO2, etc.), lithium-nickel-manganese-based oxides (e.g., LiNi 1-Y Mn Y O2 (where 0 < Y < 1), LiMn 2-z Ni z O4 (where 0 < Z < 2), etc.), lithium-nickel-cobalt-based oxides (e.g., LiNi 1-Y1 Co Y1 O2 (where 0 < Y1 < 1), etc.), lithium-manganese-cobalt-based oxides (e.g., LiCo 1-Y2 Mn Y2 O2 (where 0 < Y2 < 1), LiMn 2-z1 Co z1 O4 (where 0 < Z1 < 2), etc.), lithium-nickel-manganese-cobalt-based oxides (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 (where 0 < p1 < 2, 0 < q1 < 2, 0 < r2 < 2, p1 + q1 + r2 = 2), etc.), lithium-nickel-cobalt-transition metal (M) oxides (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, Ti, and Mo, and p2, q2, r3, and s2 are atomic fractions of independent elements, 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.

[0063] In particular, in terms of being able to improve the capacity characteristics and safety of the battery, the positive electrode active material may include at least one selected from the group consisting of lithium-cobalt oxide, lithium-manganese oxide, lithium-nickel-manganese-cobalt oxide, and lithium-nickel-cobalt-transition metal (M) oxide, and specifically may include at least one selected from lithium-cobalt oxide, lithium-nickel-manganese-cobalt oxide with a nickel content of 55 atm% or more, and lithium-nickel-cobalt-transition metal (M) oxide with a nickel content of 55 atm% or more.

[0064] Specifically, the positive electrode active material is, for example, Li(Ni 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 Mn 0.15 Co 0.15 )O2, Li(Ni 0.8 Mn 0.1 Co 0.1 )O2, and Li(Ni 0.86 Co 0.057 Mn 0.07 Al 0.02 )O2, and preferably Li(Ni 0.86 Co 0.057 Mn 0.07 Al 0.02 ) O2 may be included.

[0065] The positive electrode active material may be included in an amount of 80 wt% to 99 wt%, specifically 90 wt% to 99 wt%, based on the total weight of the solid content in the positive electrode slurry. In this case, if the content of the positive electrode active material is less than 80 wt%, the energy density may be reduced, resulting in a decrease in capacity.

[0066] The conductive material is not particularly limited as long as it does not induce chemical changes in the battery and is conductive, and examples thereof include carbon powders such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; graphite powders such as natural graphite, artificial graphite, and graphite with highly developed crystal structures; conductive fibers such as carbon fibers and metal fibers; metal powders such as carbon fluoride, aluminum, 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. The conductive material is usually added in an amount of 1 to 30% by weight based on the total weight of the solid content in the positive electrode active material layer.

[0067] The binder is a component that improves adhesion between positive electrode active material particles and between the positive electrode active material and the current collector, and is typically added in an amount of 1 to 30 wt% based on the total weight of the solids in the positive electrode active material layer. Examples of such binders include fluororesin-based binders including polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE); rubber-based binders including styrene butadiene rubber (SBR), acrylonitrile butadiene rubber, and styrene-isoprene rubber; cellulose-based binders including carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, and regenerated cellulose; polyalcohol-based binders including polyvinyl alcohol; polyolefin-based binders including polyethylene and polypropylene; polyimide-based binders; polyester-based binders; and silane-based binders.

[0068] The positive electrode of the present invention as described above may be manufactured by a method known in the art. For example, the positive electrode may be manufactured by a method of dissolving or dispersing a positive electrode active material, a binder, and / or a conductive material in a solvent to prepare a positive electrode slurry, which is then coated on a positive electrode current collector, followed by drying and rolling to form a positive electrode active material layer, or by a method of casting the positive electrode active material layer on a separate support, peeling off the support, and laminating the resulting film on a positive electrode current collector.

[0069] The positive electrode current collector is not particularly limited as long as it does not induce chemical changes in the battery and has conductivity. For example, stainless steel, aluminum, nickel, titanium, baked carbon, or aluminum or stainless steel whose surface has been treated with carbon, nickel, titanium, silver, or the like may be used.

[0070] The solvent may include an organic solvent such as NMP (N-methyl-2-pyrrolidone), and may be used in an amount that provides a preferred viscosity when the positive electrode active material, and optionally a binder and a conductive material, are contained. For example, the solvent may be contained so that the solids concentration in the active material slurry containing the positive electrode active material, and optionally a binder and a conductive material, is 10 wt % to 70 wt %, preferably 20 wt % to 60 wt %.

[0071] (2) Negative electrode Next, the negative electrode will be described. The negative electrode according to the present invention includes a negative electrode active material layer containing a negative electrode active material, and the negative electrode active material layer may further include a conductive material and / or a binder, as necessary.

[0072] The negative electrode active material may include at least one selected from the group consisting of lithium metal, a carbon material capable of reversibly intercalating / deintercalating lithium ions, a metal or an alloy of such a metal and lithium, a metal composite oxide, a material capable of doping and dedoping lithium, and a transition metal oxide.

[0073] As the carbon material capable of reversibly intercalating / deintercalating lithium ions, any carbonaceous negative electrode active material generally used in lithium ion secondary batteries may be used without particular limitation. Representative examples thereof include crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon include graphite such as amorphous, plate-like, flaky, spherical, or fibrous natural graphite or artificial graphite. Examples of the amorphous carbon include soft carbon (low-temperature calcined carbon), hard carbon, mesophase pitch carbide, calcined coke, and the like.

[0074] As the metal or an alloy of these metals and lithium, a metal selected from the group consisting of Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn or an alloy of these metals and lithium may be used.

[0075] Examples of the metal composite oxide include PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, Bi2O5, Li x Fe2O3 (0 ≦ x ≦ 1), Li x WO2 (0 ≦ x ≦ 1), and Sn x Me 1-x Me’ y O z (Me: Mn, Fe, Pb, Ge; Me’: Al, B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, halogen; 0 < x ≦ 1; 1 ≦ y ≦ 3; 1 ≦ z ≦ 8) selected from the group consisting of may be used.

[0076] As the substance capable of doping and undoping lithium, Si, SiO x(0 < x < 2), Si-Y alloy (where Y is an element selected from the group consisting of alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, transition metals, rare earth elements, and combinations thereof, and is not Si), Sn, SnO2, Sn-Y (where Y is an element selected from the group consisting of alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, transition metals, rare earth elements, and combinations thereof, and is not Sn), etc. may be mentioned, and at least one of these may be mixed with SiO2 and used. The element Y may be selected from the group consisting of Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ge, P, As, Sb, Bi, S, Se, Te, Po, and combinations thereof. Examples of the transition metal oxide include lithium-containing titanium composite oxide (LTO), vanadium oxide, lithium vanadium oxide, etc.

[0077] The negative electrode active material may be contained at 80% to 99% by weight based on the total weight of the solid content in the negative electrode slurry.

[0078] The conductive material is a component for further improving the conductivity of the negative electrode active material, and may be added at 1% to 20% by weight based on the total weight of the solid content in the negative electrode active material layer. Such a conductive material is not particularly limited as long as it does not induce a chemical change in the battery and has conductivity. For example, graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black; conductive fibers such as carbon fibers and metal fibers; metal powders such as carbon fluoride, aluminum, nickel powder; conductive whiskers such as zinc oxide, potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives may be used.

[0079] The binder is a component that aids in bonding between the conductive material, active material, and current collector, and is typically added in an amount of 1 to 30 wt % based on the total weight of the solids in the negative electrode active material layer. Examples of such binders include fluororesin-based binders including polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE); rubber-based binders including styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber, and styrene-isoprene rubber; cellulose-based binders including carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, and regenerated cellulose; polyalcohol-based binders including polyvinyl alcohol; polyolefin-based binders including polyethylene and polypropylene; polyimide-based binders; polyester-based binders; and silane-based binders.

[0080] The negative electrode may be manufactured by a method known in the art, for example, by coating a negative electrode active material slurry, prepared by dissolving or dispersing a negative electrode active material, and optionally a binder and a conductive material, in a solvent onto a negative electrode current collector, followed by rolling and drying to form a negative electrode active material layer, or by casting the negative electrode active material layer onto a separate support, peeling off the support, and laminating the resulting film onto the negative electrode current collector.

[0081] The negative electrode current collector generally has a thickness of 3 μm to 500 μm. Such a negative electrode current collector is not particularly limited as long as it does not induce chemical changes in the battery and has high conductivity, and examples of such a negative electrode current collector include copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surfaces treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloys. Similarly to the positive electrode current collector, the surface may be formed with fine irregularities to strengthen the binding force of the negative electrode active material, and the negative electrode current collector may be used in various forms such as a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0082] The solvent may include water or an organic solvent such as NMP or alcohol, and may be used in an amount that provides a preferred viscosity when containing the negative electrode active material, and optionally a binder, a conductive material, etc. For example, the solvent may be included so that the solids concentration in the active material slurry containing the negative electrode active material, and optionally a binder, a conductive material, etc. is 50 wt % to 75 wt %, preferably 50 wt % to 65 wt %.

[0083] (3) Separator The separator included in the lithium secondary battery of the present invention may be a commonly used conventional porous polymer film, for example, a porous polymer film made from a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer, either alone or in a laminate thereof, or a conventional porous nonwoven fabric, for example, a nonwoven fabric made from a high-melting point glass fiber, a polyethylene terephthalate fiber, or the like, but is not limited thereto.

[0084] The external shape of the lithium secondary battery of the present invention is not particularly limited, and may be a cylindrical shape using a can, a square shape, a pouch shape, a coin shape, or the like.

[0085] Hereinafter, the present invention will be described in detail with reference to examples. However, the examples of the present invention may be modified in various different forms, and the scope of the present invention should not be construed as being limited to the examples described below. The examples of the present invention are provided to more completely explain the present invention to those skilled in the art.

[0086] [Example] Example 1 (Production of non-aqueous electrolyte) Ethylene carbonate (EC): Propylene carbonate (PC): ethyl Propionate (EP): PropylLiPF was dissolved in a non-aqueous organic solvent containing propionate (PP) in a volume ratio of 20:10:25:45 to a concentration of 1.0 M, and then the compound represented by Formula 1a was added to the non-aqueous organic solvent in a concentration of 0.5 wt % to prepare a non-aqueous electrolyte for a lithium secondary battery (see Table 1 below).

[0087] (Lithium secondary battery manufacturing) N-methyl-2-pyrrolidone (NMP) is used as the positive electrode active material (LiNi 0.8 Co 0.1 Mn 0.1 A cathode slurry (solid content: 50 wt%) was prepared by adding 02), a conductive material (carbon black), and a binder (polyvinylidene fluoride) in a weight ratio of 97.5:1:1.5. The cathode slurry was applied to a 12 μm-thick aluminum (Al) thin film, which served as a cathode current collector, and dried. The cathode was then fabricated using a roll press.

[0088] Anode active material (artificial graphite), binder (SBR-CMC), and conductive material (carbon black) were mixed in a weight ratio of 95:3.5:1.5 with water as a solvent to prepare anode slurry (solid content: 60 wt%). The anode slurry was applied to a 6 μm-thick copper (Cu) thin film as anode current collector, dried, and then roll-pressed to prepare anode.

[0089] The positive electrode, a polyolefin-based porous separator coated with inorganic particles (Al2O3), and a negative electrode were sequentially stacked to prepare an electrode assembly, which was then placed in a pouch-type battery case, and the non-aqueous electrolyte for lithium secondary batteries was injected into the case to prepare a pouch-type lithium secondary battery with a driving voltage of 4.45 V or more.

[0090] Example 2. A non-aqueous electrolyte for a lithium secondary battery and a pouch-type lithium secondary battery including the same were prepared in the same manner as in Example 1, except that the compound represented by Chemical Formula 1b was added as an additive instead of the compound represented by Chemical Formula 1a to prepare the non-aqueous electrolyte.

[0091] Example 3 (Production of non-aqueous electrolyte) Ethylene carbonate (EC): Propylene carbonate (PC): ethyl Propionate (EP): Propyl LiPF was dissolved in a non-aqueous organic solvent containing 20:10:25:45 volume ratios of propionate (PP) to a concentration of 1.0 M, and then the compound represented by Formula 1a was added to the solution to a concentration of 1.0 wt % to prepare a non-aqueous electrolyte (see Table 1 below).

[0092] (Lithium secondary battery manufacturing) A pouch-type lithium secondary battery was manufactured in the same manner as in Example 1, except that the nonaqueous electrolyte solution for lithium secondary batteries prepared above was used instead of the nonaqueous electrolyte solution for lithium secondary batteries of Example 1.

[0093] Example 4. (Production of non-aqueous electrolyte) Ethylene carbonate (EC): Propylene carbonate (PC): ethyl Propionate (EP): Propyl LiPF was dissolved in a non-aqueous organic solvent containing 20:10:25:45 volume ratios of propionate (PP) to a concentration of 1.0 M, and then the compound represented by Formula 1a was added to the solution to a concentration of 3.0 wt % to prepare a non-aqueous electrolyte (see Table 1 below).

[0094] (Lithium secondary battery manufacturing) A pouch-type lithium secondary battery was manufactured in the same manner as in Example 1, except that the nonaqueous electrolyte solution for lithium secondary batteries prepared above was used instead of the nonaqueous electrolyte solution for lithium secondary batteries of Example 1.

[0095] Example 5. (Production of non-aqueous electrolyte) Ethylene carbonate (EC): Propylene carbonate (PC): ethyl Propionate (EP): PropylLiPF was dissolved in a non-aqueous organic solvent containing 20:10:25:45 volume ratios of propionate (PP) to a concentration of 1.0 M, and then the compound represented by Formula 1a was added to the solution to a concentration of 0.01 wt % to prepare a non-aqueous electrolyte (see Table 1 below).

[0096] (Lithium secondary battery manufacturing) A pouch-type lithium secondary battery was manufactured in the same manner as in Example 1, except that the nonaqueous electrolyte solution for lithium secondary batteries prepared above was used instead of the nonaqueous electrolyte solution for lithium secondary batteries of Example 1.

[0097] Comparative Example 1 Ethylene carbonate (EC): Propylene carbonate (PC): ethyl Propionate (EP): Propyl A pouch-type lithium secondary battery was manufactured in the same manner as in Example 1, except that a non-aqueous electrolyte solution for a lithium secondary battery was prepared by dissolving LiPF to a concentration of 1.0 M in a non-aqueous organic solvent mixed with propionate (PP) at a volume ratio of 20:10:25:45.

[0098] Comparative Example 2 A non-aqueous electrolyte for a lithium secondary battery and a pouch-type lithium secondary battery including the same were manufactured in the same manner as in Example 1, except that the non-aqueous electrolyte was manufactured by adding a compound represented by the following Chemical Formula 2 (3-(trifluoroacetyl)coumarin) instead of the compound represented by Chemical Formula 1a as an additive.

[0099] [ka]

[0100] Comparative Example 3. A non-aqueous electrolyte for a lithium secondary battery and a pouch-type lithium secondary battery including the same were prepared in the same manner as in Example 1, except that the non-aqueous electrolyte was prepared by adding a compound (7-ethynylcoumarin) represented by the following Chemical Formula 3 instead of the compound represented by Chemical Formula 1a as an additive.

[0101] [ka]

[0102] Comparative Example 4. A non-aqueous electrolyte for a lithium secondary battery and a pouch-type lithium secondary battery containing the same were prepared in the same manner as in Example 1, except that the non-aqueous electrolyte was prepared by adding coumarin (Cas No. 91-64-5, manufactured by Aldrich Chemical Co.) as an additive instead of the compound represented by Chemical Formula 1a.

[0103] [Table 1]

[0104] [Experimental Example] Experimental example 1. Initial capacity evaluation The lithium secondary batteries prepared in Examples 1 and 2 and the secondary batteries prepared in Comparative Examples 1 to 4 were each charged at room temperature (23°C) under constant current / constant voltage (CC-CV) conditions at a 0.3C rate to 4.2V and discharged at a 0.3C rate to 2.5V under CC conditions. Next, they were charged at room temperature (23°C) under constant current / constant voltage (CC / CV) conditions of 1C / 4.2V until the current reached 1 / 20 mA of the 1C current, and then discharged again at a 1C current to 2.5V to measure the initial capacity. The results are shown in Table 2 below.

[0105] Experimental example 2: High temperature cycle evaluation The lithium secondary batteries manufactured in Examples 1 and 2, whose initial capacities were measured in Experimental Example 1, and the secondary batteries manufactured in Comparative Examples 1 to 4 were each charged at 45°C under constant current / constant voltage (CC / CV) conditions at a 0.5C rate up to 4.2V until the current reached 1 / 20 (mA) of the 1C current, and then discharged again at a current of 0.5C down to 2.5V. This charge / discharge condition constitutes one cycle, and 200 cycles were repeated. Next, the capacity retention rate was calculated using the following formula 1, and the results are shown in Table 2.

[0106] [Formula 1] Capacity retention rate (%) = (discharge capacity after 200 cycles / initial discharge capacity) x 100

[0107] [Table 2]

[0108] Referring to Table 2, it can be seen that the lithium secondary batteries of Examples 1 and 2 have improved initial capacities and capacity retention rates after 200 cycles of charge / discharge compared to the secondary batteries of Comparative Examples 1 to 4, which have the same additive content.

[0109] Experimental Example 3: High-temperature storage evaluation The lithium secondary batteries prepared in Examples 1 to 4 and Comparative Examples 1 to 4 were each charged to 4.2 V at room temperature (25°C) under constant current / constant voltage conditions at a rate of 0.33 C to measure the initial capacity, and then stored at 60°C for two weeks, after which the capacity retention rate after high-temperature storage for each lithium secondary battery was measured, and the results are shown in Table 3 below.

[0110] [Table 3]

[0111] Referring to Table 3, it can be seen that the capacity retention rate after high-temperature storage of the secondary batteries of Examples 1 to 4 containing the additive of the present invention is significantly improved compared to the secondary batteries of Comparative Examples 1 to 4.

[0112] Experimental Example 4: High-rate discharge evaluation The secondary battery of Example 5 and the secondary battery of Comparative Example 1, whose initial capacity was measured in Experimental Example 1, were each charged at 25°C under constant current / constant voltage (CC / CV) conditions at a current of 1 C to 4.2 V until the current reached 1 / 20 (mA), and then discharged at a rate of 3 C to 2.5 V for three cycles to measure the rate discharge capacity. The capacity retention rate was calculated using the following equation 2, and the results are shown in Table 4 below.

[0113] [Formula 2] Capacity retention rate (%)=(3C discharge capacity / initial discharge capacity)×100 In the above formula 2, the 3C discharge capacity is the discharge capacity value at the third time out of three cycles, The initial discharge capacity is the capacity value measured at 0.3C.

[0114] [Table 4]

[0115] Referring to Table 4, it can be seen that the secondary battery of Example 5 containing a small amount of additive has an improved capacity retention rate compared to the secondary battery of Comparative Example 1 containing no additive.

Claims

1. A non-aqueous electrolyte solution for a lithium secondary battery, comprising a lithium salt, an organic solvent, and a compound represented by the following chemical formula 1 as an additive: 【Chemical 1】 In the above Chemical Formula 1, R １ ~R ６ are each independently hydrogen, an alkyl group having 1 to 5 carbon atoms, or —SiR ７ R ８ R ９ (R ７ ~R ９ are each independently an alkyl group having 1 to 10 carbon atoms), or —O—SiR １０ R １１ R １２ (R １０ ~R １２ are each independently an alkyl group having 1 to 10 carbon atoms; R １ ~R ５ At least one of the groups is —SiR ７ R ８ R ９ (R ７ ~R ９ are each independently an alkyl group having 1 to 10 carbon atoms), or —O—SiR １０ R １１ R １２ (R １０ ~R １２ are each independently an alkyl group having 1 to 10 carbon atoms.

2. In the above formula 1, R １ ~R ６ are each independently hydrogen, —SiR ７ R ８ R ９ (R ７ ~R ９ are each independently an alkyl group having 1 to 7 carbon atoms), or —O—SiR １０ R １１ R １２ (R １０ ~R １２ are each independently an alkyl group having 1 to 7 carbon atoms, and R １ or R ５ At least one of the groups is —SiR ７ R ８ R ９ (R ７ ~R ９ are each independently an alkyl group having 1 to 7 carbon atoms), or —O—SiR １０ R １１ R １２ (R １０ ~R １２ are each independently an alkyl group having 1 to 7 carbon atoms, and R ２ ~R ４ and R ６ and each independently represent hydrogen or an alkyl group having 1 to 7 carbon atoms.

3. In the above formula 1, R １ ~R ６ are each independently hydrogen, —SiR ７ R ８ R ９ (R ７ ~R ９ are each independently an alkyl group having 1 to 5 carbon atoms), or —O—SiR １０ R １１ R １２ (R １０ ~R １２ are each independently an alkyl group having 1 to 5 carbon atoms, and R １ or R ５ At least one of the groups is —SiR ７ R ８ R ９ (R ７ ~R ９ are each independently an alkyl group having 1 to 5 carbon atoms), or —O—SiR １０ R １１ R １２ (R １０ ~R １２ are each independently an alkyl group having 1 to 5 carbon atoms, and R ２ ~R ４ and R ６ and each independently represent hydrogen or an alkyl group having 1 to 5 carbon atoms.

4. 2. The nonaqueous electrolyte solution for a lithium secondary battery according to claim 1, wherein the compound represented by Chemical Formula 1 includes at least one selected from the group consisting of compounds represented by Chemical Formulas 1a and 1b: 【Chemistry 2】 【Chemistry 3】

5. 2. The non-aqueous electrolyte solution for a lithium secondary battery according to claim 1, wherein the compound represented by Formula 1 is contained in an amount of 0.01 wt % to 5.0 wt % based on the total weight of the non-aqueous electrolyte solution.

6. 6. The non-aqueous electrolyte solution for a lithium secondary battery according to claim 5, wherein the compound represented by Formula 1 is contained in an amount of 0.01 wt % to 3.0 wt % based on the total weight of the non-aqueous electrolyte solution.

7. 2. The nonaqueous electrolyte solution for a lithium secondary battery according to claim 1, wherein the organic solvent includes at least one selected from the group consisting of a cyclic carbonate organic solvent, a linear carbonate organic solvent, and a linear ester organic solvent.

8. 2. The nonaqueous electrolyte solution for a lithium secondary battery according to claim 1, further comprising at least one other additive selected from the group consisting of cyclic carbonate-based compounds, halogen-substituted carbonate-based compounds, sultone-based compounds, sulfate-based compounds, sulfite-based compounds, phosphate-based compounds, phosphite-based compounds, borate-based compounds, benzene-based compounds, amine-based compounds, silane-based compounds, and lithium salt-based compounds.

9. a negative electrode, a positive electrode, a separator interposed between the negative electrode and the positive electrode, and a non-aqueous electrolyte; A lithium secondary battery, wherein the nonaqueous electrolyte solution comprises the nonaqueous electrolyte solution for lithium secondary batteries according to claim 1 .

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