Non-aqueous electrolyte for lithium secondary battery, and lithium secondary battery comprising the same

Abstract

To provide a non-aqueous electrolyte capable of suppressing the decomposition reaction of an electrolyte and forming a reinforced film on the electrode, and a lithium secondary battery comprising the same.SOLUTION: A non-aqueous electrolyte for a lithium secondary battery comprises: a lithium salt; an organic solvent; and a compound represented by Chemical Formula 1. The invention also relates to a lithium secondary battery comprising the same. In Chemical Formula 1: R1 is an alkyl group having 1 to 10 carbon atoms; R2 is an alkylene group having 1 to 10 carbon atoms; L is a direct bond, -O-, -COO-, -RO-, or -R'COO-; R and R' are each independently an alkylene group having 1 to 10 carbon atoms; and m is an integer from 0 to 5.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2021-0131937 filed on October 5, 2021, and Korean Patent Application No. 10-2022-0115214 filed on September 13, 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] Lithium secondary batteries are generally manufactured by forming an electrode assembly by interposing a separator between a positive electrode including a positive electrode active material made of a lithium-containing transition metal oxide and a negative electrode including a negative electrode active material capable of storing lithium ions, inserting the electrode assembly into a battery case, injecting a non-aqueous electrolyte solution that serves as a medium for transferring lithium ions, and then sealing the battery case.

[0004] Lithium secondary batteries can be miniaturized and have high energy density and operating voltage, and therefore are used in a variety of fields such as mobile devices, electronic products, electric vehicles, etc. As the fields in which lithium secondary batteries are used become more diverse, the required physical properties are also becoming more stringent. In particular, there is a demand for the development of lithium secondary batteries that can be stably operated even under high voltage and high temperature conditions and have long life characteristics.

[0005] On the other hand, when a lithium secondary battery is operated under high voltage and / or high temperature conditions, lithium salts such as LiPF6 contained in the electrolyte are converted into PF6 -Thermal decomposition of anions can generate Lewis acids such as PF5, which react with water to generate HF. These decomposition products, such as PF5 and HF, can destroy the coating on the electrode surface and potentially cause decomposition reactions of the organic solvent. Furthermore, the electrolyte decomposition products can react with the decomposition products of the positive electrode active material to leach transition metal ions, which can then be electrodeposited on the negative electrode, potentially destroying the coating on the negative electrode.

[0006] If the electrolyte decomposition reaction continues on the destroyed coating in this way, the battery performance will further deteriorate, so there is a need to develop a secondary battery that can maintain excellent performance even under high voltage and high temperature conditions. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Korean Patent Publication No. 10-2003-0061219 Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention has been made to solve the above problems, and an object of the present invention is to provide a non-aqueous electrolyte solution that contains a compound having a structure in which a propargyl group is bonded to coumarin, thereby suppressing the decomposition reaction of the electrolyte and forming a reinforced coating on the electrode, and a lithium secondary battery containing the same. [Means for solving the problem]

[0009] According to one embodiment, the present invention provides a non-aqueous electrolyte for a lithium secondary battery, comprising a lithium salt, an organic solvent, and a compound represented by the following Chemical Formula 1:

[0010] [ka]

[0011] In the above Chemical Formula 1, R1 is an alkyl group having 1 to 10 carbon atoms, R2 is an alkylene group having 1 to 10 carbon atoms, L is a direct bond, -O-, -COO-, -RO-, or -R'COO-; R and R' each independently represent an alkylene group having 1 to 10 carbon atoms, m is an integer of 0 to 5.

[0012] According to another embodiment, the present invention provides a lithium secondary battery including: a positive electrode including a positive electrode active material; a negative electrode including a negative electrode active material; a separator interposed between the positive electrode and the negative electrode; and a non-aqueous electrolyte solution for the lithium secondary battery. [Effects of the Invention]

[0013] The nonaqueous electrolyte solution of the present invention contains a compound with a coumarin structure that effectively suppresses decomposition of the positive electrode by reacting with active oxygen at the positive electrode and a propargyl group that is advantageous for forming a coating on the surface of the negative electrode. This not only enables the formation of a durable coating on the electrode, but also suppresses the decomposition reaction of the electrolyte and reduces the gas generation rate of batteries containing high-nickel positive electrode active materials. This also makes it possible to provide a lithium secondary battery with fundamentally improved electrochemical characteristics. DETAILED DESCRIPTION OF THE INVENTION

[0014] The present invention will now be described in more detail.

[0015] Generally, anions contained in lithium salts such as LiPF6, which are widely used in electrolytes for lithium secondary batteries, form decomposition products such as hydrogen fluoride (HF) and PF5 due to thermal decomposition or moisture. These decomposition products have acidic properties and deteriorate the coating or electrode surface in the battery.

[0016] Due to decomposition products of the electrolyte and structural changes in the positive electrode caused by repeated charging and discharging, transition metals in the positive electrode are easily eluted into the electrolyte, and the eluted transition metals are further redeposited on the positive electrode, increasing the resistance of the positive electrode. Furthermore, if the eluted transition metals migrate to the negative electrode via the electrolyte, they are electrodeposited on the negative electrode, causing destruction of the solid electrolyte interphase (SEI) film and further electrolyte decomposition reactions, resulting in problems such as increased lithium ion consumption and resistance.

[0017] Furthermore, during initial activation of the battery, a protective coating is formed on the positive and negative electrodes due to the electrolyte reaction. If the coating becomes unstable for the reasons described above, further decomposition of the electrolyte occurs during charging and discharging or exposure to high temperatures, accelerating battery degradation and generating gas.

[0018] In particular, batteries containing a positive electrode active material with a high nickel content have improved initial capacity characteristics, but when repeatedly charged and discharged, side reactions can increase the amount of lithium by-products and gas generated, which can lead to severe decomposition reactions of the electrolyte.

[0019] To solve this problem, the present inventors discovered that adding a compound represented by the following chemical formula 1, which has a structure in which a propargyl group is bonded to coumarin, to a non-aqueous electrolyte can reduce the decomposition reaction of the electrolyte and suppress the elution of transition metals and the generation of gas. In particular, they confirmed that the inclusion of the non-aqueous electrolyte according to the present invention not only improves the initial capacity of a battery containing a high-nickel (High-Ni) positive electrode active material, but also its durability during high-temperature storage and cycling.

[0020] Each of the components constituting the present invention will be described in more detail below.

[0021] non-aqueous electrolyte The present invention provides a non-aqueous electrolyte solution for a lithium secondary battery, comprising a lithium salt, an organic solvent, and a compound represented by Chemical Formula 1.

[0022] Each component will be specifically described below.

[0023] (1) Compound represented by chemical formula 1 The non-aqueous electrolyte of the present invention contains a compound represented by the following chemical formula 1.

[0024] [ka]

[0025] In the above Chemical Formula 1, R1 is an alkyl group having 1 to 10 carbon atoms, R2 is an alkylene group having 1 to 10 carbon atoms, L is a direct bond, -O-, -COO-, -RO-, or -R'COO-; R and R' each independently represent an alkylene group having 1 to 10 carbon atoms, m is an integer of 0 to 5.

[0026] During continuous charging and discharging of a lithium secondary battery, active oxygen such as singlet oxygen and superoxide is generated at the positive electrode, which can cause a decrease in battery performance. Coumarin, contained in the compound represented by Chemical Formula 1, has a higher reactivity to active oxygen than electrolyte solvents such as ethylene carbonate. Therefore, it reacts with active oxygen before the electrolyte solvent does, thereby suppressing the decomposition of the electrolyte caused by active oxygen. Furthermore, the compound represented by Chemical Formula 1 contains a propargyl functional group, which is easily reduced, and thus can form a durable passive film on the surface of the negative electrode while undergoing reductive decomposition. In other words, because it can form a stable film at the interface between the positive and negative electrodes and the electrolyte, it can suppress side reactions and ensure stability even when using a high-nickel positive electrode active material, effectively improving not only the initial performance of lithium secondary batteries but also their high-temperature durability and long-term life.

[0027] In one embodiment of the present invention, the compound represented by Chemical Formula 1 may include at least one selected from the group consisting of compounds represented by Chemical Formula 1-1 below and compounds represented by Chemical Formula 2-1 below.

[0028] [ka]

[0029] [ka]

[0030] In the chemical formula 1-1 and the chemical formula 2-1, R1, R2, L, and m are as defined in Chemical Formula 1 above.

[0031] Preferably, the compound represented by Chemical Formula 1 may include a compound represented by Chemical Formula 1-1. When a propargyl group is substituted at the 3-position as in Chemical Formula 1-1, it is preferred because it has the effect of stabilizing radicals at the 3- and 4-positions and increasing reactivity.

[0032] In one embodiment of the present invention, L in Chemical Formula 1 may be -O- or -COO-.

[0033] In one embodiment of the present invention, the compound represented by Chemical Formula 1 may include at least one selected from the group consisting of compounds represented by the following Chemical Formula 1-2, compounds represented by the following Chemical Formula 1-3, compounds represented by the following Chemical Formula 2-2, and compounds represented by the following Chemical Formula 2-3. Preferably, the compound represented by Chemical Formula 1 may include at least one selected from the group consisting of compounds represented by the following Chemical Formula 1-2 and compounds represented by the following Chemical Formula 1-3.

[0034] [ka]

[0035] [ka]

[0036] [ka]

[0037] [ka]

[0038] In the chemical formula 1-2, the chemical formula 1-3, the chemical formula 2-2, and the chemical formula 2-3, R1, R2, and m are as defined in Chemical Formula 1. In one embodiment of the present invention, m in Chemical Formula 1 may be 0, and R2 may be an alkylene group having 1 to 5 carbon atoms, preferably an alkylene group having 1 to 3 carbon atoms, and more preferably a methylene group.

[0039] In one embodiment of the present invention, the compound represented by Chemical Formula 1 may include at least one selected from the group consisting of a compound represented by Chemical Formula 1A below, a compound represented by Chemical Formula 1B below, a compound represented by Chemical Formula 2A below, and a compound represented by Chemical Formula 2B below. Preferably, the compound represented by Chemical Formula 1 may include at least one selected from the group consisting of a compound represented by Chemical Formula 1A below and a compound represented by Chemical Formula 1B below.

[0040] [ka]

[0041] [ka]

[0042] [ka]

[0043] [ka]

[0044] In one embodiment of the present invention, the content of the compound represented by Chemical Formula 1 may be 0.1 wt % to 5 wt %, preferably 0.1 wt % to 1 wt %, and more preferably 0.2 wt % to 0.8 wt %, based on the total weight of the non-aqueous electrolyte solution.

[0045] When the content of the compound represented by Chemical Formula 1 is 0.1 wt % or more, it is preferable because the effect of suppressing decomposition of metal ions in the positive electrode, which is the object of the present invention, can be obtained. When the content is 5 wt % or less, it is preferable because it can prevent a decrease in battery performance due to an increase in resistance.

[0046] (2) Additives The nonaqueous electrolyte of the present invention may optionally further contain the following additives, as needed, to prevent the electrolyte from being decomposed in a high-voltage environment, which may cause electrode collapse, or to further improve low-temperature high-rate discharge characteristics, high-temperature stability, overcharge prevention, and the effects of suppressing battery expansion at high temperatures.

[0047] The additive may be at least one selected from cyclic carbonate compounds, halogen-substituted carbonate compounds, sultone compounds, sulfate compounds, phosphate or phosphite compounds, borate compounds, nitrile compounds, amine compounds, silane compounds, benzene compounds, and lithium salt compounds.

[0048] The cyclic carbonate compound may be at least one selected from vinylene carbonate (VC) and vinyl ethylene carbonate (VEC), and specifically may be vinylene carbonate.

[0049] The halogen-substituted carbonate compound may be fluoroethylene carbonate (FEC).

[0050] The sultone-based compound is a material capable of forming a stable SEI film on the surface of the negative electrode through a reduction reaction, and may be one or more compounds selected from 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, and specifically may be 1,3-propane sultone (PS).

[0051] The sulfate-based compound is a material that can be electrically decomposed on the surface of the negative electrode to form a stable SEI film that does not crack even when stored at high temperatures, and may be at least one selected from ethylene sulfate (Esa), trimethylene sulfate (TMS), and methyl trimethylene sulfate (MTMS).

[0052] The phosphate-based or phosphite-based compound may be one or more selected from lithium difluoro(bisoxalato)phosphate, lithium difluorophosphate, tris(trimethylsilyl)phosphate, tris(trimethylsilyl)phosphite, tris(2,2,2-trifluoroethyl)phosphate, and tris(trifluoroethyl)phosphite.

[0053] The borate-based compound may be lithium tetraphenylborate.

[0054] The nitrile compound may be one or more selected from succinonitrile (SN), adiponitrile (ADN), acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentanecarbonitrile, cyclohexanecarbonitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, 4-fluorophenylacetonitrile, ethylene glycol bis(2-cyanoethyl)ether (ASA3), 1,3,6-hexanetricarbonitrile (HTCN), 1,4-dicyano-2-butene (DCB), and 1,2,3-tris(2-cyanoethyl)propane (TCEP).

[0055] The amine compound may be at least one selected from triethanolamine and ethylenediamine, and the silane compound may be tetravinylsilane.

[0056] The benzene-based compound may be one or more selected from monofluorobenzene, difluorobenzene, trifluorobenzene, and tetrafluorobenzene.

[0057] The lithium salt-based compound is a compound different from the lithium salt contained in the non-aqueous electrolyte solution, and may be one or more compounds selected from lithium difluorophosphate (LiDFP; LiPO2F2), lithium bis(oxalato)borate (LiBOB; LiB(C2O4)2), lithium tetrafluoroborate (LiBF4), and lithium difluoro(bis(oxalato)phosphate) (LiDFOP).

[0058] Preferably, the non-aqueous electrolyte according to one embodiment of the present invention may further contain one or more additives selected from vinylene carbonate (VC), vinyl ethylene carbonate (VEC), fluoroethylene carbonate (FEC), 1,3-propane sultone (PS), 1,3-propene sultone (PRS), ethylene sulfate (ESa), succinonitrile (SN), adiponitrile (ADN), ethylene glycol bis(2-cyanoethyl)ether (ASA3), 1,3,6-hexanetricarbonitrile (HTCN), 1,4-dicyano-2-butene (DCB), 1,2,3-tris(2-cyanoethyl)propane (TCEP), lithium difluorooxalatoborate (LiODFB), lithium tetrafluoroborate (LiBF4), lithium difluoro(bisoxalato)phosphate (LiDFOP), and lithium difluorophosphate (LiDFP).

[0059] More preferably, the nonaqueous electrolyte according to an embodiment of the present invention may further contain one or more additives selected from vinylene carbonate (VC), vinyl ethylene carbonate (VEC), 1,3-propane sultone (PS), ethylene sulfate (ESa), lithium difluorooxalatoborate (LiODFB), and lithium difluorophosphate (LiDFP).

[0060] The content of the additive may be 0.1 wt % to 10 wt %, preferably 0.3 wt % to 5 wt %, based on the total weight of the non-aqueous electrolyte solution. When the content of the additive is within the above range, the side reaction suppression effect due to the formation of a coating on the positive electrode and the negative electrode can be obtained.

[0061] (3) Organic Solvent The non-aqueous electrolyte of the present invention contains an organic solvent.

[0062] The organic solvent may be any of various organic solvents commonly used in lithium electrolytes without limitation. For example, the organic solvent may be a cyclic carbonate solvent, a linear carbonate solvent, a linear ester solvent, a cyclic ester solvent, a nitrile solvent, or a mixture thereof, and preferably a mixture of a cyclic carbonate solvent and a linear carbonate solvent.

[0063] The cyclic carbonate solvent is a highly viscous organic solvent that has a high dielectric constant and can effectively dissociate the lithium salt in the electrolyte. The cyclic carbonate solvent may be one or more solvents 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 preferably contains ethylene carbonate (EC) or propylene carbonate (PC).

[0064] The linear carbonate solvent is an organic solvent having low viscosity and low dielectric constant, and may be one or more 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 may preferably contain ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), or diethyl carbonate (DEC).

[0065] The organic solvent is preferably a mixture of a cyclic carbonate solvent and a linear carbonate solvent in order to produce an electrolyte solution having high ionic conductivity.

[0066] The linear ester solvent may be one or more selected from methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, and butyl propionate, and preferably methyl propionate, ethyl propionate, or propyl propionate.

[0067] The cyclic ester solvent may be one or more selected from γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, and ε-caprolactone.

[0068] The nitrile solvent may be one or more selected from succinonitrile, acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentanecarbonitrile, cyclohexanecarbonitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile, and preferably succinonitrile.

[0069] In the total weight of the nonaqueous electrolyte solution, the remainder excluding other components other than the organic solvent, for example, the compound represented by Chemical Formula 1, the additive, and the lithium salt, is the organic solvent unless otherwise specified.

[0070] (4) Lithium salt The non-aqueous electrolyte of the present invention contains a lithium salt.

[0071] The lithium salt may be any one that is commonly used in electrolytes for lithium secondary batteries, and may be any one of those containing Li as a cation. + and as an anion, 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 - , BF2C2O4CHF - , PF4C2O4 - , PF2C4O8 - , PO2F2 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , C4F9SO3 - , CF3CF2SO3 - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , CF3(CF2)7SO3 - , and SCN - It may include any one or more selected from the following.

[0072] Specifically, the lithium salts include LiPF6, LiClO4, LiBF4, LiN(FSO2)2 (LiFSI), LiN(SO2CF3)2 (LiTFSI), lithium bis(pentafluoroethanesulfonyl)imide (LiBETI), LiSO3CF3, LiPO2F2, lithium bis(oxalate)borate (LiBOB), lithium difluoro(oxalate)borate (LiFOB), lithium difluoro(bisoxalato)phosphate (LiDFOP), lithium tetrafluoro(oxalate)phosphate (LiTFOP), and lithium fluoromalonato(difluoro)borate (Li The compound may be one or more selected from the group consisting of fluoromalonato(difluoro)borate, LiFMDFB, and LiPF6, and is preferably LiPF6.

[0073] In one embodiment of the present invention, the concentration of the lithium salt in the non-aqueous organic solution containing the lithium salt and the organic solvent may be 0.5 to 4.0 M, specifically 0.5 to 3.0 M, more specifically 0.8 to 2.0 M. When the concentration of the lithium salt is within the above range, the effects of improving low-temperature output and cycle characteristics are sufficiently ensured, and excessive increases in viscosity and surface tension are prevented, resulting in appropriate electrolyte impregnation.

[0074] Lithium secondary battery Next, the lithium secondary battery according to the present invention will be described.

[0075] The lithium secondary battery according to the present invention includes a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, a separator interposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte. At this time, the non-aqueous electrolyte is the non-aqueous electrolyte according to the present invention described above. Since the non-aqueous electrolyte is as described above, the description thereof is omitted, and other components will be described below.

[0076] (1) Positive electrode The positive electrode according to the present invention contains a positive electrode active material, and can be manufactured by coating a positive electrode slurry containing a positive electrode active material, a binder, a conductive material, a solvent, etc. on a positive electrode current collector, and then drying and rolling.

[0077] The positive electrode current collector is not particularly limited as long as it does not cause a chemical change in the battery and has conductivity. For example, stainless steel; aluminum; nickel; titanium; fired carbon; or those obtained by surface treatment of the surface of aluminum or stainless steel with carbon, nickel, titanium, silver, etc. may be used.

[0078] 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 one or more metals such as cobalt, manganese, nickel, or aluminum and lithium.

[0079] More specifically, the positive electrode active material is a lithium-cobalt-based oxide (e.g., LiCoO2, etc.), a lithium-manganese-based oxide (e.g., LiMnO2, LiMn2O4, 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-z Ni z O4 (where 0 < Z < 2), etc.), a lithium-nickel-cobalt-based oxide (e.g., LiNi 1-Y1 Co Y1O2 (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) and 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, respectively, 0 < p2 < 1, 0 < q2 < 1, 0 < r3 < 1, 0 < s2 < 1, p2 + q2 + r3 + s2 = 1)) may include one or more of them. Among them, from the point of being able to enhance the capacity characteristics and stability of the battery, the positive electrode active material may include at least one selected from the group consisting of lithium-cobalt oxide, lithium-manganese-based oxide, lithium-nickel-manganese-cobalt-based oxide, and lithium-nickel-cobalt-transition metal (M) oxide, and preferably includes at least one selected from lithium-nickel-manganese-cobalt-based 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.

[0080] As a representative 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 )O 2、 and Li(Ni 0.86 Co 0.05 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.

[0081] Furthermore, the positive electrode active material according to one embodiment of the present invention may contain a lithium composite transition metal oxide represented by the following chemical formula 3.

[0082] [Chemical formula 3] Li 1+x (Ni a Co b Mn c M d )O2

[0083] In the above Chemical Formula 3, M is one or more selected from W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo; 1+x, a, b, c, and d are the atomic fractions of each independent element, specifically the atomic fractions of Li, Ni, Co, Mn, and M, respectively; 0≦x≦0.2, 0.50≦a<1, 0 <b≦0.25、0<c≦0.25、0≦d≦0.1、a+b+c+d=1である。

[0084] Preferably, a, b, c, and d may be in the ranges 0.70≦a≦0.95, 0.025≦b≦0.20, 0.025≦c≦0.20, and 0≦d≦0.05, respectively.

[0085] Furthermore, the a, b, c, and d may be 0.80≦a≦0.95, 0.025≦b≦0.15, 0.025≦c≦0.15, and 0≦d≦0.05, respectively.

[0086] Furthermore, the a, b, c, and d may be 0.85≦a≦0.90, 0.05≦b≦0.10, 0.05≦c≦0.10, and 0≦d≦0.03, respectively.

[0087] 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. 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.

[0088] The binder is a component that aids in binding the active material and conductive material, etc., and in binding to the current collector, and may typically be added in an amount of 1 wt % to 30 wt % based on the total weight of the solids in the positive electrode slurry. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene-butadiene rubber, fluororubber, and various copolymers thereof.

[0089] The conductive material is a substance that imparts conductivity to the battery without causing any chemical change to the battery, and may be added in an amount of 0.5% by weight to 20% by weight based on the total weight of the solid content in the positive electrode slurry.

[0090] Examples of the conductive material may be selected from carbon blacks such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; graphite powders such as natural graphite, artificial graphite, carbon nanotubes, and graphite; conductive fibers such as carbon fibers and metal fibers; conductive 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; and conductive materials such as polyphenylene derivatives.

[0091] The solvent for the positive electrode slurry may include an organic solvent such as NMP (N-methyl-2-pyrrolidone), and may be used in an amount that provides a suitable viscosity when the positive electrode active material, binder, conductive material, etc. are contained. For example, the positive electrode slurry containing the positive electrode active material, binder, and conductive material may be contained so that the solids concentration in the positive electrode slurry is 40 wt % to 90 wt %, preferably 50 wt % to 80 wt %.

[0092] (2) Negative electrode The negative electrode according to the present invention includes a negative electrode active material and can be manufactured by coating a negative electrode slurry containing the negative electrode active material, a binder, a conductive material, a solvent, etc., on a negative electrode current collector, followed by drying and rolling.

[0093] The negative electrode current collector generally has a thickness of 3 μm to 500 μm. There are no particular limitations on the negative electrode current collector, so long as it does not cause chemical changes in the battery and has high conductivity. For example, copper; stainless steel; aluminum; nickel; titanium; calcined carbon; copper or stainless steel whose surface has been treated with carbon, nickel, titanium, silver, or the like; or an aluminum-cadmium alloy may be used. Furthermore, as with the positive electrode current collector, the bonding strength of the negative electrode active material may be strengthened by forming fine irregularities on the surface, and the negative electrode current collector may be used in various forms, such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0094] Further, the negative electrode active material may contain one or more selected from a carbon material capable of reversibly intercalating / deintercalating lithium ions; a metal or an alloy of these metals and lithium; a metal composite oxide; a substance capable of doping and undoping lithium; lithium metal; and a transition metal oxide.

[0095] The carbon material capable of reversibly intercalating / deintercalating lithium ions may be used without particular limitation as long as it is a carbon-based negative electrode active material generally used in lithium-ion secondary batteries. Representative examples thereof include crystalline carbon, amorphous carbon, or both of them may be used. Examples of the crystalline carbon include graphite such as amorphous, plate-like, flaky, spherical, or fibrous natural graphite or artificial graphite, and examples of the amorphous carbon include soft carbon (low-temperature fired carbon), hard carbon, mesophase pitch carbide, fired coke, and the like.

[0096] 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 can be used.

[0097] 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, elements of Group 1, Group 2, Group 3 of the periodic table, halogen; 0 < x ≦ 1; 1 ≦ y ≦ 3; 1 ≦ z ≦ 8), and one or more selected from the group can be used.

[0098] Examples of the substance capable of doping and undoping lithium include Si, SiO x (0 < x < 2), Si-Y alloy (where Y is an element selected from the group consisting of an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element, a transition metal, a rare earth element, and combinations thereof, and is not Si), Sn, SnO2, Sn-Y (where Y is an element selected from the group consisting of an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element, a transition metal, a rare earth element, and combinations thereof, and is not Sn), etc. Also, 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 (dubnium), Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ge, P, As, Sb, Bi, S, Se, Te, Po, and combinations thereof.

[0099] Examples of the transition metal oxide include lithium-containing titanium composite oxide (LTO), vanadium oxide, lithium vanadium oxide, etc.

[0100] 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.

[0101] The binder is a component that aids in bonding between the conductive material, active material, and current collector, and may be added in an amount of 1 to 30 wt % based on the total weight of the solids in the negative electrode slurry. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene-butadiene rubber, fluororubber, and various copolymers thereof.

[0102] The conductive material is a component for further improving the conductivity of the negative electrode active material and may be added in an amount of 0.5 wt % to 20 wt % based on the total weight of the solid content in the negative electrode slurry. The conductive material is not particularly limited as long as it does not cause chemical changes in the battery and has conductivity, and examples thereof include carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, or thermal black; graphite powder such as natural graphite, artificial graphite, carbon nanotubes, or graphite, which have a highly developed crystalline structure; conductive fibers such as carbon fibers or metal fibers; conductive powders such as carbon fluoride powder, aluminum powder, or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; or conductive materials such as polyphenylene derivatives.

[0103] The solvent for the negative electrode slurry may include water or an organic solvent such as NMP or alcohol, and may be used in an amount that provides a suitable viscosity when containing the negative electrode active material, binder, conductive material, etc. For example, the solvent may be included so that the solids concentration in the slurry containing the negative electrode active material, binder, and conductive material is 30 wt % to 80 wt %, preferably 40 wt % to 70 wt %.

[0104] (3) Separator The lithium secondary battery according to the present invention includes a separator between the positive electrode and the negative electrode.

[0105] The separator separates the negative electrode and the positive electrode and provides a path for lithium ions to move. Any separator that is commonly used as a separator in a lithium secondary battery can be used without any particular limitation. In particular, a separator that has low resistance to the movement of ions in the electrolyte, excellent electrolyte impregnation ability, and safety is preferred.

[0106] Specifically, the separator may be a porous polymer film, such as a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer; or a laminate structure of two or more layers thereof. Conventional porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, may also be used. To ensure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymeric substance may also be used, and may be used in a single-layer or multi-layer structure.

[0107] The lithium secondary battery according to the present invention can be usefully used in portable devices such as mobile phones, notebook computers, and digital cameras; and electric vehicles such as hybrid electric vehicles (HEVs).

[0108] Therefore, according to another embodiment of the present invention, there is provided a battery module including the lithium secondary battery as a unit cell, and a battery pack including the same.

[0109] The battery module or battery pack can be used as a power source for one or more medium- to large-sized devices, such as power tools; electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); and power storage systems.

[0110] 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.

[0111] The lithium secondary battery according to the present invention can be used not only as a battery cell used as a power source for small devices, but also as a unit battery in a medium- to large-sized battery module containing a large number of battery cells.

[0112] The present invention will be specifically described below with reference to specific examples.

[0113] <Example> Example 1 (Production of non-aqueous electrolyte) Ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed in a volume ratio of 30:70, and LiPF6 was dissolved in the mixture to a concentration of 1.0 M to prepare a non-aqueous organic solution. 0.5 wt% of the compound represented by Chemical Formula 1A (Cas No. 119827-21-3), 0.5 wt% of vinylene carbonate (VC), 0.5 wt% of 1,3-propane sultone (PS), and the remainder of the non-aqueous organic solution were mixed to prepare a 100 wt% non-aqueous electrolyte.

[0114] (Lithium secondary battery manufacturing) Cathode active material (LiNi 0.85 Co 0.05 Mn 0.07 Al 0.03A cathode mixture slurry (solid content 76.5 wt%) was prepared by adding O2, a conductive material (carbon nanotubes), and a binder (polyvinylidene fluoride) to a solvent, N-methyl-2-pyrrolidone (NMP), in a weight ratio of 98.0:0.7:1.3. The cathode mixture slurry was applied to one side of a 12 μm-thick cathode current collector (Al thin film), dried, and roll-pressed to prepare a cathode.

[0115] Anode active material (artificial graphite), conductive material (carbon black), and binder (styrene-butadiene rubber) were mixed in a weight ratio of 96.5:1.5:2.0 with distilled water as a solvent to prepare anode mixture slurry (solid content 50 wt%). The anode mixture slurry was applied to one side of an 8 μm-thick anode current collector (Cu thin film), dried, and roll-pressed to prepare anode.

[0116] A polyethylene porous film separator was interposed between the positive electrode and negative electrode prepared above in a dry room, and the non-aqueous electrolyte prepared above was then injected to prepare a secondary battery.

[0117] Example 2. A lithium secondary battery was manufactured in the same manner as in Example 1, except that the compound represented by Chemical Formula 1B (Cas No. 71387-23-0) was used instead of the compound represented by Chemical Formula 1A when preparing the non-aqueous electrolyte.

[0118] Example 3 A lithium secondary battery was produced in the same manner as in Example 1, except that VC and PS were not added during the production of the non-aqueous electrolyte solution.

[0119] Example 4. When manufacturing the positive electrode, LiNi is used as the positive electrode active material. 0.85 Co 0.05 Mn 0.07 Al 0.03 A lithium secondary battery was produced in the same manner as in Example 1, except that LiCoO2 was used instead of O2.

[0120] Example 5 A non-aqueous electrolyte and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the compound represented by Chemical Formula 2A was used instead of the compound represented by Chemical Formula 1A (Cas No. 119827-21-3) when manufacturing the non-aqueous electrolyte.

[0121] Example 6 A nonaqueous electrolyte and a lithium secondary battery were manufactured in the same manner as in Example 2, except that the compound represented by Chemical Formula 2B was used instead of the compound represented by Chemical Formula 1B (Cas No. 71387-23-0) when manufacturing the nonaqueous electrolyte.

[0122] Comparative Example 1 A lithium secondary battery was manufactured in the same manner as in Example 1, except that the compound represented by Chemical Formula 1A was not added during the preparation of the non-aqueous electrolyte solution.

[0123] Comparative Example 2 A lithium secondary battery was manufactured in the same manner as in Example 1, except that coumarin was used instead of the compound represented by Chemical Formula 1A when preparing the non-aqueous electrolyte.

[0124] Comparative Example 3. A lithium secondary battery was produced in the same manner as in Comparative Example 2, except that VC and PS were not added during the production of the non-aqueous electrolyte solution.

[0125] Comparative Example 4. When manufacturing the positive electrode, LiNi is used as the positive electrode active material. 0.85 Co 0.05 Mn 0.07 Al 0.03 A lithium secondary battery was manufactured in the same manner as in Comparative Example 1, except that LiCoO2 was used instead of O2.

[0126] Experimental example 1: High temperature life evaluation Each of the lithium secondary batteries manufactured in the Examples and Comparative Examples was subjected to an activation process at 25°C and a 0.2C rate, and then gas was removed from the battery by a degassing process. The degassed lithium secondary batteries were subjected to constant current / constant voltage (CC / CV) charging at 0.33C rate to 4.2V and 0.05C cutoff charging at 45°C, and constant current (CC) discharging at 0.33C rate to 2.5V.

[0127] Each of the above charge / discharge cycles was counted as one cycle, and the discharge capacity in the initial state (one cycle) was measured and the result is shown as the initial capacity in Table 1. After repeating the same charge / discharge cycle 200 times, the discharge capacity was measured and the retention rate relative to the initial capacity was calculated and shown as the capacity retention rate in Table 1.

[0128] Experimental example 2: High temperature storage evaluation Each of the lithium secondary batteries prepared in the Examples and Comparative Examples was subjected to an activation process at 25°C and a 0.2C rate, and then gas inside the battery was removed by a degassing process. Then, the batteries were charged at room temperature (25°C) at a 0.33C rate up to 4.2V under constant current / constant voltage conditions, followed by a 0.05C cutoff charge, and then discharged to 2.5V at 0.33C. The discharge capacity measured at this time is listed as the initial capacity in Table 1 below.

[0129] The lithium secondary battery was then stored at 60°C for 4 weeks, and then transferred to a charger / discharger at room temperature (25°C). It was then charged at a 0.33C rate under constant current / constant voltage conditions up to 4.2V, and then subjected to a 0.05C cut-off charge, followed by discharge at 0.33C to 2.5V. The measured discharge capacity and retention rate relative to the initial capacity are shown in Table 1 below.

[0130] [Table 1]

[0131] From the results in Table 1, it can be seen that the batteries of Examples 1, 2, 5, and 6, which were manufactured using an electrolyte containing the compound represented by Chemical Formula 1 of the present invention, were superior in both high-temperature life characteristics and high-temperature storage characteristics compared to the battery of Comparative Example 1, which was manufactured using an electrolyte not containing the compound represented by Chemical Formula 1, and the battery of Comparative Example 2, which was manufactured using an electrolyte containing coumarin instead of the compound represented by Chemical Formula 1.

[0132] Comparing the battery of Example 3, which was manufactured using an electrolyte solution containing neither VC nor PS, with the battery of Comparative Example 3, it can be seen that the battery of Example 3 containing the compound represented by Chemical Formula 1 has better high-temperature life characteristics and high-temperature storage characteristics.

[0133] Furthermore, even when the positive electrode material was changed to LCO, by comparing the results of Example 4 and Comparative Example 4, it was confirmed that the high-temperature life characteristics and high-temperature storage characteristics could be improved by adding the compound represented by Chemical Formula 1 to the electrolyte.

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: 【Chemical 1】 (In the above Chemical Formula 1, R1 is an alkyl group having 1 to 10 carbon atoms, R2 is an alkylene group having 1 to 10 carbon atoms, L is a direct bond, —O—, —COO—, —RO—, or —R′COO—; R and R' each independently represent an alkylene group having 1 to 10 carbon atoms, m is an integer from 0 to 5.

2. The compound represented by Chemical Formula 1 includes at least one compound selected from the group consisting of compounds represented by the following Chemical Formula 1-1 and compounds represented by the following Chemical Formula 2-1: 【Chemistry 2】 【Chemistry 3】 (In the chemical formula 1-1 and the chemical formula 2-1, R1, R2, L, and m are as defined in Chemical Formula 1 above.

3. 2. The nonaqueous electrolyte for a lithium secondary battery according to claim 1, wherein L in Formula 1 is —O— or —COO—.

4. The compound represented by Chemical Formula 1 includes at least one selected from the group consisting of a compound represented by the following Chemical Formula 1-2, a compound represented by the following Chemical Formula 1-3, a compound represented by the following Chemical Formula 2-2, and a compound represented by the following Chemical Formula 2-3. 【Chemistry 4】 【Chemistry 5】 【Chemistry 6】 【Chemistry 7】 (In the chemical formulas 1-2, 1-3, 2-2, and 2-3, R1, R2, and m are as defined in the chemical formula 1.)

5. 2. The nonaqueous electrolyte solution for a lithium secondary battery according to claim 1, wherein the compound represented by Chemical Formula 1 comprises at least one selected from the group consisting of a compound represented by Chemical Formula 1A below, a compound represented by Chemical Formula 1B below, a compound represented by Chemical Formula 2A below, and a compound represented by Chemical Formula 2B below: 【Chemistry 8】 【Chemistry 9】 【Chemistry 10】 【Chemistry 11】

6. 2. The non-aqueous electrolyte solution for a lithium secondary battery according to claim 1, wherein the content of the compound represented by Formula 1 is 0.1 wt % to 5 wt % based on the total weight of the non-aqueous electrolyte solution.

7. 2. The non-aqueous electrolyte solution for a lithium secondary battery according to claim 1, wherein the content of the compound represented by Formula 1 is 0.1 wt % to 1 wt % based on the total weight of the non-aqueous electrolyte solution.

8. 2. The nonaqueous electrolyte solution for a lithium secondary battery according to claim 1, further comprising one or more additives selected from the group consisting of vinylene carbonate, vinyl ethylene carbonate, 1,3-propane sultone, ethylene sulfate, lithium difluorooxalatoborate, and lithium difluorophosphate.

9. 2. The nonaqueous electrolyte solution for a lithium secondary battery according to claim 1, wherein the organic solvent comprises a mixture of a cyclic carbonate solvent and a linear carbonate solvent.

10. a positive electrode including a positive electrode active material; a negative electrode including a negative electrode active material; a separator interposed between the positive electrode and the negative electrode; A lithium secondary battery comprising the nonaqueous electrolyte solution according to claim 1 .

11. 11. The lithium secondary battery of claim 10, wherein the positive electrode active material comprises a lithium composite transition metal oxide represented by the following Chemical Formula 3: [Chemical formula 3] Li １＋ｘ (N ａ Co ｂ Mn ｃ M ｄ )O ２ (In the above chemical formula 3, M is one or more selected from W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo; 1+x, a, b, c, and d are the atomic fractions of Li, Ni, Co, Mn, and M, respectively; 0≦x≦0.2, 0.50≦a<1, 0<b≦0.25, 0<c≦0.25, 0≦d≦0.1, a+b+c+d=1.)

12. 12. The lithium secondary battery according to claim 11, wherein a, b, c, and d in Chemical Formula 3 are in the ranges 0.80≦a≦0.95, 0.025≦b≦0.15, 0.025≦c≦0.15, and 0≦d≦0.05, respectively.

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