Non-aqueous electrolyte for lithium secondary battery and lithium secondary battery containing the same

Abstract

The present invention relates to a non-aqueous electrolyte for a lithium secondary battery containing a compound represented by Chemical Formula 1, a lithium salt, and an organic solvent, and a lithium secondary battery containing the same.

Description

Technical Field

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0098826 filed on August 8, 2022, and Korean Patent Application No. 10-2023-0090520 filed on July 12, 2023, and all of its contents 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 including the same.

Background Art

[0003] A lithium secondary battery is generally manufactured by forming an electrode assembly with a separator interposed between a positive electrode including a positive electrode active material made of a transition metal oxide containing lithium and a negative electrode including a negative electrode active material capable of storing lithium ions, inserting the electrode assembly into a battery case, and then injecting and sealing a non-aqueous electrolyte serving as a medium for transmitting lithium ions.

[0004] Lithium secondary batteries can be miniaturized and have high energy density and operating voltage, so they are applied in various fields such as mobile devices, electronic products, and electric vehicles. As the application fields of lithium secondary batteries diversify, the required physical property conditions are becoming increasingly high. Specifically, the development of lithium secondary batteries that can be stably driven even under high-temperature conditions and have long-life characteristics is required.

[0005] On the other hand, when a lithium secondary battery is driven under high-temperature conditions, PF6 is generated from lithium salts such as LiPF6 contained in the electrolyte. -The reaction in which anions are decomposed becomes intense and may generate Lewis acids such as PF5, which reacts with moisture to produce HF. Such decomposition products as PF5 and HF may not only destroy the film formed on the surface of the electrode but also cause a decomposition reaction of the organic solvent. Further, they may react with the decomposition products of the positive electrode active material to elute transition metal ions, and the eluted transition metal ions may be electrodeposited on the negative electrode, possibly destroying the film formed on the surface of the negative electrode.

[0006] If the decomposition reaction of the electrolyte continues on the film thus destroyed, the performance of the battery further deteriorates. Therefore, there is a demand for the development of a secondary battery capable of maintaining excellent performance even under high-temperature conditions.

Summary of the Invention

Problems to be Solved by the Invention

[0007] The present invention is for solving the above problems, and an object thereof is to provide a non-aqueous electrolyte contributing to forming a strengthened film on an electrode and a lithium secondary battery including the same.

Means for Solving the Problems

[0008] According to one embodiment, the present invention provides a non-aqueous electrolyte for a lithium secondary battery including a lithium salt, an organic solvent, and a compound represented by the following Chemical Formula 1.

[0009]

Chem.

[0010] In the Chemical Formula 1, R1 is a halogen group, R2 and R3 are each independently an alkyl group having 1 to 10 carbon atoms, p is any integer from 1 to 5, q is any integer from 0 to 5 - p, r is any integer from 0 to 4, m is any one integer from 1 to 5 - r.

[0011] According to another embodiment, the present invention provides a lithium secondary battery including 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 the non-aqueous electrolyte for the lithium secondary battery.

Advantages of the Invention

[0012] The non-aqueous electrolyte according to the present invention contains a pyridine-based compound substituted with a halobenzene, and thus has an effect of forming a thin and strong film on the electrode. Therefore, it is possible to provide a lithium secondary battery with improved electrochemical characteristics even under extreme high-temperature storage conditions.

Embodiments for Carrying Out the Invention

[0013] Hereinafter, the present invention will be described in more detail.

[0014] Generally, anions contained in lithium salts such as LiPF6 widely used in electrolytes for lithium secondary batteries form decomposition products such as hydrogen fluoride (HF) and PF5 due to thermal decomposition or moisture. Such decomposition products have acidic properties and deteriorate the surface of the film or the electrode in the battery.

[0015] Due to the decomposition products of the electrolyte and the structural changes of the positive electrode caused by repeated charge and discharge, transition metals in the positive electrode are likely to elute into the interior of the electrolyte. The eluted transition metals are further re-deposited on the positive electrode, increasing the resistance of the positive electrode. Furthermore, when the eluted transition metals move to the negative electrode through the electrolyte, they are electrodeposited on the negative electrode, causing the destruction of the SEI (solid electrolyte interphase) film and further electrolyte decomposition reactions, thereby resulting in problems such as the consumption of lithium ions and an increase in resistance.

[0016] Also, during the initial activation of the battery, protective films are formed on the positive and negative electrodes due to the electrolyte reaction. However, if the films become unstable for the above reasons, further decomposition of the electrolyte occurs during charge and discharge or high-temperature exposure, accelerating the deterioration of the battery and generating gas.

[0017] To solve such problems, the inventors have found that by including a compound represented by the following Chemical Formula 1 in the non-aqueous electrolyte, the decomposition reaction of the electrolyte can be reduced, and the elution of transition metals and the generation of gas can be suppressed. Specifically, since the compound represented by Chemical Formula 1 contains a pyridine group, it is rapidly decomposed at the negative electrode to form a thin and strong SEI film on the electrode, which has the effect of improving the initial resistance when applied to a battery. In particular, since the pyridine group is substituted with a halobenzene, specifically fluorobenzene, it is possible to form a LiF film by providing an F component, which has the effect of suppressing the deterioration of the negative electrode during battery operation, and ultimately reducing the gas generation amount and the resistance increase rate under high-temperature storage conditions.

[0018] On the other hand, when a silicon-based material is used as the negative electrode active material, there is a problem that the electron conductivity is low and it is difficult to form a film. However, since the compound represented by Chemical Formula 1 enables a fast reaction, it can complement this. Also, when a high-nickel (High-Ni) active material is introduced as the positive electrode active material, due to structural instability, it can increase side reactions and the gas generation amount, which can be a factor deteriorating the battery life. However, since the compound represented by Chemical Formula 1 is excellent in the effect of improving the film characteristics of the electrode, it is possible to solve the problems caused by applying such a high-nickel positive electrode active material.

[0019] Hereinafter, each component constituting the present invention will be described in more detail.

[0020] 〔Non-aqueous electrolyte〕 The present invention provides a non-aqueous electrolyte for a lithium secondary battery, which includes a lithium salt, an organic solvent, and a compound represented by Chemical Formula 1.

[0021] Hereinafter, each component will be specifically described.

[0022] (1) The compound represented by Chemical Formula 1 The non-aqueous electrolyte of the present invention contains a compound represented by the following Chemical Formula 1.

[0023]

Chemical formula

[0024] In the above Chemical Formula 1, R1 is a halogen group, R2 and R3 are each independently an alkyl group having 1 to 10 carbon atoms, p is any integer from 1 to 5, q is any integer from 0 to 5 - p, r is any integer from 0 to 4, m is any integer from 1 to 5 - r.

[0025] In one embodiment of the present invention, R1 in Chemical Formula 1 may be fluorine. In this case, by the elimination of F, there is an effect that a film of the LiF component can be formed on the negative electrode.

[0026] On the other hand, R2 and R3 may be hydrogen or an alkyl group having 1 to 5 carbon atoms, preferably hydrogen or an alkyl group having 1 to 3 carbon atoms, more preferably hydrogen or a methyl group.

[0027] In one embodiment of the present invention, p may be 1 or 2, preferably 1.

[0028] In one embodiment of the present invention, q and r are each 0 or 1, preferably, either one of the two is 0 and the other is 1, and both may be 0. Also, m may be 1 or 2, preferably 1.

[0029] In one embodiment of the present invention, the compound represented by Chemical Formula 1 may be represented by the following Chemical Formula 1-1. In this way, when a halobenzene is substituted at the 4-position of the pyridine ring, that is, the para-position with respect to the nitrogen atom, it is preferable because it does not generate steric hindrance at the N part of the pyridine and is likely to react with the negative electrode.

[0030]

Chemical formula

[0031] In Chemical Formula 1-1, R1 to R3, p, q, and r are as defined in Chemical Formula 1.

[0032] In one embodiment of the present invention, Chemical Formula 1 may be represented by the following Chemical Formula 1A to Chemical Formula 1C.

[0033]

Chemical formula

[0034]

Chemical formula

[0035]

Chemical formula

[0036] In one embodiment of the present invention, the content of the compound represented by Chemical Formula 1 may be 0.1% by weight to 5% by weight, preferably 0.1% by weight to 1% by weight, more preferably 0.1% by weight to 0.5% by weight, based on the total weight of the non-aqueous electrolyte.

[0037] When the content of the compound represented by Chemical Formula 1 is 0.1% by weight or more, a film can be formed on the negative electrode and the above-described effects can be sufficiently exhibited. When it is 5% by weight or less, it is preferable from the viewpoint of preventing a decrease in ionic conductivity due to an increase in the viscosity of the electrolyte.

[0038] (2) Additive In order to prevent the electrolyte from being decomposed in a high-voltage environment and causing the collapse of the electrode, or to further improve effects such as low-temperature high-rate discharge characteristics, high-temperature stability, overcharge prevention, and suppression of battery swelling at high temperatures, the non-aqueous electrolyte of the present invention may optionally further contain the following additives selectively.

[0039] The additive may be any one or more selected from the group consisting of cyclic carbonate compounds, sultone compounds, sulfate compounds, phosphorus compounds, nitrile compounds, amine compounds, silane compounds, benzene compounds, and lithium salt compounds.

[0040] The cyclic carbonate compound is any one or more selected from the group consisting of vinylene carbonate (VC), vinyl ethylene carbonate (VEC), and fluoroethylene carbonate (FEC), and specifically may be vinylene carbonate.

[0041] The sultone compound is a substance capable of forming a stable SEI film by a reduction reaction on the surface of the negative electrode, and may be any one or more compounds 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, and specifically may be 1,3-propane sultone (PS).

[0042] The sulfate compound is a substance capable of being electrically decomposed on the surface of the negative electrode and forming a stable SEI film that does not crack even during high-temperature storage, and may be any one or more selected from the group consisting of ethylene sulfate (Ethylene Sulfate; Esa), trimethylene sulfate (Trimethylene sulfate; TMS), and methyl trimethylene sulfate (Methyl trimethylene sulfate; MTMS).

[0043] The phosphorus-based compound is a phosphate-based or phosphite-based compound, and specifically, it may be any one or more selected from the group consisting of tris(trimethylsilyl) phosphate, tris(trimethylsilyl) phosphite, tris(2,2,2-trifluoroethyl) phosphate, and tris(trifluoroethyl) phosphite.

[0044] The nitrile-based compound may be any one or more selected from the group consisting of 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).

[0045] The amine-based compound may be any one or more selected from the group consisting of triethanolamine and ethylenediamine, and the silane-based compound may be tetravinylsilane.

[0046] The benzene-based compound may be any one or more selected from the group consisting of monofluorobenzene, difluorobenzene, trifluorobenzene, and tetrafluorobenzene.

[0047] The lithium salt-based compound is a compound different from the lithium salt contained in the non-aqueous electrolyte, and may be any one or more compounds selected from the group consisting of lithium difluorophosphate (LiDFP; LiPO2F2), lithium bisoxalatoborate (LiBOB; LiB(C2O4)2), lithium tetrafluoroborate (LiBF4), lithium tetraphenylborate, and lithium difluoro(bisoxalato)phosphate (LiDFOP).

[0048] Preferably, the non-aqueous electrolyte according to an embodiment of the present invention may further contain any one or more additives selected from the group consisting of vinylene carbonate (VC), 1,3-propane sultone (PS), ethylene sulfate (ESa), and lithium difluorophosphate (LiDFP). In this case, there is an advantage that the negative electrode film can be strengthened and further resistance can be improved.

[0049] On the other hand, the content of the additive may be 0.1% by weight to 10% by weight based on the total weight of the non-aqueous electrolyte, and preferably may be 0.3% by weight to 5% by weight. When the content of the additive is within the above range, there is an effect of suppressing side reactions due to the formation of films on the positive electrode and the negative electrode.

[0050] (3) Organic solvent The non-aqueous electrolyte of the present invention contains an organic solvent.

[0051] As the organic solvent, various organic solvents commonly used for lithium electrolytes can be used without limitation. For example, the organic solvent may be a cyclic carbonate-based solvent, a linear carbonate-based solvent, a linear ester-based solvent, a cyclic ester-based solvent, a nitrile-based solvent, or a mixture thereof, and preferably contains a mixture of two or more selected from a cyclic carbonate-based solvent, a linear carbonate-based solvent, and a linear ester-based solvent, and more preferably may contain a mixture of a cyclic carbonate-based solvent and a linear carbonate-based solvent.

[0052] The cyclic carbonate-based solvent is a high-viscosity organic solvent. Since it has a high dielectric constant, it easily dissociates lithium salts in the electrolyte and may be any one or more 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. Preferably, it may contain ethylene carbonate (EC) or propylene carbonate (PC).

[0053] Also, the linear carbonate-based solvent is an organic solvent having low viscosity and low dielectric constant and may be any 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. Preferably, it may contain ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), or diethyl carbonate (DEC).

[0054] In order to produce an electrolyte having high ionic conductivity, it is preferable to use a mixture of a cyclic carbonate-based solvent and a linear carbonate-based solvent.

[0055] The linear ester-based solvent may be any one or more selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, and butyl propionate. Preferably, it may be methyl propionate, ethyl propionate, or propyl propionate.

[0056] The cyclic ester-based solvent may be any one or more selected from the group consisting of γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, and ε-caprolactone.

[0057] The nitrile-based solvent may be any one or more selected from the group consisting of succinonitrile, acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentanecarbonitrile, cyclohexanecarbonitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile, and preferably may be succinonitrile.

[0058] In the total weight of the non-aqueous electrolyte, unless otherwise specified, the remainder excluding the contents of other components excluding the organic solvent, for example, the compound represented by the chemical formula 1, the additive, and the lithium salt, is all organic solvent.

[0059] (4) Lithium salt The non-aqueous electrolyte of the present invention contains a lithium salt.

[0060] The lithium salt can be used without limitation, such as those commonly used in electrolytes for lithium secondary batteries. Specifically, the lithium salt contains Li as a cation + and, as an anion, F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , B 10 Cl 10 - , AlCl4 - , AlO2 - , 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 - may contain any one or more selected from

[0061] Specifically, the lithium salt may be any one or more selected from the group consisting of LiPF6, LiClO4, LiBF4, lithium bis(fluorosulfonyl)imide (LiN(FSO2)2; LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(pentafluoroethanesulfonyl)imide (LiBETI), lithium trifluoromethanesulfonate (LiSO3CF3), lithium difluorophosphate (LiPO2F2), lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LiFOB), lithium difluoro(bisoxalato)phosphate (LiDFOP), lithium tetrafluoro(oxalato)phosphate (LiTFOP), and lithium fluoromalonate(difluoro)borate (LiFMDFB), and preferably may be LiPF6.

[0062] 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 M to 4.0 M, specifically 0.5 M to 3.0 M, and more specifically 0.8 M 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 can be sufficiently ensured, while preventing the viscosity and surface tension from becoming excessively high, and appropriate electrolyte impregnation properties can be obtained.

[0063] [Lithium secondary battery] Next, the lithium secondary battery according to the present invention will be described.

[0064] 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 will be omitted, and other components will be described below.

[0065] (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, followed by drying and rolling.

[0066] 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 a material obtained by surface treatment of the surface of aluminum or stainless steel with carbon, nickel, titanium, silver, etc. may be used.

[0067] The positive electrode active material is a compound capable of reversible intercalation and deintercalation of lithium, and may be any one or more selected from the group consisting of LCO (LiCoO2); LNO (LiNiO2); LMO (LiMnO2); LiMn2O4, LiCoPO4; LFP (LiFePO4); and lithium composite transition metal oxides containing nickel (Ni), cobalt (Co), and manganese (Mn).

[0068] On the other hand, the positive electrode active material may be one in which the molar ratio of nickel in the transition metal is 70 mol% or more, preferably 80 mol% or more, more preferably 90 mol% or more. That is, even in a battery containing a positive electrode active material with a nickel molar ratio of 90 mol% or more, when the non-aqueous electrolyte according to the present invention is applied, excellent resistance characteristics and gas generation amount can be obtained.

[0069] In one embodiment of the present invention, the lithium composite transition metal oxide may be a compound represented by the following Chemical Formula 2. That is, the positive electrode active material according to one embodiment of the present invention may include a lithium composite transition metal oxide represented by the following Chemical Formula 2.

[0070] [Chemical Formula 2] Li 1+x (Ni a Co b Mn c M d )O2

[0071] In the Chemical Formula 2,[[]] M is any one or more selected from the group consisting of 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 atomic fractions of independent elements, respectively,[[]] -0.2 ≦ x ≦ 0.2, 0.6 ≦ a < 1, 0 < b ≦ 0.3, 0 < c ≦ 0.3, 0 ≦ d ≦ 0.1, and a + b + c + d = 1.[[]]

[0072] The above 1 + x represents the molar ratio of lithium in the lithium composite transition metal oxide, and may be -0.1 ≦ x ≦ 0.2 or 0 ≦ x ≦ 0.2. When the molar ratio of lithium satisfies the above range, the crystal structure of the lithium composite transition metal oxide can be stably formed.

[0073] The above a represents the molar ratio of nickel in all metals excluding lithium in the lithium composite transition metal oxide, and may be 0.70 ≦ a < 1, 0.80 ≦ a < 1, 0.85 ≦ a < 1, or 0.90 ≦ a < 1. When the molar ratio of nickel satisfies the above range, it exhibits a high energy density and high capacity can be realized.

[0074] The above b represents the molar ratio of cobalt in all metals excluding lithium in the lithium composite transition metal oxide, and may be 0 < b ≦ 0.25, 0 < b ≦ 0.20, 0 < b ≦ 0.15, or 0 < b ≦ 0.10. When the molar ratio of cobalt satisfies the above range, good resistance characteristics and output characteristics can be realized.

[0075] The above c represents the molar ratio of manganese in all metals excluding lithium in the lithium composite transition metal oxide, and may be 0 < c ≦ 0.25, 0 < c ≦ 0.20, 0 < c ≦ 0.15, or 0 < c ≦ 0.10. When the molar ratio of manganese satisfies the above range, it has excellent structural stability of the positive electrode active material.

[0076] In one embodiment of the present invention, the lithium composite transition metal oxide may contain any one or more doping elements selected from the group consisting of 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, and preferably may contain Al as the doping element. In other words, the above d representing the molar ratio of the doping element among all metals excluding lithium in the lithium composite transition metal oxide may be 0 < d ≦ 0.10, 0 < d ≦ 0.08, 0 < d ≦ 0.05, or 0 < d ≦ 0.03.

[0077] Preferably, a, b, c, and d in Chemical Formula 2 may be 0.70 ≦ a < 1, 0 < b ≦ 0.2, 0 < c ≦ 0.2, and 0 ≦ d ≦ 0.1, and more preferably 0.80 ≦ a ≦ 1, 0 < b ≦ 0.15, 0 < c ≦ 0.15, and 0 ≦ d ≦ 0.05.

[0078] The positive electrode active material may be contained in an amount of 80% by weight to 99% by weight, specifically 90% by weight to 99% by weight, based on the total weight of the solid content in the positive electrode slurry. Here, when the content of the positive electrode active material is 80% by weight or less, the energy density may be low and the capacity may decrease.

[0079] The binder is a component that assists in binding the active material and the conductive material, etc., and binding to the current collector, and is usually added in an amount of 1% by weight to 30% by weight based on the total weight of the solid content in the positive electrode slurry. Examples of such binders may 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, or various copolymers thereof.

[0080] Further, the conductive material is a substance that imparts conductivity without causing a 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.

[0081] The conductive material may be selected from, for example, 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.

[0082] Also, the solvent of the positive electrode slurry may contain an organic solvent such as NMP (N-methyl-2-pyrrolidone), and can be used in an amount that provides a suitable viscosity when containing the positive electrode active material, binder, conductive material, and the like. For example, the concentration of the solid content in the positive electrode slurry containing the positive electrode active material, binder, and conductive material may be included so as to be 40% to 90% by weight, preferably 50% to 80% by weight.

[0083] (2) Negative electrode The negative electrode according to the present invention contains a negative electrode active material, and can be manufactured by coating a negative electrode slurry containing the negative electrode active material, binder, conductive material, solvent, etc. on a negative electrode current collector, followed by drying and rolling.

[0084] 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 cause a chemical change in the battery and has high conductivity. For example, copper; stainless steel; aluminum; nickel; titanium; fired carbon; those obtained by surface treatment with carbon, nickel, titanium, silver, etc. on the surface of copper or stainless steel; or an aluminum-cadmium alloy may be used. Also, similar to the positive electrode current collector, the binding force of the negative electrode active material may be strengthened by forming fine irregularities on the surface, and it can be used in various forms such as films, sheets, foils, nets, porous bodies, foams, and non-woven bodies.

[0085] In one embodiment of the present invention, the negative electrode active material may include a silicon-based material, and the silicon-based material may be Si, SiO x (where 0 < x < 2) and 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), and preferably is SiO.

[0086] Since the silicon-based negative electrode active material has a capacity nearly about 10 times higher than that of graphite, the mass loading (mg·cm -2 ) can be reduced, and the rapid charging performance of the battery can be improved. However, the negative electrode containing the silicon-based negative electrode active material has a drawback that its electric conductivity is lower than that of the graphite negative electrode and it is difficult to form a film on the negative electrode. However, since the non-aqueous electrolyte according to the present invention contains the compound represented by the chemical formula 1, it is rapidly decomposed at the negative electrode due to the pyridine structure, and a thin and strong SEI film is formed on the negative electrode, so that the above-mentioned drawbacks can be effectively compensated.

[0087] In one embodiment of the present invention, the silicon-based material may be 1 wt% to 20 wt%, preferably 5 wt% to 15 wt% based on the total weight of the negative electrode active material. When the silicon-based material is included within the above range, there are effects of increasing the negative electrode capacity and improving the rapid charging performance.

[0088] In addition to the silicon-based material, the negative electrode active material may further include one or more selected from carbon-based materials capable of reversibly intercalating / deintercalating lithium ions; metals or alloys of these metals and lithium; metal composite oxides; materials capable of doping and dedoping lithium; lithium metal; and transition metal oxides.

[0089] As the carbonaceous material capable of reversibly intercalating / deintercalating the lithium ions, any carbonaceous negative electrode active material generally used in lithium ion secondary batteries can be used without particular limitation. Representative examples thereof include crystalline carbon, amorphous carbon, or a combination of these. 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.

[0090] 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.

[0091] 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 any one or more selected from the group consisting thereof can be used.

[0092] Examples of the material capable of doping and undoping lithium include 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. Also, at least one of these and SiO2 may be mixed and used.

[0093] In the Si-Y and Sn-Y, 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.

[0094] Examples of the transition metal oxide include lithium-containing titanium composite oxide (LTO), vanadium oxide, lithium vanadium oxide, and the like.

[0095] In one embodiment of the present invention, the negative electrode active material may be a mixture of the carbon-based material and the silicon-based material, and preferably may be a mixture of graphite and SiO.

[0096] The negative electrode active material may be contained in an amount of 80% to 99% by weight based on the total weight of the solid content in the negative electrode slurry.

[0097] The binder is a component that assists in binding between the conductive material, the active material, and the current collector, and is usually added in an amount of 1% to 30% by weight based on the total weight of the solid content in the negative electrode slurry. Examples of such binders include polyvinylidene fluoride, 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, or various copolymers thereof.

[0098] 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% by weight to 20% by weight based on the total weight of the solid content in the negative electrode slurry. Such a conductive material is not particularly limited as long as it does not cause a chemical change in the battery and has conductivity. For example, carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; graphite powder such as natural graphite, artificial graphite, carbon nanotube, and graphite; conductive fibers such as carbon fiber and metal fiber; 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 may be selected.

[0099] The solvent of the negative electrode slurry may contain water or an organic solvent such as NMP and 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, it may be contained such that the concentration of the solid content in the slurry containing the negative electrode active material, binder, and conductive material is 30% by weight to 80% by weight, preferably 40% by weight to 70% by weight.

[0100] (3) Separator The lithium secondary battery according to the present invention includes a separator between the positive electrode and the negative electrode.

[0101] The separator separates the negative electrode and the positive electrode and provides a migration path for lithium ions. It is not particularly limited as long as it is usually used as a separator in a lithium secondary battery and can be used without particular limitation. In particular, those having low resistance to the migration of ions in the electrolyte and excellent electrolyte impregnation ability and safety are preferred.

[0102] Specifically, as the separator, a porous polymer film, for example, a porous polymer film made of a polyolefin-based polymer such as a homopolymer of ethylene, a homopolymer of propylene, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer; or a laminate structure of two or more layers thereof can be used. Further, a normal porous nonwoven fabric, for example, a nonwoven fabric made of high-melting glass fibers, polyethylene terephthalate fibers, etc. may be used. Further, in order to ensure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymer substance may be used, and it may be used as a single-layer or multilayer structure.

[0103] The lithium secondary battery according to the present invention as described above can be usefully used in portable devices such as mobile phones, notebook personal computers, digital cameras; and in the field of electric vehicles such as hybrid electric vehicles (HEV).

[0104] Accordingly, according to another embodiment of the present invention, a battery module including the lithium secondary battery as a unit cell, and a battery pack including the same are provided.

[0105] The battery module or battery pack can be used as a power source for any one or more medium to large-sized devices including power tools; electric vehicles including electric vehicles (EV), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEV); and power storage systems.

[0106] The outer shape of the lithium secondary battery of the present invention is not particularly limited, and may be a cylindrical shape using a can, a rectangular shape, a pouch shape, or a coin shape.

[0107] The lithium secondary battery according to the present invention can be used not only in a battery cell used as a power source for a small device, but also preferably as a unit cell in a medium and large-sized battery module including a large number of battery cells.

[0108] Hereinafter, the present invention will be specifically described with reference to specific examples.

[0109] <Example: Manufacture of Lithium Secondary Battery> Example 1. 1) Manufacture of non-aqueous electrolyte Ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a volume ratio of 30:70, and then dissolved so that LiPF6 became 1 M to produce a non-aqueous organic solution. 0.1 wt% of the compound represented by Chemical Formula 1A, 0.5 wt% of vinylene carbonate (VC), and the remaining non-aqueous organic solution were mixed to produce 100 wt% of a non-aqueous electrolyte.

[0110] 2) Manufacture of lithium secondary battery To N-methyl-2-pyrrolidone (NMP), Li(Ni 0.9 Mn 0.03 Co 0.06 Al 0.01 )O2, a conductive material (carbon black), and a binder (polyvinylidene fluoride) were added at a weight ratio of 97.6:0.8:1.6 to produce a positive electrode slurry (solid content: 60 wt%). The positive electrode slurry was applied and dried on an aluminum (Al) thin film, which was a positive electrode current collector with a thickness of 13.5 μm, and then roll press was performed to produce a positive electrode.

[0111] The negative electrode active material (graphite:SiO = 90.0:10.0 by weight ratio), binder (SBR-CMC), and conductive material (carbon black) were added to water as a solvent at a weight ratio of 97.6:0.8:1.6 to produce a negative electrode slurry (solid content: 60% by weight). After applying and drying the negative electrode slurry on a copper (Cu) thin film, which is a negative electrode current collector with a thickness of 6 μm, a roll press was performed to produce a negative electrode. The positive electrode, a polyolefin-based porous separator coated with inorganic particles (Al2O3), and the negative electrode were laminated in sequence to produce an electrode assembly.

[0112] The assembled electrode assembly was housed in a cylindrical battery case, and a lithium secondary battery was produced by injecting the manufactured non-aqueous electrolyte.

[0113] Example 2. A lithium secondary battery was produced in the same manner as in Example 1, except that the content of the compound represented by Chemical Formula 1A was changed to 0.3 wt% during the production of the non-aqueous electrolyte.

[0114] Example 3. A lithium secondary battery was produced in the same manner as in Example 1, except that the compound represented by Chemical Formula 1B was used instead of the compound represented by Chemical Formula 1A during the production of the non-aqueous electrolyte.

[0115] Example 4. A lithium secondary battery was produced in the same manner as in Example 3, except that the content of the compound represented by Chemical Formula 1B was changed to 0.3 wt% during the production of the non-aqueous electrolyte.

[0116] Example 5. A lithium secondary battery was produced in the same manner as in Example 1, except that the compound represented by Chemical Formula 1C was used instead of the compound represented by Chemical Formula 1A during the production of the non-aqueous electrolyte.

[0117] Example 6. A lithium secondary battery was manufactured in the same manner as in Example 5, except that the content of the compound represented by Chemical Formula 1C was changed to 0.3 wt% during the production of the non-aqueous electrolyte.

[0118] 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 production of the non-aqueous electrolyte.

[0119] Comparative Example 2. A lithium secondary battery was manufactured in the same manner as in Example 1, except that the compound represented by the following Chemical Formula Z1 was used instead of the compound represented by Chemical Formula 1A during the production of the non-aqueous electrolyte.

[0120]

Chemical Formula

[0121] Comparative Example 3. A lithium secondary battery was manufactured in the same manner as in Example 1, except that the compound represented by the following Chemical Formula Z2 was used instead of the compound represented by Chemical Formula 1A during the production of the non-aqueous electrolyte.

[0122]

Chemical Formula

[0123] Comparative Example 4. A lithium secondary battery was manufactured in the same manner as in Example 1, except that the compound represented by the following Chemical Formula Z3 was used instead of the compound represented by Chemical Formula 1A during the production of the non-aqueous electrolyte.

[0124]

Chemical Formula

[0125] Comparative Example 5. A lithium secondary battery was manufactured in the same manner as in Example 1, except that a compound represented by the following Chemical Formula Z4 was used instead of the compound represented by the Chemical Formula 1A during the production of the non-aqueous electrolyte.

[0126]

Chem.

[0127] <Experimental Example: Evaluation of Battery Performance> Experimental Example 1. Measurement of Initial Resistance After performing the activation (formation) process on the lithium secondary batteries manufactured in the above Examples and Comparative Examples, at 25°C, constant current / constant voltage (CC / CV) charging (0.05C cut off) was performed up to 4.2V at a 0.33C rate, and after discharging at a constant current (CC) up to 2.80V at a 0.33C rate, the initial resistance was measured. The results are shown in Table 1 below.

[0128] Experimental Example 2. Measurement of Resistance Increase Rate after High-Temperature Storage Each battery that had completed the initial evaluation in Experimental Example 1 was fully charged to SOC100% under the same conditions and stored at a high temperature (60°C) for 4 weeks. Then, after transferring it to a charger at room temperature (25°C), the resistance was further measured, the resistance increase rate was calculated according to the following Formula 1, and the results are shown in Table 1 below.

[0129] Formula 1: Resistance Increase Rate (%) = {(Resistance after High-Temperature Storage - Initial Resistance) / Initial Resistance} × 100

[0130] Experimental Example 3. Measurement of Gas Generation Amount after High-Temperature Storage After performing the activation (formation) process on the lithium secondary batteries manufactured in the above Examples and Comparative Examples, at 25°C, charging was performed up to 4.2V under constant current / constant voltage conditions at a 0.33C rate (0.05C cut off), and the battery was fully charged to SOC100%. After storing the fully charged battery at 60°C for 4 weeks, the gas generation amount was measured at room temperature (25°C) by the buoyancy measurement method. When the gas generation amount measured in Comparative Example 1 was taken as 100%, the relative gas generation amounts of each battery were calculated and shown in Table 1 below.

[0131]

Table 1

[0132] From the results in Table 1 above, it can be confirmed that the non-aqueous electrolyte containing the compound represented by Chemical Formula 1 is effective in improving the resistance increase rate and the gas generation amount after high-temperature storage.

[0133] Specifically, the batteries of Examples 1 to 6 are compared with Comparative Example 2 using a compound represented by Chemical Formula Z1 in which pyridine is substituted for fluorobenzene in pyridine, Comparative Example 3 using a compound represented by Chemical Formula Z2 in which unsubstituted benzene is substituted for fluorobenzene, Comparative Example 4 using a compound represented by Chemical Formula Z3 which is fluorobenzene, and Comparative Example 4 using a compound represented by Chemical Formula Z4 which is fluoropyridine. It can be confirmed that they are superior in the resistance increase rate and the gas generation amount after high-temperature storage. In particular, since Comparative Examples 2 and 3 used compounds not containing F, LiF could not be formed on the negative electrode, and it can be confirmed that the resistance increase rate after high-temperature storage is not better than that of Comparative Example 1.

[0134] On the other hand, even when the non-aqueous electrolyte contains the compound represented by Chemical Formula 1, when the content is 0.3% by weight or more based on the total weight of the non-aqueous electrolyte, it can be confirmed that the improvement effect of the resistance increase rate and the gas generation amount after high-temperature storage is more pronounced.

Claims

1. 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. 【Chemical 1】 (In the Chemical Formula 1, R1 is a halogen group, R2 and R3 are each independently an alkyl group having 1 to 10 carbon atoms, p is any integer from 1 to 5, q is any integer from 0 to 5 - p, r is any integer from 0 to 4, m is any integer from 1 to 5 - r.)

2. The non-aqueous electrolyte for a lithium secondary battery according to Claim 1, wherein R1 is fluorine.

3. The non-aqueous electrolyte for a lithium secondary battery according to Claim 1, wherein q and r are each 0.

4. The non-aqueous electrolyte for a lithium secondary battery according to Claim 1, wherein the compound represented by the Chemical Formula 1 is represented by the following Chemical Formula 1-1. [Chemical 2] (In the Chemical Formula 1-1, R1 to R3, p, q, and r are as defined in Chemical Formula 1.)

5. The non-aqueous electrolyte for a lithium secondary battery according to Claim 1, wherein the content of the compound represented by the Chemical Formula 1 is 0.05% by weight to 5% by weight based on the total weight of the non-aqueous electrolyte.

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

7. The non-aqueous electrolyte for a lithium secondary battery according to Claim 1, further comprising any one or more additives selected from the group consisting of vinylene carbonate, 1,3-propanesultone, ethylene sulfate, and lithium difluorophosphate.

8. The non-aqueous electrolyte for a lithium secondary battery according to Claim 1, wherein the organic solvent includes a mixture of a cyclic carbonate solvent and a linear carbonate solvent.

9. 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, A lithium secondary battery comprising the non-aqueous electrolyte according to any one of Claims 1 to 8.

10. The lithium secondary battery according to Claim 9, wherein the positive electrode active material includes a lithium composite transition metal oxide represented by the following Chemical Formula 2. [Chemical Formula 2] Li １＋ｘ (Ni ａ Co ｂ Mn ｃ M ｄ )O ２ (In the Chemical Formula 2, M is any one or more selected from the group consisting of 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 independent elements, respectively, and -0.2 ≤ x ≤ 0.2, 0.6 ≤ a < 1, 0 < b ≤ 0.3, 0 < c ≤ 0.3, 0 ≤ d ≤ 0.1, and a + b + c + d = 1. **Claim 11** The lithium secondary battery according to claim 10, wherein a, b, c, and d in the chemical formula 2 are 0.80 ≤ a < 1, 0 < b ≤ 0.15, 0 < c ≤ 0.15, and 0 ≤ d ≤ 0.05, respectively. **Claim 12** The lithium secondary battery according to claim 9, wherein the negative electrode active material contains a silicon-based material.

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