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

Abstract

The present invention relates to a non-aqueous electrolyte for a lithium secondary battery, which contains a lithium salt, an organic solvent, and a compound represented by a specific chemical formula (Chemical Formula 1), 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. 10-2022-0039951, filed on March 30, 2022, and all contents disclosed in the documents of this Korean patent application 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 various 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 operated stably even under high temperature conditions and have long life characteristics.

[0005] On the other hand, when a lithium secondary battery is operated under high temperature conditions, lithium salts such as LiPF6 contained in the electrolyte are converted to PF6 - Thermal decomposition of the anions can generate Lewis acids such as PF5, which react with water to generate HF. These decomposition products, such as PF5 and HF, can not only destroy the coating formed on the surface of the electrode, but can also cause decomposition reactions of the organic solvent. Furthermore, the decomposition products of the electrolyte 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 and destroy the coating formed on the surface of 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 secondary batteries that can maintain excellent performance even under 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 aims to solve the above problems and provides a non-aqueous electrolyte containing an imidazolium sulfonate compound that can remove decomposition products of the electrolyte and form a reinforced coating on the electrode, and a lithium secondary battery containing the same that exhibits long life characteristics even when operated at high temperatures. [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, R is O - or OR1, wherein R1 is hydrogen; or an alkyl group having 1 to 10 carbon atoms, L1 is a direct bond; or an alkylene group having 1 to 30 carbon atoms, L2 is an alkylene group having 1 to 10 carbon atoms.

[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 nitrogen atom of the cation moiety in the structure of the compound represented by Chemical Formula 1, which is contained as an additive in the nonaqueous electrolyte according to the present invention, acts as a Lewis base, thereby effectively removing Lewis acids generated as decomposition products of the electrolyte, and forming sulfonates (-RSO3 - ) and propargyl groups (-CHC≡CH) can strengthen the coating on the positive or negative electrode, thereby realizing lithium secondary batteries with improved high-temperature storage characteristics and reduced self-discharge due to dissolution of the positive electrode. DETAILED DESCRIPTION OF THE INVENTION

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

[0015] Transition metals in the positive electrode are prone to leaching into the electrolyte due to decomposition products of the electrolyte and structural changes in the positive electrode caused by repeated charging and discharging. The leached transition metals then redeposit on the positive electrode, increasing the resistance of the positive electrode. Furthermore, if the leached transition metals migrate to the negative electrode via the electrolyte, they are electrodeposited on the negative electrode and grow, causing an internal short circuit, which leads to self-discharge of the negative electrode and low voltage failure. Furthermore, when the leached transition metals are electrodeposited on the negative electrode, they destroy the solid electrolyte interphase (SEI), causing further electrolyte decomposition reactions, resulting in problems such as lithium ion consumption and increased resistance.

[0016] Furthermore, during initial activation of the battery, a protective coating is formed on the positive and negative electrodes due to a reaction of the electrolyte. If the coating becomes unstable for the reasons described above, additional decomposition of the electrolyte occurs during charge-discharge or exposure to high temperatures, accelerating battery degradation and generating gas.

[0017] Therefore, the present inventors have developed a sulfonate (-RSO3 - The non-aqueous electrolyte solution contained a compound represented by the following chemical formula 1, which contains a sulfonate (-RSO3 - ) is reduced at the anode to form a polymerization structure and a LiSO3-based coating. In the case of the propargyl group (-CH2C≡CH), it is reduced to generate a propargyl radical, which then polymerizes to form a thin, dense coating on the surface of the anode. In addition, the compound represented by the following chemical formula 1 contains a Lewis base functional group that can remove Lewis acid decomposition products such as HF and PF5 that are generated when a lithium secondary battery is operated. Therefore, it has been confirmed that non-aqueous electrolytes containing this compound are effective in preventing battery degradation even at high temperatures of 40°C or higher. Each of the components of the present invention will be described in more detail below.

[0018] [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 the following Chemical Formula 1: Each component will be specifically described below.

[0019] (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.

[0020] [ka]

[0021] In the above Chemical Formula 1, R is O - or OR1, wherein R1 is hydrogen; or an alkyl group having 1 to 10 carbon atoms, L1 is a direct bond; or an alkylene group having 1 to 30 carbon atoms, L2 is an alkylene group having 1 to 10 carbon atoms.

[0022] The compound represented by Chemical Formula 1 has the effect of strengthening the coating on the electrode due to its structure containing sulfonate and propargyl. The sulfonate (-RSO3 - ) can be reduced at the anode to form a polymerization structure and a LiSO3-based coating. In addition, by incorporating the sulfonate into the structure, the LUMO value of the compound of Formula 1 can be lowered, further improving the reducibility of the anode.

[0023] In addition, the propargyl group (-CHC≡CH) contained in the structure of Formula 1 is reduced to generate a propargyl radical, and the generated radical can be polymerized to form a thin and dense coating on the surface of the anode.

[0024] In addition, the nitrogen present in the imidazolium of the compound represented by Formula 1 can act as a Lewis base, and thus Lewis acids such as HF generated from the decomposition products of the electrolyte can be easily removed, significantly preventing the problem of the Lewis acids attacking the positive electrode and causing the elution of transition metals.

[0025] As a result, by using the compound represented by Chemical Formula 1 as an additive in the nonaqueous electrolyte solution of the present invention, it is possible to realize a lithium secondary battery that achieves improved life performance, reduced resistance, and reduced gas, particularly at high temperatures.

[0026] In one embodiment of the present invention, the compound represented by Chemical Formula 1 may be represented by the following Chemical Formula 1-1 or 1-2.

[0027] [ka]

[0028] [ka]

[0029] In the chemical formula 1-1 and the chemical formula 1-2, R1, L1, and L2 are defined as in Chemical Formula 1 above.

[0030] Specifically, when the compound represented by Chemical Formula 1 of the present invention is a compound with a zwitterion structure, which is a neutral molecule having an anion moiety and a cation moiety in the structure, as in Chemical Formula 1-1, the ionic conductivity can be further improved by the zwitterion.

[0031] On the other hand, when the compound represented by Chemical Formula 1 of the present invention has the structure of Chemical Formula 1-2, the nitrogen atom of the cation moiety in the structure acts as a Lewis base, thereby effectively removing Lewis acids generated as decomposition products of the electrolyte.

[0032] In one embodiment of the present invention, L1 is -(CH2) n -, where n may be an integer of 1 to 20, preferably an integer of 2 to 10, and more preferably 2 or 3. On the other hand, the L2 is -(CH2) m -, wherein m is an integer of 1 to 10, preferably an integer of 1 to 3, and more preferably 1.

[0033] In one embodiment of the present invention, the compound represented by Chemical Formula 1 may be represented by the following Chemical Formula 1A or Chemical Formula 1B:

[0034] [ka]

[0035] [ka]

[0036] In one embodiment of the present invention, the content of the compound represented by Chemical Formula 1 may be 0.1 wt % or more, preferably 0.3 wt % or more, and more preferably 0.5 wt % or more, based on the total weight of the non-aqueous electrolyte solution, which is preferable in that it exhibits significant effects of removing decomposition products and improving the durability of the coating.

[0037] In addition, the content of the compound represented by Chemical Formula 1 may be 5 wt % or less, preferably 3 wt % or less, and more preferably 2 wt % or less, based on the total weight of the non-aqueous electrolyte solution, which is preferable in that side reactions and the generation of by-products due to excess additives can be prevented. Most preferably, the content of the compound represented by Chemical Formula 1 may be 1 wt % to 2 wt % based on the total weight of the non-aqueous electrolyte solution.

[0038] (2) Additives The nonaqueous electrolyte of the present invention may further include, as necessary, the following additives, selectively, to prevent electrode collapse due to decomposition of the electrolyte in a high-voltage environment, and to further improve low-temperature high-rate discharge characteristics, high-temperature stability, overcharge prevention, and the effect of suppressing battery expansion at high temperatures.

[0039] The additive may be at least one selected from a cyclic carbonate-based compound, a halogen-substituted carbonate-based compound, a sultone-based compound, a sulfate-based compound, a phosphate-based or phosphite-based compound, a borate-based compound, a nitrile-based compound, an amine-based compound, a silane-based compound, a benzene-based compound, and a lithium salt-based compound.

[0040] The cyclic carbonate compound may be at least one selected from vinylene carbonate (VC) and vinylethylene carbonate (VEC), and specifically may be vinylene carbonate. The halogen-substituted carbonate compound may be fluoroethylene carbonate (FEC).

[0041] The sultone-based compound is a substance 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).

[0042] 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).

[0043] The phosphate or phosphite 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.

[0044] The borate-based compound may be lithium tetraphenylborate. 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).

[0045] The amine compound may be one or more selected from triethanolamine and ethylenediamine, and the silane compound may be tetravinylsilane.

[0046] The benzene-based compound may be one or more selected from 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 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).

[0048] The non-aqueous electrolyte according to one embodiment of the present invention may further include 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 (LiBF), lithium difluoro(bisoxalato)phosphate (LiDFOP), and lithium difluorophosphate (LiDFP).

[0049] Preferably, the non-aqueous electrolyte may further contain one or more additives selected from vinylene carbonate (VC), 1,3-propane sultone (PS), ethylene sulfate (ESa), and lithium difluorophosphate (LiDFP).

[0050] The content of the additive may be 0.1 wt % to 10 wt %, preferably 0.3 wt % to 5 wt %, and more preferably 1 wt % to 3 wt %, based on the total weight of the non-aqueous electrolyte solution. When the content of the additive is within the above range, side reactions due to the formation of coatings on the positive and negative electrodes are suppressed.

[0051] (3) Organic Solvent The non-aqueous electrolyte of the present invention contains an organic solvent. 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. Preferably, the organic solvent may include a mixture of two or more solvents selected from the cyclic carbonate solvent, the linear carbonate solvent, and the linear ester solvent. More preferably, the organic solvent may include a mixture of a cyclic carbonate solvent and a linear carbonate solvent.

[0052] The cyclic carbonate solvent is a high-viscosity 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).

[0053] Furthermore, the linear carbonate solvent may be one or more organic solvents having low viscosity and low dielectric constant 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 include ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), or diethyl carbonate (DEC).

[0054] 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.

[0055] 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.

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

[0057] 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.

[0058] The remaining components excluding the organic solvent in the total weight of the nonaqueous electrolyte solution, for example, the compound represented by Formula 1, the additive, and the lithium salt, may be an organic solvent unless otherwise specified.

[0059] (4) Lithium salt The non-aqueous electrolyte of the present invention contains a lithium salt. As the lithium salt, any lithium salt commonly used in electrolytes for lithium secondary batteries can be used without limitation. Specifically, the lithium salt contains, as a cation, Li + and the anion is F - , Cl - , Br - , I - , NO3 -, N(CN)2 - , BF4 - , ClO4 - , B 10 Cl 10 - , AlCl4 - , AlO4 - , PF6 - , CF3SO3 - , CH3CO2 - , CF3CO2 - , AsF6 - , SbF6 - , CH3SO3 - , (CF3CF2SO2)2N - , (CF3SO2)2N - , (FSO2)2N - , BF2C2O4 - , BC4O8 - , 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 above.

[0060] 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 fluoromalonyl(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.

[0061] 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, more specifically 0.8 M to 2.0 M. When the concentration of the lithium salt is within the above range, it is possible to prevent the viscosity and surface tension from becoming excessively high, while sufficiently ensuring the effects of improving low-temperature output and cycle characteristics, and to obtain suitable electrolyte impregnation.

[0062] [Lithium secondary battery] Next, the lithium secondary battery according to the present invention will be described. The lithium secondary battery according to the present invention includes 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, where the non-aqueous electrolyte solution is the non-aqueous electrolyte solution according to the present invention. Since the non-aqueous electrolyte solution has been described above, a description thereof will be omitted and the other components will be described below.

[0063] (1) Positive electrode The positive electrode according to the present invention includes a positive electrode active material and can be manufactured by coating a positive electrode current collector with a positive electrode slurry including the positive electrode active material, a binder, a conductive material, and a solvent, followed by drying and rolling.

[0064] 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; baked carbon; or aluminum or stainless steel whose surface has been treated with carbon, nickel, titanium, silver, or the like may be used.

[0065] The positive electrode active material is a compound capable of reversible intercalation and deintercalation of lithium, and may be one or more selected from LCO (LiCoO2); LNO (LiNiO2); LMO (LiMnO2); LiMn2O4, LiCoPO4; LFP (LiFePO4); and lithium composite transition metal oxides containing nickel (Ni), cobalt (Co), and manganese (Mn). On the other hand, the molar ratio of nickel in the transition metals in the positive electrode active material may be 60 mol % or more, preferably 70 mol % or more, and more preferably 80 mol % or more.

[0066] 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, a 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.

[0067] [Chemical formula 2] Li1+x (Ni a Co b Mn c M d )O₂

[0068] In Chemical Formula 2, 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 atomic fractions of independent elements, -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.

[0069] The 1 + x represents the molar ratio of lithium in the lithium composite transition metal oxide, and -0.1 ≤ x ≤ 0.2 or 0 ≤ x ≤ 0.2 may also be applicable. When the molar ratio of lithium satisfies the above range, the crystal structure of the lithium composite transition metal oxide can be stably formed.

[0070] The a represents the molar ratio of nickel among all the metals excluding lithium in the lithium composite transition metal oxide, and 0.70 ≤ a < 1, 0.80 ≤ a < 1, or 0.85 ≤ a < 1 may also be applicable. When the molar ratio of nickel satisfies the above range, it shows a high energy density and enables the realization of a high capacity.

[0071] ]The b represents the molar ratio of cobalt among all the metals excluding lithium in the lithium composite transition metal oxide, and 0 < b ≤ 0.20, 0 < b ≤ 0.15, or 0 < b ≤ 0.10 may also be applicable. When the molar ratio of cobalt satisfies the above range, good resistance characteristics and output characteristics can be realized.

[0072] Said c represents the molar ratio of manganese among all the metals excluding lithium in the lithium composite transition metal oxide, and it may be 0 < c ≤ 0.20, 0 < c ≤ 0.15, or 0 < c ≤ 0.10. When the molar ratio of manganese satisfies the above range, excellent structural stability of the positive electrode active material is exhibited.

[0073] In one embodiment of the present invention, the lithium composite transition metal oxide may contain 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, said d representing the molar ratio of the doping element among all the metals excluding lithium in the lithium composite transition metal oxide may be 0 < d ≤ 0.10, 0 < d ≤ 0.08, or 0 < d ≤ 0.05. 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, respectively.

[0074] The positive electrode active material may be contained at 80% to 99% by weight, specifically 90% to 99% by weight, based on the total weight of the solid content in the positive electrode slurry. At this time, 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.

[0075] The binder is a component that assists in binding the active material and the conductive material, etc. and binding to the current collector, and may usually be added at a content of 1% to 30% by weight based on the total weight of the solid content in the positive electrode slurry. Examples of such binders may be polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene - propylene - diene monomer, sulfonated ethylene - propylene - diene monomer, styrene - butadiene rubber, fluorine rubber, or various copolymers thereof.

[0076] The conductive material is a substance that does not cause chemical changes in the battery and provides conductivity, 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.

[0077] The conductive material may be selected from conductive materials such as 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 polyphenylene derivatives.

[0078] The solvent for the positive electrode slurry may contain an organic solvent such as NMP (N-methyl-2-pyrrolidone) in an amount that provides a preferred viscosity when containing the positive electrode active material, binder, conductive material, etc. For example, the solvent may be contained so that the solids concentration in the positive electrode slurry containing the positive electrode active material, binder, and conductive material is 40% by weight to 90% by weight, preferably 50% by weight to 80% by weight.

[0079] (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 current collector with a negative electrode slurry including the negative electrode active material, a binder, a conductive material, and a solvent, followed by drying and rolling.

[0080] 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 chemical changes in the battery and has high conductivity, and examples thereof include copper; stainless steel; aluminum; nickel; titanium; calcined carbon; copper or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like; and aluminum-cadmium alloys. Furthermore, similar to the positive electrode current collector, the surface may be formed with fine irregularities to strengthen the binding force of the negative electrode active material, and the negative electrode current collector may be used in various forms such as a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0081] The negative electrode active material may include one or more selected from a carbon material capable of reversibly intercalating / deintercalating lithium ions; a metal or an alloy of such a metal and lithium; a metal composite oxide; a material capable of doping and dedoping lithium; lithium metal; and a transition metal oxide.

[0082] The carbonaceous material capable of reversibly intercalating / deintercalating lithium ions may be any carbonaceous negative electrode active material commonly used in lithium ion secondary batteries, and representative examples thereof include crystalline carbon, amorphous carbon, or a combination of these. Examples of crystalline carbon include graphite, such as amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite. Examples of amorphous carbon include soft carbon (low-temperature calcined carbon), hard carbon, mesophase pitch carbide, and calcined coke.

[0083] The metal or the alloy of such a metal with lithium may be 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 such a metal with lithium.

[0084] Examples of the metal composite oxide include PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, Bi2O5, Li x Fe2O3 (0 ≦ x ≦ 1), Li x WO2 (0 ≦ x ≦ 1), and Sn x Me 1-x Me’ y O z (Me: Mn, Fe, Pb, Ge; Me’: Al, B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, halogen; 0 < x ≦ 1; 1 ≦ y ≦ 3; 1 ≦ z ≦ 8), and one or more selected from the group consisting thereof may be used.

[0085] 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 a combination 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 a combination thereof and is not Sn), etc. Also, at least one of these and SiO2 may be mixed 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 a combination thereof. Examples of the transition metal oxide include lithium-containing titanium composite oxide (LTO), vanadium oxide, lithium vanadium oxide, etc.

[0086] 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. The negative electrode active material may be contained in an amount of 80 wt % to 99 wt % based on the total weight of the solid content in the negative electrode slurry.

[0087] The binder is a component that helps bind the conductive material, active material, and current collector together, 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.

[0088] 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 solids 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 is conductive. Examples of such conductive materials 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.

[0089] 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 preferred 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 %.

[0090] (3) Separator The lithium secondary battery according to the present invention includes a separator between the positive electrode and the negative electrode.

[0091] The separator separates the negative electrode and the positive electrode and provides a path for lithium ions to move. Any separator that is normally used as a separator in a lithium secondary battery can be used without any particular limitation. In particular, it is preferable that the separator has low resistance to ion movement of the electrolyte, has excellent electrolyte impregnation ability, and is excellent in safety.

[0092] Specifically, the separator may be a porous polymer film, such as a porous polymer film made from a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer; or a laminate structure of two or more layers thereof. Ordinary porous nonwoven fabrics, such as nonwoven fabrics made from high-melting-point glass fibers or polyethylene terephthalate fibers, may also be used. To ensure heat resistance or mechanical strength, a separator coated with a ceramic component or a polymer material may also be used, and may be used in a single-layer or multi-layer structure.

[0093] The lithium secondary battery according to the present invention as described above 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).

[0094] 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. 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.

[0095] 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.

[0096] The lithium secondary battery according to the present invention can be used not only as a battery cell used as a power source for a small device, but also as a unit battery in a medium- to large-sized battery module containing a plurality of battery cells. The present invention will be specifically described below with reference to specific examples.

[0097] <Example: Manufacture of lithium secondary battery> Example 1 (Production of non-aqueous electrolyte) Ethylene carbonate (EC):dimethyl carbonate (DMC) were mixed in a volume ratio of 30:70, and LiPF6 was dissolved therein to a concentration of 1.2 M to prepare a non-aqueous organic solution. 2 wt% of the compound represented by Formula 1A, 2 wt% of vinylene carbonate (VC), and the remainder of the non-aqueous organic solution were mixed to prepare a 100 wt% non-aqueous electrolyte.

[0098] (Lithium secondary battery manufacturing) N-methyl-2-pyrrolidone (NMP) was used as the positive electrode active material (Li(Ni 0.8 Co 0.1 Mn 0.1)O2), a conductive material (carbon black), and a binder (polyvinylidene fluoride) were mixed in a weight ratio of 97.5:1:1.5 to prepare a positive electrode slurry (solid content: 60 wt%). The positive electrode slurry was applied to a 15 μm-thick aluminum (Al) thin film as a positive electrode current collector, dried, and then roll-pressed to prepare a positive electrode.

[0099] Anode active material (96 wt% graphite and 4 wt% SiO), binder (SBR-CMC), and conductive material (carbon black) were mixed in a weight ratio of 95:3.5:1.5 with water as a solvent to prepare anode slurry (solid content: 60 wt%). The anode slurry was applied to a 6 μm-thick copper (Cu) thin film as anode current collector, dried, and then roll-pressed to prepare anode.

[0100] The positive electrode, a polyolefin-based porous separator coated with inorganic particles (Al2O3), and a negative electrode were sequentially stacked to prepare an electrode assembly. The assembled electrode assembly was placed in a cylindrical battery case, and the non-aqueous electrolyte solution prepared above was poured into the case to prepare a lithium secondary battery.

[0101] Example 2. A lithium secondary battery was manufactured in the same manner as in Example 1, except that the content of the compound represented by Formula 1A was changed to 1 wt % when preparing the non-aqueous electrolyte.

[0102] Example 3. A lithium secondary battery was manufactured in the same manner as in Example 1, except that the content of the compound represented by Formula 1A was changed to 1 wt % and 1,3-propane sultone (PS) was further added in the preparation of the non-aqueous electrolyte.

[0103] Example 4. A lithium secondary battery was fabricated in the same manner as in Example 1, except that the content of the compound represented by Formula 1A was changed to 0.3 wt % when preparing the non-aqueous electrolyte.

[0104] Example 5. A lithium secondary battery was manufactured in the same manner as in Example 1, except that the compound represented by Formula 1B was used instead of the compound represented by Formula 1A when preparing the non-aqueous electrolyte.

[0105] 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 Formula 1B was changed to 1 wt % when preparing the non-aqueous electrolyte.

[0106] Example 7 A lithium secondary battery was manufactured in the same manner as in Example 5, except that the content of the compound represented by Formula 1B was changed to 1 wt % and 1,3-propane sultone (PS) was further added in the preparation of the non-aqueous electrolyte.

[0107] Example 8 A lithium secondary battery was fabricated in the same manner as in Example 5, except that the content of the compound represented by Formula 1B was changed to 0.3 wt % when preparing the non-aqueous electrolyte.

[0108] Comparative Example 1 A lithium secondary battery was fabricated in the same manner as in Example 1, except that the compound represented by Formula 1A was not added during the preparation of the non-aqueous electrolyte.

[0109] Comparative Example 2 A lithium secondary battery was manufactured in the same manner as in Example 1, except that the compound represented by Formula 1A was not added and 1 wt % of 1,3-propane sultone (PS) was further added during the preparation of the non-aqueous electrolyte solution.

[0110] Comparative Example 3. A lithium secondary battery was manufactured in the same manner as in Example 3, except that the compound represented by the following Chemical Formula C was used in place of the compound represented by Chemical Formula 1A when preparing the non-aqueous electrolyte, and the content of the compound was changed to 0.3 wt %.

[0111] [ka]

[0112] 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 D was used in place of the compound represented by Chemical Formula 1A in preparing the non-aqueous electrolyte solution, and its content was 2 wt %.

[0113] [ka]

[0114] <Experimental example: Evaluation of battery performance> Experimental Example 1: Measurement of capacitance and resistance after high-temperature storage The lithium secondary batteries prepared in the examples and comparative examples were subjected to an activation process, and then constant current / constant voltage (CC / CV) charging (0.05C cutoff) was performed at 25°C at a 0.5C rate up to 4.25V, and constant current (CC) discharging was performed at a 0.5C rate up to 2.50V, and the initial discharge capacity and initial resistance were measured.

[0115] The battery was then fully charged to 100% SOC under the same conditions and stored at high temperature (55°C) for 8 weeks. After that, it was transferred to a charger / discharger at room temperature (25°C), and the capacity and resistance were measured again. The capacity retention rate and resistance increase rate were calculated using the following formulas 1 and 2, and the results are shown in Table 1 below.

[0116] Equation 1: Capacity retention rate (%) = (discharge capacity after high-temperature storage / initial discharge capacity) × 100 Equation 2: Resistance increase rate (%) = {(resistance after high-temperature storage - initial resistance) / initial resistance} x 100

[0117] Experimental Example 2: Measurement of gas generation rate after high-temperature storage The lithium secondary batteries prepared in the examples and comparative examples were subjected to an activation process, and then charged at 25°C at a 0.5C rate up to 4.25V under constant current / constant voltage conditions (0.05C cut-off) and fully charged to 100% SOC. The fully charged batteries were stored at 72°C for 4 weeks and then transferred to a charger / discharger at room temperature (25°C). The gas collected in the cylindrical can was analyzed using a GC-TCD (gas chromatography-thermal conductivity detector). The relative gas generation amount of each battery was calculated, assuming the gas generation amount measured in Comparative Example 1 as 100%, and is shown in Table 1 below.

[0118] Experimental example 3: High temperature life evaluation The lithium secondary batteries prepared in the examples and comparative examples were subjected to an activation process, and then constant current / constant voltage (CC / CV) charging (0.05C cut off) was performed at 40°C at a 0.3C rate up to 4.25V, and constant current (CC) discharging was performed at a 0.5C rate up to 2.85V.

[0119] One charge / discharge cycle was considered as one cycle, and after repeating the same charge / discharge cycle 250 times, the resistance increase rate (DCIR increase) was measured according to the following formula 3. The measurement results are shown in Table 1 below. Equation 3: Resistance increase rate (%) = {(resistance after 250 cycles - resistance after 1 cycle) / resistance after 1 cycle} x 100

[0120] Experimental Example 4: Evaluation of thermal safety The lithium secondary batteries prepared in the examples and comparative examples were subjected to an activation process, and then charged at 25°C at a 0.5C rate up to 4.25V under constant current / constant voltage conditions (0.05C cut-off) and fully charged to 100% SOC. The fully charged batteries were heated to 130°C at a heating rate of 5°C / min and left for 30 minutes, after which a hot box evaluation experiment was conducted to check for the occurrence of ignition. The results are shown in Table 1 below, with PASS indicating that the battery did not ignite and FAIL indicating that it ignited.

[0121] [Table 1]

[0122] From the results in Table 1, it can be seen that when the compound represented by Chemical Formula 1 is used as an electrolyte additive for a lithium secondary battery according to the present invention, not only is high-temperature durability improved, gas generation reduced, and resistance characteristics improved compared to Comparative Examples 1 and 2, which do not use the compound represented by Chemical Formula 1, and Comparative Example 3, which uses a compound represented by Chemical Formula C, which has a structure similar to Chemical Formula 1 but does not contain a sulfite group. On the other hand, it can be seen that in Comparative Example 4, high-temperature durability is reduced because Chemical Formula D does not contain a propargyl group that can polymerize with vinylene carbonate (VC) to form an SEI coating on the anode.

[0123] In particular, it was confirmed that the best results were obtained in all evaluation items when the content of the compound represented by Chemical Formula 1 was 1 wt % or more, most preferably 2 wt % or more. Comparisons between Examples 2 and 3, and 6 and 7, confirmed that when the same content was used, further inclusion of PS provided better results, while comparisons between Examples 1 and 3, and 5 and 7 confirmed that increasing the content of the compound represented by Chemical Formula 1 was more advantageous than using PS.

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, R is O － or OR1, wherein R1 is hydrogen; or an alkyl group having 1 to 10 carbon atoms; L1 is a direct bond; or an alkylene group having 1 to 30 carbon atoms, L2 is an alkylene group having 1 to 10 carbon atoms.

2. The nonaqueous electrolyte for a lithium secondary battery according to claim 1, wherein the compound represented by Chemical Formula 1 is represented by the following Chemical Formula 1-1 or 1-2: 【Chemistry 2】 【Chemistry 3】 In the chemical formula 1-1 and the chemical formula 1-2, R1, L1, and L2 are defined as in Chemical Formula 1 above.

3. The L1 is —(CH ２ ) n-, 2. The nonaqueous electrolyte solution for a lithium secondary battery according to claim 1, wherein n is an integer of 1 to 20.

4. The L2 is —(CH ２ ) m-, 2. The nonaqueous electrolyte for a lithium secondary battery according to claim 1, wherein m is an integer of 1 to 10.

5. 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 from 0.1 wt % to 5 wt % based on the total weight of the non-aqueous electrolyte solution.

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 from 0.5 wt % to 5 wt % based on the total weight of the non-aqueous electrolyte solution.

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

8. 2. The nonaqueous electrolyte solution for a lithium secondary battery according to claim 1, wherein the organic solvent comprises a mixture of two or more solvents selected from the group consisting of cyclic carbonate solvents, linear carbonate solvents, and linear ester solvents.

9. 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; The nonaqueous electrolyte solution according to any one of claims 1 to 8, A lithium secondary battery comprising:

10. The lithium secondary battery according to claim 9 , wherein the positive electrode active material comprises a lithium composite transition metal oxide represented by the following Chemical Formula 2: [Chemical formula 2] Li １＋ｘ (N ａ Co ｂ Mn ｃ M ｄ )O ２ In the above Chemical Formula 2, 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, -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.

11. 11. The lithium secondary battery of claim 10, wherein a, b, c, and d in Chemical Formula 2 satisfy the following conditions: 0.70≦a<1, 0<b≦0.2, 0<c≦0.2, and 0≦d≦0.1, respectively.

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