Non-aqueous electrolyte for lithium secondary batteries and lithium secondary batteries 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 priority rights under Korean Patent Application No. 10-2022-0098826 dated August 8, 2022, and Korean Patent Application No. 10-2023-0090520 dated July 12, 2023, all of which are incorporated herein by reference.

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

[0003] Lithium secondary batteries are generally manufactured by forming an electrode assembly with a separator in between a positive electrode containing a positive electrode active material made of a transition metal oxide containing lithium and a negative electrode containing a negative electrode active material capable of storing lithium ions, inserting the electrode assembly into a battery case, injecting a non-aqueous electrolyte that acts as a medium for transferring lithium ions, and then sealing it.

[0004] Lithium-ion batteries are miniaturized, have high energy density and operating voltage, and are therefore used in a wide range of fields, including mobile devices, electronic products, and electric vehicles. As the application fields of lithium-ion batteries diversify, the required physical properties are also becoming increasingly stringent. Specifically, there is a need to develop lithium-ion batteries that can operate stably even under high-temperature conditions and have long lifespan characteristics.

[0005] On the other hand, when lithium secondary batteries are operated under high-temperature conditions, lithium salts such as LiPF6 contained in the electrolyte may cause PF6 to be released. -The decomposition reaction of anions becomes intense, which may generate Lewis acids such as PF5, and these react with moisture to produce HF. Decomposition products such as PF5 and HF not only may damage the coating formed on the surface of an electrode, but also may trigger the decomposition reaction of an organic solvent. In addition, they may react with decomposition products of a positive electrode active material to elute transition metal ions, and the eluted transition metal ions are electrodeposited on a negative electrode, which may damage the coating formed on the surface of the negative electrode.

[0006] If the decomposition reaction of the electrolyte continues on the coating damaged as described above, the performance of the battery further decreases, and therefore development of a secondary battery that can maintain excellent performance even under high temperature conditions has been demanded. Summary of the Invention Problems to be Solved by the Invention

[0007] The present invention has been made to solve the problems described above, and an object of the present invention is to provide a non-aqueous electrolyte that contributes to forming an enhanced coating 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] [Chemical Formula]

[0010] In 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 an integer of any one of 1 to 5, q is an integer of any one of 0 to 5-p, r is an integer of any one of 0 to 4, m is one integer between 1 and 5-r.

[0011] According to another embodiment, the present invention provides a lithium secondary battery comprising 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 for a lithium secondary battery. [Effects of the Invention]

[0012] The non-aqueous electrolyte according to the present invention contains a pyridine compound substituted with halobenzene, which has the effect of forming a thin yet strong film on the electrode. Therefore, it is possible to provide a lithium secondary battery with improved electrochemical properties even under high-temperature storage conditions. [Modes for carrying out the invention]

[0013] The present invention will be described in more detail below.

[0014] Generally, anions contained in lithium salts such as LiPF6, which are widely used in electrolytes for lithium secondary batteries, decompose through thermal decomposition or by moisture, forming decomposition products such as hydrogen fluoride (HF) and PF5. These decomposition products have acidic properties and degrade the coating or electrode surface within the battery.

[0015] Due to the decomposition products of the electrolyte and structural changes in the positive electrode caused by repeated charging and discharging, transition metals in the positive electrode are easily dissolved into the electrolyte. These dissolved transition metals then re-deposition onto the positive electrode, increasing its resistance. Furthermore, if the dissolved transition metals move to the negative electrode through the electrolyte, they are electrodeposited onto the negative electrode, causing the destruction of the SEI (solid electrolyte interphase) film and further electrolyte decomposition reactions. This leads to problems such as increased lithium ion consumption and resistance.

[0016] Furthermore, during the initial activation of the battery, a protective film is formed on the positive and negative electrodes by an electrolyte reaction. However, if this film becomes unstable for the reasons mentioned above, further decomposition of the electrolyte occurs during charging, discharging, or exposure to high temperatures, accelerating battery degradation and generating gas.

[0017] To solve these problems, the present inventors have found that by including a compound represented by the following chemical formula 1 in a non-aqueous electrolyte, the decomposition reaction of the electrolyte can be reduced, and the elution of transition metals and the generation of gases can be suppressed. Specifically, since the compound represented by chemical formula 1 contains a pyridine group, it decomposes rapidly at the negative electrode and forms 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 halobenzene, specifically fluorobenzene, it is possible to form a LiF film by providing the F component, which has the effect of suppressing the deterioration of the negative electrode when the battery is running, and ultimately has the effect of lowering the amount of gas generated and the rate of resistance increase under high-temperature storage conditions.

[0018] On the other hand, when silicon-based materials are used as the negative electrode active material, there is a problem that the electron conductivity is low and it is difficult to form a coating. However, the compound represented by chemical formula 1 can react quickly, thus compensating for this problem. Furthermore, when high-nickel (High-Ni) active materials are introduced as the positive electrode active material, structural instability can increase side reactions and gas generation, potentially worsening the battery life. However, the compound represented by chemical formula 1 has an excellent effect in improving the coating properties of the electrode, thus solving the problems caused by applying such high-nickel positive electrode active materials.

[0019] The following describes in more detail each component of the present invention.

[0020] [Nonaqueous electrolyte] The present invention provides a non-aqueous electrolyte for lithium secondary batteries, comprising a lithium salt, an organic solvent, and a compound represented by chemical formula 1.

[0021] The following provides a detailed explanation of each component.

[0022] (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.

[0023] [ka]

[0024] In the aforementioned chemical formula 1, R1 is a halogen group, R2 and R3 are each independently alkyl groups having 1 to 10 carbon atoms. p is one integer between 1 and 5. q is one integer between 0 and 5-p, r is one integer between 0 and 4. m is one integer between 1 and 5-r.

[0025] In one embodiment of the present invention, R1 in the chemical formula 1 may be fluorine. In this case, the elimination of F has the effect of forming a LiF component film on the negative electrode.

[0026] On the other hand, R2 and R3 are hydrogen or an alkyl group having 1 to 5 carbon atoms, preferably hydrogen or an alkyl group having 1 to 3 carbon atoms, and 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 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. When halobenzene is substituted at the 4th position of the pyridine ring, i.e., the para position with the nitrogen atom, it is preferable because it does not generate a steric hindrance on the N portion of pyridine, and therefore reacts easily with the negative electrode.

[0030] [ka]

[0031] In the above chemical formula 1-1, R1-R3, p, q, and r are defined as shown in Chemical Formula 1.

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

[0033] [ka]

[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% to 5% by weight, preferably 0.1% to 1% by weight, and more preferably 0.1% 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-mentioned effects can be fully realized. When it is 5% by weight or less, it is preferable in that it prevents a decrease in ionic conductivity due to an increase in the viscosity of the electrolyte.

[0038] (2) Additives The non-aqueous electrolyte of the present invention may optionally contain the following additives to prevent the electrolyte from decomposing in a high-voltage environment, which can lead to electrode collapse, or to further improve low-temperature high-rate discharge characteristics, high-temperature stability, overcharge prevention, and suppression of battery swelling at high temperatures.

[0039] The additive may be 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 one or more selected from the group consisting of vinylene carbonate (VC), vinylethylene carbonate (VEC), and fluoroethylene carbonate (FEC), and may specifically be vinylene carbonate.

[0041] The sultone compound is a substance capable of forming a stable SEI film on the surface of the negative electrode by a reduction reaction, and may be one or more compounds selected from the group consisting of 1,3-propanesultone (PS), 1,4-butanesultone, ethensultone, 1,3-propensultone (PRS), 1,4-butensultone, and 1-methyl-1,3-propensultone, and may specifically be 1,3-propanesultone (PS).

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

[0043] The phosphorus-based compound is a phosphate or phosphite compound, and may be 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 compound may be one or more selected from the group consisting of succinonitrile (SN), adiponitrile (ADN), acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentanecarbonile, cyclohexanecarbonile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, 4-fluorophenylacetonitrile, ethylene glycol bis(2-cyanoethyl) ether (ASA3), 1,3,6-hexanetricarbonile (HTCN), 1,4-dicyano2-butene (DCB), and 1,2,3-tris(2-cyanoethyl)propane (TCEP).

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

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

[0047] The lithium salt compound is a compound different from the lithium salt contained in the non-aqueous electrolyte, and may be 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 one embodiment of the present invention may further contain one or more additives selected from the group consisting of vinylene carbonate (VC), 1,3-propanesultone (PS), ethylene sulfate (ESa), and lithium difluorophosphate (LiDFP). In this case, there is the advantage that the negative electrode coating can be strengthened and the resistance can be further improved.

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

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

[0051] The organic solvent can be any organic solvent commonly used with lithium electrolytes. 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, it includes a mixture of two or more solvents selected from a cyclic carbonate solvent, a linear carbonate solvent, and a linear ester solvent, and more preferably, it may include a mixture of a cyclic carbonate solvent and a linear carbonate solvent.

[0052] The cyclic carbonate solvent is a highly viscous organic solvent with a high dielectric constant that readily dissociates lithium salts in the electrolyte, and may be 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 containing ethylene carbonate (EC) or propylene carbonate (PC).

[0053] Furthermore, the linear carbonate solvent is an organic solvent having low viscosity and low dielectric constant, and may be one or more selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethyl methyl carbonate (EMC), methyl propyl carbonate, and ethyl propyl carbonate, and preferably may contain ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), or diethyl carbonate (DEC).

[0054] In order to produce an electrolyte with high ionic conductivity, it is preferable to use a mixture of a cyclic carbonate solvent and a linear carbonate solvent as the organic solvent.

[0055] The linear ester solvent may be one or more selected from the group consisting of 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 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 is preferably succinonitrile.

[0058] Based on the total weight of the non-aqueous electrolyte, the remainder after excluding the contents of other constituent components other than the organic solvent, for example, the compound represented by Chemical Formula 1, additives, and the lithium salt, is all an organic solvent, unless otherwise stated.

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

[0060] The lithium salt is not limited to those commonly used in electrolytes for lithium secondary batteries, and can be used without limitation. Specifically, the lithium salt contains Li as a cation + and contains, as anions, 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 - It may include one or more of the following:

[0061] Specifically, the lithium salt may be 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 fluoromalonato(difluoro)borate (LiFMDFB), and preferably 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 power output and cycle characteristics are sufficiently ensured, while preventing excessively high viscosity and surface tension, and obtaining appropriate electrolyte impregnation.

[0063] [Lithium-ion 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 comprises 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, wherein the non-aqueous electrolyte is the non-aqueous electrolyte according to the present invention described above. As the non-aqueous electrolyte is as described above, its explanation 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 the positive electrode active material, a binder, a conductive material, and a solvent onto 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 is conductive. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with a surface treatment of 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 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 have a molar ratio of nickel in the transition metal of 70 mol% or more, preferably 80 mol% or more, and more preferably 90 mol% or more. That is, even in a battery containing an ultra-high nickel 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 aforementioned chemical formula 2, M is one or more 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. 1+x, a, b, c, and d are the 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、a+b+c+d=1である。

[0072] Said 1+x represents the molar ratio of lithium in the lithium composite transition metal oxide, and may satisfy -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] Said a represents the molar ratio of nickel in all metals excluding lithium in the lithium composite transition metal oxide, and may satisfy 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, high energy density can be exhibited and high capacity can be achieved.

[0074] Said b represents the molar ratio of cobalt in all metals excluding lithium in the lithium composite transition metal oxide, and may satisfy 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 achieved.

[0075] Said c represents the molar ratio of manganese in all metals excluding lithium in the lithium composite transition metal oxide, and may satisfy 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, the positive electrode active material has excellent structural stability.

[0076] In one embodiment of the present invention, the lithium composite transition metal oxide may comprise 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 comprise Al as the doping element. In other words, said d, which represents the molar ratio of the doping element in all metals excluding lithium in the lithium composite transition metal oxide, may satisfy 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 the Chemical Formula 2 respectively satisfy 0.70≦a<1, 0<b≦0.2, 0<c≦0.2, 0≦d≦0.1, and more preferably may satisfy 0.80≦a≦1, 0<b≦0.15, 0<c≦0.15, 0≦d≦0.05.

[0078] The positive electrode active material may be included 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 solid contents in the positive electrode slurry. Here, when the content of the positive electrode active material is 80% by weight or less, there is a risk that energy density becomes low and capacity decreases.

[0079] The binder is a component that assists the binding between an active material and a conductive material, as well as binding to a current collector, and may generally be added in an amount of 1% by weight to 30% by weight based on the total weight of solid contents in the positive electrode slurry. Examples of such a binder may include 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, fluororubber, or various copolymers thereof.

[0080] Further, the conductive material is a substance that imparts conductivity without causing any chemical change to the battery, and may be added in an amount of 0.5% by weight to 20% by weight based on the total weight of solid contents in the positive electrode slurry.

[0081] The conductive material may be selected from, 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 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] Furthermore, 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 results in a suitable viscosity when the positive electrode active material, binder, and conductive material are included. For example, the concentration of solids in the positive electrode slurry containing the positive electrode active material, binder, and conductive material may 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, and solvent onto 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 chemical changes in the battery and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface treatment with carbon, nickel, titanium, silver, etc., or aluminum-cadmium alloy may be used. Also, similar to the positive electrode current collector, the bonding 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 film, sheet, foil, mesh, porous material, foam, nonwoven fabric.

[0085] In one embodiment of the present invention, the negative electrode active material may include a silicon-based material, and the silicon-based material is Si, SiO x (0 < x < 2) and Si-Y alloy (said 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 is one or more selected from the group consisting of the above, and is preferably SiO.

[0086] The capacity of silicon-based negative electrode active materials is nearly about 10 times higher than that of graphite, so that the mass loading (mg·cm -2 ) can be lowered, and the rapid charging performance of the battery can be improved. However, a negative electrode containing a silicon-based negative electrode active material has lower electrical conductivity than a graphite negative electrode, and has the disadvantage that it is difficult to form a coating film on the negative electrode. Since the non-aqueous electrolyte according to the present invention contains the compound represented by Chemical Formula 1, it is rapidly decomposed at the negative electrode due to the pyridine structure, and forms a thin and strong SEI film on the negative electrode, thereby effectively compensating for the above-mentioned disadvantages.

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

[0088] In addition, besides the silicon-based material, the negative electrode active material may include one or more selected from the group consisting of: 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 undoping lithium; lithium metal; and transition metal oxides.

[0089] The carbon-based material capable of reversibly intercalating / deintercalating lithium ions is not particularly limited as long as it is a carbon-based negative electrode active material generally used in lithium ion secondary batteries, and can be used without particular restrictions. Representative examples thereof include crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon include graphite such as amorphous, plate-like, flake, 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] As the metal composite oxide, 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, and Group 3 of the periodic table, halogens; 0<x≦1; 1≦y≦3; 1≦z≦8), any one or more selected from the group consisting of the above can be used.

[0092] Examples of the material capable of doping and undoping lithium include Sn, SnO₂, Sn-Y (wherein 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 Y is not Sn), and the like, and a mixture of at least one of these materials and SiO₂ may also be used.

[0093] In the Si-Y and Sn-Y described above, 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 aforementioned transition metal oxides include lithium-containing titanium composite oxide (LTO), vanadium oxide, and lithium vanadium oxide.

[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 a mixture of graphite and SiO.

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

[0097] The binder is a component that assists in bonding 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 solids in the negative electrode slurry. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, 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% to 20% by weight based on the total weight of the solid content in the negative electrode slurry. The conductive material is not particularly limited as long as it does not cause a chemical change in the battery and is conductive, and may be selected from, 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 nanotubes, and graphite; conductive fibers such as carbon fibers and metal fibers; conductive powders such as fluorinated carbon powder, aluminum powder, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[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 results in a suitable viscosity when the negative electrode active material, binder, and conductive material are included. For example, the solid content in the slurry containing the negative electrode active material, binder, and conductive material may be 30% to 80% by weight, preferably 40% 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 passage for lithium ions to move. Any separator commonly used in lithium secondary batteries is acceptable and not particularly limited. Preferably, the separator has low resistance to ion movement in the electrolyte and possesses excellent electrolyte impregnation ability and safety.

[0102] Specifically, as separators, porous polymer films, such as porous polymer films made from polyolefin polymers like ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or laminated structures of two or more layers thereof can be used. Alternatively, ordinary porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, may be used. Furthermore, coated separators containing ceramic components or polymeric substances may be used to ensure heat resistance or mechanical strength, and may be used as single-layer or multi-layer structures.

[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 computers, and digital cameras; and in the field of electric vehicles such as hybrid electric vehicles (HEVs).

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

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

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

[0108] The present invention will be specifically described below with reference to concrete examples.

[0109] <Example: Manufacturing of lithium secondary batteries> Example 1. 1) Production of non-aqueous electrolyte Ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed in a volume ratio of 30:70, and then dissolved to a concentration of 1 M LiPF6 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 remainder of the non-aqueous organic solution were mixed to produce a 100 wt% non-aqueous electrolyte.

[0110] 2) Manufacturing of lithium secondary batteries N-methyl-2-pyrrolidone (NMP) is used as the positive electrode active material, with Li(Ni 0.9 Mn 0.03 Co 0.06 Al 0.01 A positive electrode slurry (solid content: 60% by weight) was prepared by adding O2, a conductive material (carbon black), and a binder (polyvinylidene fluoride) in a weight ratio of 97.6:0.8:1.6. The positive electrode slurry was applied to an aluminum (Al) thin film, which was a positive electrode current collector with a thickness of 13.5 μm, and dried, after which the positive electrode was manufactured by roll pressing.

[0111] A negative electrode slurry (solid content: 60% by weight) was prepared by adding a negative electrode active material (graphite: SiO = 90.0:10.0 by weight), a binder (SBR-CMC), and a conductive material (carbon black) in a weight ratio of 97.6:0.8:1.6 to water, which was used as a solvent. The negative electrode slurry was then applied to a 6 μm thick copper (Cu) thin film, which was a negative electrode current collector, and dried. The negative electrode was then manufactured by roll pressing. An electrode assembly was manufactured by sequentially stacking the positive electrode, a polyolefin-based porous separator coated with inorganic particles (Al2O3), and the negative electrode.

[0112] A lithium secondary battery was manufactured by housing the assembled electrode assembly inside a cylindrical battery case and pouring the manufactured non-aqueous electrolyte into it.

[0113] 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 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 manufactured 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 manufactured 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 manufactured 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 the 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 a compound represented by the following chemical formula Z1 was used instead of the compound represented by the above chemical formula 1A during the production of the non-aqueous electrolyte.

[0120] [ka]

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

[0122] [ka]

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

[0124] [ka]

[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 above chemical formula 1A during the production of the non-aqueous electrolyte.

[0126] [ka]

[0127] <Experimental Example: Evaluation of Battery Performance> Experimental Example 1. Initial Resistance Measurement After performing a formation process on the lithium secondary batteries manufactured in the above examples and comparative examples, they were charged at 25°C at a rate of 0.33C to 4.2V using constant current / constant voltage (CC / CV) charging (0.05C cutoff), and then discharged at a rate of 0.33C to 2.80V using constant current (CC). The initial resistance was then measured. The results are shown in Table 1 below.

[0128] Experimental Example 2. Measurement of Resistivity Increase Rate After High-Temperature Storage Each battery, after the initial evaluation in Experimental Example 1, was fully charged to 100% SOC under identical conditions and stored at a high temperature (60°C) for 4 weeks. After that, it was transferred to a charger / discharger at room temperature (25°C), and its resistance was measured again. The resistance increase rate was calculated using Equation 1 below, and the results are shown in Table 1 below.

[0129] Equation 1: Resistance increase rate (%) = {(Resistance after high-temperature storage - Initial resistance) / Initial resistance} × 100

[0130] Experimental Example 3. Measurement of gas generation after high-temperature storage. After performing a formation process on the lithium secondary batteries manufactured in the above examples and comparative examples, they were charged at 25°C at a rate of 0.33C to 4.2V under constant current / constant voltage conditions (0.05C cutoff) until fully charged to 100% of the State of Charge (SOC). After storing the fully charged batteries at 60°C for 4 weeks, the amount of gas generated was measured at room temperature (25°C) using the buoyancy measurement method. The relative amount of gas generated for each battery was calculated and is shown in Table 1 below, with the amount of gas generated in Comparative Example 1 set to 100%.

[0131] [Table 1]

[0132] The results in Table 1 confirm that a non-aqueous electrolyte containing the compound represented by chemical formula 1 is effective in improving the resistance increase rate and gas generation amount after high-temperature storage.

[0133] Specifically, the batteries of Examples 1 to 6 were found to be superior in terms of resistance increase rate and gas generation amount after high-temperature storage compared to Comparative Example 2, which used a compound represented by chemical formula Z1 in which pyridine was substituted for fluorobenzene; Comparative Example 3, which used a compound represented by chemical formula Z2 in which unsubstituted benzene was substituted for fluorobenzene; Comparative Example 4, which used a compound represented by chemical formula Z3 which is fluorobenzene; and Comparative Example 4, which used a compound represented by chemical formula Z4 which is fluoropyridine. In particular, Comparative Examples 2 and 3, because they used compounds that did not contain F, were unable to form LiF at the negative electrode, and it was found that their resistance increase rate after high-temperature storage was not as good as that of Comparative Example 1.

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

Claims

1. A positive electrode comprising 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 a non-aqueous electrolyte for lithium secondary batteries, The aforementioned non-aqueous electrolyte for lithium secondary batteries is It comprises a lithium salt, an organic solvent, and a compound represented by the following chemical formula 1. The content of the compound represented by the chemical formula 1 is 0.1% to 1% by weight, based on the total weight of the non-aqueous electrolyte. The aforementioned negative electrode active material includes a silicon-based material in a lithium secondary battery. 【Chemistry 1】 (In the above chemical formula 1, R1 is a halogen group, R2 and R3 are each independently alkyl groups having 1 to 10 carbon atoms. p is one integer between 1 and 5. q is one integer between 0 and 5-p, r is one integer between 0 and 4. m is one integer between 1 and 5 - r.

2. The lithium secondary battery according to claim 1, wherein R1 is fluorine.

3. The lithium secondary battery according to claim 1, wherein q and r are each 0.

4. The lithium secondary battery according to claim 1, wherein the compound represented by the aforementioned chemical formula 1 is represented by the following chemical formula 1-1. 【Chemistry 2】 (In the above chemical formula 1-1, R1 to R3, p, q, and r are as defined in Chemical Formula 1.

5. The lithium secondary battery according to claim 1, wherein the non-aqueous electrolyte for the lithium secondary battery further comprises one or more additives selected from the group consisting of vinylene carbonate, 1,3-propanesultone, ethylene sulfate, and lithium difluorophosphate.

6. The lithium secondary battery according to claim 1, wherein the organic solvent comprises a mixture of a cyclic carbonate solvent and a linear carbonate solvent.

7. The lithium secondary battery according to claim 1, 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 (N ａ Co ｂ Mn ｃ M ｄ )O ２ (In the above chemical formula 2, M is 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, (-0.2 ≤ x ≤ 0.2, 0.6 ≤ a < 1, 0 < b ≤ 0.3, 0 < c ≤ 0.3, 0 ≤ d ≤ 0.1, a + b + c + d = 1.)

8. The lithium secondary battery according to claim 7, 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.

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