Non-aqueous electrolyte solutions for lithium secondary batteries and lithium secondary batteries including such solutions.

Abstract

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

Description

Technical Field

[0001] This patent application claims priority to Korean Patent Application No. 10-2021-0034084, filed on March 16, 2021, the disclosure of which is incorporated herein by reference.

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

[0003] Lithium-ion batteries are typically manufactured as follows: an electrode assembly is formed by placing a separator between a positive electrode containing a positive electrode active material made of a lithium-containing transition metal oxide and a negative electrode containing a negative electrode active material capable of storing lithium ions. The electrode assembly is then inserted into a battery case, into which a non-aqueous electrolyte solution is injected as a medium for transferring the lithium ions, and the battery case is then sealed.

[0004] Because lithium-ion batteries can be miniaturized and possess high energy density and operating voltage, they are being used in various fields, including mobile devices, electronic products, and electric vehicles. As the applications of lithium-ion batteries become more diverse, the requirements for their physical properties are also increasing, particularly the need to develop lithium-ion batteries that can operate stably even under high-temperature conditions.

[0005] When lithium-ion batteries are driven at high temperatures, PF6 - Anions can be thermally decomposed from lithium salts (e.g., LiPF6) contained in the electrolyte solution, producing Lewis acids (e.g., PF5), which can then react with water to produce HF. Decomposition products such as PF5 and HF can damage the film formed on the electrode surface and may trigger the decomposition of organic solvents. Furthermore, the decomposition products can react with the decomposition products of the positive electrode active material to dissolve transition metal ions, which can then electrodeposit on the negative electrode, thereby damaging the film formed on the negative electrode surface.

[0006] Since the performance of the battery is further degraded when the electrolyte decomposition reaction continues on the damaged membrane as described above, there is a need to develop secondary batteries that can maintain excellent performance even under high temperature conditions. Summary of the Invention

[0007] Technical issues

[0008] One aspect of the present invention provides a non-aqueous electrolyte solution that facilitates the formation of a positive electrode film by including sulfonylpyridine additives and a lithium secondary battery including the non-aqueous electrolyte solution.

[0009] Technical solution

[0010] According to an aspect of the present invention, a non-aqueous electrolyte solution for lithium secondary batteries is provided, comprising: a lithium salt; an organic solvent; and an additive comprising a compound represented by Formula 1.

[0011] [Formula 1]

[0012]

[0013] In Equation 1,

[0014] R1 is fluorine; or substituted with an alkyl group having 1 to 10 carbon atoms having at least one fluorine molecule.

[0015] R2 is an alkyl group having 1 to 10 carbon atoms, and

[0016] m is an integer from 0 to 4.

[0017] According to another aspect of the present invention, a lithium secondary battery is provided, comprising: a positive electrode comprising a positive electrode active material; a negative electrode comprising a negative electrode active material; a separator disposed between the positive electrode and the negative electrode; and the above-described non-aqueous electrolyte solution for the lithium secondary battery.

[0018] Beneficial effects

[0019] One aspect of the present invention provides a non-aqueous electrolyte solution for lithium secondary batteries, which can suppress the decomposition reaction of the electrolyte solution and reduce the dissolution of the positive electrode by forming a robust film on the surface of the positive electrode.

[0020] In addition, the present invention provides a lithium secondary battery that improves the high-temperature storage characteristics and lifespan characteristics of the battery by including the above-mentioned non-aqueous electrolyte solution for lithium secondary batteries. Detailed Implementation

[0021] The invention will be described in more detail below.

[0022] Typically, the anions contained in lithium salts such as LiPF6, which are widely used in electrolyte solutions for lithium secondary batteries, form decomposition products such as hydrogen fluoride (HF) and PF5 due to thermal decomposition or moisture. These decomposition products are acidic and degrade the membranes or electrode surfaces in the battery.

[0023] Transition metals in the positive electrode are easily leached into the electrolyte solution due to decomposition products and structural changes during repeated charging and discharging. These leached transition metals then redeposit on the positive electrode, increasing its resistance. Furthermore, when leached transition metals migrate through the electrolyte solution to the negative electrode, they electrodeposit there, disrupting the solid electrolyte interface (SEI) and triggering additional electrolyte decomposition reactions. This results in problems such as lithium-ion depletion and increased resistance.

[0024] In addition, during the initial activation of the battery, a protective film is formed on the positive and negative electrodes through the reaction of the electrolyte solution. If the film becomes unstable due to the above reasons, additional decomposition of the electrolyte solution occurs during charge-discharge or high-temperature exposure, thereby accelerating the degradation of the battery and generating gas.

[0025] To address this problem, the inventors of this invention used sulfonylpyridine compounds represented by Formula 1 as additives for non-aqueous electrolyte solutions, and it has been found that, due to these additives, the decomposition reaction of the electrolyte solution can be reduced, the dissolution of transition metals can be suppressed, and gas generation can be inhibited. Furthermore, the inventors have confirmed the effectiveness of forming a protective film on the electrodes at the positive / negative electrodes through sulfur (S)-based and fluorine (F)-based components.

[0026] Specifically, compared to lithium secondary batteries using an electrolyte solution containing LiPF6 as described above, the problem lies in battery degradation due to HF, a decomposition product of LiPF6. This degradation occurs because the pyridine group included in the compound represented by Formula 1 acts as a Lewis base, thus stabilizing PF5, which is a Lewis acid and intermediate derivative, before HF generation. In particular, the pyridine group is effective in reducing HF generation because it has a higher binding energy to PF5 compared to other nitrogen-containing (N) structures such as imidazole groups.

[0027] Furthermore, the -SO2-R1 functional group included in the compound represented by Formula 1 decomposes at the positive / negative electrodes to form a film on the electrodes, which helps to form a stable interface between the electrodes and the electrolyte solution. When the fluorine-containing R1 is substituted on the pyridine group instead of the sulfonyl group, the following problem can occur: during redox decomposition, the structure of the pyridine group is destroyed due to the action of R1; however, when R1 is substituted on the sulfonyl group as in this invention, since it does not affect the structure of the pyridine group, the film can be formed more smoothly. Additionally, the -SO2-R1 functional group of Formula 1 of this invention is advantageous because, compared to -SO3, it can also include fluorine as a functional group that contributes to the film composition, and since the -SO2-R1 functional group includes F instead of O, a LiF component can be included in the film, thus making it more advantageous to form a film with improved thermal stability and high voltage characteristics.

[0028] The various components constituting the present invention will be described in more detail below.

[0029] Non-aqueous electrolyte solution

[0030] (1) Additives

[0031] The non-aqueous electrolyte solution of the present invention includes an additive comprising a compound represented by Formula 1 below.

[0032] [Formula 1]

[0033]

[0034] In Equation 1,

[0035] R1 is fluorine, or an alkyl group having 1 to 10 carbon atoms that has at least one fluorine substituted.

[0036] R2 is an alkyl group having 1 to 10 carbon atoms, and

[0037] m is an integer from 0 to 4.

[0038] In one embodiment of the present invention, the compound represented by Formula 1 can be represented by Formula 1-1.

[0039] [Equation 1-1]

[0040]

[0041] In Equation 1-1,

[0042] R1, R2 and m are as defined in Equation 1.

[0043] In one embodiment of the invention, R1 can be an alkyl group having 1 to 5 carbon atoms substituted with at least one fluorine, particularly a methyl group substituted with at least one fluorine, and more particularly a difluoromethyl group. As the amount of substituted fluorine increases, a larger amount of LiF can be produced to enhance the film, but in the case of excessive fluorine substitution, the resistance can increase considerably. That is, considering the amount of LiF formed on the surfaces of the positive / negative electrodes, a difluoromethyl group is most preferred.

[0044] In one embodiment of the present invention, R2 may be a straight-chain or branched alkyl group having 1 to 5 carbon atoms.

[0045] In one embodiment of the present invention, m can be 0 or 1, for example, 0.

[0046] In one embodiment of the present invention, the compound represented by Formula 1 can be represented by Formula 1a.

[0047] [Equation 1a]

[0048]

[0049] In embodiments of the present invention, the amount of the compound represented by Formula 1 may be from 0.1% to 5% by weight, preferably from 0.1% to 3% by weight, and more preferably from 0.5% to 1% by weight, based on the total weight of the non-aqueous electrolyte solution.

[0050] When the amount of the compound represented by Formula 1 is within the above range, the effect of improving performance can be obtained by forming appropriate levels of positive / negative films.

[0051] Specifically, when the amount of the compound represented by Formula 1 is less than 0.1% by weight, the amount is too small to form a sufficient film on the positive / negative electrode, and when the amount of the compound represented by Formula 1 is greater than 5% by weight, the resistance increases due to the excessive increase in the amount of the compound represented by Formula 1, and thus the battery performance can be significantly degraded.

[0052] To prevent the electrolyte solution from decomposing under high voltage conditions, thereby causing electrode collapse, or to further improve the low-temperature high-rate discharge characteristics, high-temperature stability, overcharge protection, and high-temperature battery expansion suppression effect, the non-aqueous electrolyte solution of the present invention may optionally include the following other additives when necessary.

[0053] Other additives may be selected from at least one of cyclic carbonate compounds, halogen-substituted carbonate compounds, sulcinolone compounds, sulfate / ester compounds, phosphate / ester or phosphite / ester compounds, borates / ester compounds, nitriles, amines, silanes, benzenes, and lithiums.

[0054] The cyclic carbonate compound may be at least one selected from vinylene carbonate (VC) and vinyl ethylene carbonate (VEC), and specifically may be vinylene carbonate.

[0055] Halogen-substituted carbonate compounds can be fluoroethylene carbonate (FEC).

[0056] Sulfolactone compounds are materials capable of forming a stable SEI through a reduction reaction on the negative electrode surface. The sulfolactone compound can be at least one compound selected from 1,3-propanesulfonolactone (PS), 1,4-butanesulfonolactone, ethanesulfonolactone, 1,3-propenesulfonolactone (PRS), 1,4-butenesulfonolactone, and 1-methyl-1,3-propenesulfonolactone, and can be specifically 1,3-propanesulfonolactone (PS).

[0057] Sulfate / ester compounds are materials that can be electrolyzed on the surface of the negative electrode to form a stable SEI that will not crack even during high-temperature storage. The sulfate / ester compound may be at least one selected from ethylene sulfate (Esa), trimethylene sulfate (TMS), or methyltrimethylene sulfate (MTMS).

[0058] The phosphate / ester or phosphite / ester compound may be at least one selected from lithium difluoro(bis(oxalate)phosphate), lithium difluorophosphate, tris(trimethylsilyl)phosphate, tris(trimethylsilyl)phosphite, tris(2,2,2-trifluoroethyl)phosphate and tris(trifluoroethyl)phosphite.

[0059] The borate / ester compound can be lithium tetraphenylborate.

[0060] Nitrile compounds may be selected from at least one of succinate (SN), adiponitrile (ADN), acetonitrile, propionitrile, butyronitrile, valerate, octanoic acid, heptanonitrile, cyclovalerate, cyclohexanoic acid, 2-fluorobenzyl nitrile, 4-fluorobenzyl nitrile, difluorobenzyl nitrile, trifluorobenzyl nitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, 4-fluorophenylacetonitrile, ethylene glycol bis(2-cyanoethyl) ether (ASA3), 1,3,6-hexamethylenetrionitrile (HTCN), 1,4-dicyano-2-butene (DCB), and 1,2,3-tris(2-cyanoethyl)propane (TCEP).

[0061] The amine compound may be at least one selected from triethanolamine and ethylenediamine, and the silane compound may be tetraethylenesilane.

[0062] Benzene compounds can be at least one selected from monofluorobenzene, difluorobenzene, trifluorobenzene, and tetrafluorobenzene.

[0063] Lithium salt compounds are compounds that are different from the lithium salts included in the electrolyte solution. The lithium salt compounds can be at least one compound selected from lithium difluorophosphate (LiDFP; LiPO2F2), lithium bis(oxalate)borate (LiBOB; LiB(C2O4)2), lithium tetrafluoroborate (LiBF4), and lithium difluorobis(oxalate)phosphate (LiDFOP).

[0064] Preferably, the additives in the non-aqueous electrolyte solution of the embodiments of the present invention may further include at least one selected from vinylene carbonate (VC), vinyl ethylene carbonate (VEC), fluoroethylene carbonate (FEC), 1,3-propane sulpholol (PS), 1,3-propene sulpholol (PRS), ethylene sulfate (ESa), succinate (SN), adiponitrile (ADN), ethylene glycol bis(2-cyanoethyl) ether (ASA3), 1,3,6-hexamethylenetrionitrile (HTCN), 1,4-dicyano-2-butene (DCB), 1,2,3-tris(2-cyanoethyl)propane (TCEP), lithium difluoro(oxalate)borate (LiODFB), lithium tetrafluoroborate (LiBF4), lithium difluoro(oxalate)phosphate (LiDFOP), and lithium difluorophosphate (LiDFP) as other additives.

[0065] More preferably, the additives in the non-aqueous electrolyte solution of embodiments of the present invention may further include at least one selected from vinylene carbonate (VC), 1,3-propanesulfonyl lactone (PS), ethylene sulfate (ESa), and lithium difluorophosphate (LiDFP) as other additives. In this case, since a polymer film can be formed together with the positive / negative electrode film components, which are mainly formed by the compounds represented by Formula 1, the effect of further improving high-temperature performance is achieved.

[0066] Based on the total weight of the non-aqueous electrolyte solution, the amount of other additives can be from 0.1 wt% to 10 wt%, for example, from 0.3 wt% to 5 wt%. When the amount of other additives is less than 0.1 wt%, there is little improvement in high-temperature capacity and gas generation due to the limited effect of forming an additional stabilizing film. Furthermore, when the amount of other additives is greater than 10 wt%, there is a possibility of excessive side reactions occurring in the electrolyte solution during battery charging and discharging. In particular, when an excessive amount of SEI-forming additives is added, the SEI-forming additives cannot decompose sufficiently at high temperatures; therefore, at room temperature, the additives may exist as unreacted material or precipitate in the electrolyte solution. Accordingly, side reactions that degrade battery life or resistance characteristics may occur.

[0067] (2) Organic solvents

[0068] The non-aqueous electrolyte solution of the present invention includes an organic solvent.

[0069] Various organic solvents commonly used in lithium electrolytes can be used as organic solvents, but are not limited thereto. For example, the organic solvent can be a cyclic carbonate solvent, a linear carbonate solvent, a linear ester solvent, a cyclic ester solvent, a nitrile solvent, or a mixture thereof, and may preferably include a mixture of at least two selected from cyclic carbonate solvents, linear carbonate solvents, and linear ester solvents.

[0070] As a high-viscosity organic solvent, cyclic carbonate solvents can effectively dissociate lithium salts in electrolytes due to their high dielectric constant. The cyclic carbonate solvent can be at least one selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), 1,2-butyl carbonate, 2,3-butyl carbonate, 1,2-pentane carbonate, 2,3-pentane carbonate and vinylene carbonate, and specifically, may include ethylene carbonate (EC).

[0071] In addition, linear carbonate solvents are organic solvents with low viscosity and low dielectric constant. The linear carbonate solvent may be at least one 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 specifically include ethyl methyl carbonate (EMC).

[0072] To prepare electrolyte solutions with high ionic conductivity, it is desirable to use a mixture of cyclic carbonate solvents and linear carbonate solvents as organic solvents.

[0073] The linear ester solvent can be at least one selected from methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate and butyl propionate.

[0074] Cyclic ester solvents may be at least one selected from γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, and ε-caprolactone.

[0075] The nitrile solvent may be at least one selected from succinic anion, acetonitrile, propionitrile, butyronitrile, valerate, octanoic anion, heptanonitrile, cyclopentanoic anion, cyclohexanoic anion, 2-fluorobenzyl anion, 4-fluorobenzyl anion, difluorobenzyl anion, trifluorobenzyl anion, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile, and may preferably be succinic anion.

[0076] Unless otherwise stated, the remaining amount of the non-aqueous electrolyte solution, excluding other components such as organic solvents (e.g., the amount of additives and lithium salts), may be entirely organic solvents.

[0077] (3) Lithium salts

[0078] The non-aqueous electrolyte solution of the present invention includes lithium salt.

[0079] Any lithium salt commonly used in electrolyte solutions for lithium secondary batteries can be used as a lithium salt without limitation, and specifically, lithium salts may include Li + As a cation, and may include 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 - 、(CF 3)4 PF2 - (CF3)5PF - (CF3)6P - C4F9SO3 - CF3CF2SO3 - CF3CF2(CF3)2CO - (CF3SO2)2CH - CF3(CF2)7SO3 - and SCN - At least one of them is used as an anion.

[0080] Specifically, the lithium salt can be at least one selected from LiPF6, LiClO4, LiBF4, LiN(FSO2)2 (LiFSI), LiTFSI, lithium bis(pentafluoroethanesulfonyl)imide (LiBETI), LiSO3CF3, LiPO2F2, lithium di(oxalate)borate (LiBOB), lithium difluoro(oxalate)borate (LiFOB), lithium difluoro(bis(oxalate)phosphate) (LiDFOP), lithium tetrafluoro(oxalate)phosphate (LiTFOP), and lithium difluoromalonic acid (difluoro)borate (LiFMDFB), and preferably at least one selected from LiPF6 and LiN(FSO2)2 (LiFSI).

[0081] In one embodiment of the invention, the concentration of the lithium salt in the electrolyte solution can be from 0.5 M to 4.0 M, particularly from 0.5 M to 3.0 M, and more particularly from 0.8 M to 2.0 M. When the concentration of the lithium salt is within the above range, sufficient electrolyte solution impregnation can be obtained by preventing excessive increase in viscosity and surface tension, while adequately ensuring the effects of improving low-temperature output and improving cycle characteristics.

[0082] Lithium secondary batteries

[0083] Next, the lithium secondary battery of the present invention will be described.

[0084] The lithium secondary battery of the present invention includes: a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, a separator disposed between the positive and negative electrodes, and a non-aqueous electrolyte solution. In this case, the non-aqueous electrolyte solution is the non-aqueous electrolyte solution described above in the present invention. Since the non-aqueous electrolyte solution has been described above, its description will be omitted, and the other components will be described below.

[0085] (1) Positive electrode

[0086] The positive electrode of the present invention includes a positive electrode active material and can be prepared by coating a positive electrode current collector with a positive electrode slurry comprising the positive electrode active material, a binder, a conductive agent and a solvent, and then drying and rolling the coated positive electrode current collector.

[0087] The positive electrode current collector is not particularly restricted, as long as it is conductive and does not cause adverse chemical changes in the battery, and can be, for example, stainless steel; aluminum; nickel; titanium; sintered carbon; or aluminum or stainless steel surface-treated with one of carbon, nickel, titanium, silver, etc.

[0088] The positive electrode active material is a compound capable of reversibly inserting and deintercalating lithium. The positive electrode active material may be at least one selected from LCO (LiCoO2), LNO (LiNiO2), LMO (LiMnO2), LiMn2O4, LiCoPO4, LFP (LiFePO4), and lithium composite transition metal oxides containing nickel (Ni), cobalt (Co), and magnesium (Mn).

[0089] In one embodiment of the present invention, the lithium composite transition metal oxide may be selected from LiNiCoMnO2, LiNi 1-x-y-z Co x M 1 y M 2 z O2(M 1 and M 2 Each of the elements is independently selected from the group consisting of aluminum (Al), nickel (Ni), cobalt (Co), iron (Fe), manganese (Mn), vanadium (V), chromium (Cr), titanium (Ti), tungsten (W), tantalum (Ta), magnesium (Mg), and molybdenum (Mo), and x, y, and z are each independently the atomic fractions of the constituent elements of the oxide, wherein 0 ≤ x < 0.5, 0 ≤ y < 0.5, 0 ≤ z < 0.5 and x + y + z = 1) and at least one of the compounds represented by the following formula 2.

[0090] Specifically, the positive electrode active material may include a lithium composite transition metal oxide represented by Formula 2 below.

[0091] [Equation 2]

[0092] Li 1+x (Ni a Co b Mn c M d O2

[0093] In Equation 2,

[0094] M is tungsten (W), copper (Cu), iron (Fe), vanadium (V), chromium (Cr), titanium (Ti), zirconium (Zr), zinc (Zn), aluminum (Al), indium (In), tantalum (Ta), yttrium (Y), lanthanum (La), strontium (Sr), gallium (Ga), scandium (Sc), gadolinium (Gd), samarium (Sm), calcium (Ca), cerium (Ce), niobium (Nb), magnesium (Mg), boron (B), or molybdenum (Mo), and

[0095] 1+x, a, b, c, and d are the atomic fractions of each independent element.

[0096] Among them, -0.2 ≤ x ≤ 0.2, 0.50 ≤ a < 1, 0 < b ≤ 0.30, 0 < c ≤ 0.30, 0 ≤ d ≤ 0.10 and a + b + c + d = 1.

[0097] 1 + x represents the molar ratio of lithium. Among them, x can 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 formed stably.

[0098] a represents the molar ratio of nickel among all metals except lithium. Among them, a can satisfy 0.60 ≤ a < 1, 0.70 ≤ a < 1 or 0.80 ≤ a < 1. When the molar ratio of nickel satisfies the above range, high capacity can be achieved because high energy density can be exhibited.

[0099] b represents the molar ratio of cobalt among all metals except lithium. Among them, b can satisfy 0 < b ≤ 0.25, 0 < b ≤ 0.20 or 0 < b ≤ 0.15. When the molar ratio of cobalt satisfies the above range, good tolerance characteristics and output characteristics can be achieved.

[0100] c represents the molar ratio of manganese among all metals except lithium. Among them, c can satisfy 0 < c ≤ 0.25, 0 < c ≤ 0.20 or 0 < c ≤ 0.15. When the molar ratio of manganese satisfies the above range, the structural stability of the positive electrode active material is excellent.

[0101] d represents the molar ratio of the doping element among all metals except lithium. Among them, d can satisfy 0 < d ≤ 0.08, 0 < d ≤ 0.05 or 0 < d ≤ 0.03.

[0102] More specifically, the lithium composite transition metal oxide can be selected from Li(Ni 0.6 Mn 0.2 Co 0.2 )O2, Li(Ni 0.7 Mn 0.15 Co 0.15 )O2 and Li(Ni 0.8 Mn 0.1 Co [[ID=XXX]] 0.1 )O2.

[0103] Based on the total weight of the solids in the positive electrode slurry, the content of the positive electrode active material can be 80% to 99% by weight (for example, 90% to 99% by weight). When the amount of the positive electrode active material is less than 80% by weight, the capacity can be reduced due to the decrease in energy density.

[0104] The binder is a component that facilitates the bonding between the active material and the conductive agent, as well as the bonding with the current collector. The amount of binder added is typically from 1% to 30% by weight, based on the total weight of the solids in the positive electrode slurry. Examples of binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene-butadiene rubber, fluororubber, or various copolymers thereof.

[0105] In addition, conductive agents are materials that provide conductivity without causing adverse chemical changes in the battery, and their addition amount can be from 0.5% to 20% by weight, based on the total weight of solids in the positive electrode slurry.

[0106] Examples of conductive agents can be the following conductive materials, such as: carbon black, such as acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermally cracked carbon black; graphite powder, such as natural graphite, artificial graphite, carbon nanotubes, or graphite with well-developed crystal structures; conductive fibers, such as carbon fibers or metal fibers; conductive powders, such as fluorocarbon powders, aluminum powder, and nickel powder; conductive whiskers, such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides, such as titanium oxide; or polyphenylene derivatives.

[0107] Furthermore, the solvent for the positive electrode slurry may include organic solvents such as N-methyl-2-pyrrolidone (NMP), and may be used in an amount that yields the desired viscosity when the positive electrode active material, binder, and conductive agent are included. For example, the solvent content may be such that the concentration of solids in the positive electrode slurry including the positive electrode active material, binder, and conductive agent is 40% to 90% by weight (e.g., 50% to 80% by weight).

[0108] (2) Negative electrode

[0109] The negative electrode of the present invention comprises a negative electrode active material and can be prepared by coating a negative electrode current collector with a negative electrode slurry comprising a positive electrode active material, a binder, a conductive agent and a solvent, and then drying and rolling the coated negative electrode current collector.

[0110] The thickness of the negative electrode current collector is typically from 3 μm to 500 μm. There are no particular limitations on the negative electrode current collector, as long as it is conductive and does not cause adverse chemical changes in the battery. For example, it can be made of: copper; stainless steel; aluminum; nickel; titanium; sintered carbon; or copper or stainless steel surface-treated with one of carbon, nickel, titanium, silver, etc.; or an aluminum-cadmium alloy. Furthermore, similar to the positive electrode current collector, the negative electrode current collector can have fine surface roughness to improve the bonding strength with the negative electrode active material, and it can be used in various shapes such as films, sheets, foils, meshes, porous bodies, foams, and nonwoven fabrics.

[0111] In addition, the negative electrode active material may include at least one selected from carbon materials capable of reversibly inserting / extracting lithium ions; metals or alloys of lithium and such metals; metal composite oxides; materials that can be doped and undoped with lithium; lithium metal; and transition metal oxides.

[0112] As the carbon material capable of reversibly inserting / extracting lithium ions, carbon-based negative electrode active materials commonly used in lithium-ion secondary batteries can be used without particular limitation, and as typical examples, crystalline carbon, amorphous carbon, or both can be used. Examples of crystalline carbon can be graphites such as irregular, planar, flaky, spherical, or fibrous natural graphite or artificial graphite, and examples of amorphous carbon can be soft carbon (low-temperature sintered carbon) or hard carbon, mesophase pitch carbide, and calcined coke.

[0113] As the metal or alloy of lithium and such metal, metals selected from the group consisting of copper (Cu), nickel (Ni), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), francium (Fr), beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), silicon (Si), antimony (Sb), lead (Pb), indium (In), zinc (Zn), barium (Ba), radium (Ra), germanium (Ge), aluminum (Al), and tin (Sn), or alloys of lithium and such metals can be used.

[0114] As the metal composite oxide, at least one selected from the group consisting of 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, or Ge; Me': Al, B, phosphorus (P), Si, Group I, II, and III elements in the periodic table, or halogens; 0 < x ≤ 1; 1 ≤ y ≤ 3; 1 ≤ z ≤ 8) can be used.

[0115] Materials that can be doped and undoped with lithium may include Si, SiO x(0 < x ≤ 2), Si - Y alloy (where Y is an element selected from the group consisting of alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, transition metals, rare earth elements, and combinations thereof, and is not Si), Sn, SnO2, and Sn - Y (where Y is an element selected from the group consisting of alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, transition metals, rare earth elements, and combinations thereof, and is not Sn), and a mixture of SiO2 and at least one of them can also be used. Element Y can be selected from the group consisting of Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, hafnium (Hf), (Rf), V, Nb, Ta, (Db), Cr, Mo, W, (Sg), technetium (Tc), rhenium (Re), (Bh), Fe, Pb, ruthenium (Ru), osmium (Os), (Hs), rhodium (Rh), iridium (Ir), palladium (Pd), platinum (Pt), Cu, silver (Ag), gold (Au), Zn, cadmium (Cd), B, Al, Ga, Sn, In, Ge, P, arsenic (As), Sb, bismuth (Bi), sulfur (S), selenium (Se), tellurium (Te), polonium (Po), and combinations thereof.

[0116] Examples of transition metal oxides can be lithium - containing titanium composite oxide (LTO), vanadium oxide, and lithium vanadium oxide.

[0117] Based on the total weight of the solids in the negative electrode paste, the content of the negative electrode active material can be 80 wt% to 99 wt%.

[0118] The binder is a component that helps the binding between the conductive agent, the active material, and the current collector. Among them, based on the total weight of the solids in the negative electrode paste, the addition amount of the binder is generally 1 wt% to 30 wt%. Examples of the binder can be polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene - propylene - diene monomer, sulfonated ethylene - propylene - diene monomer, styrene - butadiene rubber, fluororubber, or various copolymers thereof.

[0119] A conductive agent is a component used to further improve the conductivity of the negative electrode active material. The amount of conductive agent added can range from 1% to 20% by weight, based on the total weight of solids in the negative electrode slurry. Any conductive agent can be used without particular limitation, as long as it is conductive and does not cause adverse chemical changes in the battery. Examples of conductive agents include: carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermally cracked carbon black; graphite powder such as natural graphite, artificial graphite, carbon nanotubes, or graphite with well-developed crystal structures; conductive fibers such as carbon fibers or metal fibers; conductive powders such as fluorocarbon powders, aluminum powder, and nickel powder; conductive whiskers such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides such as titanium oxide; or polyphenylene derivatives.

[0120] The solvent for the negative electrode slurry may include water; or organic solvents such as NMP and ethanol, and may be used in an amount that yields the desired viscosity when the negative electrode active material, binder, and conductive agent are included. For example, the solvent content may be such that the concentration of solids in the slurry including the negative electrode active material, binder, and conductive agent is 30% to 80% by weight (e.g., 40% to 70% by weight).

[0121] (3) Diaphragm

[0122] The lithium secondary battery of the present invention includes a separator between the positive electrode and the negative electrode.

[0123] The separator separates the negative electrode from the positive electrode and provides a path for the movement of lithium ions. Any separator can be used without particular limitation, as long as it is commonly used as a separator in lithium secondary batteries. In particular, separators with high moisture retention capacity and excellent safety of electrolyte solution and low resistance to electrolyte ion transfer can be used.

[0124] Specifically, porous polymer membranes can be used, such as porous polymer membranes made of polyolefin polymers such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers; or laminated structures having two or more layers. Alternatively, typical porous nonwoven fabrics can be used, such as nonwoven fabrics formed from high-melting-point glass fibers or polyethylene terephthalate fibers. Furthermore, coated diaphragms including ceramic components or polymer materials can be used to ensure heat resistance or mechanical strength, and diaphragms with single-layer or multi-layer structures can be used.

[0125] The lithium secondary battery of the present invention, as described above, can be used in portable devices such as mobile phones, laptop computers, and digital cameras; as well as electric vehicles such as hybrid electric vehicles (HEVs).

[0126] Therefore, according to another embodiment of the present invention, a battery module including the above-mentioned lithium secondary battery as a unit cell and a battery pack including the battery module are provided.

[0127] The battery module or battery pack can be used as a power source for at least one of the following medium and large devices: power tools; electric vehicles, including electric vehicles (EVs), hybrid electric vehicles (HEVs) and plug-in hybrid electric vehicles (PHEVs); or energy storage systems.

[0128] The shape of the lithium secondary battery of the present invention is not particularly limited, but it can be cylindrical, prismatic, pouch or coin-shaped.

[0129] The lithium secondary battery of the present invention can be used not only as a battery cell for use as a power source for small devices, but also as a unit cell in medium and large battery modules comprising multiple battery cells.

[0130] The present invention will be described in detail below with reference to specific embodiments.

[0131] Example

[0132] Example 1.

[0133] (Preparation of non-aqueous electrolyte solutions)

[0134] After mixing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) at a volume ratio of 30:70, a non-aqueous organic solution was prepared by dissolving LiPF6 to a concentration of 1.0 M. A 100 wt% non-aqueous electrolyte solution was prepared by mixing 0.5 wt% of the compound represented by Formula 1a, 0.5 wt% of ethylene carbonate (VC), and the remaining portion of the non-aqueous organic solution.

[0135] (Preparation of lithium secondary batteries)

[0136] Li(Ni) as the positive electrode active material was added to N-methyl-2-pyrrolidone (NMP) at a weight ratio of 97.5:1:1.5. 0.8 Co 0.1 Mn 0.1 O2, conductive agent (carbon black), and binder (polyvinylidene fluoride) were used to prepare a positive electrode slurry (solid content: 60% by weight). A 15 μm thick aluminum (Al) film as the positive electrode current collector was coated with the positive electrode slurry, dried, and then rolled to prepare the positive electrode.

[0137] A negative electrode slurry (solid content: 60% by weight) was prepared by adding a negative electrode active material (graphite:SiO = 94.5:5.5 by weight), a binder (SBR-CMC), and a conductive agent (carbon black) to water as a solvent in a weight ratio of 95:3.5:1.5. A 6 μm thick copper (Al) film as the negative electrode current collector was coated with the negative electrode slurry, dried, and then rolled to prepare the negative electrode.

[0138] Electrode components are prepared by sequentially stacking a positive electrode, a polyolefin porous membrane coated with inorganic particles (Al2O3), and a negative electrode.

[0139] The prepared electrode assembly is housed in a pouch-type battery casing, and the non-aqueous electrolyte solution prepared above is injected into it to prepare a lithium secondary battery.

[0140] Example 2.

[0141] The lithium secondary battery was prepared in the same manner as in Example 1, except that 1% by weight of the compound represented by Formula 1a was added during the preparation of the non-aqueous electrolyte solution.

[0142] Example 3.

[0143] The lithium secondary battery was prepared in the same manner as in Example 1, except that 2% by weight of the compound represented by Formula 1a was added during the preparation of the non-aqueous electrolyte solution.

[0144] Comparative Example 1.

[0145] The lithium secondary battery was prepared in the same manner as in Example 1, except that no compound represented by Formula 1a was added during the preparation of the non-aqueous electrolyte solution.

[0146] Compare Example 2.

[0147] The lithium secondary battery was prepared in the same manner as in Example 1, except that pyridine was added during the preparation of the non-aqueous electrolyte solution to replace the compound represented by Formula 1a.

[0148] Comparative Example 3.

[0149] The lithium secondary battery was prepared in the same manner as in Example 1, except that 2-fluoropyridine with a structure having direct fluorine substitution for pyridine was added instead of the compound represented by Formula 1a during the preparation of the non-aqueous electrolyte solution.

[0150] <Experimental Example 1: High-Temperature Lifetime Assessment>

[0151] After each lithium secondary battery prepared in the examples and comparative examples was activated at 0.1C CC, it was degassed.

[0152] Subsequently, each lithium secondary battery was charged to 4.20V at 0.33C under constant current-constant voltage (CC-CV) charging conditions at 25°C, then subjected to a 0.05C current cutoff, and discharged to 2.5V at 0.33C under CC conditions. After the above charge and discharge were defined as one cycle and three cycles were performed, the initial discharge capacity was measured using a PNE-0506 charge / discharge apparatus (manufacturer: PNESOLUTION Ltd., 5V, 6A).

[0153] Each lithium-ion battery was then charged to 4.20V at 0.33C under constant current-constant voltage (CC-CV) charging conditions at 45°C, followed by a 0.05C current cutoff and discharge to 2.50V at 0.33C under CC conditions. After defining each charge and discharge cycle as one cycle and performing 200 charge and discharge cycles, the discharge capacity after 200 cycles at 45°C was measured using a PNE-0506 charge / discharge apparatus (manufacturer: PNE SOLUTION Ltd., 5V, 6A).

[0154] The discharge capacity retention rate after 200 cycles at high temperature (45°C) was calculated using the following formula (1), and the results are presented in Table 1 below.

[0155] Equation (1): Discharge capacity retention rate (%) after 200 cycles = (Discharge capacity after 200 cycles / Initial discharge capacity) × 100

[0156] [Table 1]

[0157]

[0158] Based on the results in Table 1, it can be confirmed that the capacity retention rate is higher than that of Comparative Examples 1 to 3 compared to Examples 1 to 3, which used the compound of Formula 1a of the present invention as an additive.

[0159] These properties are due to the fact that the sulfonylpyridine additive represented by Formula 1a used in the examples stabilizes PF5 in high-temperature environments to reduce HF generation, while simultaneously forming a stable film on the electrode to improve thermal stability and high-voltage characteristics.

[0160] Compared with Examples 1 to 3, the capacity retention rate was significantly improved compared with Comparative Example 2, which used additives without sulfonyl groups and fluorine, and Comparative Example 1, which did not include pyridine additives. Accordingly, compared with Examples 1 to 3, it can be understood that, in addition to the PF5 stabilizing effect brought about by the pyridine structure, the battery life characteristics were significantly improved due to the formation of positive / negative electrode films brought about by the sulfonyl groups and fluorine included in Formula 1a.

[0161] Furthermore, compared to Examples 1 to 3, it can be confirmed that even compared to Comparative Example 3, which uses an additive in which fluorine directly replaces pyridine without a sulfonyl group, the capacity retention rate is improved. This is because, compared to Comparative Example 3, not only is the film-forming effect of the sulfonyl group lost, but stable film formation is also difficult to achieve. Additionally, the pyridine ring structure during oxidation / reduction decomposition is affected by fluorine as described above. Therefore, it can be confirmed that when Formula 1a contains both a sulfonyl group and fluorine, there is an effect of improved high-temperature life due to film formation.

[0162] That is, it can be understood that when using the non-aqueous electrolyte solution of the present invention, which includes a compound represented by Formula 1a, a lithium-ion battery with excellent high-temperature life characteristics can be provided.

[0163] <Experimental Example 2: High-Temperature Storage Assessment>

[0164] After each lithium secondary battery prepared in the examples and comparative examples was activated at 0.1C CC, it was degassed.

[0165] Subsequently, each lithium-ion battery was charged to 4.20V at 0.33C under constant current-constant voltage (CC-CV) charging conditions at 25°C, then subjected to a 0.05C current cutoff, and discharged to 2.5V at 0.33C under CC conditions. This charging and discharging cycle was defined as one cycle, and after three cycles, each lithium-ion battery was charged to 4.20V at 0.33C under constant current-constant voltage (CC-CV) charging conditions at 25°C, then subjected to a 0.05C current cutoff. Afterward, the initial thickness of the battery was measured using a plate thickness gauge with a 300g weight. Specifically, the thickness was measured as follows: the battery was placed on the plate thickness gauge, and a 300g weight was placed on the battery to check the displayed value.

[0166] After the initial thickness measurement, the secondary battery was placed in an oven at 60°C (OF-02GW, manufactured by JEIO TECH Ltd.) for 4 weeks. After 4 weeks, the secondary battery was removed from the oven and cooled at room temperature for 1 hour. The thickness after high-temperature storage was then measured using a plate thickness gauge with a 300g weight, in the same manner as the initial stage.

[0167] The thickness increase rate of the battery after high-temperature storage was calculated using the following formula (2), and the results are presented in Table 2 below.

[0168] Formula (2): Thickness increase rate (%) after 4 weeks of storage at 60℃ = (Battery thickness after 4 weeks of storage at 60℃ - Initial battery thickness) / Initial battery thickness × 100

[0169] [Table 2]

[0170]

[0171] Based on the results in Table 2, compared with Examples 1 to 3 which used the compound of Formula 1a of the present invention as an additive, it can be confirmed that the thickness increase rate after high-temperature storage is reduced compared with the thickness increase rate of Comparative Examples 1 to 3.

[0172] These properties are due to the fact that the sulfonylpyridine additive represented by Formula 1a used in the examples stabilizes PF5 in a high-temperature environment to reduce HF generation, and at the same time forms a stable film on the electrode to improve thermal stability and reduce gas generation due to side reactions in the film.

[0173] Compared with Examples 1 to 3, compared with Comparative Example 2 which used additives without sulfonyl groups and fluorine and Comparative Example 1 which did not include pyridine additives, the thickness increase rate after high-temperature storage was significantly reduced. Accordingly, compared with Examples 1 to 3, it can be understood that, in addition to the PF5 stabilizing effect brought about by the pyridine structure, the side reactions at the electrode interface were suppressed due to the formation of the positive / negative electrode film brought about by the sulfonyl groups and fluorine included in Formula 1a.

[0174] Furthermore, based on the results of Comparative Example 3, which uses an additive in which fluorine directly replaces pyridine without a sulfonyl group, it can be understood that the amount of gas produced increases compared to the case where only fluorine is substituted, since the effect of film formation on the electrode is reduced compared to the case where both the sulfonyl group and fluorine are substituted. That is, it can be confirmed that when Formula 1a contains both a sulfonyl group and fluorine, the amount of gas produced is reduced due to film formation.

[0175] That is, it can be understood that when using the non-aqueous electrolyte solution of the present invention, which includes a compound represented by Formula 1a, a lithium-ion battery with excellent properties of suppressing gas generation due to high-temperature storage can be provided.

Claims

1. A non-aqueous electrolyte solution for a lithium secondary battery, comprising: a lithium salt; an organic solvent; and an additive containing a compound represented by Formula 1, [Formula 1] wherein, in Formula 1, R1 is fluorine, or an alkyl group having 1 to 10 carbon atoms substituted with at least one fluorine, R2 is an alkyl group having 1 to 10 carbon atoms, and m is an integer from 0 to 4.

2. The non-aqueous electrolyte solution for lithium secondary batteries according to claim 1, wherein, The compound represented by Formula 1 is represented by Formula 1-1: [Formula 1-1] wherein, in Formula 1-1, R1, R2 and m are as defined in Formula 1.

3. The non-aqueous electrolyte solution for lithium secondary batteries according to claim 1, wherein, R1 is an alkyl group having 1 to 5 carbon atoms substituted with at least one fluorine.

4. The non-aqueous electrolyte solution for lithium secondary batteries according to claim 1, wherein, R1 is a methyl group substituted with at least one fluorine.

5. The non-aqueous electrolyte solution for lithium secondary batteries according to claim 1, wherein, m is 0.

6. The non-aqueous electrolyte solution for lithium secondary batteries according to claim 1, wherein, Based on the total weight of the non-aqueous electrolyte solution, the amount of the compound represented by Formula 1 is 0.1 wt% to 5 wt%.

7. The non-aqueous electrolyte solution for lithium secondary batteries according to claim 1, wherein, Based on the total weight of the non-aqueous electrolyte solution, the amount of the compound represented by Formula 1 is 0.1 wt% to 3 wt%.

8. The non-aqueous electrolyte solution for lithium secondary batteries according to claim 1, wherein, The additive further includes at least one selected from vinylene carbonate, 1,3-propane sultone, ethylene sulfite and lithium difluorophosphate.

9. The non-aqueous electrolyte solution for lithium secondary batteries according to claim 1, wherein, The lithium salt includes at least one selected from LiPF6 and LiN(FSO2)2.

10. The non-aqueous electrolyte solution for lithium secondary batteries according to claim 1, wherein, The organic solvent includes a mixture of at least two selected from cyclic carbonate solvents, linear carbonate solvents and linear ester solvents.

11. 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 disposed between the positive electrode and the negative electrode; and the non-aqueous electrolyte solution according to Claim 1.

12. The lithium secondary battery according to claim 11, wherein, The positive electrode active material includes a lithium composite transition metal oxide represented by Formula 2: [Formula 2] Li 1+x (Ni a Co b Mr c M d )O2 wherein, in Formula 2, M is W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B or Mo, and 1+x, a, b, c and d are the atomic fractions of each independent element, wherein, -0.2 < x < 0.2, 0.50 ≤ a < 1, 0 < b ≤ 0.30, 0 < c ≤ 0.30, 0 ≤ d ≤ 0.10 and a + b + c + d = 1.

13. The lithium secondary battery according to claim 12, wherein, a satisfies 0.60 ≤ a < 1.

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