Electrolyte solution for lithium secondary battery and lithium secondary battery comprising same

Abstract

An electrolyte solution for a lithium secondary battery according to an exemplary embodiment includes: an additive including a compound having a specific structure; an organic solvent; and a lithium salt. Therefore, the lithium secondary battery including the electrolyte solution for the lithium secondary battery has improved low-temperature characteristics and high-temperature stability.

Description

Technical Field

[0001] This invention relates to an electrolyte for lithium secondary batteries and a lithium secondary battery containing the electrolyte. More specifically, this invention relates to an electrolyte for lithium secondary batteries comprising a solvent and an electrolyte salt, and a lithium secondary battery containing the electrolyte. Background Technology

[0002] Rechargeable batteries are batteries that can be repeatedly charged and discharged, and they are widely used as power sources for portable electronic devices such as mobile phones and laptops (PCs). Among rechargeable batteries, lithium-ion batteries have high operating voltage and energy density per unit weight, and are advantageous for charging speed and lightweight design, thus they are being actively developed and applied.

[0003] For example, a lithium secondary battery may include: an electrode assembly including a positive electrode, a negative electrode, and a separator between the positive electrode and the negative electrode; and an electrolyte impregnating the electrode assembly.

[0004] For example, a lithium secondary battery may further include a pouch-type outer casing material that houses the electrode assembly and the electrolyte.

[0005] For example, the positive electrode of a lithium secondary battery can be manufactured by coating a positive electrode slurry onto a positive electrode current collector and then drying and calendering the slurry, which contains a positive electrode active material and a binder, and may further contain a conductive material if necessary.

[0006] During repeated charging and discharging of lithium secondary batteries, side reactions may occur between the positive electrode active material and the electrolyte, which may reduce the stability and lifespan characteristics of the lithium secondary battery. Summary of the Invention

[0007] (a) Technical problems to be solved

[0008] One technical problem of the present invention is to provide an electrolyte for lithium secondary batteries with improved low-temperature and high-temperature characteristics.

[0009] One technical problem of the present invention is to provide a lithium secondary battery with improved low-temperature and high-temperature characteristics.

[0010] (II) Technical Solution

[0011] An electrolyte for a lithium secondary battery according to an exemplary embodiment comprises: an additive having a compound having a structure represented by the following chemical formula 1; an organic solvent; and a lithium salt.

[0012] [Chemical Formula 1]

[0013]

[0014] In chemical formula 1, R 1 To R 3 Each of the following can be an alkyl group having 1 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, a hydroxyl group, a halogen atom, or a hydrogen atom; L can be a single bond, an alkylene group having 1 to 10 carbon atoms, or an alkoxy group having 1 to 10 carbon atoms; Z can be a 5- or 6-membered heteroaryl group containing at least one heteroatom selected from nitrogen, oxygen, and sulfur, or a 5- or 6-membered heterocyclic alkyl group containing at least one heteroatom selected from nitrogen, oxygen, and sulfur.

[0015] In some implementation schemes, R 1 To R 3 Each of the following can be an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, a hydroxyl group, a halogen atom, or a hydrogen atom. L can be a single bond, an alkylene group having 1 to 6 carbon atoms, or an alkoxy group having 1 to 6 carbon atoms. Z can be a 5- or 6-membered heteroaryl group containing at least one nitrogen atom, or a 5- or 6-membered heterocyclic alkyl group containing at least one oxygen atom.

[0016] In some implementation schemes, R 1 To R 3 Each of them can be an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, a hydroxyl group, a halogen atom, or a hydrogen atom. L can be a single bond, an alkylene group having 1 to 4 carbon atoms, or an alkoxy group having 1 to 4 carbon atoms. Z can be a 5-membered heteroaryl group containing 2 nitrogen atoms, or a 5-membered heterocyclic alkyl group containing 1 oxygen atom.

[0017] In some implementation schemes, R 1 To R 3 Each can be an alkyl group having 1 to 10 carbon atoms, L can be a single bond or an alkeneoxy group having 1 to 10 carbon atoms, and Z can be a 5- or 6-membered heteroaryl group containing 2 to 4 heteroatoms selected from nitrogen, oxygen and sulfur, or a 5- or 6-membered heterocyclic alkyl group containing 1 heteroatom selected from nitrogen, oxygen and sulfur.

[0018] In some embodiments, a compound having a structure represented by the chemical formula 1 may comprise a compound having a structure represented by any one of the following chemical formulas 2-1 to 2-2.

[0019] [Chemical Formula 2-1]

[0020]

[0021] [Chemical Formula 2-2]

[0022]

[0023] In some embodiments, the organic solvent may comprise at least one selected from carbonate-based organic solvents, ester-based organic solvents, ether-based organic solvents, ketone-based organic solvents, and aprotic organic solvents.

[0024] In some embodiments, the organic solvent may comprise cyclic carbonate-based solvents and linear carbonate-based solvents.

[0025] In some embodiments, the content of the additive can be from 0.1% to 10% by weight of the total weight of the electrolyte.

[0026] In some embodiments, the electrolyte may further comprise at least one auxiliary additive selected from cyclic carbonate-based compounds, fluorocarbonate-based compounds, sulopentalide-based compounds, borate-based compounds, lithium phosphate-based compounds, and sulfate-based compounds.

[0027] In some embodiments, the content of the auxiliary additive can be from 0.01% by weight to 10% by weight of the total weight of the electrolyte.

[0028] In some embodiments, the electrolyte may further contain auxiliary additives comprising cyclic carbonate-based compounds and fluorocarbonate-based compounds.

[0029] A lithium secondary battery according to an exemplary embodiment may include: an electrode assembly comprising a positive electrode and a negative electrode that are repeatedly stacked; and an electrolyte for the lithium secondary battery, the electrolyte impregnating the electrode assembly.

[0030] In some embodiments, the positive electrode may comprise a positive electrode active material, which comprises a lithium phosphate-based active material.

[0031] In some embodiments, the positive electrode active material may comprise lithium metal phosphorus oxide particles represented by the following chemical formula 3.

[0032] [Chemical Formula 3]

[0033] Li w M x P y O 4+z

[0034] In chemical formula 3, the values ​​can be 0.9≤w≤1.2, 0.99≤x≤1.01, 0.9≤y≤1.2, -0.1≤z≤0.1, and M can be at least one selected from Fe, Ni, Mn, Ti, and V.

[0035] In some implementations, M may be Fe.

[0036] (III) Beneficial Effects

[0037] According to an exemplary embodiment, the electrolyte for lithium secondary batteries can form a uniform solid electrolyte interphase (SEI) with high ionic conductivity on the electrode surface.

[0038] The lithium secondary battery according to the exemplary embodiment includes the electrolyte for the lithium secondary battery, and therefore can have improved low-temperature characteristics and high-temperature storage characteristics.

[0039] The electrolyte can be widely used in green technology fields such as electric vehicles, battery charging stations, and other battery-based solar and wind power generation. Furthermore, the lithium secondary battery can be used in eco-friendly electric vehicles and hybrid vehicles to prevent climate change by suppressing air pollution and greenhouse gas emissions. Attached Figure Description

[0040] Figure 1 This is a schematic plan view illustrating a lithium secondary battery according to an exemplary embodiment.

[0041] Figure 2 This is a schematic cross-sectional view showing a lithium secondary battery according to an exemplary embodiment. Detailed Implementation

[0042] An electrolyte for a lithium secondary battery according to an exemplary embodiment comprises: an additive, said additive comprising a compound having a specific structure; an organic solvent; and a lithium salt.

[0043] Furthermore, a lithium secondary battery according to an exemplary embodiment may include: an electrode assembly comprising a positive electrode and a negative electrode that are repeatedly stacked; and an electrolyte for the lithium secondary battery, the electrolyte impregnating the electrode assembly.

[0044] Therefore, the lifespan and high-temperature storage characteristics of lithium secondary batteries can be improved.

[0045] In this specification, "-base compound" can refer to a compound containing "-base compound" and its derivatives.

[0046] The embodiments of the present invention will now be described in more detail with reference to specific implementation methods and accompanying drawings. However, this is merely an exemplary description, and the present invention is not limited to the specific implementation methods described herein.

[0047] <Electrolyte for Lithium Secondary Batteries>

[0048] An electrolyte for a lithium secondary battery (hereinafter, simply referred to as electrolyte) according to an exemplary embodiment may include: an additive comprising a compound having a structure represented by the following chemical formula 1; an organic solvent; and a lithium salt.

[0049] The constituent elements of the present invention will now be described in more detail.

[0050] additive

[0051] The electrolyte for lithium secondary batteries according to an exemplary embodiment may contain additives, said additives comprising compounds having a structure represented by the following chemical formula 1.

[0052] [Chemical Formula 1]

[0053]

[0054] In chemical formula 1, R 1 To R 3 Each of the following can be an alkyl group having 1 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, a hydroxyl group, a halogen atom, or a hydrogen atom; L can be a single bond, an alkylene group having 1 to 10 carbon atoms, or an alkoxy group having 1 to 10 carbon atoms; Z can be a 5- or 6-membered heteroaryl group containing at least one heteroatom selected from nitrogen, oxygen, and sulfur, or a 5- or 6-membered heterocyclic alkyl group containing at least one heteroatom selected from nitrogen, oxygen, and sulfur.

[0055] For example, R 1 To R 3 Each can be independently an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, a hydroxyl group, a halogen atom, or a hydrogen atom, R 1 To R 3 Each of them can be an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, a hydroxyl group, a halogen atom, or a hydrogen atom.

[0056] For example, R 1 To R 3 Each can be independently an alkyl group having 1 to 10 carbon atoms, an alkyl group having 1 to 6 carbon atoms, an alkyl group having 1 to 4 carbon atoms, an alkyl group having 1 to 3 carbon atoms, or a methyl group, R 1 To R 3 All can be alkyl groups with the same number of carbon atoms within the above range.

[0057] For example, L can be a single bond, an alkylene group having 1 to 6 carbon atoms, or an alkene group having 1 to 6 carbon atoms.

[0058] For example, L can be a single bond or an alkene group having 1 to 10 carbon atoms, a single bond or an alkene group having 1 to 6 carbon atoms, a single bond or an alkene group having 1 to 4 carbon atoms, or a single bond or a methylene group.

[0059] For example, Z can be a 5- or 6-membered heteroaryl group containing at least one nitrogen, or a 5- or 6-membered heterocyclic alkyl group containing at least one oxygen.

[0060] For example, Z can be a 5-membered heteroaryl group containing 2 nitrogen atoms, or a 5-membered heterocyclic alkyl group containing 1 oxygen atom.

[0061] For example, Z can be a 5- or 6-membered heteroaryl group containing 2 to 4 heteroatoms selected from nitrogen, oxygen, and sulfur, or a 5- or 6-membered heterocyclic alkyl group containing 1 heteroatom selected from nitrogen, oxygen, and sulfur.

[0062] For example, Z can be a 5- or 6-membered heteroaryl group containing two heteroatoms selected from nitrogen, oxygen, and sulfur, or a 5- or 6-membered heterocyclic alkyl group containing one oxygen atom.

[0063] For example, Z can be a 5- or 6-membered heteroaryl containing at least one nitrogen, a 5-membered heteroaryl containing at least one nitrogen, a 5- or 6-membered heteroaryl containing two nitrogens, or a 5-membered heteroaryl containing two nitrogens.

[0064] For example, Z can be a 5- or 6-membered heterocyclic alkyl group containing at least one oxygen, a 5-membered heterocyclic alkyl group containing at least one oxygen, a 5- or 6-membered heterocyclic alkyl group containing one oxygen, or a 5-membered heterocyclic alkyl group containing one oxygen.

[0065] For example, Z can be imidazole, tetrahydrofuran, tetrahydrothiophene, pyrrolidine, thiophene, pyrrole, pyrazole, thiazole, thiadiazole, isothiazole, isoxazole, oxazole, oxadiazole, triazole, tetraazole, pyridine, pyrazine, or pyridazine. Z can also be imidazole or tetrahydrofuran.

[0066] For example, the hydrogen atoms of the alkyl, alkoxy, heteroaryl and heterocyclic alkyl groups mentioned above may be substituted by at least one of the following: alkyl groups having 1 to 6 carbon atoms, alkenyl groups having 2 to 6 carbon atoms, alkoxy groups having 1 to 6 carbon atoms, cycloalkyl groups having 3 to 7 carbon atoms, 5-membered to 7-membered heterocyclic alkyl groups and amino groups.

[0067] In some embodiments, a compound having a structure represented by the chemical formula 1 may comprise a compound having a structure represented by the chemical formula 2-1 or chemical formula 2-2.

[0068] [Chemical Formula 2-1]

[0069]

[0070] [Chemical Formula 2-2]

[0071]

[0072] For example, when the electrolyte for lithium secondary batteries contains an additive containing a compound having a structure represented by the chemical formula 1, a uniform solid electrolyte interphase (SEI) film with high ionic conductivity can be formed on the electrode surface.

[0073] For example, the additive can form a robust SO-based SEI film on the electrode. The SEI film stably protects the electrode surface, thus stabilizing the electrode interface, suppressing side reactions with the electrolyte, and inhibiting the rate of increase in battery internal resistance during high-temperature storage.

[0074] For example, the SEI film formed using the additive has low resistance and facilitates the migration of lithium ions between the electrode and the electrolyte, thereby improving the discharge capacity at low temperatures.

[0075] For example, when the sulfonate group in the compound is linked to a heteroaryl group, an SEI film with a stable structure can be formed through π-π (pi-pi) interactions.

[0076] For example, when the compound contains trialkylsilyl groups, hydrogen fluoride (HF) and water (H2O) in the electrolyte are removed, thereby improving cell life characteristics and high-temperature storage characteristics. The trialkylsilyl group can be trimethylsilyl.

[0077] Therefore, the high-temperature storage characteristics and low-temperature characteristics of lithium secondary batteries can be improved.

[0078] In some embodiments, the content of the additive can be from 0.1% to 10% by weight of the total weight of the electrolyte.

[0079] For example, the content of the additive may be 0.2% to 8% by weight, 0.3% to 5% by weight, 0.4% to 3% by weight, 0.5% to 2% by weight, or 0.1% to 2% by weight of the total weight of the electrolyte.

[0080] Within the aforementioned range, a uniform SEI film with high ionic conductivity can be formed, and the migration of lithium ions and the activity of the positive electrode active material are not hindered.

[0081] Additives

[0082] The electrolyte for lithium secondary batteries according to an exemplary embodiment may further include at least one auxiliary additive selected from cyclic carbonate-based compounds, fluorocarbonate-based compounds, sulcinolone-based compounds, borate-based compounds, lithium phosphate-based compounds, and sulfate-based compounds.

[0083] In some embodiments, the electrolyte may further contain auxiliary additives comprising cyclic carbonate-based compounds and fluorocarbonate-based compounds, for example, it may further contain auxiliary additives composed of cyclic carbonate-based compounds and fluorocarbonate-based compounds.

[0084] When the additives and auxiliary additives are used in combination, lithium secondary batteries with further improved low-temperature and high-temperature storage characteristics can be effectively achieved.

[0085] For example, the cyclic carbonate-based compound may include vinylene carbonate (VC), vinyl ethylene carbonate (VEC), etc.

[0086] For example, the fluorocarbonate-based compound may contain a fluorine atom or a substituent bonded with a fluorine atom (e.g., a fluorine-substituted alkyl group such as -CF3) on at least one carbon atom of the carbonate-based compound.

[0087] In some embodiments, the fluorocarbonate-based compound may include a fluorocyclic carbonate-based compound comprising a cyclic structure. For example, the fluorocyclic carbonate-based compound may have a 5- to 7-membered cyclic structure.

[0088] For example, the fluorinated cyclic carbonate compound may include fluoroethylene carbonate (FEC), etc.

[0089] In some embodiments, the sulfonyl compound may comprise at least one selected from alkyl sulfonyl compounds and alkenyl sulfonyl compounds.

[0090] In some embodiments, the sulfonyl compound may comprise both alkyl sulfonyl compounds and alkenyl sulfonyl compounds.

[0091] For example, the alkyl sulpholactone compound may include 1,3-propanesultone (PS) and 1,4-butanesultone, etc.

[0092] For example, the alkenyl sultone compound may include ethene sultone, 1,3-propene sultone (PRS), 1,4-butene sultone, and 1-methyl-1,3-propene sultone, etc.

[0093] In some embodiments, the sulfate-based compound may include a cyclic sulfate-based compound comprising a cyclic structure. The cyclic sulfate-based compound may have a 5- to 7-membered cyclic structure.

[0094] For example, the cyclic sulfate-based compound may include 1,2-ethylene sulfate (ESA), trimethylene sulfate (TMS), 1,2-propylene sulfate, and methyltrimethylene sulfate (MTMS), etc.

[0095] For example, cyclic sulfite-based compounds can include ethylene sulfite, butylene sulfite, etc.

[0096] For example, the borate-based compound may include lithium bis(oxalate)borate, etc.

[0097] For example, lithium phosphate-based compounds can include lithium difluorophosphate (LiPO2F2), lithium difluorobis(oxalato)phosphate, etc.

[0098] In one embodiment, the content of the auxiliary additive can be from 0.01% by weight to 10% by weight of the total weight of the electrolyte.

[0099] For example, the content of the auxiliary additives may be 0.05% to 9% by weight, 0.5% to 8% by weight, 0.8% to 7% by weight, 1.0% to 6% by weight, 1.5% to 5% by weight, or 2% to 4% by weight of the total weight of the electrolyte.

[0100] Within the aforementioned range, the durability of the SEI can be enhanced without hindering the effect of the additive.

[0101] In some embodiments, the weight ratio of the auxiliary additive to the additive in the electrolyte can be from 0.1 to 15.

[0102] For example, the aforementioned weight ratio can be 0.2 to 14, 0.3 to 13, 0.4 to 12, or 0.5 to 10. Within these ranges, the high-temperature storage characteristics and low-temperature characteristics of lithium secondary batteries can be further improved.

[0103] In one embodiment, cyclic carbonate-based compounds and fluorocarbonate-based compounds can be used simultaneously as the auxiliary additives.

[0104] In some embodiments, the auxiliary additive may further comprise at least one selected from borate-based compounds, nitrile-based compounds, amino-based compounds, silyl compounds, and phenyl compounds.

[0105] For example, the borate-based compound may contain at least one selected from lithium tetraphenylborate and lithium difluorooxalate borate (LiODFB).

[0106] For example, the nitrile compound may contain at least one selected from succinic anionyl nitrile, adiponitrile, acetonitrile, propionitrile, butyric anionyl nitrile, valerate, octanoic anionyl nitrile, heptanonitrile, cyclopentaneformitrile, cyclohexaneformitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile.

[0107] For example, the amine compound may contain at least one selected from triethanolamine and ethylenediamine fluorophenylacetonitrile.

[0108] For example, the silyl compound may include tetravinylsilane, etc.

[0109] For example, the phenyl compound may contain at least one selected from monofluorobenzene, difluorobenzene, trifluorobenzene, and tetrafluorobenzene.

[0110] Organic solvents and lithium salts

[0111] For example, the organic solvent may contain an organic compound that has sufficient solubility in the lithium salt, the additive, and the auxiliary additive and is non-reactive in a lithium secondary battery.

[0112] In some embodiments, the organic solvent may comprise at least one of carbonate-based solvents, ester-based solvents, ether-based solvents, ketone-based solvents, alcohol-based solvents, and aprotic solvents.

[0113] In some embodiments, the organic solvent may comprise a carbonate-based solvent, which may include linear carbonate-based solvents and cyclic carbonate-based solvents.

[0114] For example, the linear carbonate-based solvent may include dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), methyl propyl carbonate, ethyl propyl carbonate, dipropyl carbonate, etc.

[0115] For example, the cyclic carbonate-based solvent may include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, etc.

[0116] In some embodiments, the organic solvent may contain an excess of the linear carbonate-based solvent by volume compared to the cyclic carbonate-based solvent.

[0117] In some embodiments, the volume ratio of the cyclic carbonate-based solvent to the linear carbonate-based solvent in the organic solvent can be from 1 / 9 to 1. For example, the volume ratio can be from 1 / 9 to 1, 1 / 9 to 2 / 3, 1 / 6 to 2 / 3, or 1 / 4 to 2 / 3. Within these ranges, the high-temperature storage characteristics and low-temperature characteristics of the lithium secondary battery can be further improved.

[0118] For example, the ester solvent may contain at least one of methyl acetate (MA), ethyl acetate (EA), n-propyl acetate (n-PA), 1,1-dimethylethyl acetate (DMEA), methyl propionate (MP), ethyl propionate (EP), γ-butyrolactone (GBL), decanolide, valerolactone, mevalonolactone, and caprolactone.

[0119] For example, the ester-based solvent may include a carboxylic acid ester-based solvent.

[0120] For example, the ether-based solvent may contain at least one of dibutyl ether, tetraethylene glycol dimethyl ether (TEGDME), diethylene glycol dimethyl ether (DEGDME), dimethoxyethane, tetrahydrofuran (THF), and 2-methyltetrahydrofuran.

[0121] For example, the ketone solvent may include cyclohexanone, etc.

[0122] For example, the alcohol-based solvent may include at least one of ethanol (ethyl alcohol) and isopropyl alcohol (isopropyl alcohol).

[0123] For example, the aprotic solvent may include at least one of nitrile solvents, amide solvents (e.g., dimethylformamide), dioxolane solvents (e.g., 1,3-dioxolane), and sulfolane solvents.

[0124] In some implementations, the electrolyte may contain lithium salts.

[0125] The lithium salt can be made from Li + X - This indicates, for example, that the anion (X) of the lithium salt - ), can be exemplified by F - Cl - ,Br - I - NO3 - N(CN)2 - BF4 - ClO4 - PF6 - (CF3)2PF4 - (CF3)3PF3 - (CF3)4PF2 - (CF3)5PF - (CF3)6P - CF3SO3 - CF3CF2SO3 - (CF3SO2)2N - (FSO2)2N - CF3CF2(CF3)2CO -(CF3SO2)2CH - (SF5)3C - (CF3SO2)3C - CF3(CF2)7SO3 - CF3CO2 - CH3CO2 - SCN - and (CF3CF2SO2)2N - wait.

[0126] In some embodiments, the lithium salt may comprise a compound selected from LiPF6, LiClO4, LiBF4, LiFSI, LiTFSI, LiSO3CF3, LiBOB, LiFOB, LiDFOB, LiDFBP, LiTFOP, LiPO2F2, LiCl, LiBr, LiI, and LiB. 10 Cl 10 At least one of LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, CF3SO3Li, LiSCN and LiC(CF3SO2)3.

[0127] In one embodiment, the lithium salt may contain at least one selected from LiPF6, LiFSI, and LiTFSI.

[0128] In some embodiments, the concentration of the lithium salt relative to the organic solvent can be 0.01M to 5M, 0.01M to 4M, 0.5M to 3M, or 0.5M to 2M. Within these concentration ranges, lithium ions and / or electrons can migrate smoothly during the charging and discharging of the lithium secondary battery.

[0129] <Lithium secondary batteries>

[0130] Figure 1 and Figure 2 These are schematic plan views and schematic cross-sectional views of a lithium secondary battery according to an exemplary embodiment. Figure 2 It is along Figure 1 A cross-sectional view taken from the I-I' line.

[0131] Reference Figure 1 and Figure 2 The lithium secondary battery may include an electrode assembly 150, which includes a positive electrode 100, a negative electrode 130, and a separator 140 disposed between the positive electrode and the negative electrode.

[0132] For example, electrode assembly 150 may include a positive electrode 100 and a negative electrode 130 that are repeatedly stacked, and electrode assembly 150 may be contained in housing 160 and immersed in electrolyte along with the electrolyte of the above exemplary embodiment.

[0133] The positive electrode 100 may include a positive electrode current collector 105 and a positive electrode active material layer 110 disposed on at least one side of the positive electrode current collector 105.

[0134] For example, the positive electrode current collector 105 may include stainless steel, nickel, aluminum, titanium, or alloys thereof. The positive electrode current collector may include aluminum or stainless steel surface-treated with carbon, nickel, titanium, or silver. For example, the thickness of the positive electrode current collector may be from 10 μm to 50 μm, but is not limited thereto.

[0135] For example, the positive electrode active material may contain compounds that enable reversible insertion and extraction of lithium ions.

[0136] In some embodiments, the positive electrode 100 may contain a positive electrode active material containing a lithium phosphate-based active material.

[0137] In some embodiments, the positive electrode active material may comprise lithium metal phosphorus oxide particles having a structure represented by the following chemical formula 3.

[0138] [Chemical Formula 3]

[0139] Li w M x P y O 4+z

[0140] In chemical formula 3, the values ​​can be 0.9≤w≤1.2, 0.99≤x≤1.01, 0.9≤y≤1.2, -0.1≤z≤0.1, and M can be at least one selected from Fe, Ni, Mn, Ti, and V.

[0141] For example, M can be Fe, and the positive electrode active material can contain lithium iron phosphate (LFP) based active material (e.g., LiFePO4).

[0142] The lithium iron phosphate (LFP)-based active material has an olivine structure, which is a highly stable structure compared to layered structures and can have a long lifespan. For example, when the above-mentioned additives are included in the electrolyte, low-temperature characteristics can be improved, such as the power characteristics of the battery at sub-zero temperatures.

[0143] In some embodiments, the positive electrode active material may comprise lithium manganese oxide-based active material, lithium nickel oxide-based active material, or lithium iron phosphate (LFP)-based active material (e.g., LiFePO4).

[0144] In some embodiments, the positive electrode active material may include, for example, a Mn-rich based active material, a Li rich layered oxide (LLO) / Over Lithiated Oxide (OLO) based active material, or a Co-less based active material having a chemical structure or crystal structure represented by Chemical Formula 4.

[0145] For example, the positive electrode active material may include a chemical structure or crystal structure represented by the following Chemical Formula 4.

[0146] [Chemical Formula 4]

[0147] p[Li2MnO3]·(1-p)[Li q JO2]

[0148] In Chemical Formula 4, 0 < p < 1, 0.9 ≤ q ≤ 1.2, and J may include at least one element selected from Mn, Ni, Fe, Cr, V, Cu, Zn, Ti, Al, Mg, and B.

[0149] For example, the positive electrode active material may be dispersed in a solvent to prepare a positive electrode mixture. The positive electrode mixture may be coated on the positive electrode current collector 105 and then dried and calendered to fabricate the positive electrode 100. The coating process may be performed by methods such as gravure coating, slot die coating, multilayer simultaneous die coating, imprinting, doctor blade coating, dip coating, bar coating, casting, etc., and is not limited thereto. The positive electrode mixture may further include a binder and may optionally further include a conductive material, a thickening agent, etc.

[0150] Non-limiting examples of the solvent used in the preparation of the positive electrode mixture may include N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, N,N-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran, etc.

[0151] The adhesive may comprise polyvinylidene fluoride (PVDF), polyvinylidene fluoride-co-hexafluoropropylene copolymer (poly(vinylidene fluoride-co-hexafluoropropylene)), polyacrylonitrile, polymethyl methacrylate, nitrile rubber (NBR), polybutadiene rubber (BR), styrene-butadiene rubber (SBR), etc. In one embodiment, the positive electrode adhesive may be a PVDF-based adhesive.

[0152] The conductive material can be added to enhance the conductivity of the positive electrode mixture layer and / or the mobility of lithium ions or electrons. For example, the conductive material may include carbon-based conductive materials such as graphite, carbon black, acetylene black, Ketjen black, graphene, carbon nanotubes, vapor-grown carbon fiber (VGCF), and carbon fiber, and / or metal-based conductive materials containing perovskite materials such as tin, tin oxide, titanium oxide, LaSrCoO3, and LaSrMnO3.

[0153] The thickener may be, for example, carboxymethyl cellulose (CMC).

[0154] The negative electrode 130 may include a negative electrode current collector 125 and a negative electrode active material layer 120 disposed on at least one side of the negative electrode current collector 125.

[0155] For example, as non-limiting examples of the negative electrode current collector 125, copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, polymer substrates coated with conductive metals, etc., can be included. For example, the thickness of the negative electrode current collector can be from 10 μm to 50 μm, but is not limited thereto.

[0156] The negative electrode mixture layer may contain a negative electrode active material. The negative electrode active material may be a substance capable of adsorbing and desorbing lithium ions. For example, the negative electrode active material may be carbon-based materials such as crystalline carbon, amorphous carbon, carbon composites, and carbon fibers; lithium metal; lithium alloys; silicon (Si)-containing materials; or tin (Sn)-containing materials.

[0157] Examples of amorphous carbon include hard carbon, soft carbon, coke, mesocarbon microbeads (MCMB), and mesophase pitch-based carbon fiber (MPCF).

[0158] Examples of the crystalline carbon include graphite-based carbons such as natural graphite, artificial graphite, graphitized coke, graphitized MCMB, and graphitized MPCF.

[0159] Examples of the lithium metal include pure lithium metal or lithium metal formed with a protective layer for suppressing dendrite growth or the like. In one embodiment, a lithium metal-containing layer deposited or coated on a negative electrode current collector can be used as the negative electrode active material layer. In one embodiment, a lithium thin film layer can also be used as the negative electrode active material layer.

[0160] Examples of the elements contained in the lithium alloy include aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, or indium.

[0161] The silicon-containing active material can provide further increased capacity characteristics. The silicon-containing active material can include Si, SiO x (0 < x < 2), a silicon-carbon composite, a metal-doped silicate, or a metal-doped SiO x (0 < x < 2), etc. The metal can include lithium and / or magnesium.

[0162] For example, the negative electrode active material can be dispersed in a solvent to prepare a negative electrode mixture. The negative electrode mixture can be coated on a negative electrode current collector and then dried and calendered to manufacture a negative electrode. The coating process can be carried out by methods such as gravure coating, slot die coating, multilayer simultaneous die coating, imprinting, knife coating, dip coating, bar coating, casting, etc., and is not limited thereto. The negative electrode mixture can further include an adhesive and can optionally further include a conductive material, a thickener, etc.

[0163] In some embodiments, the negative electrode can further include a negative electrode active material layer in the form of lithium metal formed by a deposition / coating process.

[0164] Non-limiting examples of the solvent for the negative electrode mixture include water, pure water, deionized water, distilled water, ethanol, isopropyl alcohol, methanol, acetone, n-propanol, tert-butanol, etc.

[0165] As the adhesive, conductive material, and thickener, the above substances that can be used in manufacturing a positive electrode can be used.

[0166] In some embodiments, the negative electrode adhesive can use a styrene-butadiene rubber (SBR)-based adhesive, carboxymethyl cellulose (CMC), a polyacrylic acid-based adhesive, a poly(3,4-ethylenedioxythiophene) (PEDOT)-based adhesive, etc.

[0167] In one embodiment, a separator 140 may be disposed between the positive electrode 100 and the negative electrode 130. This separator prevents short circuits between the positive and negative electrodes and maintains ion flow. According to the embodiment, the thickness of the separator may be from 10 μm to 20 μm, but the invention is not limited thereto.

[0168] The diaphragm may comprise a porous polymer membrane or a porous nonwoven fabric. The porous polymer membrane may comprise polyolefin-based polymers such as ethylene polymers, propylene polymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers. The porous nonwoven fabric may comprise high-melting-point glass fibers, polyethylene terephthalate fibers, etc.

[0169] The membrane may also contain ceramic-based materials. For example, inorganic particles may be coated on or dispersed in the polymer membrane to improve heat resistance.

[0170] The diaphragm may have a single-layer or multi-layer structure comprising the aforementioned polymer membrane and / or nonwoven fabric.

[0171] According to an exemplary embodiment, the positive electrode 100, the negative electrode 130, and the diaphragm 140 can be repeatedly arranged to form an electrode assembly 150. In some embodiments, the electrode assembly 150 may have a jelly roll form formed by the diaphragm 140 through winding, stacking, z-folding, or stack-folding.

[0172] In one embodiment, the electrode assembly 150 may have a jelly roll form formed by winding the positive electrode 100, the negative electrode 130, and the diaphragm 140 together. In another embodiment, the electrode assembly 150 may have a jelly roll form in which the positive and negative electrodes have notches in the space formed by repeated zigzag folds of the diaphragm 140.

[0173] In one embodiment, the electrode assembly can be formed by cutting or separating the positive electrode, negative electrode, and separator layer by layer and repeatedly stacking them.

[0174] For example, tabs (positive tab and negative tab) may protrude from the positive current collector 105 and the negative current collector 125 and extend to one side of the housing 160, respectively. The tabs may be fused to said side of the housing 160 and connected to electrode leads (positive lead 107 and negative lead 127) extending to or exposed outside the housing 160.

[0175] For example, pouch-shaped shells, prismatic shells, cylindrical shells, coin-shaped shells, etc. can be used.

[0176] The electrode assembly 150 can be housed together with the electrolyte in the housing 160, thereby defining a lithium secondary battery.

[0177] The embodiments of the present invention will be further described below with reference to specific experimental examples. The embodiments and comparative examples included in the experimental examples are only for illustrating the present invention and are not intended to limit the scope of the claims. Various changes and modifications can be made to the embodiments within the scope of the present invention and its technical concept, which is obvious to those skilled in the art, and such variations and modifications naturally fall within the scope of the claims.

[0178] <Preparation Example>

[0179] Synthetic Example 1: Preparation of Additive I (Trimethylsilyl 1H-Imidazole-1-Sulfurate)

[0180] In a round-bottom flask, trimethylsilyl imidazole (1.28 g, 9.1 mmol) and 10 mL of dichloromethane were added and stirred. After cooling to 0 °C, trimethylsilyl chlorosulfonate (1.72 g, 9.1 mmol) diluted with 10 mL of dichloromethane was slowly added to the reaction solution, and the mixture was stirred at room temperature for 2 hours. After the reaction was complete, the reactants were subjected to reduced pressure to remove the solvent, and the precipitate was filtered. The obtained solid was washed with anhydrous hexane and dried under vacuum to obtain 1.61 g of additive I having the structure represented by the following chemical formula 2-1 (yield 80%).

[0181] [Chemical Formula 2-1]

[0182]

[0183] <Examples and Comparative Examples>

[0184] Example 1

[0185] (1) Preparation of electrolyte

[0186] Prepare a 1.2M LiPF6 solution (a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 25:75).

[0187] An electrolyte was prepared by adding 1% by weight of fluoroethylene carbonate (FEC) and 2% by weight of vinylene carbonate (VC) to the LiPF6 solution, based on the total weight of the electrolyte (100% by weight), and adding 0.5% by weight of additive I from the preparation example.

[0188] (2) Manufacturing of lithium secondary batteries

[0189] LiFePO4, used as the positive electrode active material, carbon black, used as the conductive material, and polyvinylidene fluoride (PVDF), used as the binder, were mixed and dispersed in N-methyl-2-pyrrolidone (NMP) at a weight ratio of 92:5:3 to prepare the positive electrode slurry.

[0190] The positive electrode slurry is uniformly coated onto the area of ​​an aluminum foil (15 μm thick) having a protrusion (positive electrode tab) on one side, excluding the protrusion, and then dried and rolled to manufacture the positive electrode.

[0191] A negative electrode slurry is prepared by mixing a negative electrode active material, which is a mixture of artificial graphite and natural graphite in a weight ratio of 7:3, carbon black as a conductive material, styrene-butadiene rubber (SBR) as a binder, and carboxymethyl cellulose (CMC) as a thickener in a weight ratio of 95:3:1:1 in distilled water.

[0192] The negative electrode slurry is uniformly coated onto the area of ​​a copper foil (15 μm thick) with a protrusion (negative electrode tab) on one side, excluding the protrusion, and then dried and rolled to manufacture the negative electrode.

[0193] A polyethylene diaphragm (20 μm thick) is placed between the positive and negative electrodes to form an electrode assembly. Then, the positive and negative leads are soldered to the positive and negative electrode tabs, respectively.

[0194] The electrode assembly is housed inside a soft package (shell) such that portions of the positive and negative leads are exposed to the outside, and the three sides except for the electrolyte injection side are sealed.

[0195] The electrolyte prepared in (1) above is injected, and the electrolyte injection part is sealed, and then immersed for 12 hours to manufacture a lithium secondary battery.

[0196] Example 2

[0197] The electrolyte and lithium secondary battery were prepared using the same method as in Example 1, except that the content of additive I was changed to 10% by weight instead of 0.5% by weight.

[0198] Example 3

[0199] The electrolyte and lithium secondary battery were prepared using the same method as in Example 1, except that the content of additive I was changed to 0.05% by weight instead of 0.5% by weight.

[0200] Example 4

[0201] The electrolyte and lithium secondary battery were prepared using the same method as in Example 1, except that the content of additive I was changed to 15% by weight instead of 0.5% by weight.

[0202] Comparative Example 1

[0203] The electrolyte and lithium secondary battery were prepared using the same method as in Example 1, except that lithium difluorophosphate (W3) was used instead of additive I.

[0204] Comparative Example 2

[0205] The electrolyte and lithium secondary battery were prepared by the same method as in Example 1, except that 0.5% by weight of additive II (trimethylsilyl ethylene sulfonate) having the structure represented by the following chemical formula 5-1 was used instead of additive I.

[0206] [Chemical Formula 5-1]

[0207]

[0208] Comparative Example 3

[0209] The electrolyte and lithium secondary battery were prepared by the same method as in Example 1, except that 0.5% by weight of additive III (trimethylsilyl 4-methylbenzenesulfonate) having the structure represented by the following chemical formula 5-2 was used instead of additive I.

[0210] [Chemical Formula 5-2]

[0211]

[0212] The composition of the electrolytes in the examples and comparative examples is described in Table 1 below.

[0213] [Table 1]

[0214]

[0215] The components listed in Table 1 are as follows.

[0216] Additive I: Trimethylsilyl 1H-imidazolium-1-sulfonate

[0217] Additive II: Trimethylsilyl vinyl sulfonate

[0218] Additive III: Trimethylsilyl 4-methylbenzenesulfonate (CAS 17872-98-9)

[0219] FEC: Fluorinated vinyl carbonate

[0220] VC: Vinylene carbonate

[0221] W3: Lithium difluorophosphate (LiPO2F2)

[0222] <Experimental Example>

[0223] Experiment Example 1: Evaluation of Initial Performance

[0224] (1) Evaluation of initial resistance (25℃)

[0225] The lithium secondary batteries of the examples and comparative examples were charged at 60% SOC and then charged at rates of 0.2C, 0.5C, 1.0C, 1.5C, 2.0C, 2.5C, and 3.0C. The endpoints of the voltages after 10 seconds of charging and discharging at the corresponding rates were used to construct a linear equation, and the slope of this equation was taken as the DCIR. The measured values ​​are recorded in Table 2 below.

[0226] Experimental Example 2: Evaluation of Low-Temperature Performance

[0227] (1) Evaluation of low-temperature resistance

[0228] The lithium secondary batteries of the examples and comparative examples were placed in a chamber at -10°C for 4 hours, and then the rate was increased to 0.2C, 0.5C, 1.0C, 1.5C, 2.0C, 2.5C, and 3.0C at 25°C and SOC 60%. The endpoints of the voltages after charging and discharging for 10 seconds at the corresponding rates were used as linear equations, and the slope of these equations was used as DCIR.

[0229] The DCIR measured during the initial resistance evaluation is taken as R1, and the DCIR measured during the low-temperature resistance evaluation is taken as R2. The DCIR increase rate is calculated as follows, and the results are recorded in Table 2 below.

[0230] DCIR increase rate (%) = R2 / R1 × 100

[0231] (2) Evaluation of low-temperature capacity retention

[0232] The lithium secondary batteries of the examples and comparative examples were subjected to 0.5C CC / CV charging (3.65V, 0.05C cut-off) and 0.5C CC discharging (2.5V cut-off) at 25°C, repeated 3 times, and the discharge capacity C1 of the third time was measured.

[0233] Subsequently, the lithium secondary battery was charged at -10℃ for 2 hours using a 0.58A, 3.65V CC-CV method, and then discharged to 2.5V using a 0.58A CC method, thereby measuring the discharge capacity C2. The capacity retention rate was calculated as follows and recorded in Table 2 below.

[0234] Capacity retention rate (%) = C2 / C1 × 100

[0235] Experimental Example 3: Evaluation of High-Temperature Storage Characteristics (60℃)

[0236] (1) Evaluation of resistance after high-temperature storage

[0237] The lithium secondary batteries of the examples and comparative examples were placed in an atmosphere exposed to 60°C for 12 weeks (using a temperature control device), and then at 25°C and SOC 60%, the rate was increased to 0.2C, 0.5C, 1.0C, 1.5C, 2.0C, 2.5C, and 3.0C. The endpoints of the voltages after charging and discharging for 10 seconds at the corresponding rates were constructed as linear equations, and the slope of these equations was taken as DCIR.

[0238] The DCIR measured during the initial resistance evaluation is taken as R1, and the DCIR measured during the resistance evaluation after high-temperature storage is taken as R3. The DCIR increase rate is calculated as follows, and the results are recorded in Table 2 below.

[0239] DCIR increase rate (%) = R3 / R1 × 100

[0240] (2) Measurement of capacity retention (Ret) after high-temperature storage

[0241] At 25°C, the lithium secondary batteries of the examples and comparative examples were repeatedly subjected to 0.5C CC / CV charging (3.65V, 0.05C cutoff) and 0.5C CC discharging (2.5V cutoff) three times, and the discharge capacity C1 of the third time was measured.

[0242] The charged lithium secondary battery was stored at 60°C for 12 weeks, then left at room temperature for 30 minutes, and subjected to a 0.5C CC discharge (2.5V cutoff). The discharge capacity C3 was measured. The capacity retention rate was calculated as follows and recorded in Table 2 below.

[0243] Capacity retention rate (%) = C3 / C1 × 100

[0244] Experimental Example 4: Evaluation of High-Temperature Lifetime Characteristics (45℃)

[0245] The lithium secondary batteries of the examples and comparative examples were charged at 1C to 3.65V and discharged at 1C to 2.5V at 45°C. The above charging and discharging was repeated 600 times, and the discharge capacity C1 of the first cycle and the discharge capacity C4 of the 600th cycle were measured.

[0246] The capacity retention rate is calculated as follows and recorded in Table 2 below.

[0247] Capacity retention rate (%) = C4 / C1 × 100

[0248] [Table 2]

[0249]

[0250] Referring to Tables 1 and 2, the low-temperature (-10°C) performance, high-temperature (60°C) storage characteristics, and high-temperature (45°C) lifespan characteristics of the lithium secondary batteries in the embodiments are improved.

[0251] On the other hand, in the lithium secondary battery of the comparative example that did not use additives containing compounds with specific structures, the initial resistance and DCIR increase rate were high, and the capacity retention rate was poor.

[0252] The above description is merely an example of applying the principles of the present invention, and other configurations may be included without departing from the scope of the present invention.

Claims

1. An electrolyte for lithium secondary batteries, comprising: Additives, said additives comprising compounds having a structure represented by the following chemical formula 1; Organic solvents; and Lithium salts [Chemical Formula 1] In chemical formula 1, R 1 To R 3 Each of the following is independently an alkyl group having 1 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, a hydroxyl group, a halogen atom, or a hydrogen atom. L is a single bond, an alkylene group having 1 to 10 carbon atoms, or an alkene group having 1 to 10 carbon atoms. Z is a 5- or 6-membered heteroaryl group containing at least one heteroatom selected from nitrogen, oxygen, and sulfur, or a 5- or 6-membered heterocyclic alkyl group containing at least one heteroatom selected from nitrogen, oxygen, and sulfur.

2. The electrolyte for lithium secondary batteries according to claim 1, wherein, R 1 To R 3 Each of the following is independently an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, a hydroxyl group, a halogen atom, or a hydrogen atom. L is a single bond, an alkylene group having 1 to 6 carbon atoms, or an alkene group having 1 to 6 carbon atoms. Z is a 5- or 6-membered heteroaryl group containing at least one nitrogen atom, or a 5- or 6-membered heterocyclic alkyl group containing at least one oxygen atom.

3. The electrolyte for lithium secondary batteries according to claim 1, wherein, R 1 To R 3 Each of the following is independently an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, a hydroxyl group, a halogen atom, or a hydrogen atom. L is a single bond, an alkylene group having 1 to 4 carbon atoms, or an alkene group having 1 to 4 carbon atoms. Z is a 5-membered heteroaryl group containing 2 nitrogen atoms, or a 5-membered heterocyclic alkyl group containing 1 oxygen atom.

4. The electrolyte for lithium secondary batteries according to claim 1, wherein, R 1 To R 3 Each is independently an alkyl group having 1 to 10 carbon atoms. L is a single bond or an alkeneoxy group having 1 to 10 carbon atoms. Z is a 5- or 6-membered heteroaryl group containing 2 to 4 heteroatoms selected from nitrogen, oxygen, and sulfur, or a 5- or 6-membered heterocyclic alkyl group containing 1 heteroatom selected from nitrogen, oxygen, and sulfur.

5. The electrolyte for lithium secondary batteries according to claim 1, wherein, Compounds having a structure represented by Chemical Formula 1 include compounds having a structure represented by Chemical Formula 2-1 or Chemical Formula 2-2. [Chemical Formula 2-1] [Chemical Formula 2-2] 。 6. The electrolyte for lithium secondary batteries according to claim 1, wherein, The organic solvent comprises at least one selected from carbonate-based organic solvents, ester-based organic solvents, ether-based organic solvents, ketone-based organic solvents, and aprotic organic solvents.

7. The electrolyte for lithium secondary batteries according to claim 1, wherein, The organic solvents include cyclic carbonate-based solvents and linear carbonate-based solvents.

8. The electrolyte for lithium secondary batteries according to claim 1, wherein, The additive content is from 0.1% to 10% by weight of the total weight of the electrolyte.

9. The electrolyte for lithium secondary batteries according to claim 1, wherein, The electrolyte further comprises at least one auxiliary additive selected from cyclic carbonate compounds, fluorocarbonate compounds, sulcinolone compounds, borate compounds, lithium phosphate compounds, and sulfate compounds.

10. The electrolyte for lithium secondary batteries according to claim 9, wherein, The content of the auxiliary additive is from 0.01% to 10% by weight of the total weight of the electrolyte.

11. The electrolyte for lithium secondary batteries according to claim 1, wherein, The electrolyte further includes auxiliary additives containing cyclic carbonate-based compounds and fluorocarbonate-based compounds.

12. A lithium secondary battery, comprising: An electrode assembly comprising repeatedly stacked positive and negative electrodes; as well as The electrolyte for a lithium secondary battery according to claim 1, wherein the electrolyte impregnates the electrode assembly.

13. The lithium secondary battery according to claim 12, wherein, The positive electrode contains a positive electrode active material, which contains a lithium phosphate-based active material.

14. The lithium secondary battery according to claim 13, wherein, The positive electrode active material comprises lithium metal phosphorus oxide particles represented by the following chemical formula 3. [Chemical Formula 3] Li w M x P y Oh 4+z In chemical formula 3, 0.9≤w≤1.2, 0.99≤x≤1.01, 0.9≤y≤1.2, -0.1≤z≤0.1, and M is at least one selected from Fe, Ni, Mn, Ti, and V.

15. The lithium secondary battery according to claim 14, wherein, M is Fe.

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