Electrolyte additive, electrolyte for lithium secondary battery containing the same, and lithium secondary battery

Abstract

Provided are an electrolyte additive, an electrolyte for a lithium secondary battery comprising the same, and a lithium secondary battery. Specifically, the present application can provide an electrolyte for a lithium secondary battery and a lithium secondary battery comprising the same, wherein the electrolyte can achieve excellent high-temperature storage characteristics and high-temperature cycle characteristics by applying an electrolyte additive comprising a compound represented by Formula 1 that can effectively suppress positive electrode deterioration and is not easily decomposed on a negative electrode.

Description

Technical Field

[0001] Cross-references to related applications

[0002] This application claims priority to Korean Patent Application No. 10-2023-0115744, filed on August 31, 2023, and Korean Patent Application No. 10-2024-0087848, filed on July 3, 2024, the entire contents of which are incorporated herein by reference. Technical Field

[0004] This disclosure relates to an electrolyte additive, an electrolyte for lithium secondary batteries comprising the same, and a lithium secondary battery. Background Technology

[0005] With modern society's increasing reliance on electricity, the development of large-capacity energy storage devices that can provide stable power and increase production has attracted much attention.

[0006] Lithium-ion batteries are the commercially available energy storage devices with the highest energy density, and therefore have been applied in various fields such as small electronic products, electric vehicles (EVs), and energy storage devices.

[0007] In particular, lithium-ion batteries used in electric vehicles require high output characteristics while maintaining cycle characteristics and performance in various environments.

[0008] A lithium-ion battery includes: a positive electrode composed of a lithium-containing transition metal oxide, a negative electrode capable of storing lithium, a non-aqueous electrolyte solution containing an organic solvent containing lithium salt, and a separator.

[0009] Meanwhile, lithium hexafluorophosphate (LiPF6), primarily used as a lithium salt, readily decomposes at high temperatures, producing Lewis acid byproducts such as HF and PF5. These byproducts react with moisture to generate even more Lewis acid byproducts (HF). These Lewis acid byproducts can erode the electrode and the passivation film formed on its surface, leading to the dissolution of transition metal ions from the positive electrode. Furthermore, the dissolved transition metal ions promote the decomposition of the electrolyte solvent, accelerating gas generation, or redepositing on the positive electrode, thus increasing its resistance. They can also be transferred to the negative electrode via the electrolyte and deposited there, resulting in additional lithium-ion consumption and increased resistance due to self-discharge of the negative electrode, damage and regeneration of the solid electrolyte interphase (SEI) film.

[0010] Since a series of such reactions reduce the amount of usable lithium ions in the battery, this is likely the main cause of battery capacity degradation. Additionally, when metal ions deposited on the negative electrode grow into dendrites, they can cause internal short circuits in the battery, leading to reduced safety of the secondary battery.

[0011] Therefore, an electrolyte is needed that can remove byproducts (HF, PF5, etc.) generated by the thermal decomposition of lithium salts, while forming a stable film on the electrode surface to inhibit the dissolution of transition metals, or to inhibit the deposition of dissolved transition metal ions on the negative electrode, thereby improving battery performance (e.g., high-rate charge / discharge performance) and safety. Summary of the Invention

[0012] Technical issues

[0013] To address the aforementioned problems, this disclosure aims to provide an electrolyte additive and an electrolyte for lithium secondary batteries containing the same, wherein the electrolyte additive can suppress the degradation of the positive electrode film and is not easily decomposed on the surface of the negative electrode, thus remaining in the electrolyte.

[0014] In addition, this disclosure aims to provide a lithium secondary battery in which high-temperature storage and high-temperature cycling characteristics are improved by including an electrolyte for the lithium secondary battery.

[0015] Technical solution

[0016] [1] This disclosure provides an electrolyte additive comprising a compound represented by Formula 1:

[0017] [Formula 1]

[0018]

[0019] In Formula 1 above, R is an alkyl group having 1 to 10 carbon atoms.

[0020] [2] This disclosure provides an electrolyte additive, wherein, in [1] above, R is an alkyl group having 1 to 6 carbon atoms.

[0021] [3] This disclosure provides an electrolyte additive, wherein, in [1] or [2] above, R is an alkyl group having 1 to 5 carbon atoms.

[0022] [4] This disclosure provides an electrolyte additive, wherein, in at least one of [1] to [3] above, the compound represented by Formula 1 is at least one of the compounds represented by Formula 1a to Formula 1d below:

[0023] [Equation 1a]

[0024]

[0025] [Equation 1b]

[0026]

[0027] [Formula 1c]

[0028]

[0029] [Formula 1d]

[0030]

[0031] [5] This disclosure provides an electrolyte additive, wherein, in at least one of [1] to [4] above, the compound represented by Formula 1 is at least one of the compounds represented by Formulas 1a and 1c above.

[0032] [6] This disclosure provides an electrolyte for lithium secondary batteries, which includes the electrolyte additives described in [1] above.

[0033] [7] This disclosure provides an electrolyte for lithium secondary batteries, wherein, in the above [6], the content of electrolyte additives in the electrolyte for lithium secondary batteries is from 0.1% by weight to 5.0% by weight.

[0034] [8] This disclosure provides an electrolyte for lithium secondary batteries, wherein, in [6] or [7] above, the electrolyte for lithium secondary batteries further comprises a lithium salt and a non-aqueous organic solvent.

[0035] [9] This disclosure provides an electrolyte for lithium secondary batteries, wherein, in at least one of [6] to [8] above, the electrolyte for lithium secondary batteries further comprises at least one additional additive selected from cyclic carbonate compounds, halogenated carbonate compounds, sulfonyl compounds, sulfate / salt compounds, phosphate / salt or phosphite / salt compounds, borate / salt compounds, benzene compounds, amine compounds, imidazole compounds, silane compounds or lithium salt compounds.

[0036]

[10] This disclosure provides a lithium secondary battery, comprising: a positive electrode; a negative electrode; a separator disposed between the positive electrode and the negative electrode; and an electrolyte for a lithium secondary battery as described in [6].

[0037]

[11] This disclosure provides a lithium secondary battery, wherein, in the above

[10] , the positive electrode comprises a positive electrode active material, and the positive electrode active material comprises a lithium composite metal oxide containing at least one metal selected from the group consisting of nickel (Ni), cobalt (Co), manganese (Mn) and aluminum (Al) and lithium.

[0038] Beneficial effects

[0039] The electrolyte additive disclosed herein is an anionic compound, and can suppress the degradation of the positive electrode by forming a durable SCN film on the positive electrode surface. This is because the reduction reaction on the negative electrode surface, which has a relatively negative (-) potential, is suppressed, and its reactivity with the positive electrode surface, which has a relatively positive (+) potential, is enhanced. Therefore, if an electrolyte for lithium secondary batteries containing the electrolyte additive of this disclosure is used, lithium secondary batteries with excellent high-temperature storage and high-temperature cycling characteristics can be achieved, while minimizing the increase in resistance. The non-aqueous electrolyte of this disclosure is particularly suitable for high-power batteries that simultaneously use high-capacity active materials (e.g., high-nickel-based positive electrode active materials or silicon-based negative electrode materials). Detailed Implementation

[0040] The terminology used in this specification and claims is for describing exemplary embodiments only and is not intended to limit this disclosure.

[0041] For example, it should be understood that terms such as “including,” “comprising,” and “having” are intended to represent a particular feature, number, step, element, or combination thereof, and other components may be added unless these terms are used in conjunction with the term “only.”

[0042] Furthermore, unless otherwise expressly stated, in this specification, "%" refers to weight.

[0043] Unless otherwise defined in the specification, the term "substitution" means that at least one hydrogen atom bonded to carbon is replaced by an element other than hydrogen, wherein the element other than hydrogen can be an alkyl group having 1 to 5 carbon atoms or a fluorine element, and specifically an alkyl group having 1 to 5 carbon atoms.

[0044] When Lewis acid byproducts and / or decomposition products (such as hydrogen fluoride (HF)) formed by the aqueous / thermal decomposition of conventional lithium salts degrade the film formed on the electrode surface, transition metal ions can readily dissolve from the positive electrode and redeposit on it, thus increasing the positive electrode resistance. Furthermore, after the dissolved transition metal ions migrate through the electrolyte to the negative electrode, they electrodeposit on it, causing self-discharge and disrupting the solid electrolyte interphase (SEI) that provides passivation to the negative electrode. This further increases the interfacial resistance of the negative electrode by promoting additional electrolyte decomposition reactions.

[0045] Because this series of side reactions reduces the amount of usable lithium ions in the battery, it not only degrades the battery's capacity but also causes decomposition reactions that lead to electrolyte loss, resulting in increased resistance and malfunctions.

[0046] Therefore, this disclosure aims to provide a lithium secondary battery, wherein an electrolyte additive is provided that can effectively remove byproducts and decomposition products of electrolyte salts that cause battery degradation and malfunction, and can continuously reduce positive electrode film degradation because it is not easily decomposed and remains in the electrolyte, and an electrolyte for lithium secondary batteries containing the electrolyte additive, thereby improving high-temperature storage and high-temperature cycling characteristics.

[0047] This disclosure will be described in more detail below.

[0048] The electrolyte additives disclosed herein, the electrolytes for lithium secondary batteries comprising them, and the lithium secondary batteries may include at least one of the compositions disclosed below, and may include any combination of the technically possible compositions below.

[0049] Electrolyte additives

[0050] Specifically, this disclosure provides an electrolyte additive comprising a compound represented by Formula 1.

[0051] [Formula 1]

[0052]

[0053] In Equation 1,

[0054] R is an alkyl group having 1 to 10 carbon atoms.

[0055] Since most electrolyte additives are first reduced and decomposed at the negative electrode surface to form a film, it is difficult to ensure the formation of a stable film at the positive electrode surface during operation. Therefore, with high-temperature storage or high-temperature cycling, the secondary battery may deteriorate due to the continuous degradation of the positive electrode surface. To solve this problem, this disclosure uses anionic compounds as additives to suppress the reduction reaction at the negative electrode, and improves the reactivity between the additive and the positive electrode by controlling the additive to remain in the electrolyte for a longer period of time.

[0056] Specifically, the compound represented by Formula 1, which serves as an electrolyte additive of this disclosure, contains Li in its structure. +The ions are dissociated by the solvent, existing as anionic compounds (where the α-position of the S and N atoms is substituted with a carboxyl group (-COO)). During operation, these anionic compounds remain in the electrolyte because the reduction reaction on the negative electrode surface with a relatively negative (-) potential is suppressed, while their reactivity with the positive electrode surface with a relatively positive (+) potential is enhanced. This allows the formation of a durable inorganic film (SCN and Li3N film) on the positive electrode surface, thereby suppressing the degradation of the positive electrode surface. In particular, since such inorganic films have high acid resistance, film degradation caused by Lewis acids (HF) can be reduced. This can suppress the dissolution of transition metals from the positive electrode. Therefore, if an electrolyte for lithium secondary batteries containing the electrolyte additives of this disclosure is used, side reactions of the positive electrode and electrolyte can be prevented, the increase in resistance can be minimized, and a lithium secondary battery with excellent high-temperature storage and high-temperature cycling characteristics can be achieved.

[0057] That is, with those that do not contain carboxyl groups (-COO) - Compared to compounds of formula 1 (e.g., compounds represented by formula 3 below), the anionic compounds of formula 1 disclosed herein (wherein a carboxyl group (-COO) is substituted) - This inhibits the reduction reaction at the negative electrode and instead enhances the reactivity with the positive electrode, thus achieving a stable film formation on the positive electrode surface. Therefore, this can effectively suppress the degradation of the positive electrode.

[0058] [Formula 3]

[0059]

[0060] Furthermore, in the compounds represented by Formula 1 of this disclosure, the α-position of the S atom is substituted with an alkyl group as an electron donor, thereby improving the reduction stability of the double bond portion (S=C, C=N) which is easily reduced due to steric hindrance. Therefore, compared with the compound represented by Formula 4 below without alkyl groups, the reduction reaction at the negative electrode is suppressed, while the reactivity with the positive electrode is improved, thereby enabling the preparation of lithium secondary batteries with improved high-temperature durability.

[0061] [Formula 4]

[0062]

[0063] Therefore, if an electrolyte for lithium secondary batteries containing the electrolyte additive represented by Formula 1 is used, the high-temperature durability (e.g., cycle characteristics and storage characteristics) of lithium secondary batteries can be improved.

[0064] Meanwhile, in the compound represented by Formula 1, R can be an alkyl group having 1 to 6 carbon atoms, or an alkyl group having 1 to 5 carbon atoms, preferably an alkyl group having 1 to 4 carbon atoms.

[0065] Alkyl groups can be substituted or unsubstituted.

[0066] Furthermore, the compound represented by Formula 1 above may include at least one of the compounds represented by Formulas 1a to 1d below. Specifically, as the number of carbon atoms in the substituent at the α-position of the S atom increases, the decomposition of the negative electrode is suppressed, thereby enabling the formation of a thicker film at the positive electrode. With this in mind, it may be at least one of Formulas 1a and 1c.

[0067] [Equation 1a]

[0068]

[0069] [Equation 1b]

[0070]

[0071] [Formula 1c]

[0072]

[0073] [Formula 1d]

[0074]

[0075] Electrolytes for lithium secondary batteries

[0076] In addition, in one embodiment, this disclosure provides an electrolyte for lithium secondary batteries, which includes the electrolyte additives of this disclosure.

[0077] The electrolyte for lithium secondary batteries may further include lithium salts, organic solvents, and optional additional additives.

[0078] (1) Electrolyte additives

[0079] The electrolyte for lithium secondary batteries disclosed herein may include an electrolyte additive comprising a compound represented by Formula 1 above. Since the description of the electrolyte additive is redundant with the above description, its description will be omitted.

[0080] Meanwhile, considering the effect of forming a stabilizing film on the electrode surface and the effect of removing the thermal decomposition products of lithium salt, the content of electrolyte additives can be from 0.1% to 5.0% by weight, based on the total weight of the non-aqueous electrolyte.

[0081] If the electrolyte additives are included within the above content range, then while suppressing the side reactions, capacity degradation and resistance increase caused by the additives as much as possible, the dissolution of transition metals of the positive electrode active material at high temperature can be effectively suppressed by forming a robust film on the positive electrode surface, and the thermal decomposition products of lithium salt can be effectively removed, thereby achieving excellent high-temperature durability.

[0082] If the electrolyte additive content is 0.1% by weight or more, the effect of removing thermal decomposition products of lithium salts can be maintained even with increased operating time, and the effect of inhibiting transition metal dissolution can be further improved by forming a stable film on the electrode surface. Furthermore, if the electrolyte additive content is 5.0% by weight or less, side reactions caused by slightly higher additive content can be prevented.

[0083] Specifically, based on the total weight of the electrolyte for lithium secondary batteries, the content of electrolyte additives can be from 0.1% to 5.0% by weight, specifically from 0.3% to 4.0% by weight, more specifically from 0.3% to 3.0% by weight, or even more specifically from 0.3% to 2.0% by weight.

[0084] (2) Lithium salts

[0085] As the lithium salt, any lithium salt commonly used in electrolytes for lithium secondary batteries can be used without limitation, and for example, the lithium salt may include Li + As a cation, and as an anion, it may include components selected from 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 - PF4C2O4 - PF2C4O8 - (CF3)2PF4 - (CF3)3PF3 - (CF3)4PF2 - (CF3)5PF -(CF3)6P - C4F9SO3 - CF3CF2SO3 - CF3CF2(CF3)2CO - (CF3SO2)2CH - CF3(CF2)7SO3 - or SCN - At least one of them.

[0086] Specifically, lithium salts may include those selected from LiCl, LiBr, LiI, LiBF4, LiClO4, and LiB. 10 Cl 10 The following materials may be used: LiAlCl4, LiAlO4, LiPF6, LiCF3SO3, LiCH3CO2, LiCF3CO2, LiAsF6, LiSbF6, LiCH3SO3, LiN(SO2F)2 (lithium bis(fluorosulfonyl)imide, LiFSI), LiN(SO2CF2CF3)2 (lithium bis(pentafluoroethanesulfonyl)imide, LiBETI), or LiN(SO2CF3)2 (lithium bis(trifluoromethanesulfonyl)imide, LiTFSI), or a mixture of two or more thereof. In addition to these, lithium salts commonly used in electrolytes for lithium secondary batteries may be used without limitation.

[0087] The lithium salt can be appropriately varied within the generally available range, but it can be included in the electrolyte at a concentration of 0.8M to 4.0M, specifically 1.0M to 3.0M, to achieve the best effect of forming a film that prevents corrosion of the electrode surface.

[0088] When the concentration of lithium salt is within the above range, the viscosity of the non-aqueous electrolyte can be controlled to achieve optimal impregnation and the mobility of lithium ions can be improved, thereby improving the capacity and cycle characteristics of lithium secondary batteries.

[0089] (3) Non-aqueous organic solvents

[0090] In addition, the above-mentioned non-aqueous organic solvents will be explained as follows.

[0091] As a non-aqueous organic solvent, there are no restrictions on the use of various organic solvents commonly used in non-aqueous electrolytes, as long as they can minimize decomposition caused by oxidation reactions, etc., during the charging and discharging of secondary batteries and can exhibit the desired properties together with additives.

[0092] Specifically, non-aqueous organic solvents may include (i) cyclic carbonate organic solvents, (ii) linear carbonate organic solvents, or (iii) mixtures thereof.

[0093] (i) Cyclic carbonate organic solvents are organic solvents with high viscosity and are capable of well dissociating lithium salts in electrolytes due to their high dielectric constant. Specific examples may include at least one organic solvent selected from ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentene carbonate, 2,3-pentene carbonate or vinylene carbonate, and specifically may include at least one of ethylene carbonate or propylene carbonate.

[0094] (ii) Linear carbonate organic solvents are organic solvents having low viscosity and low dielectric constant, wherein typical examples of linear carbonate organic solvents may include at least one organic solvent selected from dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethyl methyl carbonate (EMC), methyl propyl carbonate or ethyl propyl carbonate, and specifically, may include at least one of dimethyl carbonate or ethyl methyl carbonate.

[0095] The electrolyte for lithium secondary batteries disclosed herein can use (iii) a mixture of cyclic carbonate organic solvents and linear carbonate organic solvents to ensure high ionic conductivity, wherein the cyclic carbonate organic solvents and linear carbonate organic solvents can be mixed in a volume ratio of 10:90 to 50:50, specifically 20:80 to 40:60.

[0096] In addition, the electrolyte for lithium secondary batteries disclosed herein may further include at least one of the following organic solvents as a non-aqueous organic solvent: (iv) a linear ester organic solvent or (v) a cyclic ester organic solvent, which has a lower melting point and higher high-temperature stability compared to cyclic carbonate organic solvents and / or linear carbonate organic solvents.

[0097] (iv) Typical examples of straight-chain ester organic solvents may be at least one organic solvent selected from methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate or butyl propionate, and specifically may include at least one of ethyl propionate or propyl propionate.

[0098] (v) Cyclic ester organic solvents may include at least one organic solvent selected from γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone or ε-caprolactone.

[0099] Furthermore, unless otherwise stated, all components of the electrolyte for lithium secondary batteries, except for lithium salts, electrolyte additives, and additional additives described below, may be organic solvents.

[0100] (4) Additional additives

[0101] In addition, to prevent the electrolyte from decomposing under high output conditions and causing the negative electrode to collapse, or to further improve the low-temperature high-rate discharge characteristics, high-temperature stability, overcharge protection and battery swelling suppression effect at high temperatures, the electrolyte for lithium secondary batteries disclosed herein may, if necessary, contain other additional additives.

[0102] Examples of additional additives may be at least one selected from cyclic carbonates, halogenated carbonates, sulcolepsy compounds, sulfates / salts, phosphates / salts, borates / salts, nitriles, benzenes, amines, silanes, or lithium salts.

[0103] Cyclic carbonate compounds may include vinylene carbonate (VC) or vinyl ethylene carbonate.

[0104] Halogenated carbonate compounds can include fluoroethylene carbonate (FEC).

[0105] Sulfolactone compounds may include at least one compound selected from 1,3-propanesulfonyl lactone (PS), 1,4-butanesulfonyl lactone, ethanesulfonyl lactone, 1,3-propenesulfonyl lactone (PRS), 1,4-butenesulfonyl lactone or 1-methyl-1,3-propenesulfonyl lactone.

[0106] Sulfate / salt compounds may include ethylene sulfate (Esa), trimethylol sulfate (TMS), or methyltrimethylol sulfate (MTMS).

[0107] Phosphate ester / salt compounds may include one or more compounds selected from lithium difluoro(bis(oxalato)phosphate), lithium difluorophosphate, tri(trimethylsilyl)phosphate, tri(2,2,2-trifluoroethyl)phosphate or tri(trifluoroethyl)phosphate.

[0108] Borate / salt compounds may include tetraphenylborate or lithium oxaloyl difluoroborate.

[0109] Nitrile compounds may include at least one compound selected from butadionitrile, adiponitrile, acetonitrile, propionitrile, butadionitrile, valerate, octanoic acid, heptanoic acid, cyclopentaneformitrile, cyclohexaneformitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, or 4-fluorophenylacetonitrile.

[0110] Benzene compounds may include fluorobenzene, and amine compounds may include triethanolamine or ethylenediamine, etc.

[0111] Silane compounds can include tetravinylsilane.

[0112] Lithium salt compounds are compounds that are different from lithium salts contained in electrolytes, and may include one or more compounds selected from LiPO2F2, LiODFB, LiBOB (lithium bis(oxalate)borate (LiB(C2O4)2) or LiBF4).

[0113] In the case of adding additives such as vinylene carbonate, vinyl ethylene carbonate, or succinate, a more robust SEI can be formed on the negative electrode surface during the initial activation process of the secondary battery.

[0114] Additional additives can be used as a mixture of two or more of them, and their content can be less than 30% by weight, specifically from 0.01% to 10.0% by weight, preferably from 0.05% to 5.0% by weight, based on the total weight of the electrolyte. If the content of the additional additive is less than 0.01% by weight, the effect of improving the low-temperature output, high-temperature storage characteristics, and high-temperature life characteristics of the battery is not significant, while if the content of the additional additive is greater than 30% by weight, there is a possibility that side reactions in the electrolyte may occur excessively during the charging and discharging of the battery. In particular, if an excessive amount of SEI-forming additive is added, the additive may not be able to decompose sufficiently at high temperatures, so that they may exist in the electrolyte at room temperature as unreacted material or in a form that may precipitate out. Therefore, side reactions that reduce the life or resistance characteristics of the secondary battery may occur.

[0115] Lithium secondary batteries

[0116] Furthermore, in another embodiment of this disclosure, a lithium secondary battery comprising the electrolyte for lithium secondary batteries of this disclosure is provided.

[0117] After forming an electrode assembly in which a positive electrode, a negative electrode, and a separator between the positive and negative electrodes are stacked sequentially and housed in a battery casing, the electrolyte of the present disclosure is injected therein, thereby preparing the lithium secondary battery of the present disclosure.

[0118] The lithium secondary battery disclosed herein can be prepared and used according to conventional methods known in the art, as specifically described below.

[0119] (1) Positive electrode

[0120] The positive electrode of this disclosure may include a positive electrode active material layer comprising a positive electrode active material, and if necessary, the positive electrode active material layer may further comprise a conductive agent and / or a binder.

[0121] The positive electrode active material is a compound capable of reversibly inserting and extracting lithium, and specifically, the positive electrode active material may include a lithium composite metal oxide containing lithium and at least one metal selected from nickel (Ni), cobalt (Co), manganese (Mn), iron (Fe), or aluminum (Al). Specifically, the lithium composite metal oxide may include the compound represented by Formula 2 below.

[0122] [Formula 2]

[0123] Li 1+a Ni x Co y M 1 z M 2 w O2

[0124] In Formula 2,

[0125] M 1 is Mn, Al, or a combination thereof,

[0126] M 2 is at least one selected from Al, Zr, W, Ti, Mg, Ca, or Sr, where 0 ≤ a ≤ 0.5, 0.55 < x < 1.0, 0 < y ≤ 0.4, 0 < z ≤ 0.4, 0 ≤ w ≤ 0.1.

[0127] 1 + a represents the molar ratio of lithium in the lithium transition metal oxide, and it can be 0 ≤ a ≤ 0.5, preferably 0 ≤ a ≤ 0.2, more preferably 0 ≤ a ≤ 0.1.

[0128] x represents the molar ratio of nickel among all transition metal elements other than lithium in the lithium transition metal oxide, and it can be 0.55 < x < 1.0, specifically 0.6 ≤ x ≤ 0.98, more specifically 0.6 ≤ x ≤ 0.95.

[0129] y represents the molar ratio of cobalt among all transition metal elements other than lithium in the lithium transition metal oxide, and it can be 0 < y ≤ 0.4, specifically 0 < y ≤ 0.3, more specifically 0.05 ≤ y ≤ 0.3.

[0130] z represents the molar ratio of element M 1 among all transition metal elements other than lithium in the lithium transition metal oxide, and it can be 0 < z ≤ 0.4, more specifically 0 < z ≤ 0.3, even more specifically 0.01 ≤ z ≤ 0.3.

[0131] w represents the molar ratio of element M 2 among all transition metal elements other than lithium in the lithium transition metal oxide, and it can be 0 < w ≤ 0.1, more specifically 0 < w ≤ 0.05, even more specifically 0 < w ≤ 0.02.

[0132] Specifically, the positive electrode active material may include a lithium composite transition metal oxide having a Ni content of 0.55 atm% or more, such as Li(Ni 0.6 Mn 0.2 Co 0.2 )O2, Li(Ni 0.7 Mn 0.15 Co 0.15 )O2, Li(Ni 0.7 Mn 0.2 Co 0.1 )O2, Li(Ni 0.8 Mn 0.1 Co 0.1 )O2, Li(Ni 0.8 Co 0.15 Al 0.05 )O2, Li(Ni 0.86 Mn 0.07 Co 0.05 Al 0.02 )O2, Li(Ni 0.90 Mn 0.05 Co 0.05 )O2 or Li(Ni 0.9 Mn 0.03 Co 0.06 Al 0.01 )O2), to achieve a high-capacity battery.

[0133] In addition, as the positive electrode active material of the present disclosure, depending on the use of the secondary battery, lithium manganese-based oxides (e.g., LiMnO2, LiMn2O4, etc.), lithium cobalt-based oxides (e.g., LiCoO2, etc.), lithium nickel-based oxides (e.g., LiNiO2, etc.), lithium nickel manganese-based oxides (e.g., LiNi 1-Y Mn Y O2(0 < Y < 1), LiMn 2-z Ni z O4(0 < Z < 2)), lithium nickel cobalt-based oxides (e.g., LiNi 1-Y1 Co Y1 O2(0 < Y1 < 1)), lithium manganese cobalt-based oxides (e.g., LiCo 1-Y2 Mn Y2 O2(0 < Y2 < 1), LiMn 2- z1 Co z1 O4(0 < Z1 < 2) or Li(Ni p1 Co q1 Mn r2 )O4(0 < p1 < 2, 0 < q1 < 2, 0 < r2 < 2, p1 + q1 + r2 = 2)) etc. may be used together with the lithium composite metal oxide represented by the above formula 2.

[0134] Based on the total weight of the positive electrode active material layer, the content of the positive electrode active material can be from 80% to 98% by weight, specifically from 85% to 98% by weight. When the content of the positive electrode active material is within the above range, it can exhibit excellent capacity characteristics.

[0135] Next, a conductive agent is used to provide conductivity to the electrode. Any conductive agent can be used without particular limitation, as long as it has suitable electronic conductivity without causing adverse chemical changes in the battery. Specific examples may include carbon black, such as carbon black, acetylene black (or Denka black), Ketjen black, channel black, furnace black, lamp black, or thermally cracked carbon black; graphite powder, such as natural graphite, artificial graphite, or graphite with a well-developed crystalline structure; conductive fibers, such as carbon fibers or metal fibers; conductive powders, such as fluorocarbon powders, aluminum powder, or nickel powder; conductive whiskers, such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides, such as titanium oxide; polyphenylene derivatives, etc., and any one or a mixture of two or more of them may be used.

[0136] Based on the total weight of the positive electrode active material layer, the content of the conductive agent can be from 0.1% to 10.0% by weight, preferably from 0.1% to 5.0% by weight.

[0137] Next, the adhesive improves the adhesion between the positive electrode active material particles and the adhesion between the positive electrode active material and the current collector.

[0138] As examples of adhesives, any one or a mixture of two or more of the following may be used: fluoropolymer adhesives, including polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE); rubber adhesives, including styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber, or styrene-isoprene rubber; cellulose adhesives, including carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, or regenerated cellulose; polyol adhesives, including polyvinyl alcohol; polyolefin adhesives, including polyethylene or polypropylene; polyimide adhesives; polyester adhesives; or silane adhesives.

[0139] Based on the total weight of the positive electrode active material layer, the binder content can be from 0.1% to 15.0% by weight, preferably from 0.1% to 10.0% by weight.

[0140] The positive electrode disclosed herein can be prepared by methods known in the art for preparing positive electrodes. For example, the positive electrode can be prepared by the following methods for preparing the active material layer: coating a positive electrode current collector with a positive electrode slurry prepared by dissolving or dispersing the positive electrode active material, binder and / or conductive agent in a solvent, drying, and then rolling; or by the following methods: casting the positive electrode active material layer onto a separate support, and then pressing the film layer separated from the support onto the positive electrode current collector.

[0141] There are no particular limitations on the positive electrode current collector, as long as it is conductive and will not cause adverse chemical changes in the battery. It can be made of, for example, stainless steel, aluminum, nickel, titanium, sintered carbon, or aluminum or stainless steel surface-treated with one of carbon, nickel, titanium, or silver. Furthermore, the positive electrode current collector can typically have a thickness from 3 μm to 500 μm, and microscopic irregularities can be formed on its surface to improve the adhesion of the positive electrode material. The positive electrode current collector can be used in various shapes, such as films, sheets, foils, meshes, porous bodies, foams, and nonwoven fabrics.

[0142] The solvent can be any solvent commonly used in the art, and can include dimethyl sulfoxide (DMSO), isopropanol, N-methylpyrrolidone (NMP), acetone, or water, and any one or a mixture of two or more thereof can be used. Considering the coating thickness, manufacturing yield, and processability of the cathode material mixture, the amount of solvent used can be sufficient and is not particularly limited if the cathode material mixture can be adjusted to have an appropriate viscosity.

[0143] (2) Negative electrode

[0144] Next, the negative electrode will be described.

[0145] The negative electrode disclosed herein includes a negative electrode active material layer comprising a negative electrode active material, and if necessary, the negative electrode active material layer may further comprise a conductive agent and / or a binder.

[0146] As the negative electrode active material, various negative electrode active materials used in the art can be used, such as carbon-based negative electrode active materials, silicon-based negative electrode active materials, or mixtures thereof.

[0147] According to one embodiment, the negative electrode active material may include a carbon-based negative electrode active material, and as the carbon-based negative electrode active material, various carbon-based negative electrode active materials used in the art may be used. For example, graphite-based materials such as natural graphite, artificial graphite or Kish graphite; pyrolytic carbon, mesophase pitch-based carbon fiber, mesophase carbon microbead, mesophase pitch, high-temperature sintered carbon (such as coke derived from petroleum or coal tar pitch), soft carbon and hard carbon. The shape of the carbon-based negative electrode active material is not particularly limited, and materials of various shapes such as irregular shape, plate shape, flake shape, spherical shape or fibrous shape may be used.

[0148] Preferably, as the negative electrode active material, at least one carbon-based negative electrode active material selected from natural graphite or artificial graphite may be used. Using natural graphite and artificial graphite together can increase the adhesion to the current collector, thereby suppressing the exfoliation of the active material.

[0149] According to another embodiment, the negative electrode active material may include a silicon-based negative electrode active material and a carbon-based negative electrode active material.

[0150] The silicon-based negative electrode active material may include, for example, one or more selected from metallic silicon (Si), silicon oxide (SiO x , where 0 < x ≤ 2), silicon carbide (SiC) or Si-Y alloy (where Y is an element selected from alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, transition metals, rare earth elements or a combination thereof, and is not Si). The element Y may be selected from Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db( ), Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ti, Ge, P, As, Sb, Bi, S, Se, Te, Po or a combination thereof.

[0151] Since silicon-based anode active materials exhibit higher capacity characteristics than carbon-based anode active materials, further inclusion of silicon-based anode active materials can yield even better capacity characteristics. However, for anodes containing silicon-based active materials, compared to graphite anodes, they contain more oxygen-rich (O-rich) components in the SEI, and the O-rich SEI tends to decompose more easily when Lewis acids such as HF or PF5 are present in the electrolyte. Therefore, for anodes containing silicon-based active materials, it is necessary to suppress the formation of Lewis acids such as HF and PF5 in the electrolyte, or to remove (or eliminate) the formed Lewis acids to stably maintain the SEI. Since the electrolyte disclosed herein contains electrolyte additives that effectively remove Lewis acids while forming a stable film at both the anode and cathode, the decomposition of the SEI can be effectively suppressed when using anodes containing silicon-based active materials.

[0152] Meanwhile, silicon-based anode active materials and carbon-based anode active materials can be mixed in a ratio of 3:97 to 99:1, preferably 5:95 to 15:85. When the mixing ratio of silicon-based anode active materials to carbon-based anode active materials meets the above range, excellent cycle performance can be ensured because the volume expansion of silicon-based anode active materials is suppressed and the capacity characteristics are improved.

[0153] Based on the total weight of the negative electrode active material layer, the content of the negative electrode active material can be from 80% to 99% by weight. When the amount of negative electrode active material meets the above range, excellent capacity characteristics and electrochemical performance can be obtained.

[0154] Next, a conductive agent is used to further improve the conductivity of the negative electrode active material, wherein the amount of conductive agent added can be less than 10% by weight, preferably less than 5% by weight, based on the total weight of the negative electrode active material layer. 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, and can be, for example, carbon black, such as carbon black, acetylene black (or Denka black), Ketjen black, channel black, furnace black, lamp black, or thermally cracked carbon black; graphite powder, such as natural graphite, artificial graphite, or graphite with a well-developed crystalline structure; conductive fibers, such as carbon fibers or metal fibers; conductive powders, such as fluorocarbon powder, aluminum powder, or nickel powder; conductive whiskers, such as zinc oxide whiskers or potassium titanate whiskers; conductive metal oxides, such as titanium oxide; or polyphenylene derivatives.

[0155] The binder is a component that facilitates the bonding between the conductive agent, the active material, and the current collector, wherein the amount of binder added is typically from 0.1% to 10% by weight, based on the total weight of the negative electrode active material layer. Examples of binders may be fluoropolymer binders, including polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE); rubber binders, including styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber, or styrene-isoprene rubber; cellulose binders, including carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, or regenerated cellulose; polyol binders, including polyvinyl alcohol; polyolefin binders, including polyethylene or polypropylene; polyimide binders; polyester binders; or silane binders.

[0156] Based on the total weight of the negative electrode active material layer, the binder content can be from 0.1% to 15.0% by weight, preferably from 0.1% to 10.0% by weight.

[0157] The negative electrode can be prepared by methods known in the art for preparing negative electrodes. For example, the negative electrode can be prepared by coating a negative electrode current collector with a negative electrode slurry prepared by dissolving or dispersing the negative electrode active material and optionally a binder and a conductive agent in a solvent, rolling and drying to form a negative electrode active material layer; or it can be prepared by casting the negative electrode active material layer onto a separate support, and then pressing the film layer separated from the support onto the negative electrode current collector.

[0158] There are no particular limitations on the negative electrode current collector, as long as it has high conductivity and will not cause adverse chemical changes in the battery. Materials used include, for example, copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless steel surface-treated with one of carbon, nickel, titanium, or silver, and aluminum-cadmium alloys. The negative electrode current collector typically has a thickness from 3 μm to 500 μm, and similar to the positive electrode current collector, microscopic irregularities can be formed on its surface to improve the adhesion of the negative electrode active material. The negative electrode current collector can be used in various shapes, such as films, sheets, foils, meshes, porous bodies, foams, and nonwoven fabrics.

[0159] The solvent can be any solvent commonly used in the art, and can include dimethyl sulfoxide (DMSO), isopropanol, N-methylpyrrolidone (NMP), acetone, or water, and any one or a mixture of two or more thereof can be used. Considering the coating thickness, manufacturing yield, and processability of the negative electrode material mixture, the amount of solvent used can be sufficient and is not particularly limited if the negative electrode slurry can be adjusted to have an appropriate viscosity.

[0160] (3) Diaphragm

[0161] The lithium secondary battery disclosed herein includes a separator between the positive and negative electrodes.

[0162] The separator separates the negative and positive electrodes and provides a path for the movement of lithium ions. As a separator, any separator can be used without particular limitation, as long as it is commonly used in lithium secondary batteries. In particular, separators with high electrolyte retention capacity and low resistance to the migration of lithium salt ions are preferred.

[0163] Specifically, as the separator, porous polymer membranes can be used, such as porous polymer membranes prepared from polyolefin polymers (e.g., ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, or 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 separators comprising ceramic components or polymer materials can be used to ensure heat resistance or mechanical strength, and separators with single-layer or multi-layer structures can be optionally used.

[0164] The lithium secondary battery of this disclosure as described above can be suitably used in portable devices, such as mobile phones, laptops and digital cameras, as well as electric vehicles, such as hybrid electric vehicles (HEVs).

[0165] The shape of the lithium secondary battery disclosed herein is not particularly limited, but cylindrical, prismatic, pouch-shaped or coin-shaped batteries using containers can be used.

[0166] The lithium secondary battery disclosed herein can be used not only in battery cells for use as power sources in small devices, but also as unit cells in medium to large battery modules that include multiple battery cells.

[0167] Experimental Example

[0168] Example 1

[0169] (Preparation of non-aqueous electrolytes for lithium secondary batteries)

[0170] LiPF6 was dissolved in a non-aqueous organic solvent containing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 30:70 to achieve a LiPF6 concentration of 1.0 M. Then, 0.3 wt% of the compound represented by Formula 1a and 0.5 wt% of ethylene carbonate (VC) were added to prepare a non-aqueous electrolyte for lithium secondary batteries (see Table 1 below).

[0171] (Preparation of secondary batteries)

[0172] The positive electrode active material (Li(Ni) 0.9 Mn 0.03 Co0.06 Al 0.01 O2, conductive agent (carbon black), and binder (polyvinylidene fluoride) were added to N-methyl-2-pyrrolidone (NMP) as a solvent in a weight ratio of 97.6:0.8:1.6 to prepare a positive electrode slurry (solid content: 60.0% by weight). A positive electrode current collector (Al film) with a thickness of 13.5 μm was coated with the positive electrode slurry, dried, and rolled to prepare the positive electrode.

[0173] A negative electrode active material (graphite:SiO = 94:6 by weight), a binder (SBR-CMC), and a conductive agent (carbon black) were added to water as a solvent in a weight ratio of 97.6:0.8:1.6 to prepare a negative electrode slurry (solid content: 60% by weight). A 6 μm thick negative electrode current collector (Cu film) was coated with the negative electrode slurry, dried, and rolled to prepare the negative electrode.

[0174] An electrode assembly is prepared by placing a porous polypropylene separator between the positive and negative electrodes. The electrode assembly is then housed in a battery casing, and the electrolyte for lithium secondary batteries prepared above is injected into it to prepare a lithium secondary battery.

[0175] Example 2

[0176] The lithium secondary battery was prepared in the same manner as in Example 1, except that LiPF6 was dissolved in an organic solvent to a concentration of 1.0 M, and 0.5 wt% of the compound represented by Formula 1a and 0.5 wt% of vinylene carbonate (VC) were added to prepare a non-aqueous electrolyte for the lithium secondary battery (see Table 1 below).

[0177] Example 3

[0178] The lithium secondary battery was prepared in the same manner as in Example 1, except that LiPF6 was dissolved in an organic solvent to a concentration of 1.0 M, and 0.5 wt% of the compound represented by Formula 1b and 0.5 wt% of vinylene carbonate (VC) were added to prepare a non-aqueous electrolyte for the lithium secondary battery (see Table 1 below).

[0179] Example 4

[0180] The lithium secondary battery was prepared in the same manner as in Example 1, except that LiPF6 was dissolved in a non-aqueous organic solvent to a concentration of 1.0 M, and 0.5 wt% of the compound represented by Formula 1c and 0.5 wt% of vinylene carbonate (VC) were added to prepare the non-aqueous electrolyte for the lithium secondary battery (see Table 1 below).

[0181] Comparative Example 1

[0182] The lithium secondary battery was prepared in the same manner as in Example 1, except that LiPF6 was dissolved in a non-aqueous organic solvent to a concentration of 1.0 M, and 0.5% by weight of vinylene carbonate (VC) was added as an additive to prepare the non-aqueous electrolyte for the lithium secondary battery (see Table 1 below).

[0183] Comparative Example 2

[0184] The lithium secondary battery was prepared in the same manner as in Example 1, except that LiPF6 was dissolved in a non-aqueous organic solvent to a concentration of 1.0 M, and 0.5 wt% of the compound represented by Formula 3 was added instead of the compound represented by Formula 1a and 0.5 wt% of vinylene carbonate (VC) was added as an additive to prepare the non-aqueous electrolyte for the lithium secondary battery (see Table 1 below).

[0185] [Formula 3]

[0186]

[0187] Comparative Example 3

[0188] The lithium secondary battery was prepared in the same manner as in Example 1, except that LiPF6 was dissolved in a non-aqueous organic solvent to a concentration of 1.0 M, and 0.5 wt% of the compound represented by Formula 4 was added instead of the compound represented by Formula 1a and 0.5 wt% of vinylene carbonate (VC) was added as an additive to prepare the non-aqueous electrolyte for the lithium secondary battery (see Table 1 below).

[0189] [Formula 4]

[0190]

[0191] [Table 1]

[0192]

[0193] Meanwhile, the abbreviations for each compound in Table 1 have the following meanings.

[0194] EC: Ethylene carbonate

[0195] EMC: Ethyl methyl carbonate

[0196] VC: Vinylene carbonate

[0197] Experimental Example

[0198] Experimental Example 1. Evaluation of High-Temperature Storage Characteristics

[0199] The lithium secondary batteries prepared in the examples and comparative examples were activated (formed) at a rate of 0.1C for 3 hours, then charged at 0.33C (0.05C cutoff) to 4.2V under CC / CV conditions at 25°C, fully charged to SOC 100%, and stored at high temperature (60°C) for 16 weeks. Subsequently, they were transferred to a charge / discharger at room temperature (25°C) to measure resistance, and the rate of increase in resistance was calculated using Equation 1 below. The results are presented in Table 2 below.

[0200] [Equation 1]

[0201] Resistance increase rate (%) = {(resistance after high-temperature storage - initial resistance) / initial resistance} x 100

[0202] Experimental Example 2. Evaluation of High-Temperature Cycling Characteristics

[0203] The lithium secondary batteries prepared in the examples and comparative examples were activated (formed) at a rate of 0.1C for 3 hours, and then charged at 0.33C (0.05C cutoff) to 4.2V under CC / CV conditions at 25°C, and fully charged to 100% SOC. The fully charged batteries were then charged to 4.2V at 0.33C under CC / CV conditions at 45°C, and then discharged to 2.8V under CC conditions at 0.33C, which was defined as one cycle. After 300 cycles, the capacity retention was measured using Equation 2 below, and the results are shown in Table 2 below.

[0204] [Equation 2]

[0205] Capacity retention (%) = (Capacity after 300 cycles / Capacity after 1 cycle) x 100

[0206] [Table 2]

[0207] Resistance increase rate (%) Capacity retention rate (%) Example 1 35.89 85.21 Example 2 21.52 90.85 Example 3 25.89 88.64 Example 4 19.23 91.61 Comparative Example 1 52.44 81.89 Comparative Example 2 47.32 82.57 Comparative Example 3 48.14 82.34

[0208] Referring to Table 2 above, it can be confirmed that, compared with the lithium secondary batteries of Comparative Examples 1 to 3, the secondary batteries of Examples 1 to 4 of this disclosure exhibit improved resistance increase rate (%) after high-temperature storage and improved capacity retention rate (%) after high-temperature cycling.

Claims

1. An electrolyte additive comprising a compound represented by Formula 1: [Formula 1] In Equation 1, R is an alkyl group having 1 to 10 carbon atoms.

2. The electrolyte additive according to claim 1, in, R is an alkyl group having 1 to 6 carbon atoms.

3. The electrolyte additive according to claim 1, in, R is an alkyl group having 1 to 5 carbon atoms.

4. The electrolyte additive according to claim 1, in, The compound represented by Formula 1 is at least one of the compounds represented by Formulas 1a to 1d: [Equation 1a] [Equation 1b] [Formula 1c] [Formula 1d] 。 5. The electrolyte additive according to claim 4, wherein, The compound represented by Formula 1 is at least one of the compounds represented by Formula 1a and Formula 1c.

6. An electrolyte for lithium secondary batteries, comprising the electrolyte additive of claim 1.

7. The electrolyte for lithium secondary batteries according to claim 6, in, The electrolyte additive is present in the electrolyte for lithium secondary batteries at a content of 0.1% to 5.0% by weight.

8. The electrolyte for lithium secondary batteries according to claim 6, in, The electrolyte for the lithium secondary battery further comprises lithium salt and non-aqueous organic solvent.

9. The electrolyte for lithium secondary batteries according to claim 6, in, The electrolyte for the lithium secondary battery further comprises at least one additional additive selected from cyclic carbonate compounds, halogenated carbonate compounds, sulfonyl lactone compounds, sulfate / salt compounds, phosphate / salt or phosphite / salt compounds, borate / salt compounds, benzene compounds, amine compounds, imidazole compounds, silane compounds or lithium salt compounds.

10. A lithium secondary battery, comprising: positive electrode; negative electrode; A diaphragm is disposed between the positive electrode and the negative electrode; as well as The electrolyte for lithium secondary batteries as described in claim 6.

11. The lithium secondary battery according to claim 10, in, The positive electrode contains a positive electrode active material, and The positive electrode active material includes a lithium composite metal oxide containing lithium and at least one metal selected from nickel (Ni), cobalt (Co), manganese (Mn) or aluminum (Al).

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