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 containing the same, and a lithium secondary battery. Specifically, the present application can provide an electrolyte for a lithium secondary battery containing an electrolyte additive including a compound represented by Formula 1, which can effectively suppress the deterioration of a positive electrode and is not easily decomposed on a negative electrode, and a lithium secondary battery containing the same, thereby achieving excellent high-temperature storage characteristics and high-temperature cycle characteristics.

Description

Technical Field

[0001] Cross-reference to related applications

[0002] This application claims priority to Korean Patent Application No. 10-2023-0115745, filed on August 31, 2023, and Korean Patent Application No. 10-2024-0087849, filed on July 3, 2024, the entire contents of which are incorporated herein by reference. Technical Field

[0004] This disclosure relates to electrolyte additives, electrolytes for lithium secondary batteries containing the same, and lithium secondary batteries. 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 Equation 1,

[0020] A is a nitrogen-containing heteroaryl group having 3 to 10 carbon atoms.

[0021] [2] This disclosure provides an electrolyte additive, wherein, in the above [1], A is a nitrogen-containing heteroaryl group having 3 to 8 carbon atoms.

[0022] [3] This disclosure provides an electrolyte additive, wherein, in [1] or [2] above, A is a nitrogen-containing heteroaryl group having 3 to 5 carbon atoms.

[0023] [4] This disclosure provides an electrolyte additive, wherein, in at least one of [1] to [3] above, the compound represented by Formula 1 is a compound represented by Formula 1a or 1b:

[0024] [Equation 1a]

[0025]

[0026] [Equation 1b]

[0027] .

[0028] [5] This disclosure provides an electrolyte for lithium secondary batteries, which includes the electrolyte additives described above [1].

[0029] [6] This disclosure provides an electrolyte for lithium secondary batteries, wherein, in the above [5], the content of the electrolyte additive in the electrolyte for lithium secondary batteries is from 0.1% by weight to 5.0% by weight.

[0030] [7] This disclosure provides an electrolyte for lithium secondary batteries, wherein, in [5] or [6] above, the electrolyte for lithium secondary batteries further comprises a lithium salt and a non-aqueous organic solvent.

[0031] [8] This disclosure provides an electrolyte for lithium secondary batteries, wherein, in at least one of [5] to [7] 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.

[0032] [9] 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 [5].

[0033]

[10] This disclosure provides a lithium secondary battery, wherein in the above [9], the positive electrode comprises a positive electrode active material, and the positive electrode active material comprises a lithium composite metal oxide containing lithium and at least one metal selected from nickel (Ni), cobalt (Co), manganese (Mn) or aluminum (Al).

[0034] Beneficial effects

[0035] The electrolyte additive disclosed herein contains a nitrogen-containing heteroaryl group and -SO2 in its structure. - Functional groups are incorporated to form a durable inorganic film on the positive electrode surface, thereby suppressing positive electrode degradation and inhibiting additional oxygen release by effectively replenishing oxygen vacancies that arise during positive electrode degradation. Therefore, by using the electrolyte of this disclosure for lithium secondary batteries containing the electrolyte additives of this disclosure, 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

[0036] The terminology used in this specification and claims is for describing exemplary embodiments only and is not intended to limit this disclosure.

[0037] 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.”

[0038] Furthermore, unless otherwise expressly stated, in this specification, "%" indicates weight.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] This disclosure will be described in more detail below.

[0044] The electrolyte additives disclosed herein, the electrolytes for lithium secondary batteries comprising them, and / or the lithium secondary batteries may include at least one of the compositions disclosed below, and may include any combination of technically possible compositions among the following compositions.

[0045] Electrolyte additives

[0046] Specifically, this disclosure provides an electrolyte additive comprising a compound represented by Formula 1.

[0047] [Formula 1]

[0048]

[0049] In Equation 1,

[0050] A is a nitrogen-containing heteroaryl group having 3 to 10 carbon atoms.

[0051] Since most electrolyte additives are first reduced and decomposed at the negative electrode surface to form a film, there is a drawback that a stable film cannot be guaranteed to form 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.

[0052] 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 (in which the nitrogen-containing heteroaryl groups in the structure are replaced by anionic functional groups, namely -SO2- functional groups). Because the reduction reaction on the negative electrode surface with a relatively negative (-) potential is suppressed during operation, these anionic compounds remain in the electrolyte and decompose on the positive electrode surface with a relatively positive (+) potential as the oxidative decomposition reactivity increases, forming durable inorganic films such as Li3N, NLiSO3, or Li2SO4. These inorganic films exhibit high acid resistance, can suppress positive electrode degradation, and can effectively replenish oxygen vacancies that appear during positive electrode degradation, thereby suppressing additional oxygen release.

[0053] In particular, since the compound represented by Formula 1 of this disclosure contains a -SO2- functional group as an anionic functional group in its structure, it exhibits higher reactivity with the cathode compared to the compound represented by Formula 3 below, which does not contain such a functional group, thereby forming a more robust film on the cathode surface. Therefore, the effect of suppressing the continuous degradation of the cathode can be achieved.

[0054] [Formula 3]

[0055]

[0056] Furthermore, since the compound represented by Formula 1 of this disclosure contains a nitrogen-containing heteroaryl group in its structure, compared with the compound represented by Formula 4 below which is substituted with phenyl groups, this disclosure forms a more durable Li3N-containing film on the positive electrode surface, thereby reducing the degradation of the positive electrode. Therefore, it is possible to prepare a lithium secondary battery with improved high-temperature durability.

[0057] [Formula 4]

[0058]

[0059] Therefore, if an electrolyte for lithium secondary batteries containing such electrolyte additives is used, the high-temperature durability (e.g., cycle characteristics and storage characteristics) of lithium secondary batteries can be enhanced.

[0060] Meanwhile, in the compound represented by Formula 1, A can be a nitrogen-containing heteroaryl group having 3 to 8 carbon atoms, specifically a nitrogen-containing heteroaryl group having 3 to 5 carbon atoms.

[0061] Specifically, the compound represented by Formula 1 above may include the compound represented by Formula 1a or 1b below.

[0062] [Equation 1a]

[0063]

[0064] [Equation 1b]

[0065]

[0066] Electrolytes for lithium secondary batteries

[0067] In addition, in one embodiment, this disclosure provides an electrolyte for lithium secondary batteries, which includes the electrolyte additives of this disclosure.

[0068] The electrolyte for lithium secondary batteries may further include lithium salts, organic solvents, and optional additional additives.

[0069] (1) Electrolyte additives

[0070] 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 compound above is redundant with the description above, its description will be omitted.

[0071] Meanwhile, considering the effect of forming a stable 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.

[0072] 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.

[0073] 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. Conversely, if the electrolyte additive content is 5.0% by weight or less, side reactions caused by slightly higher additive content can be prevented.

[0074] 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 0.2% to 4.0% by weight, more specifically from 0.2% to 3.0% by weight, or even more specifically from 0.3% to 3.0% by weight.

[0075] (2) Lithium salts

[0076] 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.

[0077] 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), and LiN(SO2CF3)2 (lithium bis(trifluoromethanesulfonyl)imide, LiTFSI), or mixtures of two or more thereof. In addition to these, lithium salts commonly used in electrolytes for lithium secondary batteries may be used without limitation.

[0078] The lithium salts mentioned above can be appropriately varied within the generally available range, but can be included in the electrolyte at a concentration of 0.8 M to 4.0 M, specifically 1.0 M to 3.0 M, to achieve the best effect of forming a film that prevents corrosion of the electrode surface.

[0079] 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.

[0080] (3) Non-aqueous organic solvents

[0081] In addition, non-aqueous organic solvents will be explained below.

[0082] 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.

[0083] Specifically, non-aqueous organic solvents may include (i) cyclic carbonate organic solvents, (ii) linear carbonate organic solvents, or (iii) mixtures thereof.

[0084] (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 and propylene carbonate.

[0085] (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 and ethyl methyl carbonate.

[0086] 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.

[0087] 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) linear ester organic solvents and (v) cyclic ester organic solvents, which have a lower melting point and higher high-temperature stability compared to cyclic carbonate organic solvents and / or linear carbonate organic solvents.

[0088] (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 and propyl propionate.

[0089] (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.

[0090] 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.

[0091] (4) Additional additives

[0092] 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.

[0093] 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.

[0094] Cyclic carbonate compounds may include vinylene carbonate (VC) or vinyl ethylene carbonate.

[0095] Halogenated carbonate compounds can include fluoroethylene carbonate (FEC).

[0096] 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.

[0097] Sulfate / salt compounds may include ethylene sulfate (Esa), trimethylol sulfate (TMS), or methyltrimethylol sulfate (MTMS).

[0098] 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.

[0099] Boronate / salt compounds may include tetraphenylboronic acid esters and lithium oxaloyl difluoroborate.

[0100] 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.

[0101] Benzene compounds may include fluorobenzene, and amine compounds may include triethanolamine or ethylenediamine, etc.

[0102] Silane compounds can include tetravinylsilane.

[0103] 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).

[0104] 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.

[0105] The 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% by weight, preferably from 0.05% to 5.0% by weight, based on the total weight of the electrolyte. If the content of the additives 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 additives 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 additives is added, the additives 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.

[0106] Lithium secondary batteries

[0107] Furthermore, in another embodiment of this disclosure, a lithium secondary battery comprising the electrolyte for lithium secondary batteries of this disclosure is provided.

[0108] 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.

[0109] The lithium secondary battery disclosed herein can be prepared and used according to conventional methods known in the art, as specifically described below.

[0110] (1) Positive electrode

[0111] The positive electrode disclosed herein 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.

[0112] The positive electrode active material is a compound capable of reversibly intercalating and deintercalating 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), or aluminum (Al). Specifically, the lithium composite metal oxide may include the compound represented by Formula 2 below.

[0113] [Formula 2]

[0114] Li 1+a Ni x Co y M 1 z M 2 w O2

[0115] In Formula 2,

[0116] M 1 is Mn, Al, or a combination thereof,

[0117] 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.

[0118] 1 + a represents the molar ratio of lithium in the lithium transition metal oxide, which can be 0 ≤ a ≤ 0.5, preferably 0 ≤ a ≤ 0.2, more preferably 0 ≤ a ≤ 0.1.

[0119] x represents the molar ratio of nickel among all transition metal elements other than lithium in the lithium transition metal oxide, which can be 0.55 < x < 1.0, specifically 0.6 ≤ x ≤ 0.98, more specifically 0.6 ≤ x ≤ 0.95.

[0120] y represents the molar ratio of cobalt among all transition metal elements other than lithium in the lithium transition metal oxide, which can be 0 < y ≤ 0.4, specifically 0 < y ≤ 0.3, more specifically 0.05 ≤ y ≤ 0.3.

[0121] z represents the molar ratio of element M 1 among all transition metal elements other than lithium in the lithium transition metal oxide, which can be 0 < z ≤ 0.4, more specifically 0 < z ≤ 0.3, even more specifically 0.01 ≤ z ≤ 0.3.

[0122] w represents the molar ratio of element M 2 among all transition metal elements other than lithium in the lithium transition metal oxide, which can be 0 < w ≤ 0.1, more specifically 0 < w ≤ 0.05, even more specifically 0 < w ≤ 0.02.

[0123] 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.

[0124] 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.

[0125] 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.

[0126] 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.

[0127] 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.

[0128] 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.

[0129] 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; and silane adhesives.

[0130] Based on the total weight of the positive electrode active material layer, the content of the binder can be from 0.1% to 15.0% by weight, preferably from 0.1% to 10.0% by weight.

[0131] 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 coating a positive electrode current collector with a positive electrode slurry prepared by dissolving or dispersing a positive electrode active material, a binder, and / or a conductive agent in a solvent, drying, and then rolling; or by laminating a positive electrode active material onto a separate support, and then laminating a film separated from the support onto the positive electrode current collector.

[0132] 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 materials such as stainless steel, aluminum, nickel, titanium, sintered carbon, or aluminum or stainless steel surface-treated with one of these materials. 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.

[0133] 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.

[0134] (2) Negative electrode

[0135] Next, the negative electrode will be described.

[0136] 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.

[0137] 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.

[0138] According to one embodiment, the negative electrode active material may include a carbon-based negative electrode active material, and as a carbon-based negative electrode active material, various carbon-based negative electrode active materials used in the art can be used, such as graphite-based materials, such as natural graphite, artificial graphite and Kish graphite; pyrolytic carbon, mesophase pitch-based carbon fibers, mesophase carbon microspheres, mesophase pitch, high-temperature sintered carbon (e.g., 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, plate-like, sheet-like, spherical or fibrous can be used.

[0139] Preferably, as the negative electrode active material, at least one carbon-based negative electrode active material selected from natural graphite and artificial graphite can 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.

[0140] 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.

[0141] 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 combinations 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 combinations thereof.

[0142] Since the silicon-based negative electrode active material has higher capacity characteristics than the carbon-based negative electrode active material, better capacity characteristics can be obtained when the silicon-based negative electrode active material is further included. However, for a negative electrode containing a silicon-based negative electrode active material, compared with a graphite negative electrode, its SEI contains more oxygen-rich (O-rich) components, and when there are Lewis acids such as HF or PF5 in the electrolyte, the SEI containing O-rich components tends to be more easily decomposed. Therefore, for a negative electrode containing a silicon-based negative electrode active material, it is necessary to suppress the formation of Lewis acids such as HF and PF5 in the electrolyte, or remove (or scavenge) the formed Lewis acids to stably maintain the SEI. Since the electrolyte of the present disclosure contains an electrolyte additive with excellent Lewis acid scavenging effect while forming stable films on the negative electrode and the positive electrode, when using a negative electrode containing a silicon-based active material, the decomposition of the SEI can be effectively suppressed.

[0143] Meanwhile, the carbon-based negative electrode active material and the silicon-based negative electrode active material can be mixed in a ratio of 1:99 to 97:3, preferably 85:15 to 95:5, more preferably 90:10 to 97:3. When the mixing ratio of the silicon-based negative electrode active material and the carbon-based negative electrode active material satisfies the above range, since the volume expansion of the silicon-based negative electrode active material is suppressed while the capacity characteristics are improved, excellent cycle performance can be ensured.

[0144] 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.

[0145] Next, a conductive agent is a component used to further improve the conductivity of the negative electrode active material. The amount of conductive agent added can 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. Examples of conductive agents that can be used include, 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 powders, aluminum powder, and nickel powder; conductive whiskers, such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides, such as titanium oxide; or polyphenylene derivatives.

[0146] 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 10.0% by weight, based on the total weight of the negative electrode active material layer. Examples of binders can 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; and silane binders.

[0147] Based on the total weight of the negative electrode active material layer, the content of the binder can be from 0.1% to 15.0% by weight, preferably from 0.1% to 10.0% by weight.

[0148] 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.

[0149] 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.

[0150] 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.

[0151] (3) Diaphragm

[0152] The lithium secondary battery disclosed herein includes a separator between the positive and negative electrodes.

[0153] 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.

[0154] 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, and ethylene / methacrylate copolymers), or laminated structures having two or more layers. Alternatively, typical porous nonwoven fabrics can be used, such as nonwoven fabrics formed from high-melting-point glass fibers or polyethylene terephthalate fibers. Furthermore, coated 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.

[0155] 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).

[0156] 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.

[0157] 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.

[0158] Experimental Example

[0159] Example 1

[0160] (Preparation of non-aqueous electrolytes for lithium secondary batteries)

[0161] LiPF6 was dissolved in an organic solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed in a volume ratio of 30:70 to make the concentration of LiPF6 1.0 M. Then, 0.2 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).

[0162] (Preparation of secondary batteries)

[0163] The positive electrode active material (Li(Ni) 0.9 Mn 0.03 Co 0.06 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 wt%). 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.

[0164] 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.

[0165] 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.

[0166] Example 2

[0167] 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 0.3 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).

[0168] Example 3

[0169] 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 0.3 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).

[0170] Comparative Example 1

[0171] 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).

[0172] Comparative Example 2

[0173] 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 0.3 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) to prepare the non-aqueous electrolyte for the lithium secondary battery (see Table 1 below).

[0174] [Formula 4]

[0175]

[0176] Comparative Example 3

[0177] 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 0.3 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).

[0178] [Formula 3]

[0179]

[0180] [Table 1]

[0181]

[0182] Meanwhile, the abbreviations for each compound in Table 1 have the following meanings.

[0183] EC: Ethylene carbonate

[0184] EMC: Ethyl methyl carbonate

[0185] VC: Vinylene carbonate

[0186] Experimental Example

[0187] Experimental Example 1. Evaluation of High-Temperature Storage Characteristics

[0188] The lithium secondary batteries prepared in the examples and comparative examples were activated (formed) at a rate of 0.1 C for 3 hours, then charged at 0.33 C (0.05 C cutoff) to 4.2 V 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.

[0189] [Equation 1]

[0190] Resistance increase rate (%) = {(resistance after high-temperature storage - initial resistance) / initial resistance} x 100

[0191] [Table 2]

[0192]

[0193] 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 3 of this disclosure exhibit an improved resistance increase rate (%) after high-temperature storage.

[0194] Experimental Example 2. Evaluation of High-Temperature Cycling Characteristics

[0195] The lithium secondary batteries prepared in the examples and comparative examples were activated (formed) at a rate of 0.1 C for 3 hours, and then charged at 0.33 C (0.05 C cutoff) to 4.2 V under CC / CV conditions at 25°C, fully charged to 100% SOC. The fully charged batteries were then charged at 0.33 C to 4.2 V under CC / CV conditions at 45°C, and then discharged to 2.8 V under CC conditions at a rate of 0.33 C. This was defined as one cycle. After 300 cycles, the capacity retention was measured using Equation 2 below, and the results are shown in Table 3 below.

[0196] [Equation 2]

[0197] Capacity retention (%) = (Capacity after 300 cycles / Capacity after 1 cycle) x 100

[0198] [Table 3]

[0199]

[0200] Referring to Table 3 above, it can be confirmed that, compared with the lithium secondary battery of Comparative Example 1 which uses an electrolyte without the additives of this disclosure, or the lithium secondary batteries of Comparative Examples 2 and 3 which use an electrolyte containing the same amount of a compound of Formula 3 or 4 instead of the additives of this disclosure, the secondary batteries of Examples 1 to 3 of this disclosure exhibit improved capacity retention (%) after high-temperature cycling.

Claims

1. An electrolyte additive for lithium secondary batteries, comprising a compound represented by Formula 1: [Formula 1] In Equation 1, A is a nitrogen-containing heteroaryl group having 3 to 10 carbon atoms.

2. The electrolyte additive for lithium secondary batteries according to claim 1, in, A is a nitrogen-containing heteroaryl group having 3 to 8 carbon atoms.

3. The electrolyte additive for lithium secondary batteries according to claim 1, in, A is a nitrogen-containing heteroaryl group having 3 to 5 carbon atoms.

4. The electrolyte additive for lithium secondary batteries according to claim 1, in, The compound represented by Formula 1 is the compound represented by Formula 1a or 1b: [Equation 1a] [Equation 1b] 。 5. An electrolyte for lithium secondary batteries, comprising the electrolyte additive for lithium secondary batteries as described in claim 1.

6. The electrolyte for lithium secondary batteries according to claim 5, in, The electrolyte additive for lithium secondary batteries is present in the electrolyte for lithium secondary batteries at a content of 0.1% to 5.0% by weight.

7. The electrolyte for lithium secondary batteries according to claim 5, in, The electrolyte for the lithium secondary battery further comprises lithium salt and non-aqueous organic solvent.

8. The electrolyte for lithium secondary batteries according to claim 5, 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.

9. 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 5.

10. The lithium secondary battery according to claim 9, 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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