Electrolyte additive, electrolyte for lithium secondary battery comprising same, and lithium secondary battery

Abstract

The invention provides an electrolyte additive, an electrolyte for a lithium secondary battery containing the electrolyte additive, and the lithium secondary battery. Specifically, the present invention can provide an electrolyte for a 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, which can effectively suppress degradation of a positive electrode and is not easily decomposed on a negative electrode.

Description

Technical Field

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority from 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, which are hereby incorporated by reference herein in their entirety. Technical Field

[0003] The present disclosure relates to an electrolyte additive, an electrolyte for a lithium secondary battery containing the same, and a lithium secondary battery. Background Art

[0004] As modern society becomes increasingly dependent on electrical energy, the development of large-capacity energy storage devices that can stabilize power supply and increase production has attracted much attention.

[0005] Lithium-ion batteries have the highest energy density among commercially available energy storage devices and have therefore been used in various fields such as small electronic products, electric vehicles (EVs), and energy storage devices.

[0006] In particular, lithium-ion batteries used in electric vehicles require high output characteristics while maintaining cycle characteristics and performance in various environments.

[0007] 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 a lithium salt, and a separator.

[0008] At the same time, lithium hexafluorophosphate (LiPF6), which is mainly used as a lithium salt, is easily decomposed at high temperatures to produce Lewis acid byproducts such as HF and PF5, and these byproducts react with water to generate more Lewis acid byproducts (HF). Such Lewis acid byproducts may corrode the passivation film formed on the electrode and its surface, thereby causing transition metal ions to dissolve from the positive electrode. In addition, the dissolved transition metal ions promote the decomposition of the electrolyte solvent, thereby accelerating the generation of gas, or redeposit on the positive electrode, thereby increasing the resistance of the positive electrode, and are also transferred to the negative electrode through the electrolyte and then deposited on the negative electrode, thereby causing additional lithium ion consumption and increased resistance due to the self-discharge of the negative electrode, the destruction and regeneration of the solid electrolyte interface (SEI) film, etc.

[0009] Since a series of such reactions reduce the amount of available lithium ions in the battery, this can be the main reason for the degradation of battery capacity. In addition, when the metal ions electrodeposited on the negative electrode grow into dendrites, they cause internal short circuits in the battery, resulting in reduced safety of the secondary battery.

[0010] Therefore, an electrolyte is needed that can remove by-products (HF, PF5, etc.) generated by the thermal decomposition of lithium salts, and at the same time form a stable film on the electrode surface to inhibit the dissolution of transition metals, or inhibit the deposition of dissolved transition metal ions on the negative electrode, thereby improving battery performance (such as high-rate charge / discharge performance) and safety. Summary of the Invention

[0011] Technical issues

[0012] In order to solve the above problems, the present disclosure aims to provide an electrolyte additive and a lithium secondary battery electrolyte containing the same, wherein the electrolyte additive can suppress degradation of the positive electrode membrane and is not easily decomposed on the negative electrode surface and remains in the electrolyte.

[0013] In addition, the present disclosure aims to provide a lithium secondary battery in which high-temperature storage and high-temperature cycle characteristics are improved by including the electrolyte for a lithium secondary battery.

[0014] Technical Solution

[0015] [1] The present disclosure provides an electrolyte additive comprising a compound represented by the following formula 1:

[0016] [Formula 1]

[0017]

[0018] In Formula 1 above, R is an alkyl group having 1 to 10 carbon atoms.

[0019] [2] The present disclosure provides an electrolyte additive, wherein, in the above [1], R is an alkyl group having 1 to 6 carbon atoms.

[0020] [3] The present disclosure provides an electrolyte additive, wherein in the above [1] or [2], the above R is an alkyl group having 1 to 5 carbon atoms.

[0021] [4] The present disclosure provides an electrolyte additive, wherein, in at least one of the above [1] to [3], the compound represented by the above formula 1 is at least one of the compounds represented by the following formulas 1a to 1d:

[0022] [Formula 1a]

[0023]

[0024] [Formula 1b]

[0025]

[0026] [Formula 1c]

[0027]

[0028] [Formula 1d]

[0029]

[0030] [5] The present disclosure provides an electrolyte additive, wherein, in at least one of the above [1] to [4], the compound represented by the above formula 1 is at least one of the compounds represented by the above formulas 1a and 1c.

[0031] [6] The present disclosure provides an electrolyte for a lithium secondary battery, which contains the electrolyte additive of the above-mentioned [1].

[0032] [7] The present disclosure provides an electrolyte for a lithium secondary battery, wherein, in the above [6], the content of the electrolyte additive in the electrolyte for a lithium secondary battery is 0.1 wt % to 5.0 wt %.

[0033] [8] The present disclosure provides an electrolyte for a lithium secondary battery, wherein, in the above-mentioned [6] or [7], the electrolyte for a lithium secondary battery further contains a lithium salt and a non-aqueous organic solvent.

[0034] [9] The present disclosure provides an electrolyte for a lithium secondary battery, wherein, in at least one of the above [6] to [8], the electrolyte for a lithium secondary battery further comprises at least one additional additive selected from cyclic carbonate compounds, halogenated carbonate compounds, sultone compounds, sulfate compounds, phosphate compounds or phosphite compounds, borate compounds, benzene compounds, amine compounds, imidazole compounds, silane compounds or lithium salt compounds.

[0035]

[10] The present 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 the electrolyte for the lithium secondary battery described in [6] above.

[0036]

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

[10] , the positive electrode contains a positive electrode active material, and the positive electrode active material includes 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.

[0037] Beneficial effects

[0038] The electrolyte additive of the present disclosure is an anionic compound and can suppress the degradation of the positive electrode by forming a durable SCN film on the positive electrode surface, because the reduction reaction on the negative electrode surface with a relatively negative (-) potential is suppressed, and its reactivity with the positive electrode surface with a relatively positive (+) potential is improved. Therefore, if a lithium secondary battery electrolyte comprising an electrolyte additive of the present disclosure is used, a lithium secondary battery with excellent high temperature storage and high temperature cycle characteristics can be achieved while minimizing the increase in resistance. The non-aqueous electrolyte of the present disclosure is particularly suitable for high-power batteries that use high-capacity active materials (such as high nickel-based positive active materials or silicon-based negative electrode materials) at the same time. DETAILED DESCRIPTION

[0039] The terms used in the description and claims are for describing exemplary embodiments only and are not intended to be limiting of the present disclosure.

[0040] For example, it will be understood that terms such as "including," "comprising," and "having" are intended to recite a particular feature, number, step, element, or combination thereof, and that other components may be added unless these terms are used with the term "only."

[0041] Furthermore, in this specification, unless otherwise specifically stated, the expression "%" means % by weight.

[0042] Unless otherwise defined in the specification, the expression "substituted" means that at least one hydrogen bonded to carbon is replaced by an element other than hydrogen, wherein the element other than hydrogen may be an alkyl group having 1 to 5 carbon atoms or a fluorine element, and specifically may be an alkyl group having 1 to 5 carbon atoms.

[0043] When the Lewis acid byproducts and / or decomposition products (such as hydrogen fluoride (HF)) formed by the water / thermal decomposition of conventional lithium salts degrade the film formed on the electrode surface, transition metal ions can be easily dissolved from the positive electrode, and the dissolved transition metal ions are redeposited on the positive electrode, thereby becoming a cause of increased positive electrode resistance. In addition, after the dissolved transition metal ions move to the negative electrode through the electrolyte, they are electrodeposited on the negative electrode, causing self-discharge of the negative electrode and destroying the solid electrolyte interface (SEI) that imparts passivation capability to the negative electrode, thereby increasing the interfacial resistance of the negative electrode by promoting additional electrolyte decomposition reactions.

[0044] Since this series of side reactions reduces the amount of available lithium ions in the battery, this not only degrades the battery's capacity but also causes decomposition reactions that lead to electrolyte loss, resulting in increased resistance and malfunctioning behavior.

[0045] Therefore, the present disclosure aims to provide a lithium secondary battery, which provides an electrolyte additive that can effectively remove byproducts and decomposition products of electrolyte salts that cause battery degradation and malfunction behavior, and at the same time can continuously reduce the degradation of the positive electrode membrane because it is not easily decomposed and remains in the electrolyte, and an electrolyte for a lithium secondary battery containing the electrolyte additive, thereby improving high-temperature storage and high-temperature cycle characteristics.

[0046] Hereinafter, the present disclosure will be described in more detail.

[0047] The electrolyte additive, the lithium secondary battery electrolyte, and the lithium secondary battery including the same disclosed herein may include at least one of the configurations disclosed below, and may include any combination of technically possible configurations among the following configurations.

[0048] Electrolyte additives

[0049] Specifically, the present disclosure provides an electrolyte additive including a compound represented by the following Formula 1.

[0050] [Formula 1]

[0051]

[0052] In formula 1,

[0053] R is an alkyl group having 1 to 10 carbon atoms.

[0054] Since most electrolyte additives are first reduced and decomposed on the negative electrode surface to form a film, there is a disadvantage that it is not easy to ensure the effect of forming a stable film on the positive electrode surface during operation. Therefore, with the progress of high-temperature storage or high-temperature cycling, secondary battery degradation may occur due to the continuous degradation of the positive electrode surface. In order to solve this problem, the present invention 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 so that it remains in the electrolyte for a longer time.

[0055] Specifically, the compound represented by Formula 1 as the electrolyte additive of the present disclosure has a Li +The ions are dissociated by the solvent and exist in the form of anionic compounds (wherein the α position of the S and N atoms is substituted with a carboxyl group (-COO)). During operation, since the reduction reaction on the negative electrode surface with a relatively negative (-) potential is suppressed, these anionic compounds will remain in the electrolyte, while its reactivity with the positive electrode surface with a relatively positive (+) potential is improved. This can form 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, the film degradation caused by Lewis acid (HF) can be reduced. This can suppress the dissolution of transition metals from the positive electrode. Therefore, if a lithium secondary battery electrolyte comprising the electrolyte additive of the present disclosure is used, the side reactions of the positive electrode and the electrolyte can be prevented, the resistance increase is minimized, and a lithium secondary battery with excellent high temperature storage and high temperature cycle characteristics is achieved.

[0056] That is, with no carboxyl group (-COO - Compared with the compound represented by Formula 3 below, the anionic compound represented by Formula 1 of the present disclosure (wherein the anionic compound represented by Formula 1 is substituted with a carboxyl group (-COO - )) suppresses the reduction reaction at the negative electrode and instead increases the reactivity with the positive electrode, thereby achieving a stable film formation effect on the positive electrode surface. Therefore, this can effectively suppress the degradation of the positive electrode.

[0057] [Formula 3]

[0058]

[0059] In addition, in the compound represented by Formula 1 of the present 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) that is easily reduced due to steric hindrance. Therefore, compared with the compound represented by Formula 4 below that does not contain an alkyl group, the reduction reaction at the negative electrode is suppressed, while the reactivity with the positive electrode is improved, thereby preparing a lithium secondary battery with improved high-temperature durability.

[0060] [Formula 4]

[0061]

[0062] Therefore, if the electrolyte for a lithium secondary battery including the electrolyte additive represented by Formula 1 is used, the effect of improving the high-temperature durability (such as cycle characteristics and storage characteristics) of the lithium secondary battery can be achieved.

[0063] Meanwhile, in the compound represented by Formula 1, R may be an alkyl group having 1 to 6 carbon atoms, or an alkyl group having 1 to 5 carbon atoms, and preferably an alkyl group having 1 to 4 carbon atoms.

[0064] The alkyl group may be substituted or unsubstituted.

[0065] In addition, the compound represented by the above formula 1 may include at least one of the compounds represented by the following formulas 1a to 1d. Specifically, as the number of carbon atoms in the substituent substituted 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. In view of this, it may be at least one of formulas 1a and 1c.

[0066] [Formula 1a]

[0067]

[0068] [Formula 1b]

[0069]

[0070] [Formula 1c]

[0071]

[0072] [Formula 1d]

[0073]

[0074] Electrolytes for lithium secondary batteries

[0075] Furthermore, in one embodiment, the present disclosure provides an electrolyte for a lithium secondary battery, comprising the electrolyte additive of the present disclosure.

[0076] The electrolyte for a lithium secondary battery may further include a lithium salt, an organic solvent, and optionally additional additives.

[0077] (1) Electrolyte additives

[0078] The electrolyte for a lithium secondary battery of the present disclosure may include an electrolyte additive including a compound represented by the above Formula 1. Since the description of the electrolyte additive overlaps with the above description, the description thereof will be omitted.

[0079] Meanwhile, considering the effects of forming a stable film on the electrode surface and removing thermal decomposition products of the lithium salt, the electrolyte additive may be contained in an amount of 0.1 wt % to 5.0 wt % based on the total weight of the nonaqueous electrolyte.

[0080] If the above-mentioned electrolyte additives are included within the above-mentioned content range, it is possible to suppress the disadvantages such as side reactions, capacity degradation and resistance increase caused by the additives as much as possible, while effectively suppressing the dissolution of transition metals of the positive electrode active material at high temperatures by forming a strong film on the positive electrode surface, and effectively removing the thermal decomposition products of the lithium salt, thereby achieving excellent high-temperature durability.

[0081] If the electrolyte additive content is 0.1% by weight or greater, the effect of removing thermal decomposition products of the lithium salt can be maintained even with increased operating time, and the effect of suppressing 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.

[0082] Specifically, the electrolyte additive may be included in an amount of 0.1 to 5.0 wt %, specifically 0.3 to 4.0 wt %, more specifically 0.3 to 3.0 wt %, and even more specifically 0.3 to 2.0 wt %, based on the total weight of the electrolyte for the lithium secondary battery.

[0083] (2) Lithium salt

[0084] As the lithium salt, any lithium salt generally used in an electrolyte for a lithium secondary battery may be used without limitation, and for example, the lithium salt may include Li + As cations, and as anions, may include F - 、Cl - Br - , I - 、NO3 - 、N(CN)2 - 、BF4 - 、ClO4 - 、B 10 Cl 10 - 、AlCl4 - 、AlO4 - PF6 - CF3SO3 - 、CH3CO2 - CF3CO2 - 、AsF6 - 、SbF6 - 、CH3SO3 - 、(CF3CF2SO2)2N - 、(CF3SO2)2N - 、(FSO2)2N - 、BF2C2O4 - BC4O8 - 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.

[0085] Specifically, the lithium salt may include a selected from LiCl, LiBr, LiI, LiBF4, LiClO4, LiB 10 Cl 10 , 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 lithium secondary battery electrolytes can be used without limitation.

[0086] The lithium salt may be appropriately changed within a generally available range, but may be contained in the electrolyte at a concentration of 0.8 M to 4.0 M, specifically 1.0 M to 3.0 M, to obtain the best effect of forming a film that prevents corrosion of the electrode surface.

[0087] When the concentration of the lithium salt is within the above range, the viscosity of the nonaqueous electrolyte can be controlled to achieve optimal impregnation, and the mobility of lithium ions can be increased, thereby improving the capacity characteristics and cycle characteristics of the lithium secondary battery.

[0088] (3) Non-aqueous organic solvents

[0089] In addition, the above-mentioned nonaqueous organic solvent will be described below.

[0090] As the nonaqueous organic solvent, various organic solvents generally used in nonaqueous electrolytes can be used without limitation as long as it can minimize decomposition due to oxidation reaction or the like during charge and discharge of a secondary battery and can exhibit desired characteristics together with additives.

[0091] Specifically, the non-aqueous organic solvent may include (i) a cyclic carbonate-based organic solvent, (ii) a linear carbonate-based organic solvent, or (iii) a mixture thereof.

[0092] (i) The cyclic carbonate-based organic solvent is an organic solvent having a high viscosity and is an organic solvent that can well dissociate the lithium salt in the electrolyte due to its high dielectric constant, and specific examples thereof 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-pentylene carbonate, 2,3-pentylene carbonate or vinylene carbonate, and specifically may include at least one of ethylene carbonate or propylene carbonate.

[0093] (ii) The linear carbonate organic solvent is an organic solvent having low viscosity and low dielectric constant, wherein typical examples of the linear carbonate organic solvent may include at least one organic solvent selected from dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethyl methyl carbonate (EMC), methylpropyl carbonate or ethylpropyl carbonate, and specifically, it may include at least one of dimethyl carbonate or ethylmethyl carbonate.

[0094] The lithium secondary battery electrolyte of the present disclosure can use (iii) a mixture of a cyclic carbonate-based organic solvent and a linear carbonate-based organic solvent to ensure high ionic conductivity, wherein the cyclic carbonate-based organic solvent and the linear carbonate-based organic solvent can be mixed in a volume ratio of 10:90 to 50:50, specifically 20:80 to 40:60.

[0095] In addition, the lithium secondary battery electrolyte of the present disclosure may further contain at least one organic solvent of (iv) a linear ester organic solvent or (v) a cyclic ester organic solvent having a lower melting point and higher high-temperature stability than the cyclic carbonate organic solvent and / or the linear carbonate organic solvent as a non-aqueous organic solvent.

[0096] (iv) Typical examples of the linear ester organic solvent 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.

[0097] (v) The cyclic ester organic solvent may include at least one organic solvent selected from γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, or ε-caprolactone.

[0098] Meanwhile, unless otherwise specified, the rest of the electrolyte for lithium secondary batteries except for the lithium salt, the electrolyte additives, and the additional additives described below may be an organic solvent.

[0099] (4) Additional additives

[0100] In addition, in order to prevent the electrolyte from decomposing under high output conditions and causing the collapse of the negative electrode, or to further improve the low-temperature high-rate discharge characteristics, high-temperature stability, overcharge protection, and battery swelling inhibition effect at high temperatures, the lithium secondary battery electrolyte disclosed in the present invention may further include other additional additives in the above-mentioned electrolyte if necessary.

[0101] Examples of additional additives may be at least one selected from cyclic carbonate compounds, halogenated carbonate compounds, sultone compounds, sulfate compounds, phosphate compounds, borate compounds, nitrile compounds, benzene compounds, amine compounds, silane compounds or lithium salt compounds.

[0102] The cyclic carbonate-based compound may include vinylene carbonate (VC) or vinyl ethylene carbonate.

[0103] The halogenated carbonate compound may include fluoroethylene carbonate (FEC).

[0104] The sultone compound may include at least one compound selected from 1,3-propane sultone (PS), 1,4-butane sultone, ethane sultone, 1,3-propene sultone (PRS), 1,4-butene sultone, or 1-methyl-1,3-propene sultone.

[0105] The sulfate compound may include ethylene sulfate (Esa), trimethylene sulfate (TMS), or methyltrimethylene sulfate (MTMS).

[0106] The phosphate compound may include one or more compounds selected from lithium difluoro(bisoxalato)phosphate, lithium difluorophosphate, tris(trimethylsilyl)phosphate, tris(2,2,2-trifluoroethyl)phosphate or tris(trifluoroethyl)phosphate.

[0107] The borate compound may include tetraphenylborate or lithium oxalyldifluoroborate.

[0108] The nitrile compound may include at least one compound selected from succinonitrile, adiponitrile, acetonitrile, propionitrile, butyronitrile, valeronitrile, octanonitrile, heptonitrile, cyclopentanecarbonitrile, cyclohexanecarbonitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, benzyl cyanide, 2-fluorophenyl cyanide or 4-fluorophenyl cyanide.

[0109] The benzene compound may include fluorobenzene, and the amine compound may include triethanolamine or ethylenediamine.

[0110] The silane-based compound may include tetravinylsilane.

[0111] The lithium salt-based compound is a compound other than the lithium salt contained in the electrolyte, and may include one or more compounds selected from LiPO2F2, LiODFB, LiBOB (lithium bis(oxalato)borate (LiB(C2O4)2), or LiBF4.

[0112] In the case of including vinylene carbonate, vinyl ethylene carbonate, or succinonitrile among the additional additives, a stronger SEI may be formed on the surface of the negative electrode during the initial activation process of the secondary battery.

[0113] The additional additive may be used as a mixture of two or more thereof, and its content may be 30 wt % or less, specifically 0.01 wt % to 10.0 wt %, preferably 0.05 wt % to 5.0 wt %, based on the total weight of the electrolyte. If the content of the additional additive is less than 0.01 wt %, the effect of improving the low temperature output, high temperature storage characteristics and high temperature life characteristics of the battery is not significant, and if the content of the additional additive is greater than 30 wt %, there is a possibility that side reactions in the electrolyte may occur excessively during charging and discharging of the battery. In particular, if an excess of SEI-forming additives is added, the additives may not be fully decomposed at high temperatures, so that they may be present in the electrolyte as unreacted materials or in the form of possible precipitation at room temperature. Therefore, side reactions that reduce the life or resistance characteristics of the secondary battery may occur.

[0114] lithium secondary batteries

[0115] Furthermore, in another embodiment of the present disclosure, the present disclosure provides a lithium secondary battery including the lithium secondary battery electrolyte of the present disclosure.

[0116] The lithium secondary battery of the present disclosure may be prepared by forming an electrode assembly in which a positive electrode, a negative electrode, and a separator therebetween are sequentially stacked and housed in a battery case and then injecting the electrolyte of the present disclosure therein.

[0117] The lithium secondary battery of the present disclosure can be prepared and used according to conventional methods known in the art, and the details are the same as described below.

[0118] (1) Positive electrode

[0119] The positive electrode of the present disclosure may include a positive electrode active material layer including a positive electrode active material, and if necessary, the positive electrode active material layer may further include a conductive agent and / or a binder.

[0120] 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), iron (Fe), or aluminum (Al). Specifically, the lithium composite metal oxide may include the compound represented by Formula 2 below.

[0121] [Formula 2]

[0122] Li 1+a Ni x Co y M 1 z M 2 w O2

[0123] In Formula 2,

[0124] M 1 is Mn, Al, or a combination thereof,

[0125] 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.

[0126] 1 + a represents the molar ratio of lithium in the lithium transition metal oxide, and can be from 0 ≤ a ≤ 0.5, preferably 0 ≤ a ≤ 0.2, more preferably 0 ≤ a ≤ 0.1. <​​​​​​​​​​​​​​​​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<000^064>)O2, Li(Ni 0.8 Mn 0.1 Co 0.1 )O2, Li(Ni 0.8 Co 0.15 Al 0.05 [[ID=3^]]O2, Li(Ni 0.86 Mn 0.07 [[ID=;4]]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.

[0132] 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- <00000^1>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.

[0133] The positive electrode active material may be present in an amount of 80 to 98 wt %, specifically 85 to 98 wt %, based on the total weight of the positive electrode active material layer. When the positive electrode active material content is within the above range, excellent capacity characteristics may be exhibited.

[0134] Next, a conductive agent is used to provide conductivity to the electrode, wherein any conductive agent can be used without particular limitation, as long as it has suitable electronic conductivity and does not cause 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 thermal black; graphite powder, such as natural graphite, artificial graphite, or graphite with a well-developed crystal 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 and potassium titanate whiskers; conductive metal oxides, such as titanium oxide; polyphenylene derivatives, etc., and any one of them or a mixture of two or more thereof can be used.

[0135] The conductive agent may be included in an amount of 0.1 wt % to 10.0 wt %, preferably 0.1 wt % to 5.0 wt %, based on the total weight of the positive electrode active material layer.

[0136] Next, the binder improves adhesion between positive electrode active material particles and between the positive electrode active material and the current collector.

[0137] As examples of adhesives, any one of the following or a mixture of two or more thereof can be used: fluororesin 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.

[0138] The binder may be included in an amount of 0.1 wt % to 15.0 wt %, preferably 0.1 wt % to 10.0 wt %, based on the total weight of the positive electrode active material layer.

[0139] The positive electrode of the present disclosure can be prepared by a method for preparing a positive electrode known in the art. For example, the positive electrode can be prepared by the following method for preparing an active material layer: 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 the following method: casting a positive electrode active material layer on a separate support, and then laminating a film separated from the support on the positive electrode current collector.

[0140] The positive electrode current collector is not particularly limited as long as it has conductivity without causing adverse chemical changes in the battery, and for example, stainless steel, aluminum, nickel, titanium, fired carbon, or aluminum or stainless steel surface-treated with one of carbon, nickel, titanium or silver can be used. In addition, the positive electrode current collector can generally have a thickness of 3 μm to 500 μm, and microscopic irregularities can be formed on the surface of the current collector to improve the adhesion of the positive electrode material. The positive electrode current collector can be used in various shapes, such as a film, a sheet, a foil, a mesh, a porous body, a foam body, and a non-woven fabric body.

[0141] The solvent can be a conventional solvent in the art, and can include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methyl pyrrolidone (NMP), acetone or water, and any one thereof or a mixture of two or more thereof can be used. Considering the coating thickness, manufacturing yield and processability of the positive electrode material mixture, if the positive electrode material mixture can be adjusted to have an appropriate viscosity, the amount of the solvent used can be sufficient and is not particularly limited.

[0142] (2) Negative electrode

[0143] Next, the negative electrode will be described.

[0144] The negative electrode of the present disclosure includes a negative electrode active material layer including a negative electrode active material, and if necessary, the negative electrode active material layer may further include a conductive agent and / or a binder.

[0145] As the negative electrode active material, various negative electrode active materials used in the art may be used, such as a carbon-based negative electrode active material, a silicon-based negative electrode active material, or a mixture thereof.

[0146] 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.

[0147] 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.

[0148] 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.

[0149] 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.

[0150] Since silicon-based negative electrode active materials have higher capacity characteristics than carbon-based negative electrode active materials, better capacity characteristics can be obtained when silicon-based negative electrode active materials are further included. However, for a negative electrode containing a silicon-based negative electrode active material, it contains more oxygen-rich (O-rich) components in the SEI compared to a graphite negative electrode, and when a Lewis acid such as HF or PF5 is present in the electrolyte, the SEI containing the O-rich component 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 to remove (or clear) the formed Lewis acids to stably maintain the SEI. Since the electrolyte disclosed herein contains an electrolyte additive that has an excellent Lewis acid scavenging effect while forming a stable film at the negative electrode and the positive electrode, the decomposition of the SEI can be effectively suppressed when a negative electrode containing a silicon-based active material is used.

[0151] At the same time, the silicon-based negative electrode active material and the carbon-based negative electrode active material can be mixed in a ratio of 3:97 to 99:1, preferably 5:95 to 15:85. When the mixing ratio of the silicon-based negative electrode active material to 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 and the capacity characteristics are improved, excellent cycle performance can be ensured.

[0152] The negative electrode active material may be present in an amount of 80 to 99 wt % based on the total weight of the negative electrode active material layer. When the amount of the negative electrode active material satisfies the above range, excellent capacity characteristics and electrochemical performance may be obtained.

[0153] Next, the conductive agent is a component for further improving the conductivity of the negative electrode active material, wherein the added amount of the conductive agent can be 10% by weight or less, preferably 5% by weight or less 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 has conductivity and does not cause adverse chemical changes in the battery, and for example, carbon black such as carbon black, acetylene black (or Denka black), Ketjen black, channel black, furnace black, lamp black or thermal black can be used; graphite powder such as natural graphite, artificial graphite or graphite with a well-developed crystal structure; conductive fibers such as carbon fibers or metal fibers; conductive powders such as fluorocarbon powders, aluminum powders or nickel powders; conductive whiskers such as zinc oxide whiskers or potassium titanate whiskers; conductive metal oxides such as titanium oxide; or polyphenylene derivatives.

[0154] The binder is a component that helps to bind the conductive agent, active material and current collector, wherein the amount of the binder added is generally 0.1% to 10% by weight based on the total weight of the negative electrode active material layer. Examples of the binder may be a fluororesin binder including polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE); a rubber binder including styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber or styrene-isoprene rubber; a cellulose binder including carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose or regenerated cellulose; a polyol binder including polyvinyl alcohol; a polyolefin binder including polyethylene or polypropylene; a polyimide binder; a polyester binder; or a silane binder.

[0155] The binder may be included in an amount of 0.1 wt % to 15.0 wt %, preferably 0.1 wt % to 10.0 wt %, based on the total weight of the negative active material layer.

[0156] The negative electrode can be prepared by a method for preparing a negative electrode known in the art. 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 a negative electrode active material and an optional binder and a conductive agent in a solvent, rolling and drying to form a negative electrode active material layer; or by casting a negative electrode active material layer on a separate support, and then laminating the film separated from the support on the negative electrode current collector.

[0157] The negative electrode current collector is not particularly limited as long as it has high conductivity without causing adverse chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with one of carbon, nickel, titanium, or silver, and aluminum-cadmium alloys can be used. The negative electrode current collector can generally have a thickness of 3 μm to 500 μm, and similar to the positive electrode current collector, microscopic irregularities can be formed on the surface of the current collector 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 non-woven fabrics.

[0158] The solvent may be a commonly used solvent in the art, and may include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone or water, and any one thereof or a mixture of two or more thereof may be used. Considering the coating thickness, manufacturing yield and workability of the negative electrode material mixture, if the negative electrode slurry can be adjusted to have an appropriate viscosity, the amount of the solvent used may be sufficient and is not particularly limited.

[0159] (3) Diaphragm

[0160] The lithium secondary battery of the present disclosure includes a separator between a positive electrode and a negative electrode.

[0161] The separator separates the negative electrode and the positive electrode and provides a path for the movement of lithium ions. As the separator, any separator can be used without particular limitation as long as it is commonly used in lithium secondary batteries. In particular, a separator having high moisture retention capacity for electrolytes and low resistance to the migration of lithium salt ions is preferred.

[0162] Specifically, as a diaphragm, a porous polymer film can be used, for example, a porous polymer film prepared by a polyolefin polymer (such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer or ethylene / methacrylate copolymer), or a laminated structure with more than two layers thereof. In addition, a typical porous non-woven fabric can be used, for example, a non-woven fabric formed by high melting point glass fiber or polyethylene terephthalate fiber. In addition, a coated diaphragm including a ceramic component or a polymer material can be used to ensure heat resistance or mechanical strength, and a diaphragm with a single layer or multilayer structure can be optionally used.

[0163] The lithium secondary battery of the present disclosure as described above can be suitably used in portable devices such as mobile phones, notebook computers, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs).

[0164] The shape of the lithium secondary battery of the present disclosure is not particularly limited, but a cylindrical type using a can, a prismatic type, a pouch type, or a coin type may be used.

[0165] The lithium secondary battery of the present disclosure can be used not only in a battery cell used as a power source for small devices but also as a unit cell in a medium or large battery module including a plurality of battery cells.

[0166] Experimental example

[0167] Example 1

[0168] (Preparation of non-aqueous electrolyte for lithium secondary batteries)

[0169] LiPF6 was dissolved in a non-aqueous organic solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) mixed in a volume ratio of 30:70 so that the concentration of LiPF6 was 1.0 M, and then 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 lithium secondary batteries (see Table 1 below).

[0170] (Preparation of Secondary Battery)

[0171] The positive electrode active material (Li(Ni 0.9 Mn 0.03 Co0.06 Al 0.01 )O2), a conductive agent (carbon black), and a 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%). The positive electrode slurry was applied to a positive electrode current collector (Al thin film) with a thickness of 13.5 μm, dried, and roll-pressed to prepare a positive electrode.

[0172] The negative electrode active material (graphite:SiO = 94:6 weight ratio), binder (SBR-CMC) and conductive agent (carbon black) were added to water as a solvent at a weight ratio of 97.6:0.8:1.6 to prepare a negative electrode slurry (solid content: 60 weight%). The negative electrode slurry was used to coat a negative electrode current collector (Cu thin film) with a thickness of 6 μm, dried and roll-pressed to prepare a negative electrode.

[0173] A porous polypropylene separator was interposed between the positive electrode and the negative electrode to prepare an electrode assembly, and then the electrode assembly was housed in a battery case, and the prepared lithium secondary battery electrolyte was injected therein to prepare a lithium secondary battery.

[0174] Example 2

[0175] A lithium secondary battery was prepared in the same manner as in Example 1, except that LiPF6 was dissolved in an organic solvent so that the concentration of LiPF6 was 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 a lithium secondary battery (see Table 1 below).

[0176] Example 3

[0177] A lithium secondary battery was prepared in the same manner as in Example 1, except that LiPF6 was dissolved in an organic solvent so that the concentration of LiPF6 was 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 a lithium secondary battery (see Table 1 below).

[0178] Example 4

[0179] A lithium secondary battery was prepared in the same manner as in Example 1, except that LiPF6 was dissolved in a non-aqueous organic solvent so that the concentration of LiPF6 was 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 a non-aqueous electrolyte for a lithium secondary battery (see Table 1 below).

[0180] Comparative Example 1

[0181] A lithium secondary battery was prepared in the same manner as in Example 1, except that LiPF6 was dissolved in a non-aqueous organic solvent so that the concentration of LiPF6 was 1.0 M, and 0.5 wt % of vinylene carbonate (VC) was added as an additive to prepare a non-aqueous electrolyte for a lithium secondary battery (see Table 1 below).

[0182] Comparative Example 2

[0183] A lithium secondary battery was prepared in the same manner as in Example 1, except that LiPF6 was dissolved in a non-aqueous organic solvent so that the concentration of LiPF6 was 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) were added as additives to prepare a non-aqueous electrolyte for a lithium secondary battery (see Table 1 below).

[0184] [Formula 3]

[0185]

[0186] Comparative Example 3

[0187] A lithium secondary battery was prepared in the same manner as in Example 1, except that LiPF6 was dissolved in a non-aqueous organic solvent so that the concentration of LiPF6 was 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) were added as additives to prepare a non-aqueous electrolyte for a lithium secondary battery (see Table 1 below).

[0188] [Formula 4]

[0189]

[0190] [Table 1]

[0191]

[0192] Meanwhile, the abbreviations of the compounds in Table 1 have the following meanings.

[0193] EC: Ethylene carbonate

[0194] EMC: Ethyl Methyl Carbonate

[0195] VC: vinylene carbonate

[0196] Experimental example

[0197] Experimental Example 1. Evaluation of high-temperature storage characteristics

[0198] 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 a rate of 0.33C under CC / CV conditions at 25°C (0.05C cut-off) to 4.2V, fully charged to SOC100%, and stored at a high temperature (60°C) for 16 weeks. Subsequently, they were transferred to a charge / discharger at room temperature (25°C) to measure the resistance, and the resistance increase rate was calculated using the following equation 1, and the results are presented in Table 2 below.

[0199] [Equation 1]

[0200] Resistance increase rate (%) = {(resistance after high temperature storage - initial resistance) / initial resistance} x 100

[0201] Experimental Example 2. Evaluation of High-Temperature Cycling Characteristics

[0202] The lithium secondary batteries prepared in the examples and comparative examples were activated (formed) for 3 hours at a rate of 0.1C, and then charged (0.05C cut-off) to 4.2V at a rate of 0.33C under CC / CV conditions at 25°C, and fully charged to SOC100%. The fully charged battery was charged to 4.2V at a rate of 0.33C under CC / CV conditions at 45°C, and discharged to 2.8V at a rate of 0.33C under CC conditions, which was set as one cycle. After 300 cycles, the capacity retention rate after 300 cycles was measured using Equation 2 below, and the results are presented in Table 2 below.

[0203] [Equation 2]

[0204] Capacity retention (%) = (capacity after 300 cycles / capacity after 1 cycle) x 100

[0205] [Table 2]

[0206] 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

[0207] Referring to Table 2 above, it can be confirmed that the secondary batteries of Examples 1 to 4 of the present disclosure exhibit improved resistance increase rate (%) after high-temperature storage and improved capacity retention rate (%) after high-temperature cycling compared to the lithium secondary batteries of Comparative Examples 1 to 3.

Claims

1. An electrolyte additive comprising a compound represented by Formula 1: [Formula 1] In formula 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 Formula 1a to Formula 1d: [Formula 1a] [Formula 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 compound represented by Formula 1a and the compound represented by Formula 1c. 6 . An electrolyte for a lithium secondary battery, comprising the electrolyte additive according to claim 1 .

7. The lithium secondary battery electrolyte according to claim 6, in, The electrolyte additive is contained in the electrolyte for lithium secondary batteries in an amount of 0.1 wt % to 5.0 wt %.

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

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

10. A lithium secondary battery comprising: positive electrode; negative electrode; a separator disposed between the positive electrode and the negative electrode; as well as The electrolyte for a lithium secondary battery according to claim 6.

11. The lithium secondary battery according to claim 10, in, The positive electrode comprises 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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