Nonaqueous electrolyte and lithium secondary battery comprising same

Abstract

A lithium secondary battery includes a negative electrode including a silicon-based negative electrode active material, a positive electrode, a separator, and a non-aqueous electrolyte. The nonaqueous electrolyte includes a lithium salt, an organic solvent, a compound of Formula 1 as a first additive, and a compound of Formula 2 as a second additive. [In formula 1], R is an alkylene group having 1 to 5 carbon atoms which may be substituted with fluorine, and R1 to R3 are each independently any one selected from the group consisting of H, an alkyl group having 1 to 5 carbon atoms, and a nitrile group. [In formula 2], R4 to R7 are each independently any one selected from the group consisting of an alkyl group having 1 to 10 carbon atoms, which may be substituted with fluorine, and an alkenyl group having 2 to 10 carbon atoms, which may be substituted with fluorine. [Formula 1] # imgabs0 # [Formula 2] # imgabs1 #

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application is based on and claims the benefit of priority of Korean Patent Application No. 10-2023-0030216 filed in the Korean Intellectual Property Office on March 7, 2023, the disclosure of which is incorporated herein by reference in its entirety. Technical Field

[0003] The present disclosure relates to a nonaqueous electrolyte and a lithium secondary battery including the same. Background Art

[0004] Recently, the application of lithium secondary batteries has rapidly expanded from power sources for electricity, electronics, communications, and electronic devices (such as computers) to power storage and supply for large-scale equipment (such as automobiles and energy storage systems). Therefore, the demand for secondary batteries with high capacity, high power, and high stability is increasing.

[0005] In particular, in lithium secondary batteries for automobiles, high capacity, high power and long life characteristics are becoming important. In order to achieve high capacity of secondary batteries, silicon-based negative electrode active materials with high energy density but low stability can be used. Summary of the invention

[0006] [Technical issues]

[0007] In order to solve the above-mentioned problems, various studies have been conducted. As a result, the present invention provides a lithium secondary battery. In a lithium secondary battery using a negative electrode with a silicon-based negative electrode active material having low stability, by including a non-aqueous electrolyte capable of forming a stable SEI (solid electrolyte interphase) film on the negative electrode with extremely large volume change, the lithium secondary battery of the present invention has improved long life characteristics, high temperature storage characteristics and thermal stability, thereby improving the overall performance.

[0008] [Technical solution]

[0009] In order to achieve the above-mentioned object, an embodiment of the present disclosure provides a lithium secondary battery, which includes: a negative electrode including a silicon-based negative electrode active material; a positive electrode; a separator; and a non-aqueous electrolyte. The non-aqueous electrolyte includes: a lithium salt; an organic solvent; a compound of the following formula 1 as a first additive; and a compound of the following formula 2 as a second additive.

[0010] [Formula 1]

[0011]

[0012] In the above formula 1, R is an alkylene group having 1 to 5 carbon atoms which may be substituted with fluorine, and R 1 To R 3Each is independently any one selected from the group consisting of H, an alkyl group having 1 to 5 carbon atoms, and a nitrile group.

[0013] [Formula 2]

[0014]

[0015] In the above formula 2, R 4 To R 7 Each is independently any one selected from the group consisting of an alkyl group having 1 to 10 carbon atoms which may be substituted with fluorine and an alkenyl group having 2 to 10 carbon atoms which may be substituted with fluorine.

[0016] Another embodiment of the present disclosure provides a nonaqueous electrolyte including: a lithium salt; an organic solvent; a compound of the following Formula 1 as a first additive; and a compound of the following Formula 2 as a second additive.

[0017] [Formula 1]

[0018]

[0019] In the above formula 1, R is an alkylene group having 1 to 5 carbon atoms which may be substituted with fluorine, and R 1 To R 3 Each is independently any one selected from the group consisting of H, an alkyl group having 1 to 5 carbon atoms, and a nitrile group.

[0020] [Formula 2]

[0021]

[0022] In the above formula 2, R 4 To R 7 Each is independently any one selected from the group consisting of an alkyl group having 1 to 10 carbon atoms which may be substituted with fluorine and an alkenyl group having 2 to 10 carbon atoms which may be substituted with fluorine.

[0023] [Beneficial Effects]

[0024] The compound of formula 1 used as the first additive of the present invention can form a polyethylene oxide-based polymer SEI layer with high elasticity during reduction, and the compound of formula 2 used as the second additive of the present invention can form an SEI layer having a polysiloxane structure exhibiting a high shear elastic modulus (e.g., the degree of ability to resist shear stress) during reduction.

[0025] In particular, the first additive includes propargyl and the second additive includes tetravinyl. The presence of these additives enables the formation of a more stable polymer film. In addition, the second additive has a cyclic siloxane structure, which can promote the reduction reaction compared to the additive with a linear siloxane structure. In addition, the lone electron pair of imidazole present in the structure of the first additive accelerates the ring-opening reaction of the second additive, so that a polymer film can be easily formed. In other words, the combination of the first and second additives provides a synergistic effect, which can significantly improve the durability of the film formed on the negative electrode.

[0026] Due to the synergistic effect achieved through the interaction of the first and second additives, the present disclosure can form a highly stable and durable electrode-electrolyte interface even in a lithium secondary battery having a negative electrode containing a silicon-based negative electrode active material that undergoes a sharp volume change during charging and discharging, and can suppress unnecessary electrolyte decomposition side reactions, thereby realizing a lithium secondary battery with improved overall performance. DETAILED DESCRIPTION

[0027] The words and terms used in the detailed description and claims of this document should not be construed as limited to their ordinary meanings or dictionary meanings, but should be construed as having meanings and concepts corresponding to the technical ideas of the present disclosure based on the principle that the inventor can appropriately define the terms and concepts to best describe the purpose of the present disclosure.

[0028] In the following description, the terms "include", "comprises" and "has" are intended to specify the presence of stated features, numbers, steps, components or a combination thereof, but do not exclude the presence or addition of one or more other features, numbers, steps, components or a combination thereof.

[0029] In the expression "a to b carbon atoms" throughout the specification, "a" and "b" each refer to the number of carbon atoms contained in a particular functional group. That is, the functional group may include "a" to "b" carbon atoms. For example, "an alkylene group having 1 to 5 carbon atoms" refers to an alkylene group containing 1 to 5 carbon atoms, such as -CH 2 -、-CH 2 CH 2 -、-CH 2 CH 2 CH 2 -、-CH 2 (CH 3 )CH-、-CH(CH 3 )CH 2 - and -CH(CH 3 )CH 2 CH 2 -.

[0030] In the description herein, "alkylene" means a branched or unbranched divalent saturated hydrocarbon group.

[0031] In the description herein, the alkyl group may be substituted or unsubstituted. Unless otherwise defined, the term "substituted" means that at least one hydrogen bonded to carbon is replaced by an element other than hydrogen.

[0032] Hereinafter, the present invention will be described in more detail.

[0033] In order to achieve high energy density, lithium secondary batteries may use transition metal-based lithium metal oxides (e.g., nickel (Ni), cobalt (Co), or manganese (Mn)) in their positive electrodes, and may use silicon-based negative electrode active materials (e.g., silicon (Si) or silicon oxide (SiOx) that can be alloyed with lithium ions and has a high theoretical capacity) in their negative electrodes. However, in the case of operating a secondary battery using a negative electrode to which a silicon-based negative electrode active material is applied, the durability of a film (e.g., SEI film) formed on the surface of the negative electrode may deteriorate due to a sharp volume change during repeated charging and discharging, which may lead to degradation of capacity.

[0034] When the battery is exposed to high temperature, capacity degradation of the secondary battery tends to become faster, and as a result, the cycle characteristics of the secondary battery may deteriorate.

[0035] When lithium secondary batteries are used continuously for a long time or placed in a high temperature environment, gas is generated, causing a so-called swelling phenomenon (swelling or deformation) in which the thickness of the battery increases. It is known that the amount of gas generated at this time depends on the state of SEI.

[0036] Therefore, the present disclosure provides a lithium secondary battery including a non-aqueous electrolyte capable of suppressing a swelling phenomenon and enhancing high temperature stability.

[0037] Non-aqueous electrolytes

[0038] The nonaqueous electrolyte of the present disclosure may include: a lithium salt; an organic solvent; a compound of the following Formula 1 as a first additive; and a compound of the following Formula 2 as a second additive.

[0039] [Formula 1]

[0040]

[0041] In the above formula 1, R is an alkylene group having 1 to 5 carbon atoms which may be substituted with fluorine, and R 1 To R 3 Each is independently any one selected from the group consisting of H, an alkyl group having 1 to 5 carbon atoms, and a nitrile group.

[0042] [Formula 2]

[0043]

[0044] In the above formula 2, R 4 To R 7 Each is independently any one selected from the group consisting of an alkyl group having 1 to 10 carbon atoms which may be substituted with fluorine and an alkenyl group having 2 to 10 carbon atoms which may be substituted with fluorine.

[0045] The lithium secondary battery of the present disclosure includes a compound represented by the following formula 1 as a first additive for a non-aqueous electrolyte. The compound of formula 1 includes a propargyl group and an oxygen atom having a triple bond, and it is known that the propargyl group has metal ion adsorption properties. Therefore, the propargyl group separated by the cleavage between the nitrogen (N) atom and the carbon (C) atom of the imidazole group can be adsorbed from the positive electrode of the lithium secondary battery during high-voltage charging. The metal foreign matter such as Fe, Co, Mn and Ni eluted, thereby effectively suppressing the negative electrode degradation phenomenon caused by the electrodeposition of metal foreign matter on the negative electrode surface. In addition, in the compound represented by formula 1, the lone electron pair of the nitrogen (N) atom of the imidazole group reacts with polyvinyl carbonate on the negative electrode surface and is reduced (polyvinyl carbonate is a decomposition product of fluoroethylene carbonate (FEC) used as an organic solvent), so that a stable ion conductive membrane can be formed on the negative electrode surface. Therefore, not only can additional electrolyte decomposition reactions be suppressed during charge and discharge cycles, but lithium ion absorption and release at the negative electrode can also be promoted even during overcharge or high-temperature storage, which can improve the cycle-life characteristics and high-temperature storage performance of the secondary battery.

[0046] [Formula 1]

[0047]

[0048] In the above Formula 1, R may be an alkylene group having 1 to 5 carbon atoms which may be substituted with fluorine, for example, an alkylene group having 1 to 3 carbon atoms.

[0049] In the above formula 1, R 1 To R 3 Each of them may be independently any one selected from the group consisting of H, an alkyl group having 1 to 5 carbon atoms, and a nitrile group, for example, any one selected from H and an alkyl group having 1 to 3 carbon atoms.

[0050] For example, the compound of Formula 1 above may be any one selected from the group consisting of the following Formulae 1-1 to 1-3.

[0051] [Formula 1-1]

[0052]

[0053] [Formula 1-2]

[0054]

[0055] [Formula 1-3]

[0056]

[0057] The lithium secondary battery of the present disclosure includes a compound represented by the following formula 2 as a second additive to the non-aqueous electrolyte. The compound of formula 2 can be easily reduced by a ring-opening reaction, so that an SEI layer containing polysiloxane can be formed on the negative electrode. Since the SEI layer having a polysiloxane structure has a high shear elastic modulus (ability to resist shear stress), it can withstand the drastic volume change of the negative electrode.

[0058] [Formula 2]

[0059]

[0060] In the above formula 2, R 4 To R 7 Each independently may be any one selected from the group consisting of an alkyl group having 1 to 10 carbon atoms which may be substituted with fluorine and an alkenyl group having 2 to 10 carbon atoms which may be substituted with fluorine, for example, an alkyl group having 1 to 5 carbon atoms which may be substituted with fluorine or an alkyl group having 1 to 3 carbon atoms which may be substituted with fluorine. When a fluorine group is substituted in the compound of Formula 2, a stable and elastic polymer film containing an inorganic material (e.g., LiF) may be formed on the electrode.

[0061] For example, the compound of the above Formula 2 may be any one selected from the group consisting of the following Formulae 2-1 to 2-3.

[0062] [Formula 2-1]

[0063]

[0064] [Formula 2-2]

[0065]

[0066] [Formula 2-3]

[0067]

[0068] When the non-aqueous electrolyte of the present disclosure containing the first additive and the second additive is used, the free radicals generated by the cleavage of the ring structure of the first additive accelerate the film-forming reaction of the second additive. Due to the presence of imidazole or its derivative structure in the cycloalkyl-based film, the film formed by the interaction of the first additive and the second additive has excellent lithium ion transfer performance, thereby improving the overall performance of the lithium secondary battery, including charge / discharge characteristics and power characteristics. The film formed by the interaction of the first additive and the second additive has excellent oxidation resistance, so that the side reactions occurring in the film of the positive and negative electrodes can be suppressed even in the acidic atmosphere of the electrolyte. In addition, the film formed by the interaction of the first additive and the second additive exhibits excellent durability to the volume change of the negative electrode occurring during charging and discharging. Therefore, the non-aqueous electrolyte of the present disclosure can form an electrode-electrolyte interface having relatively high stability and durability at high temperatures and can suppress unnecessary electrolyte decomposition side reactions, thereby realizing a lithium secondary battery with improved overall performance.

[0069] In the non-aqueous electrolyte of the present disclosure, the content of the first additive may be 0.01 to 10 parts by weight, such as 0.1 to 5.0 parts by weight, or 0.5 to 3.0 parts by weight, relative to 100 parts by weight of the non-aqueous electrolyte. When the content of the first additive satisfies the above range, the effect of forming a film on the negative electrode can be fully achieved, which leads to excellent effects in terms of life characteristics at high temperatures and high temperature storage characteristics.

[0070] In the non-aqueous electrolyte of the present disclosure, the content of the second additive may be 0.01 to 10 parts by weight, for example 0.1 to 5.0 parts by weight, or 0.5 to 3.0 parts by weight, relative to 100 parts by weight of the non-aqueous electrolyte. When the content of the second additive satisfies the above range, the effect of forming a film on the negative electrode can be fully achieved, which leads to excellent effects in terms of life characteristics at high temperatures and high temperature storage characteristics.

[0071] In the non-aqueous electrolyte of the present disclosure, the first additive and the second additive may be included in a weight ratio of 1:0.002 to 1:500, for example, 1:0.1 to 1:10, or 1:0.2 to 1:5. When this range is satisfied, the elasticity of the SEI film falls within an appropriate range, so that the SEI film can remain stable during charge and discharge or at high temperatures.

[0072] The non-aqueous electrolyte of the present disclosure may contain a lithium salt. The lithium salt is used as an electrolyte salt in a lithium secondary battery and acts as a medium for transferring ions. Generally, the lithium salt includes, for example, Li + as positive ions, and including at least one selected from the following as negative ions: F - , Cl - Br -、I - 、NO 3 - 、N(CN) 2 - 、BF 4 - 、ClO 4 - 、B 10 Cl 10 - 、AlCl 4 - 、AlO 2 - 、PF 6 - 、CF 3 SO 3 - 、CH 3 CO 2 - 、CF 3 CO 2 - 、AsF 6 - 、SbF 6 - 、CH 3 SO 3 - 、(CF 3 CF 2 SO 2 ) 2 N - 、(CF 3 SO 2 ) 2 N - 、(FSO 2 ) 2 N - 、BF 2 C 2 O 4 - 、BC 4 O 8 - 、PF 4 C 2 O 4 - 、PF 2 C 4 O 8 - 、(CF 3 ) 2 PF 4 - 、(CF 3 ) 3 PF3 - ,(CF 3 ) 4 PF 2 - ,(CF 3 ) 5 PF - ,(CF 3 ) 6 P - , C 4 F 9 SO 3 - CF 3 CF 2 SO 3 - CF 3 CF 2 (CF 3 ) 2 CO - ,(CF 3 SO 2 ) 2 CH - CF 3 (CF 2 ) 7 SO 3 - and SCN - .

[0073] For example, the lithium salt may include a single substance or a mixture of two or more substances selected from the following: LiCl, LiBr, LiI, LiBF 4 、LiClO 4 , LiB 10 Cl 10 、LiAlCl 4 、LiAlO 2 、LiPF 6 、LiSO 3 CF 3 、LiCO 2 CH 3 、LiCO 2 CF 3 、LiAsF 6 、LiSbF 6 、LiSO 3 CH 3 、LiN(SO 2 F) 2 (Lithium bis(fluorosulfonyl)imide; LiFSI), LiN(SO 2 CF 2 CF 3 ) 2(Lithium bis(perfluoroethanesulfonyl)imide; LiBETI) and LiN(SO 2 CF 3 ) 2 (Lithium bis(trifluoromethanesulfonyl)imide; LiTFSI) Other lithium salts generally used for electrolytes of lithium secondary batteries may be used without limitation.

[0074] The concentration of the lithium salt can be appropriately changed within a generally allowed range, but in order to obtain the best effect of forming an anti-electrode surface corrosion film, the lithium salt can be contained in the electrolyte at a concentration of 0.5 M to 5.0 M, for example, 1.0 M to 3.0 M or 1.2 M to 2.0 M. When the concentration of the lithium salt satisfies the above range, a sufficient effect can be obtained in improving the cycle characteristics during high-temperature storage of the lithium secondary battery, and the viscosity of the non-aqueous electrolyte becomes appropriate, thereby improving electrolyte impregnation.

[0075] The non-aqueous electrolyte of the present disclosure may contain an organic solvent. The organic solvent may include at least one organic solvent selected from the group consisting of a cyclic carbonate organic solvent, a chain carbonate organic solvent, a chain ester organic solvent, and a cyclic ester organic solvent.

[0076] The additive disclosed in the present invention is particularly effective when using a cyclic carbonate solvent. When conventional electrolyte additives are used together with cyclic carbonate solvents, there is always a problem of continuous decomposition of the cyclic carbonate solvent, because the SEI film formed by the decomposition of the cyclic carbonate solvent cannot remain unchanged due to the change in the negative electrode volume that occurs as the cycle proceeds. As a result, the ionic conductivity of the electrolyte decreases, resulting in a problem of deterioration of the cycle characteristics. At the same time, when the combination of the additive disclosed in the present invention is used together with the cyclic carbonate solvent, a stable SEI film is formed, thereby improving the cycle characteristics.

[0077] The cyclic carbonate organic solvent is an organic solvent with high viscosity and high dielectric constant, which can dissociate the lithium salt in the electrolyte well, and its specific example includes at least one organic solvent selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), fluoroethylene carbonate (FEC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate and vinylene carbonate, and can be particularly fluoroethylene carbonate (FEC). When fluoroethylene carbonate (FEC) is used as an organic solvent, the excellent reducibility of FEC causes interaction with the first and second additives, so that a more stable film can be formed on the silicon-based negative electrode that undergoes significant volume changes during charging and discharging.

[0078] The linear carbonate organic solvent is an organic solvent having low viscosity and low dielectric constant, and specific examples thereof include at least one organic solvent selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethyl methyl carbonate (EMC), methyl propyl carbonate and ethyl propyl carbonate, and may particularly be ethyl methyl carbonate (EMC) and diethyl carbonate (DEC).

[0079] In addition, in order to prepare an electrolyte with high ionic conductivity, in addition to at least one carbonate organic solvent selected from the group consisting of one or more cyclic carbonate organic solvents and chain carbonate organic solvents, the organic solvent may also include at least one ester organic solvent selected from the group consisting of chain ester organic solvents and cyclic ester organic solvents.

[0080] Examples of the chain ester organic solvent include at least one organic solvent selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, and butyl propionate.

[0081] Furthermore, examples of the cyclic ester-based organic solvent include at least one organic solvent selected from the group consisting of γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, and ε-caprolactone.

[0082] Meanwhile, if necessary, the organic solvent may additionally use an organic solvent commonly used in non-aqueous electrolytes without limitation. For example, the organic solvent may further include at least one of an ether organic solvent, a glyme organic solvent, and a nitrile organic solvent.

[0083] The ether solvent may be any one selected from dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether, ethyl propyl ether, 1,3-dioxolane (DOL) and 2,2-bis(trifluoromethyl)-1,3-dioxolane (TFDOL), or a mixture of two or more thereof.

[0084] Compared with linear carbonate organic solvents, glycol diether solvents have high dielectric constants and low surface tension, and their reactivity with metals is lower. Glyme solvents may include but are not limited to at least one selected from dimethoxyethane (glycol dimethyl ether, DME), diethoxyethane, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether and tetraethylene glycol dimethyl ether (TEGDME).

[0085] The nitrile solvent may be, but is not limited to, at least one selected from acetonitrile, propionitrile, butyronitrile, valeronitrile, octanonitrile, heptanecarbonitrile, cyclopentanecarbonitrile, cyclohexanecarbonitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, benzyl cyanide, 2-fluorobenzeneacetonitrile and 4-fluorobenzeneacetonitrile.

[0086] Furthermore, if necessary, the non-aqueous electrolyte of the present disclosure may additionally include well-known electrolyte additives to prevent negative electrode collapse caused by decomposition of the non-aqueous electrolyte under high power conditions, improve low-temperature high-rate discharge characteristics and high-temperature stability, prevent overcharging, and inhibit expansion of the battery at high temperatures.

[0087] Examples of additional electrolyte additives include at least one SEI film-forming additive selected from cyclic carbonate compounds, halogenated carbonate compounds, sultone compounds, sulfate compounds, phosphate compounds, borate compounds, nitrile compounds, benzene compounds, amine compounds, silane compounds and lithium salt compounds.

[0088] The cyclic carbonate compound may be, for example, vinylene carbonate (VC) or vinylethylene carbonate.

[0089] The halogenated carbonate compound may be, for example, fluoroethylene carbonate (FEC).

[0090] The sultone compound may be, for example, at least one compound selected from the group consisting of 1,3-propane sultone (PS), 1,4-butane sultone, ethylene sultone, 1,3-propene sultone (PRS), 1,4-butene sultone, and 1-methyl-1,3-propene sultone.

[0091] The sulfate compound may be, for example, ethylene sulfate (Esa), trimethylene sulfate (TMS) or methyltrimethylene sulfate (MTMS).

[0092] The phosphate compound may be, for example, at least one compound selected from the group consisting of lithium difluoro(dioxalato)phosphate, lithium difluorophosphate, tris(trimethylsilyl)phosphate, tris(trimethylsilyl)phosphite, tris(2,2,2-trifluoroethyl)phosphate and tris(2,2,2-trifluoroethyl)phosphite.

[0093] The borate / ester compound can be tetraphenylborate, lithium oxalyldifluoroborate (LiODFB) or lithium bis(oxalatoborate) (LiB(C 2 O 4 ) 2 ,LiBOB).

[0094] The nitrile compound may be, for example, at least one compound selected from the group consisting of succinonitrile, adiponitrile, acetonitrile, propionitrile, butyronitrile, valeronitrile, octanonitrile, heptanecarbonitrile, cyclopentanecarbonitrile, cyclohexanecarbonitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, benzyl cyanide, 2-fluorophenyl cyanide and 4-fluorophenyl cyanide.

[0095] The benzene compound may be, for example, fluorobenzene, the amine compound may be triethanolamine or ethylenediamine, and the silane compound may be tetravinylsilane.

[0096] The lithium salt-based compound is a compound other than the lithium salt contained in the non-aqueous electrolyte, and may be, for example, lithium difluorophosphate (LiDFP; LiPO 2 F 2 ) or LiBF 4 .

[0097] Among the above-mentioned additional electrolyte additives, when a combination of vinylene carbonate (VC), 1,3-propane sultone (PS), ethylene sulfate (Esa) and lithium difluorophosphate (LiDFP) is additionally contained, a more stable SEI film can be formed on the negative electrode surface during the initial activation of the secondary battery, and gas generation that may occur due to decomposition of the electrolyte at high temperature can be reduced, so that the high temperature stability of the secondary battery is improved compared with conventional secondary batteries.

[0098] The additional electrolyte additive may be used as a mixture of two or more thereof, and its content may be 0.050 wt % to 20 wt %, such as 0.10 wt % to 15 wt %, or 0.30 wt % to 10 wt %, based on the total weight of the non-aqueous electrolyte. When the content of the additional electrolyte additive satisfies the above range, a more excellent effect is obtained in improving ionic conductivity and cycle characteristics compared to conventional lithium secondary batteries.

[0099] Lithium secondary battery

[0100] The present disclosure also provides a lithium secondary battery including the above-mentioned nonaqueous electrolyte.

[0101] For example, the lithium secondary battery of the present disclosure includes: a negative electrode including a silicon-based negative electrode active material; a positive electrode; a separator; and the above-mentioned nonaqueous electrolyte.

[0102] The lithium secondary battery of the present invention can be manufactured according to a commonly known method in the related art. For example, the lithium secondary battery can be manufactured by sequentially stacking a positive electrode, a negative electrode, and a separator between the positive electrode and the negative electrode to form an electrode assembly, and then inserting the electrode assembly into a battery case and injecting the non-aqueous electrolyte of the present invention.

[0103] The positive electrode included in the lithium secondary battery of the present disclosure may be manufactured by coating a positive electrode composite slurry including, for example, a positive electrode active material, a binder, a conductive agent, a solvent, etc., on a positive electrode collector.

[0104] The positive electrode current collector is not particularly limited as long as it has conductivity and does not cause chemical changes in the battery, and can be, for example, stainless steel, aluminum, nickel, titanium, sintered carbon, or aluminum or stainless steel surface-treated with, for example, carbon, nickel, titanium, or silver. Micro-irregularities can be formed on the surface of the positive electrode current collector to improve the adhesion of the positive electrode active material. The positive electrode current collector can be used in various shapes, such as films, sheets, foils, meshes, porous bodies, foams, and non-woven fabrics.

[0105] The positive electrode active material is a compound that allows reversible insertion / extraction of lithium and can include lithium metal oxides that include lithium and at least one metal such as nickel, cobalt, manganese, or aluminum. For example, the lithium metal oxide can include one or more of the following compounds: lithium-manganese-based oxides (such as LiMnO 2 , LiMn 2 O 4 etc.), lithium-cobalt-based oxides (such as LiCoO 2 etc.), lithium-nickel-based oxides (such as LiNiO 2 etc.), lithium-nickel-manganese-based oxides (such as LiNi 1-Y Mn Y O 2 (where 0 < Y < 1), LiMn 2-Z Ni z O 4 (where 0 < Z < 2) etc.), lithium-nickel-cobalt-based oxides (such as LiNi 1-Y1 Co Y1 O 2 (where 0 < Y1 < 1) etc.), lithium-manganese-cobalt-based oxides (such as LiCo 1-Y2 Mn Y2 O 2 (where 0 < Y2 < 1), LiMn 2-Z1 Co z1 O 4 (where 0 < Z1 < 2) etc.), lithium-nickel-manganese-cobalt-based oxides (such as Li(Ni p Co q Mn r )O 2 (where 0 < p < 1, 0 < q < 1, 0 < r < 1, and p + q + r = 1) or Li(Ni p1 Co q1 Mn r1 )O 4 (where 0 < p1 < 2, 0 < q1 < 2, 0 < r1 < 2, and p1 + q1 + r1 = 2) etc.), or lithium-nickel-cobalt-transition metal (M) oxides (such as Li(Ni p2 Co q2 Mn r2 MS2 )O 2 (where M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, and Mo, and p2, q2, r2, and s2 are the atomic fractions of various independent elements, where 0 < p2 < 1, 0 < q2 < 1, 0 < r2 < 1, 0 < s2 < 1, and p2 + q2 + r2 + s2 = 1), etc.)

[0106] Among the above compounds, nickel-cobalt-manganese-based oxides can be used as lithium metal oxides in terms of improving the capacity characteristics and stability of the battery.

[0107] For example, lithium-nickel-cobalt-manganese oxide can have a composition represented by the following Formula 3.

[0108] [Formula 3]

[0109] Li x Ni a Co b M 1 c M 2 d O 2

[0110] In the above Formula 3, M 1 can be Mn or a combination of Mn and Al. For example, from the viewpoint of enhancing structural stability, it is a combination of Mn and Al.

[0111] In the above Formula 3, M 2 can be at least one selected from Zr, W, Y, Ba, Ca, Ti, Mg, Ta, and Nb.

[0112] "x" represents the atomic fraction of lithium in the lithium-nickel-cobalt-manganese-based oxide and can satisfy 0.90 ≤ x ≤ 1.1, for example, 0.95 ≤ x ≤ 1.08 or 1.0 ≤ x ≤ 1.08.

[0113] "a" represents the atomic fraction of nickel among the metal elements other than lithium in the lithium-nickel-cobalt-manganese-based oxide and can satisfy 0.80 ≤ a < 1.0, for example, 0.80 ≤ a ≤ 0.95 or 0.80 ≤ a ≤ 0.90. When the content of nickel satisfies the above range, high capacity characteristics can be achieved.

[0114] "b" represents the atomic fraction of cobalt among the metal elements other than lithium in the lithium-nickel-cobalt-manganese-based oxide and can satisfy 0 < b < 0.2, 0 < b ≤ 0.15 or 0.01 ≤ b ≤ 0.10.

[0115] "c" represents M among the metal elements other than lithium in the lithium-nickel-cobalt-manganese-based oxide 1The atomic fraction of which can satisfy 0 < c < 0.2, 0 < c ≤ 0.15 or 0.01 ≤ c ≤ 0.10.

[0116] "d" represents the atomic fraction of M among the metal elements other than lithium in the lithium nickel-cobalt-manganese type oxide, 2 and can satisfy 0 ≤ d ≤ 0.1 or 0 ≤ d ≤ 0.05.

[0117] Based on the total weight of the solids other than the solvent in the positive electrode composite slurry, the content of the positive electrode active material can be 60% by weight to 99% by weight, such as 70% by weight to 99% by weight, or 80% by weight to 98% by weight.

[0118] The binder is a component that helps to bond the active material and the conductive material and bond the current collector.

[0119] Examples of the binder include polyvinylidene fluoride (PVDF), polyvinyl alcohol, starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene (PE), polypropylene, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene-butadiene rubber, fluororubber, and various copolymers thereof.

[0120] Generally, based on the total weight of the solids other than the solvent in the positive electrode composite slurry, the content of the binder can be 1% by weight to 20% by weight, such as 1% by weight to 15% by weight, or 1% by weight to 10% by weight.

[0121] The conductive agent is a component that further improves the conductivity of the positive electrode active material, and based on the total weight of the solids in the positive electrode composite slurry, its content can be 1% by weight to 20% by weight. The conductive agent is not particularly limited as long as it has conductivity without causing chemical changes in the battery, and can be, for example, the following conductive materials: carbon powder, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal cracking carbon 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; fluorocarbon powder; conductive powder, such as aluminum powder or nickel powder; conductive whiskers, such as zinc oxide and potassium titanate; conductive metal oxides, such as titanium oxide; and polyphenylene derivatives.

[0122] Generally, based on the total weight of the solids other than the solvent in the positive electrode composite slurry, the content of the conductive agent can be 1% by weight to 20% by weight, such as 1% by weight to 15% by weight, such as 1% by weight to 10% by weight.

[0123] The solvent may include an organic solvent such as N-methyl-2-pyrrolidone (NMP), and the amount thereof may be such that a desired viscosity is achieved when the positive electrode active material is included and optionally a binder, a conductive agent, etc. are included. For example, the content of the solvent may be such that the concentration of the solid including the positive electrode active material and the optional binder and conductive agent is 50% by weight to 95% by weight, for example 70% by weight to 95% by weight, or 70% by weight to 90% by weight.

[0124] The negative electrode included in the lithium secondary battery of the present disclosure can be manufactured by coating a negative electrode composite paste including, for example, a negative electrode active material, a binder, a conductive agent, a solvent, etc. on a negative electrode current collector.

[0125] For example, when manufacturing a negative electrode by coating a negative electrode composite paste on a negative electrode current collector, the negative electrode current collector generally has a thickness of 3 μm to 500 μm. The negative electrode current collector is not particularly limited as long as it has high conductivity and does not cause chemical changes in the battery. For example, it can be copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless steel surface-treated with, for example, carbon, nickel, titanium, silver, or an aluminum-cadmium alloy. Similar to the positive electrode current collector, micro-irregularities can be formed on the surface of the negative electrode current collector to improve the adhesion of the negative electrode active material. The negative electrode current collector can be used in various shapes, for example, a film, a sheet, a foil, a net, a porous material, a foam, and a non-woven fabric.

[0126] The negative electrode of the present disclosure is characterized by including a silicon-based negative electrode active material. When a silicon-based negative electrode active material is used, a lithium secondary battery with a high energy density can be provided. The silicon-based negative electrode active material can be Si or SiO x (0 < x ≤ 2). For example, it can include only Si to provide the highest energy density. In the case of using a Si-based negative electrode active material, unless a stable SEI layer is formed on the negative electrode surface during the initial activation, the life characteristics will deteriorate rapidly due to the sharp volume expansion and contraction during cycling. However, in the lithium secondary battery of the present disclosure, an elastic and stable SEI layer can be formed, so that excellent life characteristics and storage characteristics can be provided when using a Si-based negative electrode active material.

[0127] Based on the total weight of the solids in the negative electrode composite paste, the content of the negative electrode active material can be 60% by weight to 99% by weight, for example 70% by weight to 99% by weight, or 80% by weight to 98% by weight.

[0128] The example of binder comprises polyvinylidene fluoride (PVDF), polyvinyl alcohol, starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene-butadiene rubber, fluororubber and its various copolymers. Considering high thickening property, styrene-butadiene rubber (SBR)-carboxymethyl cellulose (CMC) can be used.

[0129] Typically, the binder may be included in an amount of 1 to 20 wt %, for example 1 to 15 wt % or 1 to 10 wt %, based on the total weight of solids excluding the solvent in the negative electrode composite slurry.

[0130] The conductive agent is a component that further improves the conductivity of the negative electrode active material, and the amount of the conductive agent added can be 1% to 20% by weight based on the total weight of the solid in the negative electrode composite slurry. The conductive agent is not particularly limited as long as it has conductivity and does not cause chemical changes in the battery, and can be, for example, the following conductive materials: carbon powder, such as carbon black, acetylene 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; fluorocarbon powder; conductive powders, such as aluminum powder or nickel powder; conductive whiskers, such as zinc oxide and potassium titanate; conductive metal oxides, such as titanium oxide; and polyphenylene derivatives.

[0131] The conductive agent may be included in an amount of 1 to 20 wt %, for example 1 to 15 wt %, or 1 to 10 wt %, based on the total weight of solids excluding the solvent in the negative electrode composite slurry.

[0132] The solvent may include an organic solvent, such as N-methyl-2-pyrrolidone (NMP), and its amount may be such that a desired viscosity is achieved when the negative electrode active material is included and optionally a binder and a conductive agent, etc. For example, the content of the solvent may be such that the concentration of the solid containing the negative electrode active material and the optional binder and conductive agent is 50 wt % to 95 wt %, such as 70 wt % to 90 wt %.

[0133] The diaphragm may include a common porous polymer film used as a diaphragm in the art, for example, a porous polymer film prepared from a polyolefin polymer (e.g., ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, etc.) may be used in a single layer or laminated form. Alternatively, the diaphragm may be, but is not limited to, a commonly used porous non-woven fabric, such as a non-woven fabric made of high melting point glass fiber and polyethylene terephthalate fiber, but is not limited thereto. In addition, in order to ensure heat resistance or mechanical strength, a coated diaphragm comprising a ceramic component or a polymer material may be used, and a single layer or multilayer structure may be optionally used.

[0134] For example, the diaphragm may include a porous diaphragm substrate and a porous coating completely coated on one or both surfaces of the diaphragm substrate, and the coating may include a mixture of inorganic particles selected from metal oxides, semi-metal oxides, metal fluorides, metal hydroxides and combinations thereof and a binder polymer that connects and fixes the inorganic particles.

[0135] As inorganic particles, the coating may include a 2 O 3 、SiO 2 、TiO 2 SnO 2 、CeO 2 , MgO, NiO, CaO, ZnO, ZrO 2 , Y 2 O 3 、SrTiO 3 、BaTiO 3 Mg(OH) 2 and MgF. Here, the inorganic particles can improve the thermal stability of the separator. That is, the inorganic particles can prevent the separator from shrinking at high temperatures. In addition, the binder polymer can improve the mechanical stability of the separator by fixing the inorganic particles.

[0136] The appearance of the lithium secondary battery of the present disclosure is not particularly limited, and may have, for example, a cylindrical shape having a circular or rectangular cross-section, a angular shape, a pouch shape, or a coin shape.

[0137] Hereinafter, the present disclosure will be described in more detail using embodiments. The following embodiments are intended only to facilitate understanding of the present disclosure and are not intended to limit the scope of the present disclosure. It is apparent to those skilled in the art that various modifications and changes may be made within the technical scope of the present disclosure, and these modifications and changes are included within the scope of the appended claims.

[0138] Example

[0139] Example 1

[0140] (Preparation of non-aqueous electrolyte)

[0141] LiPF 6 LiPF was dissolved in an organic solvent (fluoroethylene carbonate (FEC): ethyl methyl carbonate (EMC): diethyl carbonate (DEC) = 20:70:10 volume ratio) to make 6 The concentration of was 1.3 M to prepare a non-aqueous solvent. Then, 0.1 g of the compound of the following formula 1-1 and 0.1 g of the compound of the following formula 2-1 were added to 99.8 g of the non-aqueous solvent to prepare a non-aqueous electrolyte.

[0142] [Formula 1-1]

[0143]

[0144] [Formula 2-1]

[0145]

[0146] (Manufacturing of lithium secondary batteries)

[0147] The positive electrode active material (LiNi 0.85 Co 0.05 Mn 0.08 Al 0.02 O 2 ), a conductive agent (carbon nanotubes) and a binder (polyvinylidene fluoride) were added to a solvent N-methyl-2-pyrrolidone (NMP) solvent at a weight ratio of 97.74:0.7:1.56 to prepare a positive electrode slurry (75.5 wt% solid). The positive electrode slurry was coated on one side of a positive electrode current collector (Al film) with a thickness of 15 μm, dried and rolled to prepare a positive electrode.

[0148] The negative electrode active material (silicon; Si), conductive agent (carbon black), binder (styrene-butadiene rubber (SBR)-carboxymethyl cellulose (CMC)) was added to N-methyl-2-pyrrolidone (NMP) solvent at a weight ratio of 70:20.3:9.7 to prepare a negative electrode slurry (26 wt% solid). The negative electrode slurry was coated on one surface of a negative electrode current collector (Cu film) with a thickness of 15 μm, dried and rolled to prepare a negative electrode.

[0149] In the drying chamber, the inorganic particles Al 2 O 3 The polyolefin-based porous separator is placed between the prepared positive electrode and negative electrode, and then the prepared non-aqueous electrolyte is injected, thereby manufacturing a secondary battery.

[0150] Example 2

[0151] A secondary battery was prepared in the same manner as in Example 1, except that 0.1 g of the compound of Formula 1-1 and 5 g of the compound of Formula 2-1 were added to 94.9 g of the nonaqueous solvent prepared in Example 1 to prepare a nonaqueous electrolyte.

[0152] Example 3

[0153] A secondary battery was prepared in the same manner as in Example 1, except that 5 g of the compound of Formula 1-1 and 0.1 g of the compound of Formula 2-1 were added to 94.9 g of the nonaqueous solvent prepared in Example 1 to prepare a nonaqueous electrolyte.

[0154] Example 4

[0155] A secondary battery was prepared in the same manner as in Example 1, except that 2 g of the compound of Formula 1-1 and 2 g of the compound of Formula 2-1 were added to 96 g of the nonaqueous solvent prepared in Example 1 to prepare a nonaqueous electrolyte.

[0156] Example 5

[0157] A secondary battery was prepared in the same manner as in Example 1, except that 0.1 g of the compound of the following Formula 1-2 and 0.1 g of the compound of Formula 2-1 were added to 99.8 g of the nonaqueous solvent prepared in Example 1 to prepare a nonaqueous electrolyte.

[0158] [Formula 1-2]

[0159]

[0160] Example 6

[0161] A secondary battery was prepared in the same manner as in Example 1, except that 0.1 g of the compound of the following Formula 1-3 and 0.1 g of the compound of Formula 2-1 were added to 99.8 g of the nonaqueous solvent prepared in Example 1 to prepare a nonaqueous electrolyte.

[0162] [Formula 1-3]

[0163]

[0164] Example 7

[0165] A secondary battery was prepared in the same manner as in Example 1, except that 0.1 g of the compound of Formula 1-1 and 0.1 g of the compound of the following Formula 2-2 were added to 99.8 g of the nonaqueous solvent prepared in Example 1 to prepare a nonaqueous electrolyte.

[0166] [Formula 2-2]

[0167]

[0168] Example 8

[0169] A secondary battery was prepared in the same manner as in Example 1, except that 0.1 g of the compound of Formula 1-1 and 0.1 g of the compound of the following Formula 2-3 were added to 99.8 g of the nonaqueous solvent prepared in Example 1 to prepare a nonaqueous electrolyte.

[0170] [Formula 2-3]

[0171]

[0172] Comparative Example 1

[0173] A secondary battery was prepared in the same manner as in Example 1, except that 0.1 g of the compound of Formula 1-1 was added to 99.9 g of the nonaqueous solvent prepared in Example 1 to prepare a nonaqueous electrolyte.

[0174] Comparative Example 2

[0175] A secondary battery was prepared in the same manner as in Example 1, except that 5 g of the compound of Formula 1-1 was added to 95 g of the nonaqueous solvent prepared in Example 1 to prepare a nonaqueous electrolyte.

[0176] Comparative Example 3

[0177] A secondary battery was prepared in the same manner as in Example 1, except that 0.1 g of the compound of Formula 2-1 was added to 99.9 g of the nonaqueous solvent prepared in Example 1 to prepare a nonaqueous electrolyte.

[0178] Comparative Example 4

[0179] A secondary battery was prepared in the same manner as in Example 1, except that a nonaqueous electrolyte was prepared by adding 5 g of the compound of Formula 2-1 to 95 g of the nonaqueous solvent prepared in Example 1.

[0180] Experimental Example 1-Evaluation of High Temperature Cycle Characteristics

[0181] The cycle characteristics of each of the secondary batteries manufactured in Examples 1 to 8 and Comparative Examples 1 to 4 were evaluated.

[0182] For example, each battery manufactured in Examples 1 to 8 and Comparative Examples 1 to 4 was charged to 4.2V (0.05C cut-off) at a rate of 0.33C under constant current-constant voltage conditions at 45°C, and discharged to 3.0V at a rate of 0.33C under constant current conditions. The charging and discharging process was set as one cycle, and 200 cycles were performed. Then, the capacity retention rate after 200 cycles relative to the initial capacity after one cycle was measured. In addition, the rate of increase of the resistance after 200 cycles relative to the initial resistance after one cycle was measured. Table 1 below provides the results.

[0183] [Table 1]

[0184] Capacity retention rate (%) Resistance increase rate (%) Example 1 82.8 50.5 Example 2 87.3 45.7 Example 3 86.1 46.6 Example 4 91.5 38.6 Example 5 78.5 60.2 Example 6 83.1 49.0 Example 7 84.6 48.6 Example 8 85.6 47.2 Comparative Example 1 63.8 98.4 Comparative Example 2 66.2 96.2 Comparative Example 3 64.5 97.1 Comparative Example 4 68.4 93.5

[0185] Experimental Example 2-Evaluation of High Temperature Storage Characteristics

[0186] The high-temperature storage characteristics of each of the secondary batteries manufactured in Examples 1 to 8 and Comparative Examples 1 to 4 were evaluated.

[0187] For example, each of the secondary batteries manufactured in Examples 1 to 8 and Comparative Examples 1 to 4 was fully charged to 4.2 V and then stored at 60° C. for 8 weeks.

[0188] Before storage, the capacity of the fully charged secondary battery was measured and set as the initial capacity of the secondary battery.

[0189] After 8 weeks, the capacity of the stored secondary battery was measured to calculate the capacity reduced by 8 weeks of storage time. The capacity after the decrease was calculated as a percentage relative to the initial capacity of the secondary battery to obtain the capacity retention rate after 8 weeks. In addition, the percentage of the resistance increased from the initial resistance of the secondary battery was calculated to obtain the resistance increase rate after 8 weeks. The following table 2 provides the results.

[0190] [Table 2]

[0191] Capacity retention rate (%) Resistance increase rate (%) Example 1 86.6 16.4 Example 2 92.1 12.9 Example 3 92.3 10.5 Example 4 96.6 6.6 Example 5 82.4 20.1 Example 6 88.5 15.6 Example 7 89.6 14.1 Example 8 90.9 13.8 Comparative Example 1 67.1 39.6 Comparative Example 2 70.3 36.3 Comparative Example 3 67.8 38.9 Comparative Example 4 73.5 33.6

[0192] Experimental Example 3-Evaluation of Thermal Stability

[0193] The thermal stability of each of the secondary batteries manufactured in Examples 1 to 8 and Comparative Examples 1 to 4 was evaluated.

[0194] For example, each lithium secondary battery prepared in the above-mentioned embodiment and comparative example is subjected to formation treatment, and then charged to 4.2V (0.05C cut-off) at a rate of 0.33C under constant current-constant voltage conditions at 25°C to fully charge (SOC100%). The fully charged battery is heated to 140°C at a rate of 5°C / min and then placed for 1 hour to perform a hot box evaluation experiment to check whether a fire occurs. The following table 3 provides the results, where "pass" refers to an evaluation result without a fire, and "failure" refers to an evaluation result in which a fire occurs.

[0195] [Table 3]

[0196] Hot Box Test Results Example 1 pass Example 2 pass Example 3 pass Example 4 pass Example 5 pass Example 6 pass Example 7 pass Example 8 pass Comparative Example 1 fail Comparative Example 2 pass Comparative Example 3 fail Comparative Example 4 pass

Claims

1. A lithium secondary battery, comprising: A negative electrode comprising a silicon-based negative electrode active material; a positive electrode; a separator; and a non-aqueous electrolyte; The non-aqueous electrolyte comprises: a lithium salt; an organic solvent; a compound of the following formula 1 as a first additive; and a compound of the following formula 2 as a second additive; [Formula 1] In Formula 1, R is an unsubstituted or fluorine-substituted alkylene group having 1 to 5 carbon atoms, and R1 to R3 are each independently any one selected from the group consisting of H, an alkyl group having 1 to 5 carbon atoms, and a nitrile group, [Formula 2] In Formula 2, R4 to R7 are each independently any one selected from the group consisting of an alkyl group having 1 to 10 carbon atoms which is unsubstituted or substituted with fluorine and an alkenyl group having 2 to 10 carbon atoms which is unsubstituted or substituted with fluorine.

2. The lithium secondary battery according to claim 1, wherein The compound of Formula 1 is any one selected from the group consisting of the following Formulas 1-1 to 1-3, [Formula 1-1] [Formula 1-2] [Formula 1-3] 3. The lithium secondary battery according to claim 1, wherein The compound of Formula 2 is any one selected from the group consisting of the following Formula 2-1 to Formula 2-3, [Formula 2-1] [Formula 2-2] [Formula 2-3] 4. The lithium secondary battery according to claim 1, wherein The first additive may be included in an amount of 0.01 parts by weight to 10 parts by weight based on 100 parts by weight of the non-aqueous electrolyte.

5. The lithium secondary battery according to claim 1, wherein The second additive may be included in an amount of 0.01 parts by weight to 10 parts by weight based on 100 parts by weight of the non-aqueous electrolyte.

6. The lithium secondary battery according to claim 1, wherein The first additive and the second additive are included in a weight ratio of 1:0.002 to 1:

500.

7. The lithium secondary battery according to claim 1, wherein The lithium salt is selected from LiCl, LiBr, LiI, LiBF4, LiClO4, LiB 10 Cl 10 , LiAlCl4, LiAlO2, LiPF6, LiSO3CF3, LiCO2CH3, LiCO2CF3, LiAsF6, LiSbF6, LiSO3CH3, LiN(SO2F)2, LiN(SO2CF2CF3)2 and at least one of the group consisting of LiN(SO2CF3)2.

8. The lithium secondary battery according to claim 1, wherein The concentration of the lithium salt is 0.5M to 5.0M.

9. The lithium secondary battery according to claim 1, wherein: The organic solvent includes at least one organic solvent selected from the group consisting of a cyclic carbonate-based organic solvent, a chain carbonate-based organic solvent, a chain ester-based organic solvent, and a cyclic ester-based organic solvent.

10. The lithium secondary battery according to claim 1, wherein The silicon-based negative electrode active material contains only Si.

11. The lithium secondary battery according to claim 1, wherein The positive electrode includes a lithium nickel-cobalt-manganese-based oxide as a positive electrode active material.

12. The lithium secondary battery according to claim 11, wherein The lithium nickel-cobalt-manganese-based oxide has a composition represented by the following Formula 3: [Formula 3] Li x Ni a Co b M 1 c M 2 d O2 Among them, M 1 It is Mn or a combination of Mn and Al. 2 is at least one selected from the group consisting of Zr, W, Y, Ba, Ca, Ti, Mg, Ta and Nb, 0.90≤x≤1.1, 0.80≤a<1.0, 0 <b<0.2,0<c<0.2,0≤d≤0.1。 13 . An electronic device comprising the lithium secondary battery according to claim 10 .

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