Lithium secondary battery

Abstract

The present invention provides a lithium secondary battery including a positive electrode; a negative electrode; a separator disposed between the negative electrode and the positive electrode; and a non-aqueous electrolyte, in which the negative electrode includes a negative electrode active material, the negative electrode active material includes a silicon-based active material, and the non-aqueous electrolyte includes a lithium salt, ethylene fluorocarbonate, ethylene 1, 2-difluorocarbonate, and a coumarin-based compound of a specific chemical formula.

Description

[0001] Cross-references to related applications

[0002] This application claims priority to Korean Patent Application No. 10-2023-0126666, filed on September 21, 2023, the disclosure of which is incorporated herein by reference. Technical Field

[0003] This invention relates to a lithium secondary battery. Background Technology

[0004] In recent years, as the application fields of lithium secondary batteries have rapidly expanded not only to the power supply of electrical, electronic, communication and electronic devices such as computers, but also to the power storage supply of large-area devices such as automobiles or power storage devices, the demand for secondary batteries with high stability, high capacity and high output is increasing.

[0005] A lithium-ion secondary battery can mainly consist of a positive electrode made of lithium-containing transition metal oxide, a negative electrode capable of storing lithium, an electrolyte as a medium for transporting lithium ions, and a separator. In this case, the negative electrode may include a negative electrode active material, such as a carbon-based active material or a silicon-based active material.

[0006] For lithium-ion rechargeable batteries, a solid electrolyte interphase (SEI) film is formed on the positive and / or negative electrodes during initialization. This film protects the positive and negative electrodes during battery operation and prevents electrolyte depletion due to electrolyte side reactions. If a robust electrode film is not formed on the positive and / or negative electrodes during initialization, problems such as capacity degradation and reduced lifespan may occur.

[0007] In particular, silicon-based anode active materials have attracted attention due to their higher capacity and energy density compared to carbon-based active materials, but they suffer from the drawback of large volume changes caused by lithium insertion and extraction. This volume expansion of silicon-based active materials leads to many problems, such as reduced durability of the formed SEI film, continuous electrolyte consumption due to the formation of new surfaces in the anode active material, and increased SEI film thickness, all of which result in capacity degradation and reduced lifetime. Summary of the Invention

[0008] [Technical Issues]

[0009] One aspect of the present invention provides a lithium secondary battery in which high-temperature cycle life performance and high-temperature storage performance can be improved and electrolyte side reactions can be reduced by forming a flexible and durable film on a negative electrode comprising a silicon-based active material.

[0010] [Technical Solution]

[0011] [1] The present invention provides a lithium secondary battery comprising: a positive electrode; a negative electrode; a separator disposed between the positive electrode and the negative electrode; and a non-aqueous electrolyte, wherein the negative electrode comprises a negative electrode active material, the negative electrode active material comprises a silicon-based active material, and the non-aqueous electrolyte comprises a lithium salt, ethylene fluorocarbonate, ethylene 1,2-difluorocarbonate and a compound represented by Formula 1.

[0012] [Formula 1]

[0013]

[0014] In Formula 1, R1 includes halogen, nitrile, propargyl, ester, ether, ketone, carboxyl, unsubstituted or substituted alkyl, unsubstituted or substituted alkenyl, unsubstituted or substituted alkynyl, unsubstituted or substituted alkoxy, boron, borate ester, isocyanate, isothiocyanate, silyl, siloxane, sulfone, sulfonate, sulfate ester, or a combination of two or more thereof, and n is an integer from 0 to 6.

[0015] [2] The present invention provides the lithium secondary battery described in [1] above, wherein the silicon-based active material comprises silicon-based particles, and the silicon-based particles contain a compound represented by formula A.

[0016] [Formula A]

[0017] SiO x

[0018] In equation A, 0 ≤ x < 2.

[0019] [3] The present invention provides a lithium secondary battery according to at least one of [1] and [2] above, wherein the silicon-based particles are formed of silicon (Si).

[0020] [4] The present invention provides a lithium secondary battery according to at least one of [1] to [3] above, wherein the compound represented by Formula 1 includes at least one of the compounds represented by Formula 1-A and Formula 1-B.

[0021] [Equation 1-A]

[0022]

[0023] [Equation 1-B]

[0024]

[0025] In Equations 1-A and 1-B, R1 is defined as in Equation 1.

[0026] [5] The present invention provides a lithium secondary battery according to at least one of [1] to [4] above, wherein the compound represented by Formula 1 includes at least one of the compounds selected from the group consisting of compounds represented by Formulas 1-1 to 1-9.

[0027] [Equation 1-1]

[0028]

[0029] [Equation 1-2]

[0030]

[0031] [Equation 1-3]

[0032]

[0033] [Equations 1-4]

[0034]

[0035] [Equations 1-5]

[0036]

[0037] [Equations 1-6]

[0038]

[0039] [Equations 1-7]

[0040]

[0041] [Equations 1-8]

[0042]

[0043] [Equations 1-9]

[0044]

[0045] [6] The present invention provides a lithium secondary battery according to at least one of [1] to [5] above, wherein the content of the fluoroethylene carbonate in the non-aqueous electrolyte is 3% to 20% by volume.

[0046] [7] The present invention provides a lithium secondary battery according to at least one of [1] to [6] above, wherein the content of 1,2-difluoroethylene carbonate in the non-aqueous electrolyte is from 10% to 35% by volume.

[0047] [8] The present invention provides a lithium secondary battery according to at least one of [1] to [7] above, wherein the content of the compound represented by Formula 1 is from 0.1% to 10% by weight, based on the weight of the non-aqueous electrolyte.

[0048] [9] The present invention provides a lithium secondary battery according to at least one of [1] to [8] above, wherein the volume ratio of fluoroethylene carbonate to 1,2-difluoroethylene carbonate is 5:95 to 50:50.

[0049]

[10] The present invention provides a lithium secondary battery according to at least one of [1] to [9] above, wherein, based on the total weight of the non-aqueous electrolyte, the total amount of ethylene fluorocarbonate and ethylene 1,2-difluorocarbonate is greater than 10% by weight and less than or equal to 50% by weight.

[0050]

[11] The present invention provides a lithium secondary battery according to at least one of [1] to

[10] above, wherein the lithium salt comprises at least one selected from the group consisting of: LiCl, LiBr, LiI, LiBF4, LiClO4, LiAlO4, LiAlCl4, LiPF6, LiSbF6, LiAsF6, LiB 10 Cl 10 , LiBOB(LiB(C2O4)2), LiCF3SO3, LiFSI(LiN(SO2F)2), LiCH3SO3, LiCF3CO2, LiCH3CO2 and LiBETI(LiN(SO2CF2CF3)2).

[0051]

[12] The present invention provides a lithium secondary battery according to at least one of [1] to

[11] above, wherein, after the formation of the lithium secondary battery, a solid electrolyte interface film is formed on the negative electrode, the solid electrolyte interface film comprising inorganic components, and the inorganic components comprising LiF and CO3. 2- The weight of the LiF is related to the weight of the CO3. 2- The weight ratio is 1.4 or higher.

[0052] [Beneficial Effects]

[0053] The lithium secondary battery of the present invention is characterized in that it uses a silicon-based active material as the positive electrode active material and uses fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate (DFEC) and a compound represented by Formula 1 as non-aqueous electrolyte components.

[0054] When 1,2-difluoroethylene carbonate is used alone and decomposes spontaneously, undesirable degradation of battery performance occurs because the CO2 generation reaction becomes more dominant. To address this problem, the present invention is characterized by using a compound represented by Formula 1 with 1,2-difluoroethylene carbonate, wherein the compound represented by Formula 1, as a coumarin-like compound, undergoes ring-opening during negative electrode reduction to form free radicals. These free radicals, in this case, can defluorinate during the negative electrode reduction of 1,2-difluoroethylene carbonate while simultaneously forming an inorganic-SEI film such as LiF. Furthermore, due to the defluorination, propargyl groups (C≡C) can be formed, and ring-opening can occur to form a polymer-SEI film. The organic / inorganic composite film formed from the above components exhibits significantly superior chemical and electrochemical stability.

[0055] When 1,2-difluoroethylene carbonate is combined with the compound represented by Formula 1, since the above compound reacts rapidly and is consumed in initial processes such as initialization, it has the effect of obtaining a flexible and highly durable solid electrolyte interface (SEI) film through SEI film reaction during initialization. However, it has drawbacks in terms of long-term durability. In this case, in the present invention, fluoroethylene carbonate with a low consumption rate and continuous participation in SEI film formation is included in the non-aqueous electrolyte. Therefore, when using a negative electrode including a silicon-based active material (which may generate a new negative electrode surface due to extreme volume expansion), the long-term durability of the SEI film can be further improved.

[0056] Therefore, since the lithium secondary battery of the present invention forms and maintains a flexible and highly durable SEI film during battery operation and initial processes when using a negative electrode comprising silicon-based active materials, the lithium secondary battery of the present invention can have excellent life performance and storage performance, especially excellent high-temperature life performance and high-temperature storage performance. Detailed Implementation

[0057] It will be understood that the words or terms used in the specification and claims should not be interpreted as having the meaning defined in a common dictionary, and it will be further understood that, based on the principle that the inventors may appropriately define the meaning of words or terms to best interpret the invention, the words or terms should be interpreted as having a meaning consistent with their meaning in the context of the related art and in the technical concept of the invention.

[0058] It will be further understood that the terms “comprising,” “including,” or “having” in this specification specify the presence of the said feature, number, step, element, or combination thereof, but do not exclude the presence or addition of one or more other features, numbers, steps, elements, or combinations thereof.

[0059] Before describing the invention, unless otherwise specified in the invention, the expression "*" indicates the same or different atoms or portions (binding sites) connected between the ends of the formula.

[0060] Furthermore, in the description of "a to b carbon atoms" in this specification, "a" and "b" each represent the number of carbon atoms contained in a specific functional group. That is, a functional group can contain "a" to "b" carbon atoms. For example, the expression "alkyl group having 1 to 5 carbon atoms" means an alkyl group containing 1 to 5 carbon atoms, namely, CH3-, CH3CH2-, CH3CH2CH2-, (CH3)2CH-, CH3CH2CH2CH2-, (CH3)2CHCH2-, CH3CH2CH2CH2CH2-, or (CH3)2CHCH2CH2-.

[0061] Furthermore, the alkyl or aryl groups in this specification may be entirely substituted or unsubstituted. Unless otherwise defined, the term "substituted" means that at least one hydrogen atom bonded to a carbon atom is substituted by an element other than hydrogen, such as an alkyl group having 1 to 20 carbon atoms, an alkenyl group having 2 to 20 carbon atoms, an alkynyl group having 2 to 20 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, a cycloalkyl group having 3 to 12 carbon atoms, a cycloalkenyl group having 3 to 12 carbon atoms, a cycloalkynyl group having 3 to 12 carbon atoms, a heterocyclic alkyl group having 3 to 12 carbon atoms, a heterocyclic alkenyl group having 3 to 12 carbon atoms, a heterocyclic alkynyl group having 3 to 12 carbon atoms, an aryloxy group having 6 to 12 carbon atoms, a halogen atom, a fluoroalkyl group having 1 to 20 carbon atoms, a nitro group, an aryl group having 6 to 20 carbon atoms, a heteroaryl group having 2 to 20 carbon atoms, or a haloaryl group having 6 to 20 carbon atoms.

[0062] The invention will be described in more detail below.

[0063] Lithium secondary batteries

[0064] This invention relates to a lithium secondary battery.

[0065] The lithium secondary battery of the present invention is characterized in that it comprises: a negative electrode; a positive electrode; a separator disposed between the negative electrode and the positive electrode; and a non-aqueous electrolyte, wherein the negative electrode comprises a negative electrode active material, the negative electrode active material comprises a silicon-based active material, and the non-aqueous electrolyte comprises a lithium salt, ethylene fluorocarbonate, 1,2-difluoroethylene carbonate, and a compound represented by Formula 1.

[0066] [Formula 1]

[0067]

[0068] In Formula 1, R1 includes halogen, nitrile, propargyl, ester, ether, ketone, carboxyl, unsubstituted or substituted alkyl, unsubstituted or substituted alkenyl, unsubstituted or substituted alkynyl, unsubstituted or substituted alkoxy, boron, borate ester, isocyanate, isothiocyanate, silyl, siloxane, sulfone, sulfonate, sulfate ester, or a combination of two or more thereof, and n is an integer from 0 to 6.

[0069] A lithium-ion secondary battery includes a negative electrode, a positive electrode, a separator, and a non-aqueous electrolyte. Specifically, a lithium-ion secondary battery includes a negative electrode, a positive electrode facing the negative electrode, a separator disposed between the negative electrode and the positive electrode, and a non-aqueous electrolyte. A lithium-ion secondary battery can be manufactured by housing an electrode assembly including a negative electrode, a positive electrode facing the negative electrode, and a separator disposed between the negative electrode and the positive electrode in a battery casing, and then injecting a non-aqueous electrolyte.

[0070] (1) Negative electrode

[0071] The negative electrode includes the negative electrode active material.

[0072] Negative electrode active materials include silicon-based active materials.

[0073] Silicon-based active materials offer advantages such as higher capacity and energy density compared to carbon-based active materials like graphite. However, they suffer from significant volume changes during charging and discharging. This volume expansion and contraction of silicon-based active materials disrupts conductive connections in the negative electrode, leading to increased resistance and decreased lifetime performance. Furthermore, the solid electrolyte interphase (SEI) film formed during lithium-ion battery formation may rupture due to these volume changes in the silicon-based active material. This can promote electrolyte side reactions, causing problems such as increased resistance due to increased SEI film thickness and electrolyte depletion, potentially degrading lifetime performance and storage characteristics.

[0074] To address these issues, the present invention is characterized by including fluoroethylene carbonate, 1,2-difluoroethylene carbonate, and a compound represented by Formula 1, which will be described later, in the non-aqueous electrolyte. By combining 1,2-difluoroethylene carbonate with the compound of Formula 1, not only can a highly flexible, resilient, and durable SEI film be formed during initialization, but the fluoroethylene carbonate can also continuously undergo an SEI film formation reaction during battery operation. This results in the formation of a significantly superior flexible, resilient, and durable SEI film on the negative electrode comprising a silicon-based active material, thereby significantly improving the high-temperature cycling performance and high-temperature storage performance of lithium-ion batteries. In the case of using carbon-based active materials (e.g., graphite) and the aforementioned non-aqueous electrolyte, the corresponding components of the non-aqueous electrolyte may have undesirable effects on battery performance (e.g., the corresponding components act as resistors), making it difficult to achieve the desired effect in a negative electrode comprising only a carbon-based active material.

[0075] Silicon-based active materials include silicon-based particles, and the silicon-based particles may contain at least one selected from compounds represented by formula A and silicon-carbon composites.

[0076] [Formula A]

[0077] SiO x

[0078] In equation A, 0 ≤ x < 2.

[0079] In Formula A, compared to SiO2, which does not react with lithium ions and cannot store lithium, x is expected to be within the aforementioned range. Specifically, the silicon-based particles included in the silicon-based active material can be formed of silicon (Si), or in Formula A, x can be 0. Furthermore, the silicon-based particles can include silicon oxide, for example, in Formula A, x can satisfy 0.7 ≤ x ≤ 1.2, specifically, x = 1.

[0080] In addition to silicon-based particles, the silicon-based active material may further include a metal doped into the silicon-based particles. Furthermore, in addition to silicon-based particles, the silicon-based active material may further include a metal present on the surface and / or inside the silicon-based particles. The metal may be at least one of lithium (Li), magnesium (Mg), calcium (Ca), and aluminum (Al), specifically at least one of Li and Mg, more specifically Mg.

[0081] When a metal is included in a silicon-based active material, its content in the silicon-based active material can be from 1% by weight to 30% by weight.

[0082] The silicon-based active material may further include a carbon coating disposed on the surface of the silicon-based particles. The carbon coating may include amorphous carbon.

[0083] When a carbon coating is included in a silicon-based active material, the carbon coating content in the silicon-based active material can be from 0.5% to 10% by weight, specifically from 1% to 5% by weight.

[0084] In ensuring structural stability during charging and discharging and reducing side reactions with the electrolyte, the average particle size (D) of silicon-based active materials is crucial. 50 The size can be in the range of 1μm to 30μm, preferably 2μm to 15μm.

[0085] In addition to silicon-based active materials, anode active materials can also include carbon-based active materials.

[0086] Carbon-based active materials may include at least one selected from the group consisting of artificial graphite, natural graphite, hard carbon, soft carbon, carbon black, graphene, and fibrous carbon, and preferably may include at least one selected from the group consisting of artificial graphite and natural graphite.

[0087] In ensuring structural stability during charging and discharging and reducing side reactions with the electrolyte, the average particle size (D) of carbon-based active materials is crucial. 50 The size can be in the range of 10μm to 30μm, preferably 15μm to 25μm.

[0088] When the negative electrode active material includes silicon-based active material and carbon-based active material, the weight ratio of silicon-based active material to carbon-based active material can be 1:99 to 50:50, particularly 3:97 to 20:80, and even more particularly 3:97 to 10:90.

[0089] In some implementations, the negative electrode active material may not include carbon-based active materials.

[0090] The negative electrode may include a negative electrode current collector and a layer of negative electrode active material disposed on at least one surface of the negative electrode current collector. In this case, the negative electrode active material may be contained within the negative electrode active material layer.

[0091] There are no particular restrictions on the negative electrode current collector, as long as it has high conductivity and does not cause chemical changes in the battery. Specifically, as a negative electrode current collector, copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless steel surface-treated with one of carbon, nickel, titanium or silver, and aluminum-cadmium alloys can be used.

[0092] Negative electrode current collectors can typically have a thickness ranging from 3 μm to 500 μm.

[0093] Microscopic 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, such as membranes, sheets, foils, meshes, porous bodies, foams, and nonwoven fabrics.

[0094] The negative electrode active material layer is disposed on at least one surface of the negative electrode current collector. Specifically, the negative electrode active material layer may be disposed on one or both surfaces of the negative electrode current collector.

[0095] The content of the negative electrode active material in the negative electrode active material layer can be from 60% to 99% by weight, preferably from 75% to 95% by weight.

[0096] The negative electrode active material layer may further include a binder and / or a conductive agent together with the negative electrode active material.

[0097] The adhesive is used to improve battery performance by enhancing the adhesion between the negative electrode active material layer and the negative electrode current collector. The adhesive may include, for example, at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and materials in which hydrogen is substituted by Li, sodium (Na), or Ca, and may also include various copolymers thereof.

[0098] The content of the binder in the negative electrode active material layer can be from 0.5% to 30% by weight, preferably from 1% to 15% by weight, and more preferably from 5% to 10% by weight.

[0099] There are no particular restrictions on the conductive agent, as long as it is conductive and does not cause chemical changes in the battery. For example, the following conductive materials can be used: graphite, such as natural or artificial graphite; carbon black, such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermally cracked carbon black; conductive fibers, such as carbon fibers or metal fibers; conductive tubes, such as carbon nanotubes; fluorocarbons; metal powders, such as aluminum powder and nickel powder; conductive whiskers, such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides, such as titanium oxide; or polyphenylene derivatives.

[0100] The content of the conductive agent in the negative electrode active material layer can be from 0.5% to 30% by weight, preferably from 1% to 25% by weight.

[0101] The thickness of the negative electrode active material layer can be from 10 μm to 100 μm, preferably from 50 μm to 80 μm.

[0102] The negative electrode can be prepared by coating at least one surface of the negative electrode current collector with a negative electrode slurry containing a negative electrode active material, a binder, a conductive agent and / or a negative electrode slurry forming solvent, and then drying and rolling the coated negative electrode current collector.

[0103] In promoting the dispersion of the negative electrode active material, binder and / or conductive agent, the solvent for forming the negative electrode slurry may, for example, include at least one selected from the group consisting of distilled water, NMP (N-methyl-2-pyrrolidone), ethanol, methanol and isopropanol, and preferably may include distilled water.

[0104] (2) Positive electrode

[0105] The positive electrode faces the negative electrode.

[0106] The positive electrode may include a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector.

[0107] There are no particular limitations on the positive electrode current collector, as long as it has high conductivity and does not cause chemical changes in the battery. Specifically, the positive electrode current collector may include at least one selected from the group consisting of copper, stainless steel, aluminum, nickel, titanium, sintered carbon, and aluminum-cadmium alloys, and preferably may include aluminum.

[0108] Positive current collectors can typically have a thickness ranging from 3 μm to 500 μm.

[0109] Microscopic 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 membranes, sheets, foils, meshes, porous bodies, foams, and nonwoven fabrics.

[0110] The positive electrode active material layer is disposed on at least one surface of the positive electrode current collector. Specifically, the positive electrode active material layer may be disposed on one or both surfaces of the positive electrode current collector.

[0111] The positive electrode active material layer may contain positive electrode active material.

[0112] The positive electrode active material is a compound capable of reversibly inserting and deintercalating lithium. Specifically, the positive electrode active material may include a lithium transition metal composite oxide comprising lithium and at least one transition metal selected from the group consisting of nickel, cobalt, manganese and aluminum. Preferably, it is a lithium transition metal composite oxide comprising lithium and a transition metal containing nickel, cobalt and manganese.

[0113] For example, lithium transition metal composite oxides may include: lithium manganese oxides (e.g., LiMnO2, LiMn2O4, etc.), lithium cobalt oxides (e.g., LiCoO2, etc.), lithium nickel oxides (e.g., LiNiO2, etc.), and lithium nickel manganese oxides (e.g., LiNi...).1-Y Mn Y O2 (where 0 < Y < 1), LiMn 2-z Ni z O4 (where 0 < Z < 2), etc., lithium nickel cobalt oxides (e.g., LiNi 1- Y1 Co Y1 O2 (where 0 < Y1 < 1), lithium manganese cobalt oxides (e.g., LiCo 1-Y2 Mn Y2 O2 (where 0 < Y2 < 1), LiMn 2-Z1 Co z1 O4 (where 0 < Z1 < 2), etc., lithium nickel manganese cobalt oxides (e.g., Li(Ni p Co q Mn r1 )O2 (where 0 < p < 1, 0 < q < 1, 0 < r1 < 1, and p + q + r1 = 1) or Li(Ni p1 Co q1 Mn r2 )O4 (where 0 < p1 < 2, 0 < q1 < 2, 0 < r2 < 2, and p1 + q1 + r2 = 2), etc., or lithium nickel cobalt transition metal (M) oxides (e.g., Li(Ni p2 Co q2 Mn r3 M S2 )O2 (where M is selected from the group consisting of aluminum (Al), iron (Fe), vanadium (V), chromium (Cr), titanium (Ti), tantalum (Ta), magnesium (Mg), and molybdenum (Mo), and p2, q2, r3, and s2 are the atomic fractions of each independent element, where 0 < p2 < 1, 0 < q2 < 1, 0 < r3 < 1, 0 < S2 < 1, and p2 + q2 + r3 + S2 = 1), etc.), and may include any one of them or a mixture of two or more of them. Among these materials, in terms of improving the capacity characteristics and stability of the battery, the lithium transition metal composite oxide can be LiCoO2, LiMnO2, LiNiO2, lithium nickel manganese cobalt oxides (e.g., Li(Ni 0.6 Mn 0.2 Co 0.2 )O2, Li(Ni 0.5 Mn 0.3 Co 0.2 )O2, Li(Ni 0.7 Mn 0.15 Co 0.15 )O2, or Li(Ni 0.8 Mn 0.1 Co 0.1 )O2, etc.) or lithium nickel cobalt aluminum oxides (e.g., Li(Ni 0.8 Co0.15 Al 0.05 (O2, etc.), and considering the significant improvement effect brought about by controlling the type and content ratio of the components constituting lithium transition metal composite oxides, lithium transition metal composite oxides can be Li(Ni) 0.6 Mn 0.2 Co 0.2 O2, Li(Ni) 0.5 Mn 0.3 Co 0.2 O2, Li(Ni) 0.7 Mn 0.15 Co 0.15 O2 or Li(Ni) 0.8 Mn 0.1 Co 0.1 O2, and any one or a mixture of two or more of them can be used.

[0114] More specifically, as a positive electrode active material, the lithium transition metal composite oxide may contain more than 60 mol% nickel, based on the total molar number of transition metals included in the lithium transition metal composite oxide. Specifically, the positive electrode active material is a lithium transition metal composite oxide, wherein the transition metals include nickel; and at least one selected from manganese, cobalt, and aluminum, and the positive electrode active material may contain nickel in an amount based on the total molar number of transition metals being more than 60 mol%, specifically 60 mol% to 90 mol%. When a lithium transition metal composite oxide with a high nickel content is used in conjunction with the aforementioned non-aqueous electrolyte, it is preferable to reduce gaseous byproducts generated by structural collapse.

[0115] In addition, the positive electrode active material may contain a lithium composite transition metal oxide represented by the following formula B.

[0116] [Formula B]

[0117] Li 1+x (Ni a Co b Mn c M d O2

[0118] In Formula B, M is at least one selected from tungsten (W), copper (Cu), iron (Fe), vanadium (V), chromium (Cr), titanium (Ti), zirconium (Zr), zinc (Zn), aluminum (Al), indium (In), tantalum (Ta), yttrium (Y), lanthanum (La), strontium (Sr), gallium (Ga), scandium (Sc), gadolinium (Gd), samarium (Sm), calcium (Ca), cerium (Ce), niobium (Nb), magnesium (Mg), boron (B), and molybdenum (Mo), and 1 + x, a, b, c, and d are atomic fractions of each independent element, where 0 ≤ x ≤ 0.2, 0.50 ≤ a < 1, 0 < b ≤ 0.25, 0 < c ≤ 0.25, 0 ≤ d ≤ 0.1, and a + b + c + d = 1.

[0119] Preferably, a, b, c, and d can respectively satisfy 0.70 ≤ a ≤ 0.95, 0.025 ≤ b ≤ 0.20, 0.025 ≤ c ≤ 0.20, and 0 ≤ d ≤ 0.05.

[0120] In addition, a, b, c, and d can respectively satisfy 0.80 ≤ a ≤ 0.95, 0.025 ≤ b ≤ 0.15, 0.025 ≤ c ≤ 0.15, and 0 ≤ d ≤ 0.05.

[0121] In addition, a, b, c, and d can respectively satisfy 0.85 ≤ a ≤ 0.90, 0.05 ≤ b ≤ 0.10, 0.05 ≤ c ≤ 0.10, and 0 ≤ d ≤ 0.03.

[0122] Considering the sufficient capacity of the positive electrode active material, the content of the positive electrode active material in the positive electrode active material layer can be 80% to 99% by weight, preferably 92% to 98.5% by weight.

[0123] The positive electrode active material layer can further include a binder and / or a conductive agent together with the above positive electrode active material.

[0124] The binder is a component that aids in the binding between the conductive agent and the active material and the binding with the current collector, and specifically can include at least one selected from the group consisting of polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene - propylene - diene terpolymer (EPDM), sulfonated EPDM, styrene - butadiene rubber, and fluororubber, preferably polyvinylidene fluoride.

[0125] In terms of fully ensuring the binding force between each component such as the positive electrode active material, the content of the binder in the positive electrode active material layer can be 1% to 20% by weight, preferably 1.2% to 10% by weight.

[0126] Conductive agents can be used to assist and improve the conductivity in secondary batteries, and there are no particular limitations, as long as they are conductive and do not cause chemical changes. Specifically, conductive agents may include at least one selected from the group consisting of: graphite, such as natural or artificial graphite; carbon black, such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermally cracked carbon black; conductive fibers, such as carbon fibers or metal fibers; conductive tubes, such as carbon nanotubes; fluorocarbon compounds; metal powders, such as aluminum powder and nickel powder; conductive whiskers, such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides, such as titanium oxide; and polyphenylene derivatives, and preferably may include carbon black for improving conductivity.

[0127] To ensure sufficient electronic conductivity, the content of the conductive agent in the positive electrode active material layer can be from 1% to 20% by weight, preferably from 1.2% to 10% by weight.

[0128] The thickness of the positive electrode active material layer can be from 30 μm to 400 μm, preferably from 40 μm to 110 μm.

[0129] The positive electrode can be prepared by coating a positive electrode slurry containing a positive electrode active material and optional binders, conductive agents and a solvent for forming the positive electrode slurry onto a positive electrode current collector, and then drying and rolling the coated positive electrode current collector.

[0130] The solvent used to form the positive electrode slurry may include an organic solvent, such as NMP (N-methyl-2-pyrrolidone). The solids content of the positive electrode slurry may be from 40% to 90% by weight, specifically from 50% to 80% by weight.

[0131] (3) Diaphragm

[0132] The diaphragm can be placed between the positive and negative electrodes.

[0133] Furthermore, as a separator, conventional porous polymer membranes commonly used as separators can be used alone or in laminated form, such as porous polymer membranes prepared from polyolefin polymers (e.g., ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers), and typical porous nonwoven fabrics, such as nonwoven fabrics formed from high-melting-point glass fibers or polyethylene terephthalate fibers, can be used, but the invention is not limited thereto. Additionally, coated separators comprising ceramic components or polymer materials can be used to ensure heat resistance or mechanical strength, and separators having single-layer or multi-layer structures can optionally be used.

[0134] (4) Non-aqueous electrolytes

[0135] The non-aqueous electrolyte of the present invention includes lithium salts, fluoroethylene carbonate, 1,2-difluoroethylene carbonate, and compounds represented by Formula 1 below. In some cases, the non-aqueous electrolyte may further include organic solvents and additives.

[0136] 1) Lithium salts

[0137] As the lithium salt used in this invention, various lithium salts commonly used in non-aqueous electrolytes for lithium secondary batteries can be used without limitation. For example, the lithium salt may contain Li. + It is a cation, and may contain at least one selected from the group consisting of: F - Cl - ,Br - I - NO3 - N(CN)2 - BF4 - ClO4 - AlO4 - AlCl4 - PF6 - SbF6 - AsF6 - B 10 Cl 10 - BF2C2O4 - BC4O8 - PF4C2O4 - PF2C4O8 - (CF3)2PF4 - (CF3)3PF3 - (CF3)4PF2 - (CF3)5PF - (CF3)6P - CF3SO3 - C4F9SO3 - CF3CF2SO3 - (FSO2)2N - CF3CF2(CF3)2CO - (CF3SO2)2CH - CH3SO3 - CF3(CF2)7SO3 - CF3CO2 - CH3CO2 - SCN - and (CF3CF2SO2)2N - .

[0138] Specifically, lithium salts may include those selected from LiCl, LiBr, LiI, LiBF4, LiClO4, LiAlO4, LiAlCl4, LiPF6, LiSbF6, LiAsF6, and LiB. 10 Cl 10 The lithium salt may include at least one selected from the group consisting of LiBF4, LiClO4, LiPF6, LiBOB (LiB(C2O4)2), LiCF3SO3, LiTFSI (LiN(SO2CF3)2), LiFSI (LiN(SO2F)2), and LiBETI (LiN(SO2CF2CF3)2). Specifically, the lithium salt may include at least one selected from the group consisting of LiBF4, LiClO4, LiPF6, LiBOB (LiB(C2O4)2), LiCF3SO3, LiTFSI (LiN(SO2CF3)2), LiFSI (LiN(SO2F)2), and LiBETI (LiN(SO2CF2CF3)2).

[0139] Lithium salts can be included in non-aqueous electrolytes at concentrations of 0.5 M to 5 M, particularly 0.8 M to 4 M, and even more particularly 0.8 M to 2.0 M. When the concentration of the lithium salt meets the above range, the lithium-ion yield (Li) can be increased. + The output characteristics of a battery can be improved by using the migration number and the degree of lithium-ion dissociation.

[0140] In addition, lithium salts can be included in the non-aqueous electrolyte as a component other than the compounds represented by Formula 1, Formula 2, and optional organic solvents and additives.

[0141] 2) Fluorinated ethylene carbonate

[0142] Fluoroethylene carbonate (FEC) decomposes during battery operation, providing a composite composition of organic and inorganic components (e.g., LiF) for the SEI film. SEI films derived from FEC exhibit excellent long-term durability. In particular, the combination of 1,2-difluoroethylene carbonate and compounds of Formula 1, described later, and their reaction products show excellent effects during initialization, but struggle to demonstrate additional benefits during long-term battery operation. In this case, FEC can improve the long-term durability of the SEI film by continuously providing SEI film components when new surfaces are formed on the negative electrode due to volume expansion of the silicon-based active material during battery charging and discharging, leading to SEI film rupture. Because FEC contains less fluorine than 1,2-difluoroethylene carbonate and contributes less to the overall increase in LiF content of the SEI film, the desired effects are difficult to achieve when FEC is used alone.

[0143] Fluorinated ethylene carbonate can refer to monofluoroethylene carbonate.

[0144] The content of fluoroethylene carbonate in the non-aqueous electrolyte can be from 3 vol% to 20 vol%, particularly from 5 vol% to 15 vol%, and even more particularly from 7 vol% to 12 vol%. When the amount is within the above range, an appropriate level of SEI film can be formed on the negative electrode including the silicon-based active material, and the increase in resistance caused by excessive addition can be prevented.

[0145] Furthermore, the content of fluoroethylene carbonate in non-aqueous electrolytes can be from 3% to 20% by weight, particularly from 5% to 15% by weight, and even more particularly from 7% to 12% by weight.

[0146] 3) 1,2-Difluoroethylene carbonate

[0147] 1,2-Difluoroethylene carbonate, a compound containing two fluorine atoms in its molecular structure, suggests an increased amount of inorganic components (e.g., LiF) that can contribute to improved SEI film durability. Furthermore, defluorination of 1,2-difluoroethylene carbonate leads to the formation of carbon-carbon triple bonds or propargyl groups (C≡C), and this component is expected to form polymeric SEI films during ring-opening of its chemical structure. However, the problem with 1,2-difluoroethylene carbonate is that, due to the dominance of CO2 generation and the formation of unimolecular structures rather than ring-opening in polymeric form during its self-decomposition reaction, it is difficult to form SEI films with the desired organic / inorganic composite composition.

[0148] To address these issues, this invention utilizes the compound represented by Formula 1 (described below) in conjunction with ethylene 1,2-difluorocarbonate. Since the compound represented by Formula 1 forms free radicals during negative electrode reduction, the ring-opening reaction of ethylene 1,2-difluorocarbonate can be promoted, thereby inducing the formation of an SEI film with an organic / inorganic composite composition and simultaneously improving its flexibility, resilience, and durability. That is, it is understood that the formation of an SEI film derived from ethylene 1,2-difluorocarbonate can preferably be achieved only when the compound represented by Formula 1 is used in combination. Specifically, the SEI film derived from ethylene 1,2-difluorocarbonate through the free radical reaction induced by the compound represented by Formula 1 has an organic / inorganic composite composition, thus simultaneously improving the flexibility, resilience, and durability of the SEI film. This is particularly suitable for silicon-based active materials that experience significant volume expansion / contraction during initialization and battery operation.

[0149] The content of 1,2-difluoroethylene carbonate in non-aqueous electrolytes can be from 10 vol% to 35 vol%, particularly from 15 vol% to 30 vol%, and even more particularly from 17 vol% to 22 vol%.

[0150] The content of 1,2-difluoroethylene carbonate in non-aqueous electrolytes can be from 10% to 35% by weight, particularly from 15% to 32% by weight, and even more particularly from 18% to 25% by weight.

[0151] The volume ratio of fluoroethylene carbonate to 1,2-difluoroethylene carbonate can be 5:95 to 50:50, particularly 25:75 to 40:60, and even more particularly 28:72 to 35:65.

[0152] The weight ratio of fluoroethylene carbonate to 1,2-difluoroethylene carbonate can be 5:95 to 50:50, particularly 15:85 to 45:55, and even more particularly 30:70 to 35:65.

[0153] Based on the total weight of the non-aqueous electrolyte, the total amount of fluoroethylene carbonate and 1,2-difluoroethylene carbonate can be greater than 10% by weight and less than or equal to 50% by weight, particularly 15% to 45% by weight, more particularly 25% to 42% by weight, and even more particularly 30% to 35% by weight. When this total amount is within the above range, the aforementioned effects of fluoroethylene carbonate and 1,2-difluoroethylene carbonate can be synergistically enhanced and achieved.

[0154] 4) Compounds represented by Formula 1

[0155] The non-aqueous electrolyte of the present invention includes compounds represented by Formula 1.

[0156] [Formula 1]

[0157]

[0158] In Formula 1, R1 includes halogen, nitrile, propargyl, ester, ether, ketone, carboxyl, unsubstituted or substituted alkyl, unsubstituted or substituted alkenyl, unsubstituted or substituted alkynyl, unsubstituted or substituted alkoxy, boron, borate ester, isocyanate, isothiocyanate, silyl, siloxane, sulfone, sulfonate, sulfate ester, or a combination of two or more thereof, and n is an integer from 0 to 6.

[0159] The compound represented by Formula 1 exhibits excellent negative electrode reducing ability and can form free radicals during negative electrode reduction. Since the free radicals formed thereby can promote the ring-opening reaction of 1,2-difluoroethylene carbonate as described above, a SEI membrane with high flexibility, resilience and durability can be achieved during the initialization process.

[0160] Furthermore, the compound represented by Formula 1 can be ring-opened during initialization to form a polymeric membrane based on polyethylene oxide on the electrode, and the polymeric membrane has excellent flexibility and resilience.

[0161] In Formula 1, R1 can specifically be a halogen (the halogen can be selected from fluorine (F), chlorine (Cl), bromine (Br), and iodine (I), specifically F), a nitrile group, a propargyl group, an ester group, an ether group, or a combination of two or more of them. Since these substituents can enhance the reducing power of the first additive, they can also achieve the effect of smoothly forming an SEI film and improving lithium-ion transport performance.

[0162] In Equation 1, n can be an integer selected from 0 to 6, specifically an integer selected from 1 to 6, and more specifically, n can be 1. In Equation 1, when n is 2 or more, the individual R1s can be the same or different from each other.

[0163] Specifically, the compound represented by Formula 1 may include at least one selected from the group consisting of compounds represented by Formulas 1-A and 1-B.

[0164] [Equation 1-A]

[0165]

[0166] [Equation 1-B]

[0167]

[0168] In Equations 1-A and 1-B, R1 is defined as in Equation 1.

[0169] The compounds represented by Formulas 1-A and 1-B have structures in which substituents are located at the 3 and 7 positions of the ring structure, respectively (based on IUPAC nomenclature), and in this case, it is preferred that the synthesis be carried out at the above positions compared with other substitution positions.

[0170] Specifically, the compound represented by Formula 1 may include at least one selected from the group consisting of compounds represented by Formulas 1-1 to 1-9 below. In respect of the fact that more favorable reduction at the negative electrode leads to SEI film formation, the compound represented by Formula 1 may specifically include at least one selected from the group consisting of compounds represented by Formulas 1-1, 1-2, 1-3, 1-4, and 1-9, more specifically including at least one selected from the group consisting of compounds represented by Formulas 1-1 and 1-2 below, and even more specifically including the compound represented by Formula 1-1 below.

[0171] [Equation 1-1]

[0172]

[0173] [Equation 1-2]

[0174]

[0175] [Equation 1-3]

[0176]

[0177] [Equations 1-4]

[0178]

[0179] [Equations 1-5]

[0180]

[0181] [Equations 1-6]

[0182]

[0183] [Equations 1-7]

[0184]

[0185] [Equations 1-8]

[0186]

[0187] [Equations 1-9]

[0188]

[0189] The compound represented by Formula 1 can be present in a non-aqueous electrolyte at a concentration of 0.1% to 10% by weight, particularly 1% to 7% by weight, and even more particularly 3.5% to 6% by weight. When the amount of the compound represented by Formula 1 is within the above range, the ring-opening reaction of 1,2-difluoroethylene carbonate can be sufficiently induced, and concerns about increased resistance when added in excess can be prevented.

[0190] The weight ratio of the compound represented by Formula 1 to the weight of 1,2-difluoroethylene carbonate can be from 0.2 to 1, particularly from 0.25 to 0.95, and even more particularly from 0.4 to 0.7. When this ratio is within the above range, and when the amount of the compound represented by Formula 1 is within the above range, the ring-opening reaction of 1,2-difluoroethylene carbonate can be sufficiently induced, and an organic / inorganic composite SEI film according to the corresponding configuration combination can be formed at a sufficient level.

[0191] The weight ratio of the compound represented by Formula 1 to the weight of fluoroethylene carbonate can be from 0.1 to 0.5, specifically from 0.15 to 0.45. Furthermore, the weight ratio of the compound represented by Formula 1 to the total weight of fluoroethylene carbonate and 1,2-difluoroethylene carbonate can be from 0.1 to 0.3, specifically from 0.12 to 0.20. When this ratio is within the above range, it is advantageous that the initial performance and long-term lifespan performance of the negative electrode and lithium secondary battery using silicon-based active materials can be improved to an excellent level.

[0192] 5) Organic solvents

[0193] In addition to the above-mentioned components, non-aqueous electrolytes may further include organic solvents.

[0194] There are no particular restrictions on any non-aqueous solvent commonly used in lithium secondary batteries as an organic solvent, as long as it can minimize decomposition caused by oxidation reactions during the charging and discharging of the lithium secondary battery.

[0195] Organic solvents may be included in the non-aqueous electrolyte as a volume percentage (volume %) of the remaining amount other than fluoroethylene carbonate and 1,2-difluoroethylene carbonate.

[0196] Specifically, the organic solvent may include at least one selected from the group consisting of cyclic carbonate organic solvents, linear carbonate organic solvents, linear ester organic solvents, and cyclic ester organic solvents.

[0197] Specifically, the organic solvent may include at least one selected from cyclic carbonate organic solvents and linear carbonate organic solvents. Furthermore, given that the aforementioned fluoroethylene carbonate and 1,2-difluoroethylene carbonate replace the cyclic carbonate organic solvents, the organic solvent may include linear carbonate organic solvents.

[0198] Cyclic carbonate organic solvents, as high-viscosity organic solvents, are organic solvents that can effectively dissociate lithium salts in electrolytes due to their high dielectric constant. Specifically, cyclic carbonate organic solvents may include at least one organic solvent selected from the group consisting of ethylene carbonate (EC), fluoroethylene carbonate (FEC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentene carbonate, 2,3-pentene carbonate, and vinylene carbonate, more specifically including ethylene carbonate (EC). Furthermore, the non-aqueous electrolyte of the present invention may not include cyclic carbonate organic solvents or ethylene carbonate.

[0199] Furthermore, linear carbonate organic solvents are organic solvents with low viscosity and low dielectric constant, wherein linear carbonate organic solvents specifically may include at least one 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, more specifically may include at least one selected from the group consisting of ethyl methyl carbonate (EMC) and diethyl carbonate (DEC), more specifically may include ethyl methyl carbonate (EMC) and diethyl carbonate (DEC), and even more specifically may include ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) in a volume ratio of 50:50 to 99:1, particularly 60:40 to 90:10, more particularly 60:40 to 75:25, and even more particularly 62:38 to 66:34.

[0200] When the organic solvent includes a linear carbonate solvent, the ratio of the total volume of fluoroethylene carbonate and 1,2-difluoroethylene carbonate to the volume of the linear carbonate solvent can be from 10:90 to 50:50, specifically from 20:80 to 45:55.

[0201] Linear ester organic solvents may specifically include at least one selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, and butyl propionate.

[0202] In addition, cyclic ester organic solvents may specifically include at least one selected from the group consisting of γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone and ε-caprolactone.

[0203] Where necessary, organic solvents may be used without limitation by adding organic solvents commonly used in non-aqueous electrolytes. For example, organic solvents may further include at least one organic solvent selected from ether organic solvents, glycol diether solvents, and nitrile organic solvents.

[0204] As an ether solvent, any one or a mixture of two or more of the following can be used: 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), but the ether solvent is not limited thereto.

[0205] Glycol diether solvents are solvents that have a higher dielectric constant and lower surface tension than linear carbonate organic solvents and are less reactive with metals. Glycol diether solvents may include, but are not limited to, at least one selected from the group consisting of dimethoxyethane (glycol dimethyl ether, DME), diethoxyethane, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether and tetraethylene glycol dimethyl ether (TEGDME).

[0206] Nitrile solvents may be at least one selected from the group consisting of acetonitrile, propionitrile, butyronitrile, valerate, octanoic acid, heptanonitrile, cyclopentanoic acid, cyclohexanoic acid, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile, but are not limited thereto.

[0207] 6) Additives

[0208] In addition to the above-mentioned components, non-aqueous electrolytes may further include additives.

[0209] Specifically, the additive may be at least one selected from the group consisting of vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, propane sulpholactone, propene sulpholactone, succinic acid nitrile, adiponitrile, ethylene sulfate, LiODFB (lithium difluorooxalatoborate), LiBOB (lithium bis(oxalatoborate)), TMSPa (tris(trimethylsilyl) phosphate), and TMSPi (tris(trimethylsilyl) phosphite).

[0210] The additive content in the non-aqueous electrolyte can be from 0.1% to 15% by weight, but the present invention is not limited thereto.

[0211] In the lithium secondary battery of the present invention, after the lithium secondary battery is formed, a solid electrolyte interface film is formed on the negative electrode. This solid electrolyte interface film includes inorganic components, and the inorganic components include LiF and CO3. 2- The weight of LiF is related to that of CO3. 2- The weight ratio can be 1.4 or higher.

[0212] Non-aqueous electrolyte components (e.g., ethylene carbonate fluorocarbonate, ethylene carbonate 1,2-difluorocarbonate, compounds represented by Formula 1, etc.) can be decomposed through a formation process to form a solid electrolyte interphase (SEI) membrane.

[0213] As the formation process, methods known in the art can be used without limitation, and the formation process itself is not particularly limited. For example, the formation process can be carried out by charging at a C rate of 0.1C to 1C at room temperature (20±5°C) to a state of charge (SOC) of 10% or more, particularly 60% or more, and more particularly 100% SOC. Furthermore, the formation process can be carried out at a temperature of 45°C to 60°C and a C rate of 0.5 kgf / cm³. 2 Up to 20 kgf / cm 2 The experiment was conducted under the aforementioned C-rate and SOC conditions under pressure.

[0214] The inorganic components and their amounts in a solid electrolyte interface membrane can be measured by a method including the following steps.

[0215] (a) Separating the negative electrode by disassembling the formed lithium secondary battery;

[0216] (b) The negative electrode separated by washing;

[0217] (c) Extracting the solid electrolyte interface film on the surface of the negative electrode by immersing the washed negative electrode in an extraction solvent; and

[0218] (d) Use capillary electrophoresis to analyze the inorganic components in the extraction solvent;

[0219] The separation of the negative electrode can be carried out in an inert gas atmosphere.

[0220] The separated negative electrode is washed to prevent interference from non-aqueous electrolyte components. Washing can be performed by immersing the negative electrode in a washing solvent.

[0221] The washing solvent may include at least one organic solvent selected from the group consisting of cyclic ether solvents, ester organic solvents, or nitrile organic solvents. For example, when using propionate organic solvents as the organic solvent for non-aqueous electrolytes, carbonate organic solvents may be used as the washing solvent, or when using linear carbonate organic solvents as the organic solvent for non-aqueous electrolytes, propionate organic solvents may be used as the washing solvent.

[0222] During washing, the washing solvent and washing time can be varied depending on the size of the negative electrode. Specifically, washing can be performed through the following process: when based on a 15cm... 2 Up to 35cm 2 When the negative electrode area is reached, immerse the electrode in 10 mL to 50 mL of washing solvent for 15 minutes to 1 hour.

[0223] After washing, an additional step of drying the electrode in an inert gas atmosphere to remove the washing solvent can be performed. Depending on the electrode condition, drying can be carried out at room temperature (20±5℃) for approximately 5 minutes to 2 hours.

[0224] The extraction solvent can be a highly polar solvent, and the highly polar solvent can include at least one solvent selected from the group consisting of deuterium oxide (D2O), tetrahydrofuran (THF), acetonitrile, acetone, hexamethylphosphoramide (HMPA), N,N-dimethylformamide and dimethyl sulfoxide.

[0225] The extraction of the solid electrolyte interface membrane can be appropriately modified according to experimental conditions such as electrode size, battery cycling, and storage conditions during extraction. Specifically, extraction can be performed as follows: when based on a 15cm... 2 Up to 35cm 2When the negative electrode area is large enough, the electrode is immersed in 1 mL to 5 mL of extraction solvent at room temperature (25±5℃) for 12 to 48 hours.

[0226] There are instances where electrode metal components dissolved from partially deteriorated electrodes dissolve during extraction and remain in the extraction solvent. In such cases, since clear analysis is difficult to perform in subsequent processes, a filtration step for removing these impurities may be further included.

[0227] Depending on the amount of byproducts, centrifugation or filtration may be used as appropriate.

[0228] Subsequently, capillary electrophoresis can be used to analyze the inorganic components in the extracted solvent obtained after filtration.

[0229] In this specification, "capillary electrophoresis" refers to a method for measuring the structure and quantity of components by utilizing the chemical phenomenon of charges in a solution moving towards electrodes of opposite charge under an electric field between electrodes, wherein the structure or quantity of the component (type) does not change based on specific equipment and conditions. In this invention, measurements can be performed using an AB SCIEX MDQ plus device (capillary: 75 μm ID, 50 cm; injection: 0.5 psi, 3 seconds; separation: 20 kV, 0.1 psi; detector: 230 nm UV) using SCIEX anion analyzer reagent (pH 5.5) as the run buffer.

[0230] In addition to the above description, the composition measurement of the solid electrolyte interface membrane can be found in Korean Patent Application Publication No. 10-2020-0005870.

[0231] For the lithium secondary battery of the present invention, the weight of LiF and CO3 2- The weight ratio can be 1.4 or higher, particularly 1.4 to 3.0, more particularly 1.5 to 2.7, and even more particularly 2.0 to 2.6. When this ratio is within the above range, it can be evaluated that the composite film of inorganic and organic components of the SEI film in the negative electrode is appropriately formed at a sufficient level, which can significantly improve the overall performance of the battery including the silicon-based negative electrode.

[0232] The LiF weight per unit area of ​​a solid electrolyte interface film can be 100 μg / cm³. 2 The above, especially 100 μg / cm 2 Up to 250 μg / cm 2 More importantly, 190 μg / cm 2 Up to 240 μg / cm 2 .

[0233] CO3 per unit area of ​​solid electrolyte interfacial membrane 2-The weight can be 60 μg / cm 2 The above, especially 75 μg / cm 2 Up to 100 μg / cm 2 More importantly, 77 μg / cm 2 Up to 82 μg / cm 2 .

[0234] The shape of the lithium secondary battery of the present invention is not particularly limited, but it can be cylindrical, prismatic, pouch or coin-shaped.

[0235] The present invention will be described in detail below with reference to specific embodiments. However, the following embodiments are merely presented to illustrate the invention, and the scope of the invention is not limited thereto. It will be apparent to those skilled in the art that various modifications and changes are possible within the scope and spirit of the invention. Such modifications and changes fall within the scope of the claims included herein.

[0236] Examples and Comparative Examples

[0237] Example 1

[0238] (Preparation of non-aqueous electrolytes)

[0239] An organic solvent was prepared by mixing fluoroethylene carbonate, 1,2-difluoroethylene carbonate, diethyl carbonate, and ethyl methyl carbonate in a volume ratio of 5:20:45:30.

[0240] A non-aqueous electrolyte was prepared by adding LiPF6, a lithium salt, and the compound represented by Formula 1-1 to the above-mentioned organic solvent.

[0241] Lithium salts were added to the non-aqueous electrolyte at a molar concentration of 1.5 M.

[0242] The compound represented by Formula 1-1 is added to the non-aqueous electrolyte in an amount of 5% by weight.

[0243] In the non-aqueous electrolyte, the weight percentage of fluoroethylene carbonate is 5.5% by weight, and the weight percentage of 1,2-difluoroethylene carbonate is 22.2% by weight.

[0244] (Lithium-ion secondary battery manufacturing)

[0245] The positive electrode active material (LiNi) 0.85 Co 0.05 Mn 0.07 Al 0.03O2): Conductive agent (carbon nanotubes): Binder (polyvinylidene fluoride) were added to N-methyl-2-pyrrolidone (NMP) as a solvent in a weight ratio of 97.74:0.70:1.56 to prepare a cathode material mixture slurry (75.5% by weight solids). This cathode material mixture slurry was then coated onto one surface of a 15 μm thick cathode current collector (Al film), dried, and then rolled to prepare the cathode.

[0246] A negative electrode active material (Si), conductive agent (carbon black), and binder (styrene-butadiene rubber) were added to distilled water as a solvent in a weight ratio of 70.0:20.3:9.7 to prepare a negative electrode material mixture slurry (solid content 26% by weight). This negative electrode material mixture slurry was then coated onto one surface of a 15 μm thick negative electrode current collector (Cu film), dried, and then rolled to prepare the negative electrode.

[0247] In a drying chamber, a polyethylene porous membrane is placed between the positive and negative electrodes prepared above, and then the non-aqueous electrolyte prepared above is injected to prepare a lithium secondary battery.

[0248] (Compositional analysis of solid electrolyte interfacial membranes)

[0249] The lithium secondary battery prepared above was charged to 100% SOC at a C rate of 0.33C at room temperature (20±5℃) for formation.

[0250] The formed lithium-ion batteries were disassembled individually in an inert gas atmosphere to obtain the negative electrode (area: 65 cm²). 2 The negative electrode was then immersed in 30 mL of dimethyl carbonate (DMC) washing solvent for 30 minutes for washing.

[0251] Next, the washed electrode was immersed in 10 mL of deuterium oxide (D2O) at room temperature (25±5℃) for 24 hours for extraction.

[0252] Subsequently, after extraction, the extraction solvent was filtered using a filter, and capillary electrophoresis was used for qualitative and quantitative analysis of the inorganic components in the extraction solvent. Among them, LiF and CO3 were identified. 2- The content analysis results are presented in Table 1 below.

[0253] Capillary electrophoresis was performed using an AB SCIEX MDQ plus device (capillary: 75 μm ID, 50 cm; injection: 0.5 psi, 3 sec; separation: 20 kV, 0.1 psi; detector: 230 nm UV) with SCIEX anion assay reagent (pH 5.5) as the run buffer.

[0254] Example 2

[0255] (Preparation of non-aqueous electrolytes)

[0256] An organic solvent was prepared by mixing fluoroethylene carbonate, 1,2-difluoroethylene carbonate, diethyl carbonate, and ethyl methyl carbonate in a volume ratio of 15:20:45:20.

[0257] A non-aqueous electrolyte was prepared by adding LiPF6, a lithium salt, and the compound represented by Formula 1-1 to the above-mentioned organic solvent.

[0258] Lithium salts were added to the non-aqueous electrolyte at a molar concentration of 1.5 M.

[0259] The compound represented by Formula 1-1 is added to the non-aqueous electrolyte in an amount of 5% by weight.

[0260] In the non-aqueous electrolyte, the weight percentage of fluoroethylene carbonate is 15.9% by weight, and the weight percentage of 1,2-difluoroethylene carbonate is 21.4% by weight.

[0261] (Lithium-ion secondary battery manufacturing)

[0262] A lithium secondary battery was prepared in the same manner as in Example 1, except that the non-aqueous electrolyte prepared above was used.

[0263] Example 3

[0264] (Preparation of non-aqueous electrolytes)

[0265] An organic solvent was prepared by mixing fluoroethylene carbonate, 1,2-difluoroethylene carbonate, diethyl carbonate, and ethyl methyl carbonate in a volume ratio of 10:15:45:30.

[0266] A non-aqueous electrolyte was prepared by adding LiPF6, a lithium salt, and the compound represented by Formula 1-1 to the above-mentioned organic solvent.

[0267] Lithium salts were added to the non-aqueous electrolyte at a molar concentration of 1.5 M.

[0268] The compound represented by Formula 1-1 is added to the non-aqueous electrolyte in an amount of 5% by weight.

[0269] In the non-aqueous electrolyte, the weight percentage of fluoroethylene carbonate is 11.0 wt%, and the weight percentage of 1,2-difluoroethylene carbonate is 16.6 wt%.

[0270] (Lithium-ion secondary battery manufacturing)

[0271] A lithium secondary battery was prepared in the same manner as in Example 1, except that the non-aqueous electrolyte prepared above was used.

[0272] Example 4

[0273] (Preparation of non-aqueous electrolytes)

[0274] An organic solvent was prepared by mixing fluoroethylene carbonate, 1,2-difluoroethylene carbonate, diethyl carbonate, and ethyl methyl carbonate in a volume ratio of 10:20:45:25.

[0275] A non-aqueous electrolyte was prepared by adding LiPF6, a lithium salt, and the compound represented by Formula 1-1 to the above-mentioned organic solvent.

[0276] Lithium salts were added to the non-aqueous electrolyte at a molar concentration of 1.5 M.

[0277] The compound represented by Formula 1-1 is added to the non-aqueous electrolyte in an amount of 5% by weight.

[0278] In the non-aqueous electrolyte, the weight percentage of fluoroethylene carbonate is 10.8 wt%, and the weight percentage of 1,2-difluoroethylene carbonate is 21.8 wt%.

[0279] (Lithium-ion secondary battery manufacturing)

[0280] A lithium secondary battery was prepared in the same manner as in Example 1, except that the non-aqueous electrolyte prepared above was used.

[0281] Example 5

[0282] (Preparation of non-aqueous electrolytes)

[0283] An organic solvent was prepared by mixing fluoroethylene carbonate, 1,2-difluoroethylene carbonate, diethyl carbonate, and ethyl methyl carbonate in a volume ratio of 10:30:45:15.

[0284] A non-aqueous electrolyte was prepared by adding LiPF6, a lithium salt, and the compound represented by Formula 1-1 to the above-mentioned organic solvent.

[0285] Lithium salts were added to the non-aqueous electrolyte at a molar concentration of 1.5 M.

[0286] The compound represented by Formula 1-1 is added to the non-aqueous electrolyte in an amount of 5% by weight.

[0287] In the non-aqueous electrolyte, the weight percentage of fluoroethylene carbonate is 10.4% by weight, and the weight percentage of 1,2-difluoroethylene carbonate is 31.5% by weight.

[0288] (Lithium-ion secondary battery manufacturing)

[0289] A lithium secondary battery was prepared in the same manner as in Example 1, except that the non-aqueous electrolyte prepared above was used.

[0290] Example 6

[0291] (Preparation of non-aqueous electrolytes)

[0292] The non-aqueous electrolyte was prepared in the same manner as in Example 1, except that instead of using the compound represented by Formula 1-1, the compound represented by Formula 1-2 was included in the non-aqueous electrolyte in an amount of 5% by weight.

[0293] (Lithium-ion secondary battery manufacturing)

[0294] A lithium secondary battery was prepared in the same manner as in Example 1, except that the non-aqueous electrolyte prepared above was used.

[0295] Example 7

[0296] (Preparation of non-aqueous electrolytes)

[0297] The non-aqueous electrolyte was prepared in the same manner as in Example 1, except that instead of using the compound represented by Formula 1-1, the compound represented by Formula 1-3 was included in the non-aqueous electrolyte in an amount of 5% by weight.

[0298] (Lithium-ion secondary battery manufacturing)

[0299] A lithium secondary battery was prepared in the same manner as in Example 1, except that the non-aqueous electrolyte prepared above was used.

[0300] Example 8

[0301] (Preparation of non-aqueous electrolytes)

[0302] The non-aqueous electrolyte was prepared in the same manner as in Example 1, except that instead of using the compound represented by Formula 1-1, the compound represented by Formula 1-4 was included in the non-aqueous electrolyte in an amount of 5% by weight.

[0303] (Lithium-ion secondary battery manufacturing)

[0304] A lithium secondary battery was prepared in the same manner as in Example 1, except that the non-aqueous electrolyte prepared above was used.

[0305] Example 9

[0306] (Preparation of non-aqueous electrolytes)

[0307] The non-aqueous electrolyte was prepared in the same manner as in Example 1, except that instead of using the compounds represented by Formula 1-1, the compounds represented by Formula 1-9 were included in the non-aqueous electrolyte in an amount of 5% by weight.

[0308] (Lithium-ion secondary battery manufacturing)

[0309] A lithium secondary battery was prepared in the same manner as in Example 1, except that the non-aqueous electrolyte prepared above was used.

[0310] Comparative Example 1

[0311] (Preparation of non-aqueous electrolytes)

[0312] An organic solvent was prepared by mixing ethylene carbonate, 1,2-difluoroethylene carbonate, diethyl carbonate, and ethyl methyl carbonate in a volume ratio of 10:20:45:25.

[0313] A non-aqueous electrolyte was prepared by adding LiPF6, a lithium salt, and the compound represented by Formula 1-1 to the above-mentioned organic solvent.

[0314] Lithium salts were added to the non-aqueous electrolyte at a molar concentration of 1.5 M.

[0315] The compound represented by Formula 1-1 is added to the non-aqueous electrolyte in an amount of 5% by weight.

[0316] In the non-aqueous electrolyte, ethylene carbonate accounts for 9.6% by weight and 1,2-difluoroethylene carbonate accounts for 22.1% by weight.

[0317] (Lithium-ion secondary battery manufacturing)

[0318] A lithium secondary battery was prepared in the same manner as in Example 1, except that the non-aqueous electrolyte prepared above was used.

[0319] Comparative Example 2

[0320] (Preparation of non-aqueous electrolytes)

[0321] An organic solvent was prepared by mixing fluoroethylene carbonate, diethyl carbonate, and ethyl methyl carbonate in a volume ratio of 10:45:45.

[0322] A non-aqueous electrolyte was prepared by adding LiPF6, a lithium salt, and the compound represented by Formula 1-1 to the above-mentioned organic solvent.

[0323] Lithium salts were added to the non-aqueous electrolyte at a molar concentration of 1.5 M.

[0324] The compound represented by Formula 1-1 is added to the non-aqueous electrolyte in an amount of 5% by weight.

[0325] In non-aqueous electrolytes, fluoroethylene carbonate has a weight percentage of 11.6%.

[0326] (Lithium-ion secondary battery manufacturing)

[0327] A lithium secondary battery was prepared in the same manner as in Example 1, except that the non-aqueous electrolyte prepared above was used.

[0328] Comparative Example 3

[0329] (Preparation of non-aqueous electrolytes)

[0330] The non-aqueous electrolyte was prepared in the same manner as in Example 1, except that the non-aqueous electrolyte did not contain the compound represented by Formula 1-1.

[0331] (Lithium-ion secondary battery manufacturing)

[0332] A lithium secondary battery was prepared in the same manner as in Example 1, except that the non-aqueous electrolyte prepared above was used.

[0333] Comparative Example 4

[0334] (Preparation of non-aqueous electrolytes)

[0335] An organic solvent was prepared by mixing 1,2-difluoroethylene carbonate, diethyl carbonate, and ethyl methyl carbonate in a volume ratio of 20:45:35.

[0336] A non-aqueous electrolyte was prepared by adding LiPF6, a lithium salt, and the compound represented by Formula 1-1 to the above-mentioned organic solvent.

[0337] Lithium salts were added to the non-aqueous electrolyte at a molar concentration of 1.5 M.

[0338] The compound represented by Formula 1-1 is added to the non-aqueous electrolyte in an amount of 5% by weight.

[0339] In non-aqueous electrolytes, ethylene 1,2-difluorocarbonate has a weight percentage of 22.6%.

[0340] (Lithium-ion secondary battery manufacturing)

[0341] A lithium secondary battery was prepared in the same manner as in Example 1, except that the non-aqueous electrolyte prepared above was used.

[0342] [Table 1]

[0343]

[0344] Experimental Example 1: Evaluation of High-Temperature Cyclic Charge and Discharge Performance

[0345] Using an electrochemical charge / discharge apparatus, the lithium secondary batteries of Examples 1 to 9 and Comparative Examples 1 to 4 prepared above were each charged to 4.2V at 0.33C under constant current / constant voltage (CC / CV) conditions at 45°C, and then discharged to 3.0V at 0.33C CC. This was considered one cycle, and 200 charge and discharge cycles were performed. The capacity retention rate, resistance increase rate, gas generation, and metal dissolution were evaluated as follows.

[0346] Experimental Example 1-1: Evaluation of Capacity Retention

[0347] After charging and discharging under the above conditions, the capacity retention rate is calculated using the following equation, and the results are presented in Table 2 below.

[0348] Capacity retention (%) = (Discharge capacity after 200 cycles / Discharge capacity after one cycle) × 100

[0349] Experimental Example 1-2: Evaluation of Resistance Increase Rate

[0350] After one charge and discharge cycle, the discharge capacity after one cycle was measured using an electrochemical charge / discharge device. The state of charge (SOC) was adjusted to 50%, and then a 2.5C pulse was applied for 10 seconds. The initial resistance was calculated by the difference between the voltage before and after the pulse.

[0351] After 200 charge and discharge cycles, the resistance after 200 cycles was calculated in the same way as above. The rate of increase in resistance was calculated using the following equation, and the results are presented in Table 2 below.

[0352] Resistance increase rate (%) = (Resistance after 200 cycles - Initial resistance) / Initial resistance × 100

[0353] Experiment Example 2: High-Temperature Storage Performance Evaluation

[0354] The lithium secondary batteries of Examples 1 to 9 and Comparative Examples 1 to 3 were initially charged and discharged at 0.33C to 2.5V under constant current / constant voltage (CC / CV) conditions at room temperature, and then charged to 4.2V / 55mA under constant current / constant voltage (CC / CV) conditions at room temperature, and then stored at 60°C.

[0355] Experimental Example 2-1: Evaluation of Capacity Retention

[0356] After storage, the secondary battery was charged to 4.2V / 55mA at room temperature under constant current / constant voltage (CC / CV) conditions of 0.33C / 4.2V, and then discharged to 2.5V at 0.33C to measure the capacity during discharge.

[0357] Capacity retention (%) = (Discharge capacity after 8 weeks of storage / Initial discharge capacity) × 100

[0358] Experimental Example 2-2: Evaluation of Resistance Increase Rate

[0359] During initial charging and discharging, after checking the capacity at room temperature, the secondary battery was charged to 50% SOC based on its discharge capacity and discharged at 2.5C for 10 seconds. The voltage drop under these conditions was used to measure the resistance, which was used as the initial resistance. After storage at 60°C for 8 weeks, the resistance was measured using the same method and used as the final resistance. The rate of increase in resistance was calculated using the following equation. The results are presented in Table 2 below.

[0360] Resistance increase rate (%) = (final resistance - initial resistance) / (initial resistance) × 100

[0361] [Table 2]

[0362]

[0363] Referring to Table 2, it can be confirmed that compared with Comparative Examples 1 to 4, the lithium secondary batteries of Examples 1 to 9 (which include a non-aqueous electrolyte containing fluoroethylene carbonate, 1,2-difluoroethylene carbonate and all compounds represented by Formula 1, and a negative electrode containing silicon-based active materials) exhibit significantly better cycle charge and discharge performance and high-temperature storage performance.

[0364] Reference Example

[0365] Reference Example 1

[0366] (Preparation of non-aqueous electrolytes)

[0367] The non-aqueous electrolyte was prepared in the same manner as in Comparative Example 1.

[0368] (Lithium-ion secondary battery manufacturing)

[0369] The positive electrode active material (LiNi) 0.85 Co 0.05 Mn 0.07 Al 0.03 O2): Conductive agent (carbon nanotubes): Binder (polyvinylidene fluoride) were added to N-methyl-2-pyrrolidone (NMP) as a solvent in a weight ratio of 97.74:0.70:1.56 to prepare a cathode material mixture slurry (75.5% by weight solids). This cathode material mixture slurry was then coated onto one surface of a 15 μm thick cathode current collector (Al film), dried, and then rolled to prepare the cathode.

[0370] A negative electrode material mixture slurry (50% by weight) was prepared by adding the negative electrode active material (a mixture of artificial and natural graphite in a weight ratio of 50.3:49.7), a conductive agent (carbon black), and a binder (styrene-butadiene rubber) to distilled water as a solvent in a weight ratio of 96.7:1.0:2.3. This negative electrode material mixture slurry was then coated onto one surface of an 8 μm thick negative electrode current collector (Cu film), dried, and then rolled to prepare the negative electrode.

[0371] In a drying chamber, a polyethylene porous membrane separator is placed between the positive and negative electrodes prepared above, and then the non-aqueous electrolyte prepared above is injected to prepare a secondary battery.

[0372] See Example 2

[0373] A lithium secondary battery was prepared in the same manner as in Reference Example 1, except that a non-aqueous electrolyte prepared in the same manner as in Example 4 was used.

[0374] See Example 3

[0375] A lithium secondary battery was prepared in the same manner as in Reference Example 1, except that a non-aqueous electrolyte prepared in the same manner as in Comparative Example 3 was used.

[0376] See Example 4

[0377] A lithium secondary battery was prepared in the same manner as in Reference Example 1, except that a non-aqueous electrolyte prepared in the same manner as in Comparative Example 4 was used.

[0378] Refer to Experiment Example 1: Evaluation of High-Temperature Cyclic Charge and Discharge Performance

[0379] The experiments were conducted using the same methods as in Experiment 1 (Experiments 1-1 and 1-2). The results are presented in Table 3 below.

[0380] Refer to Experiment Example 2: High-Temperature Storage Performance Evaluation

[0381] The experiment was conducted using the same method as in Experiment 2 (Experiments 2-1 and 2-2). The results are presented in Table 3 below.

[0382] [Table 3]

[0383]

[0384] Referring to Table 3, for the lithium secondary batteries of Reference Examples 1 to 4 that use only carbon-based active materials as negative electrode active materials, compared with Reference Example 1 (using the non-aqueous electrolyte used in Comparative Example 1), Reference Example 3 (using the non-aqueous electrolyte used in Comparative Example 3), and Reference Example 4 (using the non-aqueous electrolyte used in Comparative Example 4), Reference Example 2 (using the non-aqueous electrolyte used in Example 4) exhibited lower capacity retention and higher resistance increase during charge and discharge cycles and high-temperature storage. This is considered to be due to the combined use of fluoroethylene carbonate and 1,2-difluoroethylene carbonate causing unnecessary problems in the carbon-based active material, for example, it acts as a resistor.

[0385] Therefore, based on the experimental results in Table 3, it can be understood that the non-aqueous electrolyte of the present invention exhibits the required lifetime performance and high-temperature storage performance in anodes containing silicon-based active materials and lithium secondary batteries.

Claims

1. A lithium secondary battery, comprising: Positive electrode; negative electrode; a membrane disposed between the positive electrode and the negative electrode; And non-aqueous electrolytes, The negative electrode comprises a negative electrode active material, and the negative electrode active material comprises a silicon-based active material. The non-aqueous electrolyte comprises lithium salt, fluoroethylene carbonate, 1,2-difluoroethylene carbonate, and a compound represented by Formula 1: [Formula 1] In Formula 1, R1 includes halogen, nitrile, propargyl, ester, ether, ketone, carboxyl, unsubstituted or substituted alkyl, unsubstituted or substituted alkenyl, unsubstituted or substituted alkynyl, unsubstituted or substituted alkoxy, boron, borate ester, isocyanate, isothiocyanate, silyl, siloxane, sulfone, sulfonate, sulfate ester, or a combination of two or more thereof, and n is an integer from 0 to 6.

2. The lithium secondary battery as described in claim 1, wherein, The silicon-based active material includes silicon-based particles. The silicon-based particles contain a compound represented by formula A: [Formula A] Not. x In equation A, 0 ≤ x < 2.

3. The lithium secondary battery as described in claim 2, wherein, The silicon-based particles are formed from silicon (Si).

4. The lithium secondary battery as described in claim 1, wherein, The compound represented by Formula 1 includes at least one selected from the group consisting of compounds represented by Formulas 1-A and 1-B: [Equation 1-A] [Equation 1-B] In Equations 1-A and 1-B, R1 is defined as in Equation 1.

5. The lithium secondary battery as described in claim 1, wherein, The compound represented by Formula 1 includes at least one selected from the group consisting of compounds represented by Formulas 1-1 to 1-9: [Equation 1-1] [Equation 1-2] [Equation 1-3] [Equations 1-4] [Equations 1-5] [Equations 1-6] [Equations 1-7] [Equations 1-8] [Equations 1-9] 6. The lithium secondary battery as described in claim 1, wherein, The content of fluoroethylene carbonate in the non-aqueous electrolyte is from 3% to 20% by volume.

7. The lithium secondary battery as described in claim 1, wherein, The content of 1,2-difluoroethylene carbonate in the non-aqueous electrolyte is from 10% to 35% by volume.

8. The lithium secondary battery as described in claim 1, wherein, Based on the weight of the non-aqueous electrolyte, the content of the compound represented by Formula 1 is from 0.1% to 10% by weight.

9. The lithium secondary battery as described in claim 1, wherein, The volume ratio of fluoroethylene carbonate to 1,2-difluoroethylene carbonate is 5:95 to 50:

50.

10. The lithium secondary battery as described in claim 1, wherein, Based on the total weight of the non-aqueous electrolytes, the total amount of fluoroethylene carbonate and 1,2-difluoroethylene carbonate is greater than 10% by weight and less than or equal to 50% by weight.

11. The lithium secondary battery as described in claim 1, wherein, The lithium salt includes at least one selected from the group consisting of: LiCl, LiBr, LiI, LiBF4, LiClO4, LiAlO4, LiAlCl4, LiPF6, LiSbF6, LiAsF6, LiB 10 Cl 10 , LiBOB(LiB(C2O4)2), LiCF3SO3, LiFSI(LiN(SO2F)2), LiCH3SO3, LiCF3CO2, LiCH3CO2 and LiBETI(LiN(SO2CF2CF3)2).

12. The lithium secondary battery as described in claim 1, wherein, After the lithium secondary battery is formed, a solid electrolyte interface film is formed on the negative electrode. The solid electrolyte interface membrane includes inorganic components, and The inorganic components include LiF and CO3. 2- , Wherein, the weight of LiF is related to the weight of CO3. 2- The weight ratio is 1.4 or higher.

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