Lithium secondary battery

Description

1 / 52 “SECONDARY LITHIUM BATTERY” TECHNICAL FIELD Cross-reference to related requests.

[001] This application claims priority over Korean Patent Application No. 102023-0126666, filed on September 21, 2023, the disclosure of which is incorporated by reference herein. Technical Field

[002] The present invention relates to a secondary lithium battery. BACKGROUND OF THE TECHNIQUE

[003] Recently, the demand for a secondary battery with high stability, high capacity and high efficiency is increasing, as the application area of ​​lithium secondary batteries is expanding rapidly, not only for electricity, electronics, communication and power supply for electronic devices such as computers, but also for energy storage supply for automobiles or large-area devices such as energy storage devices.

[004] A secondary lithium battery can be composed, in large part, of a positive electrode that is composed of a transition metal oxide containing lithium, a negative electrode capable of storing lithium, an electrolyte that becomes a medium for the transfer of lithium ions, and a separator. In this case, a negative electrode active material, such as a carbon-based active material and a silicon-based active material, can be included in the negative electrode.

[005] With regard to the secondary lithium battery, a film (solid electrolyte interface film (SEI)) is formed on the positive and / or negative electrode in an initial formation process, and the film can protect the positive and negative electrodes during battery operation and can prevent electrolyte consumption due to a side reaction of the electrolyte. If a robust electrode film is not formed Petition 870250086545, dated 09 / 24 / 2025, page 9 / 68 2 / 52 on the positive electrode and / or on the negative electrode during the initial formation process, problems may occur, such as capacity degradation and reduced lifespan.

[006] Specifically, silicon-based negative electrode active material among negative electrode active materials is attracting attention because it exhibits higher capacitance and higher energy density than carbon-based active material, but has the disadvantage of a large degree of volume change due to lithium intercalation and deintercalation. This volume expansion of the silicon-based active material causes many problems, such as reduced durability of the already formed SEI film, continuous electrolyte consumption due to the generation of a new surface of the negative electrode active material, and increased SEI film thickness, which causes capacitance degradation and reduced service life. DISCLOSURE OF THE INVENTION TECHNICAL PROBLEM

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

[008] [1] The present invention provides a lithium secondary battery including: 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 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, fluoroethylene carbonate, 1,2-difluoroethylene carbonate and a compound represented by Formula 1. [Formula 1] Petition 870250086545, dated 09 / 24 / 2025, p. 10 / 68 3 / 52

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

[010] [2] The present invention provides the lithium secondary battery of [1] above, wherein the silicon-based active material includes a silicon-based particle, and the silicon-based particle includes a compound represented by Formula A. [Formula A] SiOx

[011] In Formula A, 0 < x < 2.

[012] [3] The present invention provides a lithium secondary battery of at least one of [1] and [2] above, wherein the silicon-based particle is formed from silicon (Si).

[013] [4] The present invention provides a lithium secondary battery of at least one of [1] to [3] above, wherein the compound represented by Formula 1 includes at least one compound selected from the group consisting of a compound represented by Formula 1-A and a compound represented by Formula 1-B. [Formula 1-A] Petition 870250086545, dated 09 / 24 / 2025, p. 11 / 68 4 / 52 [Formula 1-B]

[014] In Formula 1-A and Formula 1-B, Ri is as defined in Formula 1.

[015] [5] The present invention provides a lithium secondary battery of at least one of [1] to [4] above, wherein the compound represented by Formula 1 includes at least one compound selected from the group consisting of the compounds represented by Formulas 1-1 to 1-9. [Formula 1-2] Petition 870250086545, dated 09 / 24 / 2025, p. 12 / 68 5 / 52 [Formula 1-4] [Formula 1-8] [Formula 1-9] Petition 870250086545, dated 09 / 24 / 2025, p. 13 / 68 6 / 52

[016] [6] The present invention provides a lithium secondary battery of at least one of [1] to [5] above, wherein fluoroethylene carbonate is included in the non-aqueous electrolyte in an amount of 3% by volume to 20% by volume.

[017] [7] The present invention provides a lithium secondary battery of at least one of [1] to [6] above, wherein 1,2-difluoroethylene carbonate is included in the non-aqueous electrolyte in an amount of 10% by volume to 35% by volume.

[018] [8] The present invention provides the lithium secondary battery of at least one of [1] to [7] above, wherein the compound represented by Formula 1 is included in an amount of 0.1% by weight to 10% by weight based on the weight of the non-aqueous electrolyte.

[019] [9] The present invention provides the lithium secondary battery of at least one of [1] to [8] above, wherein the volume ratio of fluoroethylene carbonate to 1,2-difluoroethylene carbonate is in a range of 5:95 to 50:50.

[020]

[10] The present invention provides a lithium secondary battery of at least one of [1] to [9] above, wherein 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 based on the total weight of the non-aqueous electrolyte.

[021]

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

[10] above, wherein the lithium salt includes at least one selected from the group consisting of LiCl, LiBr, LiI, LiBF4, LiCO4, LiAlO4, LiAlCk, LiPF6, LiSbF6, LiAsF6, LiB10Cl10, LiBOB (LiB(C2O4)2), UCF3SO3, LiFSI (LiN(SO2F)2), UCH3SO3, UCF3CO2, UCH3CO2 and LiBETI (LiN(SO2CF2CF3)2).

[022]

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

[11] above, wherein a solid electrolyte interface film is formed on the negative electrode after the formation of the lithium secondary battery, the solid electrolyte interface film includes an inorganic component and the component Petition 870250086545, dated 09 / 24 / 2025, page 14 / 68 7 / 52 inorganic includes LiF and CO32-, where the ratio between the weight of LiF and the weight of CO32- is 1.4 or more. ADVANTAGEOUS EFFECTS

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

[024] When 1,2-difluoroethylene carbonate is used alone and decomposes on its own, since the CO2 generation reaction is more dominant, an undesirable degradation of battery performance occurs. In relation to this, the present invention is characterized by the use of the compound represented by Formula 1 together with 1,2-difluoroethylene carbonate, wherein the compound represented by Formula 1, as a coumarin-based compound, is ring-opened during the reduction of the negative electrode to form a radical, and the radical formed in this case can form an inorganic SEI film, such as LiF, while being defluorinated during the reduction of the negative electrode of 1,2-difluoroethylene carbonate, it can form a propargyl (C^C) ​​group due to defluorination and can be ring-opened to form a polymer SEI film at the same time. The organic / inorganic composite film formed by the above components has significantly excellent chemical and electrochemical stability.

[025] When 1,2-difluoroethylene carbonate and the compound represented by Formula 1 are combined, since the above compounds react rapidly and are consumed in an initial process, such as initial formation, there is an effect of obtaining a flexible and highly durable solid electrolyte interface (SEI) film through an SEI film reaction during initial formation, but there is a disadvantage in terms of long-term durability. In this case, in Petition 870250086545, dated 09 / 24 / 2025, page 15 / 68 8 / 52 of the present invention, fluoroethylene carbonate, which has a low consumption rate and is continuously involved in the formation of the SEI film, is included in the non-aqueous electrolyte and, therefore, the long-term durability of the SEI film can be further improved when using a negative electrode including the silicon-based active material, in which a new negative electrode surface can be generated due to an extreme degree of volume expansion.

[026] As a result, since the secondary lithium battery according to the present invention forms and maintains the flexible and highly durable SEI film during battery operation, as well as in the initial process when using the negative electrode including the silicon-based active material, the secondary lithium battery according to the present invention can have excellent service life performance and storage performance, specifically, excellent high-temperature service life performance and high-temperature storage performance. METHOD OF IMPLEMENTING THE INVENTION

[027] It is understood that the words or terms used in the descriptive report and claims should not be interpreted as having the meaning defined in commonly used dictionaries, and it will be further understood that the words or terms should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and the technical idea of ​​the invention, based on the principle that an inventor can adequately define the meaning of words or terms to best explain the invention.

[028] It is further understood that the terms “including”, “comprising” or “having” in this descriptive report specify the presence of resources, numbers, steps, elements or combinations thereof, but do not exclude the presence or addition of one or more other resources, numbers, steps, elements or combinations thereof.

[029] Before describing the present invention, unless otherwise specified Petition 870250086545, dated 09 / 24 / 2025, p. 16 / 68 9 / 52 In another form in the present invention, the expression “*” denotes the same or different atom or a connected portion between the ends of a formula (bonding site).

[030] Furthermore, the expressions “a” and “b” in the description of “aab carbon atoms” in this descriptive report denote the number of carbon atoms included in a specific functional group. That is, the functional group may include “a” to “b” carbon atoms. For example, the expression “alkyl group with 1 to 5 carbon atoms” denotes an alkyl group including 1 to 5 carbon atoms, i.e., CH3, CH3CH2-, CH3CH2CH2-, (CH3)2CH-, CH3CH2CH2CH2-, (CH3)2CHCH2-, CH3CH2CH2CH2CH2- or (CH3ECHCH2CH2-.

[031] In addition, an alkyl group or an aryl group in this descriptive report may be substituted or not substituted.Unless otherwise defined, the term "substitution" indicates that at least one hydrogen atom bonded to carbon is replaced by an element other than hydrogen, for example, an alkyl group with 1 to 20 carbon atoms, an alkenyl group with 2 to 20 carbon atoms, an alkoxy group with 1 to 20 carbon atoms, a cycloalkyl group with 3 to 12 carbon atoms, a cycloalkenyl group with 3 to 12 carbon atoms, a cycloalkynyl group with 3 to 12 carbon atoms, a heterocycloalkyl group with 3 to 12 carbon atoms, a heterocycloalkenyl group with 3 to 12 carbon atoms, a heterocycloalkynyl group with 3 to 12 carbon atoms, an aryloxy group with 6 to 12 carbon atoms, a halogen atom, a fluoroalkyl group with 1 to 20 carbon atoms, a nitro group, an aryl group with 6 to 20 carbon atoms, a heteroaryl group with 2 to 20 carbon atoms, or a haloaryl group with 6 to 20 carbon atoms.

[032] The present invention is described in more detail below. Secondary Lithium Battery

[033] The present invention relates to a secondary lithium battery. Petition 870250086545, dated 09 / 24 / 2025, p. 17 / 68 10 / 52

[034] The lithium secondary battery according to the present invention is characterized by including: 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 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, fluoroethylene carbonate, 1,2-difluoroethylene carbonate and a compound represented by Formula 1 below.

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

[036] A secondary lithium battery includes a negative electrode, a positive electrode, a separator, and a non-aqueous electrolyte. Specifically, a secondary lithium battery includes a negative electrode; a positive electrode facing the negative electrode; a separator arranged between the negative and positive electrodes; and a non-aqueous electrolyte. A secondary lithium battery can be prepared by accommodating an electrode assembly, including the negative electrode, the positive electrode facing the negative electrode, and the separator arranged between the negative and positive electrodes. Petition 870250086545, dated 09 / 24 / 2025, page 18 / 68 11 / 52 negative and the positive electrode in a battery box and then injecting the non-aqueous electrolyte. (1) Negative Electrode

[037] The negative electrode includes a negative electrode active material.

[038] The active material of the negative electrode includes a silicon-based active material.

[039] Silicon-based active material has the advantage of having higher capacity and higher energy density than a carbon-based active material, such as graphite, but has the disadvantage of a large change in the volume of the active material during charging and discharging. This expansion and contraction of the volume of the silicon-based active material causes disconnection of the conductive connections in the negative electrode, causing an increase in resistance and degradation of service life performance.Furthermore, a solid electrolyte interface (SEI) film of the negative electrode, which was formed in a secondary lithium battery formation process, can be disrupted by changes in the volume of the silicon-based active material. This promotes a side reaction of the electrolyte, causing problems such as increased resistance due to increased SEI film thickness and electrolyte depletion. Consequently, performance in terms of lifespan and storage characteristics can be degraded.

[040] To solve these problems, the present invention is characterized by including fluoroethylene carbonate, 1,2-difluoroethylene carbonate, and the compound represented by Formula 1, which are described below, in the non-aqueous electrolyte. Through the combined use of 1,2-difluoroethylene carbonate and the compound of Formula 1, since a SEI film with high flexibility, recovery capacity, and durability can not only be formed during the initial formation, but fluoroethylene carbonate can also continuously carry out an SEI film formation reaction in a battery operation process, a film Petition 870250086545, dated 09 / 24 / 2025, page 19 / 68 12 / 52 SEI with significantly excellent flexibility, recovery capacity, and durability is consequently formed in the negative electrode, including the silicon-based active material, and therefore the high-temperature cycle performance and high-temperature storage performance of the lithium secondary battery can be significantly improved. In a case where carbon-based active material, such as graphite, and the non-aqueous electrolyte described above are used, since the corresponding components of the non-aqueous electrolyte can cause an unnecessary effect on battery performance, for example, the corresponding components act as resistance, it is difficult to obtain an effect in a negative electrode including only carbon-based active material.

[041] The silicon-based active material includes a silicon-based particle, and the silicon-based particle may include at least one selected compound represented by Formula A and a silicon-carbon composite. [Formula A] SiOx

[042] In Formula A, 0 < x < 2.

[043] In Formula A, compared to SiO2, which does not react with lithium ions and cannot store lithium, it is desirable that x be within the above range. Specifically, the silicon-based particle including the silicon-based active material may be formed of silicon (Si), or in Formula A, x may be 0. Furthermore, the silicon-based particle may include silicon oxide and, for example, in Formula A, x may satisfy 0.7 < x < 1.2 and, specifically, x = 1.

[044] The silicon-based active material may also include a metal doped into the silicon-based particle, in addition to the silicon-based particle. Furthermore, the silicon-based active material may include a metal present on a surface, in the interior, or both on the surface and in the interior of the silicon-based particle, in addition to the silicon-based particle. The metal may be at least one of the following metals: lithium Petition 870250086545, dated 09 / 24 / 2025, page 20 / 68 13 / 52 (Li), magnesium (Mg), calcium (Ca) and aluminum (Al), specifically at least one of the following metals: Li and Mg, and more specifically Mg.

[045] In a case where the metal is included in the silicon-based active material, it may be included in the silicon-based active material in an amount of 1% by weight to 30% by weight.

[046] The silicon-based active material may also include a carbon coating layer disposed on the surface of the silicon-based particle. The carbon coating layer may include amorphous carbon.

[047] In a case where the carbon coating layer is included in the silicon-based active material, the carbon coating layer may be included in the silicon-based active material in an amount of 0.5% by weight to 10% by weight and, specifically, from 1% by weight to 5% by weight.

[048] An average particle diameter (D50) of the silicon-based active material may be in a range of 1 μm to 30 μm and preferably 2 μm to 15 μm in order to ensure structural stability during charging and discharging and reduce side reaction with the electrolyte.

[049] The active material of the negative electrode may also include a carbon-based active material, in addition to the silicon-based active material.

[050] The carbon-based active material 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.

[051] An average particle diameter (D50) of the carbon-based active material may be in a range of 10 μm to 30 μm and preferably 15 μm to 25 μm in order to ensure structural stability during charging and discharging and reduce side reaction with the electrolyte. Petition 870250086545, dated 09 / 24 / 2025, p. 21 / 68 14 / 52

[052] In a case where the active material of the negative electrode includes silicon-based active material and carbon-based active material, the weight ratio of silicon-based active material to carbon-based active material may be in a range of 1:99 to 50:50, specifically 3:97 to 20:80 and, more specifically, 3:97 to 10:90.

[053] In some embodiments, the active material of the negative electrode may not include carbon-based active material.

[054] 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 included in the negative electrode active material layer.

[055] The negative electrode current collector is not specifically limited, provided it has high conductivity without causing chemical changes in the battery. Specifically, copper, stainless steel, aluminum, nickel, titanium, burnt carbon, copper or stainless steel with surface treatment with carbon, nickel, titanium, silver and the like, and an aluminum-cadmium alloy can be used as a negative electrode current collector.

[056] The current collector of the negative electrode can have a thickness of 3 μm to 500 μm.

[057] Microscopic irregularities can be formed on the surface of the negative electrode current collector to improve the adhesion of an active material to the negative electrode. The negative electrode current collector, for example, can be used in various forms such as film, sheet, blade, mesh, porous body, foam body, nonwoven fabric body and the like.

[058] The active material layer of the negative electrode is arranged on at least one surface of the negative electrode current collector. Specifically, Petition 870250086545, dated 09 / 24 / 2025, page 22 / 68 15 / 52 The active material layer of the negative electrode may be arranged on one surface or on both surfaces of the negative electrode current collector.

[059] The active material of the negative electrode may be included in an amount of 60% by weight to 99% by weight and, preferably, 75% by weight to 95% by weight in the active material layer of the negative electrode.

[060] The active material layer of the negative electrode may also include a binder and / or a conductive agent along with the active material of the negative electrode.

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

[062] The binder may be included in an amount of 0.5% by weight to 30% by weight, preferably 1% by weight to 15% by weight and, more preferably, 5% by weight to 10% by weight in the active material layer of the negative electrode.

[063] The conductive agent is not specifically limited, provided it has conductivity without causing chemical changes in the battery and, for example, a conductive material such as graphite, such as natural or artificial graphite; carbon black, such as acetylene black, Ketjen black, channel black, furnace black, lamp black and thermal black; conductive fibers such as carbon fibers or metallic fibers; tubes Petition 870250086545, dated 09 / 24 / 2025, page 23 / 68 16 / 52 conductors, such as carbon nanotubes; fluorocarbon; metal powder, such as aluminum powder and nickel powder; conductive whiskers, such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxide, such as titanium oxide; or polyphenylene derivatives.

[064] The conductive agent may be included in an amount of 0.5% by weight to 30% by weight and, preferably, 1% by weight to 25% by weight in the active material layer of the negative electrode.

[065] The active material layer of the negative electrode can have a thickness of 10 μm to 100 μm and, preferably, 50 μm to 80 μm.

[066] The negative electrode can be prepared by coating at least one surface of the negative electrode current collector with a negative electrode paste, including the negative electrode active material, the binder, the conductive agent and / or a solvent to form a negative electrode paste and then drying and laminating the coated negative electrode current collector.

[067] The solvent for forming a negative electrode paste, for example, may include at least one selected from the group consisting of distilled water, NMP (N-methyl-2-pyrrolidone), ethanol, methanol and isopropyl alcohol in terms of facilitating the dispersion of the negative electrode active material, the binder and / or the conductive agent, and may preferably include distilled water. (2) Positive Electrode

[068] The positive electrode faces the negative electrode.

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

[070] The current collector of the positive electrode is not specifically limited, provided it has high conductivity without causing chemical changes in the battery. Specifically, the current collector of the positive electrode may include at Petition 870250086545, dated 09 / 24 / 2025, page 24 / 68 17 / 52 less one element selected from the group consisting of copper, stainless steel, aluminum, nickel, titanium, burnt carbon and an aluminum-cadmium alloy, and may preferably include aluminum.

[071] The current collector of the positive electrode can have a thickness of 3 μm to 500 μm.

[072] Microscopic irregularities can be formed on the surface of the positive electrode current collector to improve the adhesion of an active material to the positive electrode. The positive electrode current collector, for example, can be used in various forms such as film, sheet, blade, mesh, porous body, foam body, nonwoven fabric body and the like.

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

[074] The active material layer of the positive electrode may include an active material of the positive electrode.

[075] The active material of the positive electrode is a compound capable of reversibly intercalating and deintercalating lithium, wherein the active material of the positive electrode may specifically include a lithium transition metal oxide composite, including lithium and at least one transition metal selected from the group consisting of nickel, cobalt, manganese and aluminum and, preferably, a lithium transition metal oxide composite, including lithium and a transition metal containing nickel, cobalt and manganese.

[076] For example, lithium transition metal oxide composites may include lithium-manganese based oxides (e.g., LiMnO2, LiMn2O4, etc.), lithium-cobalt based oxides (e.g., LiCoO2, etc.), lithium-nickel based oxides (e.g., LiNO2, etc.), lithium-nickel-manganese based oxides (e.g., LiNi Petition 870250086545, dated 09 / 24 / 2025, p. 25 / 68 18 / 52 γMnηγθ2 (where 0 < Y < 1), LiMn2-zNizO4 (where 0 < Z < 2) etc.), lithium-nickel-cobalt oxide (e.g., LiNi-yiCoyiO2 (where 0 < Y1 < 1), lithium-manganese-cobalt oxide (e.g., LiCo1-Y2MnY2O2 (where 0 < Y2 < 1), LiMn2ziCoziO4 (where 0 < Z1 < 2), etc.), lithium-nickel-manganese-cobalt oxide (e.g., Li(NipCoqMnr1)O2 (where 0 < p < 1, 0 < q < 1, 0 < r1 < 1, ep + q + r1 = 1) or Li(Nip1Coq1Mnr2)O4 (where 0 < p1 < 2, 0 < q1 < 2, 0 < r2 < 2, and p1 + q1 + r2 = 2), etc.), or lithium-nickel-cobalt transition metal oxide (M) (e.g., Li(Nip2Coq2Mnr3MS2)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 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 any one of them, or a mixture of two or more of them, may be included. Among these materials, in terms of improving battery capacity and stability characteristics, lithium transition metal oxide composites can be LiCoO2, LiMnO2, LiNiO2, lithium-nickel-manganese-cobalt oxide (e.g., Li(Ni0.6Mn0.2Co0.2)O2, Li(Ni0.5Mn0.3Co0.2)O2, Li(Ni0.7Mn0.15Co0.15)O2 or Li(Ni0.8Mn0.1Co0.1)O2, etc.), or lithium-nickel-cobalta-aluminum oxide (e.g., Li(Ni0.8Co0.15Al0.05)O2, etc.), and, considering a significant improvement effect due to the control of the types and content proportions of the components that constitute the lithium transition metal oxide composite, the lithium transition metal oxide composite can be... Li(Ni0.6Mn0.2Co0.2)O2, Li(Ni0.5Mn0.3Co0.2)O2, Li(Ni0.7Mn0.15Co0.15)O2 or Li(Ni0.8Mn0.1Co0.1)O2, and any one of these or a mixture of two or more of them may be used.

[077] More specifically, as the active material of the positive electrode, a lithium transition metal oxide composite, it may include 60 mol% or more of nickel based on the total number of moles of transition metals included in the lithium transition metal oxide composite. Specifically, the active material Petition 870250086545, dated 09 / 24 / 2025, page 26 / 68 19 / 52 of the positive electrode is a lithium transition metal oxide composite, wherein the transition metal includes nickel; and at least one selected from manganese, cobalt, and aluminum, and the active material of the positive electrode may include nickel in an amount of 60 mol% or more and, specifically, 60 mol% to 90 mol% based on the total number of moles of transition metals. When the lithium transition metal oxide composite using a high nickel content is used together with the non-aqueous electrolyte described above, it is desirable in terms of reducing a gas-phase byproduct generated by structural collapse.

[078] In addition, the active material of the positive electrode may include a lithium composite transition metal oxide represented by Formula B below. [Formula B] Li1+x(NiaCobMncMd)O2

[079] In Formula B, M is at least one of the following elements: 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 c 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.

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

[081] Furthermore, a, b, c and d can satisfy 0.80 < a < 0.95, 0.025 < b < 0.15, 0.025 < c < 0.15 and 0 < d < 0.05, respectively.

[082] Furthermore, a, b, c and d can satisfy 0.85 < a < 0.90, 0.05 < b < 0.10, 0.05 < c < 0.10 and 0 < d < 0.03, respectively.

[083] The active material of the positive electrode may be included in an amount of 80% by weight to 99% by weight and, preferably, 92% by weight Petition 870250086545, dated 09 / 24 / 2025, page 27 / 68 20 / 52 to 98.5% by weight in the active material layer of the positive electrode, considering the display of sufficient capacity of the active material of the positive electrode.

[084] The active material layer of the positive electrode may also include a binder and / or a conductive agent along with the active material of the positive electrode described above.

[085] The binder is a component that assists in the bonding between the conductive agent and the active material and in the bonding with the current collector, and may specifically include at least one component selected from the group consisting of polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC) starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, an ethylene-propylene-diene terpolymer (EPDM), a sulfonated EPDM, a styrene-butadiene rubber and a fluorinated rubber and, preferably, polyvinylidene fluoride.

[086] The binder may be included in an amount of 1% to 20% by weight and, preferably, 1.2% by weight to 10% by weight in the active material layer of the positive electrode to ensure sufficient bonding strength between the components, such as the active material of the positive electrode.

[087] The conductive agent may be used to assist and improve conductivity in the secondary battery, and is not specifically limited, provided it has conductivity without causing chemical changes. Specifically, the conductive agent 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 thermal black; conductive fibers, such as carbon fibers or metallic fibers; conductive tubes, such as carbon nanotubes; fluorocarbon; metallic powder, such as aluminum powder and nickel powder; conductive whiskers, such as zinc oxide whiskers and potassium titanate whiskers; conductive metallic oxide, such as titanium oxide; and derivatives of Petition 870250086545, dated 09 / 24 / 2025, p. 28 / 68 21 / 52 polyphenylene, preferably including carbon black to improve conductivity.

[088] The conductive agent may be included in an amount of 1% by weight to 20% by weight and, preferably, 1.2% by weight to 10% by weight in the active material layer of the positive electrode, in order to sufficiently guarantee electrical conductivity.

[089] The active material layer of the positive electrode can have a thickness of 30 μm to 400 μm and, preferably, 40 μm to 110 μm.

[090] The positive electrode can be prepared by coating a positive electrode paste, including the active material of the positive electrode, as well as optionally the binder, the conducting agent and a solvent to form the positive electrode paste on the current collector of the positive electrode and then drying and laminating the coated current collector of the positive electrode.

[091] The solvent for forming the positive electrode paste may include an organic solvent, such as NMP (N-methyl-2-pyrrolidone). The solid content of the positive electrode paste may be in a range of 40% by weight to 90% by weight and, specifically, 50% by weight to 80% by weight. (3) Separator

[092] The separator can be placed between the positive electrode and the negative electrode.

[093] In addition, a conventional porous polymer film normally used as a separator, for example, a porous polymer film prepared from a polyolefin-based polymer, such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer and an ethylene / methacrylate copolymer, can be used alone or in a lamination with it as a separator, and a typical porous nonwoven fabric, for example, a nonwoven fabric formed from high-melting-point glass fibers or Petition 870250086545, dated 09 / 24 / 2025, page 29 / 68 22 / 52 polyethylene terephthalate fibers can be used, but the present invention is not limited to this. Furthermore, a coated separator, including a ceramic component or a polymeric material, can be used to ensure heat resistance or mechanical strength, and the separator with a single-layer or multi-layer structure can optionally be used. (4) Non-Aqueous Electrolyte

[094] The non-aqueous electrolyte according to the present invention includes a lithium salt, fluoroethylene carbonate, 1,2-difluoroethylene carbonate and the compound represented by Formula 1 to be described later. In some cases, the non-aqueous electrolyte may also include an organic solvent and an additive. 1) Lithium Salt

[095] Various lithium salts commonly used in a non-aqueous electrolyte for a secondary lithium battery can be used as the lithium salt used in the present invention, without limitation. For example, lithium salt may include Li+ as a cation, and may include at least one selected from the group consisting of F-, Cl-, Br, I-, NO3-, N(CN)2-, BF4-, ClO4-, AlO4-, AlCl4-, PF6-, SbF6-, AsF6-, B10Cl10-, BF2C2O4-, BC4O8-, PF4C2O4-, PF2C4O8-, (CF3)2PF4-, (CF3)3PF3-, (CF3)4PF2-, (CF^PF-, (CF3)6P-, CF3SO3-, C4F9SO3-, CF3CF2SO3-, (FSO2)2N-, CF3CF2(CF3)2CO-, (CF3SO2ECH-, CH3SO3-, CF3(CF2)7SO3-, CF3CO2-, CH3CO2-, SCN- and (CF3CF2SO2EN- as an anion.

[096] Specifically, the lithium salt may include at least one selected from the group consisting of LiCl, LiBr, LiI, LiBF4, LiClO4, LiAlO4, LiAlCl4, LiPF6, LiSbF6, LiAsF6, LiBioCIio, LiBOB (LiB(C2O4)2), UCF3SO3, LiFSI (LiN(SO2F)2), UCH3SO3, UCF3CO2, UCH3CO2 and LiBETI (LiN(SO2CF2CF3)2). Specifically, the lithium salt may include at least one selected from the group consisting of LiBF4, LiCIO4, LiPF6, LiBOB (LiB(C2O4)2), UCF3SO3, LiTFSI (LiN(SO2CF3)2), LiFSI (LiN(SO2F)2) and LiBETI (LiN(SO2CF2CF3)2).

[097] Lithium salt can be included in a concentration of 0.5 M to 5 M, Petition 870250086545, dated 09 / 24 / 2025, page 30 / 68 23 / 52 specifically from 0.8 M to 4 M and more specifically from 0.8 M to 2.0 M in the non-aqueous electrolyte. When the lithium salt concentration meets the above range, the battery output characteristics can be improved, enhancing the lithium-ion yield (Li+ transfer number) and the degree of lithium-ion dissociation.

[098] In addition, the lithium salt may be included in the non-aqueous electrolyte as a remainder, excluding the components of the non-aqueous electrolyte, for example, the compound represented by Formula 1, a compound represented by Formula 2 and, optionally, an organic solvent and an additive. 2) Fluoroethylene Carbonate

[099] Fluoroethylene carbonate (FEC) can be decomposed in the battery operation process to provide a composite component of an organic component and an inorganic component, such as LiF, for the SEI film. The SEI film derived from fluoroethylene carbonate has excellent long-term durability. Specifically, a product by combining 1,2-difluoroethylene carbonate and the compound of Formula 1 to be described later and a reaction thereof exhibits an excellent effect in a process such as initial formation, but it is difficult to exhibit an additional effect during long-term battery operation. In this case, fluoroethylene carbonate can improve the long-term durability of the SEI film by continuously providing an SEI film component when a new negative electrode surface is generated and the SEI film is broken down due to the volume expansion of the silicon-based active material during battery charging and discharging.Since fluoroethylene carbonate has a lower number of fluorines than 1,2-difluoroethylene carbonate and contributes little to an overall increase in the LiF content of the SEI film, it is difficult to achieve the desired effect using only fluoroethylene carbonate.

[0100] Fluoroethylene carbonate may mean carbonate of Petition 870250086545, dated 09 / 24 / 2025, page 31 / 68 24 / 52 monofluoroethylene.

[0101] Fluoroethylene carbonate can be included in the non-aqueous electrolyte in an amount of 3% by vol to 20% by vol, especially 5% by vol to 15% by vol and more specifically 7% by vol to 12% by vol. When the amount is within the above range, it is possible to obtain an adequate level of SEI film formation on the negative electrode, including the silicon-based active material, and an increase in resistance, which is a concern when an excessive amount is added, can be avoided.

[0102] In addition, fluoroethylene carbonate may be included in the non-aqueous electrolyte in an amount of 3% by weight to 20% by weight, especially 5% by weight to 15% by weight and more specifically 7% by weight to 12% by weight. 3) 1,2-Difluoroethylene Carbonate

[0103] 1,2-Difluoroethylene carbonate is a compound containing two fluorine atoms in its molecular structure, where an increase in the amount of an inorganic component, such as LiF, can be expected, which contributes to improving the durability of the SEI film. Furthermore, a carbon-carbon triple bond or a propargyl (C^C) ​​group is formed by the defluorination of 1,2-difluoroethylene carbonate, and this component can be expected to form a polymer-type SEI film during the ring-opening of the chemical structure. However, 1,2-Difluoroethylene carbonate has a problem, as it is difficult to form an SEI film with the desired organic / inorganic composite component because CO2 generation and the formation of a single-molecule structure are dominant, rather than ring-opening in a polymer form during its own decomposition reaction.

[0104] To solve these problems, since the present invention uses the compound represented by Formula 1, to be described later, Petition 870250086545, dated 09 / 24 / 2025, p. 32 / 68 25 / 52 together with 1,2-difluoroethylene carbonate, and the compound represented by Formula 1 forms a radical during the reduction of the negative electrode, a ring-opening reaction of 1,2-difluoroethylene carbonate can be promoted to induce the formation of a SEI film with the organic / inorganic composite component and, simultaneously, improve flexibility, recovery capacity, and durability. That is, it can be understood that the formation of the SEI film derived from 1,2-difluoroethylene carbonate can be obtained preferentially only when the compound represented by Formula 1 is used in combination. In other words, the SEI film derived from 1,2-difluoroethylene carbonate by a radical reaction caused by the compound represented by Formula 1 has the organic / inorganic composite component and, therefore, the flexibility, recovery capacity, and durability of the SEI film can be improved simultaneously.This is very suitable for use in silicon-based active material, where a degree of volume expansion / contraction is severe during the initial formation process and battery operation.

[0105] 1,2-Difluoroethylene carbonate may be included in the non-aqueous electrolyte in an amount of 10 % by vol to 35 % by vol, especially 15 % by vol to 30 % by vol and more specifically 17 % by vol to 22 % by vol.

[0106] 1,2-Difluoroethylene carbonate may be included in the non-aqueous electrolyte in an amount of 10% by weight to 35% by weight, especially 15% by weight to 32% by weight and more specifically 18% by weight to 25% by weight.

[0107] The volume ratio of fluoroethylene carbonate to 1,2-difluoroethylene carbonate may be in a range of 5:95 to 50:50, especially 25:75 to 40:60 and more specifically 28:72 to 35:65.

[0108] The weight ratio of fluoroethylene carbonate to 1,2-difluoroethylene carbonate may be in the range of 5:95 to 50:50, especially of Petition 870250086545, dated 09 / 24 / 2025, page 33 / 68 26 / 52 15:85 to 45:55 and more specifically from 30:70 to 35:65.

[0109] The total amount of fluoroethylene carbonate and 1,2-difluoroethylene carbonate may be greater than 10% by weight and less than or equal to 50% by weight, specifically from 15% by weight to 45% by weight, more specifically from 25% by weight to 42% by weight, and even more specifically from 30% by weight to 35% by weight based on the total weight of the non-aqueous electrolyte. When the total amount is within the above range, the effects described above of fluoroethylene carbonate and 1,2-difluoroethylene carbonate may be harmoniously enhanced and achieved. 4) The Compound Represented by Formula 1

[0110] The non-aqueous electrolyte of the present invention includes the compound shown by Formula 1 below.

[0111] In Formula 1, Ri includes a halogen, a nitrile group, a propargyl group, an ester group, an ether group, a ketone group, a carboxyl group, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted alkynyl group, a substituted or unsubstituted alkoxy group, a boron group, a borate group, an isocyanate group, an isothiocyanate group, a silyl group, a siloxane group, a sulfone group, a sulfonate group, a sulfate group, or a combination of two or more of them, and en is an integer from 0 to 6.

[0112] The compound represented by Formula 1 has excellent negative electrode reducing power and can form a radical during electrode reduction. Petition 870250086545, dated 09 / 24 / 2025, p. 34 / 68 27 / 52 negative. Since the radical formed can promote the ring-opening reaction of 1,2-difluoroethylene carbonate, as described above, a SEI film with high flexibility, recovery capacity, and durability can be obtained in the initial formation process.

[0113] Furthermore, the compound represented by Formula 1 can be ring-opened during initial formation to form a polyethylene oxide-based polymer-type film on the electrode, and this polymer-type film has excellent flexibility and recovery capability.

[0114] In Formula 1, Ri can specifically be a halogen (the halogen can be selected from fluorine (F), chlorine (Cl), bromine (Br), and iodine (I), and can specifically be F), a nitrile group, a propargyl group, an ester group, an ether group, or a combination of two or more of these. Because these substituents can increase the reducing power of a first additive, the effects of smooth SEI film formation and improved lithium ion transfer performance can also be achieved.

[0115] In Formula 1, n can be any integer selected from 0 to 6, and can specifically be any integer selected from 1 to 6, and more specifically, n can be 1. In Formula 1, when n is 2 or more, each Ri can be the same or different from the others.

[0116] Specifically, the compound represented by Formula 1 may include at least one selected from the group consisting of a compound represented by Formula 1-A below and a compound represented by Formula 1-B below. [Formula 1-A] Petition 870250086545, dated 09 / 24 / 2025, p. 35 / 68 28 / 52 [Formula 1-B]

[0117] In Formula 1-A and Formula 1-B, Ri is as defined in Formula 1.

[0118] The compounds represented by Formulas 1-A and 1-B have structures in which the substituents exist in positions 3 and 7 (based on IUPAC nomenclature) of a ring structure, respectively, which, in this case, is desirable in terms of the fact that it is advantageous to synthesize in the positions described above compared to other substitution positions.

[0119] Specifically, the compound represented by Formula 1 may include at least one compound selected from the group consisting of the compounds represented by Formula 1-1 to Formula 1-9 below. The compound represented by Formula 1 may specifically include at least one selected from the group consisting of the compounds represented by Formula 1-1, Formula 1-2, Formula 1-3, Formula 1-4 and Formula 1-9, in terms of the fact that it is more advantageous to form an SEI film by being more smoothly reduced at the negative electrode, may more specifically include at least one selected from the group consisting of the compounds represented by Formula 1-1 and Formula 1-2 below, and may more specifically include the compound represented by Formula 1-1 below. [Formula 1-1] [Formula 1-2] Petition 870250086545, dated 09 / 24 / 2025, page 36 / 68 29 / 52 Petition 870250086545, dated 09 / 24 / 2025, pp. 37 / 68 30 / 52 [Formula 1-8]

[0120] The compound represented by Formula 1 can be included in the non-aqueous electrolyte in an amount of 0.1% by weight to 10% by weight, specifically from 1% by weight to 7% by weight and more specifically from 3.5% by weight to 6% by weight. When the amount of the compound represented by Formula 1 is within the range described above, the ring-opening reaction of 1,2-difluoroethylene carbonate can be sufficiently caused, and the concern about an increase in resistance when an excessive amount is added can be avoided.

[0121] The ratio of one weight of the compound represented by Formula 1 to one weight of 1,2-difluoroethylene carbonate may be in a range of 0.2 to 1, specifically from 0.25 to 0.95 and more specifically from 0.4 to 0.7. When the ratio is within the above range, the ring-opening reaction of 1,2-difluoroethylene carbonate may be sufficiently caused when the amount of the compound represented by Formula 1 is within the range described above, and an organic / inorganic composite SEI film according to the corresponding configuration combination may be formed to a sufficient degree.

[0122] The ratio between the weight of the compound represented by Formula 1 and the weight of fluoroethylene carbonate may be in the range of 0.1 to 0.5, and may specifically be in the range of 0.15 to 0.45. Furthermore, the ratio between the weight of the compound represented by Formula 1 and the total weight of fluoroethylene carbonate and 1,2-difluoroethylene carbonate may be in the range of 0.1 to 0.3 and, Petition 870250086545, dated 09 / 24 / 2025, pp. 38 / 68 Specifically, the 31 / 52 ratio can be in the range of 0.12 to 0.20. When the ratio is within the above range, it is good that the initial and long-term performance of the secondary lithium battery and the negative electrode using silicon-based active material can be improved to an excellent level. 5) Organic Solvent

[0123] The non-aqueous electrolyte may also include an organic solvent along with the components described above.

[0124] As an organic solvent, any non-aqueous solvent commonly used in a secondary lithium battery is not specifically limited, provided that decomposition due to an oxidation reaction during charging and discharging of the secondary lithium battery can be minimized.

[0125] The organic solvent may be included in the non-aqueous electrolyte in a volume percentage (% vol) of a remaining amount, excluding fluoroethylene carbonate and 1,2-difluoroethylene carbonate.

[0126] Specifically, the organic solvent may include at least one of those selected from the group consisting of a cyclic carbonate-based organic solvent, a linear carbonate-based organic solvent, a linear ester-based organic solvent, and a cyclic ester-based organic solvent.

[0127] Specifically, the organic solvent may include at least one cyclic carbonate-based organic solvent and one linear carbonate-based organic solvent. In addition, the organic solvent may include a linear carbonate-based organic solvent, in that the fluoroethylene carbonate and 1,2-difluoroethylene carbonate described above replace the cyclic carbonate organic solvent.

[0128] The cyclic carbonate-based organic solvent is an organic solvent that can dissociate the lithium salt in the electrolyte due to its high permittivity as a highly viscous organic solvent, wherein the cyclic carbonate-based organic solvent Petition 870250086545, dated 09 / 24 / 2025, pp. 39 / 68 32 / 52 Cyclic carbonate may specifically 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-pentylene carbonate, 2,3-pentylene carbonate, and vinylene carbonate, including more specifically ethylene carbonate (EC). Furthermore, the cyclic carbonate-based organic solvent or ethylene carbonate may not be included in the non-aqueous electrolyte of the present invention.

[0129] Furthermore, linear carbonate-based organic solvent is a low-viscosity, low-permittivity organic solvent, wherein linear carbonate-based organic solvent may specifically include at least one of those selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethylmethyl carbonate (EMC), methylpropyl carbonate and ethylpropyl carbonate, may more specifically include at least one selected from the group consisting of ethylmethyl carbonate (EMC) and diethyl carbonate (DEC), may more specifically include ethylmethyl carbonate (EMC) and diethyl carbonate (DEC), and may further specifically include ethylmethyl carbonate (EMC) and diethyl carbonate (DEC) in a volume ratio of 50:50 to 99:1, specifically 60:40 to 90:10, more specifically 60:40 to 75:25, and up to more specifically from 62:38 to 66:34.

[0130] In a case where the organic solvent includes the linear carbonate-based solvent, the ratio of a total volume of fluoroethylene carbonate and 1,2-difluoroethylene carbonate to a volume of linear carbonate-based solvent may be in a range of 10:90 to 50:50 and, specifically, 20:80 to 45:55.

[0131] The linear ester-based organic solvent 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. Petition 870250086545, dated 09 / 24 / 2025, page 40 / 68 33 / 52

[0132] In addition, the cyclic ester-based organic solvent may specifically include at least one selected from the group consisting of γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone and ε-caprolactone.

[0133] The organic solvent may be used by adding an organic solvent normally used in a non-aqueous electrolyte, without limitation, if necessary. For example, the organic solvent may further include at least one organic solvent selected from an ether-based organic solvent, a glucose-based solvent, and a nitrile-based organic solvent.

[0134] As an ether-based solvent, any solvent selected from the group consisting of dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methylpropyl ether, ethylpropyl ether, 1,3-dioxolane (DOL) and 2,2bis(trifluoromethyl)-1,3-dioxolane (TFDOL) or a mixture of two or more of these may be used, but the ether-based solvent is not limited to this.

[0135] A glime-based solvent is a solvent that has higher permittivity and lower surface tension than a linear carbonate-based organic solvent, as well as lower reactivity with metal, wherein the glime-based solvent may include at least one solvent selected from the group consisting of dimethoxyethane (glime, DME), dietoxyethane, diglime, tri-glime (triglime) and tetra-glime (TEGDME), but is not limited to these.

[0136] The nitrile-based solvent may be at least one selected from the group consisting of, but not limited to, acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylontrile, heptanenitrile, cyclopentane carbonitrile, cyclohexane carbonitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile and 4-fluorophenylacetonitrile. 6) Additive

[0137] The non-aqueous electrolyte may also include an additive along with the Petition 870250086545, dated 09 / 24 / 2025, page 41 / 68 34 / 52 components described above.

[0138] Specifically, the additive may be at least one selected from the group consisting of vinylene carbonate, vinylethylene carbonate, fluoroethylene carbonate, propane sultone, propene sultone, succinonitrile, adiponitrile, ethylene sulfate, LiODFB (lithium difluorooxalatoborate), LiBOB (lithium bis-(oxalato)borate), TMSPa (tris(trimethylsilyl) phosphate) and TMSPi (tris(trimethylsilyl) phosphite).

[0139] The additive may be included in the non-aqueous electrolyte in an amount of 0.1% by weight to 15% by weight, but the present invention is not limited to this.

[0140] In the lithium secondary battery of the present invention, a solid electrolyte interface film is formed on the negative electrode after the formation of the lithium secondary battery, the solid electrolyte interface film includes an inorganic component, and the inorganic component includes LiF and CO32-, wherein the ratio between the weight of LiF and the weight of CO32- may be 1.4 or more.

[0141] The components of the non-aqueous electrolyte (e.g., fluoroethylene carbonate, 1,2-difluoroethylene carbonate, the compound represented by Formula 1, etc.) can be decomposed by the formation process to form a solid electrolyte interface film (SEI film).

[0142] A method known in the art can be used as a forming process without limitation, and the forming process is not specifically limited. For example, the forming process can be carried out by charging at a rate C of 0.1 C to 1 C at room temperature (20 ± 5 °C) to a state of charge (SOC) of 10% or more, specifically to a SOC of 60% or more, and more specifically to a SOC of 100%. Furthermore, the forming process can be carried out under the above C rate and SOC conditions at a temperature of 45 °C to 60 °C and a pressure of 0.5 kgf / cm² to 20 kgf / cm².

[0143] The inorganic component of the solid electrolyte interface film and an amount thereof can be measured by a method that includes the following Petition 870250086545, dated 09 / 24 / 2025, page 42 / 68 35 / 52 steps. (a) separate a negative electrode by disassembling the secondary lithium battery subject to formation; (b) wash the negative electrode separately; (c) extract a solid electrolyte interface film on a negative electrode surface by immersing the washed negative electrode in an extraction solvent; and (d) analyze an inorganic component in the extraction solvent using capillary electrophoresis.

[0144] Separation of the negative electrode can be carried out in an inert gas atmosphere.

[0145] Washing the separate negative electrode serves to prevent interference from non-aqueous components of the electrolyte. Washing can be performed by immersing the negative electrode in a washing solvent.

[0146] The washing solvent may include at least one organic solvent selected from the group consisting of a cyclic ether-based solvent, an ester-based organic solvent, or a nitrile-based organic solvent. For example, in a case where a propionate-based organic solvent is used as the organic solvent for the non-aqueous electrolyte, a carbonate-based organic solvent may be used as the washing solvent, or in a case where a linear carbonate-based organic solvent is used as the organic solvent for the non-aqueous electrolyte, a propionate-based organic solvent may be used as the washing solvent.

[0147] In washing, the washing solvent used and the washing time may vary depending on the size of the negative electrode, where washing may specifically be performed by immersing the electrode in 10 mL to 50 mL of washing solvent for 15 minutes to 1 hour based on a negative electrode area of Petition 870250086545, dated 09 / 24 / 2025, page 43 / 68 36 / 52 cm2a 35 cm2.

[0148] After washing, an additional electrode drying step in an inert gas atmosphere to remove the washing solvent used may be performed. Drying may be carried out at room temperature (20 ± 5 °C) for approximately 5 minutes to 2 hours, depending on the electrode conditions.

[0149] The extraction solvent may be a highly polar solvent, including 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.

[0150] The extraction of the solid electrolyte interface film can be suitably altered according to experimental conditions, such as electrode size, battery cycle and storage conditions during extraction, wherein extraction can be performed specifically by immersing the electrode in 1 mL to 5 mL of extraction solvent at room temperature (25 ± 5 °C) for 12 hours to 48 hours, based on the negative electrode area of ​​15 cm2 to 35 cm2.

[0151] There is a case where the metallic components of the partially degraded electrode are dissolved and are present in the extraction solvent during extraction. In this case, as it is difficult to perform a clear analysis in a subsequent process, a filtration step to remove these impurities may be included.

[0152] Filtration can appropriately use a method such as centrifugation or filtration, depending on the quantities of by-products.

[0153] After that, the analysis of the inorganic component in the extraction solvent obtained after filtration can be performed using capillary electrophoresis.

[0154] In this descriptive report, “capillary electrophoresis” refers to a method of measuring the structure and quantity of a component using a phenomenon Petition 870250086545, dated 09 / 24 / 2025, page 44 / 68 37 / 52 chemical in which charges in a solution move toward an electrode of opposite charge under an electric field between electrodes, wherein the structure or quantity of the component (type) does not change depending on specific devices and conditions. In the present invention, the measurement can be performed using an AB SCIEX MDQ plus device (Capillary: 75 μm ID, 50 cm; Injection: 0.5 psi, 3 s; Separation: 20 kV, 0.1 psi; Detector: 230 nm UV) using an SCIEX anion analysis kit (pH 5.5) as a running buffer.

[0155] In addition to the above description, measurement of the solid electrolyte interface film component may refer to Korean Patent Application Publication No. 10-2020-0005870.

[0156] With regard to the lithium secondary battery according to the present invention, the ratio between the weight of LiF and the weight of CO32- may be in a range of 1.4 or more, specifically from 1.4 to 3.0, more specifically from 1.5 to 2.7, and even more specifically from 2.0 to 2.6. When the ratio is within the above range, it can be assessed that a composite film of the inorganic component and the organic component of the SEI film on the negative electrode is adequately formed to a sufficient degree and, specifically, the overall performance of the battery, including the silicon-based negative electrode, can be significantly improved.

[0157] The weight of LiF per area of ​​the solid electrolyte interface film can be 100 μg / cm2 or more, specifically from 100 μg / cm2 to 250 μg / cm2 and more specifically from 190 μg / cm2 to 240 μg / cm2

[0158] The weight of CO32- per area of ​​the solid electrolyte interface film can be 60 μg / cm2 or more, specifically from 75 μg / cm2 to 100 μg / cm2 and more specifically from 77 μg / cm2 to 82 μg / cm2

[0159] The shape of the secondary lithium battery of the present invention is not specifically limited, but a cylindrical type using a can, a prismatic type, a pouch type or a coin type may be used. Petition 870250086545, dated 09 / 24 / 2025, pp. 45 / 68 38 / 52

[0160] The present invention is described in detail herein, according to specific examples. However, the following examples are presented only to illustrate the present invention, and the scope of the present invention is not limited to them. It is evident to those skilled in the art that various modifications and alterations are possible within the scope and technical spirit of the present invention. Such modifications and alterations fall within the scope of the claims included in this document. Examples and Comparative Examples Example 1 (Preparation of Non-Aqueous Electrolyte)

[0161] An organic solvent was prepared by mixing fluoroethylene carbonate, 1,2-difluoroethylene carbonate, diethyl carbonate and ethylmethyl carbonate in a volume ratio of 5:20:45:30.

[0162] A non-aqueous electrolyte was prepared by adding LiPFs, as a lithium salt, and the compound represented by Formula 1-1 to the organic solvent above.

[0163] Lithium salt was added to the non-aqueous electrolyte at a molar concentration of 1.5 M.

[0164] The compound represented by Formula 1-1 was added in an amount of 5% by weight to the non-aqueous electrolyte.

[0165] In the non-aqueous electrolyte, the weight percentage of fluoroethylene carbonate was 5.5% by weight, and the weight percentage of 1,2-difluoroethylene carbonate was 22.2% by weight. (Preparation of the Secondary Lithium Battery)

[0166] A positive electrode active material (LiNi0.85Co0.05Mn0.07Al0.03O2): a conducting agent (carbon nanotubes): a binder (polyvinylidene fluoride) were added in a weight ratio of 97.74:0.70:1.56 to N-methyl-2-pyrrolidone (NMP), as solvent, to prepare a paste of mixed materials. Petition 870250086545, dated 09 / 24 / 2025, pp. 46 / 68 39 / 52 positive electrode (75.5% by weight solid content). A 15 μm thick positive electrode current collector surface (thin Al film) was coated with the positive electrode material mixture paste, dried, and then rolled to prepare a positive electrode.

[0167] A negative electrode active material (Si): a conductive agent (carbon black): a binder (styrene-butadiene rubber) were added to distilled water as solvent in a weight ratio of 70.0:20.3:9.7 to prepare a negative electrode material mixture paste (26% by weight solid content). A 15 μm thick negative electrode current collector surface (thin Cu film) was coated with the negative electrode material mixture paste, dried, and then rolled to prepare a negative electrode.

[0168] After a porous polyethylene film separator was placed between the positive and negative electrodes prepared above in a dry room, the non-aqueous electrolyte prepared above was injected to prepare a secondary lithium battery. (Analysis of Solid Electrolyte Interface Film Components)

[0169] The lithium secondary battery prepared above was subjected to formation by charging it at a C rate of 0.33 C to a SOC of 100% at room temperature (20 ± 5 °C).

[0170] Each of the secondary lithium batteries subjected to formation was disassembled in an inert gas atmosphere to obtain a negative electrode (area: 65 cm2), and the negative electrode was washed by immersing it in 30 mL of a dimethyl carbonate (DMC) washing solvent for 30 minutes.

[0171] Next, the extraction was performed by immersing the washed electrode in 10 ml of deuterium oxide (D2O) for 24 hours at room temperature (25 ± 5 °C).

[0172] Subsequently, after extraction, the extraction solvent was filtered Petition 870250086545, dated 09 / 24 / 2025, pp. 47 / 68 40 / 52 using a filter, and the qualitative and quantitative analysis of the inorganic components in the extraction solvent was performed using capillary electrophoresis. Among them, the results of the LiF and CO32- content analysis are presented in Table 1 below.

[0173] Capillary electrophoresis was performed using an AB SCIEX MDQ plus device (Capillary: 75 μm ID, 50 cm; Injection: 0.5 psi, 3 s; Separation: 20 kV, 0.1 psi; Detector: 230 nm UV) using an SCIEX anion analysis kit (pH 5.5) as running buffer. Example 2 (Preparation of Non-Aqueous Electrolyte)

[0174] An organic solvent was prepared by mixing fluoroethylene carbonate, 1,2-difluoroethylene carbonate, diethyl carbonate and ethylmethyl carbonate in a volume ratio of 15:20:45:20.

[0175] A non-aqueous electrolyte was prepared by adding LiPF6, as a lithium salt, and the compound represented by Formula 1-1 to the organic solvent above.

[0176] Lithium salt was added to the non-aqueous electrolyte at a molar concentration of 1.5 M.

[0177] The compound represented by Formula 1-1 was added in an amount of 5% by weight to the non-aqueous electrolyte.

[0178] In the non-aqueous electrolyte, the weight percentage of fluoroethylene carbonate was 15.9% by weight, and the weight percentage of 1,2-difluoroethylene carbonate was 21.4% by weight. (Preparation of the Secondary Lithium Battery)

[0179] A secondary lithium battery was prepared in the same way as in Example 1, except that the non-aqueous electrolyte prepared above was used. Example 3 (Preparation of Non-Aqueous Electrolyte)

[0180] An organic solvent was prepared by mixing carbonate of Petition 870250086545, dated 09 / 24 / 2025, pp. 48 / 68 41 / 52 fluoroethylene, 1,2-difluoroethylene carbonate, diethyl carbonate and ethyl methyl carbonate in a volume ratio of 10:15:45:30.

[0181] A non-aqueous electrolyte was prepared by adding LiPF6, as a lithium salt, and the compound represented by Formula 1-1 to the organic solvent above.

[0182] Lithium salt was added to the non-aqueous electrolyte at a molar concentration of 1.5 M.

[0183] The compound represented by Formula 1-1 was added in an amount of 5% by weight to the non-aqueous electrolyte.

[0184] In the non-aqueous electrolyte, the weight percentage of fluoroethylene carbonate was 11.0 % by weight, and the weight percentage of 1,2-difluoroethylene carbonate was 16.6 % by weight. (Preparation of the Secondary Lithium Battery)

[0185] A secondary lithium battery was prepared in the same way as in Example 1, except that the non-aqueous electrolyte prepared above was used. Example 4 (Preparation of Non-Aqueous Electrolyte)

[0186] An organic solvent was prepared by mixing fluoroethylene carbonate, 1,2-difluoroethylene carbonate, diethyl carbonate and ethylmethyl carbonate in a volume ratio of 10:20:45:25.

[0187] A non-aqueous electrolyte was prepared by adding LiPF6, as a lithium salt, and the compound represented by Formula 1-1 to the organic solvent above.

[0188] Lithium salt was added to the non-aqueous electrolyte at a molar concentration of 1.5 M.

[0189] The compound represented by Formula 1-1 was added in an amount of 5% by weight to the non-aqueous electrolyte.

[0190] In the non-aqueous electrolyte, the weight percentage of fluoroethylene carbonate was 10.8% by weight and the weight percentage of carbonate was 1.2 Petition 870250086545, dated 09 / 24 / 2025, pp. 49 / 68 42 / 52 difluoroethylene was 21.8% by weight. (Preparation of the Secondary Lithium Battery)

[0191] A secondary lithium battery was prepared in the same way as in Example 1, except that the non-aqueous electrolyte prepared above was used. Example 5 (Preparation of Non-Aqueous Electrolyte)

[0192] An organic solvent was prepared by mixing fluoroethylene carbonate, 1,2-difluoroethylene carbonate, diethyl carbonate and ethylmethyl carbonate in a volume ratio of 10:30:45:15.

[0193] A non-aqueous electrolyte was prepared by adding LiPF6, as a lithium salt, and the compound represented by Formula 1-1 to the organic solvent above.

[0194] Lithium salt was added to the non-aqueous electrolyte at a molar concentration of 1.5 M.

[0195] The compound represented by Formula 1-1 was added in an amount of 5% by weight to the non-aqueous electrolyte.

[0196] In the non-aqueous electrolyte, the weight percentage of fluoroethylene carbonate was 10.4% by weight, and the weight percentage of 1,2-difluoroethylene carbonate was 31.5% by weight. (Preparation of the Secondary Lithium Battery)

[0197] A secondary lithium battery was prepared in the same way as in Example 1, except that the non-aqueous electrolyte prepared above was used. Example 6 (Preparation of Non-Aqueous Electrolyte)

[0198] A non-aqueous electrolyte was prepared in the same manner as in Example 1, except that the compound represented by Formula 1-1 was not used and the compound represented by Formula 1-2 was included in the non-aqueous electrolyte in an amount of 5% by weight. Petition 870250086545, dated 09 / 24 / 2025, pp. 50 / 68 43 / 52 (Preparation of the Secondary Lithium Battery)

[0199] A secondary lithium battery was prepared in the same way as in Example 1, except that the non-aqueous electrolyte prepared above was used. Example 7 (Preparation of Non-Aqueous Electrolyte)

[0200] A non-aqueous electrolyte was prepared in the same manner as in Example 1, except that the compound represented by Formula 1-1 was not used and the compound represented by Formula 1-3 was included in the non-aqueous electrolyte in an amount of 5% by weight. (Preparation of the Secondary Lithium Battery)

[0201] A secondary lithium battery was prepared in the same way as in Example 1, except that the non-aqueous electrolyte prepared above was used. Example 8 (Preparation of Non-Aqueous Electrolyte)

[0202] A non-aqueous electrolyte was prepared in the same manner as in Example 1, except that the compound represented by Formula 1-1 was not used and the compound represented by Formula 1-4 was included in the non-aqueous electrolyte in an amount of 5% by weight. (Preparation of the Secondary Lithium Battery)

[0203] A secondary lithium battery was prepared in the same way as in Example 1, except that the non-aqueous electrolyte prepared above was used. Example 9 (Preparation of Non-Aqueous Electrolyte)

[0204] A non-aqueous electrolyte was prepared in the same manner as in Example 1, except that the compound represented by Formula 1-1 was not used and the compound represented by Formula 1-9 was included in the non-aqueous electrolyte in an amount of 5% by weight. Petition 870250086545, dated 09 / 24 / 2025, pp. 51 / 68 44 / 52 (Preparation of the Secondary Lithium Battery)

[0205] A secondary lithium battery was prepared in the same way as in Example 1, except that the non-aqueous electrolyte prepared above was used. Comparative Example 1 (Preparation of Non-Aqueous Electrolyte)

[0206] An organic solvent was prepared by mixing ethylene carbonate, 1,2-difluoroethylene carbonate, diethyl carbonate and ethylmethyl carbonate in a volume ratio of 10:20:45:25.

[0207] A non-aqueous electrolyte was prepared by adding LiPFs, as a lithium salt, and the compound represented by Formula 1-1 to the organic solvent above.

[0208] Lithium salt was added to the non-aqueous electrolyte at a molar concentration of 1.5 M.

[0209] The compound represented by Formula 1-1 was added in an amount of 5% by weight to the non-aqueous electrolyte.

[0210] In the non-aqueous electrolyte, the weight percentage of ethylene carbonate was 9.6% by weight, and the weight percentage of 1,2-difluoroethylene carbonate was 22.1% by weight. (Preparation of the Secondary Lithium Battery)

[0211] A secondary lithium battery was prepared in the same way as in Example 1, except that the non-aqueous electrolyte prepared above was used. Comparative Example 2 (Preparation of Non-Aqueous Electrolyte)

[0212] An organic solvent was prepared by mixing fluoroethylene carbonate, diethyl carbonate and ethyl methyl carbonate in a volume ratio of 10:45:45.

[0213] A non-aqueous electrolyte was prepared by adding LiPFs, as a lithium salt, and the compound represented by Formula 1-1 to the organic solvent above. Petition 870250086545, dated 09 / 24 / 2025, pp. 52 / 68 45 / 52

[0214] Lithium salt was added to the non-aqueous electrolyte at a molar concentration of 1.5 M.

[0215] The compound represented by Formula 1-1 was added in an amount of 5% by weight to the non-aqueous electrolyte.

[0216] In the non-aqueous electrolyte, the weight percentage of fluoroethylene carbonate was 11.6% by weight. (Preparation of the Secondary Lithium Battery)

[0217] A secondary lithium battery was prepared in the same way as in Example 1, except that the non-aqueous electrolyte prepared above was used. Comparative Example 3 (Preparation of Non-Aqueous Electrolyte)

[0218] A non-aqueous electrolyte was prepared in the same manner as in Example 1, except that the compound represented by Formula 1-1 was not included in the non-aqueous electrolyte. (Preparation of the Secondary Lithium Battery)

[0219] A secondary lithium battery was prepared in the same way as in Example 1, except that the non-aqueous electrolyte prepared above was used. Comparative Example 4 (Preparation of Non-Aqueous Electrolyte)

[0220] An organic solvent was prepared by mixing 1,2-difluoroethylene carbonate, diethyl carbonate and ethylmethyl carbonate in a volume ratio of 20:45:35.

[0221] A non-aqueous electrolyte was prepared by adding LiPFs, as a lithium salt, and the compound represented by Formula 1-1 to the organic solvent above.

[0222] Lithium salt was added to the non-aqueous electrolyte at a molar concentration of 1.5 M.

[0223] The compound represented by Formula 1-1 was added in a Petition 870250086545, dated 09 / 24 / 2025, pp. 53 / 68 46 / 52 quantity of 5% by weight to the non-aqueous electrolyte.

[0224] In the non-aqueous electrolyte, the weight percentage of 1,2-difluoroethylene carbonate was 22.6% by weight. (Preparation of the Secondary Lithium Battery)

[0225] A secondary lithium battery was prepared in the same way as in Example 1, except that the non-aqueous electrolyte prepared above was used. [Table 1] LiF content (per negative electrode area, pg / cm2) CO32- content (per negative electrode area, pg / cm2) LiF content / CO32- content Example 1 150 85 1.8 Example 2 140 75 1.9 Example 3 185 95 1.9 Example 4 200 80 2.5 Example 5 135 80 1.7 Example 6 120 75 1.6 Example 7 130 80 1.6 Example 8 120 70 1.7 Example 9 135 85 1.6 Comparative Example 1 35 40 0.9 Comparative Example 2 40 40 1 Comparative Example 3 40 35 1.1 Comparative Example 4 35 30 1.2 Experimental Example 1: Evaluation of Loading and Unloading Performance in High Temperature Cycles

[0226] Each of the lithium secondary batteries prepared above, from Examples 1 to 9 and Comparative Examples 1 to 4, was charged from 0.33 C to 4.2 V under a constant current / constant voltage (DC / CV) condition at 45 °C using electrochemical charge / discharge equipment and then discharged at a DC of 0.33 C to 3.0 V, which was defined as one cycle, 200 charge and discharge cycles were performed and the capacity retention, resistance increase rate, amount of gas generation and amount of metal dissolution were evaluated as follows. Petition 870250086545, dated 09 / 24 / 2025, pp. 54 / 68 47 / 52 Experimental Example 1-1: Capacity Retention Assessment

[0227] After loading and unloading under the above conditions, the capacity retention was calculated using the following equation, and the results are presented in Table 2 below.

[0228] Capacity retention (%) = (discharge capacity after 200 cycles / discharge capacity after one cycle) χ 100 Experimental Example 1-2: Evaluation of the Rate of Increase in Resistance

[0229] After a charge and discharge cycle, the discharge capacity after a cycle was measured using an electrochemical charge / discharge apparatus, a state of charge (SOC) was set to 50% and a 2.5 C pulse was then applied for 10 seconds to calculate the initial resistance by means of a difference between a voltage before the application of the pulse and a voltage after the application of the pulse.

[0230] After 200 charge and discharge cycles, the resistance after 200 cycles was calculated in the same way as above, a rate of resistance increase was calculated using the following equation, and the results are presented in Table 2 below.

[0231] Rate of increase in resistance (%) = (resistance after 200 cycles - initial resistance) / initial resistance χ 100 Experimental Example 2: Performance Evaluation of High-Temperature Storage

[0232] The secondary lithium batteries in Examples 1 to 9 and Comparative Examples 1 to 3 were charged at 4.2 V / 55 mA under constant current / constant voltage (DC / CV) conditions of 0.33 C / 4.2 V at room temperature and discharged at 0.33 C at 2.5 V to perform the initial charge and discharge, and after that, the secondary lithium batteries were charged at 4.2 V / 55 mA under constant current / constant voltage (DC / CV) conditions of 0.33 C / 4.2 V at room temperature and then stored at 60 °C. Petition 870250086545, dated 09 / 24 / 2025, pp. 55 / 68 48 / 52 Experimental Example 2-1: Capacity Retention Assessment

[0233] After storage, the secondary batteries were charged at 4.2 V / 55 mA under constant current / constant voltage (CC / CV) conditions of 0.33 C / 4.2 V at room temperature and discharged at 0.33 C to 2.5 V to measure capacity during discharge.

[0234] Capacity retention (%) = (discharge capacity after 8 weeks of storage / initial discharge capacity) χ 100 Experimental Example 2-2: Evaluation of the Rate of Increase in Resistance

[0235] During the initial charging and discharging, the secondary battery was charged to a SOC of 50 based on the discharge capacity after verifying the capacity at room temperature, and discharged at a current of 2.5 C for 10 seconds to measure the resistance using a difference in voltage drop; in this case, the resistance was used as the initial resistance and, after 8 weeks of storage at 60 °C, the resistance was measured by the same method and used as the final resistance to calculate a resistance increase rate using the following equation. The results are presented in Table 2 below.

[0236] Rate of increase in resistance (%) = (final resistance - initial resistance) / (initial resistance) χ 100 [Table 2] Experimental Example 1-1 Experimental Example 1-2 Experimental Example 2-1 Experimental Example 2-2 Capacity Retention (%) Rate of Resistance Increase (%) Capacity Retention (%) Rate of Resistance Increase (%) Example 1 93 8 94 10 Example 2 94 7 91 11 Example 3 95 7 91 9 Example 4 98 6 95 8 Example 5 96 9 90 10 Example 6 92 8 93 9 Example 7 93 7 92 8 Example 8 93 8 93 8 Petition 870250086545, dated 09 / 24 / 2025, pp. 56 / 68 49 / 52 Example 9 94 9 94 9 Comparative Example 1 61 55 58 58 Comparative Example 2 75 43 71 45 Comparative Example 3 76 40 71 43 Comparative Example 4 74 41 73 43

[0237] Referring to Table 2, it can be confirmed that the secondary lithium batteries according to Examples 1 to 9, which included the non-aqueous electrolyte including all fluoroethylene carbonate, 1,2-difluoroethylene carbonate and the compound represented by Formula 1 and the negative electrode containing the silicon-based active material, showed significantly better charge and discharge cycle performance and high-temperature storage performance than Comparative Examples 1 to 4. Reference Examples Reference Example 1 (Preparation of Non-Aqueous Electrolyte)

[0238] A non-aqueous electrolyte was prepared in the same way as in Comparative Example 1. (Preparation of the Secondary Lithium Battery)

[0239] A positive electrode active material (LiNi0.85Co0.05Mn0.07Al0.03O2): a conducting agent (carbon nanotubes): a binder (polyvinylidene fluoride) were added in a weight ratio of 97.74:0.70:1.56 to N-methyl-2-pyrrolidone (NMP), as solvent, to prepare a positive electrode material mixing paste (75.5% by weight solid content). A 15 μm thick positive electrode current collector surface (Al thin film) was coated with the positive electrode material mixing paste, dried, and then rolled to prepare a positive electrode.

[0240] A negative electrode active material (mixture of artificial graphite and Petition 870250086545, dated 09 / 24 / 2025, pp. 57 / 68 50 / 52 natural graphite in a weight ratio of 50.3:49.7; a conductive agent (carbon black); and a binder (styrene-butadiene rubber) were added to distilled water as a solvent in a weight ratio of 96.7:1.0:2.3 to prepare a negative electrode material mixture paste (50% solid content by weight). An 8 μm thick negative electrode current collector surface (thin Cu film) was coated with the negative electrode material mixture paste, dried, and then rolled to prepare a negative electrode.

[0241] After a porous polyethylene film separator was placed between the positive and negative electrodes prepared above in a dry room, the non-aqueous electrolyte prepared above was injected to prepare a secondary battery. Example of Reference 2

[0242] A secondary lithium battery was prepared in the same way as in Reference Example 1, except that a non-aqueous electrolyte was used, prepared in the same way as in Example 4. Example of Reference 3

[0243] A secondary lithium battery was prepared in the same way as in Reference Example 1, except that a non-aqueous electrolyte was used, prepared in the same way as in Comparative Example 3. Example of Reference 4

[0244] A secondary lithium battery was prepared in the same way as in Reference Example 1, except that a non-aqueous electrolyte was used, prepared in the same way as in Comparative Example 4. Reference Experimental Example 1: Evaluation of Load and Discharge Performance in High-Temperature Cycles

[0245] An experiment was carried out using the same method as in Example Petition 870250086545, dated 09 / 24 / 2025, pages 58 / 68 51 / 52 Experiment 1 (Experimental Examples 1-1 and 1-2). The results are presented in Table 3 below. Reference Experimental Example 2: Evaluation of High-Temperature Storage Performance

[0246] An experiment was conducted using the same method as in Experimental Example 2 (Experimental Examples 2-1 and 2-2). The results are presented in Table 3 below. [Table 3] Reference Experiment Example 1 Reference Experiment Example 2 Capacity Retention (%) Rate of Resistance Increase (%) Capacity Retention (%) Rate of Resistance Increase (%) Reference Example 1 69 48 62 52 Reference Example 2 63 52 58 55 Reference Example 3 66 52 59 58 Reference Example 4 65 51 59 53

[0247] Referring to Table 3, with respect to the secondary lithium batteries of Reference Examples 1 to 4 that use only the carbon-based active material as the negative electrode active material, the performance of Reference Example 2 (using the non-aqueous electrolyte used in Example 4) showed lower capacity retention and a higher rate of resistance increase during the charge and discharge cycle and high-temperature storage than 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). This is considered due to the fact that the combined use of fluoroethylene carbonate and 1,2-difluoroethylene carbonate caused unnecessary problems in the carbon-based active material, for example, acting as resistance.

[0248] Thus, according to the experimental results in Table 3, it can Petition 870250086545, dated 09 / 24 / 2025, pp. 59 / 68 52 / 52 if it is understood that the non-aqueous electrolyte of the present invention exhibited the desired service life performance and high-temperature storage performance in the secondary lithium battery and in the negative electrode containing the silicon-based active material. Petition 870250086545, dated 09 / 24 / 2025, pages 60 / 68

Claims

1 / 5 CLAIMS 1. Secondary lithium battery comprising: a positive electrode; a negative electrode; a separator disposed between the positive electrode and the negative electrode;and a non-aqueous electrolyte, CHARACTERIZED in that 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, fluoroethylene carbonate, 1,2-difluoroethylene carbonate and a compound represented by Formula 1: wherein, in Formula 1, Ri comprises a halogen, a nitrile group, a propargyl group, an ester group, an ether group, a ketone group, a carboxyl group, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted alkynyl group, a substituted or unsubstituted alkoxy group, a boron group, a borate group, an isocyanate group, an isothiocyanate group, a silyl group, a siloxane group, a sulfone group, a sulfonate group, a sulfate group or a combination of two or more thereof, and n is an integer from 0 to 6.; 2. Secondary lithium battery, according to claim 1, CHARACTERIZED in that the silicon-based active material comprises a silicon-based particle, wherein the silicon-based particle comprises a compound represented by Formula A: [Formula A] SiOx where, in Formula A, 0 < x < 2.

3. Secondary lithium battery, according to claim 2, CHARACTERIZED in that the silicon-based particle is formed from silicon (Si).

4. Lithium secondary battery, according to claim 1, CHARACTERIZED in that the compound represented by Formula 1 comprises at least one selected from the group consisting of a compound represented by Formula 1-A and a compound represented by Formula 1-B: [Formula 1-A] [Formula 1-B] wherein, in Formulas 1-A and 1-B, Ri is defined in Formula 1.

5. Lithium secondary battery, according to claim 1, CHARACTERIZED in that the compound represented by Formula 1 comprises at least one compound selected from the group represented by Formulas 1-1 to 1-9: [Formula 1-1] Petition 870250086545, dated 09 / 24 / 2025, p. 62 / 68 3 / 5 [Formula 1-2] Petition 870250086545, dated 09 / 24 / 2025, p. 63 / 68 4 / 5 [Formula 1-7] [Formula 1-8] [Formula 1-9] 6. Secondary lithium battery, according to claim 1, CHARACTERIZED in that fluoroethylene carbonate is included in the non-aqueous electrolyte in an amount of 3% by vol to 20% by vol.

7. Secondary lithium battery, according to claim 1, CHARACTERIZED in that 1,2-difluoroethylene carbonate is included in the non-aqueous electrolyte in an amount of 10 to 35% by volume.

8. Secondary lithium battery, according to claim 1, CHARACTERIZED in that the compound represented by Formula 1 is included in an amount of 0.1% to 10% by weight, based on the weight of the non-aqueous electrolyte.

9. Secondary lithium battery, according to claim 1, CHARACTERIZED in that the volume ratio of fluoroethylene carbonate to 1,2-difluoroethylene carbonate is in a range of 5:95 to 50:

50.

10. Secondary lithium battery, according to claim 1, Petition 870250086545, dated 09 / 24 / 2025, page 64 / 68 5 / 5 CHARACTERIZED in that 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, based on the total weight of the non-aqueous electrolyte.

11. Lithium secondary battery, according to claim 1, CHARACTERIZED in that the lithium salt comprises at least one selected from the group consisting of LiCl, LiBr, LiI, LiBF4, LiCO4, LiAlO4, LiAlCl4, LiPF6, LiSbF6, LiAsF6, LiBioCIio, LiBOB (LiB(C2O4)2), UCF3SO3, LiFSI (LiN(SO2F)2), UCH3SO3, UCF3CO2, UCH3CO2 and LiBETI (LiN(SO2CF2CF3)2).

12. Lithium secondary battery, according to claim 1, CHARACTERIZED in that a solid electrolyte interface film is formed on the negative electrode after the formation of the lithium secondary battery, the solid electrolyte interface film comprising an inorganic component, and the inorganic component comprising LiF and CO32; wherein the ratio between the weight of LiF and the weight of CO32 is 1.4 or more. Petition 870250086545, dated 09 / 24 / 2025, pp. 65 / 68