Nonaqueous electrolyte and lithium secondary battery comprising same

Abstract

The present invention relates to a nonaqueous electrolyte and a lithium secondary battery comprising same. Particularly, the nonaqueous electrolyte of the present invention comprises a lithium salt, an organic solvent, and an additive, wherein the additive comprises a first additive and a second additive, the first additive is a compound represented by chemical formula 1, the second additive is a compound represented by chemical formula 2, the total content of the additive is 8-20 wt% on the basis of the total weight of the nonaqueous electrolyte, and the weight ratio of the first additive to the second additive may be 10:90 to 40:60.

Description

Non-aqueous electrolyte and lithium secondary battery containing the same

[0001] Cross-citation with related application(s)

[0002] This application claims the benefit of priority based on Korean Patent Application No. 10-2024-0164626 filed November 18, 2024 and Korean Patent Application No. 10-2025-0165692 filed November 5, 2025, and all contents disclosed in the documents of said Korean patent applications are incorporated herein as part of this specification.

[0003] Technology field

[0004] The present invention relates to a non-aqueous electrolyte and a lithium secondary battery containing the same.

[0005] As dependence on electrical energy gradually increases in modern society, the development of large-capacity power storage devices capable of stably supplying power while simultaneously increasing production is emerging. Furthermore, the need for high-capacity portable power is growing due to the performance improvements of electronic products, ranging from small devices such as mobile phones to medium-to-large devices such as electric vehicles. Lithium-ion batteries, which possess the highest potential, satisfy high-capacity power storage performance requirements and are therefore utilized in a wide range of applications, from small electronic devices to electric vehicles (EVs) and energy storage systems (ESS).

[0006] The above lithium secondary battery generally consists of a positive electrode containing a positive active material, a negative electrode containing a negative active material, an electrolyte serving as a medium for transmitting lithium ions, and a separator. As the positive active material, lithium transition metal oxides such as lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium nickel-cobalt-manganese composite oxide, and lithium iron phosphate may be used, and as the negative active material, carbon-based active material, silicon-based active material, lithium transition metal oxide, lithium metal, etc. may be used.

[0007] In lithium secondary batteries, lithium ions are generated from the positive electrode during charging and can be converted into stacked or alloy forms for storage on the negative electrode, while discharge proceeds in the opposite direction. At this time, most of the lithium ions are stacked or alloyed within the negative electrode active material, but some are reduced together with the organic and inorganic materials constituting the electrolyte to form nano-sized organic-inorganic composites on the negative electrode surface; this formed organic-inorganic film is called the solid electrolyte interface layer (SEI layer). A solid electrolyte interface layer can also be formed on the surface of the positive electrode active material through the oxidation reaction of the materials constituting the electrolyte.

[0008] Meanwhile, carbon-based active materials such as conventional graphite have been mainly used as the above-mentioned cathode active material, but recently, the use of silicon-based active materials, which have a higher capacity than carbon-based active materials, is being considered.

[0009] The above silicon-based active material not only has a higher capacity compared to carbon-based active materials, but is also low-cost, non-toxic, environmentally friendly, and has a low operating voltage, so it is emerging as a next-generation anode material for lithium-ion batteries requiring high energy density.

[0010] However, silicon-based active materials have the disadvantage of lower initial efficiency compared to carbon-based anode active materials due to severe lithium depletion caused by their high initial irreversible capacity. In particular, silicon-based active materials exhibit significant volume expansion and contraction during the charge-discharge process due to changes in crystal structure resulting from the insertion and extraction of lithium ions. This large volume expansion and contraction not only degrades the durability of the solid-electrolyte interface layer and significantly reduces anode conductivity, thereby lowering lifespan performance, but also triggers a thick film formation reaction accompanied by continuous electrolyte decomposition on the anode surface, leading to an extreme increase in resistance and performance degradation within the battery.

[0011] Therefore, forming a highly flexible solid-electrolyte interface layer with enhanced resilience and stability capable of withstanding volume changes of silicon-based anodes during silicon-based battery operation is emerging as an important challenge.

[0012] The present invention aims to solve the above-mentioned problems by providing a non-aqueous electrolyte capable of forming a flexible and mechanically durable solid-electrolyte interface layer on the surface of a cathode.

[0013] In addition, the present invention provides a lithium secondary battery that includes the above-mentioned non-aqueous electrolyte, thereby reducing gas generation during high-temperature storage and improving lifespan characteristics.

[0014] [1] The present invention provides a non-aqueous electrolyte comprising a lithium salt, an organic solvent, and an additive, wherein the additive comprises a first additive and a second additive, the first additive is a compound represented by the following chemical formula 1 and the second additive is a compound represented by the following chemical formula 2, the total content of the additive is 8% to 20% by weight based on the total weight of the non-aqueous electrolyte, and the weight ratio of the first additive and the second additive is 10:90 to 40:60.

[0015] [Chemical Formula 1]

[0016] N≡C-R1-F

[0017] (In the above Chemical Formula 1, R1 is an alkylene group having 1 to 5 carbon atoms.)

[0018] [Chemical Formula 2]

[0019] N≡C-R2

[0020] (In the above Chemical Formula 2, R2 is an alkyl group having 2 to 10 carbon atoms.)

[0021] [2] The present invention provides a non-aqueous electrolyte in which the organic solvent is a cyclic carbonate compound, as in [1].

[0022] [3] The present invention provides a non-aqueous electrolyte in which the cyclic carbonate compound of [2] is selected from the group consisting of at least one of ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate and vinylene carbonate.

[0023] [4] The present invention provides a non-aqueous electrolyte in which the cyclic carbonate compound in [2] or [3] is ethylene carbonate (EC).

[0024] [5] The present invention provides a non-aqueous electrolyte comprising, in at least one of [1] to [4], a compound represented by Formula 1, selected from the group consisting of compounds represented by Formulas 1A to 1C.

[0025] [Chemical Formula 1A]

[0026] N≡C-CH2F

[0027] [Chemical Formula 1B]

[0028] N≡C-CH2CH2F

[0029] [Chemical Formula 1C]

[0030] N≡C-CH2CH2CH2F

[0031] [6] The present invention provides a non-aqueous electrolyte comprising, in at least one of [1] to [5], a compound represented by Formula 2, selected from the group consisting of compounds represented by Formulas 2A to 2C.

[0032] [Chemical Formula 2A]

[0033] N≡C-CH(CH3)2

[0034] [Chemical Formula 2B]

[0035] N≡C-CH(CH2CH3)2

[0036] [Chemical Formula 2C]

[0037] N≡C-CH(CH3)CH2CH3

[0038] [7] The present invention provides a non-aqueous electrolyte in which, in at least one of [1] to [6], the weight ratio of the first additive and the second additive is 10:90 to 30:70.

[0039] [8] The present invention provides a non-aqueous electrolyte in which, in at least one of [1] to [7], the total content of the additive is 10% to 20% by weight based on the total weight of the non-aqueous electrolyte.

[0040] [9] The present invention provides a non-aqueous electrolyte in which, in at least one of [1] to [8], the non-aqueous electrolyte further comprises at least one auxiliary additive selected from the group consisting of cyclic carbonate compounds, halogen-substituted carbonate compounds, sulfone compounds, sulfate compounds, phosphate compounds, borate compounds, benzene compounds, amine compounds, silane compounds and lithium salt compounds.

[0041]

[0010] The present invention provides a lithium secondary battery comprising: a positive electrode; a negative electrode facing the positive electrode; a separator interposed between the negative electrode and the positive electrode; and a non-aqueous electrolyte according to [1].

[0042]

[0011] The present invention provides a lithium secondary battery according to

[0010] , wherein the negative electrode comprises a silicon-based active material.

[0043] The non-aqueous electrolyte according to the present invention can form a flexible solid-electrolyte interface layer with excellent mechanical durability on the surface of the negative electrode by including two types of nitrile compounds having a specific structure as electrolyte additives in a specific compositional ratio. When the non-aqueous electrolyte of the present invention is applied to a lithium secondary battery, it can absorb the deposition of mechanical stress caused by the continuous volume expansion and contraction of the negative electrode, and can suppress the acceleration of electrolyte side reactions, increased resistance, and gas generation caused by the deterioration of the durability of the solid-electrolyte interface layer on the surface of the negative electrode, thereby significantly improving the overall performance, such as the lifespan characteristics of the lithium secondary battery. In particular, the non-aqueous electrolyte of the present invention can be preferably used in a negative electrode containing a silicon-based active material that undergoes a large volume change during charging and discharging, and in a lithium secondary battery containing the same.

[0044] The terms and words used in this specification and claims are used merely to describe exemplary embodiments and should not be interpreted as being limited to their ordinary or dictionary meanings, and should be interpreted in a meaning and concept consistent with the technical spirit of the invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe his invention.

[0045] For example, in this specification, terms such as “comprising,” “having,” or “having” are intended to specify the existence of the implemented features, numbers, steps, components, or combinations thereof, and should be understood as not excluding in advance the existence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0046] In addition, in the description of “carbon number a to b” within this specification, “a” and “b” refer to 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, “alkylene group having 1 to 5 carbon atoms” refers to an alkylene group containing carbon atoms having 1 to 5 carbon atoms, namely -CH2-, -CH2CH2-, -CH2CH2CH2-, -CH2(CH3)CH-, -CH2CH2CH2CH2CH2-, and -CH(CH3)CH2CH2-, etc.

[0047] Additionally, in this specification, the term “alkylene group” means a branched or unbranched aliphatic hydrocarbon group or a functional group in which one hydrogen atom is removed from each carbon atom located at both ends of the aliphatic hydrocarbon group. In one embodiment, the alkylene group may be substituted or unsubstituted. The alkylene group includes, but is not limited to, methylene groups, ethylene groups, propylene groups, isopropylene groups, butylene groups, isobutylene groups, tert-butylene groups, pentylene groups, 3-pentylene groups, etc., and each of these may be optionally substituted in other embodiments.

[0048] Additionally, in this specification, the term “substitution” means that at least one hydrogen bonded to carbon is substituted with another element, such as fluorine, unless otherwise defined.

[0049] Additionally, in this specification, “%” means weight % unless otherwise explicitly indicated.

[0050]

[0051] The present invention will be described in detail below.

[0052] The non-aqueous electrolyte and lithium secondary battery according to the present invention comprise at least one of the configurations disclosed below and may comprise any combination of technically feasible configurations among the configurations below.

[0053]

[0054] Non-aqueous electrolytes

[0055] The present invention relates to a non-aqueous electrolyte, and more specifically, to a non-aqueous electrolyte for a lithium secondary battery.

[0056] Specifically, the present invention provides a non-aqueous electrolyte comprising a lithium salt, an organic solvent, and an additive.

[0057] The above additive may include a first additive and a second additive.

[0058] The first additive above may be a compound represented by the following chemical formula 1.

[0059] The above second additive may be a compound represented by the following chemical formula 2.

[0060] The total content of the above additive may be 8% to 20% by weight based on the total weight of the non-aqueous electrolyte.

[0061] The weight ratio of the first additive and the second additive may be 10:90 to 40:60.

[0062] [Chemical Formula 1]

[0063] N≡C-R1-F

[0064] (In the above Chemical Formula 1, R1 is an alkylene group having 1 to 5 carbon atoms.)

[0065] [Chemical Formula 2]

[0066] N≡C-R2

[0067] (In the above Chemical Formula 2, R2 is an alkyl group having 2 to 10 carbon atoms.)

[0068] The non-aqueous electrolyte according to the present invention comprises a cyclic carbonate compound and two types of nitrile compounds having a specific structure in a specific composition as an organic solvent, thereby forming a flexible and durable film on the surface of the negative electrode. Therefore, when the non-aqueous electrolyte of the present invention is applied to a lithium secondary battery, a lithium secondary battery with improved lifespan characteristics and reduced gas generation during high-temperature storage can be provided.

[0069]

[0070] (1) Lithium salt

[0071] As the lithium salt used in the present invention, various lithium salts commonly used in non-aqueous electrolytes for lithium secondary batteries may be used without limitation. For example, Li as a cation + It includes, and as anion, F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , B 10 Cl 10 - , AlCl4 - , AlO2 - , PF6 - , CF3SO3 - , CH3CO2 - , CF3CO2 - , AsF6 - , SbF6 - , CH3SO3 - , (CF3CF2SO2)2N - , (CF3SO2)2N - , (FSO2)2N - , BF2C2O4 - , BC4O8 - , PF4C2O4 - , PF2C4O8 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , C4F9SO3 - , CF3CF2SO3 - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - and CF3(CF2)7SO3 -At least one selected from the group consisting of can be cited.

[0072] Specifically, the lithium salt is LiCl, LiBr, LiI, LiBF4, LiClO4, LiB 10 Cl 10 It may include a single substance selected from the group consisting of LiAlCl4, LiAlO2, LiPF6, LiCF3SO3, LiCH3CO2, LiCF3CO2, LiAsF6, LiSbF6, LiCH3SO3, LiN(SO2F)2(Lithium bis(fluorosulfonyl)imide, LiFSI), LiN(SO2CF2CF3)2(lithium bis(pentafluoroethanesulfonyl)imide, LiBETI), and LiN(SO2CF3)2(lithium bis(trifluoromethanesulfonyl)imide, LiTFSI), or a mixture of two or more substances. 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).

[0073] The above lithium salt can be appropriately modified within a range that is typically usable, but in order to obtain the effect of forming a corrosion-preventing film on the optimal electrode surface, it may be included in the electrolyte at a concentration of 0.8M to 4.0M, specifically at a concentration of 1.0M to 3.0M.

[0074] When the concentration of the above lithium salt is included within the above range, the viscosity of the non-aqueous electrolyte can be controlled to achieve optimal impregnation, and the mobility of lithium ions can be improved to obtain the effect of improving the capacity characteristics and cycle characteristics of the lithium secondary battery.

[0075]

[0076] (2) Organic solvent

[0077] The non-aqueous electrolyte of the present invention may include a cyclic carbonate compound as an organic solvent.

[0078] The above-mentioned cyclic carbonate compound may be a high-viscosity organic solvent that minimizes decomposition due to oxidation reactions, etc. during the charging and discharging process and effectively dissociates lithium salts in a non-aqueous electrolyte due to its high dielectric constant, and may include at least one organic solvent selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, and vinylene carbonate as specific examples, and among these, may include ethylene carbonate, which has the best effect on dissociating lithium salts and forming a film.

[0079] Meanwhile, even if the non-aqueous electrolyte of the present invention contains only cyclic carbonate compounds as the organic solvent, the dissolution of non-aqueous electrolyte components, such as lithium salts and additives described later, can be facilitated, and the mobility of the lithium salt and the appropriate viscosity of the non-aqueous electrolyte can be achieved. Furthermore, in order to suppress the generation of byproducts acting as resistors at the cathode during reduction and to reduce the generation of CO and CO2 gases during high-temperature storage, it is preferable to avoid the use of linear carbonate compounds containing carbonate functional groups in the non-aqueous electrolyte of the present invention.

[0080] Meanwhile, the remainder of the non-aqueous electrolyte of the present invention, excluding the lithium salt, the electrolyte additive and auxiliary additive described below, may all be organic solvents unless otherwise noted.

[0081]

[0082] (3) Additives

[0083] The non-aqueous electrolyte of the present invention may include two types of nitrile compounds with different structures as additives.

[0084] Specifically, the additive comprises a first additive and a second additive, wherein the first additive is a compound represented by the following chemical formula 1 and the second additive may be a compound represented by the following chemical formula 2.

[0085] [Chemical Formula 1]

[0086] N≡C-R1-F

[0087] (In the above Chemical Formula 1, R1 is an alkylene group having 1 to 5 carbon atoms)

[0088] [Chemical Formula 2]

[0089] N≡C-R2

[0090] (In the above chemical formula 2, R2 is an alkyl group having 2 to 10 carbon atoms)

[0091] Specifically, the nitrile compound represented by Chemical Formula 1 contains only one fluorine atom at the terminal, resulting in a small molecular size. Since it contains a fluorine component within its structure, it can form a solvated structure containing anions. Furthermore, upon decomposition at the cathode surface during charging and discharging, it can form an inorganic-based solid-electrolyte interface layer, such as lithium-nitrogen / fluorine (LiF-Li3N), which exhibits high conductivity, flexibility, and excellent mechanical durability. Consequently, the degradation of the solid-electrolyte interface layer due to the continuous volume expansion and contraction of the cathode can be effectively suppressed, and resistance can be reduced. Meanwhile, if two or more fluorine groups are substituted in the compound represented by Chemical Formula 1, for example, -CHF2 or - When a CF3 group is included, or when at least one hydrogen contained in an alkylene group connecting a terminal nicryl group and a fluorine atom is substituted with fluorine, the molecular size becomes bulky, and the detachment of the fluorine atom is not smooth, so the effect of forming a LiF film may be reduced.

[0092] In addition, the compound represented by Chemical Formula 2 has a lower freezing point and viscosity, and a higher dielectric constant value compared to the compound represented by Chemical Formula 1. Therefore, when the compound represented by Chemical Formula 1 and the compound represented by Chemical Formula 2 are used in combination as electrolyte additives, the viscosity of the electrolyte is lowered and the ionic conductivity is improved, thereby enhancing the impregnation, low-temperature performance, and metal charging performance of the non-aqueous electrolyte. Accordingly, when the non-aqueous electrolyte of the present invention is applied to a lithium secondary battery, excellent lifespan and storage performance can be achieved even under repeated charge and discharge conditions, while output performance can be improved.

[0093] In particular, Li3N, a film component formed by two types of nitrile compounds with different structures, can secure high lithium ion mobility. Therefore, ion conductivity can be improved by forming a film with high lithium ion mobility on the surface of a negative electrode using a silicon-based active material, which has lower conductivity compared to a negative electrode using a graphite active material.

[0094] In addition, the compounds represented by Chemical Formula 1 or Chemical Formula 2 both contain a polar nitrile group (-CN) having a high dipole moment within their structure, and thus can form a stable CEI film on the surface of the anode by forming a ligand with the transition metal, thereby preventing side reactions between the anode and the electrolyte and suppressing metal leaching during high-temperature storage. Furthermore, the compounds represented by Chemical Formula 1 or Chemical Formula 2 can further improve the high-temperature storage characteristics of the secondary battery because the lone pair of electrons of the nitrogen atom contained within their structure stabilizes the anion of the lithium salt, thereby suppressing the generation of HF caused by the decomposition of the lithium salt. Additionally, since the compounds represented by Chemical Formula 1 or 2 do not contain functional groups capable of generating CO and CO2, the generation of CO and CO2 gases during high-temperature storage can be reduced.

[0095] Meanwhile, in the above chemical formula 1, R1 may be an alkylene group having 1 to 3 carbon atoms.

[0096] Specifically, the compound represented by the above chemical formula 1 may be at least one of the compounds represented by the following chemical formulas 1A to 1C.

[0097] [Chemical Formula 1A]

[0098] N≡C-CH2F

[0099] [Chemical Formula 1B]

[0100] N≡C-CH2CH2F

[0101] [Chemical Formula 1C]

[0102] N≡C-CH2CH2CH2F

[0103] In addition, in the above chemical formula 2, R2 may be an alkyl group having 3 to 7 carbon atoms.

[0104] Specifically, the compound represented by the above chemical formula 2 may be at least one of the compounds represented by the following chemical formulas 2A to 2C.

[0105] [Chemical Formula 2A]

[0106] N≡C-CH(CH3)2

[0107] [Chemical Formula 2B]

[0108] N≡C-CH(CH2CH3)2

[0109] [Chemical Formula 2C]

[0110] N≡C-CH(CH3)CH2CH3

[0111] The additive of the present invention may include a first additive and a second additive, wherein the weight ratio of the first additive and the second additive may be 10:90 to 40:60, or 10:90 to 35:65, and specifically 10:90 to 30:70.

[0112] When the composition ratio of the first additive and the second additive satisfies the above range, it is possible to form a film of appropriate thickness that can increase the durability of the anode / cathode without increasing cell resistance while appropriately controlling the electrolyte viscosity and ion conductivity. Accordingly, since the deterioration of the solid-electrolyte interface layer due to the continuous volume expansion and contraction of the cathode during repeated charging and discharging can be effectively suppressed, excellent high-temperature durability and low-temperature output performance can be realized. For example, if the weight ratio of the second additive to the first additive is less than 60, the content of the first additive containing a fluorine element with relatively high reducing activity is high within the electrolyte solvation structure. Consequently, the fluorine-containing film formation effect attributed to the first additive is promoted during the charging process, causing the thickness of the fluorine-containing film to increase. As a result, the film resistance increases excessively, which may lead to a deterioration in high-temperature durability. Furthermore, as the proportion of the second additive having a low freezing point, low viscosity, and high dielectric constant value decreases, the low-temperature properties of the electrolyte are consequently degraded, which may lead to a deterioration in high-temperature durability and low-temperature output characteristics. Additionally, if the weight ratio of the second additive to the first additive exceeds 90, the content of the first additive within the electrolyte solvation structure is significantly reduced, thereby reducing the fluorine-containing film-forming effect attributed to the first additive, resulting in the formation of a film with inferior mechanical durability, which may lead to a deterioration in the high-temperature durability of the battery.

[0113] The total content of the additive may be 8% by weight or more, 9% by weight or more, or 10% by weight or more based on the total weight of the non-aqueous electrolyte. The total content of the additive may be 20% by weight or less, 19% by weight or less, 18% by weight or less, 17% by weight or less, 16% by weight or less, or 15% by weight based on the total weight of the non-aqueous electrolyte. The above numerical ranges may be combined with one another without limitation. For example, the total content of the additive may be 8% to 20% by weight, 8% to 18% by weight, or 8% to 15% by weight based on the total weight of the non-aqueous electrolyte. When the total content of the above additive satisfies the above numerical range, a robust inorganic film is uniformly formed on the surfaces of the anode and cathode while suppressing disadvantages such as side reactions, capacity reduction, and increased resistance caused by the additive to the maximum extent, thereby effectively operating as an ion carrier and effectively suppressing side reactions between the electrolyte and the electrode. Furthermore, the deterioration of the solid-electrolyte interface layer caused by continuous volume expansion and contraction of the cathode during repeated charging and discharging can be effectively suppressed, thereby enabling excellent high-temperature durability and low-temperature output performance. On the other hand, if the total content of the electrolyte additive in the above non-aqueous electrolyte is less than 8 weight%, physical properties such as the ionic conductivity and viscosity of the electrolyte are degraded, and as the film-forming effect attributed to the electrolyte additive is reduced, the deterioration of the solid-electrolyte interface layer caused by continuous volume expansion and contraction of the cathode cannot be effectively suppressed, and an increase in cell resistance may be induced. In addition, if the total content of the electrolyte additive in the above-mentioned non-aqueous electrolyte exceeds 20% by weight, there is a disadvantage that the cell resistance actually increases during charging and discharging as the solid-electrolyte interface layer is excessively formed.

[0114]

[0115] (3) Auxiliary additives

[0116] The non-aqueous electrolyte of the present invention may additionally include auxiliary additives within the electrolyte as needed to prevent the decomposition of the electrolyte in a high-power environment from causing cathode collapse, or to further improve low-temperature high-rate discharge characteristics, high-temperature stability, prevention of overcharging, and suppression of battery expansion at high temperatures. When an auxiliary additive is included in the non-aqueous electrolyte of the present invention, the auxiliary additive may be referred to as a third additive.

[0117] The above auxiliary additive may include at least one selected from the group consisting of cyclic carbonate compounds, halogen-substituted carbonate compounds, sulfone compounds, sulfate compounds, phosphate compounds, borate compounds, benzene compounds, amine compounds, silane compounds, and lithium salt compounds.

[0118] Examples of the above-mentioned cyclic carbonate compounds include vinylene carbonate (VC) or vinylethylene carbonate. The above-mentioned cyclic carbonate compounds may be included in an amount of 1.0% to 10% by weight, specifically 1.0% to 5.0% by weight, of the total weight of the non-aqueous electrolyte. When the content of the above-mentioned cyclic carbonate compounds satisfies the above range, low-temperature output of the battery and high-temperature storage characteristics and high-temperature life characteristics can be effectively improved while suppressing side reactions.

[0119] Examples of the above halogen-substituted carbonate compounds include fluoroethylene carbonate (FEC).

[0120] The above sulfonate compound may include at least one compound selected from the group consisting of 1,3-propane sulfonate (PS), 1,4-butane sulfonate, ethene sulfonate, 1,3-propene sulfonate (PRS), 1,4-butene sulfonate, and 1-methyl-1,3-propene sulfonate, and preferably may include 1,3-propane sulfonate (PS). The above sulfonate compound forms a stable SEI film by a reduction reaction on the surface of the cathode, thereby preventing side reactions between the cathode and the electrolyte at high temperatures, suppressing gas generation, and enabling increased durability during high-temperature storage. Such a sulfonate compound may be included in an amount of 1.0% to 10% by weight, specifically 1.0% to 5.0% by weight, of the total weight of the non-aqueous electrolyte. When the content of the above sulfonate compound satisfies the above range, a robust film is formed on the surfaces of the anode and cathode, which can effectively prevent deterioration of the anode and cathode during high-voltage charging and high-temperature storage.

[0121] Examples of the above sulfate-based compounds include ethylene sulfate (Esa), trimethylene sulfate (TMS), or methyl trimethylene sulfate (MTMS). The above sulfate-based compounds may be included in an amount of 0.01 to 10 weight%, specifically 0.05 to 5.0 weight%, of the total weight of the non-aqueous electrolyte. If the content of the above sulfate-based compounds satisfies the above range, side reactions within the electrolyte during charging and discharging of the battery are suppressed, and a robust SEI film is formed, thereby achieving an effect of improving excellent lifespan characteristics.

[0122] The above phosphate-based compound may be one or more compounds selected from the group consisting of lithium difluoro(bisoxalato)phosphate, lithium difluorophosphate, tris(trimethylsilyl)phosphate, tris(2,2,2-trifluoroethyl)phosphate, and tris(trifluoroethyl)phosphate. The above phosphate-based compound may be included in an amount of 0.01 to 10 weight%, specifically 0.05 to 5.0 weight%, based on the total weight of the non-aqueous electrolyte. When the content of the above phosphate-based compound satisfies the above range, a robust SEI film is formed, thereby achieving the effect of improving low-temperature output, high-temperature storage characteristics, and high-temperature life characteristics of the battery.

[0123] The above borate-based compound may include tetraphenylborate, lithium difluoro(oxalato)borate (LIODFB), or lithium bisoxalatoborate (LiB(C2O4)2; LiBOB), and preferably may include lithium difluoro(oxalato)borate. The above borate-based compound may be included in an amount of 1.0% to 10% by weight, specifically 1.0% to 5.0% by weight, of the total weight of the non-aqueous electrolyte. When the content of the above borate-based compound satisfies the above range, it is possible to effectively prevent deterioration of the anode and cathode during high-voltage charging and high-temperature storage by forming a robust film on the surfaces of the anode and cathode while preventing side reactions within the electrolyte.

[0124] The above nitrile-based compound may be at least one compound selected from the group consisting of succinonitrile, adiponitrile, acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanitrile, cyclopentane carbonitrile, cyclohexane carbonitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile. The above nitrile-based compound may be included in an amount of 1.0% to 10% by weight, specifically 1.0% to 5.0% by weight, of the total weight of the non-aqueous electrolyte. When the content of the above nitrile-based compound satisfies the above range, a stable film is formed on the surfaces of the cathode and anode to suppress gas generation caused by side reactions between the anode and the electrolyte, and to effectively suppress the leaching of metal foreign substances.

[0125] The above benzene-based compound may be fluorobenzene, and the above amine-based compound may be triethanolamine or ethylenediamine, etc. The above benzene-based compound may be included in an amount of 0.01 to 10 weight%, specifically 0.05 to 5.0 weight%, based on the total weight of the non-aqueous electrolyte.

[0126] Tetravinylsilane may be an example of the above silane compound. The above silane compound may be included in an amount of 0.01 to 10 weight%, specifically 0.05 to 5.0 weight%, based on the total weight of the non-aqueous electrolyte.

[0127] The above lithium salt-based compound is a compound different from the lithium salt included in the electrolyte, and may include one or more compounds selected from the group consisting of LiPO2F2, LiODFB, LiBOB (lithium bisoxalate toborate (LiB(C2O4)2)) and LiBF4.

[0128] Among these auxiliary additives, if vinylene carbonate, vinylethylene carbonate, or succinonitrile is included, a more robust SEI film can be formed on the negative electrode surface during the initial activation process of the secondary battery.

[0129] Meanwhile, the above auxiliary additives may be used in a mixture of two or more types and may be included in an amount of 30% by weight or less, specifically 0.01 to 10.0% by weight, based on the total weight of the electrolyte, and preferably 0.05 to 5.0% by weight. If the content of the above auxiliary additive is less than 0.01% by weight, the effect of improving low-temperature output, high-temperature storage characteristics, and high-temperature life characteristics of the battery is negligible, and if the content of the above auxiliary additive exceeds 30% by weight, there is a possibility that excessive side reactions may occur within the electrolyte during charging and discharging of the battery. In particular, when the above SEI film-forming additives are added in excess, they may not decompose sufficiently at high temperatures and may remain as unreacted substances or precipitated within the electrolyte at room temperature. Accordingly, side reactions that degrade the lifespan or resistance characteristics of the secondary battery may occur.

[0130]

[0131] lithium secondary battery

[0132] In addition, another embodiment of the present invention provides a lithium secondary battery comprising: a positive electrode; a negative electrode facing the positive electrode; a separator interposed between the negative electrode and the positive electrode; and the aforementioned non-aqueous electrolyte.

[0133] The lithium secondary battery of the present invention can be manufactured by forming an electrode assembly in which a positive electrode, a separator, and a negative electrode are sequentially stacked, housing this in a battery case, and then introducing the electrolyte of the present invention. The method for manufacturing the lithium secondary battery of the present invention can be manufactured and applied according to conventional methods known in the art.

[0134] As the non-aqueous electrolyte has been described above, the anode, cathode, and separator will be described below.

[0135]

[0136] (1) positive electrode

[0137] The anode according to the present invention may include an anode active material.

[0138] The above-mentioned cathode active material is a compound capable of reversible intercalation and deintercalation, and is not particularly limited as long as it is a cathode active material used in the field; specifically, it may include a lithium metal composite oxide. More specifically, the lithium metal composite oxide is a layered compound such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; lithium iron oxide such as LiFe3O4; lithium iron phosphate such as LiFePO4; and a compound with the chemical formula Li 1+c1 Mn 2-c1 Lithium manganese oxides such as O4 (0≤c1≤0.33), LiMnO3, LiMn2O3, LiMnO2, etc.; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, Cu2V2O7, etc.; chemical formula LiNi 1-c2 M c2 Ni-site type lithium nickel oxide represented by O2 (wherein M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, satisfying 0.01≤c2≤0.3); chemical formula LiMn 2-c3 M c3 Lithium manganese composite oxides represented by O2 (wherein M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn and Ta, satisfying 0.01≤c3≤0.1) or Li2Mn3MO8 (wherein M is at least one selected from the group consisting of Fe, Co, Ni, Cu and Zn); etc., but are not limited to these.

[0139] Specifically, the lithium metal composite oxide may include at least one selected from the group consisting of lithium cobalt oxide (LiCoO2), lithium nickel-cobalt-manganese oxide, lithium-manganese-rich oxide, and lithium iron phosphate.

[0140] More specifically, the lithium nickel-cobalt-manganese oxide can be represented by the following chemical formula P-1.

[0141] [Chemical Formula P-1]

[0142] Li 1+a Ni x Co y M 1 z M 2 w O2

[0143] In the above chemical formula P-1,

[0144] M 1 is Mn, Al, or a combination thereof, and

[0145] M 2 is at least one selected from the group consisting of Al, Zr, W, Ti, Mg, Ca, and Sr, and 0≤a≤0.5, 0.55 <x<1.0, 0<y≤0.4, 0<z≤0.4, 0≤w≤0.1 이다. 이때, x+y+z+w는 1일 수 있다.

[0146] In the above chemical formula P-1, 1+a represents the molar ratio of lithium in the lithium nickel-cobalt-manganese composite oxide, and may be 0≤a≤0.5, preferably 0≤a≤0.2, more preferably 0≤a≤0.1.

[0147] In the above chemical formula P-1, x represents the molar ratio of nickel among the total transition metals excluding lithium in the lithium nickel-cobalt-manganese composite oxide, 0.55 <x<1.0, 더욱 구체적으로는 0.6≤x≤0.98, 보다 더 구체적으로는 0.7≤x≤0.98일 수 있다.

[0148] In the above chemical formula P-1, y represents the molar ratio of cobalt among the total transition metals excluding lithium in the lithium nickel-cobalt-manganese composite oxide, where 0 <y≤0.4, 구체적으로 0<y≤0.3, 더욱 구체적으로는 0.05≤y≤0.3일 수 있다.

[0149] In the above chemical formula P-1, z is M among the total transition metals excluding lithium in the lithium nickel-cobalt-manganese composite oxide. 1 Representing the molar ratio of elements, 0 <z≤0.4, 바람직하게는 0<z≤0.3, 더 바람직하게는 0.01≤z≤0.3일 수 있다.

[0150] In the above chemical formula P-1, w is M among the total transition metals excluding lithium in the lithium nickel-cobalt-manganese composite oxide. 2 Representing the molar ratio of elements, 0 <w≤0.1, 바람직하게는 0<w≤0.05, 더 바람직하게는 0<w≤0.02이다.

[0151] The above lithium nickel-cobalt-manganese oxide is Li(Ni with a Ni content of 0.55 atm% or more to realize a high-capacity battery. 0.6 Mn 0.2 Co 0.2 )O2, Li(Ni) 0.7 Mn 0.15 Co 0.15 )O2, Li(Ni 0.7 Mn 0.2 Co 0.1 )O2, Li(Ni 0.8 Mn 0.1 Co 0.1 )O2, Li(Ni 0.8 Co 0.15 Al 0.05 )O2, Li(Ni 0.86 Mn 0.07 Co 0.05 Al 0.02 )O2, Li(Ni 0.90 Mn 0.05 Co 0.05 )O2 or Li(Ni 0.9 Mn 0.03 Co 0.06 Al0.01 It can be )O2).

[0152] Meanwhile, the above-mentioned positive active material may be in the form of particles. Specifically, the average particle size (D) of the above-mentioned positive active material. 50 ) can be 1㎛ to 30㎛.

[0153]

[0154] The above positive electrode may include a positive current collector; and a positive active material layer disposed on at least one surface of the positive current collector. In this case, the positive active material layer may include the aforementioned positive active material.

[0155] Various positive current collectors used in the relevant technical field may be used as the positive current collector. For example, the positive current collector may be stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface treated with carbon, nickel, titanium, silver, etc.

[0156] The thickness of the anode current collector can typically be 3 to 500 μm, and fine irregularities can be formed on the surface of the anode current collector to increase the adhesion of the anode active material. The anode current collector can be used in various forms, such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0157] The positive active material layer is disposed on at least one surface of the positive current collector. Specifically, the positive active material layer may be disposed on one or both surfaces of the positive current collector.

[0158] The above-mentioned positive active material may be included in the positive active material layer in an amount of 70% to 99% by weight, specifically 80% to 98% by weight, taking into consideration the sufficient capacity exertion of the positive active material.

[0159] The thickness of the above positive active material layer may be 5㎛ to 500㎛, preferably 20㎛ to 200㎛.

[0160] In addition, the positive active material layer may further include a conductive material and / or a binder together with the aforementioned positive active material.

[0161] The above conductive material is used to impart conductivity to the electrode, and in the battery being constructed, it may be used without special restrictions as long as it has electronic conductivity without causing chemical changes. Specific examples of the above conductive material include carbon black such as acetylene black (or Denka black), Ketjen black, channel black, furnace black, lamp black, or thermal black; graphite powder such as natural graphite, artificial graphite, or graphite with a highly developed crystal structure; conductive fibers such as carbon fibers or metal fibers; conductive powders such as carbon fluoride powder, aluminum powder, or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; polyphenylene derivatives, etc., and one of these alone or a mixture of two or more may be used.

[0162] The conductive material may be included in the anode composite layer in an amount of 0.1 to 10.0 weight%, preferably 0.1 to 5.0 weight%, based on the total weight of the anode composite layer.

[0163] Next, the binder serves to improve adhesion between positive active material particles and adhesion between the positive active material and the current collector. Examples of such binders include fluoropolymer-based binders comprising polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE); rubber-based binders comprising styrene butadiene rubber (SBR), acrylonitrile-butadiene rubber, or styrene-isoprene rubber; cellulose-based binders comprising carboxyl methyl cellulose (CMC), starch, hydroxypropyl cellulose, or regenerated cellulose; polyalcohol-based binders comprising polyvinyl alcohol; polyolefin-based binders comprising polyethylene or polypropylene; polyimide-based binders; and polyester-based binders. One type of silane binder alone or a mixture of two or more types may be used.

[0164] The above binder may be included in the anode composite layer in an amount of 0.1 to 15.0 weight%, preferably 0.1 to 10.0 weight%, based on the total weight of the anode composite layer.

[0165]

[0166] (2) Negative electrode

[0167] The present invention may include a cathode opposite to a positive electrode.

[0168] The above cathode may include a cathode active material.

[0169] The above negative electrode active material may include a silicon-based active material.

[0170] Representative examples of such silicon-based negative electrode active materials include metallic silicon (Si) and silicon oxide (SiO₂). x, where 0≤x<2) may include one or more selected from the group consisting of silicon carbide (SiC) and Si-Y alloy (where Y is an element selected from the group consisting of alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, transition metals, rare earth elements, and combinations thereof, and is not Si), and specifically SiO x It may include at least one selected from the group consisting of compounds represented by (0≤x<2) and silicon-carbon composites. Since the silicon-based active material is SiO2 and therefore cannot store lithium, it is preferable that x be within the above range, and more preferably, the silicon-based active material may be SiO.

[0171] The above element Y may be selected from the group consisting of Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db (dubnium), Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ti, Ge, P, As, Sb, Bi, S, Se, Te, Po, and combinations thereof.

[0172] Average particle size (D) of the above silicon-based active material 50 ) can be 1㎛ to 30㎛, preferably 2㎛ to 15㎛, in terms of reducing adverse reactions with the electrolyte while ensuring structural stability during charging and discharging.

[0173]

[0174] In addition, the cathode may additionally include a carbon-based active material as needed. The carbon-based active material may include at least one selected from the group consisting of graphite, hard carbon, soft carbon, carbon black, graphene, and fibrous carbon, and preferably may include graphite. The graphite may be, for example, at least one of artificial graphite and natural graphite.

[0175] Average particle size (D of the above carbon-based active material) 50 ) can be 10㎛ to 30㎛, preferably 15㎛ to 25㎛, in terms of ensuring structural stability during charging and discharging and reducing adverse reactions with the electrolyte.

[0176] When the cathode of the present invention includes a carbon-based active material together with a silicon-based cathode active material, the weight ratio of the silicon-based active material to the carbon-based active material may be 1:99 to 30:70, specifically 3:97 to 15:85. When the mixing ratio of the silicon-based active material and the carbon-based active material satisfies the above range, excellent cycle performance can be secured by suppressing the volume expansion of the silicon-based active material while improving capacity characteristics.

[0177]

[0178] The above cathode may include a cathode current collector; and a cathode active material layer disposed on at least one surface of the cathode current collector. In this case, the cathode active material layer may include the aforementioned cathode active material.

[0179] As the above-mentioned negative current collector, negative current collectors generally used in the relevant technical field may be used, for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy may be used. The above-mentioned negative current collector may typically have a thickness of 3 to 500 μm, and, similar to the anode current collector, fine irregularities may be formed on the surface of the current collector to strengthen the bonding strength of the negative active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0180] The above-mentioned 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.

[0181] The thickness of the above negative electrode active material layer may be 5㎛ to 500㎛, preferably 5㎛ to 100㎛.

[0182] The above negative electrode active material may be included in the negative electrode active material layer in an amount of 60% to 99% by weight to minimize the effect of volume expansion / contraction on the battery while sufficiently expressing capacity in the secondary battery.

[0183]

[0184] The above cathode active material layer may further include a conductive material and / or a binder together with the cathode active material.

[0185] The above conductive material is a component for further improving the conductivity of the negative electrode active material, and may be added in an amount of 10% by weight or less, preferably 5% by weight or less, specifically 0.1% to 5% by weight, based on the total weight of the negative electrode active material layer. Such conductive material is not particularly limited as long as it is conductive without causing chemical changes in the battery, and for example, carbon black such as acetylene black (or Denka black), Ketjen black, channel black, furnace black, lamp black, or thermal black; graphite powder such as natural graphite, artificial graphite, or graphite with a highly developed crystal structure; conductive fibers such as carbon fibers or metal fibers; conductive powders such as carbon fluoride powder, aluminum powder, nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; polyphenylene derivatives, etc. may be used.

[0186] The above binder is a component that assists in the bonding between a conductive material, an active material, and a current collector, and specific examples include a fluoropolymer-based binder comprising polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE); a rubber-based binder comprising styrene butadiene rubber (SBR), acrylonitrile-butadiene rubber, or styrene-isoprene rubber; a cellulose-based binder comprising carboxyl methyl cellulose (CMC), starch, hydroxypropyl cellulose, or regenerated cellulose; a polyalcohol-based binder comprising polyvinyl alcohol; a polyolefin-based binder comprising polyethylene or polypropylene; a polyimide-based binder; a polyester-based binder; and a silane-based binder.

[0187] The above binder may be included in an amount of 0.1 to 15.0 weight%, preferably 0.1 to 10.0 weight%, based on the total weight of the negative electrode active material layer.

[0188]

[0189] (3) Separator

[0190] The above separator separates the negative and positive electrodes and provides a pathway for the movement of lithium ions. It can be used without any specific restrictions as long as it is a separator typically used in lithium secondary batteries, and it is particularly desirable that it has low resistance to the movement of lithium salt ions while having excellent electrolyte moisture retention capacity.

[0191] Specifically, as a separator, a porous polymer film made of a polyolefin-based polymer such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof may be used. In addition, a conventional porous nonwoven fabric, such as a nonwoven fabric made of high-melting-point glass fiber or polyethylene terephthalate fiber, may be used. Furthermore, a coated separator containing a ceramic component or a polymer material may be used to ensure heat resistance or mechanical strength, and may optionally be used in a single-layer or multi-layer structure.

[0192]

[0193] The lithium secondary battery according to the present invention as described above can be usefully applied in portable devices such as mobile phones, laptop computers, and digital cameras, as well as in the field of electric vehicles such as hybrid electric vehicles (HEVs).

[0194] The external shape of the lithium secondary battery of the present invention is not particularly limited, but can be a cylindrical shape using a can, a prismatic shape, a pouch shape, or a coin shape.

[0195] The lithium secondary battery according to the present invention can be used not only as a battery cell used as a power source for a small device, but can also preferably be used as a unit cell in a medium-to-large battery module comprising a plurality of battery cells.

[0196]

[0197] Hereinafter, the present invention will be described in detail with reference to examples in order to specifically explain the invention. However, the embodiments according to the present invention may be modified in various different forms, and the scope of the present invention should not be interpreted as being limited to the embodiments described below. The embodiments of the present invention are provided to more completely explain the invention to those with average knowledge in the art.

[0198]

[0199] Examples

[0200] Example 1.

[0201] (Preparation of non-aqueous electrolytes)

[0202] A non-aqueous electrolyte for a lithium secondary battery was prepared by dissolving LiPF6 in ethylene carbonate (EC) to a concentration of 1.0 M, and then adding a compound represented by Formula 1A, a compound represented by Formula 2A, and vinylene carbonate (VC) as additives. The compound represented by Formula 1A, the compound represented by Formula 2A, and vinylene carbonate (VC) were included in the non-aqueous electrolyte for a lithium secondary battery at concentrations of 2 wt%, 6 wt%, and 0.5 wt%, respectively. Additionally, the weight ratio of the compound of Formula 1A and the compound of Formula 2A may be 25:75.

[0203] (Secondary battery manufacturing)

[0204] Anode active material (Li(Ni) in solvent N-methyl-2-pyrrolidone (NMP) 0.8 Mn 0.1 Co 0.1An anode slurry (solid content 60.0 wt%) was prepared by adding O2), a conductive material (carbon black), and a binder (polyvinylidene fluoride) in a weight ratio of 97.6:0.8:1.6. The anode slurry was applied to an anode current collector (Al thin film) with a thickness of 13.5 μm and dried, then a roll press was performed to produce an anode.

[0205] A cathode slurry (solid content: 60 wt%) was prepared by adding a cathode active material (Si), a binder (SBR-CMC), and a conductive material (carbon black) to water, a solvent, in a weight ratio of 97.6:0.8:1.6. The cathode slurry was applied to a 6 μm thick copper (Cu) thin film serving as a cathode current collector, dried, and then subjected to a roll press to manufacture the cathode.

[0206] An electrode assembly was manufactured by interposing a porous polypropylene separator between the anode and cathode manufactured above, then housing it in a battery case, and a lithium secondary battery was manufactured by injecting the non-aqueous electrolyte manufactured above.

[0207]

[0208] Example 2.

[0209] (Preparation of non-aqueous electrolytes)

[0210] A non-aqueous electrolyte for a lithium secondary battery was prepared by dissolving LiPF6 in ethylene carbonate (EC) to a concentration of 1.0 M, and then adding a compound represented by Formula 1A, a compound represented by Formula 2A, and vinylene carbonate (VC) as additives. The compound represented by Formula 1A, the compound represented by Formula 2A, and vinylene carbonate (VC) were included in the non-aqueous electrolyte for a lithium secondary battery at concentrations of 2.5 wt%, 7.5 wt%, and 0.5 wt%, respectively. Additionally, the weight ratio of the compound of Formula 1A and the compound of Formula 2A may be 25:75.

[0211] (Secondary battery manufacturing)

[0212] A lithium secondary battery was manufactured in the same manner as in Example 1, except that the above-manufactured non-aqueous electrolyte was injected.

[0213]

[0214] Example 3.

[0215] (Preparation of non-aqueous electrolytes)

[0216] A non-aqueous electrolyte for a lithium secondary battery was prepared by dissolving LiPF6 in ethylene carbonate (EC) to a concentration of 1.0 M, and then adding a compound represented by Formula 1A, a compound represented by Formula 2A, and vinylene carbonate (VC) as additives. The compound represented by Formula 1A, the compound represented by Formula 2A, and vinylene carbonate (VC) were included in the non-aqueous electrolyte for a lithium secondary battery at concentrations of 3.75 wt%, 11.25 wt%, and 0.5 wt%, respectively. Additionally, the weight ratio of the compound of Formula 1A and the compound of Formula 2A may be 25:75.

[0217] (Secondary battery manufacturing)

[0218] A lithium secondary battery was manufactured in the same manner as in Example 1, except that the above-manufactured non-aqueous electrolyte was injected.

[0219]

[0220] Example 4.

[0221] (Preparation of non-aqueous electrolytes)

[0222] A non-aqueous electrolyte for a lithium secondary battery was prepared by dissolving LiPF6 in ethylene carbonate (EC) to a concentration of 1.0 M, and then adding a compound represented by Formula 1A, a compound represented by Formula 2A, and vinylene carbonate (VC) as additives. The compound represented by Formula 1A, the compound represented by Formula 2A, and vinylene carbonate (VC) were included in the non-aqueous electrolyte for a lithium secondary battery at concentrations of 5 wt%, 15 wt%, and 0.5 wt%, respectively. Additionally, the weight ratio of the compound of Formula 1A and the compound of Formula 2A may be 25:75.

[0223] (Secondary battery manufacturing)

[0224] A lithium secondary battery was manufactured in the same manner as in Example 1, except that the above-manufactured non-aqueous electrolyte was injected.

[0225]

[0226] Example 5.

[0227] (Preparation of non-aqueous electrolytes)

[0228] A non-aqueous electrolyte for a lithium secondary battery was prepared by dissolving LiPF6 in ethylene carbonate (EC) to a concentration of 1.0 M, and then adding a compound represented by Formula 1A, a compound represented by Formula 2B, and vinylene carbonate (VC) as additives. The compound represented by Formula 1A, the compound represented by Formula 2B, and vinylene carbonate (VC) were included in the non-aqueous electrolyte for a lithium secondary battery at concentrations of 2 wt%, 6 wt%, and 0.5 wt%, respectively. Additionally, the weight ratio of the compound of Formula 1A and the compound of Formula 2B may be 25:75.

[0229] (Secondary battery manufacturing)

[0230] A lithium secondary battery was manufactured in the same manner as in Example 1, except that the above-manufactured non-aqueous electrolyte was injected.

[0231]

[0232] Example 6.

[0233] (Preparation of non-aqueous electrolytes)

[0234] A non-aqueous electrolyte for a lithium secondary battery was prepared by dissolving LiPF6 in ethylene carbonate (EC) to a concentration of 1.0 M, and then adding a compound represented by Formula 1A, a compound represented by Formula 2C, and vinylene carbonate (VC) as additives. The compound represented by Formula 1A, the compound represented by Formula 2C, and vinylene carbonate (VC) were included in the non-aqueous electrolyte for a lithium secondary battery at concentrations of 2 wt%, 6 wt%, and 0.5 wt%, respectively. Additionally, the weight ratio of the compound of Formula 1A and the compound of Formula 2C may be 25:75.

[0235] (Secondary battery manufacturing)

[0236] A lithium secondary battery was manufactured in the same manner as in Example 1, except that the above-manufactured non-aqueous electrolyte was injected.

[0237]

[0238] Example 7.

[0239] (Preparation of non-aqueous electrolytes)

[0240] A non-aqueous electrolyte for a lithium secondary battery was prepared by dissolving LiPF6 in ethylene carbonate (EC) to a concentration of 1.0 M, and then adding a compound represented by Formula 1B, a compound represented by Formula 2A, and vinylene carbonate (VC) as additives. The compound represented by Formula 1B, the compound represented by Formula 2A, and vinylene carbonate (VC) were included in the non-aqueous electrolyte for a lithium secondary battery at concentrations of 2 wt%, 6 wt%, and 0.5 wt%, respectively. Additionally, the weight ratio of the compound of Formula 1B and the compound of Formula 2A may be 25:75.

[0241] (Secondary battery manufacturing)

[0242] A lithium secondary battery was manufactured in the same manner as in Example 1, except that the above-manufactured non-aqueous electrolyte was injected.

[0243]

[0244] Example 8.

[0245] (Preparation of non-aqueous electrolytes)

[0246] A non-aqueous electrolyte for a lithium secondary battery was prepared by dissolving LiPF6 in ethylene carbonate (EC) to a concentration of 1.0 M, and then adding a compound represented by Formula 1C, a compound represented by Formula 2A, and vinylene carbonate (VC) as additives. The compound represented by Formula 1C, the compound represented by Formula 2A, and vinylene carbonate (VC) were included in the non-aqueous electrolyte for a lithium secondary battery at concentrations of 2 wt%, 6 wt%, and 0.5 wt%, respectively. Additionally, the weight ratio of the compound of Formula 1C and the compound of Formula 2A may be 25:75.

[0247] (Secondary battery manufacturing)

[0248] A lithium secondary battery was manufactured in the same manner as in Example 1, except that the above-manufactured non-aqueous electrolyte was injected.

[0249]

[0250] Example 9.

[0251] (Preparation of non-aqueous electrolytes)

[0252] A non-aqueous electrolyte for a lithium secondary battery was prepared by dissolving LiPF6 in ethylene carbonate (EC) to a concentration of 1.0 M, and then adding a compound represented by Formula 1B, a compound represented by Formula 2B, and vinylene carbonate (VC) as additives. The compound represented by Formula 1B, the compound represented by Formula 2B, and vinylene carbonate (VC) were included in the non-aqueous electrolyte for a lithium secondary battery at concentrations of 2 wt%, 6 wt%, and 0.5 wt%, respectively. Additionally, the weight ratio of the compound of Formula 1B and the compound of Formula 2B may be 25:75.

[0253] (Secondary battery manufacturing)

[0254] A lithium secondary battery was manufactured in the same manner as in Example 1, except that the above-manufactured non-aqueous electrolyte was injected.

[0255]

[0256] Example 10.

[0257] (Preparation of non-aqueous electrolytes)

[0258] A non-aqueous electrolyte for a lithium secondary battery was prepared by dissolving LiPF6 in ethylene carbonate (EC) to a concentration of 1.0 M, and then adding a compound represented by Formula 1A, a compound represented by Formula 2A, and vinylene carbonate (VC) as additives. The compound represented by Formula 1A, the compound represented by Formula 2A, and vinylene carbonate (VC) were included in the non-aqueous electrolyte for a lithium secondary battery at concentrations of 0.8 wt%, 7.2 wt%, and 0.5 wt%, respectively. Additionally, the weight ratio of the compound of Formula 1A and the compound of Formula 2A may be 10:90.

[0259] (Secondary battery manufacturing)

[0260] A lithium secondary battery was manufactured in the same manner as in Example 1, except that the above-manufactured non-aqueous electrolyte was injected.

[0261]

[0262] Example 11.

[0263] (Preparation of non-aqueous electrolytes)

[0264] A non-aqueous electrolyte for a lithium secondary battery was prepared by dissolving LiPF6 in ethylene carbonate (EC) to a concentration of 1.0 M, and then adding a compound represented by Formula 1A, a compound represented by Formula 2A, and vinylene carbonate (VC) as additives. The compound represented by Formula 1A, the compound represented by Formula 2A, and vinylene carbonate (VC) were included in the non-aqueous electrolyte for a lithium secondary battery at concentrations of 3.2 wt%, 4.8 wt%, and 0.5 wt%, respectively. Additionally, the weight ratio of the compound of Formula 1A and the compound of Formula 2A may be 40:60.

[0265] (Secondary battery manufacturing)

[0266] A lithium secondary battery was manufactured in the same manner as in Example 1, except that the above-manufactured non-aqueous electrolyte was injected.

[0267]

[0268] Comparative Example 1.

[0269] (Preparation of non-aqueous electrolytes)

[0270] A non-aqueous electrolyte for a lithium secondary battery was prepared by dissolving LiPF6 in ethylene carbonate (EC) to a concentration of 1.0 M, and then adding a compound represented by Formula 1A, a compound represented by Formula 2A, and vinylene carbonate (VC) as additives. The compound represented by Formula 1A, the compound represented by Formula 2A, and vinylene carbonate (VC) were included in the non-aqueous electrolyte for a lithium secondary battery at 4 wt%, A wt%, and 0.5 wt%, respectively. Additionally, the weight ratio of the compound of Formula 1A and the compound of Formula 2A may be 50:50.

[0271] (Secondary battery manufacturing)

[0272] A lithium secondary battery was manufactured in the same manner as in Example 1, except that the above-manufactured non-aqueous electrolyte was injected.

[0273]

[0274] Comparative Example 2.

[0275] (Preparation of non-aqueous electrolytes)

[0276] A non-aqueous electrolyte for a lithium secondary battery was prepared by dissolving LiPF6 in ethylene carbonate (EC) to a concentration of 1.0 M, and then adding vinylene carbonate (VC) as an additive. The vinylene carbonate (VC) was included in the non-aqueous electrolyte for a lithium secondary battery at a concentration of 0.5 wt%.

[0277] (Secondary battery manufacturing)

[0278] A lithium secondary battery was manufactured in the same manner as in Example 1, except that the above-manufactured non-aqueous electrolyte was injected.

[0279]

[0280] Comparative Example 3.

[0281] (Preparation of non-aqueous electrolytes)

[0282] A non-aqueous electrolyte for a lithium secondary battery was prepared by dissolving LiPF6 in ethylene carbonate (EC) to a concentration of 1.0 M, and then adding a compound represented by Formula 1A, a compound represented by Formula 2A, and vinylene carbonate (VC) as additives. The compound represented by Formula 1A, the compound represented by Formula 2A, and vinylene carbonate (VC) were included in the non-aqueous electrolyte for a lithium secondary battery at concentrations of 1.5 wt%, 4.5 wt%, and 0.5 wt%, respectively. Additionally, the weight ratio of the compound of Formula 1A and the compound of Formula 2A may be 25:75.

[0283] (Secondary battery manufacturing)

[0284] A lithium secondary battery was manufactured in the same manner as Comparative Example 1, except that the above-manufactured non-aqueous electrolyte was injected.

[0285]

[0286] Comparative Example 4.

[0287] (Preparation of non-aqueous electrolytes)

[0288] A non-aqueous electrolyte for a lithium secondary battery was prepared by dissolving LiPF6 in ethylene carbonate (EC) to a concentration of 1.0 M, and then adding a compound represented by Formula 1A, a compound represented by Formula 2A, and vinylene carbonate (VC) as additives. The compound represented by Formula 1A, the compound represented by Formula 2A, and vinylene carbonate (VC) were included in the non-aqueous electrolyte for a lithium secondary battery at concentrations of 5.5 wt%, 16.5 wt%, and 0.5 wt%, respectively. Additionally, the weight ratio of the compound of Formula 1A and the compound of Formula 2A may be 25:75.

[0289] (Secondary battery manufacturing)

[0290] A lithium secondary battery was manufactured in the same manner as Comparative Example 2, except that the above-mentioned non-aqueous electrolyte was injected.

[0291]

[0292] Comparative Example 5.

[0293] (Preparation of non-aqueous electrolytes)

[0294] A non-aqueous electrolyte for a lithium secondary battery was prepared by dissolving LiPF6 in ethylene carbonate (EC) to a concentration of 1.0 M, and then adding a compound represented by Chemical Formula 1A and vinylene carbonate (VC) as additives. The compound represented by Chemical Formula 1A and vinylene carbonate (VC) were included in the non-aqueous electrolyte for a lithium secondary battery at 8 wt% and 0.5 wt%, respectively.

[0295] (Secondary battery manufacturing)

[0296] A lithium secondary battery was manufactured in the same manner as in Example 1, except that the above-manufactured non-aqueous electrolyte was injected.

[0297]

[0298] Comparative Example 6.

[0299] (Preparation of non-aqueous electrolytes)

[0300] A non-aqueous electrolyte for a lithium secondary battery was prepared by dissolving LiPF6 in ethylene carbonate (EC) to a concentration of 1.0 M, and then adding a compound represented by Chemical Formula 2A and vinylene carbonate (VC) as additives. The compound represented by Chemical Formula 2A and vinylene carbonate (VC) were included in the non-aqueous electrolyte for a lithium secondary battery at 8 wt% and 0.5 wt%, respectively.

[0301] (Secondary battery manufacturing)

[0302] A lithium secondary battery was manufactured in the same manner as in Example 1, except that the above-manufactured non-aqueous electrolyte was injected.

[0303]

[0304] Comparative Example 7.

[0305] (Preparation of non-aqueous electrolytes)

[0306] A non-aqueous electrolyte for a lithium secondary battery was prepared by dissolving LiPF6 in ethylene carbonate (EC) to a concentration of 1.0 M, and then adding difluoroacetonitrile, a compound represented by Formula 2A, and vinylene carbonate (VC) as additives. The difluoroacetonitrile, the compound represented by Formula 2A, and vinylene carbonate (VC) were included in the non-aqueous electrolyte for a lithium secondary battery at concentrations of 2 wt%, 6 wt%, and 0.5 wt%, respectively. Additionally, the weight ratio of the difluoroacetonitrile and the compound of Formula 2A may be 25:75.

[0307] (Secondary battery manufacturing)

[0308] A lithium secondary battery was manufactured in the same manner as in Example 1, except that the above-manufactured non-aqueous electrolyte was injected.

[0309]

[0310] Comparative Example 8.

[0311] (Preparation of non-aqueous electrolytes)

[0312] A non-aqueous electrolyte for a lithium secondary battery was prepared by dissolving LiPF6 in ethylene carbonate (EC) to a concentration of 1.0 M, and then adding a compound represented by Formula 1A, a compound represented by Formula 2A, and vinylene carbonate (VC) as additives. The compound represented by Formula 1A, the compound represented by Formula 2A, and vinylene carbonate (VC) were included in the non-aqueous electrolyte for a lithium secondary battery at concentrations of 0.56 wt%, 7.44 wt%, and 0.5 wt%, respectively. Additionally, the weight ratio of the compound of Formula 1A and the compound of Formula 2A may be 7:93.

[0313] (Secondary battery manufacturing)

[0314] A lithium secondary battery was manufactured in the same manner as in Example 1, except that the above-manufactured non-aqueous electrolyte was injected.

[0315]

[0316] Experimental Example

[0317] Experimental Example 1. Evaluation of High-Temperature Storage Characteristics

[0318] For the lithium secondary batteries prepared in the examples and comparative examples, respectively, a formation process was performed by charging at a rate of 0.1C for 3 hours, and then the batteries were fully charged to 100% SOC by charging under constant current / constant voltage conditions (0.05C cut-off) at a rate of 0.33C at 25℃ up to 4.2V, and stored at a high temperature (60℃) for 8 weeks. Afterward, the batteries were transferred to a charge / discharger at room temperature (25℃) to measure the resistance, and the resistance increase rate was calculated using Equation 1 below, and the results are shown in Table 1 below.

[0319] [Equation 1]

[0320] Resistance increase rate (%) = {(Resistance after high-temperature storage - Initial resistance) / Initial resistance} × 100

[0321]

[0322] Experimental Example 2. Evaluation of High-Temperature Cycle Characteristics

[0323] For each lithium secondary battery prepared in the examples and comparative examples, a formation process was performed by charging at a rate of 0.1C for 3 hours, and then the battery was fully charged to 100% SOC by charging under constant current / constant voltage conditions (0.05C cut-off) at a rate of 0.33C at 25℃ to 4.2V. Each fully charged secondary battery was charged at 45℃ under constant current / constant voltage conditions at a rate of 0.33C to 4.2V, and discharged under constant current conditions at a rate of 0.33C to 2.8V, with 300 cycles performed, with 300 cycles defined as one cycle. The capacity retention rate after 300 cycles was calculated using Equation 2 below, and the results are shown in Table 1 below.

[0324] [Equation 2]

[0325] Capacity Retention Rate (%) = (Capacity after 300 cycles / Capacity after 1 cycle) × 100

[0326]

[0327] Experimental Example 3. Evaluation of High-Temperature Storage Characteristics

[0328] For each lithium secondary battery prepared in the examples and comparative examples, a formation process was performed by charging at a rate of 0.1C for 3 hours, and then the battery was fully charged to 100% SOC by charging under constant current / constant voltage conditions (0.05C cut-off) at a rate of 0.33C at 25℃ up to 4.2V, and then the volume of the secondary battery was measured and set as the initial secondary battery volume.

[0329] Then, the fully charged battery was stored at a high temperature (60℃) for 8 weeks, and the volume of the stored secondary battery was measured again to calculate the increase in volume during the 8-week storage period.

[0330] The ratio of the increased volume to the initial volume of the secondary battery was calculated using Equation 3 below to derive the volume increase rate after 8 weeks, and the results are shown in Table 1 below.

[0331] [Equation 3]

[0332] Volume increase rate (%) = {(Volume after 8 weeks of high-temperature storage - Initial volume) / Initial volume} × 100

[0333] Resistance Increase Rate (%) Capacitance Retention Rate (%) Volume Increase Rate (%) Example 1 6.49 1.6 7.2 Example 2 10.58 5.3 11.6 Example 3 14.28 3.5 12.4 Example 4 16.78 1.2 13.1 Example 5 8.38 9.09.3 Example 6 8.98 8.2 9.9 Example 76.99 0.1 7.7 Example 8 7.68 9.78.5 Example 99.88 6.4 10.8 Example 10 10.38 5.6 11.4 Example 1 110.08 6.1 11.1 Comparative Example 1 19.18 0.6 15.2 Comparative Example 2 36.06 4.4 30.6 Comparative Example 325.375.819.4 Comparative Example 424.077.317.8 Comparative Example 527.273.822.5 Comparative Example 629.471.924.1 Comparative Example 726.874.521.0 Comparative Example 822.279.116.4

[0334]

[0335] Looking at Table 1 above, it can be seen that in the case of the secondary batteries of Examples 1 to 11 of the present invention, the resistance increase rate (%) after high-temperature storage and the capacity retention rate (%) after high-temperature cycling are both improved compared to the lithium secondary batteries of Comparative Examples 1 to 8.

[0336]

[0337] Experimental Example 4. Evaluation of High-Rate Discharge Output

[0338] For each lithium secondary battery prepared in the examples and comparative examples, an activation process was carried out by charging at a C-rate of 0.1C for 2 hours, and then the battery was fully charged to 100% SOC by charging at a C-rate of 0.33C at 25℃ to 4.2V under constant current / constant voltage conditions (0.05C cut-off). Subsequently, the battery was discharged at a C-rate of 0.2C to 2.8V under constant current conditions, and the discharge capacity was measured and set as the initial discharge capacity.

[0339] Then, each fully charged secondary battery was charged to 100% SOC at 25℃ with a C-rate of 0.33C, and each fully charged secondary battery was discharged under constant current conditions to a C-rate of 2.0C, and the discharge capacity was measured and set as the high-rate discharge capacity.

[0340] The ratio of the high-rate discharge capacity to the above initial discharge capacity was calculated using Equation 4 below to derive the high-rate discharge output, and the results are shown in Table 2 below.

[0341] [Equation 4]

[0342] High-rate discharge output (%) = (High-rate discharge capacity / Initial discharge capacity) × 100

[0343] High-Rate Discharge Output (%) Example 188.7 Example 289.2 Example 390.0 Example 481.4 Example 584.2 Example 683.7 Example 785.3 Example 884.8 Example 982.5 Example 1087.9 Example 1187.1 Comparative Example 179.3 Comparative Example 272.1 Comparative Example 378.4 Comparative Example 477.6 Comparative Example 573.5 Comparative Example 674.3 Comparative Example 775.8 Comparative Example 880.2

[0344]

[0345] Looking at Table 2 above, it can be seen that the high-rate discharge output (%) of the secondary batteries of Examples 1 to 11 of the present invention is improved compared to the lithium secondary batteries of Comparative Examples 1 to 8.

[0346]

[0347] Although the present invention has been described above with reference to preferred embodiments, those skilled in the art or those with ordinary knowledge in the relevant technical field will understand that various modifications and changes can be made to the invention without departing from the spirit and technical scope of the invention as set forth in the claims below. Accordingly, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification, but should be determined by the claims.

Claims

1. A non-aqueous electrolyte comprising a lithium salt, an organic solvent, and an additive, The above additive includes a first additive and a second additive, and The above first additive is a compound represented by the following chemical formula 1, and The above second additive is a compound represented by the following chemical formula 2, and The total content of the above additive is 8% to 20% by weight based on the total weight of the non-aqueous electrolyte, and A non-aqueous electrolyte in which the weight ratio of the first additive and the second additive is 10:90 to 40:60: [Chemical Formula 1] N≡C-R1-F (In the above Chemical Formula 1, R1 is an alkylene group having 1 to 5 carbon atoms) [Chemical Formula 2] N≡C-R2 (In the above chemical formula 2, R2 is an alkyl group having 2 to 10 carbon atoms).

2. In Paragraph 1, The above organic solvent is a non-aqueous electrolyte that is a cyclic carbonate compound.

3. In Paragraph 2, The above cyclic carbonate compound is a non-aqueous electrolyte selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, and vinylene carbonate.

4. In Paragraph 3, The above cyclic carbonate compound is a non-aqueous electrolyte, which is ethylene carbonate (EC).

5. In Paragraph 1, A non-aqueous electrolyte comprising at least one selected from the group consisting of compounds represented by the following chemical formulas 1A to 1C, wherein the compound represented by the above chemical formula 1: [Chemical Formula 1A] N≡C-CH2F [Chemical Formula 1B] N≡C-CH2CH2F [Chemical Formula 1C] N≡C-CH2CH2CH2F.

6. In Paragraph 1, A non-aqueous electrolyte comprising at least one selected from the group consisting of compounds represented by the following chemical formulas 2A to 2C, wherein the compound represented by the above chemical formula 2: [Chemical Formula 2A] N≡C-CH(CH3)2 [Chemical Formula 2B] N≡C-CH(CH2CH3)2 [Chemical Formula 2C] N≡C-CH(CH3)CH2CH3.

7. In Paragraph 1, A non-aqueous electrolyte in which the weight ratio of the first additive and the second additive is 10:90 to 30:

70.

8. In Paragraph 1, A non-aqueous electrolyte in which the total content of the above additive is 10% to 20% by weight based on the total weight of the non-aqueous electrolyte.

9. In Paragraph 1, The above-mentioned non-aqueous electrolyte further comprises at least one auxiliary additive selected from the group consisting of cyclic carbonate compounds, halogen-substituted carbonate compounds, sulfone compounds, sulfate compounds, phosphate compounds, borate compounds, benzene compounds, amine compounds, silane compounds, and lithium salt compounds.

10. A lithium secondary battery comprising: a positive electrode; a negative electrode facing the positive electrode; a separator interposed between the negative electrode and the positive electrode; and a non-aqueous electrolyte according to claim 1.

11. In Paragraph 10, The above negative electrode is a lithium secondary battery containing a silicon-based active material.