Non-aqueous electrolyte and lithium secondary battery comprising same

Abstract

The present invention provides a non-aqueous electrolyte comprising: a lithium salt; an organic solvent; and an additive, wherein the additive comprises an imidazolium-based ionic liquid. The non-aqueous electrolyte according to the present invention can greatly improve the cycle characteristics and output characteristics of a lithium secondary battery comprising same, by not only stably forming a film on a negative electrode and a positive electrode to suppress electrolyte decomposition at an electrode interface, but also by improving the conductive characteristics of lithium ions.

Description

Non-aqueous electrolyte and lithium secondary battery containing the same

[0001] The present invention relates to a non-aqueous electrolyte and a lithium secondary battery containing the same.

[0002]

[0003] With the recent rise in interest in energy storage technology, the application fields of secondary batteries are expanding from small devices such as mobile phones, tablets, and laptop PCs to medium and large devices such as electric vehicles and power storage systems, leading to a rapid increase in demand for high-performance lithium-ion batteries.

[0004] A lithium secondary battery, composed of a negative electrode, a positive electrode, an electrolyte, and a separator, is an energy storage device that converts, stores, and utilizes electrical energy by repeatedly inserting and extracting lithium ions through the electrolyte into the negative and positive electrodes located on opposite sides of the separator. During the process of repeated insertion and extraction of lithium ions into the negative and positive electrodes, the organic solvent and lithium salt constituting the electrolyte undergo reductive decomposition on the surface of the negative electrode to form a film (solid electrolyte interphase, SEI) composed of various organic and inorganic materials.

[0005] At this time, the highly reactive electrolyte reacts with graphite, which is the negative electrode, or lithium metal oxide, which is the positive electrode, to form compounds based on alkyl carbonate, Li2CO3, Li2O, etc., on the electrode surface. Since the cycle characteristics of the lithium secondary battery are significantly affected by properties such as ion conductivity and mechanical properties of the film formed on the electrode surface, research on film-forming additives is actively being conducted to improve the lifespan and output characteristics of the lithium secondary battery by forming a stable and robust film on the negative and positive electrode surfaces to prevent side reactions between the electrolyte and the electrode and to facilitate the mobility of lithium ions.

[0006]

[0007] One objective of the present invention is to provide a non-aqueous electrolyte that can form a stable film on the surfaces of the negative and positive electrodes during initial charging and discharging to improve lithium ion conductivity on the surface of the active material and suppress the decomposition of the electrolyte, and to achieve excellent cycle characteristics and output characteristics when applied to a lithium secondary battery.

[0008] In addition, another objective of the present invention is to provide a lithium secondary battery comprising the aforementioned non-aqueous electrolyte.

[0009]

[0010] The present invention provides a non-aqueous electrolyte comprising a lithium salt; an organic solvent; and an additive, wherein the additive comprises a compound represented by the following chemical formula 1.

[0011] [Chemical Formula 1]

[0012]

[0013] In the above chemical formula 1, R1 is an alkenyl group having 2 to 5 carbon atoms, R2 to R4 are independently fluorine (F) or alkyl groups having 1 to 10 carbon atoms substituted with one or more fluorines, and L1 is an alkylene group having 1 to 10 carbon atoms or an arylene group having 6 to 20 carbon atoms.

[0014] In addition, the present invention provides a lithium secondary battery comprising: a cathode; an anode facing the cathode; a separator interposed between the cathode and the anode; and the aforementioned non-aqueous electrolyte.

[0015]

[0016] The non-aqueous electrolyte of the present invention is characterized by comprising an imidazolium-based ionic liquid represented by the above chemical formula 1. The non-aqueous electrolyte according to the present invention can suppress side reactions between the electrolyte and the electrodes by forming a stable and robust film on the surface of the negative electrode and the positive electrode through the imidazolium-based ionic liquid represented by the above chemical formula 1, thereby improving the cycle life of a lithium secondary battery containing the non-aqueous electrolyte.

[0017] In addition, when using the non-aqueous electrolyte according to the present invention, the imidazolium-based ionic liquid component represented by Chemical Formula 1 reacts with the electrode before the electrolyte solvent and lithium salt, so the proportion of the inorganic component that strengthens the physical properties of the film formed on the surface of the negative and positive electrodes increases, and the lithium ion conductivity characteristics are improved, thereby improving the lifespan characteristics and high rate characteristics of the lithium secondary battery using the same.

[0018] In addition, the imidazolium-based ionic liquid represented by Chemical Formula 1 of the present invention has excellent thermal stability and non-flammability due to electrostatic attraction caused by interactions between ions in its chemical structure, and thus can improve the high-temperature stability of a lithium secondary battery using a non-aqueous electrolyte containing it.

[0019]

[0020] Figure 1 is a schematic diagram showing the synthesis process of [FSPVI][TFSI] obtained in the manufacturing example of the present invention.

[0021] Figure 2 is the FT-IR spectrum of [FSPVI][TFSI] obtained in the manufacturing example of the present invention.

[0022] FIG. 3 is [FSPVI][TFSI] obtained in the manufacturing example of the present invention. 1 This is the H NMR spectrum.

[0023] FIG. 4 is [FSPVI][TFSI] obtained in the manufacturing example of the present invention. 19 This is the F NMR spectrum.

[0024] Figure 5 is a differential charge / discharge graph of a cathode half cell using the non-aqueous electrolyte of Example 2.

[0025] Figure 6 is a differential charge / discharge graph of a cathode half cell using the non-aqueous electrolyte of Comparative Example 1.

[0026] Figure 7 is a differential charge / discharge graph of an anode half cell using the non-aqueous electrolyte of Example 2.

[0027] Figure 8 is a differential charge / discharge graph of an anode half cell using the non-aqueous electrolyte of Comparative Example 1.

[0028] Figure 9 is a graph showing the charge / discharge capacity of a lithium secondary battery manufactured using the non-aqueous electrolyte of Example 2 over 300 charge / discharge cycles.

[0029] Figure 10 is a graph showing the charge / discharge capacity of a lithium secondary battery manufactured using the non-aqueous electrolyte of Comparative Example 1 during 300 charge / discharge cycles.

[0030] FIG. 11 is a graph comparing the discharge capacity of lithium secondary batteries prepared using the non-aqueous electrolytes of Examples 1 to 3 and Comparative Examples 1 to 3 over 300 charge-discharge cycles.

[0031] Figure 12 is the F 1s XPS spectrum of the negative electrode surface after activation of a lithium secondary battery prepared using the non-aqueous electrolyte of Example 2.

[0032] Figure 13 is the S 2p XPS spectrum of the negative electrode surface after activation of a lithium secondary battery prepared using the non-aqueous electrolyte of Example 2.

[0033] Figure 14 is the N 1s XPS spectrum of the negative electrode surface after activation of a lithium secondary battery prepared using the non-aqueous electrolyte of Example 2.

[0034] Figure 15 is the F 1s XPS spectrum of the negative electrode surface after activation of a lithium secondary battery prepared using the non-aqueous electrolyte of Comparative Example 1.

[0035] Figure 16 is the S 2p XPS spectrum of the negative electrode surface after activation of a lithium secondary battery prepared using the non-aqueous electrolyte of Comparative Example 1.

[0036] Figure 17 is the N 1s XPS spectrum of the negative electrode surface after activation of a lithium secondary battery prepared using the non-aqueous electrolyte of Comparative Example 1.

[0037] Figure 18 is the F 1s XPS spectrum of the positive electrode surface after activation of a lithium secondary battery prepared using the non-aqueous electrolyte of Example 2.

[0038] Figure 19 is the S 2p XPS spectrum of the positive electrode surface after activation of a lithium secondary battery prepared using the non-aqueous electrolyte of Example 2.

[0039] Figure 20 is the N 1s XPS spectrum of the positive electrode surface after activation of a lithium secondary battery prepared using the non-aqueous electrolyte of Example 2.

[0040] Figure 21 is the F 1s XPS spectrum of the positive electrode surface after activation of a lithium secondary battery prepared using the non-aqueous electrolyte of Comparative Example 1.

[0041] Figure 22 is the S 2p XPS spectrum of the positive electrode surface after activation of a lithium secondary battery prepared using the non-aqueous electrolyte of Comparative Example 1.

[0042] Figure 23 is the N 1s XPS spectrum of the positive electrode surface after activation of a lithium secondary battery prepared using the non-aqueous electrolyte of Comparative Example 1.

[0043] FIG. 24 is a graph comparing the discharge capacity according to the change in C rate of lithium secondary batteries prepared using the non-aqueous electrolytes of Example 2 and Comparative Examples 1, 4 to 6.

[0044] Figure 25 is a graph showing the discharge capacity according to the change in C rate of a lithium secondary battery manufactured using the non-aqueous electrolyte of Example 2.

[0045] FIG. 26 is a graph showing the discharge capacity according to the change in C rate of a lithium secondary battery manufactured using the non-aqueous electrolyte of Comparative Example 1 of the present invention.

[0046] FIG. 27 is a graph showing the change in interfacial resistance during the first cycle of a lithium secondary battery prepared using the non-aqueous electrolyte of Example 2 and Comparative Example 1.

[0047] Figure 28 is a graph showing the change in interfacial resistance during the 300th cycle of a lithium secondary battery prepared using the non-aqueous electrolyte of Example 2 and Comparative Example 1.

[0048] Figure 29 is an SEM image of a graphite negative electrode before 300 charge-discharge cycles of a lithium secondary battery prepared using the non-aqueous electrolyte of Comparative Example 1.

[0049] Figure 30 is an SEM image of a graphite negative electrode after 300 charge-discharge cycles of a lithium secondary battery prepared using the non-aqueous electrolyte of Comparative Example 1.

[0050] Figure 31 is an SEM image of a graphite negative electrode before 300 charge-discharge cycles of a lithium secondary battery prepared using the non-aqueous electrolyte of Example 2.

[0051] Figure 32 is an SEM image of the graphite negative electrode after 300 charge-discharge cycles of a lithium secondary battery prepared using the non-aqueous electrolyte of Example 2.

[0052] Figure 33 is an SEM image of the NCM cathode before 300 charge-discharge cycles of a lithium secondary battery prepared using the non-aqueous electrolyte of Comparative Example 1.

[0053] Figure 34 is an SEM image of the NCM cathode after 300 charge-discharge cycles of a lithium secondary battery prepared using the non-aqueous electrolyte of Comparative Example 1.

[0054] Figure 35 is an SEM image of the NCM cathode before 300 charge-discharge cycles of a lithium secondary battery prepared using the non-aqueous electrolyte of Example 2.

[0055] Figure 36 is an SEM image of the NCM cathode after 300 charge-discharge cycles of a lithium secondary battery prepared using the non-aqueous electrolyte of Example 2.

[0056] FIG. 37 is a graph comparing the discharge capacity after 200 charge-discharge cycles of lithium secondary batteries prepared using the non-aqueous electrolytes of Example 2 and Comparative Examples 1, 4 to 6.

[0057]

[0058] Terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but 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.

[0059] In this specification, terms such as “comprising,” “comprising,” 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.

[0060] Meanwhile, prior to describing the present invention, unless otherwise specifically stated in the present invention, "*" refers to a connected portion (bonding site) between identical or different atoms or terminal portions of a chemical formula.

[0061] In addition, in the description of "a to b carbon atoms" 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, "alkyl group having 1 to 5 carbon atoms" refers to an alkyl group containing 1 to 5 carbon atoms, namely CH3-, CH3CH2-, CH3CH2CH2-, (CH3)2CH-, CH3CH2CH2CH2-, (CH3)2CHCH2-, CH3CH2CH2CH2CH2-, (CH3)2CHCH2CH2-, etc.

[0062] In addition, in this specification, alkyl groups or aryl groups may all be substituted or unsubstituted. Unless otherwise defined, the term "substitution" above means that at least one hydrogen bonded to a carbon is substituted with an element other than hydrogen, for example, an alkyl group having 1 to 20 carbon atoms, an alkenyl group having 2 to 20 carbon atoms, an alkynyl group having 2 to 20 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, a cycloalkyl group having 3 to 12 carbon atoms, a cycloalkenyl group having 3 to 12 carbon atoms, a cycloalkynyl group having 3 to 12 carbon atoms, a heterocycloalkyl group having 3 to 12 carbon atoms, a heterocycloalkynyl group having 2 to 12 carbon atoms, an aryloxy group having 6 to 12 carbon atoms, a halogen atom, a fluoroalkyl group having 1 to 20 carbon atoms, a nitro group, an aryl group having 6 to 20 carbon atoms, and a group having 2 to It means that it is substituted with a heteroaryl group of 20 carbon atoms, a haloaryl group having 6 to 20 carbon atoms, etc.

[0063]

[0064] The present invention will be described in more detail below.

[0065]

[0066] Non-aqueous electrolytes

[0067] The present invention relates to a non-aqueous electrolyte. More specifically, the non-aqueous electrolyte may be a non-aqueous electrolyte for a lithium secondary battery.

[0068] The non-aqueous electrolyte according to the present invention comprises a lithium salt; an organic solvent; and an additive; and is characterized in that the additive comprises a compound represented by the following chemical formula 1.

[0069] [Chemical Formula 1]

[0070]

[0071] In the above chemical formula 1, R1 is an alkenyl group having 2 to 5 carbon atoms, R2 to R4 are independently fluorine (F) or alkyl groups having 1 to 10 carbon atoms substituted with one or more fluorines, and L1 is an alkylene group having 1 to 10 carbon atoms or an arylene group having 6 to 20 carbon atoms.

[0072] The non-aqueous electrolyte of the present invention can suppress adverse reactions between the electrolyte and the electrodes by forming a stable and robust film on the surfaces of the cathode and anode through an additive containing an imidazolium-based ionic liquid, and can improve lithium ion conductivity characteristics by increasing the proportion of inorganic components that enhance the physical properties within the film formed on the surfaces of the cathode and anode. Therefore, the life characteristics, including cycle life, and high-rate characteristics of a lithium secondary battery containing the non-aqueous electrolyte can be improved.

[0073]

[0074] (1) Lithium salt

[0075] 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, the lithium salt is Li as a cation. + It includes, and as anion, F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , AlO4 - , AlCl4 - , PF6 - , SbF6 - , AsF6 - , B 10 Cl 10 - , BF2C2O4 - , BC4O8 - , PF4C2O4 - , PF2C4O8 - , (CF3)2PF4 -, (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , C4F9SO3 - , CF3CF2SO3 - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , CH3SO3 - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - It may include at least one selected from a group consisting of

[0076] Specifically, the lithium salt is lithium chloride (LiCl), lithium bromide (LiBr), lithium iodide (LiI), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium tetraoxoaluminate (LiAlO4), lithium tetrachloroaluminate (LiAlCl4), lithium hexafluorophosphate (LiPF6), lithium hexafluoroantimonate (LiSbF6), lithium hexafluoroarsenate (LiAsF6), lithium decachlorodecarborate (LiB 10 Cl 10It may include at least one selected from the group consisting of lithium bis-oxalatoborate (LiBOB (LiB(C2O4)2)), lithium trifluoromethanesulfonate (LiCF3SO3), bis(fluorosulfonimide) lithium (LiFSI (LiN(SO2F)2)), lithium methanesulfonate (LiCH3SO3), lithium trifluoroacetate (LiCF3CO2), lithium acetate (LiCH3CO2), lithium bis-trifluoromethanesulfonylimide (LiN(SO2F)2), and bis(trifluoromethylsulfonimide) lithium (LiBETI (LiN(SO2CF2CF3)2)). Specifically, the lithium salt may include at least one selected from the group consisting of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium trifluoromethanesulfonate (LiCF3SO3), lithium bistrifluoromethanesulfonylimide (LiN(SO2F)2), lithium perchlorate (LiClO4), and lithium bisoxalatoborate (LiBOB (LiB(C2O4)2)).

[0077] The above lithium salt may be included in the above-mentioned non-aqueous electrolyte at a concentration of 0.5M to 5M, specifically 0.8M to 4M, and more specifically 0.8M to 2.0M. When the concentration of the above-mentioned lithium salt satisfies the above range, the lithium ion yield (Li + The transference number and the degree of dissociation of lithium ions are improved, which can enhance the output characteristics of the battery.

[0078]

[0079] (2) Organic solvent

[0080] The above organic solvent is a non-aqueous solvent commonly used in lithium secondary batteries, and is not particularly limited as long as it minimizes decomposition due to oxidation reactions, etc., during the charging and discharging process of the secondary battery.

[0081] Specifically, the organic solvent may include at least one selected from the group consisting of cyclic carbonate-based organic solvents, linear carbonate-based organic solvents, linear ester-based organic solvents, and cyclic ester-based organic solvents.

[0082] The above-mentioned cyclic carbonate-based organic solvent is a high-viscosity organic solvent that has a high dielectric constant and can effectively dissociate lithium salts in the electrolyte. Specifically, it 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, and more specifically, it may include ethylene carbonate.

[0083] In addition, the linear carbonate-based organic solvent is an organic solvent having low viscosity and low dielectric constant, and specifically may include at least one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethylmethyl carbonate (EMC), methylpropyl carbonate, and ethylpropyl carbonate, and more specifically may include ethylmethyl carbonate (EMC).

[0084] The above organic solvent may be a mixture of a cyclic carbonate-based organic solvent and a linear carbonate-based organic solvent. In this case, the cyclic carbonate-based organic solvent and the linear carbonate-based organic solvent may be mixed in a volume ratio of 10:90 to 40:60, specifically a volume ratio of 10:90 to 30:70, and more specifically a volume ratio of 15:85 to 30:70. When the mixing ratio of the cyclic carbonate-based organic solvent and the linear carbonate-based organic solvent satisfies the above range, high dielectric constant and low viscosity characteristics are simultaneously satisfied, and excellent ionic conductivity characteristics can be achieved.

[0085] In addition, to produce an electrolyte having high ionic conductivity, the organic solvent may further include at least one ester-based organic solvent selected from the group consisting of a linear ester-based organic solvent and a cyclic ester-based organic solvent in addition to at least one carbonate-based organic solvent selected from the group consisting of a cyclic carbonate-based organic solvent and a linear carbonate-based organic solvent.

[0086] The above 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.

[0087] In addition, the above-mentioned 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.

[0088] Meanwhile, the above organic solvent may be used without limitation by adding organic solvents commonly used in non-aqueous electrolytes as needed. For example, it may additionally include at least one organic solvent among ether-based organic solvents, glyme-based solvents, and nitrile-based organic solvents.

[0089] As the above ether-based solvent, any one selected from the group consisting of dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methylpropyl ether, ethyl propyl ether, 1,3-dioxolane (DOL), and 2,2-bis(trifluoromethyl)-1,3-dioxolane (TFDOL), or a mixture of two or more of these may be used, but is not limited thereto.

[0090] The above-mentioned glyme-based solvent has a high dielectric constant and low surface tension compared to linear carbonate-based organic solvents and is a solvent with low reactivity with metals. It may include at least one selected from the group consisting of dimethoxyethane (glyme, DME), diethoxyethane, diglyme, triglyme, and tetraglyme (TEGDME), but is not limited thereto.

[0091] The above nitrile-based solvent may be one or more selected from the group consisting of acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanitrile, cyclopentane carbonitrile, cyclohexane carbonitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile, but is not limited thereto.

[0092]

[0093] (3) Additives

[0094] The non-aqueous electrolyte according to the present invention includes an additive. Specifically, the additive includes a compound represented by the following chemical formula 1.

[0095] [Chemical Formula 1]

[0096]

[0097] In the above chemical formula 1, R1 is an alkenyl group having 2 to 5 carbon atoms, R2 to R4 are independently fluorine (F) or alkyl groups having 1 to 10 carbon atoms substituted with one or more fluorines, and L1 is an alkylene group having 1 to 10 carbon atoms or an arylene group having 6 to 20 carbon atoms.

[0098] Specifically, in the above formula 1, R1 may be an alkenyl group having 2 to 5 carbon atoms, specifically an alkenyl group having 2 to 4 carbon atoms, more specifically an alkenyl group having 2 to 3 carbon atoms, and even more specifically an ethenyl group. In the case of the above alkenyl group having 2 to 4 carbon atoms, for example, it may be the following formula R1-1, formula R1-2, or formula R1-3, and more specifically, formula R1-1.

[0099] [Chemical Formula R1-1]

[0100]

[0101] [Chemical Formula R1-2]

[0102]

[0103] [Chemical Formula R1-3]

[0104]

[0105] R2 to R4 may independently be fluorine or an alkyl group having 1 to 10 carbon atoms substituted with one or more fluorine atoms, specifically, may be fluorine or an alkyl group having 1 to 6 carbon atoms substituted with one or more fluorine atoms, more specifically, may be fluorine or an alkyl group having 1 to 4 carbon atoms substituted with one or more fluorine atoms, and even more specifically, may be fluorine or a trifluoromethyl group. More specifically, R2 may be fluorine. Additionally, R3 and R4 may each be a trifluoromethyl group.

[0106] L1 may be an alkylene group having 1 to 10 carbon atoms or an arylene group having 6 to 20 carbon atoms, specifically an alkylene group having 1 to 5 carbon atoms or an arylene group having 6 to 20 carbon atoms, more specifically an alkylene group having 1 to 3 carbon atoms or an arylene group having 6 to 15 carbon atoms, even more specifically an alkylene group having 1 to 3 carbon atoms or an arylene group having 6 to 10 carbon atoms, even more specifically an arylene group having 6 to 10 carbon atoms, and even more specifically a phenyl group. In the case of the phenyl group, for example, it may be formula L1-1, formula L1-2, or formula L1-3, and more specifically formula L1-1.

[0107] [Chemical Formula L1-1]

[0108]

[0109] [Chemical Formula L1-2]

[0110]

[0111] [Chemical Formula L1-3]

[0112]

[0113] The compound of Chemical Formula 1 above is an imidazolium-based ionic liquid in which cations and anions are bonded by electrical attraction, and it has the characteristics of high thermal stability, electrical conductivity, and non-flammability. In addition, due to the imidazolium ring structure, it has a resonance stabilization effect and does not easily undergo deformation or decomposition even at high temperatures.

[0114] In addition, since the above R1 has a highly reactive carbon-carbon double bond, it reacts with the cathode and anode before the electrolyte solvent and lithium salt during initial charging and discharging to form SEI and CEI, respectively.

[0115] The above L1 is an alkylene group having 1 to 10 carbon atoms or an arylene group having 6 to 20 carbon atoms, and contributes to strengthening the physical properties of the film formed when the additive according to the present invention forms a film at the cathode and anode.

[0116] In the above chemical formula 1, R2 to R4 are independently fluorine or alkyl groups having 1 to 10 carbon atoms substituted with one or more fluorine atoms, which contribute to the formation of a uniform and thin film on the cathode and anode and improve the mobility characteristics of lithium ions. Specifically, when forming the SEI layer, the fluorine-containing compound generates a stable component such as lithium fluoride (LiF), thereby allowing the SEI layer to be formed more uniformly and thinly. Additionally, the high electronegativity of fluorine reduces the solvation energy of lithium ions in the lithium ion solvation structure, thereby allowing lithium ions to move more freely.

[0117] Therefore, using the non-aqueous electrolyte according to the present invention strengthens the physical properties of the film, suppresses the reduction in battery capacity due to the loss of electrolyte solvent and lithium salt, and improves the mobility characteristics of lithium ions at the electrode interface.

[0118] Specifically, the compound represented by the above chemical formula 1 may include the compound represented by the following chemical formula 1-1.

[0119] [Chemical Formula 1-1]

[0120]

[0121] When 3-(4-(fluorosulfonyl)phenyl)-1-vinyl-imidazolium trifluoromethanesulfonylimide (which may be represented as [FSPVI][TFSI] in this specification), a compound represented by the above chemical formula 1-1, is included in the electrolyte of a lithium secondary battery, the suppression of side reactions between the electrolyte and the electrodes and the improvement of lithium ion conductivity characteristics can be achieved more smoothly due to the formation of a stable and robust film on the surfaces of the negative and positive electrodes. Therefore, using the compound represented by the above chemical formula 1-1 as an additive is desirable in that it can more effectively realize the improvement of the lifespan and output characteristics of the lithium secondary battery, which is the core effect of the present invention.

[0122] The compound represented by Chemical Formula 1 above may be included in the non-aqueous electrolyte in an amount of 0.15 wt% or more, 0.2 wt% or more, 0.3 wt% or more, 0.4 wt% or more, or 0.5 wt% or more. The compound represented by Chemical Formula 1 above may be 20 wt% or less, 15 wt% or less, 12 wt% or less, 10 wt% or less, 8 wt% or less, 5 wt% or less, 3 wt% or less, 2 wt% or less, 1.5 wt% or less, 1 wt% or less, or 0.8 wt% or less. The above ranges may be combined without limitation.

[0123] More specifically, the compound represented by Chemical Formula 1 may be included in the non-aqueous electrolyte in an amount of 0.15% to 10% by weight, specifically in an amount of 0.2% to 5% by weight, more specifically in an amount of 0.2% to 3% by weight, even more specifically in an amount of 0.3% to 2% by weight, even more specifically in an amount of 0.4% to 1% by weight, and even more specifically in an amount of 0.4% to 0.8% by weight. When the content of the compound represented by Chemical Formula 1 satisfies the above range, a stable film is formed on the anode and cathode, thereby improving the cycle life.

[0124]

[0125] The additive of the present invention may include additional additives in addition to the compound represented by Formula 1. The additional additives may be included in the non-aqueous electrolyte to prevent the decomposition of the non-aqueous electrolyte in a high-power environment, thereby preventing cathode collapse, or to provide low-temperature high-rate discharge characteristics, high-temperature stability, prevention of overcharging, and suppression of battery expansion at high temperatures. Even when using a co-additive that includes the additional additives in addition to the compound represented by Formula 1 of the present invention, it can be used without side effects, and a superior effect in improving cycle performance can be achieved compared to using the compound represented by Formula 1 alone in the same amount.

[0126] Specifically, the above additional additives are vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, propane sultone, propene sultone, butane sultone, biphenyl, divinyl sulfone, succinonitrile, adiponitrile, ethylene sulfate, ethylene sulfite, propylene sulfite, diallyl sulfonate, lithium difluorooxalatoborate (LiODFB), lithium bis-(oxalato)borate (LiBOB), tris(trimethylsilyl) phosphate (TMSPa, It may further include at least one selected from the group consisting of Tris(trimethylsilyl) phosphate, and Tris(trimethylsilyl) phosphite (TMSPi, Tris(trimethylsilyl) Phosphite), specifically, it may further include at least one of vinylene carbonate and propansulfone, and more specifically, it may include vinylene carbonate.

[0127] The above additional additive may be included in the above non-aqueous electrolyte in an amount of 0.1% to 10% by weight, specifically 0.1% to 5% by weight, more specifically 0.1% to 2% by weight, and even more specifically 0.1% to 0.9% by weight.

[0128]

[0129] lithium secondary battery

[0130] In addition, the present invention provides a lithium secondary battery comprising the aforementioned non-aqueous electrolyte.

[0131] Specifically, the lithium secondary battery may include a positive electrode; a negative electrode facing the positive electrode; a separator interposed between the positive electrode and the negative electrode; and the aforementioned non-aqueous electrolyte.

[0132] At this time, the lithium secondary battery of the present invention can be manufactured according to conventional methods known in the art. For example, it can be manufactured by sequentially stacking a positive electrode, a negative electrode, and a separator between the positive and negative electrodes to form an electrode assembly, inserting the electrode assembly into a battery case, and injecting a non-aqueous electrolyte according to the present invention.

[0133]

[0134] (1) positive electrode

[0135] 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.

[0136] The above positive current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. Specifically, the above positive current collector may include at least one selected from the group consisting of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, and aluminum-cadmium alloy, preferably aluminum.

[0137] The thickness of the above positive current collector can typically be 3 to 500 μm.

[0138] The above positive current collector may also strengthen the bonding force of the negative active material by forming fine irregularities on its surface. For example, the above positive current collector can be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0139] 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.

[0140] The above positive active material layer may include a positive active material.

[0141] The above-mentioned positive electrode active material is a compound capable of reversible intercalation and deintercalation of lithium, and specifically, may include a lithium transition metal composite oxide comprising lithium and at least one transition metal comprising nickel, cobalt, manganese, and aluminum, preferably a lithium transition metal composite oxide comprising lithium and a transition metal comprising nickel, cobalt, and manganese.

[0142] For example, the above lithium transition metal composite oxide includes a lithium-manganese oxide (e.g., LiMnO2, LiMn2O4, etc.), a lithium-cobalt oxide (e.g., LiCoO2, etc.), a lithium-nickel oxide (e.g., LiNiO2, etc.), and a lithium-nickel-manganese oxide (e.g., LiNi 1-Y Mn Y O2(here, 0 <Y<1), LiMn 2-z Ni z O4 (where 0 < Z < 2), etc.), lithium-nickel-cobalt oxides (e.g., LiNi 1-Y1 Co Y1 O2(here, 0 <Y1<1) 등), 리튬-망간-코발트계 산화물(예를 들면, LiCo 1-Y2 Mn Y2 O2(here, 0 <Y2<1), LiMn 2-z1 Co z1 O4 (where 0 < Z1 < 2), etc.), lithium-nickel-manganese-cobalt oxides (e.g., Li(Ni p Co q Mn r1 )O2(where, 0<p<1, 0<q<1, 0<r1<1, p+q+r1=1) or Li(Ni p1 Co q1 Mn r2)O4 (where 0<p1<2, 0<q1<2, 0<r2<2, p1+q1+r2=2), etc.), or lithium-nickel-cobalt-transition metal (M) oxide (e.g., Li(Ni p2 Co q2 Mn r3 M S2 Examples include )O2 (wherein M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, and Mo, and p2, q2, r3, and s2 are each atomic fractions of independent elements, such that 0 < p2 < 1, 0 < q2 < 1, 0 < r3 < 1, 0 < s2 < 1, and p2 + q2 + r3 + s2 = 1), etc., and any one or more of these compounds may be included. Among these, the lithium transition metal composite oxide is LiCoO2, LiMnO2, LiNiO2, and lithium nickel-manganese-cobalt oxide (for example, Li(Ni 0.6 Mn 0.2 Co 0.2 )O2, Li(Ni 0.5 Mn 0.3 Co 0.2 )O2, Li(Ni 0.7 Mn 0.15 Co 0.15 )O2 or Li(Ni 0.8 Mn 0.1 Co 0.1 )O2, etc.), or lithium nickel-cobalt-aluminum oxide (e.g., Li(Ni 0.8 Co 0.15 Al 0.05 It may be )O2, etc., and considering the significant improvement effect resulting from controlling the type and content ratio of constituent elements forming the lithium transition metal composite oxide, the lithium transition metal composite oxide is Li(Ni 0.6 Mn 0.2 Co 0.2 )O2, Li(Ni 0.5 Mn 0.3 Co 0.2 )O2, Li(Ni 0.7 Mn 0.15 Co 0.15 )O2 or Li(Ni0.8 Mn 0.1 Co 0.1 It may be O2, etc., and any one of these or a mixture of two or more may be used.

[0143] More specifically, the positive electrode active material may be a lithium transition metal composite oxide containing 60 mol% or more of nickel based on the total molar amount of the transition metal contained in the lithium transition metal composite oxide. Specifically, the positive electrode active material may be a lithium transition metal composite oxide, wherein the transition metal comprises nickel; and at least one selected from manganese, cobalt, and aluminum, and may contain 60 mol% or more, specifically 60 mol% to 90 mol%, based on the total molar amount of the transition metal. When such a lithium transition metal composite oxide containing a high amount of nickel is used together with the aforementioned non-aqueous electrolyte, it is desirable in that it can reduce gaseous by-products generated by structural collapse.

[0144] In addition, the above positive active material may include a lithium complex transition metal oxide represented by the following chemical formula 2.

[0145] [Chemical Formula 2]

[0146] Li 1+x (Ni a Co b Mn c M d )O2

[0147] In the above chemical formula 2, M is one or more selected from W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, and 1+x, a, b, c, and d are each atomic fractions of independent elements, where 0≤x≤0.2, 0.50≤a<1, 0 <b≤0.25, 0<c≤0.25, 0≤d≤0.1, a+b+c+d=1이다.

[0148] Preferably, a, b, c, and d may each be 0.70≤a≤0.95, 0.025≤b≤0.20, 0.025≤c≤0.20, and 0≤d≤0.05.

[0149] In addition, the above a, b, c, and d may each be 0.80≤a≤0.95, 0.025≤b≤0.15, 0.025≤c≤0.15, and 0≤d≤0.05.

[0150] In addition, the above a, b, c, and d may each be 0.85≤a≤0.90, 0.05≤b≤0.10, 0.05≤c≤0.10, and 0≤d≤0.03.

[0151] The above positive active material may be included in the positive active material layer in an amount of 80% to 99% by weight, preferably 92% to 98.5% by weight, taking into consideration the sufficient capacity exertion of the positive active material.

[0152] The above positive active material layer may further include a binder and / or a conductive material together with the aforementioned positive active material.

[0153] The above binder is a component that assists in the binding of active materials and conductive materials, and in binding to current collectors, and specifically may include at least one selected from the group consisting of polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene ter polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, and fluororubber, preferably polyvinylidene fluoride.

[0154] The above binder may be included in the positive active material layer in an amount of 1% to 20% by weight, preferably 1.2% to 10% by weight, in order to sufficiently secure binding strength between components such as the positive active material.

[0155] The above conductive material can be used to assist and improve conductivity in a secondary battery, and is not particularly limited as long as it is conductive without causing chemical changes. Specifically, the above cathode conductive material may include at least one selected from the group consisting of graphite such as natural graphite or artificial graphite; carbon black such as carbon black, acetylene black, Ketjen black, channel black, Farnes black, lamp black, thermal black; conductive fibers such as carbon fibers or metal fibers; conductive tubes such as carbon nanotubes; fluorocarbons; metal powders such as aluminum or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; and polyphenylene derivatives, and preferably may include carbon black in terms of improving conductivity.

[0156] The above conductive material may be included in the above positive active material layer in an amount of 1% to 20% by weight, preferably 1.2% to 10% by weight, in order to sufficiently ensure electrical conductivity.

[0157] The thickness of the above positive active material layer may be 30㎛ to 400㎛, preferably 40㎛ to 110㎛.

[0158] The above anode can be manufactured by coating an anode slurry comprising an anode active material and optionally a binder, a conductive material, and a solvent for forming an anode slurry onto the above anode current collector, and then drying and rolling.

[0159] The solvent for forming the anode slurry may include an organic solvent such as NMP (N-methyl-2-pyrrolidone). The solid content of the anode slurry may be 40% to 90% by weight, specifically 50% to 80% by weight.

[0160]

[0161] (2) Negative electrode

[0162] The above cathode is opposite to the above anode.

[0163] 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.

[0164] The above-mentioned negative current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. Specifically, the above-mentioned negative current collector may be copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface treated with carbon, nickel, titanium, silver, etc., or aluminum-cadmium alloy.

[0165] The above-mentioned cathode current collector can typically have a thickness of 3 to 500 μm.

[0166] The above-mentioned negative current collector may form fine irregularities on its surface to strengthen the bonding force of the negative active material. For example, the above-mentioned negative current collector can be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0167] 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.

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

[0169] The above-mentioned negative electrode active material is a material capable of reversibly inserting / extracting lithium ions and may include at least one selected from the group consisting of carbon-based active materials, (quasi)metal-based active materials, and lithium metal, and specifically may include at least one selected from carbon-based active materials and (quasi)metal-based active materials. Alternatively, the above-mentioned negative electrode active material may include carbon-based active materials and (quasi)metal-based active materials.

[0170] The above 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.

[0171] 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.

[0172] Specifically, the above (quasi)metallic active material may include at least one (quasi)metal selected from the group consisting of Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, V, Ti, and Sn; an alloy of lithium with at least one (quasi)metal selected from the group consisting of Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, V, Ti, and Sn; an oxide of at least one (quasi)metal selected from the group consisting of Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, V, Ti, and Sn; lithium titanium oxide (LTO); lithium vanadium oxide; etc.

[0173] More specifically, the above (quasi)metallic active material may include a silicon-based active material.

[0174] The above silicon-based active material is SiO x It may include compounds represented by (0≤x<2). Since SiO2 does not react with lithium ions 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.

[0175] Average particle size (D) of the above silicon-based active material50 ) 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.

[0176] The above-mentioned negative electrode active material may be included in the negative electrode active material layer in an amount of 60% to 99% by weight, preferably 75% to 98% by weight.

[0177] The above cathode active material layer may further include a binder and / or a conductive material together with the cathode active material.

[0178] The above binder is used to improve the performance of the battery by enhancing the adhesion between the negative electrode active material layer and the negative electrode current collector, and may include, for example, at least one selected from the group consisting of polyvinylidenefluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidenefluoride (PVDF), polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluororubber, and materials in which hydrogens thereof are substituted with Li, Na, or Ca, etc., and may also include various copolymers thereof. there is.

[0179] The above binder may be included in the above negative electrode active material layer in an amount of 0.5% to 10% by weight.

[0180] The above conductive material is not particularly limited as long as it is conductive without causing chemical changes in the battery, and for example, graphite such as natural graphite or artificial graphite; carbon black such as carbon black, acetylene black, Ketjen black, channel black, Farnes black, lamp black, thermal black; conductive fibers such as carbon fibers or metal fibers; conductive tubes such as carbon nanotubes; fluorocarbons; metal powders such as aluminum or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives may be used.

[0181] The above conductive material may be included in the above negative electrode active material layer in an amount of 0.5% to 10% by weight, preferably 1% to 7% by weight.

[0182] The thickness of the above negative electrode active material layer may be 10㎛ to 100㎛.

[0183] The above cathode can be manufactured by coating a cathode slurry comprising a cathode active material, a binder, a conductive material, and / or a solvent for forming a cathode slurry on at least one surface of a cathode current collector, and then drying and rolling.

[0184] The solvent for forming the cathode slurry may include, for example, at least one selected from the group consisting of distilled water, NMP (N-methyl-2-pyrrolidone), ethanol, methanol, and isopropyl alcohol, preferably distilled water, in order to facilitate the dispersion of the cathode active material, binder, and / or conductive material. The solid content of the cathode slurry may be 30% to 80% by weight, specifically 40% to 70% by weight.

[0185]

[0186] (3) Separator

[0187] In addition, as a separator, a conventional porous polymer film that has been used as a separator in the past, such as a porous polymer film made of a polyolefin-based polymer like ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, may be used alone or in a laminate thereof, or a conventional porous nonwoven fabric, such as a nonwoven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc., may be used, but is not limited thereto. In addition, 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.

[0188]

[0189] 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.

[0190]

[0191] The present invention will be explained in more detail below through specific embodiments. However, the following embodiments are merely examples to aid in understanding the invention and do not limit the scope of the invention. It is obvious to those skilled in the art that various changes and modifications are possible within the scope and spirit of this description, and it is natural that such variations and modifications fall within the scope of the appended claims.

[0192]

[0193] Examples and Comparative Examples

[0194] Preparation Example: Synthesis of 3-(4-(fluorosulfonyl)phenyl)-1-vinyl-imidazolium bistrifluoromethylsulfonylimide ([FSPVI][TFSI])

[0195] (1) Step 1: Synthesis of 3-(4-(fluorosulfonyl)phenyl)-1-vinyl-imidazolium chloride ([FSPVI][Cl])

[0196] Figure 1 is a schematic diagram illustrating the synthesis process of 3-(4-(fluorosulfonyl)phenyl)-1-vinyl-imidazol-3-ium chloride ([FSPVI][Cl]) from 1-vinylimidazole and 4-fluorobenzenesulfonyl chloride. First, the reactants given in Table 1 are dissolved in dichloromethane (DCM) solvent and placed in a double-jacketed container. After placing all the reactants into the reactor at 25 °C, the reaction is carried out for 6 hours. The reaction-completed compound was precipitated using an ether solvent and vacuum dried at 40°C for 12 hours to obtain 3-(4-(fluorosulfonyl)phenyl)-1-vinyl-imidazolium chloride ([FSPVI][Cl]), and its structure was confirmed through the FT-IR spectrum in Figure 2.

[0197] 1-Vinylimidazole (g)4-Fluorobenzene sulfonyl chloride (g)Dichloromethane (DCM) (ml)13.732.1100.0

[0198] (2) Step 2: Synthesis of 3-(4-(fluorosulfonyl)phenyl)-1-vinyl-imidazolium bistrifluoromethylsulfonylimide ([FSPVI][TFSI])

[0199] A schematic diagram for the synthesis of 3-(4-(fluorosulfonyl)phenyl)-1-vinyl-imidazolium bistrifluoromethylsulfonylimide ([FSPVI][TFSI]) is given in Step 2 of Fig. 1. First, the reactants given in Table 2 are dissolved in deionized water (DI) and placed in a double-jacketed container. After adding all the reactants to the reactor at 25 °C, the reaction is carried out for 2 hours. After removing the deionized water from the resulting solution, byproducts were removed by phase separation using water and dichloromethane solvents. The final product synthesized by the above method was vacuum dried at 40 °C for 24 hours, and its chemical structure is shown in the FT-IR spectrum of Fig. 2 and the one in Fig. 3 1 H NMR spectrum, of Fig. 4 19 It was confirmed through the F NMR spectrum.

[0200] 1 H NMR (DMSO), δ (ppm): 9.41 (s, 1H), 8.19 (s, 1H), 7.81 (s, 1H), 7.63 (m, 2H), 7.31 (m, 1H), 7.13 (t, 2H), 5.97 (m, 1H), 5.4 (m, 1H)

[0201] 19 F NMR (DMSO), δ (ppm): -78.8 (s), -113.3 (m)

[0202] 3-(4-(fluorosulfonyl) phenyl)-1-vinyl-1H-imidazol-3-ium chloride (g)LiTFSI (g)Deionized water (DI) (ml)16.714.450.0

[0203] Comparative Example 1: Non-aqueous electrolyte prepared by mixing a lithium salt and an organic solvent

[0204] The non-aqueous electrolyte of Comparative Example 1 was prepared by adding a lithium hexafluorophosphate (LiPF6) salt at a concentration of 1 M to a mixed solvent of ethylene carbonate (EC) / ethyl methyl carbonate (EMC) (volume ratio 30 / 70).

[0205]

[0206] Comparative Example 2

[0207] The non-aqueous electrolyte of Comparative Example 2 was prepared by adding 3-(4-(fluorosulfonyl)phenyl)-1-vinyl-imidazolium bistrifluoromethylsulfonylimide ([FSPVI][TFSI]) obtained in the preparation example to the non-aqueous electrolyte of Comparative Example 1 above at a content of 0.1 wt% of the total weight of the non-aqueous electrolyte.

[0208]

[0209] Comparative Example 3

[0210] The non-aqueous electrolyte of Comparative Example 3 was prepared by adding 3-(4-(fluorosulfonyl)phenyl)-1-vinyl-imidazolium bistrifluoromethylsulfonylimide ([FSPVI][TFSI]) obtained in the preparation example to the non-aqueous electrolyte of Comparative Example 1 above at a content of 5.0 wt% of the total weight of the non-aqueous electrolyte.

[0211]

[0212] Comparative Example 4

[0213] A non-aqueous electrolyte of Comparative Example 4 was prepared by adding a compound represented by the following chemical formula 3 to the non-aqueous electrolyte of Comparative Example 1 in an amount of 0.5% by weight of the total weight of the non-aqueous electrolyte.

[0214] [Chemical Formula 3]

[0215]

[0216]

[0217] Comparative Example 5

[0218] A non-aqueous electrolyte of Comparative Example 5 was prepared by adding a compound represented by the following chemical formula 4 to the non-aqueous electrolyte of Comparative Example 1 in an amount of 0.5% by weight of the total weight of the non-aqueous electrolyte.

[0219] [Chemical Formula 4]

[0220]

[0221]

[0222] Comparative Example 6

[0223] A non-aqueous electrolyte of Comparative Example 6 was prepared by adding a compound represented by the following chemical formula 5 to the non-aqueous electrolyte of Comparative Example 1 in an amount of 0.5% by weight of the total weight of the non-aqueous electrolyte.

[0224] [Chemical Formula 5]

[0225]

[0226]

[0227] Example 1

[0228] A non-aqueous electrolyte was prepared by adding 3-(4-(fluorosulfonyl)phenyl)-1-vinyl-imidazolium bistrifluoromethylsulfonylimide ([FSPVI][TFSI]) obtained in the preparation example to the non-aqueous electrolyte of Comparative Example 1 above, such that the content was 0.2% by weight of the total weight of the non-aqueous electrolyte.

[0229]

[0230] Example 2

[0231] A non-aqueous electrolyte was prepared by adding 3-(4-(fluorosulfonyl)phenyl)-1-vinyl-imidazolium bistrifluoromethylsulfonylimide ([FSPVI][TFSI]) obtained in the preparation example to the non-aqueous electrolyte of Comparative Example 1 above at a content of 0.5% by weight of the total weight of the non-aqueous electrolyte.

[0232]

[0233] Example 3

[0234] A non-aqueous electrolyte was prepared by adding 3-(4-(fluorosulfonyl)phenyl)-1-vinyl-imidazolium bistrifluoromethylsulfonylimide ([FSPVI][TFSI]) obtained in the preparation example to the non-aqueous electrolyte of Comparative Example 1 above, such that the content was 3.0 wt% of the total weight of the non-aqueous electrolyte.

[0235]

[0236] Experimental Example

[0237] Experimental Example 1: Evaluation of Electrochemical Properties

[0238] The electrochemical characteristics of the non-aqueous electrolytes prepared in Example 2 and Comparative Example 1 were evaluated. Fig. 5 is a differential charge / discharge graph of a negative half-cell using the non-aqueous electrolyte of Example 2, and Fig. 6 is a differential charge / discharge graph of a negative half-cell using the non-aqueous electrolyte of Comparative Example 1. Specifically, Figs. 5 and 6 are graphs plotted with the X-axis as voltage (V) and the Y-axis as the value obtained by differentiating the battery capacity (Q) with respect to voltage (V) (dQ / dV), after applying a current corresponding to 0.01 C to a negative half-cell using a graphite negative electrode as the working electrode and lithium metal as the reference electrode and charging it to 0.01 V. Fig. 7 is a differential charge / discharge graph of a positive half-cell using the non-aqueous electrolyte of Example 2, and Fig. 8 is a differential charge / discharge graph of a positive half-cell using the non-aqueous electrolyte of Comparative Example 1. Specifically, FIGS. 7 and 8 show LiNi as the positive electrode active material. 0.8 Co 0.1 Mn 0.1 This is a graph in which a positive half-cell, in which a positive electrode containing O2 (hereinafter NCM811) is used as the working electrode and a lithium metal is used as the reference electrode, is charged to 4.3 V by applying a current corresponding to 0.01 C, with the X-axis representing voltage (V) and the Y-axis representing the value obtained by differentiating the battery capacity (Q) with respect to voltage (V) (dQ / dV).

[0239] Unlike in Fig. 6, a new reduction peak is observed in the 1.3 V region for the non-aqueous electrolyte of Example 2 in Fig. 5, which is due to the reduction reaction of the imidazolium-based ionic liquid ([FSPVI][TFSI]) additive. Also, unlike in Fig. 8, a new oxidation peak is observed in the 3.58 V region for the non-aqueous electrolyte of Example 2 in Fig. 7, which is due to the oxidation reaction of the imidazolium-based ionic liquid ([FSPVI][TFSI]) additive. Through these results, it can be seen that when the imidazolium-based ionic liquid ([FSPVI][TFSI]) additive of the present invention is applied to an electrolyte, a film can be formed on the surfaces of the cathode and anode through reduction and oxidation reactions.

[0240]

[0241] Experimental Example 2: Evaluation of Cycle Characteristics

[0242] (Lithium secondary battery manufacturing)

[0243] Graphite as the negative electrode active material, PVDF (poly(vinylidene fluoride)) binder, and Super P conductive material were mixed in a weight ratio of 90:3:7, respectively, and a negative electrode slurry was prepared by dispersing the mixture in N-methyl-2-pyrrolidone (NMP) solvent through stirring for at least 12 hours. The prepared negative electrode slurry was coated onto a copper current collector with a thickness of 15 μm and vacuum dried at 100 °C for at least 12 hours to remove residual solvent and moisture. An anode active material (LiNi) with a composition of 80% Ni content 0.8 Co 0.1 Mn 0.1 O2 (hereinafter NCM811), PVDF binder, and super P conductive material were mixed in a weight ratio of 95:3:2, respectively, and an anode slurry was prepared by dispersing the mixture through stirring for more than 12 hours in an NMP solvent. The prepared NCM811 slurry was coated onto an aluminum current collector with a thickness of 15 μm and then vacuum dried at 80°C for 12 hours to remove residual solvent and moisture.

[0244] A polyethylene separator with a diameter of 18 mm was sandwiched between an NCM811 anode with a diameter of 14 mm and a graphite cathode with a diameter of 16 mm, and then the non-aqueous electrolytes of Examples 1 to 3 and Comparative Examples 1 to 6 were injected to manufacture a 2032 type coin cell.

[0245] A lithium secondary battery prepared using the non-aqueous electrolytes of Examples 1 to 3 and Comparative Examples 1 to 3 was charged and discharged 300 times in the range of 3.0 to 4.3 V at a current corresponding to 1 C, and the discharge capacity according to the cycle was measured, and the results obtained are shown in FIGS. 9 to 11 and Table 3. Specifically, FIG. 9 is a graph showing the charge-discharge capacity according to the progress of the charge-discharge cycle of a lithium secondary battery prepared using the non-aqueous electrolyte of Example 2, FIG. 10 is a graph showing the charge-discharge capacity according to the progress of the charge-discharge cycle of a lithium secondary battery prepared using the non-aqueous electrolyte of Comparative Example 1, and FIG. 11 is a graph showing the charge-discharge capacity according to the progress of the charge-discharge cycle of a lithium secondary battery prepared using the non-aqueous electrolytes of Examples 1 to 3 and Comparative Examples 1 to 3.

[0246] In addition, lithium secondary batteries prepared using the non-aqueous electrolytes of Example 2 and Comparative Examples 1, 4 to 6 were charged and discharged 200 times in the range of 3.0 to 4.3 V at a current corresponding to 1 C, and the discharge capacity according to the charge-discharge cycle was measured, and the obtained results are shown in FIG. 37. Specifically, FIG. 37 is a graph comparing the discharge capacity after 200 charge-discharge cycles of lithium secondary batteries prepared using the non-aqueous electrolytes of Example 2 and Comparative Examples 1, 4 to 6.

[0247]

[0248] A lithium secondary battery using the non-aqueous electrolyte of Examples 1 to 3 containing the imidazolium-based ionic liquid additive according to the present invention exhibited superior lifespan characteristics compared to a secondary battery using the non-aqueous electrolyte of Comparative Examples 1 to 6. Based on these results, it can be seen that when the imidazolium-based ionic liquid additive of the present invention is applied in an amount ranging from 0.2 wt% to 3.0 wt%, a stable film is formed on the surfaces of the negative and positive electrodes through reduction and oxidation reactions, thereby improving the lifespan characteristics of the lithium secondary battery.

[0249] Capacity retention rate (300 cycles, %) Comparative Example 151.7 Comparative Example 250.7 Comparative Example 351.5 Example 163.0 Example 281.9 Example 367.1

[0250] Experimental Example 3: Analysis of Cathode and Anode Surface Film Components

[0251] X-ray Photoelectron Spectroscopy (XPS) surface analysis was performed to investigate the effect of imidazolium-based ionic liquid ([FSPVI][TFSI]) additives on the electrode surface. After performing three charge-discharge cycles on the lithium secondary batteries prepared using Example 2 and Comparative Example 1 at 25°C with a voltage range of 3.0 to 4.3 V and a current corresponding to 0.1 C applied, the cells were disassembled to analyze the difference in composition between the negative and positive electrode surface films.

[0252] F 1s, S 2p, and N 1s XPS spectra of graphite cathode and NCM anode CF (688.6 eV), PF (687.6 eV), Li-F (685.5 eV), -SO4 2- (170.8 eV), -ROSO2 - (169.5 eV), -SO3 2-The XPS spectra obtained from each cathode and anode were decomposed into (168.3 eV), C=N (401.8 eV), and N-SO2 (400.1 eV), respectively, and are shown in Figures 12 to 23. Specifically, FIGS. 12 to 14 show the F 1s XPS spectrum, S 2p XPS spectrum, and N 1s XPS spectrum of the negative electrode surface after activation of a lithium secondary battery prepared using the non-aqueous electrolyte of Example 2; FIGS. 15 to 17 show the F 1s XPS spectrum, S 2p XPS spectrum, and N 1s XPS spectrum of the negative electrode surface after activation of a lithium secondary battery prepared using the non-aqueous electrolyte of Comparative Example 1; FIGS. 18 to 20 show the F 1s XPS spectrum, S 2p XPS spectrum, and N 1s XPS spectrum of the positive electrode surface after activation of a lithium secondary battery prepared using the non-aqueous electrolyte of Example 2; and FIGS. 21 to 23 show the F 1s XPS spectrum, S 2p XPS spectrum, and N 1s XPS spectrum of the positive electrode surface after activation of a lithium secondary battery prepared using the non-aqueous electrolyte of Comparative Example 1.

[0253] Li-F (685.5 eV) possesses robust properties, enabling the maintenance of a stable film shape on the surface of the electrode active material. PF (687.6 eV) is associated with POF3 and PF5, which can be formed by electrolyte decomposition. The electrolyte containing the imidazolium-based ionic liquid ([FSPVI][TFSI]) additive exhibits a high ratio of Li-F components and a low ratio of PF components, indicating that a stable and robust electrode surface film (SEI, CEI) is formed, resulting in reduced electrolyte decomposition. The two peaks observed in the N 1s spectrum indicate the formation of the electrode surface film due to the electrochemical decomposition of the imidazolium-based ionic liquid ([FSPVI][TFSI]).

[0254] XPS analysis results show that the electrode with the non-aqueous electrolyte of Example 2 has an increased proportion of Li-F components that strengthen the physical properties of the film compared to the electrode with the non-aqueous electrolyte of Comparative Example 1, and forms a sulfone-based negative electrode surface film with excellent lithium ion conductivity, thereby improving the lifespan and high-rate characteristics of the lithium secondary battery.

[0255]

[0256] Experimental Example 4: Evaluation of High Rate Characteristics

[0257] Each lithium secondary battery prepared using the non-aqueous electrolytes of Example 2 and Comparative Examples 1, 4 to 6 was charged to 4.3 V at 25°C with a constant current of 0.5 C, and then discharged to 2.5 V at rate limits of 0.5 C, 1.0 C, 2.0 C, 3.0 C, and 5.0 C, with 5 cycles of charge and discharge being performed. The results are shown in FIGS. 24 to 26 below. Specifically, FIG. 24 is a graph comparing the discharge capacity according to the change in C rate of lithium secondary batteries prepared using the non-aqueous electrolytes of Example 2 and Comparative Examples 1, 4 to 6; FIG. 25 is a graph showing the discharge capacity according to the change in C rate of lithium secondary batteries prepared using the non-aqueous electrolyte of Example 2; and FIG. 26 is a graph showing the discharge capacity according to the change in C rate of lithium secondary batteries prepared using the non-aqueous electrolyte of Comparative Example 1.

[0258] As shown in FIG. 24, a lithium secondary battery using the non-aqueous electrolyte of Example 2 containing an imidazolium-based ionic liquid ([FSPVI][TFSI]) additive showed superior performance in high-rate characteristics of 2.0 C or higher compared to the non-aqueous electrolytes of Comparative Examples 1, 4 to 6. Through these results, it can be seen that when the imidazolium-based ionic liquid ([FSPVI][TFSI]) additive of the present invention is applied to the electrolyte, a film with stable lithium ion conductivity characteristics is formed on the electrode surface through reduction and oxidation reactions.

[0259]

[0260] Experimental Example 5: Verification of change in interfacial resistance

[0261] Electrochemical impedance spectroscopy (EIS) was performed to verify changes in lithium secondary battery interfacial resistance following the application of an imidazolium-based ionic liquid ([FSPVI][TFSI]) additive. Generally, the semicircle observed at high frequencies represents the film resistance (R) formed on the electrode surface. f It represents ), and the semicircle observed in the intermediate frequency region represents the resistance (R) of the charge transfer reaction at the electrode surface. ct Fig. 27 is a graph showing the change in interfacial resistance during the first cycle of a lithium secondary battery prepared using the non-aqueous electrolyte of Example 2 and Comparative Example 1, and Fig. 28 is a graph showing the change in interfacial resistance during the 300th cycle of a lithium secondary battery prepared using the non-aqueous electrolyte of Example 2 and Comparative Example 1.

[0262] As shown in FIGS. 27 and 28, a lithium secondary battery using the non-aqueous electrolyte of Example 2, which applied 0.5 wt% imidazolium-based ionic liquid ([FSPVI][TFSI]) additive, showed a lower increase in interfacial resistance after 300 cycles compared to a lithium secondary battery using the non-aqueous electrolyte of Comparative Example 1. These results demonstrate that when the imidazolium-based ionic liquid ([FSPVI][TFSI]) additive of the present invention is applied to the electrolyte, a stable and robust SEI and CEI layer is formed on the electrode surface, which improves lithium mobility and prevents side reactions between the electrode and the electrolyte, thereby suppressing the increase in cell impedance.

[0263]

[0264] Experimental Example 6: Morphology of cathode and anode active materials after cycling (SEM)

[0265] Scanning Electron Microscopy (SEM) images of a graphite cathode and an NCM811 anode containing the non-aqueous electrolyte prepared in Example 2 and Comparative Example 1 above are shown in FIGS. 29 to 36 below. Specifically, FIGS. 29 and 30 are SEM images of a graphite anode before and after 300 charge-discharge cycles of a lithium secondary battery prepared using the non-aqueous electrolyte of Comparative Example 1 of the present invention, FIGS. 31 and 32 are SEM images of a graphite anode before and after 300 charge-discharge cycles of a lithium secondary battery prepared using the non-aqueous electrolyte of Example 2 of the present invention, FIGS. 33 and 34 are SEM images of an NCM cathode before and after 300 charge-discharge cycles of a lithium secondary battery prepared using the non-aqueous electrolyte of Comparative Example 1 of the present invention, FIGS. 35 and 36 are SEM images of an NCM cathode before and after 300 charge-discharge cycles of a lithium secondary battery prepared using the non-aqueous electrolyte of Example 2 of the present invention.

[0266] As can be seen in FIGS. 29, 30, 33, and 34, cracks were observed on the surfaces of the graphite anode and NCM811 cathode of the lithium secondary battery using the non-aqueous electrolyte of Comparative Example 1 after repeated charge-discharge cycles, indicating that the electrode surface film did not function as a robust protective layer. In contrast, FIGS. 31, 32, 35, and 36 show that cracks on the electrode surface were suppressed in the lithium secondary battery using the non-aqueous electrolyte of Example 2. These results indicate that the imidazolium-based ionic liquid ([FSPVI][TFSI]) additive decomposes on the electrode surface and participates in the formation of stable SEI and CEI layers, thereby preventing adverse reactions between the electrode and the electrolyte.

Claims

1. Lithium salt; Organic solvent; and Includes additives; The above additive is a non-aqueous electrolyte comprising a compound represented by the following chemical formula 1: [Chemical Formula 1] In the above chemical formula 1, R1 is an alkenyl group having 2 to 5 carbon atoms, R2 to R4 are independently fluorine or alkyl groups having 1 to 10 carbon atoms substituted with one or more fluorine atoms, and L1 is an alkylene group having 1 to 10 carbon atoms or an arylene group having 6 to 20 carbon atoms.

2. In Claim 1, The above R1 is a non-aqueous electrolyte having 2 to 4 carbon atoms and is an alkenyl group.

3. In Claim 1, The above R1 is an ethenyl group, a non-aqueous electrolyte.

4. In Claim 1, The above R2 to R4 are non-aqueous electrolytes having 1 to 6 carbon atoms, with one or more fluorine atoms substituted.

5. In Claim 1, The above R2 to R4 are non-aqueous electrolytes having 1 to 4 carbon atoms, with one or more fluorine atoms substituted.

6. In Claim 1, The above R2 is a fluorine-based non-aqueous electrolyte.

7. In Claim 1, The above R3 and R4 are each non-aqueous electrolytes that are trifluoromethyl groups.

8. In Claim 1, The above L1 is a non-aqueous electrolyte having 1 to 5 carbon atoms, an alkylene group, or 6 to 20 carbon atoms, an arylene group.

9. In Claim 1, The above L1 is a non-aqueous electrolyte having 1 to 3 carbon atoms, an alkylene group, or 6 to 10 carbon atoms, an arylene group.

10. In Claim 1, The above R1 is a non-aqueous electrolyte selected from the group consisting of substituents represented by the following chemical formulas R1-1, R1-2, and R1-3: [Chemical Formula R1-1] [Chemical Formula R1-2] [Chemical Formula R1-3] 11. In Claim 1, The compound represented by the above chemical formula 1 is a non-aqueous electrolyte comprising the compound represented by the following chemical formula 1-1: [Chemical Formula 1-1] 12. In Claim 1, The above additive is a non-aqueous electrolyte included in the above non-aqueous electrolyte at a concentration of 0.15% to 10% by weight.

13. In Claim 1, The above lithium salt is a non-aqueous electrolyte selected from lithium hexafluorophosphate, lithium tetrafluoroborate, lithium trifluoromethanesulfonate, lithium bistrifluoromethanesulfonylimide, lithium fluorosulfonylimide, lithium perchlorate, lithium bisoxalatoborate, and mixtures of two or more of these.

14. In Claim 1, The above lithium salt is a non-aqueous electrolyte containing a concentration of 0.5 M to 5.0 M.

15. In Claim 1, A non-aqueous electrolyte comprising at least one organic solvent selected from the group consisting of cyclic carbonate-based organic solvents, linear carbonate-based organic solvents, linear ester-based organic solvents, and cyclic ester-based organic solvents.

16. Cathode; An anode facing the above cathode; A separator disposed between the above-mentioned cathode and anode; and A lithium secondary battery comprising a non-aqueous electrolyte according to claim 1.

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