Electrolyte for lithium secondary battery and lithium secondary battery including the same

Abstract

Provided is an electrolyte for a lithium secondary battery, including a nonaqueous organic solvent, a lithium salt, and an additive, the additive including a compound represented by Chemical Formula 1. Details in Chemical Formula 1 are the same as those described in the specification.

Description

Technical Field

[0001] Disclosed are an electrolyte for a lithium secondary battery and a lithium secondary battery including the same. Background Art

[0002] Lithium secondary batteries can be recharged and have a high energy density per unit weight that is three times or more than that of conventional lead-acid batteries, nickel-cadmium batteries, nickel-metal hydride batteries, and nickel-zinc batteries, and can also be charged at a high rate, and are therefore commercially manufactured for use in laptop computers, cellular phones, power tools, and electric bicycles, etc., and research on further improving the energy density has been actively conducted.

[0003] Such a lithium secondary battery is manufactured by injecting an electrolyte into a battery cell including a positive electrode containing a positive electrode active material capable of inserting / deinserting lithium ions and a negative electrode containing a negative electrode active material capable of inserting / deinserting lithium ions.

[0004] In particular, the electrolyte includes an organic solvent in which a lithium salt is dissolved, and critically determines the stability and performance of a lithium secondary battery.

[0005] LiPF6, the lithium salt most commonly used as an electrolyte, has the problem of reacting with the electrolyte solvent to cause the solvent to be consumed and generate a large amount of gas. When LiPF6 decomposes, it generates LiF and PF5, resulting in electrolyte consumption in the battery, resulting in decreased high temperature performance and poor safety.

[0006] There is a need for an electrolyte that suppresses the side reaction of such lithium salts and improves the performance of the battery. Summary of the invention

[0007] Technical issues

[0008] Embodiments provide an electrolyte for a lithium secondary battery that can improve battery performance by ensuring high temperature stability.

[0009] Another embodiment provides a lithium secondary battery including an electrolyte for a lithium secondary battery.

[0010] Technical Solution

[0011] An embodiment of the present invention provides an electrolyte for a lithium secondary battery, which includes a nonaqueous organic solvent, a lithium salt, and an additive, wherein the additive includes a compound represented by Chemical Formula 1.

[0012] [Chemical formula 1]

[0013]

[0014] In Chemical Formula 1,

[0015] R 1 To R5 each independently represents hydrogen, halogen, substituted or unsubstituted C1 to C10 alkyl, substituted or unsubstituted C1 to C10 alkoxy, substituted or unsubstituted C2 to C10 alkenyl, substituted or unsubstituted C3 to C10 cycloalkyl, substituted or unsubstituted C3 to C10 cycloalkenyl, substituted or unsubstituted C2 to C10 alkynyl, substituted or unsubstituted C3 to C10 cycloalkynyl, or substituted or unsubstituted C6 to C20 aryl,

[0016] R 1 To R 3 At least one of them is a fluorine group (-F),

[0017] R 6 is a substituted or unsubstituted C1 to C10 alkyl group, a substituted or unsubstituted C1 to C10 alkoxy group, a substituted or unsubstituted C2 to C10 alkenyl group, a substituted or unsubstituted C3 to C10 cycloalkyl group, a substituted or unsubstituted C3 to C10 cycloalkenyl group, a substituted or unsubstituted C2 to C10 alkynyl group, or a substituted or unsubstituted C3 to C10 cycloalkynyl group, and

[0018] n is an integer of any one of 1 to 20.

[0019] R in Formula 1 1 To R 3 One or both of them may be a fluorine group (—F).

[0020] For example, it may be represented by Chemical Formula 1A.

[0021] [Chemical Formula 1A]

[0022]

[0023] In Chemical Formula 1A,

[0024] R 2 To R 6 The definitions of and n are the same as above.

[0025] For example, n in Chemical Formula 1 may be any integer of 1 to 10.

[0026] As a specific example, n in Chemical Formula 1 may be any integer of 1 to 5.

[0027] For example, Chemical Formula 1 may be represented by Chemical Formula 1A-1.

[0028] [Chemical Formula 1A-1]

[0029]

[0030] In Chemical Formula 1A-1,

[0031] R 2 To R 6 The definitions of and n are the same as above.

[0032] R 4a , R 4b , R 4c , R 5a , R 5b and R 5c Each may independently be hydrogen, halogen, substituted or unsubstituted C1 to C10 alkyl, substituted or unsubstituted C1 to C10 alkoxy, substituted or unsubstituted C2 to C10 alkenyl, substituted or unsubstituted C3 to C10 cycloalkyl, substituted or unsubstituted C3 to C10 cycloalkenyl, substituted or unsubstituted C2 to C10 alkynyl, substituted or unsubstituted C3 to C10 cycloalkynyl, or substituted or unsubstituted C6 to C20 aryl.

[0033] For example, in Formula 1, R 1 To R 3 and R 6 may each independently be halogen, substituted or unsubstituted C1 to C10 alkyl, or substituted or unsubstituted C2 to C5 alkenyl, and R 1 To R 3 Any one of them may be a fluoro group (—F).

[0034] The compound represented by Chemical Formula 1 may be included in an amount of 0.1 wt % to 10 wt % based on the total amount of the electrolyte for a lithium secondary battery.

[0035] The compound represented by Chemical Formula 1 may be included in an amount of 0.2 wt % to 2.0 wt % based on the total amount of the electrolyte for a lithium secondary battery.

[0036] Another embodiment of the present invention provides a lithium secondary battery including a positive electrode including a positive electrode active material; a negative electrode including a negative electrode active material; and the aforementioned electrolyte.

[0037] The negative electrode active material may include a Si—C composite material including a Si-based active material and a carbon-based active material.

[0038] The negative electrode active material may further include crystalline carbon.

[0039] The crystalline carbon may include graphite, and the graphite may include natural graphite, artificial graphite, or a mixture thereof.

[0040] The Si—C composite material may further include a shell surrounding a surface of the Si—C composite material, and the shell may include amorphous carbon.

[0041] The amorphous carbon may include soft carbon, hard carbon, a product of carbonization of mesophase pitch, calcined coke, or a mixture thereof.

[0042] The positive electrode active material may be a composite oxide containing nickel metal and lithium.

[0043] The positive electrode active material can be represented by Chemical Formula 5.

[0044] [Chemical formula 5]

[0045] Li a M 1 1-y1-z1 M 2 y1 M 3 z1 O2

[0046] In Chemical Formula 5,

[0047] 0.9≤a≤1.8, 0≤y1≤1, 0≤z1≤1, 0≤y1+z1<1, and M 1 、M 2 and M 3 Each is independently selected from metals such as Ni, Co, Mn, Al, Sr, Mg or La and combinations thereof.

[0048] Beneficial Effects

[0049] A lithium secondary battery having improved high temperature stability and cycle life characteristics may be implemented. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 A schematic diagram illustrating a lithium secondary battery according to an embodiment of the present invention.

[0051] Figure 2 is a graph showing cycle life characteristics of the secondary battery cells according to Examples 5 to 8 and Comparative Examples 6 to 10 at room temperature (25° C.).

[0052] Figure 3 Graph showing the internal resistance increase rate of the secondary battery cells according to Examples 5 to 8 and Comparative Examples 6 to 10 when left at high temperature.

[0053] Figure 4 It is a graph measuring the CID (current interrupt device) operation time of the secondary battery cells according to Examples 5 to 8 and Comparative Examples 6 to 10.

[0054] Figure 5 Graph showing cycle life characteristics of secondary battery cells according to Examples 1 to 4 and Comparative Examples 1 to 5 at room temperature (25° C.).

[0055] Figure 6A graph for explaining the internal resistance increase rate of the secondary battery cells according to Examples 1 to 4 and Comparative Examples 1 to 5 when left at high temperature.

[0056] Figure 7 It is a graph measuring the CID (current interrupt device) operation time of the secondary battery cells according to Examples 1 to 4 and Comparative Examples 1 to 5.

[0057] <symbol description>

[0058] 100: Lithium secondary battery

[0059] 112: Negative electrode

[0060] 113: Partition

[0061] 114: Positive electrode

[0062] 120: Battery housing

[0063] 140: Sealing member DETAILED DESCRIPTION

[0064] Hereinafter, embodiments of the present invention are described in detail. However, these embodiments are exemplary, the present invention is not limited thereto, and the present invention is defined by the scope of the claims.

[0065] In the present specification, when no limitation is provided otherwise, "substituted" means that a hydrogen atom of a compound is replaced by a substituent selected from the group consisting of a halogen atom (F, Br, Cl or I), a hydroxyl group, an alkoxy group, a nitro group, a cyano group, an amino group, an azido group, an amidino group, a hydrazine group, a hydrazone group, a carbonyl group, a carbamoyl group, a thiol group, an ester group, a carboxyl group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphate group or a salt thereof, a C1 to C20 alkyl group, a C2 to C20 alkenyl group, a C2 to C20 alkynyl group, a C6 to C30 aryl group, a C7 to C30 arylalkyl group, a C1 to C4 alkoxy group, a C1 to C20 heteroalkyl group, a C3 to C20 heteroarylalkyl group, a C3 to C30 cycloalkyl group, a C3 to C15 cycloalkenyl group, a C6 to C15 cycloalkynyl group, a C2 to C20 heterocycloalkyl group and combinations thereof.

[0066] Hereinafter, an electrolyte for a lithium secondary battery according to an embodiment is described.

[0067] An electrolyte for a lithium secondary battery according to an embodiment of the present invention includes a nonaqueous organic solvent, a lithium salt, and an additive, wherein the additive includes a compound represented by Chemical Formula 1.

[0068] [Chemical formula 1]

[0069]

[0070] In Chemical Formula 1,

[0071] R1 To R 5 each independently represents hydrogen, halogen, substituted or unsubstituted C1 to C10 alkyl, substituted or unsubstituted C1 to C10 alkoxy, substituted or unsubstituted C2 to C10 alkenyl, substituted or unsubstituted C3 to C10 cycloalkyl, substituted or unsubstituted C3 to C10 cycloalkenyl, substituted or unsubstituted C2 to C10 alkynyl, substituted or unsubstituted C3 to C10 cycloalkynyl, or substituted or unsubstituted C6 to C20 aryl,

[0072] R 1 To R 3 At least one of them is a fluorine group (-F),

[0073] R 6 is a substituted or unsubstituted C1 to C10 alkyl group, a substituted or unsubstituted C1 to C10 alkoxy group, a substituted or unsubstituted C2 to C10 alkenyl group, a substituted or unsubstituted C3 to C10 cycloalkyl group, a substituted or unsubstituted C3 to C10 cycloalkenyl group, a substituted or unsubstituted C2 to C10 alkynyl group, or a substituted or unsubstituted C3 to C10 cycloalkynyl group, and

[0074] n is an integer of any one of 1 to 20.

[0075] Meanwhile, when n is an integer of 2 or more, at least two R 4 Or at least two R's 5 Can be the same or different.

[0076] The compound represented by Chemical Formula 1 included in the additive according to an embodiment of the present invention includes a silyl functional group substituted with a sulfite group (—SO 3 —) and at least one fluorine group in one molecule.

[0077] These decompose into lithium salts in the electrolyte to form films on the surfaces of the positive electrode and the negative electrode, respectively, thereby lowering initial resistance, suppressing the high-temperature storage resistance increase rate, and reducing gas generation.

[0078] Specifically, LiSO3R 6+ , lithium salts including sulfite functional groups migrate to the negative electrode, and thus are reduced and decomposed on the surface of the negative electrode, and can form an excellent SEI (solid electrolyte interface) film having excellent ion conductivity and being strong on the surface of the negative electrode, and accordingly, the formation of the initial SEI film can inhibit the decomposition of the negative electrode surface that can occur during high-temperature cycle operation, and in addition, can prevent the collapse of the initially formed SEI film that may occur during high-temperature storage. In addition, sulfite can also form a film on the surface of the positive electrode, and thus prevent oxidation of the electrolyte at the positive electrode, and thus reduce the resistance increase rate in the lithium secondary battery.

[0079] Additionally, during the initial reduction of the electrolyte on the negative electrode surface, F - SEI including LiF having strong adhesion can be formed, and thus the volume expansion degree of the negative electrode including Si can be reduced. Accordingly, the lithium secondary battery using the negative electrode including Si can show the effect of reducing the amount of gas generated during high temperature storage and improving the effect of long-term cycle life.

[0080] For example, R in Formula 1 1 To R 3 One or both of may be a fluorine group (—F).

[0081] When the number of substituted fluorine groups is kept at a maximum of two, the amount of gas generated during high temperature storage can be minimized.

[0082] For example, R in Formula 1 1 To R 3 One of the groups may be a fluorine group (—F), and may, for example, be represented by Chemical Formula 1A.

[0083] [Chemical Formula 1A]

[0084]

[0085] In Chemical Formula 1A,

[0086] R 2 To R 6 The definitions of and n are the same as above.

[0087] For example, n in Chemical Formula 1 may be any integer of 1 to 10.

[0088] As a specific example, n in Chemical Formula 1 may be any integer of 1 to 5.

[0089] As a more specific example, n in Chemical Formula 1 may be any integer of 2 to 5.

[0090] For example, n in Chemical Formula 1 may be an integer of 3, and may be represented by Chemical Formula 1A-1.

[0091] [Chemical Formula 1A-1]

[0092]

[0093] In Chemical Formula 1A-1,

[0094] R 2 To R 6 The definitions of and n are the same as above, and

[0095] R 4a , R4b , R 4c , R 5a , R 5b and R 5c Each may independently be hydrogen, halogen, substituted or unsubstituted C1 to C10 alkyl, substituted or unsubstituted C1 to C10 alkoxy, substituted or unsubstituted C2 to C10 alkenyl, substituted or unsubstituted C3 to C10 cycloalkyl, substituted or unsubstituted C3 to C10 cycloalkenyl, substituted or unsubstituted C2 to C10 alkynyl, substituted or unsubstituted C3 to C10 cycloalkynyl, or substituted or unsubstituted C6 to C20 aryl.

[0096] For example, in Formula 1, R 1 To R 3 and R 6 may each independently be halogen, substituted or unsubstituted C1 to C10 alkyl, or substituted or unsubstituted C2 to C5 alkenyl, and R 1 To R 3 Any one of them may be a fluoro group (—F).

[0097] As a specific example, in Chemical Formula 1, R 1 To R 3 and R 6 may be each independently halogen, or a substituted or unsubstituted C1 to C10 alkyl group, and R 1 To R 3 Any one of them may be a fluoro group (—F).

[0098] In addition, as an example, R in Chemical Formula 1 4 and R 5 Each may independently be hydrogen, a substituted or unsubstituted C1 to C10 alkyl group, or a substituted or unsubstituted C2 to C10 alkenyl group.

[0099] As a specific example, R in Chemical Formula 1 4 and R 5 Each of may be hydrogen, or at least one may be a C1 to C5 alkyl group, but is not limited thereto.

[0100] The compound represented by Chemical Formula 1 may be included in an amount of 0.1 wt % to 10 wt %, specifically 0.1 wt % to 5.0 wt % or more specifically 0.2 wt % to 2.0 wt %, based on the total amount of the electrolyte for a lithium secondary battery.

[0101] When the content range of the compound represented by Chemical Formula 1 is as described above, a lithium secondary battery having improved cycle-life characteristics may be implemented by preventing an increase in resistance at high temperature and suppressing gas generation.

[0102] That is, when the content of the compound represented by Formula 1 is less than 0.1 wt %, high temperature storage characteristics may be reduced, and when it exceeds 10 wt %, cycle life may be reduced due to an increase in interface resistance.

[0103] The nonaqueous organic solvent serves as a medium for transporting ions participating in the electrochemical reaction of the battery.

[0104] The non-aqueous organic solvent may include carbonates, esters, ethers, ketones, alcohols or aprotic solvents.

[0105] Carbonate solvents can be dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), ethyl methyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC) and butylene carbonate (BC) etc. Ester solvents can be methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, decanoic acid lactone, mevalonate lactone and caprolactone etc. Ether solvents can be dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, dimethoxyethane, 2-methyltetrahydrofuran and tetrahydrofuran etc. In addition, ketone solvents can be cyclohexanone etc. In addition, the alcohol solvent may be ethanol and isopropanol, etc., and the aprotic solvent may be a nitrile, such as R-CN is a C2 to C20 straight chain, branched or cyclic hydrocarbon group and may include an aromatic ring with a double bond or an ether bond, an amide such as dimethylformamide, a dioxolane such as 1,3-dioxolane and cyclopentane, etc.

[0106] The nonaqueous organic solvent may be used alone or in a mixture, and when the organic solvent is used in a mixture, the mixing ratio may be controlled in accordance with desired battery performance.

[0107] The carbonate-based solvent is prepared by mixing a cyclic carbonate and a chain carbonate. In this case, when the cyclic carbonate and the chain carbonate are mixed in a volume ratio of 1:1 to 1:9, the performance of the electrolyte may be improved.

[0108] The non-aqueous organic solvent may further include an aromatic hydrocarbon organic solvent in a carbonate-based solvent. In this case, the carbonate-based solvent and the aromatic hydrocarbon solvent may be mixed in a volume ratio of 1:1 to 30:1.

[0109] As the aromatic hydrocarbon solvent, an aromatic hydrocarbon compound represented by Chemical Formula 3 may be used.

[0110] [Chemical formula 3]

[0111]

[0112] In chemical formula 3, R 7 To R 12are the same or different and are selected from hydrogen, halogen, C1 to C10 alkyl, haloalkyl, and combinations thereof.

[0113] Specific examples of the aromatic hydrocarbon solvents may be selected from benzene, fluorobenzene, 1,2-difluorobenzene, 1,3-difluorobenzene, 1,4-difluorobenzene, 1,2,3-trifluorobenzene, 1,2,4-trifluorobenzene, chlorobenzene, 1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene, 1,2,3-trichlorobenzene, 1,2,4-trichlorobenzene, iodobenzene, 1,2-diiodobenzene, 1,3-diiodobenzene, 1,4-diiodobenzene, 1,2,3-triiodobenzene, 1,2,4-triiodobenzene, toluene, fluorotoluene, , 2,3-difluorotoluene, 2,4-difluorotoluene, 2,5-difluorotoluene, 2,3,4-trifluorotoluene, 2,3,5-trifluorotoluene, chlorotoluene, 2,3-dichlorotoluene, 2,4-dichlorotoluene, 2,5-dichlorotoluene, 2,3,4-trichlorotoluene, 2,3,5-trichlorotoluene, iodotoluene, 2,3-diiodotoluene, 2,4-diiodotoluene, 2,5-diiodotoluene, 2,3,4-triiodotoluene, 2,3,5-triiodotoluene, xylene, and combinations thereof.

[0114] In order to improve the cycle life of the battery, the electrolyte may further include vinylene carbonate or an ethylene carbonate-based compound represented by Chemical Formula 4 as a cycle life improving additive to improve the cycle life of the battery.

[0115] [Chemical formula 4]

[0116]

[0117] In chemical formula 4, R 13 and R 14 are the same or different and are selected from hydrogen, halogen, cyano (CN), nitro (NO2) and fluorinated C1 to C5 alkyl, provided that R 13 and R 14 At least one of is halogen, cyano (CN), nitro (NO2) and fluorinated C1 to C5 alkyl, and R 13 and R 14 Neither is hydrogen.

[0118] Examples of ethylene carbonate compounds may include difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate, or fluoroethylene carbonate. The amount of the additive for improving the cycle life may be used within an appropriate range.

[0119] The lithium salt is dissolved in a non-aqueous organic solvent, supplies lithium ions to the battery, enables the basic operation of the lithium secondary battery, and improves the transmission of lithium ions between the positive electrode and the negative electrode. Examples of lithium salts include one or more selected from the following: LiPF6, LiBF4, LiSbF6, LiAsF6, LiN(SO2C2F5)2, Li(CF3SO2)2N, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide: LiFSI), LiC4F9SO3, LiClO4, LiAlO2, LiAlCl4, LiN(C x F 2x+1 SO2)(C y F 2y+1 SO2) (wherein, x and y are natural numbers, such as integers of 1 to 20), LiCl, LiI, and LiB(C2O4)2 (lithium bis(oxalato)borate: LiBOB). The lithium salt may be used in a concentration range of 0.1 M to 2.0 M. When the lithium salt is included in the above concentration range, the electrolyte may have excellent performance and lithium ion mobility due to optimal electrolyte conductivity and viscosity.

[0120] Another embodiment of the present invention provides a lithium secondary battery including a positive electrode including a positive electrode active material; a negative electrode including a negative electrode active material; and the aforementioned electrolyte.

[0121] The positive electrode may include a current collector and a positive active material layer including a positive active material formed on the current collector.

[0122] The positive active material may include a lithiated intercalation compound that reversibly intercalates and deintercalates lithium ions.

[0123] Specifically, a composite oxide containing nickel metal and lithium may be used.

[0124] A specific example thereof may be a compound represented by one of the following chemical formulae.

[0125] Li a A 1-b X b D2(0.90≤a≤1.8, 0≤b≤0.5); Li a A 1-b X b O 2-c D c (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05); Li a E 1-b X b O 2-c D c (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05); Li aHAVE BEEN 2-b X b O 4-c D c (0.90≤a≤1.8,0≤b≤0.5,0≤c≤0.05);Li a Ni 1-b-c Co b X c D α (0.90≤a≤1.8,0≤b≤0.5,0≤c≤0.5,0<α≤2);Li a Ni 1-b-c Co b X c O 2-α T α (0.90≤a≤1.8,0≤b≤0.5,0≤c≤0.05,0<α<2);Li a Ni 1-b-c Co b X c O 2-α T2(0.90≤a≤1.8,0≤b≤0.5,0≤c≤0.05,0<α<2);Li a Ni 1-b-c Mr b X c D α (0.90≤a≤1.8,0≤b≤0.5,0≤c≤0.05,0<α≤2);Li a Ni 1-b-c Mr b X c O 2-α T α (0.90≤a≤1.8,0≤b≤0.5,0≤c≤0.05,0<α<2);Li a Ni 1-b-c Mr b X c O 2-α T2(0.90≤a≤1.8,0≤b≤0.5,0≤c≤0.05,0<α<2);Li a Ni b HAVE BEEN c G d O2(0.90≤a≤1.8,0≤b≤0.9,0≤c≤0.5,0.001≤d≤0.1);Li a Ni b Co c Mr d G e O2(0.90≤a≤1.8,0≤b≤0.9,0≤c≤0.5,0≤d≤0.5,0.001≤e≤0.1);Lia NeG b O2(0.90≤a≤1.8, 0.001≤b≤0.1); Li a CoG b O2(0.90≤a≤1.8, 0.001≤b≤0.1); Li a Mn 1-b G b O2(0.90≤a≤1.8, 0.001≤b≤0.1); Li a Mn b O4(0.90≤a≤1.8, 0.001≤b≤0.1); Li a Mn 1-g G g PO4(0.90≤a≤1.8, 0≤g≤0.5); QO2; QS2; LiQS2; V2O5; LiV2O5; LiZO2; LiNiVO4; Li (3-f) J2(PO4)3(0≤f≤2);Li (3-f) Fe2(PO4)3(0≤f≤2);Li a FePO4(0.90≤a≤1.8).

[0126] In the above chemical formula, A is selected from Ni, Co, Mn and combinations thereof; X is selected from Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, rare earth elements and combinations thereof; D is selected from O, F, S, P and combinations thereof; E is selected from Co, Mn and combinations thereof; T is selected from F, S, P and combinations thereof; G is selected from Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V and combinations thereof; Q is selected from Ti, Mo, Mn and combinations thereof; Z is selected from Cr, V, Fe, Sc, Y and combinations thereof; and J is selected from V, Cr, Mn, Co, Ni, Cu and combinations thereof.

[0127] The positive electrode active material may include a positive electrode active material with a coating, or a compound of a positive electrode active material and a positive electrode active material coated with a coating. The coating may include the following coating element compounds: oxides or hydroxides of coating elements, oxyhydroxides of coating elements, oxycarbonates of coating elements, or basic carbonates of coating elements. The compound used for the coating may be amorphous or crystalline. The coating element included in the coating may be Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or a mixture thereof. The coating process may include any conventional process as long as it does not cause any adverse effects on the characteristics of the positive electrode active material (e.g., spraying or dipping), which is well understood by those skilled in the relevant art, so a detailed description will be omitted.

[0128] More specifically, at least one type of lithium composite oxide represented by Chemical Formula 5 may be used.

[0129] [Chemical formula 5]

[0130] Li a M 1 1-y1-z1 M 2 y1 M 3 z1 O2

[0131] In Chemical Formula 5,

[0132] 0.9≤a≤1.8, 0≤y1≤1, 0≤z1≤1, 0≤y1+z1<1, and M 1 、M 2 and M 3 Each is independently selected from metals such as Ni, Co, Mn, Al, Sr, Mg or La and combinations thereof.

[0133] For example, M 1 can be Ni, and M 2 and M 3 Each may independently be a metal such as Co, Mn, Al, Sr, Mg or La.

[0134] More specifically, M 1 Can be Ni, M 2 Can be Co, and M 3 It may be Mn or Al, but is not limited thereto.

[0135] Specific examples of the positive electrode active material according to the embodiment of the present invention include Li x Ni y Co z Al 1-y-z O2(1≤x≤1.2, 0.5≤y≤1, and 0≤z≤0.5).

[0136] The positive active material may be included in an amount of 90 wt % to 98 wt % based on the total weight of the positive active material layer.

[0137] In an embodiment, the positive active material layer may include a binder and a conductive material. Here, each amount of the binder and the conductive material may be 1 wt % to 5 wt % based on the total weight of the positive active material layer.

[0138] The binder improves the bonding properties between the positive electrode active material particles and the bonding properties between the positive electrode active material particles and the collector, and examples thereof may include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin and nylon, but are not limited thereto.

[0139] A conductive material is included to improve the conductivity of the electrode, and any conductive material can be used as the conductive material unless it causes a chemical change, and examples of the conductive material include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black and carbon fiber, etc.; metal-based materials of metal powder or metal fiber, including copper, nickel, aluminum and silver, etc.; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0140] The current collector may be Al, but is not limited thereto.

[0141] The negative electrode includes a current collector and a negative active material layer formed on the current collector.

[0142] The negative electrode active material may be a material that reversibly intercalates / deintercalates lithium ions, lithium metal, a lithium metal alloy, a material capable of doping and dedoping lithium, or a transition metal oxide.

[0143] The material that reversibly intercalates / deintercalates lithium ions includes a carbon material, and the carbon material may be any commonly used carbon-based negative electrode active material in a lithium ion secondary battery, and examples of the carbon material include crystalline carbon, amorphous carbon, and combinations thereof. The crystalline carbon may be shapeless, or flake, scale, spherical or fibrous natural graphite or artificial graphite, and the amorphous carbon may be soft carbon, hard carbon, a product of carbonization of mesophase pitch, and calcined coke, etc.

[0144] The lithium metal alloy may include lithium and a metal selected from the group consisting of Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn.

[0145] Materials that can be doped and dedoped with lithium may include Si, SiO x(0 < x < 2), Si-Q alloys (where Q is selected from alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, Group 15 elements, Group 16 elements, transition metals, rare earth elements, and combinations thereof, and is not Si), Sn, SnO2, and Sn-R alloys (where R is an alkali metal, alkaline earth metal, Group 13 element, Group 14 element, Group 15 element, Group 16 element, transition element, rare earth element, or combination thereof, and is not Sn), etc., and at least one of them can be mixed with SiO2. Elements Q and R can be selected from Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, 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, Tl, Ge, P, As, Sb, Bi, S, Se, Te, Po, and combinations thereof.

[0146] The transition metal oxide can be vanadium oxide, lithium vanadium oxide, etc.

[0147] The negative electrode active material according to an embodiment can include a Si-C composite material including a Si-based active material and a carbon-based active material.

[0148] The Si-based active material can have an average particle size of 50 nm to 200 nm.

[0149] When the Si-based active material has an average particle size within this range, volume expansion occurring during charging and discharging can be suppressed, and disconnection of the conduction path caused by particles crushed during charging and discharging can be prevented.

[0150] Based on the total weight of the Si-C composite material, the amount of the Si-based active material included can be 1 wt% to 60 wt%, or for example, 3 wt% to 60 wt%.

[0151] According to another exemplary embodiment, in addition to the Si-C composite material, the negative electrode active material can further include crystalline carbon.

[0152] When the negative electrode active material includes a Si-C composite material and crystalline carbon, the Si-C composite material and crystalline carbon can be included in the form of a mixture, and in this case, the Si-C composite material and crystalline carbon can be included in a weight ratio of 1:99 to 50:50. More specifically, the Si-C composite material and crystalline carbon can be included in a weight ratio of 5:95 to 20:80.

[0153] The crystalline carbon can include, for example, graphite, and more specifically, includes natural graphite, artificial graphite, or a mixture thereof.

[0154] The average particle size of the crystalline carbon can be 5 μm to 30 μm.

[0155] In this specification, the average particle size may be the particle size (D 50 ).

[0156] The Si—C composite material may further include a shell surrounding a surface of the Si—C composite material, and the shell may include amorphous carbon.

[0157] The amorphous carbon may include soft carbon, hard carbon, a product of carbonization of mesophase pitch, calcined coke, or a mixture thereof.

[0158] The amorphous carbon may be included in an amount of 1 to 50 parts by weight, for example, 5 to 50 parts by weight, or 10 to 50 parts by weight, based on 100 parts by weight of the carbon-based active material.

[0159] In the negative active material layer, the negative active material may be included in an amount of 95 wt % to 99 wt % based on the total weight of the negative active material layer.

[0160] In an embodiment, the negative electrode active material layer may include a binder and optionally a conductive material. In the negative electrode active material layer, the amount of the binder may be 1wt% to 5wt% based on the total weight of the negative electrode active material layer. When it further includes a conductive material, it may include 90wt% to 98wt% of the negative electrode active material, 1wt% to 5wt% of the binder and 1wt% to 5wt% of the conductive material.

[0161] The binder improves the bonding characteristics between the negative electrode active material particles and between the negative electrode active material particles and the current collector. The binder may be a non-water-soluble binder, a water-soluble binder or a combination thereof.

[0162] The non-water-soluble binder may be polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyimide or a combination thereof.

[0163] The water-soluble binder can be a rubber-based binder or a polymer resin binder. The rubber-based binder can be selected from styrene-butadiene rubber, acrylated styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber, acrylic rubber, butyl rubber, fluororubber and a combination thereof. The polymer resin binder can be selected from polytetrafluoroethylene, ethylene propylene copolymer, polyethylene oxide, polyvinyl pyrrolidone, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, polystyrene, ethylene propylene diene copolymer, polyvinyl pyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol and a combination thereof.

[0164] When a water-soluble binder is used as a negative electrode binder, a cellulose compound may be further used to provide viscosity. The cellulose compound includes one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose or an alkali metal salt thereof. The alkali metal may be Na, K or Li. Based on 100 parts by weight of the negative electrode active material, the amount of such a thickener included may be 0.1 parts by weight to 3 parts by weight.

[0165] A conductive material is included to provide electrode conductivity, and any conductive material can be used as the conductive material unless it causes a chemical change, and examples thereof can be carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black and carbon fiber, etc.; metal-based materials such as metal powder or metal fiber of copper, nickel, aluminum and silver, etc.; conductive polymers such as polyphenylene derivatives, etc., or mixtures thereof.

[0166] The current collector may be selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof.

[0167] The separator may be present between the positive electrode and the negative electrode, depending on the type of lithium secondary battery. Such a separator may include a multilayer film of polyethylene, polypropylene, polyvinylidene fluoride or two or more layers thereof, such as a polyethylene / polypropylene double-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, and a polypropylene / polyethylene / polypropylene three-layer separator.

[0168] refer to Figure 1 According to an embodiment, a lithium secondary battery 100 includes: a battery cell including a negative electrode 112; a positive electrode 114 facing the negative electrode 112; a separator 113 inserted between the negative electrode 112 and the positive electrode 114; and an electrolyte (not shown) impregnating the negative electrode 112, the positive electrode 114 and the separator 113; a battery case 120 configured to accommodate the battery cell; and a sealing member 140 that seals the battery case 120.

[0169] Hereinafter, examples of the present invention and comparative examples are described. However, these examples are by no means construed as limiting the scope of the present invention.

[0170] Manufacturing of lithium secondary battery cells

[0171] Preparation Example: Synthesis of the compound represented by chemical formula a

[0172]

[0173] Step 1: Synthesis of allyloxytrimethylsilane

[0174] After heating the dried flask, allyl alcohol (1.0 eq) and trimethylchlorosilane (0.1 eq) were added and stirred under a nitrogen atmosphere. Subsequently, hexamethyldisilazane (0.5 eq) was slowly added dropwise at 0°C. When the dropwise addition was completed, after stirring the mixture for 1 hour and then connecting a reflux cooler to the flask, the flask was heated at 110°C for 19 hours. The resultant was purified by simple distillation to obtain allyloxytrimethylsilane.

[0175] bp = 97-99°C / 760 mmHg;

[0176] 1 H NMR (400MHz, CDCl3): δ5.94 (m, 1H), 5.25 (d, 1H), 5.10 (d, 1H), 4.14 (d, 1H), 0.15 (s, 9H)

[0177] Step 2: Synthesis of 3-(chlorodimethylsilyl)propoxy]trimethylsilane

[0178] After heating the dry flask, platinum oxide (10 mg to 40 mg) and allyloxytrimethylsilane (1.0 eq) were added and stirred. Subsequently, 1.2 eq to 2.0 eq of dimethylchlorosilane was slowly added dropwise at 0°C until all the allyloxytrimethylsilane reacted. When the dropwise addition was completed, the mixture was stirred for 2 hours. 1 The reaction was monitored by H NMR until all the allyloxytrimethylsilane was consumed. When it was confirmed that allyloxytrimethylsilane was consumed, the catalyst was removed with a diatomaceous earth pad, and the excess dimethylchlorosilane was removed by a pressure reducer to obtain a light yellow opaque liquid. The liquid can be purified by distillation, but since other substances are known to be produced during the purification process, the following reaction was carried out without purification.

[0179] 1 H NMR (400MHz, CDCl3): δ3.56 (t, 2H), 1.67-1.59 (m, 2H), 0.84-0.79 (m, 2H), 0.41 (s, 6H), 0.11 (s, 9H)

[0180] Step 3: Synthesis of 3-(fluorodimethylsilyl)-1-propanol

[0181] 3-[(Chlorodimethylsilyl)propoxy]trimethylsilane was put into a TEFLON (tetrafluoroethylene) tube, an excess of HF (48 wt %) was added thereto, and then, stirred for about 3 hours, and passed through 1The reaction was monitored by H NMR. The solution thus obtained was washed several times with sodium bicarbonate and distilled water, dried with MgSO4, and filtered to obtain a yellow transparent liquid. The liquid was purified by vacuum distillation to obtain 3-(fluorodimethylsilyl)-1-propanol as a colorless transparent liquid.

[0182] bp = 71°C (10 Torr);

[0183] 1 H NMR (400MHz, CDCl3): δ3.62 (t, 2H), 1.65 (m, 2H), 1.57 (s, 1H), 0.72 (m, 2H)

[0184] Step 4: 3-(Fluorodimethylsilyl)-1-propyl methanesulfonate

[0185] After molecular sieve is put into the flask of heat drying, under argon atmosphere, 3-(fluorodimethylsilyl)-1-propyl alcohol (1.0eq) and triethylamine (1.2eq) are put into wherein and stirred 10 minutes. Subsequently, methanesulfonic anhydride (1.2eq) is dissolved in methylene dichloride, and then the flask in ice water is added in a dropwise manner. The solution obtained is rinsed with distilled water several times, MgSO is used Drying, and by underpressure distillation purification, 3-(fluorodimethylsilyl)-1-propyl methanesulfonate is obtained.

[0186] bp = 88°C (0.1 Torr);

[0187] 1 H NMR (400MHz, CDCl3): δ4.20 (t, 2H), 3.08 (s, 3H), 1.89-1.81 (m, 2H), 0.78-0.72 (m, 2H), 0.27-0.23 (m, 6H)

[0188] Comparative Preparation Example: Synthesis of the compound represented by chemical formula b

[0189] Synthesis of 3-(fluorodimethylsilyl)propyl methanesulfonate:

[0190] After molecular sieve is put into the flask of heat drying, 3-(trimethylsilyl)-1-propanol (1.0eq) and triethylamine (1.2eq) are put into it and stirred for 10 minutes under argon atmosphere. Subsequently, the dichloromethane dissolved with methanesulfonic anhydride (1.2eq) is added to the flask in ice water in a dropwise manner. The resulting solution is rinsed with distilled water several times, MgSO is used and dried, and purified by underpressure distillation to obtain 3-(fluorodimethylsilyl)-1-propyl methanesulfonate.

[0191] bp = 111°C (96 mmHg);

[0192] 1H NMR (400MHz, CDCl3): δ4.35 (t, 2H), 3.12 (s, 3H), 1.85 (m, 2H), 0.81 (m, 2H), 0.17 (m, 9H)

[0193]

[0194] Example 1

[0195] LiNi as the positive electrode active material 0.88 Co 0.105 Al 0.015 O2, polyvinylidene fluoride as a binder, and carbon black as a conductive material were mixed at a weight ratio of 97:1.6:1.4, respectively, and then, dispersed in N-methylpyrrolidone to prepare a positive electrode active material slurry.

[0196] The positive electrode active material slurry was coated in a 20 μm thick Al foil, dried at 100° C., and pressed to produce a positive electrode.

[0197] On the other hand, a mixture of graphite and Si—C composite material at a weight ratio of 89:11 as a negative electrode active material, a styrene-butadiene rubber binder and carboxymethyl cellulose at a weight ratio of 98:1:1 were mixed and dispersed in distilled water to prepare a negative electrode active material slurry.

[0198] The Si-C composite material has a core including artificial graphite and silicon particles, and coal tar pitch coated on a surface of the core, wherein an amount of the silicon particles is about 3 wt % based on the total weight of the Si-C composite material.

[0199] The negative electrode active material slurry was coated on a 10 μm thick Cu foil, dried at 100° C., and pressed to produce a negative electrode.

[0200] The fabricated positive and negative electrodes, a 25 μm thick polyethylene separator, and an electrolyte were used to fabricate a lithium secondary battery cell.

[0201] The composition of the electrolyte is as follows.

[0202] (Electrolyte composition)

[0203] Salt: LiPF61.5M

[0204] Solvent: ethylene carbonate: ethyl methyl carbonate: dimethyl carbonate (EC:EMC:DMC=2:1:7 volume ratio) + 7wt% ethylene fluorocarbonate

[0205] Additive: 0.5 wt% of the compound represented by chemical formula a

[0206] (Herein, the composition of the electrolyte, "wt %" is based on the total amount of the electrolyte (lithium salt + non-aqueous organic solvent + additives))

[0207] Example 2

[0208] A lithium secondary battery cell was manufactured in the same manner as in Example 1, except that the amount of the additive was changed to 2.0 wt %.

[0209] Example 3

[0210] A lithium secondary battery cell was manufactured in the same manner as in Example 1, except that the amount of the additive was changed to 1.0 wt %.

[0211] Example 4

[0212] A lithium secondary battery cell was manufactured in the same manner as in Example 1, except that the amount of the additive was changed to 0.2 wt %.

[0213] Examples 5 to 8

[0214] Lithium secondary battery cells were manufactured in the same manner as in Examples 1 to 4, respectively, except that the negative electrode active material was changed to 100 wt % of crystalline graphite.

[0215] Comparative Example 1

[0216] A lithium secondary battery cell was manufactured in the same manner as in Example 1 except that no additive was used.

[0217] Comparative Examples 2 to 5

[0218] Lithium secondary battery cells were manufactured in the same manner as in Examples 1 to 4, respectively, except that the additive was changed to the compound represented by Chemical Formula b according to Comparative Preparation Example.

[0219] Comparative Example 6

[0220] A lithium secondary battery cell was manufactured in the same manner as in Example 5 except that no additive was used.

[0221] Comparative Examples 7 to 10

[0222] Lithium secondary battery cells were respectively manufactured in the same manner as in Examples 5 to 8, except that the additive was changed to the compound represented by Chemical Formula b according to Comparative Preparation Example.

[0223] Evaluation of battery cell characteristics

[0224] Evaluation 1: Evaluation of room temperature cycle life characteristics

[0225] The lithium secondary battery cells according to Examples 1 to 8 and Comparative Examples 1 to 10 were charged at a constant current-constant voltage of 1.6C and 4.2V, cut off at 0.03C, and discharged to 2.5V at a constant current of 8C at room temperature (25°C), and when charged and discharged 250 times, the discharge capacity was measured, and then, the capacity retention rate of the discharge capacity at the 200th cycle relative to the discharge capacity at the 1st cycle was shown in Figure 2 and Figure 5 middle.

[0226] Figure 2 is a graph showing cycle life characteristics of the secondary battery cells according to Examples 5 to 8 and Comparative Examples 6 to 10 at room temperature (25° C.).

[0227] Figure 5 Graph showing cycle life characteristics of secondary battery cells according to Examples 1 to 4 and Comparative Examples 1 to 5 at room temperature (25° C.).

[0228] refer to Figure 2 and Figure 5 The lithium secondary battery cells of Examples 1 to 8 exhibited improved recycling capacity compared to Comparative Examples 1 and 6 including no additive and Comparative Examples 2 to 5 and 7 to 10 including the compound represented by Chemical Formula b as an additive.

[0229] In particular, Figure 5 It is shown in Figure 2 that when a Si-C composite material is included as the negative electrode active material, the improvement effect is further increased.

[0230] In other words, compared with Comparative Examples 1 to 10, Examples 1 to 8 according to the present invention exhibit excellent room temperature cycle life characteristics, and accordingly, the lithium secondary battery cell including the compound represented by Chemical Formula 1 as an additive exhibits excellent cycle life characteristics, and this improvement effect is particularly prominent in Examples 1 to 4 including the Si-C composite as the negative electrode active material.

[0231] Evaluation 2: Evaluating DC Internal Resistance (DC-IR)

[0232] The lithium secondary battery cells of Examples 1 to 8 and Comparative Examples 1 to 10 were left at 60° C. for 30 days in a charged state (SOC=100%), and then, the internal resistance increase rate at high temperature (60° C.) was evaluated, and the results showed that Figure 3 and Figure 6 middle.

[0233] The DC-IR was measured in the following manner.

[0234] The cells according to Examples 1 to 8 and Comparative Examples 1 to 10 were charged at 4A (1.6C) and 4.2V, and when a constant voltage of 4.2V was applied thereto at room temperature (25°C), they were cut off at a current of 75mA, and then paused for 30 minutes. Subsequently, the cells were discharged at 10A for 10 seconds, 1A for 10 seconds, and 10A for 4 seconds, respectively, and then the current and voltage were measured at 18 seconds and 23 seconds, which were used to calculate the initial resistance (the difference between the resistance at 18 seconds and the resistance at 23 seconds) according to ΔR=ΔV / ΔI.

[0235] The single cell was charged under the above buffer charge conditions, allowed to stand at 60° C. for 30 days, and then the DC-IR was measured, which was used to calculate the resistance increase rate before and after the stand according to Equation 1.

[0236] <Equation 1>

[0237] Resistance increase rate = [(DC-IR after 30 days - initial DC-IR) / initial DC-IR] × 100

[0238] Figure 3 Graph showing the internal resistance increase rate of the secondary battery cells according to Examples 5 to 8 and Comparative Examples 6 to 10 when left at high temperature.

[0239] Figure 6 A graph for explaining the internal resistance increase rate of the secondary battery cells according to Examples 1 to 4 and Comparative Examples 1 to 5 when left at high temperature.

[0240] refer to Figure 3 and Figure 6 Compared with Comparative Examples 1 to 10, the secondary battery cells of Examples 1 to 8 showed significantly deteriorated resistance increase rates before and after being placed at high temperatures. Figure 6 As shown in FIG. 1 , in Examples 1 to 4 including Si—C negative electrode active materials, this alleviation of the resistance increase is more significant.

[0241] Accordingly, the secondary battery cells according to Examples 1 to 8 exhibited improved high temperature stability compared to Comparative Examples 1 to 10.

[0242] Assessment 3: Evaluation of high temperature storage characteristics

[0243] The high temperature storage characteristics of lithium secondary battery cells were evaluated by measuring the CID operation time, and the results were shown in Figure 4 and Figure 7 middle.

[0244] The secondary battery cells of Examples 1 to 8 and Comparative Examples 1 to 10 were charged through multiple stages of 0.2C → 0.5C → 1.0C, and then, discharged at 0.5C for formation charge / discharge. After one additional charge / discharge, the cell was buffered to 4.2V, and then the CID (current interrupt device) operation time was measured while placed in a chamber at 90°C.

[0245] Figure 4 It is a graph measuring the CID (current interrupt device) operation time of the secondary battery cells according to Examples 5 to 8 and Comparative Examples 6 to 10.

[0246] Figure 7 It is a graph measuring the CID (current interrupt device) operation time of the secondary battery cells according to Examples 1 to 4 and Comparative Examples 1 to 5.

[0247] A current interrupt device (CID) is used to detect changes in the internal pressure of a battery cell, and when the internal pressure of the cell reaches a predetermined level or higher, the CID operates and stops charging of the cell to prevent overcharging.

[0248] refer to Figure 4 When stored at a high temperature of 90°C, Comparative Example 6 which did not include the compound represented by Chemical Formula a as an additive showed a sharp voltage drop after 30 to 35 hours, Comparative Examples 7 to 10 which included the compound represented by Chemical Formula b as an additive showed a rapid voltage drop before 30 hours, but Examples 5 to 8 which included the compound represented by Chemical Formula a as an additive delayed the decomposition of the electrolyte and slowed down the increase in resistance, which showed the effect of delaying the OCV drop.

[0249] In addition, refer to Figure 7 , when stored at a high temperature of 90°C, Comparative Example 1 not including the compound represented by Chemical Formula a as an additive exhibited a sharp voltage drop before 80 hours, and Comparative Examples 2 to 5 including the compound represented by Chemical Formula b as an additive exhibited a sharp voltage drop after about 100 hours, but Examples 1 to 4 including the compound represented by Chemical Formula a as an additive delayed the decomposition of the electrolyte and slowed down the increase in resistance, which exhibited an effect of delaying the decrease in OCV. In particular, as Figure 7 It is shown in Figure 2 that when a Si-C composite material is included as a negative electrode active material, the delay effect is greatly improved.

[0250] In other words, the lithium secondary battery cell according to the present invention exhibits an excellent effect of suppressing gas generation during high-temperature storage.

[0251] While the invention has been described in conjunction with what are presently considered to be practical example embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. On the contrary, the invention is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Claims

1. An electrolyte for a lithium secondary battery, comprising Non-aqueous organic solvents, lithium salts and additives, The additive comprises a compound represented by Chemical Formula 1: [Chemical formula 1] in, In Chemical Formula 1, R 1 To R 5 each independently represents hydrogen, halogen, substituted or unsubstituted C1 to C10 alkyl, substituted or unsubstituted C1 to C10 alkoxy, substituted or unsubstituted C2 to C10 alkenyl, substituted or unsubstituted C3 to C10 cycloalkyl, substituted or unsubstituted C3 to C10 cycloalkenyl, substituted or unsubstituted C2 to C10 alkynyl, substituted or unsubstituted C3 to C10 cycloalkynyl, or substituted or unsubstituted C6 to C20 aryl, R 1 To R 3 At least one of them is a fluorine group (-F), R 6 is a substituted or unsubstituted C1 to C10 alkyl group, a substituted or unsubstituted C1 to C10 alkoxy group, a substituted or unsubstituted C2 to C10 alkenyl group, a substituted or unsubstituted C3 to C10 cycloalkyl group, a substituted or unsubstituted C3 to C10 cycloalkenyl group, a substituted or unsubstituted C2 to C10 alkynyl group, or a substituted or unsubstituted C3 to C10 cycloalkynyl group, and n is an integer of any one of 1 to 20.

2. The electrolyte for lithium secondary battery according to claim 1, wherein R in Chemical Formula 1 1 To R 3 One or both of them are fluorine groups (-F).

3. The electrolyte for a lithium secondary battery according to claim 1, wherein Chemical Formula 1 is represented by Chemical Formula 1A: [Chemical Formula 1A] in, In Chemical Formula 1A, R 2 To R 6 The definitions of and n are the same as those in claim 1. 4 . The electrolyte for a lithium secondary battery according to claim 1 , wherein n is an integer of any one of 1 to 10.

5. The electrolyte for a lithium secondary battery according to claim 1, wherein n is an integer of any one of 1 to 5.

6. The electrolyte for a lithium secondary battery according to claim 1, wherein Chemical Formula 1 is represented by Chemical Formula 1A-1: [Chemical Formula 1A-1] in, In Chemical Formula 1A-1, R 2 To R 6 and n are defined as in claim 1, and R 4a , R 4b , R 4c , R 5a , R 5b and R 5c Each is independently hydrogen, halogen, substituted or unsubstituted C1 to C10 alkyl, substituted or unsubstituted C1 to C10 alkoxy, substituted or unsubstituted C2 to C10 alkenyl, substituted or unsubstituted C3 to C10 cycloalkyl, substituted or unsubstituted C3 to C10 cycloalkenyl, substituted or unsubstituted C2 to C10 alkynyl, substituted or unsubstituted C3 to C10 cycloalkynyl, or substituted or unsubstituted C6 to C20 aryl.

7. The electrolyte for a lithium secondary battery according to claim 1, wherein R 1 To R 3 are each independently halogen, substituted or unsubstituted C1 to C10 alkyl, or substituted or unsubstituted C2 to C5 alkenyl, and R 6 is a substituted or unsubstituted C1 to C10 alkyl group or a substituted or unsubstituted C2 to C5 alkenyl group, and R 1 To R 3 Any one of them is a fluoro group (-F). 8 . The electrolyte for a lithium secondary battery according to claim 1 , wherein the compound represented by Chemical Formula 1 is included in an amount of 0.1 wt % to 10 wt % based on the total amount of the electrolyte for a lithium secondary battery. 9 . The electrolyte for a lithium secondary battery according to claim 1 , wherein the compound represented by Chemical Formula 1 is included in an amount of 0.2 wt % to 2.0 wt % based on the total amount of the electrolyte for a lithium secondary battery.

10. A lithium secondary battery comprising: a positive electrode comprising a positive active material; a negative electrode comprising a negative active material; and An electrolyte according to any one of claims 1 to 9. 11 . The lithium secondary battery according to claim 10 , wherein the negative electrode active material comprises a Si—C composite material including a Si-based active material and a carbon-based active material. 12 . The lithium secondary battery according to claim 11 , wherein the negative electrode active material further comprises crystalline carbon.

13. The lithium secondary battery according to claim 12, wherein The crystalline carbon includes graphite, and The graphite includes natural graphite, artificial graphite or a mixture thereof.

14. The lithium secondary battery according to claim 11, wherein The Si-C composite material further includes a shell surrounding a surface of the Si-C composite material, and The shell includes amorphous carbon. 15 . The lithium secondary battery according to claim 14 , wherein the amorphous carbon comprises soft carbon, hard carbon, a carbonized product of mesophase pitch, calcined coke, or a mixture thereof. 16 . The lithium secondary battery according to claim 10 , wherein the positive electrode active material is a composite oxide containing nickel metal and lithium.

17. The lithium secondary battery according to claim 16, wherein the positive electrode active material is represented by Chemical Formula 5: [Chemical formula 5] Li a M 1 1-y1-z1 M 2 y1 M 3 z1 O2 in, In Chemical Formula 5, 0.9≤a≤1.8, 0≤y1≤1, 0≤z1≤1, 0≤y1+z1<1, and M 1 、M 2 and M 3 Each is independently selected from the group consisting of Ni, Co, Mn, Al, Sr, Mg or La and combinations thereof.

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