Additive for rechargeable lithium battery, electrolyte and rechargeable lithium battery

Abstract

An additive for a rechargeable lithium battery, an electrolyte, and a rechargeable lithium battery including the same, wherein the additive is represented by Chemical Formula 1 or Chemical Formula 2: [Chemical Formula 1] [Chemical Formula 2]

Description

Technical Field

[0001] Embodiments relate to an additive for a rechargeable lithium battery, an electrolyte, and a rechargeable lithium battery. Background Art

[0002] The rechargeable lithium battery can be recharged and has a high energy density per unit weight that is three or more times that of a lead storage battery, a nickel-cadmium battery, a nickel-hydrogen battery, or a nickel-zinc battery, etc. The rechargeable lithium battery can also be charged at a high rate, and therefore, can be commercially manufactured for use in laptop computers, cellular phones, power tools, electric bicycles, etc., and research on further improving the energy density has been actively conducted.

[0003] Such a rechargeable lithium battery can be manufactured by injecting an electrolyte into a battery cell, wherein the battery cell includes a positive electrode including a positive electrode active material capable of inserting / deinserting lithium ions; and a negative electrode including a negative electrode active material capable of inserting / deinserting lithium ions. Summary of the invention

[0004] The embodiment may be implemented by providing an additive represented by Chemical Formula 1 or Chemical Formula 2:

[0005] [Chemical formula 1]

[0006]

[0007] [Chemical formula 2]

[0008]

[0009] In the chemical formula 1 and the chemical formula 2, R 1 To R 8 are each independently a substituted or unsubstituted C1 to C10 alkyl 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, a substituted or unsubstituted C3 to C10 cycloalkynyl group or a substituted or unsubstituted C6 to C20 aryl group, R 1 To R 8 Existing alone, or R 1 and R 2 ; R 3 and R 4 ; R 5 and R 6 ; and R 7 and R 8At least one pair of L is connected to each other to provide a substituted or unsubstituted monocyclic aliphatic heterocycle, a substituted or unsubstituted polycyclic aliphatic heterocycle, a substituted or unsubstituted monocyclic aromatic heterocycle, or a substituted or unsubstituted polycyclic aromatic heterocycle, and L 1 To L 4 Each is independently a substituted or unsubstituted C1 to C20 alkylene group.

[0010] The additive may be represented by Chemical Formula 1, and Chemical Formula 1 may be represented by Chemical Formula 1A or Chemical Formula 1B:

[0011] [Chemical Formula 1A]

[0012]

[0013] In Chemical Formula 1A, R 11 To R 30 may each independently be hydrogen, halogen, or substituted or unsubstituted C1 to C10 alkyl, n1 to n4 may each independently be an integer from 0 to 4, and L 1 and L 2 may each independently be a substituted or unsubstituted C1 to C20 alkylene group;

[0014] [Chemical formula 1B]

[0015]

[0016] In Chemical Formula 1B, R 31 and R 32 may each independently be a substituted or unsubstituted C2 to C10 alkylene group, and L 1 and L 2 Each independently may be a substituted or unsubstituted C1 to C20 alkylene group.

[0017] The additive may be represented by Chemical Formula 1B, and Chemical Formula 1B may be represented by Chemical Formula 1B-I or Chemical Formula 1B-II:

[0018] [Chemical Formula 1B-I]

[0019]

[0020] [Chemical formula 1B-II]

[0021]

[0022] In Formula 1B-I and Formula 1B-II, R 101 To R 120 may each independently be hydrogen, halogen, or substituted or unsubstituted C1 to C10 alkyl, and L 1 and L 2Each independently may be a substituted or unsubstituted C1 to C20 alkylene group.

[0023] The additive may be represented by Chemical Formula 2, which may be represented by Chemical Formula 2A or Chemical Formula 2B:

[0024] [Chemical Formula 2A]

[0025]

[0026] In Chemical Formula 2A, R 33 To R 52 may each independently be hydrogen, halogen, or substituted or unsubstituted C1 to C10 alkyl, n5 to n8 may each independently be an integer from 0 to 4, and L 3 and L 4 may each independently be a substituted or unsubstituted C1 to C20 alkylene group;

[0027] [Chemical formula 2B]

[0028]

[0029] In Chemical Formula 2B, R 53 and R 54 may each independently be a substituted or unsubstituted C2 to C10 alkylene group, and L 3 and L 4 Each independently may be a substituted or unsubstituted C1 to C20 alkylene group.

[0030] The additive may be represented by Chemical Formula 2B, which may be represented by Chemical Formula 2B-I or Chemical Formula 2B-II:

[0031] [Chemical formula 2B-I]

[0032]

[0033] [Chemical formula 2B-Ⅱ]

[0034]

[0035] In the chemical formula 2B-I and the chemical formula 2B-II, R 121 To R 140 may each independently be hydrogen, halogen, or substituted or unsubstituted C1 to C10 alkyl, and L 3 and L 4 Each independently may be a substituted or unsubstituted C1 to C20 alkylene group.

[0036] The additive may be represented by Chemical Formula 1B-I-1 or Chemical Formula 2B-I-1:

[0037] [Chemical formula 1B-I-1]

[0038]

[0039] [Chemical formula 2B-I-1]

[0040]

[0041] In Formula 1B-I-1 and Formula 2B-I-1, R 101 To R 108 , R 121 To R 128 and R 141 To R 156 They may each independently be hydrogen, halogen, or substituted or unsubstituted C1 to C10 alkyl.

[0042] The embodiments may be implemented by providing an electrolyte for a rechargeable lithium battery, the electrolyte including a nonaqueous organic solvent, a lithium salt, and an additive according to the embodiments.

[0043] The additive may be included in an amount of about 0.1 wt % to about 10 wt % based on the total weight of the electrolyte for a rechargeable lithium battery.

[0044] The embodiments may be implemented by providing a rechargeable lithium battery including a positive electrode including a positive active material, a negative electrode including a negative active material, and an electrolyte according to the embodiments.

[0045] The positive electrode active material can be represented by chemical formula 5:

[0046] [Chemical formula 5]

[0047] Li x M 1 1-y-z M 2 y M 3 z O2

[0048] In Chemical Formula 5, 0.5≤x≤1.8, 0≤y≤1, 0≤z≤1, 0≤y+z<1, and M 1 、M 2 and M 3 Each independently may be Ni, Co, Mn, Al, Sr, Mg, La or a combination thereof.

[0049] The positive electrode active material may be a lithium composite oxide represented by Chemical Formula 5-1, Chemical Formula 5-2, or Chemical Formula 5-3:

[0050] [Chemical formula 5-1]

[0051] Li x1 Ni y1 Co z1 Al 1-y1-z1 O2

[0052] In Chemical Formula 5-1, 1 ≤ x1 ≤ 1.2, 0 < y1 < 1, and 0 < z1 < 1.

[0053] [Chemical Formula 5-2]

[0054] Li x2 Ni y2 Co z2 Mn 1-y2-z2 O2

[0055] In Chemical Formula 5-2, 1 ≤ x2 ≤ 1.2, 0 < y2 < 1, and 0 < z2 < 1.

[0056] [Chemical Formula 5-3]

[0057] Li x3 CoO2

[0058] In Chemical Formula 5-3, 0.5 < x3 ≤ 1. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] The features will be apparent to those skilled in the art from a detailed description of exemplary embodiments with reference to the accompanying drawings, in which:

[0060] Figure 1 Is an exploded perspective view showing a rechargeable lithium battery according to an embodiment of the present disclosure.

[0061] Figure 2 Is a graph showing the operation time of the CID (current interrupt device) of a rechargeable lithium battery single cell according to Example 1, Example 2, Example 4, and Comparative Example 1.

[0062] Figure 3 Is a graph showing the resistance increase rate after measuring the DC internal resistance after placing the rechargeable lithium battery single cells according to Example 1 and Example 6 and Comparative Example 2 and Comparative Example 3 at 60 °C for 30 days. DETAILED DESCRIPTION

[0063] Example embodiments will now be described more fully hereinafter with reference to the accompanying drawings; however, the example embodiments may be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the exemplary implementation to those skilled in the art.

[0064] In the drawings, dimensions of layers and regions may be exaggerated for clarity of illustration. It will also be understood that when a layer or element is referred to as being "on" another layer or element, it can be directly on the other layer or element, or there may be intervening layers. Additionally, it will be understood that when a layer is referred to as being "between" two layers, it can be the only layer between the two layers, or there may be one or more intervening layers. Like reference numerals refer to like elements throughout.

[0065] As used herein, when no limitation is otherwise provided, the term "substituted" means that a hydrogen atom in a compound is replaced with a substituent other than hydrogen.

[0066] In some embodiments, the term "substituted" refers to that a hydrogen atom of the compound is replaced by a substituent selected from, for example, a halogen atom (F, Br, Cl and / 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 aralkyl group, a C1 to C4 alkoxy group, a C1 to C20 heteroalkyl group, a C3 to C20 heteroaralkyl 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.

[0067] Rechargeable lithium batteries can be classified into lithium ion batteries, lithium ion polymer batteries, and lithium polymer batteries depending on the types of separators and electrolytes. Rechargeable lithium batteries can also be classified into cylindrical, prismatic, coin-type, and pouch-type batteries, etc., depending on the shape. In addition, rechargeable lithium batteries can be block-type and film-type, depending on the size.

[0068] Herein, as an example of a rechargeable lithium battery, a cylindrical rechargeable lithium battery is described. Figure 1 The structure of a rechargeable lithium battery according to an embodiment is schematically shown. Figure 1 According to an embodiment, a rechargeable lithium battery 100 may include a battery cell, wherein the battery cell includes a positive electrode 114, a negative electrode 112 facing the positive electrode 114, a separator 113 between the positive electrode 114 and the negative electrode 112, and an electrolyte (not shown) impregnating the positive electrode 114, the negative electrode 112, and the separator 113; a battery case 120 accommodating the battery cell; and a sealing member 140 for sealing the battery case 120.

[0069] Hereinafter, additives according to embodiments will be described.

[0070] The additive according to an embodiment of the present disclosure may be represented by Chemical Formula 1 or Chemical Formula 2, for example.

[0071] [Chemical formula 1]

[0072]

[0073] [Chemical formula 2]

[0074]

[0075] In Chemical Formula 1 and Chemical Formula 2, R 1 To R 8 Each independently may be or include, for example, substituted or unsubstituted C1 to C10 alkyl, 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. As used herein, the term "or" is not an exclusive term, for example, "A or B" will include A, B or A and B.

[0076] In implementation, R 1 To R 8 Can exist independently or alone, or R 1 and R 2 ; R 3 and R 4 ; R 5 and R 6 ; and R 7 and R 8 At least one pair of may be connected to each other to provide, for example, a substituted or unsubstituted monocyclic aliphatic heterocycle, a substituted or unsubstituted polycyclic aliphatic heterocycle, a substituted or unsubstituted monocyclic aromatic heterocycle, or a substituted or unsubstituted polycyclic aromatic heterocycle.

[0077] L 1 To L 4 Each independently may be or include, for example, a substituted or unsubstituted C1 to C20 alkylene group.

[0078] The additive according to an embodiment of the present disclosure may be a bisphosphonate compound or a bisphosphite compound, and may have a structure connected by a disulfide linker.

[0079] These bisphosphonate compounds and bisphosphite compounds can be decomposed into two phosphate compounds or two phosphite compounds with a disulfide linker as the center.

[0080] These compounds can form films on the positive electrode and the negative electrode, and thus can suppress an increase in resistance of the film during high-temperature storage and can improve film stability to contribute to enhancement of high-temperature cycle life and thermal safety characteristics.

[0081] In implementations, the additive may be represented by, for example, Chemical Formula 1A or Chemical Formula 1B.

[0082] [Chemical Formula 1A]

[0083]

[0084] In Chemical Formula 1A, R 11 To R 30 Each independently may be, for example, hydrogen, halogen, or substituted or unsubstituted C1 to C10 alkyl.

[0085] n1 to n4 may each independently be, for example, an integer of 0 to 4.

[0086] L 1 and L 2 Each independently may be, for example, a substituted or unsubstituted C1 to C20 alkylene group.

[0087] [Chemical formula 1B]

[0088]

[0089] In Chemical Formula 1B, R 31 and R 32 Each independently may be, for example, a substituted or unsubstituted C2 to C10 alkylene group.

[0090] L 1 and L 2 Each independently may be, for example, a substituted or unsubstituted C1 to C20 alkylene group.

[0091] In implementation, R 11 To R 30 may each independently be, for example, hydrogen, halogen, or substituted or unsubstituted C1 to C5 alkyl, n1 to n4 may each independently be, for example, an integer from 0 to 3, and L 1 and L 2 Each independently may be, for example, a substituted or unsubstituted C2 to C20 alkylene group.

[0092] In implementation, R 11 To R 30 may each independently be, for example, hydrogen, halogen, or substituted or unsubstituted C1 to C3 alkyl, n1 to n4 may each independently be, for example, an integer from 0 to 2, and L 1 and L 2 Each independently may be, for example, a substituted or unsubstituted C2 to C10 alkylene group.

[0093] In implementation, R 31 and R 32may each independently be, for example, a substituted or unsubstituted C2 to C5 alkylene group, and L 1 and L 2 Each independently may be, for example, a substituted or unsubstituted C2 to C20 alkylene group.

[0094] In implementation, R 31 and R 32 may each independently be, for example, a substituted or unsubstituted C2 to C4 alkylene group, and L 1 and L 2 Each independently may be, for example, a substituted or unsubstituted C2 to C10 alkylene group.

[0095] In implementation, Chemical Formula 1B may be represented by, for example, Chemical Formula 1B-I or Chemical Formula 1B-II.

[0096] [Chemical Formula 1B-I]

[0097]

[0098] [Chemical formula 1B-II]

[0099]

[0100] In Formula 1B-I and Formula 1B-II, R 101 To R 120 Each independently may be, for example, hydrogen, halogen, or substituted or unsubstituted C1 to C10 alkyl.

[0101] L 1 and L 2 May be the same as defined above.

[0102] In implementation, R 101 To R 120 Each independently may be, for example, hydrogen, halogen, or substituted or unsubstituted C1 to C5 alkyl.

[0103] In implementation, R 101 To R 120 Each may be hydrogen.

[0104] In implementations, the additive may be represented by, for example, Chemical Formula 2A or Chemical Formula 2B.

[0105] [Chemical Formula 2A]

[0106]

[0107] In Chemical Formula 2A, R 33 To R 52 Each independently may be, for example, hydrogen, halogen, or substituted or unsubstituted C1 to C10 alkyl.

[0108] n5 to n8 may each independently be, for example, an integer of 0 to 4.

[0109] L 3 and L 4 Each independently may be, for example, a substituted or unsubstituted C1 to C20 alkylene group.

[0110] [Chemical formula 2B]

[0111]

[0112] In Chemical Formula 2B, R 53 and R 54 Each independently may be, for example, a substituted or unsubstituted C2 to C10 alkylene group.

[0113] L 3 and L 4 Each independently may be, for example, a substituted or unsubstituted C1 to C20 alkylene group.

[0114] In implementation, R 33 To R 52 may each independently be, for example, hydrogen, halogen, or substituted or unsubstituted C1 to C5 alkyl, n5 to n8 may each independently be, for example, an integer from 0 to 3, and L 3 and L 4 Each independently may be, for example, a substituted or unsubstituted C2 to C20 alkylene group.

[0115] In implementation, R 33 To R 52 may each independently be, for example, hydrogen, halogen, or substituted or unsubstituted C1 to C3 alkyl, n5 to n8 may each independently be, for example, an integer from 0 to 2, and L 3 and L 4 Each independently may be, for example, a substituted or unsubstituted C2 to C10 alkylene group.

[0116] In an embodiment, R 53 and R 54 may each independently be, for example, a substituted or unsubstituted C2 to C5 alkylene group and L 3 and L 4 Each independently may be, for example, a substituted or unsubstituted C2 to C20 alkylene group.

[0117] In implementation, R 53 and R 54 may each independently be, for example, a substituted or unsubstituted C2 to C4 alkylene group and L 3 and L 4Each independently may be, for example, a substituted or unsubstituted C2 to C10 alkylene group.

[0118] In implementation, Chemical Formula 2B may be represented by, for example, Chemical Formula 2B-I or Chemical Formula 2B-II.

[0119] [Chemical Formula 2B-I]

[0120]

[0121] [Chemical formula 2B-Ⅱ]

[0122]

[0123] In Formula 2B-I and Formula 2B-II, R 121 To R 140 Each independently may be, for example, hydrogen, halogen, or substituted or unsubstituted C1 to C10 alkyl.

[0124] L 3 and L 4 May be the same as defined above.

[0125] In implementation, R 121 To R 140 Each independently may be, for example, hydrogen, halogen, or substituted or unsubstituted C1 to C5 alkyl.

[0126] In implementation, R 121 To R 140 Each may be hydrogen.

[0127] In implementation, the additive may be represented by, for example, Chemical Formula 1B-I-1 or Chemical Formula 2B-I-1.

[0128] [Chemical formula 1B-I-1]

[0129]

[0130] [Chemical formula 2B-I-1]

[0131]

[0132] In Formula 1B-I-1 and Formula 2B-I-1, R 101 To R 108 , R 121 To R 128 and R 141 To R 156 Each independently may be, for example, hydrogen, halogen, or substituted or unsubstituted C1 to C10 alkyl.

[0133] L 3 and L4 May be the same as defined above.

[0134] In implementation, R 101 To R 108 , R 121 To R 128 and R 141 To R 156 Each independently may be, for example, hydrogen, halogen, or substituted or unsubstituted C1 to C5 alkyl.

[0135] In implementation, R 101 To R 108 , R 121 To R 128 and R 141 To R 156 Each may be hydrogen.

[0136] The additive according to the embodiment of the present disclosure may be synthesized by an appropriate method, and may be synthesized by modifying the process to the extent that it may be changed as needed.

[0137] In practice, a process of treating with a basic substance may be included in the process of synthesizing the additive, and in this case, the basic substance may be used by changing the material that can be used as the basic substance and the amine compound. In practice, triethylamine, 1,8-diazabicyclo[5,4,0]undec-7-ene (DBU), imidazole, dimethylaminopyridine, 1,4-diazabicyclo[2.2.2]octane (DABCO) or diethylpropylamine may be used.

[0138] An electrolyte for a rechargeable lithium battery according to another embodiment of the present disclosure may include a nonaqueous organic solvent, a lithium salt, and the aforementioned additives.

[0139] The additive may be included in an amount of about 0.1 wt % to about 10 wt %, for example, 0.1 wt % to 5.0 wt %, or 0.1 wt % to 3.0 wt %, based on the total weight of the electrolyte for a rechargeable lithium battery.

[0140] When the content of the additive is within the range as described above, resistance increase at high temperature may be prevented to provide a rechargeable lithium battery having improved cycle-life characteristics.

[0141] When the content of the additive is less than about 0.1 wt %, high temperature storage characteristics may be deteriorated, and when the content of the additive exceeds about 10 wt %, cycle life may be reduced due to an increase in interface resistance.

[0142] The nonaqueous organic solvent may be used as a medium for transferring ions participating in the electrochemical reaction of the battery.

[0143] The non-aqueous organic solvent may be a carbonate, an ester, an ether, a ketone, an alcohol or an aprotic solvent.

[0144] Carbonate solvents may include 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 may include methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, propyl propionate, decanoic acid lactone, mevalonate lactone and caprolactone etc. Ether solvents may include dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, dimethoxyethane, 2-methyltetrahydrofuran and tetrahydrofuran etc. In addition, ketone solvents may include cyclohexanone etc. Alcohol solvents may include ethanol and isopropyl alcohol etc. The aprotic solvent may include nitriles such as R—CN (wherein R is a hydrocarbon group having a linear, branched or cyclic structure of C2 to C20 and may include a double bond, an aromatic ring or an ether bond), etc.; dioxolanes such as 1,3-dioxolane, etc.; and sulfolane, etc.

[0145] The nonaqueous organic solvent may be used alone or in a mixture of two or more. When the nonaqueous organic solvent is used in a mixture, the mixture ratio may be controlled according to the desired battery performance.

[0146] In an implementation, the carbonate solvent may be prepared by mixing a cyclic carbonate and a chain carbonate. When the cyclic carbonate and the chain carbonate are mixed together in a volume ratio of about 1:1 to about 1:9, electrolyte performance may be improved.

[0147] In addition to the carbonate solvent, the non-aqueous organic solvent may further include an aromatic hydrocarbon organic solvent. In implementations, the carbonate solvent and the aromatic hydrocarbon organic solvent may be mixed in a volume ratio of about 1:1 to about 30:1.

[0148] The aromatic hydrocarbon organic solvent may be an aromatic hydrocarbon compound of Chemical Formula 3.

[0149] [Chemical formula 3]

[0150]

[0151] In chemical formula 3, R 201 To R 206 Each may independently be, for example, hydrogen, halogen, C1 to C10 alkyl, haloalkyl or a combination thereof.

[0152] Examples of aromatic hydrocarbon organic solvents may include 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.

[0153] The electrolyte may further include a vinylene carbonate or ethylene carbonate compound represented by Chemical Formula 4 so as to help improve the cycle life of the battery.

[0154] [Chemical formula 4]

[0155]

[0156] In chemical formula 4, R 207 and R 208 Each of R and R is independently, for example, hydrogen, halogen, cyano (CN), nitro (NO2) or fluorinated C1 to C5 alkyl. 207 and R 208 At least one of them may be halogen, cyano (CN), nitro (NO2) or fluorinated C1 to C5 alkyl and R 207 and R 208 It is not necessary to be hydrogen at the same time.

[0157] Examples of the ethylene carbonate compound 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.

[0158] Lithium salts dissolved in non-organic solvents can supply lithium ions in the battery, ensure the basic operation of the rechargeable lithium battery, and improve the transfer of lithium ions between the positive electrode and the negative electrode. Examples of lithium salts may include LiPF6, LiBF4, LiDFOP, LiDFOB, LiPO2F2, 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+ 1SO2)(C y F 2y+1 SO2), wherein x and y are natural numbers, for example, integers ranging from 1 to 20, LiCl, LiI, and LiB(C2O4)2 (lithium bis(oxalato)borate; LiBOB). The concentration range of the lithium salt that can be used is about 0.1 M to about 2.0 M. When the lithium salt is included within the above concentration range, the electrolyte can have excellent performance and lithium ion mobility due to optimal electrolyte conductivity and viscosity.

[0159] Another embodiment of the present disclosure provides a rechargeable lithium battery including a positive electrode including a positive electrode active material; a negative electrode including a negative electrode active material; and the aforementioned electrolyte.

[0160] The positive electrode may include a positive current collector and a positive active material layer on the positive current collector, and the positive active material layer includes a positive active material.

[0161] The positive active material may include a lithiated intercalation compound that reversibly intercalates and deintercalates lithium ions.

[0162] In implementations, a composite oxide of a metal, for example, cobalt, manganese, nickel, or a combination thereof, and lithium may be used.

[0163] In implementation, a composite oxide having a coating on the surface of the composite oxide may be used, or a mixture of a composite oxide and a composite oxide having a coating may be used. The coating may include a coating element compound selected from the following: an oxide of a coating element, a hydroxide of a coating element, an oxyhydroxide of a coating element, an oxycarbonate of a coating element, and a hydroxycarbonate of a coating element. The compound used for the coating may be amorphous or crystalline. The coating elements included in the coating may include, for example, Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or a mixture thereof. By using these elements in the compound, a coating may be provided in a method that has no adverse effect on the performance of the positive active material. In implementation, the method may include an appropriate coating method (e.g., spraying or dipping, etc.).

[0164] The positive electrode active material may be, for example, a lithium composite oxide represented by Chemical Formula 5.

[0165] [Chemical formula 5]

[0166] Li x M 1 1-y-z M 2 y M 3 z O2

[0167] In Chemical Formula 5,

[0168] 0.5≤x≤1.8, 0≤y<1, 0≤z<1, 0≤y+z<1, and M 1 、M 2 and M 3 Each independently may be, for example, Ni, Co, Mn, Al, Sr, Mg or La, and combinations thereof.

[0169] In implementation, M 1 may be, for example, Co, Mn, Al, Sr, Mg or La, and M 2 and M 3 Each independently may be, for example, Ni or Co.

[0170] In implementation, M 1 Mn or Al, and M 2 and M 3 Each independently may be Ni or Co.

[0171] In an implementation, the positive electrode active material may be a lithium composite oxide represented by at least one of Chemical Formula 5-1 to Chemical Formula 5-3.

[0172] [Chemical formula 5-1]

[0173] Li x1 Ni y1 Co z1 Al 1-y1-z1 O2

[0174] In Chemical Formula 5-1, 1 ≤ x1 ≤ 1.2, 0 < y1 < 1, and 0 < z1 < 1.

[0175] [Chemical Formula 5-2]

[0176] Li x2 Ni y2 Co z2 Mn 1-y2-z2 O2

[0177] In Chemical Formula 5-2,

[0178] 1 ≤ x2 ≤ 1.2, 0 < y2 < 1, and 0 < z2 < 1.

[0179] [Chemical Formula 5-3]

[0180] Li x3 CoO2

[0181] In Chemical Formula 5-3,

[0182] 0.5 < x3 ≤ 1.

[0183] In practice, in Chemical Formula 5-1, 1 ≤ x1 ≤ 1.2, 0.5 ≤ y1 < 1, and 0 < z1 ≤ 0.5.

[0184] In practice, in Chemical Formula 5-2, 1 ≤ x2 ≤ 1.2, 0.3 ≤ y2 < 1, and 0.3 ≤ z2 < 1.

[0185] Based on the total weight of the positive electrode active material layer, the amount of the positive electrode active material included can be about 90 wt% to about 98 wt%.

[0186] In practice, the positive electrode active material layer may optionally include a conductive material and a binder. In practice, based on the total weight of the positive electrode active material layer, the amount of the binder included can be about 1 wt% to about 5 wt%.

[0187] Based on the total weight of the positive electrode active material layer, the amount of the conductive material included can be about 1 wt% to about 5 wt%.

[0188] The conductive material can provide electrode conductivity. Suitable conductive materials can be used as the conductive material unless they cause chemical changes. Examples of the conductive material can include carbon materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, or carbon fiber, etc.; metal materials including metal powders or metal fibers such as copper, nickel, aluminum, or silver; conductive polymers such as poly(phenylene) derivatives; or mixtures thereof.

[0189] The binder can help improve the binding characteristics of the positive electrode active material particles to each other and the binding characteristics of the positive electrode active material particles to the current collector. Examples of the binder can include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinylidene fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, or nylon, etc.

[0190] For the positive current collector, Al can be used, for example.

[0191] The negative electrode includes a negative current collector and a negative electrode active material layer including a negative electrode active material and disposed on the negative current collector.

[0192] The negative electrode active material can include a material that reversibly intercalates / deintercalates lithium ions, lithium metal, a lithium metal alloy, a material capable of doping / dedoping lithium, or a transition metal oxide.

[0193] The material that reversibly intercalates / deintercalates lithium ions can include carbon materials. The carbon materials can be suitable carbon negative electrode active materials for rechargeable lithium batteries. Examples of the carbon materials can include crystalline carbon, amorphous carbon, or a mixture thereof. The crystalline carbon can be shapeless, or flaky, scaly, spherical, or fibrous natural graphite or artificial graphite. The amorphous carbon can be soft carbon, hard carbon, mesophase pitch carbonized product, or calcined coke, etc.

[0194] The lithium metal alloy can include an alloy of lithium with, for example, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, or Sn.

[0195] The material capable of doping / dedoping lithium can be Si, Si-C composite material, SiO x (0 < x < 2), Si-Q alloy (where Q is an alkali metal, alkaline earth metal, Group 13 element, Group 14 element, Group 15 element, Group 16 element, transition metal, rare earth element, or a combination thereof, and is not Si), Sn, SnO2, and Sn-R alloy (where R is an alkali metal, alkaline earth metal, Group 13 element, Group 14 element, Group 15 element, Group 16 element, transition metal, rare earth element, or a combination thereof, and is not Sn), etc. At least one of these materials can be mixed with SiO2.

[0196] 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.

[0197] The transition metal oxide may include vanadium oxide, lithium vanadium oxide, or lithium titanium oxide.

[0198] In an implementation, the negative electrode active material may be a Si—C composite material including a Si active material and a carbon active material.

[0199] In the Si—C composite material, the average particle size of the Si active material may be about 50 nm to about 200 nm.

[0200] When the average particle diameter of the Si active material is within the above range, volume expansion occurring during charge and discharge can be suppressed, and interruption of a conductive path due to particle crushing during charge and discharge can be prevented.

[0201] The Si active material may be included in an amount of about 1 wt % to about 60 wt %, for example, about 3 wt % to about 60 wt %, based on the total weight of the Si—C composite material.

[0202] In implementations, the negative electrode active material may further include crystalline carbon together with the aforementioned Si—C composite material.

[0203] When the negative electrode active material includes the Si-C composite material and the crystalline carbon together, the Si-C composite material and the crystalline carbon may be included in the form of a mixture, and in this case, the Si-C composite material and the crystalline carbon may be included in a weight ratio of about 1:99 to about 50:50. In an implementation, the Si-C composite material and the crystalline carbon may be included in a weight ratio of about 5:95 to about 20:80.

[0204] The crystalline carbon may include graphite, for example, natural graphite, artificial graphite, or a mixture thereof.

[0205] The average particle size of the crystalline carbon may be about 5 μm to about 30 μm.

[0206] In the present specification, the average particle diameter may be a particle diameter (D50) at 50% by volume in a cumulative size distribution curve.

[0207] 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.

[0208] The amorphous carbon may include soft carbon, hard carbon, mesophase pitch carbonization product, burned coke, or a mixture thereof.

[0209] The amorphous carbon may be included in an amount of about 1 part to about 50 parts by weight, for example, about 5 parts to about 50 parts by weight, or about 10 parts to about 50 parts by weight, based on 100 parts by weight of the carbon active material.

[0210] In the negative active material layer, the negative active material may be included in an amount of about 95 wt % to about 99 wt % based on the total weight of the negative active material layer.

[0211] In an implementation, the negative electrode active material layer may include a binder, and optionally a conductive material. In the negative electrode active material layer, the content of the binder may be about 1wt% to about 5wt% based on the total weight of the negative electrode active material layer. When the negative electrode active material layer includes a conductive material, the negative electrode active material layer includes about 90wt% to about 98wt% of the negative electrode active material, about 1wt% to about 5wt% of the binder, and about 1wt% to about 5wt% of the conductive material.

[0212] The binder may help improve the binding properties between the negative electrode active material particles and between the negative electrode active material particles and the current collector. The binder may include a non-water-soluble binder, a water-soluble binder, or a combination thereof.

[0213] The non-water-soluble binder may include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or a combination thereof.

[0214] The water-soluble binder can be a rubber binder or a polymer resin binder. The rubber binder can include 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 include 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 or a combination thereof.

[0215] When a water-soluble binder is used as a negative electrode binder, a cellulose compound may be further included as a thickener to provide viscosity. The cellulose compound may include, for example, carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose or an alkali metal salt thereof. The alkali metal may include 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 from about 0.1 parts by weight to about 3 parts by weight.

[0216] The conductive material can provide electrode conductivity. Any suitable conductive material can be used as the conductive material unless it causes a chemical change. Examples of the conductive material may include carbon materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, and carbon fiber, etc.; metal materials including metal powders or metal fibers of copper, nickel, aluminum, and silver, etc.; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0217] The negative 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.

[0218] Depending on the type of the rechargeable lithium battery, the rechargeable lithium battery may further include a separator between the negative electrode and the positive electrode. Such a separator may be a porous substrate; or a composite porous substrate.

[0219] The porous substrate is a substrate including pores through which lithium ions can move. The porous substrate may include, for example, polyethylene, polypropylene, polyvinylidene fluoride, and multilayers thereof, such as a polyethylene / polypropylene double-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, or a polypropylene / polyethylene / polypropylene three-layer separator.

[0220] The composite porous substrate may have a form including a porous substrate and a functional layer on the porous substrate. From the perspective of ensuring the addition of additional functions, the functional layer may be, for example, a heat-resistant layer and an adhesive layer. In implementation, the heat-resistant layer may include a heat-resistant resin and optionally a filler.

[0221] In implementations, the adhesive layer may include an adhesive resin and optionally a filler.

[0222] The filler may be an organic filler or an inorganic filler.

[0223] refer to Figure 1 According to an embodiment, a rechargeable lithium battery 100 may include a battery cell, wherein the battery cell includes a negative electrode 112, a positive electrode 114 facing the negative electrode 112, a separator 113 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 that accommodates the battery cell; and a sealing member 140 for sealing the battery case 120.

[0224] The following examples and comparative examples are provided to emphasize the characteristics of one or more embodiments, but it will be understood that the examples and comparative examples are not to be construed as limiting the scope of the embodiments, nor are the comparative examples to be construed as being outside the scope of the embodiments. Further, it will be understood that the embodiments are not limited to the specific details described in the examples and comparative examples.

[0225] Synthesis of additives

[0226] Synthesis Example 1: Compound of Chemical Formula a-1

[0227] [Reaction Scheme 1]

[0228]

[0229] After the temperature was set at -5 ° C, bis (2-hydroxyethyl) disulfide (6.8g, 0.04mol) and triethylamine (TEA, 8.9g, 0.09mol) were placed in 50mL of dry dichloromethane under a nitrogen atmosphere. The mixed solution was slowly added dropwise to 100mL of dry dichloromethane solution in which 2-chloro-2-oxo-1,3,2-dioxaphospholane (COP, 12.54g, 0.088mol) was dissolved. After the mixture was stirred for 8 hours, the salt produced therein was filtered and removed, and the filtrate therefrom was dried. Subsequently, 50mL of toluene was added to the dry mixture to obtain a white solid (12.9g, 88%) produced therein; 1 H NMR (400MHz, CDCl3): δ4.40 (m, 12H), 3.01 (m, 4H); 31 P NMR: δ17.98

[0230] Synthesis Example 2: Compound of Chemical Formula a-2

[0231] [Reaction Scheme 2]

[0232]

[0233] After setting the temperature at -5°C, bis(2-hydroxyethyl) disulfide (6.8 g, 0.04 mol) and triethylamine (8.9 g, 0.09 mol) were added to 50 mL of dry dichloromethane under a nitrogen atmosphere. The mixed solution was slowly added dropwise to 100 mL of dry dichloromethane solution in which 2-chloro-1,3,2-dioxaphospholane (11.1 g, 0.09 mol) was dissolved. After the mixture was stirred for 8 hours, the salt produced therein was filtered and removed, and the filtrate therefrom was dried. Subsequently, 50 mL of diethyl ether was added to the dry mixture to remove the salt produced therein, and the filtrate therefrom was dried to obtain a transparent oil. (10.7 g, 80%); 1 H NMR (400MHz, CDCl3): δ4.24(m, 4H), 3.98(m, 8H), 2.81(m, 4H); 31 P NMR: δ137.11

[0234] Synthesis Example 3: Compound of Chemical Formula b-1

[0235] The compound represented by chemical formula b-1 was synthesized as described in Chinese patent reference CN111217856.

[0236]

[0237] Synthesis Example 4: Compound of Chemical Formula b-2

[0238] The compound represented by Chemical Formula b-2 was synthesized as described in [Heteroatom Chemistry 2010, 21, 515-520].

[0239]

[0240] Manufacturing of rechargeable lithium battery cells

[0241] Example 1

[0242] By using LiNi as the positive electrode active material with a weight ratio of 97:2:1 0.91 Co 0.07 Al 0.02 O2, polyvinylidene fluoride as a binder, and Ketjen black as a conductive material were mixed, and the resulting mixture was dispersed in N-methylpyrrolidone to prepare a positive electrode active material slurry.

[0243] The positive electrode active material slurry was coated on a 14 μm thick Al foil, dried at 110° C., and pressed to produce a positive electrode.

[0244] A negative active material was prepared by mixing graphite and Si-C composite material in a weight ratio of 93:7, and then, the negative active material, styrene-butadiene rubber binder and carboxymethyl cellulose were mixed in a weight ratio of 97:1:2 and then, dispersed in distilled water to prepare negative active material slurry.

[0245] The Si-C composite material has a core including artificial graphite and silicon particles and a mesophase pitch carbonization product is coated on the surface thereof, wherein the content of silicon is about 3 wt % based on the total weight of the Si-C composite material.

[0246] 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.

[0247] An electrode assembly was manufactured by assembling the fabricated positive electrode and negative electrode and a separator made of polyethylene having a thickness of 25 μm, and an electrolyte was injected to prepare a rechargeable lithium battery cell.

[0248] The electrolyte had the following composition.

[0249] (Electrolyte composition)

[0250] Salt: LiPF6 1.5M

[0251] Solvent: Ethylene carbonate: Ethyl methyl carbonate: Dimethyl carbonate (EC: EMC: DMC = 20: 10: 70 volume ratio)

[0252] Additive: 1.0 wt% of the compound of formula a-1 according to Synthesis Example 1

[0253] (Herein, in the electrolyte composition, "wt%" is based on the total weight of the electrolyte (lithium salt + non-aqueous organic solvent + additives))

[0254] Example 2

[0255] A rechargeable lithium battery cell was manufactured according to the same method as Example 1, except that the compound of Chemical Formula a-1 was used in an amount of 2.0 wt %.

[0256] Example 3

[0257] A rechargeable lithium battery cell was manufactured according to the same method as Example 1, except that the compound of Chemical Formula a-1 was used in an amount of 0.5 wt %.

[0258] Example 4

[0259] A rechargeable lithium battery cell was manufactured according to the same method as Example 1, except that the compound of Chemical Formula a-1 was used in an amount of 0.4 wt %.

[0260] Example 5

[0261] A rechargeable lithium battery cell was manufactured according to the same method as Example 1, except that the compound of Chemical Formula a-2 according to Synthesis Example 2 was used in an amount of 0.5 wt %.

[0262] Example 6

[0263] A rechargeable lithium battery cell was manufactured according to the same method as Example 1, except that the compound of Chemical Formula a-2 was used in an amount of 1.0 wt %.

[0264] Example 7

[0265] A rechargeable lithium battery cell was manufactured according to the same method as Example 1, except that the compound of Chemical Formula a-2 was used in an amount of 2.0 wt %.

[0266] Comparative Example 1

[0267] A rechargeable lithium battery cell was manufactured according to the same method as in Example 1, except that an electrolyte without additives was used.

[0268] Comparative Example 2

[0269] A rechargeable lithium battery cell was manufactured according to the same method as Example 1, except that the compound of Chemical Formula b-1 according to Synthesis Example 3 was used in an amount of 1.0 wt %.

[0270] Comparative Example 3

[0271] A rechargeable lithium battery cell was manufactured according to the same method as Example 1, except that the compound of Chemical Formula b-2 according to Synthesis Example 4 was used in an amount of 1.0 wt %.

[0272] Evaluation 1: DSC measurement

[0273] The electrolytes according to Example 2 and Comparative Example 1 were analyzed in a differential scanning calorimeter (DSC) method, and the results are shown in Table 1.

[0274] Table 1

[0275] Starting temperature (℃) Comparative Example 1 210 Example 2 230

[0276] Referring to Table 1, the starting temperature of the electrolyte according to Example 2 increases compared to the electrolyte according to Comparative Example 1. In other words, when an electrolyte containing an additive according to an embodiment of the present disclosure is used, thermal characteristics are improved, and accordingly, high temperature safety and reliability of a rechargeable lithium battery are expected to be improved.

[0277] Evaluation 2: Measuring the operating time of the CID

[0278] The rechargeable lithium battery cells of Examples 1, 2 and 4 and Comparative Example 1 were charged at a charge and discharge rate of 0.5C in a 4.35V CC / CV mode for 3 hours, and then placed in a 90°C chamber for 90 hours to measure the operation time of the CID (current interrupt device).

[0279] A CID (current interrupt device) is a device that detects a pressure change (ie, a pressure increase in a closed and sealed device) and interrupts the current itself when the pressure exceeds a certain pressure.

[0280] The results are shown in Figure 2 middle.

[0281] Figure 2 Graph showing the operation time of CID (current interrupt device) of the rechargeable lithium battery cells according to Examples 1, 2, and 4 and Comparative Example 1.

[0282] The CID operation time was measured to evaluate the storage characteristics of the rechargeable lithium battery cells at high temperatures.

[0283] refer to Figure 2 , when stored at a high temperature of 90° C., Comparative Example 1 exhibited a sharp voltage drop before about 30 hours, and the example including the additive according to the embodiment of the present disclosure exhibited a voltage drop after at least 80 hours, and thus exhibited an effect of delaying the open circuit voltage (OCV) drop by delaying the decomposition of the electrolyte and thus suppressing the increase in resistance. In other words, gas generation in the rechargeable lithium battery cell according to the example was suppressed even when stored at a high temperature.

[0284] Evaluation 3: Evaluation of internal resistance characteristics when left at high temperature

[0285] The rechargeable lithium battery cells according to Examples 1 to 3 and Examples 5 to 7 and Comparative Examples 1 to 3 were placed at 60° C. for 30 days in a charged state (=100%, SOC) to evaluate the internal resistance increase rate when stored at a high temperature of 60° C., and the results are shown in Tables 2 and 3. Figure 3 middle.

[0286] The direct current internal resistance (DC-IR) was measured in the following method.

[0287] At room temperature of 25° C., the cells according to Examples 1 to 3 and Examples 5 to 7 and Comparative Examples 1 to 3 were charged at 4A and 4.2V, and cut off at 100 mA, and then, paused for 30 minutes. Subsequently, the cells were discharged at 10A for 10 seconds, at 1A for 10 seconds, and at 10A for 4 seconds, respectively, and then, the current and voltage were measured at 18 seconds and 23 seconds to calculate the initial resistance (the difference between the resistance at 18 seconds and the resistance at 23 seconds) according to the equation of ΔR=ΔV / ΔI.

[0288] The single cell was charged under the conditions of 0.2C and 4.2V and placed at 60°C for 30 days to measure DC-IR, which was used to calculate the resistance increase rate (ΔDC-IR) before and after placement. Herein, the resistance increase rate (%) is the percentage of DC-IR after 30 days of placement relative to the initial DC-IR.

[0289] Table 2

[0290]

[0291] Figure 3 is a graph showing the resistance increase rate after the DC internal resistance of the rechargeable lithium battery cells according to Example 1 and Example 6 and Comparative Examples 2 and Comparative Examples 3 was measured after being left at 60° C. for 30 days.

[0292] Refer to Table 2 and Figure 3, the resistance increase rate of the rechargeable lithium battery cells of Examples 1 to 3 and Examples 5 to 7 before and after being placed at high temperature was reduced compared to the resistance increase rate of the cells of Comparative Examples 1 to 3 before and after being placed at high temperature. Accordingly, the secondary battery cells of Examples 1 to 3 and Examples 5 to 7 exhibited improved high temperature stability compared to the cells of Comparative Examples 1 to 3.

[0293] By way of summary and review, the electrolyte may include an organic solvent in which a lithium salt is dissolved, and such an electrolyte may determine the stability and performance of a rechargeable lithium battery.

[0294] LiPF6 (the lithium salt most commonly used as an electrolyte) can react with the organic solvent of the electrolyte to promote the consumption of the solvent and generate a large amount of gas. When LiPF6 decomposes, it generates LiF and PF5, which leads to the consumption of the electrolyte in the battery, resulting in the deterioration of high temperature performance and poor safety.

[0295] Accordingly, the electrolyte may have improved safety without deteriorating performance even under high temperature conditions.

[0296] One or more embodiments may provide additives with improved thermal stability.

[0297] One or more embodiments may provide a rechargeable lithium battery including the additive having improved high temperature cycle-life characteristics and high temperature storage characteristics by improving high temperature safety and high temperature reliability and reducing voltage drop and resistance increase rate during high temperature storage.

[0298] By applying an additive having improved thermal safety, a rechargeable lithium battery having improved high temperature characteristics may be implemented by suppressing an increase in the internal resistance of the battery and suppressing a voltage drop after being left at a high temperature.

[0299] Example embodiments have been disclosed herein, and although specific terms are employed, they are used and interpreted in a general and descriptive sense only and not for limiting purposes. In some cases, unless specifically indicated otherwise, as will be apparent to one of ordinary skill in the art to which this application is submitted, the features, characteristics, and / or elements described in conjunction with a specific embodiment may be used alone or in combination with the features, characteristics, and / or elements described in conjunction with other embodiments. Accordingly, it will be understood by those skilled in the art that various changes may be made in form and detail without departing from the spirit and scope of the invention as set forth in the appended claims.

Claims

1. An electrolyte for a rechargeable lithium battery, the electrolyte comprising: a non-aqueous organic solvent, a lithium salt, and an additive represented by Chemical Formula 1B-I, Chemical Formula 1B-II, Chemical Formula 2B-I or Chemical Formula 2B-II: [Chemical Formula 1B-I] [Chemical Formula 1B-II] In Chemical Formula 1B-I and Chemical Formula 1B-II, R 101 To R 120 are each independently hydrogen or substituted or unsubstituted C1 to C10 alkyl, and L 1 and L 2 are each independently a substituted or unsubstituted C1 to C20 alkylene group, [Chemical Formula 2B-I] [Chemical Formula 2B-II] wherein, in Chemical Formula 2B-I and Chemical Formula 2B-II, R 121 To R 140 are each independently hydrogen or substituted or unsubstituted C1 to C10 alkyl, and L 3 and L 4 are each independently a substituted or unsubstituted C1 to C20 alkylene group, the substituted means that the hydrogen atom of the compound is replaced by a C1 to C20 alkyl group.

2. The electrolyte according to claim 1, wherein: the additive is represented by Chemical Formula 1B-I-1 or Chemical Formula 2B-I-1: [Chemical Formula 1B-I-1] [Chemical Formula 2B-I-1] In Formula 1B-I-1 and Formula 2B-I-1, R 101 To R 108 , R 121 To R 128 and R 141 To R 156 Each is independently hydrogen or a substituted or unsubstituted C1 to C10 alkyl group.

3. The electrolyte according to claim 1, wherein the amount of the additive included is 0.1 wt% to 10 wt% based on the total weight of the electrolyte for the rechargeable lithium battery.

4. A rechargeable lithium battery, the rechargeable lithium battery comprising: a positive electrode including a positive electrode active material; a negative electrode including a negative electrode active material; and the electrolyte according to any one of claims 1 to 3.

5. The rechargeable lithium battery according to claim 4, wherein: the positive electrode active material is represented by Chemical Formula 5: [Chemical Formula 5] Li x M 1 1-y-z M 2 y M 3 z O2 In Chemical Formula 5, 0.5≤x≤1.8, 0≤y≤1, 0≤z≤1, 0≤y+z<1, and M 1 、M 2 and M 3 Each is independently Ni, Co, Mn, Al, Sr, Mg, La or a combination thereof.

6. The rechargeable lithium battery according to claim 4, wherein: the positive electrode active material is a lithium composite oxide represented by Chemical Formula 5-1, Chemical Formula 5-2 or Chemical Formula 5-3: [Chemical Formula 5-1] Li x1 Ni y1 Co z1 Al 1-y1-z1 O2 In Chemical Formula 5-1, 1 ≤ x1 ≤ 1.2, 0 < y1 < 1, and 0 < z1 < 1, [Chemical Formula 5-2] Li x2 Ni y2 Co z2 Mr 1-y2-z2 O2 In Chemical Formula 5-2, 1 ≤ x2 ≤ 1.2, 0 < y2 < 1, and 0 < z2 < 1, [Chemical Formula 5-3] <h2 style=";text-align:left;direction:ltr">Li<h2 style=";text-align:left;direction:ltr"> x3 <h2 style=";text-align:left;direction:ltr"> CoO2 In Chemical Formula 5-3, 0.5 < x3 ≤ 1.

Images