Additives, including electrolytes for lithium secondary batteries and lithium secondary batteries

Abstract

Additives represented by Chemical Formula 1, electrolytes including the additives, and lithium secondary batteries are provided. Details of Chemical Formula 1 are described in the specification.

Description

Technical Field

[0001] Additives, electrolytes including those for lithium secondary batteries, and lithium secondary batteries are disclosed. Background Technology

[0002] Lithium-ion batteries are rechargeable and have an energy density three times or more per unit weight than conventional lead-acid, nickel-cadmium, nickel-metal hydride, and nickel-zinc batteries. They can also be charged at high rates and are therefore commercially manufactured for use in laptops, cell phones, power tools, and electric bicycles, and research is actively underway to further improve their energy density.

[0003] This lithium secondary battery is manufactured by injecting an electrolyte into a single battery cell, which includes a positive electrode comprising a positive electrode active material capable of intercalating / deintercalating lithium ions and a negative electrode comprising a negative electrode active material capable of intercalating / deintercalating lithium ions.

[0004] In particular, the electrolyte, including the organic solvent in which lithium salts are dissolved, is crucial in determining the stability and performance of lithium secondary batteries.

[0005] LiPF6, the most commonly used lithium salt as an electrolyte, has the problem of reacting with the electrolyte solvent, leading to solvent consumption and the generation of large amounts of gas. When LiPF6 decomposes, it generates LiF and PF5, which results in electrolyte consumption in the battery, leading to decreased high-temperature performance and poor safety.

[0006] An electrolyte is needed to suppress the side reactions of this lithium salt and improve battery performance. Summary of the Invention

[0007] [Technical Issues]

[0008] The implementation provides an electrolyte for lithium secondary batteries that can improve the high-temperature cycle life characteristics of lithium secondary batteries.

[0009] Another embodiment provides an electrolyte for lithium secondary batteries that includes additives.

[0010] Another embodiment provides a lithium secondary battery that includes an electrolyte for use in lithium secondary batteries.

[0011] [Technical Solution]

[0012] Embodiments of the present invention provide an additive represented by chemical formula 1.

[0013] [Chemical Formula 1]

[0014]

[0015] In chemical formula 1,

[0016] R 1 and R 2 Each of these is independently a substituted or unsubstituted C1 to C10 alkyl, a substituted or unsubstituted C2 to C10 alkenyl, a substituted or unsubstituted C3 to C10 cycloalkyl, a substituted or unsubstituted C3 to C10 cycloalkenyl, a substituted or unsubstituted C2 to C10 ynyl, a substituted or unsubstituted C3 to C10 cycloalkenyl, or a substituted or unsubstituted C6 to C20 aryl.

[0017] L represents a substituted or unsubstituted C1 to C10 alkylene group.

[0018] As an example, chemical formula 1 can be represented by chemical formula 1-1.

[0019] [Chemical Formula 1-1]

[0020]

[0021] In chemical formula 1-1,

[0022] n is an integer from 1 to 5, and R 1 and R 2 The limitations are the same as those mentioned above.

[0023] As a concrete example, R in chemical formula 1 1 and R 2 Each can be independently a substituted or unsubstituted C1 to C10 alkyl, a substituted or unsubstituted C2 to C10 alkenyl, or a substituted or unsubstituted C6 to C20 aryl.

[0024] As a more specific example, R in chemical formula 1 1 and R 2 Each can be independently a substituted or unsubstituted C1 to C10 alkyl or a substituted or unsubstituted C2 to C10 alkenyl.

[0025] For example, R in chemical formula 1 1 and R 2 Each can be independently a substituted or unsubstituted C1 to C5 alkyl group.

[0026] In the implementation method, R in chemical formula 1 1 and R 2 They can be the same.

[0027] Another embodiment of the present invention provides an electrolyte for lithium secondary batteries, comprising a non-aqueous organic solvent, a lithium salt, and the aforementioned additives.

[0028] The amount of additives included may be from 0.1 wt% to 10 wt%, depending on the total weight of the electrolyte used in the lithium secondary battery.

[0029] As a specific example, the amount of additives included may be from 0.1 wt% to 3.0 wt%, depending on the total weight of the electrolyte used in the lithium secondary battery.

[0030] Another embodiment of the present invention provides a lithium secondary battery, comprising: a positive electrode including a positive electrode active material; a negative electrode including a negative electrode active material; and the aforementioned electrolyte.

[0031] The positive electrode active material can be a composite oxide containing nickel metal and lithium.

[0032] The positive electrode active material can be, for example, represented by chemical formula 4.

[0033] [Chemical Formula 4]

[0034] Li a M 1 1-y1-z1 M 2 y1 M 3 z1 O2

[0035] In chemical formula 4,

[0036] 0.9≤a≤1.8, 0≤y1≤1, 0≤z1≤1, 0≤y1+z1<1, M 1 M 2 and M 3 Each metal can be independently selected from, for example, Ni, Co, Mn, Al, Sr, Mg, or La and combinations thereof.

[0037] [Beneficial Effects]

[0038] Lithium-ion batteries with improved high-temperature cycle life can be implemented. Attached Figure Description

[0039] Figure 1 A schematic diagram illustrating a lithium secondary battery according to an embodiment of the present invention.

[0040] Figure 2 The 1H NMR spectrum is shown for the compound synthesized as an additive according to an embodiment of the present invention.

[0041] Figure 3 The 13C NMR spectrum is shown for the compound synthesized as an additive according to an embodiment of the present invention.

[0042] <Symbol Description>

[0043] 100: Lithium secondary battery

[0044] 112: Negative electrode

[0045] 113: partition

[0046] 114: Positive electrode

[0047] 120: Battery casing

[0048] 140: Sealing component Detailed Implementation

[0049] The embodiments of this disclosure will be described in detail below. However, these embodiments are exemplary, and the invention is not limited thereto and is defined by the scope of the claims.

[0050] As used herein, unless otherwise specified, “substitution” means that the hydrogen atoms of a compound are replaced by a substituent selected from the following: halogen atom (F, Br, Cl or I), hydroxyl, alkoxy, nitro, cyano, amino, azide, amido, hydrazine, hydrazone, carbonyl, carbamoyl, thiol, ester, carboxyl or a salt thereof, sulfonic acid or a salt thereof, phosphate or a salt thereof, C1 to C20 alkyl, C2 to C20 alkenyl, C2 to C20 alkynyl, C6 to C30 aryl, C7 to C30 aralkyl, C1 to C4 alkoxy, C1 to C20 heteroalkyl, C3 to C20 heteroaralkyl, C3 to C30 cycloalkyl, C3 to C15 cycloalkenyl, C6 to C15 cycloalkynyl, C2 to C20 heterocycloalkyl and combinations thereof.

[0051] The additives according to the embodiments are described below.

[0052] The additive according to an embodiment of the present invention is represented by chemical formula 1.

[0053] [Chemical Formula 1]

[0054]

[0055] In chemical formula 1,

[0056] R 1 and R 2 Each of these is independently a substituted or unsubstituted C1 to C10 alkyl, a substituted or unsubstituted C2 to C10 alkenyl, a substituted or unsubstituted C3 to C10 cycloalkyl, a substituted or unsubstituted C3 to C10 cycloalkenyl, a substituted or unsubstituted C2 to C10 ynyl, a substituted or unsubstituted C3 to C10 cycloalkenyl, or a substituted or unsubstituted C6 to C20 aryl.

[0057] L represents a substituted or unsubstituted C1 to C10 alkylene group.

[0058] The additive according to embodiments of the present invention comprises a dithioester functional group, which forms a film on each surface of the positive and negative electrodes in an electrolyte solution to suppress the increase in resistance in the film during storage at high temperatures, and thus exhibits the effect of improving cycle life characteristics.

[0059] In particular, the thiocarbonyl (=S) included in the dithioester functional group can form a stronger film than the carbonyl (=O) film, which has excellent heat resistance, thereby improving the high-temperature characteristics of batteries made by using additives containing the dithioester functional group represented by Formula 1.

[0060] As an example, an additive can be represented by chemical formula 1-1.

[0061] [Chemical Formula 1-1]

[0062]

[0063] In chemical formula 1-1, n is an integer from 1 to 5, and

[0064] R 1 and R 2 The limitations are the same as those mentioned above.

[0065] The additive according to the embodiments may have the following structure: two dithioester functional groups are linked by a dioxyalkylene group having an even number of carbons, as shown in chemical formula 1-1.

[0066] Additives with this structure induce the stability of the positive electrode by binding the ligands to the transition metal, since the two thiocarbonyl groups can act as scavengers optimized for the intermetallic geometry of the positive electrode active material on the positive electrode surface, thereby preventing the positive electrode from decomposing and resulting in a reduction in the rate of increase in resistance in lithium secondary batteries.

[0067] For example, R 1 and R 2 Each can be independently a substituted or unsubstituted C1 to C10 alkyl, a substituted or unsubstituted C2 to C10 alkenyl, or a substituted or unsubstituted C6 to C20 aryl.

[0068] In a specific example, R 1 and R 2 Each can be independently a substituted or unsubstituted C1 to C10 alkyl or a substituted or unsubstituted C2 to C10 alkenyl.

[0069] For example, R 1 and R 2 Each can be independently a substituted or unsubstituted C1 to C5 alkyl group.

[0070] In the implementation, R 1 and R2 They can be the same.

[0071] When R 1 and R 2 When the additives have the same substituents and a symmetrical structure, they have a structure that is more appropriately coordinated with the geometry of the positive electrode active material, thereby further maximizing the positive electrode stability effect.

[0072] An electrolyte for a lithium secondary battery according to another embodiment of the present invention comprises a non-aqueous organic solvent, a lithium salt, and the aforementioned additives.

[0073] Based on the total weight of the electrolyte used in lithium secondary batteries, the amount of additives included can be from 0.1 wt% to 10 wt%, specifically from 0.1 wt% to 5.0 wt%, and more specifically from 0.1 wt% to 3.0 wt%.

[0074] When the content of the additive is within the range mentioned above, the increase in resistance at high temperatures can be prevented, thereby enabling the implementation of a lithium secondary battery with improved cycle life characteristics.

[0075] That is, when the content of the additive is less than 0.1 wt%, the storage characteristics at high temperature can be reduced, and when it exceeds 10 wt%, the cycle life can be reduced due to the increase in interfacial resistance.

[0076] Non-aqueous organic solvents are used as media for transporting ions that participate in the electrochemical reactions of the battery.

[0077] Non-aqueous organic solvents can be carbonates, esters, ethers, ketones, alcohols, or proton-inert solvents.

[0078] Carbonate solvents may include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene glycol carbonate (EC), propylene glycol carbonate (PC), and butylene glycol carbonate (BC), etc. Ester solvents may include methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, decanolactone, mevalonolactone, and caprolactone, etc. Ether solvents may include dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, dimethoxyethane, 2-methyltetrahydrofuran, and tetrahydrofuran, etc. Additionally, ketone solvents may include cyclohexanone, etc. Alcohol solvents may include ethanol and isopropanol, and proton-inert solvents may include nitriles such as R-CN (where R is a hydrocarbon group having a C2 to C20 straight chain, branched chain or cyclic structure, and may include double bonds, aromatic rings or ether bonds), dioxolane such as 1,3-dioxolane, and sulfolane.

[0079] Non-aqueous organic solvents can be used alone or in mixtures. When organic solvents are used in mixtures, the mixing ratio can be controlled according to the desired battery performance.

[0080] Carbonate solvents are prepared by mixing cyclic and chain carbonates. Electrolyte performance can be improved when cyclic and chain carbonates are mixed together in a volume ratio of 1:1 to 1:9.

[0081] In addition to carbonate solvents, non-aqueous organic solvents may further include aromatic hydrocarbon organic solvents. In this document, carbonate solvents and aromatic hydrocarbon organic solvents may be mixed in volume ratios ranging from 1:1 to 30:1.

[0082] Aromatic hydrocarbon organic solvents can be aromatic hydrocarbon compounds of chemical formula 2.

[0083] [Chemical Formula 2]

[0084]

[0085] In chemical formula 2, R 7 To R 12 They may be the same or different, and are selected from hydrogen, halogens, C1 to C10 alkyl groups, haloalkyl groups and combinations thereof.

[0086] Specific examples of aromatic hydrocarbon organic 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, and fluoromethylbenzene. Benzene, 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.

[0087] The electrolyte may further include vinylene carbonate or ethylene glycol carbonate compounds represented by Formula 3 in order to improve the cycle life of the battery.

[0088] [Chemical Formula 3]

[0089]

[0090] In chemical formula 3, R 13 and R14 Identical or different, and selected from hydrogen, halogen, cyano (CN), nitro (NO2), and fluorinated C11 to C5 alkyl groups, under the condition that R 13 and R 14 At least one of them is a halogen, a cyano (CN), a nitro (NO2), and a fluorinated C1 to C5 alkyl group, and R 13 and R 14 They are not both hydrogen.

[0091] Examples of ethylene carbonate compounds may be difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate, or fluoroethylene carbonate. The amount of additives used to improve cycle life may be used within appropriate limits.

[0092] Lithium salts dissolved in non-organic solvents supply lithium ions in batteries, ensuring basic operation of lithium secondary batteries and improving lithium ion transport between the positive and negative electrodes. Examples of lithium salts include at least one 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 (where x and y are natural numbers, for example, integers ranging from 1 to 20), LiCl, LiI, and LiB(C2O4)2 (lithium bis(oxalate)borate: LiBOB). Lithium salts can be used at concentrations ranging from 0.1M to 2.0M. When lithium salts are included in the above concentration range, the electrolyte can exhibit excellent performance and lithium-ion mobility due to optimal electrolyte conductivity and viscosity.

[0093] Another embodiment provides a lithium secondary battery, comprising: a positive electrode including a positive electrode active material; a negative electrode including a negative electrode active material; and the aforementioned electrolyte.

[0094] The positive electrode includes a current collector and a layer of positive active material disposed on the current collector and including positive active material.

[0095] Positive electrode active materials may include lithiated intercalation compounds that can reversibly insert and deintercalate lithium ions.

[0096] Specifically, a composite oxide containing nickel metal and lithium can be used.

[0097] Examples of positive electrode active materials may include compounds represented by any of the following chemical formulas.

[0098] 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 a E 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 Mn 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 Mn 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 Mn b X c About 2-α T2(0.90≤a≤1.8,0≤b≤0.5,0≤c≤0.05,0<α<2);Li a Ni b E 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 Mn 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);Li a NiG 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 Mn2G 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)

[0099] In the 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.

[0100] These compounds may form a coating on a surface or may be mixed with another coating compound. The coating may include at least one coating element compound selected from the following: oxides of the coating element, hydroxides of the coating element, hydroxy oxides of the coating element, oxycarbonates of the coating element, and hydroxycarbonates of the coating element. The compounds used for coating may be amorphous or crystalline. Coating elements included in the coating may include Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or mixtures thereof. By using these elements in the compounds, the coating can be formed in a manner that does not adversely affect the properties of the positive electrode active material. For example, this method may include any coating method (e.g., spraying, dipping, etc.), but is not described in more detail as it is well known to those skilled in the art.

[0101] More specifically, at least one type of lithium composite oxide represented by chemical formula 4 may be used.

[0102] [Chemical Formula 4]

[0103] Li a M 1 1-y1-z1 M 2 y1 M 3 z1 O2

[0104] In chemical formula 4,

[0105] 0.9≤a≤1.8, 0≤y1≤1, 0≤z1≤1, 0≤y1+z1<1, M 1 M 2 and M 3 Each metal can be independently selected from, for example, Ni, Co, Mn, Al, Sr, Mg, or La and combinations thereof.

[0106] For example, M 1 It can be Ni, and M 2 and M 3 They can each be independently metals such as Co, Mn, Al, Sr, Mg, or La.

[0107] More specifically, M 1 It can be Ni, M 2 It can be Co, and M 3 It can be Mn or Al, but they are not limited to these.

[0108] Specific examples of positive electrode active materials according to embodiments 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).

[0109] Based on the total weight of the positive electrode active material layer, the amount of positive electrode active material included can be from 90 wt% to 98 wt%.

[0110] In embodiments of the present invention, the positive electrode active material layer may include a binder and a conductive material. Hereinafter, based on the total amount of the positive electrode active material layer, the amounts of the binder and conductive material may be from 1 wt% to 5 wt%, respectively.

[0111] The binder serves to bond the positive electrode active material particles together and, in addition, to the positive electrode active material particles and the current collector. Examples of binders include, but are not limited to, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylic styrene-butadiene rubber, epoxy resin, and nylon.

[0112] This includes conductive materials to provide electrode conductivity. Any conductive material can be used as a conductive material unless it causes a chemical change, and examples of conductive materials may include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, and carbon fibers; metallic materials including metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0113] The current collector can use Al, but is not limited to this.

[0114] The negative electrode includes a current collector and a negative electrode active material layer formed on the current collector and including negative electrode active material.

[0115] The negative electrode active material may include materials that can reversibly insert / deintercalate lithium ions, lithium metal, lithium metal alloys, materials that can be doped / dedoped with lithium, or transition metal oxides.

[0116] Materials that can reversibly embed / detach lithium ions may include carbon materials. The carbon materials can be any commonly used carbon-based negative electrode active materials in lithium ion secondary batteries. Examples thereof can be crystalline carbon, amorphous carbon, or a mixture thereof. The crystalline carbon can be amorphous, or flaky, scaly, spherical, or fibrous natural graphite or artificial graphite. The amorphous carbon can be soft carbon, hard carbon, mesophase pitch carbonization products, calcined coke, etc.

[0117] The lithium metal alloy includes an alloy of lithium and a metal selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn.

[0118] Materials that can dope / dedope lithium can be Si, Si-C composite materials, SiO x (0 < x < 2), Si-Q alloys (where Q is an element 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, but not Si), Sn, SnO2, and Sn-R alloys (where R is an element 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, but not Sn), etc., and at least one of these materials can be mixed with SiO2. The 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.

[0119] The transition metal oxide can be vanadium oxide, lithium vanadium oxide, or lithium titanium oxide.

[0120] In the negative electrode active material layer, based on the total weight of the negative electrode active material layer, the amount of the negative electrode active material included can be 95 wt% to 99 wt%.

[0121] In an embodiment of the present disclosure, the negative electrode active material layer includes a binder and optionally a conductive material. In the negative electrode active material layer, based on the total weight of the negative electrode active material layer, the content of the binder can be 1 wt% to 5 wt%. When the negative electrode active material layer includes a conductive material, the negative electrode active material layer includes 90 wt% to 98 wt% of the negative electrode active material, 1 wt% to 5 wt% of the binder, and 1 wt% to 5 wt% of the conductive material.

[0122] Binders improve the bonding properties between negative electrode active material particles and between negative electrode active material particles and current collectors. Binders include non-water-soluble binders, water-soluble binders, or combinations thereof.

[0123] The non-water-soluble adhesive may be polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyimide, or a combination thereof.

[0124] Water-soluble adhesives can be rubber-based adhesives or polymer resin adhesives. Rubber-based adhesives can be selected from styrene-butadiene rubber, acrylic styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber, acrylic rubber, butyl rubber, fluororubber, and combinations thereof. Polymer resin adhesives can be selected from polytetrafluoroethylene, ethylene-propylene copolymer, polyethylene oxide, polyvinylpyrrolidone, polyepoxychloropropane, polyphosphazene, polyacrylonitrile, polystyrene, ethylene-propylene-diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0125] When a water-soluble binder is used as a negative electrode binder, a cellulose compound, acting as a thickener, can be further used to provide viscosity. The cellulose compound includes one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, or their alkali metal salts. The alkali metal can be Na, K, or Li. Based on 100 parts by weight of the negative electrode active material, the amount of this thickener can be from 0.1 parts by weight to 3 parts by weight.

[0126] This includes conductive materials to provide electrode conductivity. Any conductive material can be used as a conductive material unless it causes a chemical change, and examples of conductive materials include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, and carbon fiber; metallic materials including metal powders or metal fibers such as copper, nickel, and aluminum silver; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0127] The current collector may include one selected from the following: copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, polymer substrate coated with conductive metal, and combinations thereof.

[0128] Depending on the type of lithium-ion secondary battery, the lithium-ion secondary battery may further include a separator between the negative electrode and the positive electrode. Examples of suitable separator materials include polyethylene, polypropylene, polyvinylidene fluoride, and multilayers thereof, such as polyethylene / polypropylene double-layer separators, polyethylene / polypropylene / polypropylene triple-layer separators, and polypropylene / polypropylene / polypropylene triple-layer separators.

[0129] refer to Figure 1The lithium secondary battery 100 according to the embodiment includes a single battery cell: the single battery cell includes 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 113 (not shown) for impregnating the negative electrode 112, the positive electrode 114 and the separator 113 for the lithium secondary battery; a battery casing 120 for housing the single battery cell; and a sealing member 140 for sealing the battery casing 120.

[0130] Detailed description of the implementation method

[0131] The following describes embodiments and comparative examples of the present invention. However, these embodiments are in no way intended to limit the scope of the invention.

[0132] Manufacturing of lithium secondary battery single cells

[0133] Preparation example: Synthesis of the compound represented by chemical formula a (carbonodithioic acid, O,O'-1,2-ethanediyl-S,S'-dimethyl ester (9Cl))

[0134] <Reaction Protocol>

[0135]

[0136] Ethylene glycol (1.0 eq) was dissolved in DMSO and then added dropwise to carbon disulfide (1.2 eq) at room temperature, followed by stirring for 12 hours. When the reaction was complete, water was added to the reaction mixture, and the organic layer was extracted to separate the layers. The collected organic layer was dried with MgSO4 and filtered, and the filtrate was concentrated and then recrystallized in n-hexane / benzene to give a pale yellow solid (yield = 66%).

[0137] from Figure 2 and Figure 3 The 1H NMR and 13C NMR spectra shown in the figure were used to check whether the compound was synthesized.

[0138] Figure 2 The 1H NMR spectrum of the compound synthesized as an additive according to an embodiment of the present invention.

[0139] Figure 3 The 13C NMR spectrum of the compound synthesized as an additive according to an embodiment of the present invention.

[0140] refer to Figure 2 and Figure 3 The information of specific peaks in the NMR spectrum is as follows.

[0141] Example 1

[0142] LiNi will be used 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 are mixed in a weight ratio of 97:1.6:1.4, and then dispersed in N-methylpyrrolidone to prepare a positive electrode active material slurry.

[0143] The positive electrode is manufactured by coating a slurry of positive active material onto a 20 μm thick Al foil, drying it at 100 °C, and then extruding it.

[0144] A negative electrode active material slurry was prepared by mixing graphite, styrene-butadiene rubber binder, and carboxymethyl cellulose as negative electrode active materials in a weight ratio of 98:1:1 and dispersing the mixture in distilled water.

[0145] The negative electrode is manufactured by coating a slurry of negative electrode active material onto a 10 μm thick Cu foil, and then drying and extruding it at 100 °C.

[0146] Positive electrode, negative electrode, 25μm thick separator made of polyethylene material, and electrolyte are used to manufacture lithium secondary battery single cells.

[0147] Electrolytes have the following composition.

[0148] (Composition of electrolytes)

[0149] Salt: LiPF6 1.5M

[0150] Solvent: Ethylene glycol carbonate: Ethyl methyl carbonate: Dimethyl carbonate (EC:EMC:DMC = 2:1:7 volume ratio)

[0151] Additive: Compound represented by chemical formula a, 0.1 wt%.

[0152] (In this article, “wt%” in the composition of electrolytes refers to the total amount of electrolyte (lithium salt + non-aqueous organic solvent + additives).)

[0153] Example 2

[0154] The lithium secondary battery single cell was manufactured in the same manner as in Example 1, except that the content of the additive was changed to 0.5 wt%.

[0155] Example 3

[0156] The lithium secondary battery single cell was manufactured in the same manner as in Example 1, except that the content of the additive was changed to 1.0 wt%.

[0157] Example 4

[0158] The lithium secondary battery single cell was manufactured in the same manner as in Example 1, except that the content of the additive was changed to 2.0 wt%.

[0159] Example 5

[0160] The lithium secondary battery single cell was manufactured in the same manner as in Example 1, except that the content of the additive was changed to 3.0 wt%.

[0161] Comparative Example 1

[0162] The lithium secondary battery single cell was manufactured in the same manner as in Example 1, except that no additives were used.

[0163] Comparative Example 2

[0164] The lithium secondary battery single cell was manufactured in the same manner as in Example 1, except that the additive was changed to a compound represented by chemical formula b.

[0165] [Chemical formula b]

[0166]

[0167] (Ethyl xanthate (C3H6OS2), ethoxymethane dithiocarboxylic acid, CAS 151-01-9)

[0168] Comparative Examples 3 to 5

[0169] The lithium secondary battery single cells were manufactured in the same manner as in Example 1, except that the content of the additives was changed to 0.5 wt%, 2.0 wt%, and 3.0 wt%, respectively.

[0170] Assessment: Evaluation of high-temperature cycling life characteristics

[0171] The lithium secondary battery cells of Examples 1 to 5 and Comparative Examples 1 to 5 were charged 150 times at a constant current-constant voltage of 0.5C and 4.3V under a cutoff condition of 0.05C, and discharged at a constant current of 0.5C under a cutoff condition of 2.8V at 45°C. The capacity ratio (capacity retention rate) of the discharge capacity of the 150th cycle to the discharge capacity of the first cycle was then measured, as shown in Table 1.

[0172] Table 1

[0173]

[0174]

[0175] Referring to Table 1, compared with lithium secondary battery cells that do not include the additives according to Comparative Example 1 and lithium secondary battery cells that include the additives represented by chemical formula b according to Comparative Examples 2 to 5, the lithium secondary battery cells according to Examples 1 to 5 exhibit improved capacity degradation and thus improved high-temperature cycle life characteristics.

[0176] Although the invention has been described in conjunction with exemplary embodiments now regarded as practice, it should be understood that the invention is not limited to the disclosed embodiments. Rather, 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 lithium secondary batteries, comprising: Non-aqueous organic solvents Lithium salts, and Additives represented by chemical formula 1: [Chemical Formula 1] In chemical formula 1, R 1 and R 2 Each of these is independently a substituted or unsubstituted C1 to C10 alkyl, a substituted or unsubstituted C2 to C10 alkenyl, a substituted or unsubstituted C3 to C10 cycloalkyl, a substituted or unsubstituted C3 to C10 cycloalkenyl, a substituted or unsubstituted C2 to C10 alkynyl, a substituted or unsubstituted C3 to C10 cycloalkynyl, or a substituted or unsubstituted C6 to C20 aryl. L is a substituted or unsubstituted C1 to C10 alkylene group; The amount of the additives included is from 0.1 wt% to 10 wt%, based on the total weight of the electrolyte used in the lithium secondary battery.

2. The electrolyte for lithium secondary batteries according to claim 1, wherein... Chemical formula 1 is represented by chemical formula 1-1: [Chemical Formula 1-1] in, In chemical formula 1-1, n is an integer from 1 to 5, and R 1 and R 2 The limitation is the same as that in claim 1.

3. The electrolyte for lithium secondary batteries according to claim 1, wherein... R in chemical formula 1 1 and R 2 Each is independently a substituted or unsubstituted C1 to C10 alkyl, a substituted or unsubstituted C2 to C10 alkenyl, or a substituted or unsubstituted C6 to C20 aryl.

4. The electrolyte for a lithium secondary battery according to claim 1, wherein... R in chemical formula 1 1 and R 2 Each is independently a substituted or unsubstituted C1 to C10 alkyl or a substituted or unsubstituted C2 to C10 alkenyl.

5. The electrolyte for a lithium secondary battery according to claim 1, wherein... R in chemical formula 1 1 and R 2 Each is independently a substituted or unsubstituted C1 to C5 alkyl group.

6. The electrolyte for a lithium secondary battery according to claim 1, wherein... R in chemical formula 1 1 and R 2 same.

7. The electrolyte for a lithium secondary battery according to claim 1, wherein... Based on the total weight of the electrolyte for the lithium secondary battery, the amount of the additives included is from 0.1 wt% to 3.0 wt%.

8. A lithium secondary battery, comprising: The positive electrode includes the positive electrode active material; The negative electrode includes the negative electrode active material; The electrolyte according to any one of claims 1 to 7.

9. The lithium secondary battery according to claim 8, wherein... The positive electrode active material is a composite oxide containing nickel metal and lithium.

10. The lithium secondary battery according to claim 8, wherein The positive electrode active material is represented by chemical formula 4: [Chemical Formula 4] Li a M 1 1-y1-z1 M 2 y1 M 3 z1 O2 in, In chemical formula 4, 0.9≤a≤1.8, 0≤y1≤1, 0≤z1≤1, 0≤y1+z1<1, M 1 M 2 and M 3 Each can be a metal selected independently from Ni, Co, Mn, Al, Sr, Mg, or La, or a combination thereof.

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