Additives, electrolyte for rechargeable lithium batteries including the same, and rechargeable lithium battery

Abstract

Provided are an additive represented by Chemical Formula 1, an electrolyte for a rechargeable lithium battery including the same, and a rechargeable lithium battery. Details of Chemical Formula 1 are set forth in the specification.

Description

Technical Field

[0001] This disclosure relates to additives, electrolytes including those for rechargeable lithium batteries, and rechargeable lithium batteries. Background Technology

[0002] Rechargeable lithium batteries are rechargeable and have three or more times the energy density per unit weight of 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, electric bicycles, etc., and research is actively underway to further improve their energy density.

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

[0004] In particular, the electrolyte uses an organic solvent in which lithium salts are dissolved, and this electrolyte is important for determining the stability and performance of rechargeable lithium batteries.

[0005] LiPF6, the most commonly used lithium salt in electrolytes, has the problem of accelerating solvent consumption and generating large amounts of gas by reacting with the organic solvents in the electrolyte. When LiPF6 decomposes, it produces LiF and PF5, which cause electrolyte consumption in the battery, leading to high-temperature performance degradation and poor safety.

[0006] In particular, at low temperatures, the voltage drop during discharge can be large due to the increased internal resistance of the battery, making it difficult to obtain sufficient discharge voltage. Summary of the Invention

[0007] Technical issues

[0008] The implementation provides an additive that exhibits superior output characteristics even under low-temperature conditions by suppressing the increase in internal resistance of the battery at low temperatures.

[0009] Another embodiment provides an electrolyte for rechargeable lithium batteries that has improved lifespan characteristics by applying additives.

[0010] Another embodiment provides a rechargeable lithium battery that includes an electrolyte for use in rechargeable lithium 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] X is C(=O) or S(=O)2, and

[0017] R 1 and R 2 Each is independently a fluorinated group or a C1-C5 fluoroalkyl group substituted with at least one fluorinated group. For example, Formula 1 can be represented by one of Formula 1-1 or Formula 1-8.

[0018] [Chemical Formula 1-1][Chemical Formula 1-2]

[0019]

[0020] [Chemical Formulas 1-3]

[0021]

[0022] [Chemical Formulas 1-4]

[0023]

[0024] [Chemical Formulas 1-5]

[0025]

[0026] [Chemical Formulas 1-6]

[0027]

[0028] [Chemical Formulas 1-7]

[0029]

[0030] [Chemical Formulas 1-8]

[0031]

[0032] In chemical formula 1-1 or chemical formula 1-8,

[0033] R a R b R c and R d Each is independently either hydrogen or fluorine-based, and

[0034] n and m are each an independent integer of 0 or 4.

[0035] As a specific example, the additive may be represented by chemical formula 1-1 or chemical formula 1-2.

[0036] Another embodiment of the present invention provides an electrolyte for a rechargeable lithium battery, which includes a non-aqueous organic solvent, a lithium salt, and the aforementioned additive.

[0037] Based on 100 parts by weight of the electrolyte for a rechargeable lithium battery, the amount of the additive included may be 0.01 parts by weight to 5.0 parts by weight.

[0038] Another embodiment of the present invention provides a rechargeable lithium battery, which includes: a positive electrode including a positive electrode active material; a negative electrode including a negative electrode active material; and the aforementioned electrolyte.

[0039] The positive electrode active material may be a lithium composite oxide represented by Chemical Formula 4.

[0040] [Chemical Formula 4]

[0041] Li x M 1 y M 2 z M 3 1-y-z O 2-a X a <* <*

[0042] In Chemical Formula 4, <* <*

[0043] 0.5 ≤ x ≤ 1.8, 0 ≤ a ≤ 0.05, 0 < y ≤ 1, 0 ≤ z ≤ 1, 0 ≤ y + z ≤ 1, M 1 、M 2 和M[[ID=J40]] 3 each independently includes at least one element selected from metals such as Ni, Co, Mn, Al, B, Ba, Ca, Ce, Cr, Fe, Mo, Nb, Si, Sr, Mg, Ti, V, W, Zr or La and combinations thereof, and X includes at least one element selected from F, S, P or Cl.<* <*

[0044] In Chemical Formula 4, 0.8 ≤ y ≤ 1, 0 ≤ z ≤ 0.2, and M 1 may be Ni.

[0045] The negative electrode active material may be graphite or may include a Si composite and graphite together.

[0046] The Si composite may include a core containing Si-based particles and an amorphous carbon coating.

[0047] The Si-based particles may include one or more of a Si-C composite, SiO x (0 < x ≤ 2) and a Si alloy.

[0048] Note: The tags ,

[0042] , ,

[0043] , , <*

[0044] are preserved as they are because they are 7-digit tags. If there are specific requirements for these tags in the actual application scenarios, further adjustments may be needed according to the rules.Si-C composites may include a core comprising Si particles and crystalline carbon, and an amorphous carbon coating on the core surface.

[0049] The average particle size of Si particles can be 50 nm to 200 nm.

[0050] Beneficial effects

[0051] It can realize rechargeable lithium batteries with excellent output characteristics and high-rate charging characteristics. Attached Figure Description

[0052] Figure 1 This is a schematic diagram illustrating a rechargeable lithium battery according to an embodiment of the present invention.

[0053] Figure 2 The image shows the 1H-NMR spectrum of the intermediate product generated during the synthesis of the additive represented by chemical formula 1-1.

[0054] Figure 3 The image shows the 1H-NMR spectrum of the additive represented by chemical formula 1-1.

[0055] Figure 4 The image shows the 1H-NMR spectrum of the intermediate product generated during the synthesis of the additive represented by chemical formulas 1-2.

[0056] Figure 5 The image shows the 1H-NMR spectrum of the additives represented by chemical formulas 1-2.

[0057] Figure 6 To show the discharge capacity retention rate of the rechargeable lithium battery cells according to Examples 1 to 4, Comparative Examples 1 and 2 at low temperature (10°C).

[0058] <Explanation of Figure Markers>

[0059] 100: Rechargeable lithium battery

[0060] 112: Negative electrode

[0061] 113: Diaphragm

[0062] 114: Positive electrode

[0063] 120: Battery casing

[0064] 140: Sealing component Detailed Implementation

[0065] The following description, with reference to the accompanying drawings, details a rechargeable lithium battery according to embodiments of the present invention. However, these embodiments are exemplary, and the invention is not limited thereto; rather, it is defined by the scope of the claims.

[0066] Depending on the type of separator and electrolyte, rechargeable lithium batteries can be classified as lithium-ion batteries, lithium-ion polymer batteries, and lithium polymer batteries. Depending on their shape, they can also be classified as cylindrical, prismatic, coin-shaped, pouch-shaped, etc. Furthermore, depending on their size, they can be block-shaped or thin-film type. The structures and manufacturing methods for lithium-ion batteries disclosed herein are well known in the art.

[0067] In this paper, a cylindrical rechargeable lithium battery is described as an example of a rechargeable lithium battery. Figure 1 The structure of a rechargeable lithium battery according to an embodiment is illustrated schematically. (Reference) Figure 1 According to an embodiment, a rechargeable lithium battery 100 includes: a battery cell including 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 casing 120 for housing the battery cell; and a sealing member 140 for sealing the battery casing 120.

[0068] The additives according to the embodiments will be described below.

[0069] The additive according to an embodiment of the present invention may be represented by chemical formula 1.

[0070] [Chemical Formula 1]

[0071]

[0072] In chemical formula 1,

[0073] X is C(=O) or S(=O)2, and

[0074] R 1 and R 2 Each is independently a fluorinated group or a C1-C5 fluoroalkyl group substituted with at least one fluorinated group.

[0075] The additive according to embodiments of the present invention has a structure comprising a cesium salt of fluorosulfonyl imide.

[0076] The additives decompose in the electrolyte, thus forming films on the surfaces of the positive and negative electrodes, respectively. Specifically, the film on the positive electrode surface effectively controls the deposition of lithium ions from the positive electrode, thereby preventing the decomposition of the positive electrode.

[0077] Furthermore, the additive is reduced and decomposed earlier than carbonate solvents included in non-aqueous organic solvents, and forms an SEI (solid electrolyte interface) on the negative electrode to prevent electrolyte decomposition and electrode decomposition, thereby suppressing the increase in internal resistance due to gas generation. A portion of the SEI film formed on the negative electrode decomposes during reduction reactions during charging and discharging, migrates towards the positive electrode surface, and also forms a film on the positive electrode surface through oxidation reactions to prevent decomposition of the positive electrode surface and oxidation of the electrolyte, contributing to improved high-temperature and low-temperature cycle life characteristics.

[0078] For example, chemical formula 1 can be represented by one of chemical formulas 1-1 and 1-8.

[0079] [Chemical Formula 1-1][Chemical Formula 1-2]

[0080]

[0081] [Chemical Formulas 1-3]

[0082]

[0083] [Chemical Formulas 1-4]

[0084]

[0085] [Chemical Formulas 1-5]

[0086]

[0087] [Chemical Formulas 1-6]

[0088]

[0089] [Chemical Formulas 1-7]

[0090]

[0091] [Chemical Formulas 1-8]

[0092]

[0093] In chemical formula 1-1 or chemical formula 1-8,

[0094] R a R b R c and R d Each is independently either hydrogen or fluorine-based, and

[0095] n and m are each an independent integer of 0 or 4.

[0096] For example, additives can be represented by chemical formula 1-1 or chemical formula 1-2.

[0097] An electrolyte for a rechargeable lithium battery according to another embodiment of the present invention comprises a non-aqueous organic solvent, a lithium salt, and the aforementioned additives.

[0098] The amount of additives included in 100 parts by weight of the electrolyte for rechargeable lithium batteries may be from 0.01 parts by weight to 5.0 parts by weight, for example, 0.01 parts by weight to 3.0 parts by weight, 0.01 parts by weight to 2.0 parts by weight, 0.01 parts by weight to 1.0 parts by weight, 0.05 parts by weight to 1.0 parts by weight, 0.1 parts by weight to 1.0 parts by weight, or 0.2 parts by weight to 1.0 parts by weight.

[0099] When the additive content is within this range, a rechargeable lithium battery with cycle life characteristics and low-temperature output characteristics can be achieved by preventing the increase of resistance during long-term charging / discharging or at low temperatures.

[0100] Non-aqueous organic solvents are used as media for transporting ions that participate in the electrochemical reactions of the battery.

[0101] Carbonate solvents, ester solvents, ether solvents, ketone solvents, alcohol solvents, or aprotic solvents can be used as non-aqueous organic solvents.

[0102] Carbonate solvents can include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), and butyl carbonate (BC), etc. Ester solvents can include methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, decanolactone, mevalonolactone, caprolactone, etc. Ether solvents can include dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, etc. Additionally, ketone solvents can include cyclohexanone, etc. Alcohol solvents may include ethanol, isopropanol, etc., and aprotic solvents may include nitriles (such as R-CN (where R is a hydrocarbon group having a C2-C20 straight chain, branched chain or cyclic structure, and may include double bonds, aromatic rings or ether bonds), amides (such as dimethylformamide), dioxolane (such as 1,3-dioxolane), sulfolane, etc.

[0103] Non-aqueous organic solvents can be used alone or in mixtures, and when used in mixtures, the mixing ratio can be appropriately adjusted according to the desired battery performance, as is widely understood by those skilled in the art.

[0104] Carbonate solvents are prepared by mixing cyclic and linear carbonates. When cyclic and linear carbonates are mixed together in a volume ratio of 1:1 to 1:9, the performance of the electrolyte can be improved.

[0105] In addition to carbonate solvents, non-aqueous organic solvents may further include aromatic hydrocarbon organic solvents. In this paper, carbonate solvents and aromatic hydrocarbon organic solvents can be mixed in volume ratios of 1:1 to 30:1.

[0106] Aromatic hydrocarbon organic solvents can be aromatic hydrocarbon compounds of chemical formula 2.

[0107] [Chemical Formula 2]

[0108]

[0109] In chemical formula 2, R 201 ~R 206 They may be the same or different and are hydrogen, halogen, C1-C10 alkyl, haloalkyl or a combination thereof.

[0110] Specific examples of aromatic hydrocarbon organic solvents 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, and 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, or combinations thereof.

[0111] The electrolyte may further include vinylene carbonate, vinyl ethylene carbonate, or ethylene carbonate compounds represented by chemical formula 3 as additives to improve the cycle life of the battery.

[0112] [Chemical Formula 3]

[0113]

[0114] In chemical formula 3, R 207 and R 208 Identical or different, and selected from hydrogen, halogen, cyano (CN), nitro (NO2), and fluorinated C1-C5 alkyl groups, under the condition that R207 and R 208 At least one of them is selected from halogen, cyano (CN), nitro (NO2) and fluorinated C1-C5 alkyl, and R 207 and R 208 Neither of them is hydrogen.

[0115] Examples of ethylene carbonate compounds may include difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, brominated ethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate, or fluoroethylene carbonate. When this additive is further used to improve cycle life, its amount may be adjusted appropriately.

[0116] Lithium salts dissolved in non-aqueous organic solvents supply lithium ions in batteries, ensuring basic operation of rechargeable lithium batteries and improving lithium ion transport between the positive and negative electrodes. Examples of lithium salts may include at least one selected from the following: 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+1 SO2)(C y F 2y+1 SO2 (where x and y are natural numbers, such as integers 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 exhibits excellent performance and lithium-ion mobility due to optimal electrolyte conductivity and viscosity.

[0117] Another embodiment of the present invention provides a rechargeable lithium battery comprising: a positive electrode including a positive electrode active material; a negative electrode including a negative electrode active material; and the aforementioned electrolyte.

[0118] The positive electrode includes a positive electrode current collector and a positive electrode active material layer on the positive electrode current collector, and the positive electrode active material layer includes a positive electrode active material.

[0119] The positive electrode active material may include lithiated intercalation compounds that can reversibly insert and deintercalate lithium ions.

[0120] Specifically, at least one of a composite oxide of a metal selected from cobalt, manganese, nickel and combinations thereof and lithium may be used.

[0121] Of course, composite oxides can be used in which a portion of the metal is replaced by a metal other than the other metal, and phosphate compounds of the composite oxide can be used, for example, at least one selected from LiFePO4, LiCoPO4, and LiMnPO4. The lithium composite oxide may have a coating on its surface, or the lithium composite oxide may be mixed with another composite oxide having a coating. The coating may include at least one coating element compound selected from 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 compound used for the 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. The coating process may include any conventional process, provided that it does not cause any adverse effects on the properties of the positive electrode active material (e.g., inkjet coating, dipping), which is well known to those skilled in the art, and therefore its detailed description is omitted.

[0122] The positive electrode active material may be, for example, at least one of lithium composite oxides represented by chemical formula 4.

[0123] [Chemical Formula 4]

[0124] Li x M 1 y M 2 z M 3 1-y-z O 2-a X a

[0125] In chemical formula 4,

[0126] 0.5≤x≤1.8, 0≤a≤0.05, 0 <y≤1,0≤z≤1,0≤y+z≤1,M 1 M 2 and M 3 Each element independently comprises at least one element selected from metals such as Ni, Co, Mn, Al, B, Ba, Ca, Ce, Cr, Fe, Mo, Nb, Si, Sr, Mg, Ti, V, W, Zr, or La, and combinations thereof, and X comprises at least one element selected from F, S, P, or Cl.

[0127] For example, in chemical formula 4, M 1 It can be Ni, and M 2 and M 3Each can be an element selected independently from metals such as Co, Mn, Al, B, Ba, Ca, Ce, Cr, Fe, Mo, Nb, Si, Sr, Mg, Ti, V, W, Zr, or La, or a combination thereof.

[0128] In chemical formula 4, 0.6≤x≤1.8, 0.3≤y≤1, and 0.01≤z≤0.7.

[0129] For example, in chemical formula 4, M 1 It can be Ni, M 2 It can be Co, and M 3 It may be one or more elements selected from metals such as Mn, Al, B, Ba, Ca, Ce, Cr, Fe, Mo, Nb, Si, Sr, Mg, Ti, V, W, Zr, or La, and combinations thereof.

[0130] In chemical formula 4, 0.7≤x≤1.8, 0.3≤y≤1, and 0≤z≤0.6; 0.8≤x≤1.8, 0.4≤y≤1, and 0≤z≤0.5; 0.9≤x≤1.8, 0.5≤y≤1, and 0≤z≤0.4; 0.6≤y≤1, and 0≤z≤0.3; or 0.7≤y≤1, and 0≤z≤0.2.

[0131] For example, in chemical formula 4, M 1 It can be Ni, and

[0132] In chemical formula 4, 0.8 ≤ y ≤ 1 and 0 ≤ z ≤ 0.2.

[0133] In this embodiment, the active material for the positive electrode may be selected from LiCoO2, LiNiO2, LiMnO2, LiMn2O4, and LiNi. a Mn b Co c O2(a+b+c=1), LiNi a Mn b Co c Al d O2(a+b+c+d=1) and LiNi e Co f Al g At least one of O2 (e+f+g=1).

[0134] For example, selected from LiNi a Mn b Co c O2(a+b+c=1), LiNi a Mn b Co c Al dO2(a+b+c+d=1) and LiNi e Co f Al g The positive electrode active material of O2 (e+f+g=1) can be a high-Ni type positive electrode active material.

[0135] For example, in LiNi a Mn b Co c O2(a+b+c=1) and LiNi a Mn b Co c Al d In the case of O2 (a+b+c+d=1), the nickel content can be greater than or equal to 60% (a≥0.6), and more specifically, greater than or equal to 80% (a≥0.8).

[0136] For example, in LiNi e Co f Al g In the case of O2 (e+f+g=1), the nickel content can be greater than or equal to 60% (e≥0.6), and more specifically, greater than or equal to 80% (e≥0.8).

[0137] Based on the total weight of the positive electrode active material layer, the content of the positive electrode active material can be 90wt% to 98wt%.

[0138] In embodiments of the present invention, the positive electrode active material layer may optionally include a conductive material and a binder. In this case, based on the total weight of the positive electrode active material layer, the content of the conductive material and the binder may be 1.0 wt% to 5.0 wt%, respectively.

[0139] This includes conductive materials to impart conductivity to the positive electrode, and any conductive material can be used as a conductive material unless it causes a chemical change in the battery in which it is configured. Examples of conductive materials may include carbon-based materials (such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, etc.); metallic materials including metal powders or metal fibers of copper, nickel, aluminum, silver, etc.; conductive polymers (such as polyphenylene derivatives); or mixtures thereof.

[0140] The binder improves the adhesion properties between the positive electrode active material particles and between the positive electrode active material particles and the current collector. Examples of binders include 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, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc., but are not limited to these.

[0141] The positive electrode current collector may include Al, but is not limited thereto.

[0142] The negative electrode includes a negative electrode current collector and a negative electrode active material layer, and the negative electrode active material layer includes a negative electrode active material formed on the negative electrode current collector.

[0143] The negative electrode active material may include a material that reversibly intercalates / deintercalates lithium ions, lithium metal, a lithium metal alloy, a material capable of doping / de-doping lithium, or a transition metal oxide.

[0144] The material that reversibly intercalates / deintercalates lithium ions includes carbon materials. The carbon materials can be any carbon-based negative electrode active materials in common rechargeable lithium batteries, and examples of the carbon materials include crystalline carbon, amorphous carbon, and combinations thereof. The crystalline carbon can be amorphous natural graphite or artificial graphite, or can be flaky, sheet-like, spherical or fibrous natural graphite or artificial graphite, and the amorphous carbon can be soft carbon, hard carbon, mesophase pitch carbonization products, calcined coke, etc.

[0145] The lithium metal alloy may include 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.

[0146] The material capable of doping / de-doping lithium can be a Si-based compound, such as Si, Si-C composite, SiO x (0 < x < 2), Si-Q alloy (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, Sn-R (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. At least one of these materials can be mixed with SiO2.

[0147] 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.

[0148] The transition metal oxide can be a vanadium oxide, a lithium vanadium oxide, etc.

[0149] In an embodiment, the negative electrode active material may be graphite or may include a Si composite and graphite together.

[0150] When the negative electrode active material includes a Si composite and graphite together, the Si composite and graphite may be included in the form of a mixture, and the Si composite and graphite may be included in a weight ratio of 1:99 to 50:50. More specifically, the Si composite and graphite may be included in a weight ratio of 3:97 to 20:80 or 5:95 to 20:80.

[0151] The Si composite may include a core containing Si-based particles and an amorphous carbon coating. For example, the Si-based particles may include a Si-C composite, SiO x (0 < x ≤ 2), a Si alloy, or a mixture thereof. For example, the Si-C composite may include a core containing Si particles and crystalline carbon, and an amorphous carbon coating on the surface of the core.

[0152] The crystalline carbon may include, for example, graphite, and more specifically, natural graphite, artificial graphite, or a mixture thereof.

[0153] The average particle size of the crystalline carbon may be 5 μm to 30 μm.

[0154] In this specification, the average particle size may be the particle size (D50) at which the volume ratio is 50% in the cumulative size distribution curve.

[0155] In the Si-C composite, the average particle size of the Si particles may be 50 nm to 200 nm.

[0156] When the average particle size of the Si particles is within the above range, the volume expansion occurring during charging and discharging can be suppressed, and the interruption of the conduction path due to particle fragmentation during charging and discharging can be prevented.

[0157] Based on the total weight of the Si-C composite, the Si particles may be included in an amount of 1 wt% to 60 wt% (for example, 3 wt% to 60 wt%).

[0158] The amorphous carbon precursor may be coal tar pitch, mesophase pitch, petroleum-based pitch, coal tar oil, petroleum-based heavy oil, or a polymer resin (such as phenolic resin, furan resin, or polyimide resin).

[0159] Based on 100 parts by weight of the crystalline carbon, the amorphous carbon may be included in an amount of 1 part by weight to 50 parts by weight (for example, 5 parts by weight to 50 parts by weight or 10 parts by weight to 50 parts by weight).

[0160] In the negative electrode active material layer, based on the total weight of the negative electrode active material layer, the negative electrode active material may be included in an amount of 95 wt% to 99 wt%.

[0161] In one embodiment, the negative electrode active material layer may include a binder and optionally a conductive material. Based on the total weight of the negative electrode active material layer, the binder content in the negative electrode active material layer may be 1 wt% to 5 wt%. Alternatively, when further including a conductive material, 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 may be used.

[0162] The binder improves the adhesion properties between the active material particles of the negative electrode and the adhesion properties between the active material particles of the negative electrode and the current collector. The binder can be a non-water-soluble binder, a water-soluble binder, or a combination thereof.

[0163] 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.

[0164] Water-soluble adhesives can be rubber-based adhesives or polymer resin adhesives. Rubber-based adhesives can be selected from styrene-butadiene rubber, acrylated 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, or combinations thereof.

[0165] When a water-soluble binder is used as a negative electrode binder, a cellulose compound can be used as a thickener to further improve viscosity. Cellulose compounds include 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, this thickener can be included in an amount of 0.1 to 3 parts by weight.

[0166] Conductive materials are included to improve electrode conductivity, and any conductive material can be used as a conductive material unless it causes a chemical change. Examples of conductive materials include carbon-based materials (such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, etc.); metallic materials including metal powders or metal fibers of copper, nickel, aluminum, silver, etc.; conductive polymers (such as polyphenylene derivatives); or mixtures thereof.

[0167] The negative electrode current collector can be selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, polymer substrate coated with conductive metal, and combinations thereof.

[0168] Depending on the type of battery, rechargeable lithium batteries may further include a separator between the negative and positive electrodes. This separator may be a porous substrate or a composite porous substrate.

[0169] The porous substrate may be a substrate comprising pores through which lithium ions can move. The porous substrate may, for example, comprise polyethylene, polypropylene, polyvinylidene fluoride, and multilayers thereof (such as polyethylene / polypropylene bilayer membranes, polyethylene / polypropylene / polypropylene trilayer membranes, and polypropylene / polypropylene / polypropylene trilayer membranes).

[0170] The composite porous substrate may take the form of a porous substrate and a functional layer on the porous substrate. From the perspective of ensuring additional functionality, the functional layer may be, for example, at least one of a heat-resistant layer and an adhesive layer. For example, the heat-resistant layer may include a heat-resistant resin and optionally a filler.

[0171] Additionally, the adhesive layer may include an adhesive resin and optionally a filler.

[0172] The packing material can be organic or inorganic.

[0173] refer to Figure 1 According to an embodiment, a rechargeable lithium battery 100 includes: a battery cell including a negative electrode 112, a positive electrode 114 facing the negative electrode 112, a separator 113 inserted between the negative electrode 112 and the positive electrode 114, and an electrolyte (not shown) for a rechargeable lithium battery impregnating the negative electrode 112, the positive electrode 114 and the separator 113; a battery casing 120 housing the battery cell; and a sealing member 140 sealing the battery casing 120.

[0174] Example

[0175] 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.

[0176] Synthesis of additives

[0177] Synthesis Example 1: Synthesis of a compound represented by chemical formula 1-1

[0178] [Reaction Scheme 1]

[0179]

[0180] ClSO₂NCO (4.5 g, 0.03 mol) was added to 7.5 mL of benzene at 0 °C. Aminosulfonyl fluoride (3 g, 0.036 mol) was dissolved in 15 mL of dichloromethane at 30 °C, and then this solution was added to the above solution. The mixture was stirred for 24 hours. Subsequently, non-reactive materials were removed by evaporation. In this paper, the intermediate product generated was confirmed by 1H-NMR, and the results showed... Figure 2 As shown in the image.

[0181] Figure 2 The image shows the 1H-NMR spectrum of the intermediate product generated during the synthesis of the additive represented by chemical formula 1-1.

[0182] refer to Figure 2 The intermediate product CO5S2F2N2H2 has the following 1H-NMR peak data.

[0183] 1H NMR (400MHz, DMSO-d6): δ11.68 (s, 2H)

[0184] Subsequently, a solution prepared by dissolving 2.5 M Cs₂CO₃ (2.5 eq.) in n-hexane was added at 0 °C, and the mixture was stirred for 1 hour. The resulting semi-solid product was passed through silica gel, precipitated with a small amount of ethyl acetate, and then concentrated to obtain an additive represented by chemical formula 1-1 as a white solid (yield of CO₅S₂F₂N₂Cs₂: 54%).

[0185] The synthesis results of the additive represented by chemical formula 1-1 were examined by 1H-NMR, and the results showed that... Figure 3 As shown in the image.

[0186] Figure 3 The image shows the 1H-NMR spectrum of the additive represented by chemical formula 1-1.

[0187] refer to Figure 3 The result, shown by the disappearance of the peak appearing in the 1H-NMR spectrum of the intermediate product CO5S2F2N2H2, proves that the target compound was produced.

[0188] 1H NMR (400MHz, DMSO-d6): δ-(s, H)

[0189] Synthesis Example 2: Synthesis of compounds represented by chemical formulas 1-2

[0190] [Reaction Scheme 2]

[0191]

[0192] Thionyl chloride (2.72 g, 0.02 mol) was added to FSO₂NH₂ (5 g, 0.05 mol) at 0 °C. The resulting mixture was then stirred at 25 °C for 6 hours, and non-reactive materials were removed by evaporation. In this paper, the intermediate product generated was confirmed by 1H-NMR, and the results showed that… Figure 4 As shown in the image.

[0193] Figure 4The image shows the 1H-NMR spectrum of the intermediate product generated during the synthesis of the additives represented by chemical formulas 1-2.

[0194] refer to Figure 4 The 1H-NMR peak data of the intermediate product O6S3F2N2H2 are as follows.

[0195] 1H NMR (400MHz, DMSO-d6): δ10.34 (s, 2H)

[0196] The obtained intermediate product was then dissolved in 15 ml of dichloromethane, to which a solution prepared by dissolving 2.5 MCs₂CO₃ (2.5 eq.) in n-hexane was added. The mixture was then stirred at 0 °C for 1 hour. The obtained semi-solid product was passed through silica gel using a small amount of ethyl acetate as a precipitate and then concentrated to obtain an additive represented by chemical formula 1-2 as a white solid (yield of O₆S₃F₂N₂Cs₂: 60%).

[0197] The synthesis of the additives represented by chemical formulas 1-2 was confirmed by 1H-NMR, and the results were in Figure 5 As shown in the image.

[0198] Figure 5 The image shows the 1H-NMR spectrum of the additives represented by chemical formulas 1-2.

[0199] refer to Figure 5 The results, shown by the disappearance of the peak appearing in the 1H-NMR spectrum of the intermediate product O6S3F2N2Cs2, prove that the target compound was produced.

[0200] 1H NMR (400MHz, DMSO-d6): δ-(s, H)

[0201] Manufacturing of rechargeable lithium battery cells

[0202] Example 1

[0203] LiNi will be used as the active material for the positive electrode. 0.88 Co 0.07 Al 0.05 O2, polyvinylidene fluoride as a binder, and Ketjen black as a conductive material are mixed in a weight ratio of 97:2:1 and then dispersed in N-methylpyrrolidone to prepare a slurry for positive electrode active material.

[0204] The positive electrode active material slurry was coated onto a 14 μm thick Al foil, dried at 110 °C, and pressed to manufacture the positive electrode.

[0205] The negative electrode active material slurry was prepared as follows: a mixture of artificial graphite and Si-C composite was prepared as the negative electrode active material in a weight ratio of 93:7; the negative electrode active material was mixed with styrene-butadiene rubber binder and carboxymethyl cellulose in a weight ratio of 97:1:2; and the mixture was dispersed in distilled water.

[0206] The Si-C composite has a core (comprising artificial graphite and silicon particles) and coal pitch coated on the surface of the core.

[0207] The negative electrode active material slurry was coated onto a 10 μm thick Cu substrate, and then dried and rolled at 100 °C to manufacture the negative electrode.

[0208] The positive and negative electrodes are assembled using a 25μm thick polyethylene diaphragm to manufacture an electrode assembly, and an electrolyte is injected into it to manufacture a rechargeable lithium battery cell.

[0209] The electrolyte has the following composition.

[0210] (Composition of the electrolyte)

[0211] Salt: 1.5M LiPF6

[0212] Solvent: Ethylene carbonate: Ethyl methyl carbonate: Dimethyl carbonate (EC:EMC:DMC = 20:10:70 by volume)

[0213] Additive: 0.25 parts by weight of the compound represented by chemical formulas 1-2 according to Synthesis Example 1

[0214] (However, in the composition of the electrolyte, "parts by weight" means the relative weight of additives based on 100 parts by weight of the total electrolyte (lithium salt + non-aqueous organic solvent + additives).)

[0215] Example 2

[0216] The rechargeable lithium battery was manufactured in the same manner as in Example 1, except that 0.5 parts by weight of the compound represented by chemical formulas 1-2 was added as an additive.

[0217] Example 3

[0218] The rechargeable lithium battery was manufactured in the same manner as in Example 1, except that 1.0 part by weight of the compound represented by chemical formulas 1-2 was added as an additive.

[0219] Example 4

[0220] The rechargeable lithium battery was manufactured in the same manner as in Example 1, except that 0.5 parts by weight of a compound represented by chemical formula 1-1 was added as an additive.

[0221] Comparative Example 1

[0222] The rechargeable lithium battery was manufactured in the same manner as in Example 1, except that an electrolyte without additives was used.

[0223] Comparative Example 2

[0224] The rechargeable lithium battery was manufactured in the same manner as in Example 1, except that 0.5 parts by weight of cesium bis(fluorosulfonyl)imide, represented by chemical formula A, was used as an additive.

[0225] [Chemical Formula A]

[0226]

[0227] Evaluation: Assessment of low-temperature (10°C) cycle life characteristics

[0228] The following evaluation of the cycle life characteristics of lithium-ion battery cells according to Examples 1 to 4, and Comparative Examples 1 and 2 is shown in Table 1 and 2. Figure 6 middle.

[0229] Charge and discharge experiments were conducted at 10°C, with initialization efficiency evaluated at 0.1C charge / 0.1C discharge and cycle life evaluated by 100 cycles of 1.5C charge / 1.0C discharge. Cycle life characteristics were evaluated by calculating the capacity retention rate defined by Equation 1.

[0230] <Equation 1>

[0231] Capacity retention rate [%] = [Discharge capacity per cycle / Discharge capacity in the first cycle] * 100

[0232] While performing 100 charge and discharge cycles within the range of 2.5V to 4.2V at a C-rate of 1.5C charge / 1.0C discharge at 10℃, the change in discharge capacity of individual battery cells was measured. The results show that... Figure 6 In particular, the discharge capacity retention rate after the 100th cycle is shown in Table 1.

[0233] (Table 1)

[0234]

[0235] Figure 6 To show the discharge capacity retention rate of the rechargeable lithium battery cells according to Examples 1 to 4, Comparative Examples 1 and 2 at low temperature (10°C).

[0236] Refer to Table 1 and Figure 6 Compared with Comparative Example 1 and Comparative Example 2, Examples 1 to 4 show improved low-temperature cycle life characteristics.

[0237] Although the invention has been described in conjunction with exemplary embodiments now considered to be in practice, it should be understood that the invention is not limited to the disclosed embodiments, but rather is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Claims

1. An additive, represented by chemical formula 1, for use in the electrolyte of a rechargeable lithium battery: [Chemical Formula 1] in, In chemical formula 1, X is C(=O) or S(=O)2, and R 1 and R 2 Each is independently a fluorinated group or a C1-C5 fluoroalkyl group substituted with at least one fluorinated group.

2. The additive according to claim 1, wherein, Chemical formula 1 can be represented by any one of chemical formulas 1-1 to 1-8: [Chemical Formula 1-1][Chemical Formula 1-2] [Chemical Formulas 1-3] [Chemical Formulas 1-4] [Chemical Formulas 1-5] [Chemical Formulas 1-6] [Chemical Formulas 1-7] [Chemical Formulas 1-8] Among them, in chemical formulas 1-1 to 1-8, R a R b R c and R d Each is independently either hydrogen or fluorine-based, and n and m are each an independent integer of 0 or 4.

3. The additive according to claim 2, wherein, The additive is represented by chemical formula 1-1 or chemical formula 1-2.

4. An electrolyte for a rechargeable lithium battery, comprising: Non-aqueous organic solvents Lithium salts, and The additive according to any one of claims 1 to 3.

5. The electrolyte for a rechargeable lithium battery according to claim 4, wherein, The amount of the additives included in 100 parts by weight of the electrolyte for rechargeable lithium batteries is from 0.01 parts by weight to 5.0 parts by weight.

6. A rechargeable lithium battery, comprising: A positive electrode, including the positive electrode active material; A negative electrode, including the negative electrode active material; and The electrolyte for rechargeable lithium batteries according to claim 4 or 5.

7. The rechargeable lithium battery according to claim 6, wherein, The active material of the positive electrode is represented by chemical formula 4: [Chemical Formula 4] Li x M 1 y M 2 z M 3 1-y-z O 2-a X a In chemical formula 4, 0.5≤x≤1.8, 0≤a≤0.05, 0 <y≤1,0≤z≤1,0≤y+z≤1,M 1 M 2 and M 3 Each element independently comprises at least one element and combination thereof selected from metals selected from Ni, Co, Mn, Al, B, Ba, Ca, Ce, Cr, Fe, Mo, Nb, Si, Sr, Mg, Ti, V, W, Zr or La, and X comprises at least one element selected from F, S, P and Cl.

8. The rechargeable lithium battery according to claim 7, wherein, In chemical formula 4, 0.8≤y≤1, 0≤z≤0.2, and M 1 For Ni.

9. The rechargeable lithium battery according to claim 6, wherein, The active material of the negative electrode is graphite or includes a Si composite and graphite together.

10. The rechargeable lithium battery according to claim 9, wherein, The Si composite includes a core containing Si particles and an amorphous carbon coating.

11. The rechargeable lithium battery according to claim 10, wherein, The Si-type particles include Si-C composites and SiO2. x (0 < x ≤ 2) and one or more of Si alloys.

12. The rechargeable lithium battery according to claim 11, wherein, The Si-C composite comprises a core containing Si particles and crystalline carbon, and an amorphous carbon coating on the surface of the core. The average particle size of the Si particles is 50 nm to 200 nm.

Images