Electrolyte for rechargeable lithium battery and rechargeable lithium battery including same

Abstract

The present application discloses an electrolyte for a rechargeable lithium battery and a rechargeable lithium battery including the same. The electrolyte for a rechargeable lithium battery includes: a lithium salt; a non-aqueous organic solvent; a first additive represented by Chemical Formula 1; and a second additive represented by Chemical Formula 2. The description of each chemical formula is provided in the specification. Chemical formula 1 # imgabs0 # and chemical formula 2 # imgabs1 #

Description

Technical Field

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

[0002] Recently, with the rapid popularization of electronic devices using batteries (such as mobile phones, laptop computers and electric vehicles), the demand for rechargeable lithium batteries with high energy density and high capacity is rapidly increasing. Accordingly, research and development to improve the performance of rechargeable lithium batteries is actively underway.

[0003] Rechargeable lithium batteries include positive and negative electrodes containing active materials capable of inserting / deinserting lithium ions, and an electrolyte, and generate electric energy through oxidation and reduction reactions if lithium ions are inserted / deinserted into / from the positive and negative electrodes.

[0004] One of the latest development directions of rechargeable lithium batteries is to improve high voltage and / or high temperature characteristics. Generally speaking, rechargeable lithium batteries have problems of reduced cycle life and / or increased resistance at high voltage and / or high temperature. Summary of the invention

[0005] Some embodiments provide an electrolyte for a rechargeable lithium battery that improves high voltage and / or high temperature characteristics of the rechargeable lithium battery.

[0006] Some embodiments provide a rechargeable lithium battery including an electrolyte for a rechargeable lithium battery.

[0007] Some embodiments provide an electrolyte for a rechargeable lithium battery, comprising: a lithium salt; a non-aqueous organic solvent; a first additive represented by Chemical Formula 1; and a second additive represented by Chemical Formula 2:

[0008] Chemical formula 1

[0009]

[0010] Chemical formula 2

[0011]

[0012] Some embodiments provide a rechargeable lithium battery including: a positive electrode including a positive electrode active material; a negative electrode including a negative electrode active material; and an electrolyte.

[0013] An electrolyte for a rechargeable lithium battery according to some embodiments may improve high voltage and / or high temperature characteristics of the rechargeable lithium battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The accompanying drawings, together with the specification, illustrate embodiments of the presently disclosed subject matter, and, together with the description, serve to explain principles of embodiments of the presently disclosed subject matter.

[0015] Figure 1 to Figure 4 is a schematic diagram illustrating a rechargeable lithium battery according to some embodiments.

[0016] Description of Reference Numerals

[0017] 100: Rechargeable lithium battery 10: Positive electrode

[0018] 11: Positive lead lug 12: Positive terminal

[0019] 20: Negative electrode 21: Negative lead lug

[0020] 22: Negative terminal 30: Separator

[0021] 40: electrode assembly 50: shell

[0022] 60: Sealing member 70: Electrode terminal piece

[0023] 71: Positive electrode terminal tab 72: Negative electrode terminal tab DETAILED DESCRIPTION

[0024] Hereinafter, embodiments of the present disclosure will be described in more detail. However, these embodiments are examples, the present disclosure is not limited thereto, and the present disclosure is defined by the scope of the claims and their equivalents.

[0025] As used herein, if no specific limitations are provided otherwise, it will be understood that if an element (such as a layer, film, region or substrate) is referred to as being "on" another element (such as a layer, film, region or substrate), it can be directly on the other element (such as a layer, film, region or substrate) or intervening elements may also be present.

[0026] As used herein, if no specific limitation is provided otherwise, the singular may also include the plural. In some embodiments, "A or B" may mean "including A, including B, or including A and B", unless otherwise specified.

[0027] As used herein, "combination thereof" may mean a mixture, stack, composite, copolymer, alloy, blend, and / or reaction product of the components.

[0028] As used herein, if no definition is otherwise provided, in a chemical formula, if a chemical bond is not drawn at a position where a chemical bond should be drawn, a hydrogen atom is bonded to that position.

[0029] As used herein, if no specific limitation is otherwise provided, "*" indicates a point where the same or different atoms or chemical formulas are attached.

[0030] As used herein, "fluoroalkyl" refers to an alkyl group in which some or all of the hydrogen atoms are replaced by fluorine atoms.

[0031] As used herein, "perfluoroalkyl" refers to an alkyl group in which all hydrogen atoms are replaced by fluorine atoms.

[0032] In the present specification, the “number average molecular weight” may be a value measured by gel permeation chromatography (GPC, PLGPC220, Agilent Technologies) using polystyrene and corrected with a cubic function.

[0033] Electrolyte

[0034] Some embodiments provide an electrolyte for a rechargeable lithium battery, which includes a lithium salt; a non-aqueous organic solvent; a first additive represented by Chemical Formula 1; and a second additive represented by Chemical Formula 2:

[0035] Chemical formula 1

[0036]

[0037] Chemical formula 2

[0038]

[0039] The first additive functions as a surfactant having both a hydrophilic group and a hydrophobic group in one molecule. The first additive includes *-[O-CH(R 1 )-CH2] y -*, where *-[O-CH2-CH2] x -*block and *-[O-CH2-CH2] z -* blocks on both sides (e.g., in *-[O-CH(R 1 )-CH2] y - two separate sides of *). In this article, *-[O-CH(R 1 )-CH2] y -* block is a hydrophobic block, and *-[O-CH2-CH2] x -*block and *-[O-CH2-CH2] z -* blocks are each a hydrophilic block.

[0040] Accordingly, if the electrolyte including the first additive is used, the wettability of the electrolyte to the positive electrode and the negative electrode is improved, and the lithium cation (Li+ ) is uniformly formed at the interface between the positive electrode and the electrolyte, and a stable SEI film is formed at the interface between the negative electrode and the electrolyte, thereby inhibiting or reducing the precipitation of lithium dendrites.

[0041] In some embodiments, the second additive is a compound represented by Chemical Formula 2, wherein the fluorine atom of the compound represented by Chemical Formula 2 stabilizes the lithium salt (e.g., LiPF6). Accordingly, if an electrolyte including the second additive is used, the generation of HF can be suppressed or reduced, and the dissolution of transition metals from the positive electrode active material and the damage to the SEI film at the interface between the negative electrode and the electrolyte can be prevented or reduced.

[0042] Therefore, if an electrolyte for a rechargeable lithium battery including the first additive and the second additive is used, the dissolution of transition metals from the positive electrode active material is inhibited or reduced and a stable SEI film is formed on the negative electrode surface, thereby improving the high voltage and / or high temperature characteristics of the rechargeable lithium battery.

[0043] Hereinafter, an electrolyte for a rechargeable lithium battery according to some embodiments will be described in more detail.

[0044] First Additive

[0045] In Chemical Formula 1, R 1 It is a hydrogen atom or a C1-C10 alkyl group.

[0046] For example, R 1 It may be methyl.

[0047] In Chemical Formula 1, x, y and z are independently integers of 1-20.

[0048] Herein, the molar ratio of x:y may be about 10:1 to about 1:10, about 5:1 to about 1:5, or about 3:1 to about 1:3. In some embodiments, the molar ratio of y:z may be about 10:1 to about 1:10, about 5:1 to about 1:5, or about 3:1 to about 1:3.

[0049] The first additive may have a number average molecular weight of about 500 g / mol to about 10,000 g / mol, about 700 g / mol to about 8,000 g / mol, or about 1,000 g / mol to about 2,000 g / mol.

[0050] If the number average molecular weight of the first additive exceeds the above range, the viscosity of the electrolyte including the first additive may be excessively increased, and the wettability of the electrolyte to the positive electrode and the negative electrode may actually be reduced. If the number average molecular weight of the first additive is less than the above range, the effect of the first additive as a surfactant may be minimized or reduced.

[0051] Representative examples of the first additive are as follows:

[0052] Chemical formula 1-1

[0053]

[0054] The first additive represented by Chemical Formula 1-1 is poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) (PEG-b-PPG-b-PEG).

[0055] In Chemical Formula 1-1, x, y and z are as defined above.

[0056] Second additive

[0057] In chemical formula 2, R 2 and R 3 Each is independently a halogen atom or a C1-C10 fluoroalkyl group. In this context, the halogen atom may be a fluorine atom, a chlorine atom, a bromine atom or an iodine atom.

[0058] For example, R 2 and R 3 Both may be fluorine atoms.

[0059] Representative examples of the second additive are as follows:

[0060] Chemical formula 2-1

[0061]

[0062] The second additive represented by Chemical Formula 2-1 is lithium difluoro(oxalato)borate (LiDFOB).

[0063] Content of the first additive and the second additive

[0064] The first additive may be included in an amount of about 0.1 wt % to about 5 wt %, about 0.3 wt % to about 4 wt %, or about 0.5 wt % to about 3 wt %, based on the total amount of the electrolyte.

[0065] If the amount of the first additive included exceeds the above range, the viscosity of the electrolyte including the first additive may increase excessively, and the wettability of the electrolyte to the positive electrode and the negative electrode may actually decrease. If the first additive is included in a small amount below the above range, the effect of the first additive as a surfactant may be minimized or reduced.

[0066] The second additive may be included in an amount of about 0.1 wt % to about 5 wt %, about 0.25 wt % to about 2 wt %, or about 0.25 wt % to about 1.5 wt %, based on the total amount of the electrolyte.

[0067] If the second additive is included in an amount exceeding the above range, a side reaction may occur. If the second additive is included in a small amount below the above range, the effect of stabilizing the lithium salt may be minimized or reduced.

[0068] The weight ratio of the first additive to the second additive in the electrolyte may be about 5:1 to about 1:10, about 2:1 to about 3:10, or about 2:1 to about 1:3.

[0069] When the weight ratio of the first additive to the second additive in the electrolyte is within these ranges, the effects of the first additive and the second additive may be coordinated (eg, provide a synergistic effect).

[0070] Non-aqueous organic solvent

[0071] The nonaqueous organic solvent serves as a medium for transmitting ions participating in the electrochemical reaction of the battery.

[0072] The non-aqueous organic solvent may include a carbonate-based solvent, an ester-based solvent (eg, a propionate-based solvent), an ether-based solvent, a ketone-based solvent, an alcohol-based solvent, an aprotic solvent, or a combination thereof.

[0073] 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), butylene carbonate (BC), etc. Ester solvents may include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, propyl propionate, decanoic acid lactone, mevalonolactone, valerolactone, caprolactone, etc.

[0074] Ether solvents may include dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, tetrahydrofuran, etc. Ketone solvents may include cyclohexanone, etc. Alcohol solvents may include ethanol, isopropanol, etc., and aprotic solvents may include nitrile (such as R-CN (wherein R is a C2 to C20 straight chain, branched and / or cyclic hydrocarbon group, and may include a double bond, an aromatic ring and / or an ether group), an amide (such as, for example, dimethylformamide)), a dioxolane (such as, for example, 1,3-dioxolane or 1,4-dioxolane), sulfolane, etc.

[0075] The nonaqueous organic solvent may be used alone or in combination of two or more thereof.

[0076] In some embodiments, if used in combination of two or more of the non-aqueous organic solvents, the non-aqueous organic solvent may include a carbonate-based solvent and a propionate-based solvent.

[0077] The propionate-based solvent may be included in an amount greater than or equal to about 70% by volume based on the total amount of the non-aqueous organic solvent. In some embodiments, high voltage and / or high temperature characteristics of a rechargeable lithium battery may be improved.

[0078] For example, the nonaqueous organic solvent may be a mixed solvent of ethylene carbonate (EC), propylene carbonate (PC), and propyl propionate (PP).

[0079] Lithium salts

[0080] The lithium salt dissolved in the nonaqueous organic solvent supplies lithium ions in the battery, ensures the basic operation of the rechargeable lithium battery, and improves the transport of lithium ions between the positive electrode and the negative electrode.

[0081] For example, LiPF6 may be used as the lithium salt, and its structure may be stabilized by the second additive.

[0082] The concentration of the lithium salt may be about 0.1M to about 2.0M.

[0083] Rechargeable lithium battery

[0084] Some embodiments provide a rechargeable lithium battery including: a positive electrode including a positive electrode active material; a negative electrode including a negative electrode active material; and an electrolyte.

[0085] Charging upper limit voltage

[0086] Since the rechargeable lithium battery according to some embodiments includes the electrolyte of the above-described embodiments, an increase in battery thickness and a decrease in cycle life may be suppressed or reduced even at a high voltage.

[0087] For example, a rechargeable lithium battery may have a charge upper limit voltage greater than or equal to about 4.5V.

[0088] Hereinafter, descriptions repeated above may not be repeated, and a rechargeable lithium battery according to some embodiments will be described in more detail.

[0089] Positive electrode active material

[0090] The positive electrode active material may be a compound capable of intercalating / deintercalating lithium (lithiated intercalation compound). In some embodiments, a composite oxide of lithium and one or more types (or species) of metals selected from cobalt, manganese, nickel, and combinations thereof may be used.

[0091] The composite oxide may be a lithium transition metal composite oxide, and examples thereof may include lithium nickel-based oxides, lithium cobalt-based oxides, lithium manganese-based oxides, lithium iron phosphate-based compounds, cobalt-free lithium nickel manganese-based oxides, or combinations thereof.

[0092] As an example, a compound represented by any one of the following chemical formulas may be used: 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 Mn 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 O 2-α D α (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.5, 0<α<2); Li a Ni 1-b- c Mn b X c O 2-α D α (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.5, 0<α<2); Li a Ni b Co c L 1 d G e O2 (0.90≤a≤1.8, 0≤b≤0.9, 0≤c≤0.5, 0≤d≤0.5, 0≤e≤0.1); Li a NeG b O2(0.90≤a≤1.8, 0.001≤b≤0.1); Li a CoG b O2(0.90≤a≤1.8, 0.001≤b≤0.1); Li a Mn 1-b G b O2(0.90≤a≤1.8, 0.001≤b≤0.1); Li a Mn b O4(0.90≤a≤1.8, 0.001≤b≤0.1); Li a Mn 1-g G g PO4(0.90≤a≤1.8, 0≤g≤0.5); Li (3-f) Fe2(PO4)3(0≤f≤2); and Li a FePO4(0.90≤a≤1.8).

[0093] In the above chemical formula, A is Ni, Co, Mn or a combination thereof; X is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element or a combination thereof; D is O, F, S, P or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V or a combination thereof; and L 1 It is Mn, Al or a combination thereof.

[0094] As an example, based on 100 mol% of metals other than lithium in the lithium transition metal composite oxide, the positive electrode active material may have a nickel content of greater than or equal to about 80 mol%, greater than or equal to about 85 mol%, greater than or equal to about 90 mol%, greater than or equal to about 91 mol%, or greater than or equal to about 94 mol%, and may be a high nickel-based positive electrode active material having a nickel content of less than or equal to about 99 mol%. The high nickel-based positive electrode active material can achieve high capacity and can be used for high capacity, high density rechargeable lithium batteries.

[0095] The positive electrode active material may be, for example, a lithium nickel-based oxide represented by Chemical Formula 11, a lithium cobalt-based oxide represented by Chemical Formula 12, a lithium iron phosphate-based compound represented by Chemical Formula 13, a cobalt-free lithium nickel manganese-based oxide represented by Chemical Formula 14, or a combination thereof.

[0096] Chemical formula 11

[0097] Li a1 Ni x1 M 1 y1 M 2 z1 O 2-b1 X b1

[0098] In Chemical Formula 11, 0.9≤a1≤1.8, 0.3≤x1≤1, 0≤y1≤0.7, 0≤z1≤0.7, 0.9≤x1+y1+z1≤1.1, and 0≤b1≤0.1, M 1 and M 2 Each is independently one or more elements selected from Al, B, Ba, Ca, Ce, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W and Zr, and X is one or more elements selected from F, P and S.

[0099] In some embodiments, in Chemical Formula 11, 0.6≤x1≤1, 0≤y1≤0.4, and 0≤z1≤0.4, or 0.8≤x1≤1, 0≤y1≤0.2, and 0≤z1≤0.2.

[0100] Chemical formula 12

[0101] Li a2 Co x2 M 3 y2 O 2-b2 X b2

[0102] In Chemical Formula 12, 0.9 ≤ a2 ≤ 1.8, 0.7 ≤ x2 ≤ 1, 0 ≤ y2 ≤ 0.3, 0.9 ≤ x2 + y2 ≤ 1.1, and 0 ≤ b2 ≤ 0.1, M 3 is one or more elements selected from Al, B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mn, Mo, Ni, Se, Si, Sn, Sr, Ti, V, W, Y, Zn, and Zr, and X is one or more elements selected from F, P, and S.

[0103] Chemical Formula 13

[0104] Li a3 Fe x3 M 4 y3 PO 4-b3 X b3

[0105] In Chemical Formula 13, 0.9 ≤ a3 ≤ 1.8, 0.6 ≤ x3 ≤ 1, 0 ≤ y3 ≤ 0.4, 0.9 ≤ x3 + y3 ≤ 1.1, and 0 ≤ b3 ≤ 0.1, M 4 is one or more elements selected from Al, B, Ba, Ca, Ce, Co, Cr, Cu, Mg, Mn, Mo, Ni, Se, Si, Sn, Sr, Ti, V, W, Y, Zn, and Zr, and X is one or more elements selected from F, P, and S.

[0106] Chemical Formula 14

[0107] Li a4 Ni x4 Mn y4 M 5 z4 O 2-b4 X b4

[0108] In Chemical Formula 14, 0.9 ≤ a4 ≤ 1.8, 0.8 ≤ x4 < 1, 0 < y4 ≤ 0.2, 0 ≤ z4 ≤ 0.2, 0.9 ≤ x4 + y4 + z4 ≤ 1.1, and 0 ≤ b4 ≤ 0.1. M 5 is one or more elements selected from Al, B, Ba, Ca, Ce, Cr, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, and Zr, and X is one or more elements selected from F, P, and S.

[0109] In some embodiments, the electrolyte of the above embodiments may use the lithium cobalt-based oxide represented by Chemical Formula 12 to significantly improve high voltage and / or high temperature characteristics of the battery.

[0110] Positive electrode

[0111] The positive electrode for a rechargeable lithium battery may include a positive electrode current collector and a positive electrode active material layer on the positive electrode current collector. The positive electrode active material layer may include a positive electrode active material and may further include a binder and / or a conductive material (eg, an electrically conductive material).

[0112] For example, the positive electrode may further include an additive that may function as a sacrificial positive electrode.

[0113] The positive electrode active material may be included in an amount of about 90 wt % to about 99 wt %, and the binder and the conductive material may be included in an amount of about 0.5 wt % to about 5 wt %, respectively, based on 100 wt % of the positive electrode active material layer.

[0114] The binder is used to attach the positive electrode active material particles to each other well or properly, and also to attach the positive electrode active material to the positive electrode current collector well or properly. Examples of binders may include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth) acrylated styrene-butadiene rubber, epoxy resin, (meth) acrylic resin, polyester resin, nylon, etc. as non-limiting examples.

[0115] Conductive materials can be used to impart conductivity (e.g., electrical conductivity) to the electrodes. Any suitable material that does not cause chemical changes (e.g., does not cause undesirable chemical changes in a rechargeable lithium battery) and conducts electrons can be used for the battery. Examples of conductive materials may include carbon-based materials (such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fibers, carbon nanofibers, and carbon nanotubes); metal-based materials including copper, nickel, aluminum, silver, etc. in the form of metal powders and / or metal fibers; conductive polymers (e.g., conductive polymers) (such as polyphenylene derivatives); or mixtures thereof.

[0116] Al foil may be used as a positive electrode current collector, but is not limited thereto.

[0117] Negative electrode active material

[0118] The negative electrode active material may be a material that reversibly intercalates / deintercalates lithium ions, lithium metal, a lithium metal alloy, a material capable of doping / dedoping lithium, and / or a transition metal oxide.

[0119] Materials that can reversibly embed / extract lithium ions may include carbonaceous negative electrode active materials, such as crystalline carbon, amorphous carbon, or combinations thereof. The crystalline carbon may be graphite, such as amorphous, flaky, lamellar, spherical, and / or fibrous natural graphite and / or artificial graphite. The amorphous carbon may be soft carbon, hard carbon, mesophase pitch carbonization products, calcined coke, etc.

[0120] 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.

[0121] Materials capable of doping / dedoping lithium may be Si-based negative electrode active materials and / or Sn-based negative electrode active materials. The Si-based negative electrode active materials may include silicon, silicon-carbon composites, SiO x (0 < x ≤ 2), Si-Q alloys (where Q is selected from alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements (excluding Si), Group 15 elements, Group 16 elements, transition metals, rare earth elements, and combinations thereof). The Sn-based negative electrode active materials may include Sn, SnO2, Sn-based alloys, SnO x (0 < x < 2) or combinations thereof.

[0122] The silicon-carbon composite may be a composite of silicon and amorphous carbon. According to some embodiments, the silicon-carbon composite may be in the form of silicon particles and amorphous carbon coated on the surface of the silicon particles. For example, the silicon-carbon composite may include secondary particles (cores) in which primary silicon particles are aggregated and an amorphous carbon coating (shell) on the surface of the secondary particles. The amorphous carbon may also be between the primary silicon particles, and, for example, the primary silicon particles may be coated with amorphous carbon. The secondary particles may be dispersed in the amorphous carbon matrix.

[0123] The silicon-carbon composite may further include crystalline carbon. For example, the silicon-carbon composite may include: a core including crystalline carbon and silicon particles and an amorphous carbon coating on the surface of the core.

[0124] The Si-based negative electrode active materials or the Sn-based negative electrode active materials may be used in combination with the carbonaceous negative electrode active materials.

[0125] Negative electrode

[0126] The negative electrode for a rechargeable lithium battery includes a negative electrode current collector and a negative electrode active material layer on the negative electrode current collector. The negative electrode active material layer includes negative electrode active materials and may further include a binder and / or a conductive material (e.g., a conductive material).

[0127] For example, the negative electrode active material layer may include about 90 wt % to about 99 wt % of the negative electrode active material, about 0.5 wt % to about 5 wt % of the binder, and about 0 wt % to about 5 wt % of the conductive material based on the total amount of the negative electrode active material layer.

[0128] The binder can be used to well attach the negative electrode active material particles to each other and also well attach the negative electrode active material to the negative electrode current collector. The binder may include a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof.

[0129] The non-aqueous binder may include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or a combination thereof.

[0130] The aqueous binder can be selected from styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluororubber, polyethylene oxide, polyvinyl pyrrolidone, polyepichlorohydrin, polyphosphazene, poly(meth)acrylonitrile, ethylene propylene diene copolymer, polyvinyl pyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol and combinations thereof.

[0131] If the aqueous binder is used as a binder in the negative electrode active material layer, it may further include a cellulose compound capable of imparting or increasing viscosity. The cellulose compound includes one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose and alkali metal salts thereof. The alkali metal may be Na, K and / or Li.

[0132] The dry binder may be a polymer material capable of fiberization, and may be, for example, polytetrafluoroethylene, polyvinylidene fluoride, a polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0133] The conductive material is included to provide electrode conductivity (e.g., electrical conductivity), and any suitable conductive material may be used as the conductive material unless it causes chemical changes (e.g., causes undesirable chemical changes in a rechargeable lithium battery). Examples of the conductive material may be carbon-based materials (such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanofiber, carbon nanotube, etc.); metal-based materials in the form of metal powders and / or metal fibers including copper, nickel, aluminum silver, etc.; conductive polymers (e.g., conductive polymers) (such as polyphenylene derivatives); or mixtures thereof.

[0134] The negative electrode current collector may include one selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal (eg, an electrically conductive metal), and combinations thereof, but is not limited thereto.

[0135] Diaphragm

[0136] Depending on the type (or kind) of the rechargeable lithium battery, the separator may be present between the positive electrode and the negative electrode. The separator may include a polyethylene separator, a polypropylene separator, a polyvinylidene fluoride separator, or a multilayer film of two or more layers thereof (such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, a polypropylene / polyethylene / polypropylene three-layer separator, etc.).

[0137] The separator may include a porous substrate and a coating on one or both surfaces (eg, two opposite surfaces) of the porous substrate, the coating including an organic material, an inorganic material, or a combination thereof.

[0138] The porous substrate may be a polymer film formed from: any one of a polymer selected from polyolefins (such as, for example, polyethylene and polypropylene), polyesters (such as, for example, polyethylene terephthalate and polybutylene terephthalate), polyacetals, polyamides, polyimides, polycarbonates, polyether ketones, polyaryletherketones, polyetherimides, polyamideimides, polybenzimidazoles, polyethersulfones, polyphenylene oxides, cyclic olefin copolymers, polyphenylene sulfide, polyethylene naphthalate, glass fibers, and polytetrafluoroethylene (e.g., Teflon), or a copolymer or mixture of two or more thereof.

[0139] The organic material may include a polyvinylidene fluoride-based polymer and / or a (meth)acrylic-based polymer.

[0140] The inorganic material may include inorganic particles selected from Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, boehmite and combinations thereof, but is not limited thereto.

[0141] An organic material and an inorganic material may be mixed together in one coating layer, or a coating layer including an organic material and a coating layer including an inorganic material may be stacked.

[0142] Rechargeable lithium battery

[0143] The rechargeable lithium battery may be classified into a cylindrical battery, a prismatic battery, a pouch type battery, a coin type battery, etc., depending on the shape of the rechargeable lithium battery. Figure 1 to Figure 4 A schematic diagram for explaining a rechargeable lithium battery according to an embodiment. Figure 1 A cylindrical battery is shown, Figure 2 A prismatic cell is shown, and Figure 3-4 A pouch type battery is shown. Figure 1 to Figure 4 , the rechargeable lithium battery 100 may include an electrode assembly 40 including a separator 30 between a positive electrode 10 and a negative electrode 20, and a case 50 in which the electrode assembly 40 is accommodated. The positive electrode 10, the negative electrode 20, and the separator 30 may be impregnated with an electrolyte. Figure 1 As shown, the rechargeable lithium battery 100 may include a sealing member 60 that seals the housing 50. Figure 2 In the embodiment, the rechargeable lithium battery 100 may include a positive electrode lead tab 11, a positive electrode terminal 12, a negative electrode lead tab 21, and a negative electrode terminal 22. Figure 3-4 As shown, the rechargeable lithium battery 100 may include an electrode tab 70 ( Figure 4 ), which may be, for example, a positive electrode tab 71 and a negative electrode tab 72 ( Figure 3 ).

[0144] A rechargeable lithium battery according to some embodiments may be used in automobiles, mobile phones, and / or various appropriate types (kinds) of electronic devices, but the present disclosure is not limited thereto.

[0145] Hereinafter, examples and comparative examples of the present disclosure are described. However, these examples are not to be construed as limiting the scope of the present disclosure in any sense.

[0146] Preparation of electrolyte

[0147] Example 1

[0148] 1.3M LiPF6 was dissolved in a non-aqueous organic solvent in which ethylene carbonate (EC), propylene carbonate (PC) and propyl propionate (PP) were mixed together in a volume ratio of 10:15:75, and 0.5wt% of the first additive and 0.25wt% of the second additive were added thereto based on the total amount of the electrolyte to prepare an electrolyte.

[0149] The first additive represented by Chemical Formula 1-1 is used:

[0150] Chemical formula 1-1

[0151]

[0152] Poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) (PEG-b-PPG-b-PEG, CAS No.: 9003-11-6, x=1-20, y=1-20, z=1-20, number average molecular weight: 1,100 g / mol)

[0153] A second additive represented by Chemical Formula 2-1 is used:

[0154] Chemical formula 2-1

[0155]

[0156] Lithium difluoro(oxalato)borate (LiDFOB, CAS No.: 409071-16-5)

[0157] In the composition of the electrolyte, the content "wt %" of each additive is based on 100 wt % of the total electrolyte (lithium salt+nonaqueous organic solvent+first additive+second additive).

[0158] Example 2

[0159] An electrolyte was prepared in substantially the same manner as in Example 1, except that 0.5 wt % of the first additive and 0.5 wt % of the second additive were added.

[0160] Example 3

[0161] An electrolyte was prepared in substantially the same manner as in Example 1, except that 0.5 wt % of the first additive and 1 wt % of the second additive were added.

[0162] Example 4

[0163] An electrolyte was prepared in substantially the same manner as in Example 1, except that 0.5 wt % of the first additive and 1.5 wt % of the second additive were added.

[0164] Example 5

[0165] An electrolyte was prepared in substantially the same manner as in Example 1, except that 0.5 wt % of the first additive and 2 wt % of the second additive were added.

[0166] Example 6

[0167] An electrolyte was prepared in substantially the same manner as in Example 1, except that 1 wt % of the first additive and 1 wt % of the second additive were added.

[0168] Comparative Example 1 (reference)

[0169] An electrolyte was prepared in substantially the same manner as in Example 1, except that no additive was added.

[0170] Comparative Example 2

[0171] An electrolyte was prepared in substantially the same manner as in Example 1, except that 0.5 wt % of the first additive was added and the second additive was not added.

[0172] Comparative Example 3

[0173] An electrolyte was prepared in substantially the same manner as in Example 1, except that the first additive was not added and 1 wt % of the second additive was added.

[0174] Preparation of rechargeable lithium battery cells

[0175] LiCoO 2 as a positive electrode active material, polyvinylidene fluoride as a binder, and acetylene black as a conductive material were mixed together at a weight ratio of 96:3:1, respectively, and then dispersed in N-methylpyrrolidone to prepare a positive electrode active material slurry.

[0176] The positive electrode active material slurry was coated on a 15 μm thick Al foil, dried at 100° C., and pressed to prepare a positive electrode.

[0177] Artificial graphite as a negative electrode active material, a styrene-butadiene rubber binder, and carboxymethyl cellulose were dispersed in distilled water at a weight ratio of about 98:1:1 to prepare a negative electrode active material slurry.

[0178] The negative electrode active material slurry was coated on a 10 μm-thick Cu foil, dried at 100° C., and pressed to prepare a negative electrode.

[0179] An electrode assembly was prepared by assembling a positive electrode, a negative electrode, and a separator made of polyethylene having a thickness of 10 μm, and the electrolytes according to Examples 1 to 6 and Comparative Examples 1 to 3 were respectively injected to prepare each rechargeable lithium battery cell.

[0180] Evaluation Example

[0181] Rechargeable lithium battery cells prepared using the electrolytes according to Examples 1 to 6 and Comparative Examples 1 to 3 were evaluated as follows, and the evaluation results are shown in Tables 1 to 3.

[0182] Evaluation 1: Evaluation of high voltage (4.53V) and high temperature (45°C) charge / discharge cycle characteristics

[0183] The rechargeable lithium battery cell was charged and discharged 200 times under the conditions of 45° C., 2.0 C charge (CC / CV, 4.53 V, 0.025 C cutoff) / 1.0 C discharge (CC, 3 V cutoff).

[0184] The thickness increase rate was calculated according to Equation 1, the capacity retention rate was calculated according to Equation 2, and the results are shown in Table 1.

[0185] Equation 1

[0186] Thickness increase rate = {(fully charged thickness after 200th cycle) – (fully charged thickness after 1st cycle)} / (fully charged thickness after 1st cycle) * 100

[0187] In Equation 1, "fully charged thickness" refers to the thickness of a rechargeable lithium battery cell measured after charging at SOC 100% (if the total charge capacity of the battery is set to 100%, charging to 100% charge capacity) after each cycle.

[0188] Equation 2

[0189] Capacity retention rate = (discharge capacity after 200th cycle / discharge capacity after 1st cycle)*100

[0190] Table 1

[0191]

[0192]

[0193] Evaluation 2: Evaluation of storage characteristics at high temperature

[0194] The initial DC internal resistance (initial DC-IR) of the rechargeable lithium battery cell before storage at high temperature was measured by ΔV / ΔI (voltage change / current change).

[0195] After the maximum energy state inside the rechargeable lithium battery cell reached a fully charged state (SOC 100%), the battery cell was then stored at high temperature (60° C.) for 28 days in this state, and the DC resistance of the battery cell was measured (DC-IR after 28 days).

[0196] The DC-IR increase rate was calculated according to Equation 3, and the results are shown in Table 2.

[0197] Equation 3

[0198] DC-IR increase rate = (DC-IR after 28 days) / (initial DC-IR)*100

[0199] Table 2

[0200]

[0201] summary

[0202] Referring to Tables 1 and 2, the electrolyte that simultaneously (e.g., synchronously) includes the first additive and the second additive (Examples 1 to 6) improves the high voltage and high temperature characteristics of the rechargeable lithium battery cell, compared to an electrolyte that does not include any additives at all (Comparative Example 1) and an electrolyte that includes one type or type of additives from two types (kinds) of additives (Comparative Examples 2 and Comparative Examples 3).

[0203] Even if the rechargeable lithium battery cell is charged and discharged under high voltage and high temperature conditions, the electrolyte (Examples 1 to 6) including the first additive and the second additive simultaneously (eg, synchronously) suppresses an increase in thickness and generally improves the cycle life of the battery cell.

[0204] In addition, even if the rechargeable lithium battery cell is stored at a high temperature, the electrolytes (Examples 1 to 6) including the first additive and the second additive simultaneously (eg, simultaneously) generally suppress an increase in resistance.

[0205] On the other hand, in the electrolyte including the first additive and the second additive simultaneously (eg, synchronously) (Examples 1 to 6), the content of each additive and the mixing ratio thereof may be controlled according to appropriate or desired characteristics.

[0206] While the subject matter of the present disclosure has been described in conjunction with what are presently considered to be practical example embodiments, it should be understood that the disclosure should not be limited to the disclosed embodiments, but, on the contrary, is intended to cover one or more suitable modifications and equivalent arrangements included within the spirit and scope of the claims and their equivalents.

Claims

1. An electrolyte for a rechargeable lithium battery, comprising: Lithium salts; Non-aqueous organic solvents; A first additive represented by Chemical Formula 1; as well as The second additive represented by Chemical Formula 2: Chemical formula 1 Wherein, in Chemical Formula 1, R 1 is a hydrogen atom or a C1-C10 alkyl group; and x, y and z are each independently an integer from 1 to 20; Chemical formula 2 Wherein, in Chemical Formula 2, R 2 and R 3 Each is independently a halogen atom or a C1-C10 fluoroalkyl group.

2. The electrolyte according to claim 1, wherein: R 1 It is methyl.

3. The electrolyte according to claim 1, wherein: The number average molecular weight of the first additive is 500 g / mol to 10,000 g / mol.

4. The electrolyte according to claim 1, wherein: R 2 and R 3 All are fluorine atoms.

5. The electrolyte according to claim 1, wherein: The first additive is included in an amount of 0.1 wt % to 5 wt % based on the total amount of the electrolyte.

6. The electrolyte according to claim 1, wherein: The second additive is included in an amount of 0.1 wt % to 5 wt % based on the total amount of the electrolyte.

7. The electrolyte according to claim 1, wherein: The weight ratio of the first additive to the second additive in the electrolyte is 5:1 to 1:

10.

8. The electrolyte according to claim 1, wherein: The non-aqueous organic solvent includes carbonate solvents and propionate solvents.

9. The electrolyte according to claim 8, wherein: The propionate solvent is included in an amount greater than or equal to 70 volume % based on the total amount of the non-aqueous organic solvent.

10. The electrolyte according to claim 1, wherein: The lithium salt is LiPF6.

11. The electrolyte according to claim 1, wherein The concentration of the lithium salt is 0.1M to 2.0M.

12. A rechargeable lithium battery comprising: a positive electrode, including a positive electrode active material; a negative electrode, including a negative electrode active material; as well as The electrolyte according to any one of claims 1 to 11.

13. The rechargeable lithium battery of claim 12, wherein: The positive electrode active material includes lithium nickel oxide, lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate compound, cobalt-free lithium nickel manganese oxide or a combination thereof.

14. The rechargeable lithium battery of claim 12, wherein: The negative electrode active material includes a carbon-based negative electrode active material, a Si-based negative electrode active material or a combination thereof.

15. The rechargeable lithium battery of claim 12, wherein: The rechargeable lithium battery has a charge upper limit voltage greater than or equal to 4.5V.

Images