Rechargeable lithium battery

Abstract

The present application discloses 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, in which the active mass density of the negative electrode is greater than or equal to about 1.7 g / cc, and the electrolyte 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. Chemical formula 1R1-O-R2 chemical formula 2 # imgabs0 #

Description

Technical Field

[0001] A rechargeable lithium battery is disclosed. Background Art

[0002] Recently, with the rapid popularization of electronic devices using batteries (such as, for example, mobile phones, laptop computers and electric vehicles), interest in 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 being actively carried out.

[0003] The rechargeable lithium battery includes positive and negative electrodes (including active materials capable of intercalating / deintercalating lithium ions), and an electrolyte, and generates electric energy through oxidation and reduction reactions if lithium ions are intercalated / deintercalated from the positive and negative electrodes.

[0004] One of the latest development directions of rechargeable lithium batteries is to increase the active mass density of the negative electrode. However, if the active mass density of the negative electrode increases, the void volume decreases, which increases the amount of electrolyte impregnated into the negative electrode, thereby causing the battery thickness to increase and the cycle life to decrease. Summary of the invention

[0005] Some embodiments of the present disclosure provide a rechargeable lithium battery that increases the active mass density of the negative electrode and suppresses or reduces the increase in battery thickness and the decrease in cycle life that would otherwise occur if the active mass density of the negative electrode is increased.

[0006] Some embodiments provide a rechargeable lithium battery, comprising: a positive electrode including a positive electrode active material; a negative electrode including a negative electrode active material; and an electrolyte, wherein the active mass density of the negative electrode is greater than or equal to about 1.7 g / cc, and the electrolyte comprises: 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:

[0007] Chemical formula 1

[0008] R 1 -OR 2

[0009] Chemical formula 2

[0010]

[0011] A rechargeable lithium battery according to some embodiments can increase the active mass density of the negative electrode while suppressing or reducing an increase in battery thickness and a decrease in cycle life that would otherwise occur by increasing the active mass density of the negative electrode. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The accompanying drawings, together with the description, 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.

[0013] Figure 1 to Figure 4 is a schematic diagram illustrating a rechargeable lithium battery according to some embodiments.

[0014] Description of Reference Numerals

[0015] 100: Rechargeable lithium battery 10: Positive electrode

[0016] 11: Positive electrode lead tab 12: Positive terminal

[0017] 20: Negative electrode 21: Negative electrode lead lug

[0018] 22: Negative terminal 30: Separator

[0019] 40: electrode assembly 50: shell

[0020] 60: Sealing member 70: Electrode terminal piece

[0021] 71: Positive electrode terminal tab 72: Negative electrode terminal tab DETAILED DESCRIPTION

[0022] 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.

[0023] As used herein, if no specific definition is 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.

[0024] As used herein, if no specific definition 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.

[0025] As used herein, "combination thereof" may mean a mixture, stack, composite, copolymer, alloy, blend, and / or reaction product of the components.

[0026] As used herein, “active mass density of the negative electrode” is a value calculated by dividing the weight of components (active material, conductive material (eg, electrically conductive material), binder, etc.) in the negative electrode excluding the negative electrode current collector by its volume.

[0027] As used herein, if a definition is not provided otherwise, in a chemical formula, if a chemical bond should be given but is not drawn, a hydrogen atom is bonded to that position.

[0028] As used herein, "fluoroalkyl" refers to an alkyl group in which some or all of the hydrogen atoms are replaced by fluorine atoms.

[0029] As used herein, "perfluoroalkyl" refers to an alkyl group in which all hydrogen atoms are replaced by fluorine atoms.

[0030] Rechargeable lithium battery

[0031] Some embodiments provide a rechargeable lithium battery, comprising: a positive electrode including a positive electrode active material; a negative electrode including a negative electrode active material; and an electrolyte, wherein the active mass density of the negative electrode is greater than or equal to about 1.7 g / cc, and the electrolyte comprises 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:

[0032] Chemical formula 1

[0033] R 1 -OR 2

[0034] Chemical formula 2

[0035]

[0036] The first additive functions as a surfactant having both a hydrophilic group and a hydrophobic group in one molecule.

[0037] The first additive includes an ether group located in the main chain (e.g., located in the center) and fluorine atoms or C1-C10 fluoroalkyl groups located on both sides of the ether group (e.g., located on the opposite sides of the main chain or the center). In this article, the ether group is a hydrophilic group, and the fluorine atom and the C1-C10 fluoroalkyl group are hydrophobic groups.

[0038] In some embodiments, the second additive is an oxalatoborate compound substituted with a halogen atom (eg, a fluorine atom), wherein the fluorine atom stabilizes the lithium salt (eg, LiPF6).

[0039] Accordingly, if the electrolyte including the second additive is used, generation of HF may be suppressed or reduced, and dissolution of transition metals from the positive electrode active material and damage to the SEI film at the interface between the negative electrode and the electrolyte may be prevented or reduced.

[0040] Therefore, by using an electrolyte including a first additive and a second additive and simultaneously increasing the active mass density of the negative electrode to 1.7 g / cc or greater, an increase in battery thickness and a decrease in cycle life can be suppressed or reduced, which would otherwise occur if the active mass density of the negative electrode was increased (for example, as a result of the high active mass density).

[0041] Hereinafter, a rechargeable lithium battery according to some embodiments will be described in more detail.

[0042] Active mass density of negative electrode

[0043] Generally, rechargeable lithium batteries use a negative electrode having an active mass density less than about 1.7 g / cc, but rechargeable lithium batteries according to some embodiments use a negative electrode having a mixed density (eg, active mass density) greater than or equal to about 1.7 g / cc.

[0044] The upper limit of the active mass density of the negative electrode is not particularly limited, but may be less than or equal to about 2.0 g / cc, less than or equal to about 1.9 g / cc, or less than or equal to about 1.8 g / cc.

[0045] Charging upper limit voltage

[0046] Since the rechargeable lithium battery according to some embodiments includes the electrolyte of the above embodiments, an increase in battery thickness and a decrease in cycle life, which would otherwise occur, may be suppressed or reduced even at a high voltage.

[0047] In some embodiments, the rechargeable lithium battery may have a charge upper limit voltage greater than or equal to about 4.5V.

[0048] First Additive

[0049] In Chemical Formula 1, R 1 and R 2 Each is independently a fluorine atom or a C1-C10 fluoroalkyl group.

[0050] For example, R 1 It may be a fluoroalkyl group having 2 carbon atoms.

[0051] In some embodiments, R 2 It may be a fluoroalkyl group having 3 carbon atoms.

[0052] The first additive can be represented by Chemical Formula 1-1:

[0053] Chemical formula 1-1

[0054]

[0055] In Chemical Formula 1-1, R 11 ~R 15 are each a hydrogen atom or a fluorine atom, provided that they are selected from R 11 ~R 15 At least one of is a fluorine atom; and R 21 ~R 27 are each a hydrogen atom or a fluorine atom, provided that they are selected from R 21 ~R 27 At least one of them is a fluorine atom.

[0056] Representative examples of the first additive are as follows:

[0057] Chemical formula 1-1-1

[0058]

[0059] Second additive

[0060] In chemical formula 2, R 3 and R 4 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.

[0061] For example, R 3 and R 4 They may all be fluorine atoms.

[0062] Representative examples of the second additive are as follows:

[0063] Chemical formula 2-1

[0064]

[0065] The second additive represented by Chemical Formula 2-1 is lithium difluoro(oxalato)borate (LiDFOB).

[0066] Content of the first additive and the second additive

[0067] The first additive may be included in an amount of about 1 wt % to about 20 wt %, about 1 wt % to about 15 wt %, or about 1 wt % to about 10 wt %, based on the total amount of the electrolyte.

[0068] If the first additive is included in an amount exceeding 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 first additive is included in a small amount below the above range, the effect as a surfactant may be minimized or reduced.

[0069] The second additive may be included in an amount of about 0.1 to about 10 wt %, about 0.5 to about 5 wt %, or about 1 to about 2 wt %, based on the total amount of the electrolyte.

[0070] 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.

[0071] A weight ratio of the first additive to the second additive may be about 20:1 to about 2:1, about 15:1 to about 3:1, or about 10:1 to about 5:1.

[0072] Within these ranges, the effects of the first additive and the second additive may be coordinated (eg, may provide a synergistic effect).

[0073] Non-aqueous organic solvent

[0074] The nonaqueous organic solvent serves as a medium for transmitting ions participating in the electrochemical reaction of the battery.

[0075] 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.

[0076] 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 (EP), propyl propionate (PP), decanoic acid lactone, mevalonolactone, valerolactone, caprolactone, etc.

[0077] Ether solvents may include dibutyl ether, tetraglyme, diglyme, 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 nitriles (such as R-CN, where R is a C2-C20 straight chain hydrocarbon group, a branched hydrocarbon group and / or a cyclic hydrocarbon group, and may include a double bond, an aromatic ring and / or an ether group), an amide (such as dimethylformamide), a dioxolane (such as 1,3-dioxolane and / or 1,4-dioxolane), sulfolane, etc.

[0078] The nonaqueous organic solvent may be used alone or in combination of two or more thereof.

[0079] In an embodiment in which the nonaqueous organic solvent is used in combination of two or more, the nonaqueous organic solvent may include a carbonate-based solvent and a propionate-based solvent.

[0080] The propionate-based solvent may be included in an amount of greater than or equal to about 70 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.

[0081] For example, the nonaqueous organic solvent may be a mixed solvent including ethylene carbonate (EC), propylene carbonate (PC), ethyl propionate (EP), and propyl propionate (PP).

[0082] Lithium salts

[0083] 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.

[0084] LiPF6 can be used as a lithium salt.

[0085] The concentration of the lithium salt may be about 0.1M to about 2.0M.

[0086] Positive electrode active material

[0087] The positive electrode active material may be a compound capable of intercalating / deintercalating lithium (lithiated intercalation compound). In some embodiments, a composite oxide of one or more types (or species) of lithium and a metal selected from cobalt, manganese, nickel, and combinations thereof may be used.

[0088] 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, lithium nickel manganese-based oxides not containing cobalt, or combinations thereof.

[0089] 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 Dα (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).

[0090] 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.

[0091] As an example, based on 100 mol% of metals excluding 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 based on 100 mol% of metals excluding lithium in the lithium transition metal composite oxide, the positive electrode active material 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 applied to high capacity, high density rechargeable lithium batteries.

[0092] 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 lithium nickel manganese-based oxide not containing cobalt represented by Chemical Formula 14, or a combination thereof.

[0093] Chemical formula 11

[0094] Li a1 Ni x1 M 1 y1 M 2 z1 O 2-b1 X b1

[0095] 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.

[0096] 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.

[0097] Chemical formula 12

[0098] Li a2 Co x2 M 3 y2 O 2-b2 X b2

[0099] 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.

[0100] Chemical Formula 13

[0101] Li a3 Fe x3 M 4 y3 PO 4-b3 X b3

[0102] 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.

[0103] Chemical Formula 14

[0104] Li a4 Ni x4 Mn y4 M 5 z4 O 2-b4 X b4

[0105] 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.

[0106] In some embodiments, the electrolyte of the above embodiments can significantly improve the high voltage and / or high temperature characteristics of a battery using a lithium cobalt oxide represented by Chemical Formula 12.

[0107] Positive electrode

[0108] 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).

[0109] For example, the positive electrode may further include an additive that may function as a sacrificial positive electrode.

[0110] 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.

[0111] The binder is used to attach the positive electrode active material particles to each other well, and also to attach the positive electrode active material to the positive electrode current collector well. Examples of the binder may include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers including ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth) acrylated styrene-butadiene rubber, epoxy resin, (meth) acrylic resin, polyester resin and nylon, etc. as non-limiting examples.

[0112] Conductive materials can be used to impart electrical 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 in 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 containing 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.

[0113] Al foil may be used as a positive electrode current collector, but is not limited thereto.

[0114] Negative electrode active material

[0115] 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.

[0116] The material that reversibly intercalates / deintercalates lithium ions may include a carbon-based negative electrode active material, for example, crystalline carbon, amorphous carbon, or a combination thereof. Crystalline carbon may be graphite (such as amorphous, flaky, sheet-like, spherical and / or fibrous natural graphite and / or artificial graphite). Amorphous carbon may be soft carbon, hard carbon, mesophase pitch carbonization product, calcined coke, etc.

[0117] 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.

[0118] The material capable of doping / dedoping lithium may be a Si-based negative electrode active material and / or a Sn-based negative electrode active material. The Si-based negative electrode active material may include silicon, a silicon-carbon composite, SiO x (0 < x ≤ 2) and / or a Si-Q alloy (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 material may include Sn, SnO2, SnO x (0 < x < 2), a Sn-based alloy, or a combination thereof.

[0119] 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 assembled and an amorphous carbon coating (shell) on the surface of the secondary particles. Amorphous carbon is also 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.

[0120] The silicon-carbon composite may further include crystalline carbon. For example, the silicon-carbon composite may include a core containing crystalline carbon and silicon particles and an amorphous carbon coating on the surface of the core.

[0121] The Si-based negative electrode active material and / or the Sn-based negative electrode active material may be used in combination with a carbon-based negative electrode active material.

[0122] Negative electrode

[0123] 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 a negative electrode active material and may further include a binder and / or a conductive material (e.g., a conductive material).

[0124] For example, the negative electrode active material layer may include, based on 100 wt% of the negative electrode active material layer, 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.

[0125] The binder can be used to well attach the negative electrode active material particles to each other and also to 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.

[0126] 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.

[0127] 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.

[0128] If an 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.

[0129] 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.

[0130] 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., 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 containing copper, nickel, aluminum, silver, etc. in the form of metal powder and / or metal fiber; conductive polymers (e.g., conductive polymers) (such as polyphenylene derivatives); or mixtures thereof.

[0131] 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.

[0132] Diaphragm

[0133] 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, and / or a polypropylene / polyethylene / polypropylene three-layer separator, etc.).

[0134] The separator may include a porous substrate and a coating on one or both surfaces of the porous substrate, the coating including an organic material, an inorganic material, or a combination thereof.

[0135] The porous substrate may be a polymer film formed from any one selected from the following: polyolefins (such as, for example, polyethylene and / or polypropylene), polyesters (such as polyethylene terephthalate and / or polybutylene terephthalate), polyacetals, polyamides, polyimides, polycarbonates, polyetherketones, polyaryletherketones, polyetherimides, polyamideimides, polybenzimidazoles, polyethersulfones, polyphenylene oxides, cyclic olefin copolymers, polyphenylene sulfide, polyethylene naphthalate, glass fibers and / or polytetrafluoroethylene (e.g., Teflon), or copolymers or mixtures of two or more thereof.

[0136] The organic material may include a polyvinylidene fluoride-based polymer and / or a (meth)acrylic-based polymer.

[0137] 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.

[0138] The organic material and the 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.

[0139] Rechargeable lithium battery

[0140] The rechargeable lithium battery may be classified into a cylindrical battery, a prismatic battery, a pouch type battery, a coin type battery, or the like, 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 Pouch type battery is shown. Figure 1 to Figure 4 , the rechargeable lithium battery 100 may include an electrode assembly 40 and a case 50 in which the electrode assembly 40 is accommodated, the battery assembly 40 including a separator 30 between a positive electrode 10 and a negative electrode 20. The positive electrode 10, the negative electrode 20, and the separator 30 may be impregnated with an electrolyte. Figure 1As 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 ).

[0141] A rechargeable lithium battery according to some embodiments may be applied to automobiles, mobile phones, and / or various appropriate types (or kinds) of electronic devices, but the present disclosure is not limited thereto.

[0142] Hereinafter, examples and comparative examples of the present disclosure are described. However, these examples are by no means interpreted as limiting the scope of the present disclosure.

[0143] Examples and Comparative Examples

[0144] The electrolyte and rechargeable lithium battery cells were prepared as follows.

[0145] Example 1

[0146] Preparation of electrolyte

[0147] 1.3M LiPF6 was dissolved in a non-aqueous organic solvent in which ethylene carbonate (EC), propylene carbonate (PC), ethyl propionate (EP) and propyl propionate (PP) were mixed together in a volume ratio of 10:15:30:45, and 5wt% of a first additive and 1wt% of a second additive based on the total amount of the electrolyte were added thereto to prepare an electrolyte.

[0148] A first additive represented by Chemical Formula 1-1-1 is used, and a second additive represented by Chemical Formula 2-1 is used:

[0149] Chemical formula 1-1-1

[0150]

[0151] 1,1,2,2-Tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (CAS No.: 16627-68-2)

[0152] Chemical formula 2-1

[0153]

[0154] Lithium difluoro(oxalato)borate (LiDFOB, CAS No.: 409071-16-5)

[0155] (2) Manufacturing of rechargeable lithium battery cells

[0156] 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.

[0157] The positive electrode active material slurry was coated on a 15 μm thick Al foil, dried at 100° C., and pressed to produce a positive electrode.

[0158] 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 98:1:1 to prepare a negative electrode active material slurry.

[0159] The negative electrode active material slurry was coated on a 10 μm thick Cu foil, dried at 100° C., and pressed to produce a negative electrode. At this time, the active mass density of the negative electrode was set to 1.7 g / cc.

[0160] An electrode assembly was manufactured by assembling a positive electrode, a negative electrode, and a separator made of polyethylene having a thickness of 10 μm, and an electrolyte was injected to manufacture a rechargeable lithium battery cell.

[0161] Example 2

[0162] An electrolyte and a rechargeable lithium battery cell were prepared in substantially the same manner as in Example 1, except that 10 wt % of the first additive and 1 wt % of the second additive were added when preparing the electrolyte.

[0163] Example 3

[0164] An electrolyte and a rechargeable lithium battery cell were prepared in substantially the same manner as in Example 1, except that 10 wt % of the first additive and 2 wt % of the second additive were added when preparing the electrolyte.

[0165] Example 4

[0166] An electrolyte and a rechargeable lithium battery cell were prepared in substantially the same manner as in Example 1, except that 10 wt % of the first additive and 2 wt % of the second additive were added when preparing the electrolyte, and the active mass density was set to 1.75 g / cc when preparing the negative electrode.

[0167] Example 5

[0168] An electrolyte and a rechargeable lithium battery cell were prepared in substantially the same manner as in Example 1, except that 10 wt % of the first additive and 2 wt % of the second additive were added when preparing the electrolyte, and the active mass density was set to 1.8 g / cc when preparing the negative electrode.

[0169] Comparative Example 1

[0170] An electrolyte and a rechargeable lithium battery cell were prepared in substantially the same manner as in Example 1, except that no additive was added when preparing the electrolyte, and the active mass density was set to 1.65 g / cc when preparing the negative electrode.

[0171] Comparative Example 2

[0172] An electrolyte and a rechargeable lithium battery cell were prepared in substantially the same manner as in Example 1, except that no additive was added when preparing the electrolyte, and the active mass density was set to 1.67 g / cc when preparing the negative electrode.

[0173] Comparative Example 3

[0174] An electrolyte and a rechargeable lithium battery cell were prepared in substantially the same manner as in Example 1, except that no additive was added when preparing the electrolyte, and the active mass density was set to 1.7 g / cc when preparing the negative electrode.

[0175] Comparative Example 4

[0176] An electrolyte and a rechargeable lithium battery cell were prepared in substantially the same manner as in Example 1, except that 5 wt % of the first additive was added and the second additive was not added when the electrolyte was prepared.

[0177] Comparative Example 5

[0178] An electrolyte and a rechargeable lithium battery cell were 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 when preparing the electrolyte, and the active mass density was set to 1.7 g / cc when preparing the negative electrode.

[0179] Evaluation Example

[0180] The negative electrodes and rechargeable lithium battery cells of Examples and Comparative Examples were evaluated in the following manner.

[0181] Evaluation 1: Impregnation properties of the electrolyte on the negative electrode

[0182] The negative electrode according to Example 1 was manufactured into a sample having a width*length=3 cm*5 cm. 0.02 g of the electrolyte according to Example 1 was dropped on the sample and left for 1 minute. Thereafter, the amount of the electrolyte immersed in the sample in 100 wt % of the electrolyte dropped on the sample was evaluated as a value selected from 0 to 5 according to the following standard, and the evaluation results are shown in Table 1.

[0183] 0: If the amount of electrolyte immersed in the sample is 0wt% or more and less than 10wt%

[0184] 1: If the amount of electrolyte immersed in the sample is 10wt% or more and less than 20wt%

[0185] 2: If the amount of electrolyte immersed in the sample is 20wt% or more and less than 40wt%

[0186] 3: If the amount of electrolyte immersed in the sample is 40wt% or more and less than 60wt%

[0187] 4: If the amount of electrolyte immersed in the sample is 60wt% or more and less than 80wt%

[0188] 5: If the amount of electrolyte immersed in the sample is 80wt% or more and less than 100wt%

[0189] Each of the negative electrodes according to Example 2 to Example 5 and Comparative Examples 1 to Comparative Examples 5 was evaluated in substantially the same manner as in Evaluation 1, and the evaluation results are shown in Table 1.

[0190] Table 1

[0191]

[0192] Evaluation 2: Evaluation of high temperature and high voltage charge and discharge cycle characteristics

[0193] The rechargeable lithium battery cell was charged and discharged 200 times under the conditions of 2.0C charge (CC / CV, 4.53V, 0.025C cutoff) / 1.0C discharge (CC, 3V cutoff) at 45°C.

[0194] The thickness increase rate was calculated according to Equation 1, and the capacity retention rate (cycle life) was calculated according to Equation 2, and the results are shown in Table 2.

[0195] Equation 1

[0196] Thickness increase rate = {(full charge thickness after 200th cycle) – (full charge thickness after 1st cycle)} / (full charge thickness after 1st cycle) * 100

[0197] In Equation 1, “full charge thickness” refers to the thickness of the rechargeable lithium battery cell measured after charging at SOC 100% (if the total charge capacity of the rechargeable lithium battery cell is set to 100%, it is charged to 100% charge capacity) after each cycle.

[0198] Equation 2

[0199] Capacity retention rate = (discharge capacity after 200th cycle / discharge capacity after 1st cycle)*100

[0200] Table 2

[0201]

[0202] Summarize

[0203] Referring to Tables 1 and 2, when the electrolyte (Comparative Examples 1 to 3) does not include any additives at all, as the active mass density of the negative electrode increases from 1.65 g / cc to 1.7 g / cc, the impregnation property of the electrolyte to the negative electrode decreases, the thickness of the rechargeable lithium battery cell increases at high temperature and high voltage, and the cycle life decreases.

[0204] However, when the active mass density of the negative electrode is set to 1.7 g / cc, the electrolyte comprising both the first additive and the second additive (Examples 1 to 3) exhibits increased impregnation properties of the electrolyte to the negative electrode, reduced thickness of the rechargeable lithium battery cell at high temperature and high voltage, and increased cycle life, compared to the electrolyte that does not include any additives at all (Comparative Example 3).

[0205] On the other hand, the electrolytes including any one of the first additive and the second additive (Comparative Examples 4 and 5) stably formed SEI films on the negative electrode surface to grow lithium dendrites, and thus the capacity retention rate was sharply deteriorated at high temperature and high voltage. Accordingly, it is beneficial to use an electrolyte including both the first additive and the second additive.

[0206] In addition, the electrolyte including both the first additive and the second additive suppresses the increase in thickness of the rechargeable lithium battery cell and the decrease in cycle life at high temperature and high voltage even if the active mass density of the negative electrode is increased from 1.7 g / cc to 1.8 g / cc (Examples 4 and 5).

[0207] Although 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 present disclosure is not limited to the disclosed embodiments. However, on the contrary, the present disclosure is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the claims and their equivalents.

Claims

1. A rechargeable lithium battery comprising: a positive electrode, including a positive electrode active material; a negative electrode, including a negative electrode active material; and Electrolyte, in: The negative electrode has an active mass density greater than or equal to 1.7 g / cc, and The electrolyte comprises: Lithium salts; Non-aqueous organic solvents; a first additive represented by Chemical Formula 1; and The second additive represented by Chemical Formula 2: Chemical formula 1 R1-OR Wherein, in Chemical Formula 1, R 1 and R 2 Each is independently a fluorine atom or a C1-C10 fluoroalkyl group; Chemical formula 2 Wherein, in Chemical Formula 2, R 3 and R 4 Each is independently a halogen atom or a C1-C10 fluoroalkyl group.

2. The rechargeable lithium battery of claim 1, wherein: The first additive is represented by chemical formula 1-1: Chemical formula 1-1 Among them, in chemical formula 1-1, R 11 ~R 15 are each a hydrogen atom or a fluorine atom, provided that R 11 ~R 15 At least one of is a fluorine atom; and R 21 ~R 27 are each a hydrogen atom or a fluorine atom, provided that R 21 ~R 27 At least one of them is a fluorine atom.

3. The rechargeable lithium battery of claim 1, wherein: The first additive is represented by chemical formula 1-1-1: Chemical formula 1-1-1 4. The rechargeable lithium battery of claim 1, wherein: R 3 and R 4 All are fluorine atoms.

5. The rechargeable lithium battery of claim 1, wherein: The first additive is included in an amount of 1 wt % to 20 wt % based on the total amount of the electrolyte.

6. The rechargeable lithium battery of claim 1, wherein: The second additive is included in an amount of 0.1 wt % to 10 wt % based on the total amount of the electrolyte.

7. The rechargeable lithium battery of claim 1, wherein: The weight ratio of the first additive to the second additive is 20:1 to 2:

1.

8. The rechargeable lithium battery of claim 1, wherein: The non-aqueous organic solvent includes carbonate solvents and propionate solvents.

9. The rechargeable lithium battery of claim 8, wherein: The propionate-based solvent is included in an amount of greater than or equal to 70 volume % based on the total amount of the nonaqueous organic solvent.

10. The rechargeable lithium battery of claim 1, wherein: The lithium salt is LiPF6.

11. The rechargeable lithium battery of claim 1, wherein: The concentration of the lithium salt is 0.1M to 2.0M.

12. The rechargeable lithium battery of claim 1, wherein: The positive electrode active material includes lithium nickel oxide, lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate compound, lithium nickel manganese oxide without cobalt or a combination thereof.

13. The rechargeable lithium battery of claim 1, 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.

14. The rechargeable lithium battery of claim 1, wherein: The rechargeable lithium battery has a charge upper limit voltage greater than or equal to 4.5V.

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