Electrolyte for rechargeable lithium battery and rechargeable lithium battery including same

Abstract

The present invention relates to an electrolyte for a rechargeable lithium battery and a rechargeable lithium battery including same, the electrolyte comprising: a lithium salt; a non-aqueous organic solvent containing a solvent represented by chemical formula 1; and an additive represented by chemical formula 2. [Chemical formula 1] [Chemical formula 2] (The descriptions of each chemical formula are as given in the specification.)

Description

Electrolyte for lithium secondary batteries and lithium secondary batteries containing the same

[0001] The present invention relates to an electrolyte for a lithium secondary battery and a lithium secondary battery including the same.

[0002]

[0003] The recent rapid proliferation of battery-powered electronic devices, such as mobile phones, laptops, and electric vehicles, has led to a rapid increase in demand for high-energy density, high-capacity secondary batteries. Accordingly, active research and development is underway to improve the performance of lithium secondary batteries.

[0004] A lithium secondary battery is a battery that includes a positive electrode and a negative electrode that contain active materials capable of intercalating and deintercalating lithium ions, and an electrolyte, and produces electrical energy through oxidation and reduction reactions when lithium ions are intercalated / deintercalated from the positive electrode and the negative electrode.

[0005] One of the recent development directions for lithium secondary batteries is high capacity. High-capacity lithium secondary batteries require high-voltage charging conditions, but existing electrolytes (e.g., electrolytes containing lithium salts and carbonate-based solvents) are prone to oxidation and decomposition on the cathode surface under high-voltage charging conditions of 4.5 V or higher.

[0006] As the oxidation and decomposition of the electrolyte continues, problems such as depletion of the electrolyte, gas generation and increased resistance within the lithium secondary battery occur, which causes an increase in the thickness of the lithium secondary battery and a decrease in its lifespan.

[0007] Furthermore, the above-mentioned problem becomes more severe as the charge / discharge cycle of the lithium secondary battery continues, which may lead to safety issues such as structural deterioration of the positive electrode active material and thermal runaway of the lithium secondary battery.

[0008]

[0009] One embodiment provides an electrolyte for a lithium secondary battery that can suppress an increase in thickness and a decrease in lifespan of the lithium secondary battery even under high-voltage charging conditions.

[0010] Another embodiment provides a lithium secondary battery comprising the electrolyte for the lithium secondary battery.

[0011]

[0012] One embodiment provides an electrolyte for a lithium secondary battery, comprising: a lithium salt; a non-aqueous organic solvent comprising a solvent represented by the following chemical formula 1; and an additive represented by the following chemical formula 2:

[0013] [Chemical Formula 1]

[0014]

[0015] [Chemical Formula 2]

[0016] .

[0017] Another embodiment provides a lithium secondary battery comprising a positive electrode including a positive active material; a negative electrode including a negative active material; and the electrolyte.

[0018]

[0019] An electrolyte for a lithium secondary battery according to one embodiment can suppress an increase in thickness and a decrease in lifespan of a lithium secondary battery even under high voltage charging conditions.

[0020]

[0021] Figures 1 to 4 are schematic diagrams illustrating a lithium secondary battery according to one embodiment.

[0022]

[0023] Hereinafter, embodiments of the present invention will be described in detail. However, these are presented as examples and are not intended to limit the present invention. The present invention is defined solely by the scope of the claims set forth below.

[0024] Unless otherwise specified herein, when a part such as a layer, film, region, or plate is said to be “on top of” another part, this includes not only cases where it is “directly on top of” the other part, but also cases where there are other parts in between.

[0025] Unless otherwise specified herein, the singular may also include the plural. Furthermore, unless otherwise specified, "A or B" may mean "including A, including B, or including A and B."

[0026] As used herein, “combination thereof” may mean mixtures, laminates, composites, copolymers, alloys, blends, and reaction products of the components.

[0027] Unless otherwise defined herein, 'substitution' means that a hydrogen atom in a compound is replaced by a halogen atom (F, Cl, Br or I), a hydroxy group, an alkoxy group, a nitro group, a cyano group, an amino group, an azido group, an amidino group, a hydrazino group, a hydrazono group, a carbonyl group, a carbamyl group, a thiol group, an ester group, a carboxyl group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid or a salt thereof, a C1 to C20 alkyl group, a C2 to C20 alkenyl group, a C2 to C20 alkynyl group, a C6 to C30 aryl group, a C7 to C30 arylalkyl group, a C1 to C4 alkoxy group, a C1 to C20 heteroalkyl group, a C3 to C20 heteroarylalkyl group, a C3 to C30 cycloalkyl group, a C3 to C15 cycloalkenyl group, a C6 to C15 cycloalkynyl group, It means substituted with a substituent selected from C2 to C20 heterocycloalkyl groups and combinations thereof.

[0028] Unless otherwise defined in the chemical formulas herein, if a chemical bond is not drawn at a position where a chemical bond should be drawn, it means that a hydrogen atom is bonded at that position.

[0029]

[0030] (electrolyte)

[0031] One embodiment provides an electrolyte for a lithium secondary battery, comprising: a lithium salt; a non-aqueous organic solvent comprising a solvent represented by the following chemical formula 1; and an additive represented by the following chemical formula 2:

[0032] [Chemical Formula 1]

[0033]

[0034] In the above chemical formula 1,

[0035] R 1 is a substituted or unsubstituted alkyl group having 3 to 10 carbon atoms,

[0036] R 2 may be a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms.

[0037] [Chemical Formula 2]

[0038] .

[0039] In the above chemical formula 2,

[0040] R 3 and R 4 Each independently may be a halogen atom or a fluoroalkyl group having 1 to 10 carbon atoms.

[0041]

[0042] In the above chemical formula 1, R 1 When the carbon number is 3 or more, the solvent represented by the chemical formula 1 may be suitable for use in a high voltage environment of 4.5 V or more, as it has high oxidation resistance.

[0043] Meanwhile, the second additive is an oxalatoborate compound substituted with a halogen group (e.g., a fluoro group), and the halogen group can stabilize a lithium salt (e.g., LiPF6).

[0044] Accordingly, when an electrolyte solution containing the second additive is used, the generation of HF is suppressed, thereby preventing the elution 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.

[0045] Therefore, an electrolyte solution of one embodiment simultaneously including a solvent represented by the above chemical formula 1 and an additive represented by the above chemical formula 2 can suppress an increase in thickness and a decrease in lifespan of a lithium secondary battery.

[0046]

[0047] Hereinafter, an electrolyte for a lithium secondary battery according to an embodiment is described in more detail.

[0048]

[0049] non-aqueous organic solvent

[0050] The above non-aqueous organic solvent acts as a medium through which ions involved in the electrochemical reaction of the battery can move.

[0051] An electrolyte for a lithium secondary battery according to one embodiment includes, as described above, a solvent represented by the chemical formula 1.

[0052] In the above chemical formula 1, R 1 can be a propyl group or a butyl group, and R 2 can be an ethyl group or a propyl group.

[0053] The solvent represented by the above chemical formula 1 may include, for example, a solvent represented by the following chemical formula 1-1, a solvent represented by the following chemical formula 1-2, or a combination thereof:

[0054] [Chemical Formula 1-1]

[0055]

[0056] [Chemical Formula 1-2]

[0057] .

[0058]

[0059] The solvent represented by the above chemical formula 1 may be included in an amount of 40% by volume or more, 50% by volume or more, 60% by volume or more, 70% by volume or more, or 75% by volume or more, based on the total volume of the non-aqueous organic solvent. The upper limit is not specific, but may be 85% by volume or less, or 80% by volume or less.

[0060] When the above ranges are satisfied, the oxidation resistance of the electrolyte can be increased while suppressing changes in the thickness of the lithium secondary battery.

[0061] Meanwhile, in comparison to the case where only one of the solvent represented by the above chemical formula 1-1 and the solvent represented by the above chemical formula 1-2 is used, when the solvent represented by the above chemical formula 1-1 and the solvent represented by the above chemical formula 1-2 are mixed and used, the effect of increasing the oxidation resistance of the electrolyte while suppressing the change in thickness of the lithium secondary battery is more outstandingly exhibited, which may be advantageous in improving the lifespan of the lithium secondary battery.

[0062] When the solvent represented by the above chemical formula 1-1 and the solvent represented by the above chemical formula 1-2 are mixed and used, the solvent represented by the above chemical formula 1-1 may be included in an amount of 35 to 55% by volume, or 40 to 50% by weight, based on the total volume of the non-aqueous organic solvent; and the solvent represented by the above chemical formula 1-2 may be included in an amount of 20 to 40% by weight, or 25 to 35% by weight.

[0063] The above non-aqueous organic solvent may further include a carbonate solvent. The carbonate solvent has the effect of improving the mobility of lithium ions and improving battery life characteristics.

[0064] Examples of the above carbonate solvents that can be used include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), ethylmethyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC).

[0065] The above carbonate solvents can be used alone or in combination of two or more.

[0066] For example, the carbonate solvent may include ethylene carbonate (EC) and propylene carbonate (PC).

[0067] In this case, with respect to the total volume of the non-aqueous organic solvent, the solvent represented by the chemical formula 1 may be included in an amount of 70 to 90% by volume, or 70 to 80% by volume; the ethylene carbonate (EC) may be included in an amount of 1 to 15% by volume, or 5 to 10% by volume; and the propylene carbonate (PC) may be included in an amount of 5 to 20% by volume, or 15 to 20% by volume. Within this range, the effects of the solvent represented by the chemical formula 1 and the carbonate-based solvents may be harmonized.

[0068]

[0069] additives

[0070] An electrolyte for a lithium secondary battery according to one embodiment includes, as described above, an additive represented by the chemical formula 2.

[0071] The additive represented by the above chemical formula 2 may be, for example, a compound represented by the following chemical formula 2-1.

[0072] [Chemical Formula 2-1]

[0073]

[0074]

[0075] The additive may be included in an amount of 0.1 to 10 wt%, 0.5 to 7 wt%, or 1 to 5 wt%, based on the total amount of the electrolyte. Within this range, the electrolyte including the additive represented by the chemical formula 2 can effectively suppress the generation and growth of lithium dendrites.

[0076] Preferably, the additive may be included in an amount of 0.5 to 1 wt% relative to the total amount of the electrolyte. When the type and mixing ratio of the non-aqueous organic solvent are the same, the effect may be excellent when the additive content is within 0.5 to 1 wt% compared to when it exceeds 1 wt%.

[0077]

[0078] lithium salt

[0079] The above lithium salt is a substance that is dissolved in an organic solvent and acts as a source of lithium ions within the battery, enabling the basic operation of a lithium secondary battery and promoting the movement of lithium ions between the positive and negative electrodes.

[0080] LiPF6 can be used as the above lithium salt.

[0081] The concentration of the lithium salt may be 0.1 M to 2.0 M.

[0082]

[0083] (lithium secondary battery)

[0084] Another embodiment provides a lithium secondary battery comprising a positive electrode including a positive active material; a negative electrode including a negative active material; and the electrolyte.

[0085]

[0086] A lithium secondary battery according to one embodiment includes the electrolyte of the above-described embodiment, so that even if the charging voltage of the battery is increased and / or the composite density of the negative electrode is increased, the lifespan can be improved while the increase in resistance can be suppressed.

[0087]

[0088] Hereinafter, descriptions overlapping with the above will be omitted, and a lithium secondary battery according to an embodiment will be described in more detail.

[0089]

[0090] upper limit charging voltage

[0091] A lithium secondary battery according to one embodiment can have an improved lifespan even at high voltage while suppressing an increase in resistance by including the electrolyte of the above-described embodiment.

[0092] Specifically, the lithium secondary battery may have a charging upper limit voltage of 4.5 V or higher.

[0093]

[0094] positive electrode active material

[0095] A compound capable of reversible intercalation and deintercalation of lithium (a lithiated intercalation compound) can be used as a cathode active material. Specifically, one or more of a composite oxide of lithium and a metal selected from cobalt, manganese, nickel, and combinations thereof can be used.

[0096] The above composite oxide may be a lithium transition metal composite oxide, and specific examples thereof include lithium nickel-based oxide, lithium cobalt-based oxide, lithium manganese-based oxide, lithium iron phosphate-based compound, cobalt-free nickel-manganese-based oxide, or a combination thereof.

[0097] 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 Cob 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 NiG b O2(0.90≤a≤1.8, 0.001≤b≤0.1); Li a CoG b O2(0.90≤a≤1.8, 0.001≤b≤0.1); Li a Mn 1-b G b O2(0.90≤a≤1.8, 0.001≤b≤0.1); Li a Mn2G b O4(0.90≤a≤1.8, 0.001≤b≤0.1); Li a Mn 1-g G g PO4(0.90≤a≤1.8, 0≤g≤0.5); Li (3-f) Fe2(PO4)3(0≤f≤2); Li a FePO4(0.90≤a≤1.8).

[0098] 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; L 1 is Mn, Al or a combination thereof.

[0099] For example, the cathode active material may be a high-nickel cathode active material in which the nickel content is 80 mol% or more, 85 mol% or more, 90 mol% or more, 91 mol% or more, or 94 mol% or more and 99 mol% or less, based on 100 mol% of metals excluding lithium in the lithium transition metal composite oxide. The high-nickel cathode active material can realize high capacity and thus can be applied to high-capacity, high-density lithium secondary batteries.

[0100] The cathode active material may include, for example, a lithium nickel-based oxide represented by the following chemical formula 11, a lithium cobalt-based oxide represented by the following chemical formula 12, a lithium iron phosphate-based compound represented by the following chemical formula 13, a cobalt-free lithium nickel-manganese-based oxide represented by the following chemical formula 14, or a combination thereof.

[0101] [Chemical Formula 11]

[0102] Li a1 Ni x1 M 1 y1 M 2 z1 O 2-b1 X b1

[0103] In the above 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, and M 1 and M 2 are each independently one or more elements selected from the group consisting of 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 the group consisting of F, P, and S.

[0104] In the above chemical formula 1, 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.

[0105] [Chemical Formula 12]

[0106] Li a2 Co x2 M 3 y2 O 2-b2 X b2

[0107] In the above 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, and M 3 is one or more elements selected from the group consisting of 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 the group consisting of F, P and S.

[0108] [Chemical Formula 13]

[0109] Li a3 Fe x3 M 4 y3 PO 4-b3 X b3

[0110] In the above chemical formula 13, 0.9≤a3≤1.8, 0.6≤x3≤1, 0≤y3≤0.4, and 0≤b3≤0.1, and M 4 is one or more elements selected from the group consisting of 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 the group consisting of F, P and S.

[0111] [Chemical Formula 14]

[0112] Li a4 Ni x4 Mn y4 M 5 z4 O 2-b4 X b4

[0113] In the above chemical formula 14, 0.9≤a2≤1.8, 0.8≤x4<1, 0 <y4≤0.2, 0≤z4≤0.2, 0.9≤x4+y4+z4≤1.1, 및 0≤b4≤0.1이고 M 5 is one or more elements selected from the group consisting of 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 the group consisting of F, P, and S.

[0114] In particular, the electrolyte of the above-described embodiment can significantly improve the high-voltage characteristics of a battery using a lithium cobalt-based oxide represented by the chemical formula 12.

[0115]

[0116] anode

[0117] A positive electrode for a lithium secondary battery may include a current collector and a positive electrode active material layer formed on the current collector. The positive electrode active material layer includes a positive electrode active material and may further include a binder and / or a conductive material.

[0118] For example, the anode may further include an additive that can act as a sacrificial anode.

[0119] The content of the positive electrode active material may be 90 wt% to 99.5 wt% with respect to 100 wt% of the positive electrode active material layer, and the contents of the binder and conductive material may be 0.5 wt% to 5 wt%, respectively, with respect to 100 wt% of the positive electrode active material layer.

[0120] The above binder serves to adhere the positive electrode active material particles well to each other and also to adhere the positive electrode active material well to the current collector. Representative examples of the binder include, but are not limited to, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing 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, nylon, etc.

[0121] The conductive material is used to provide conductivity to the electrode, and any material that does not cause chemical changes and is electronically conductive can be used in the battery. Examples of the conductive material include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanofiber, and carbon nanotube; metal-based materials containing copper, nickel, aluminum, silver, etc. in the form of metal powder or metal fiber; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0122] Al may be used as the above current collector, but is not limited thereto.

[0123]

[0124] Negative active material

[0125] The negative electrode active material includes a material capable of reversibly intercalating / deintercalating lithium ions, lithium metal, an alloy of lithium metal, a material capable of doping and dedoping lithium, or a transition metal oxide.

[0126] The material capable of reversibly intercalating / deintercalating the lithium ions may include a carbon-based negative electrode active material, for example, crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon include graphite such as natural graphite or artificial graphite in an amorphous, plate-like, flake-like, spherical, or fibrous form, and examples of the amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, calcined coke, and the like.

[0127] As the above lithium metal alloy, an alloy of lithium and a metal selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn can be used.

[0128] As the material capable of doping and dedoping the lithium, a Si-based negative electrode active material or a Sn-based negative electrode active material may be used. The Si-based negative electrode active material may be silicon, a silicon-carbon composite, SiOx (0 < x < 2), a Si-Q alloy (wherein 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), or a combination thereof. The Sn-based negative electrode active material may be Sn, SnO2, a Sn-based alloy, or a combination thereof.

[0129] The silicon-carbon composite may be a composite of silicon and amorphous carbon. According to one embodiment, 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 composite may include secondary particles (cores) in which silicon primary particles are assembled and an amorphous carbon coating layer (shell) positioned on the surface of the secondary particles. The amorphous carbon may also be positioned between the silicon primary particles, such that, for example, the silicon primary particles may be coated with amorphous carbon. The secondary particles may be dispersed and present in an amorphous carbon matrix.

[0130] The silicon-carbon composite may further comprise crystalline carbon. For example, the silicon-carbon composite may comprise a core comprising crystalline carbon and silicon particles and an amorphous carbon coating layer positioned on the surface of the core.

[0131] The above Si-based negative electrode active material or Sn-based negative electrode active material can be used in a mixture with a carbon-based negative electrode active material.

[0132]

[0133] cathode

[0134] A negative electrode for a lithium secondary battery includes a current collector and a negative electrode active material layer positioned on the 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.

[0135] For example, the negative electrode active material layer may include 90 to 99 wt% of the negative electrode active material, 0.5 to 5 wt% of the binder, and 0 to 5 wt% of the conductive material.

[0136] The above binder serves to adhere the negative electrode active material particles well to each other and also to adhere the negative electrode active material well to the current collector. The binder may be a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof.

[0137] Examples of the non-aqueous binder include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or combinations thereof.

[0138] The above-mentioned aqueous binder may be selected from styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluoroelastomer, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, poly(meth)acrylonitrile, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenol resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0139] When using an aqueous binder as the above-mentioned negative electrode binder, a cellulose-based compound capable of imparting viscosity may be further included. The cellulose-based compound may be a mixture of one or more of carboxymethyl cellulose, hydroxypropylmethyl cellulose, methyl cellulose, or an alkali metal salt thereof. The alkali metal may be Na, K, or Li.

[0140] The above dry binder is a polymeric material capable of being fiberized, and may be, for example, polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0141] The conductive material is used to provide conductivity to the electrode, and any material that does not cause chemical changes and is electronically conductive can be used in the battery. Specific examples 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 in the form of metal powder or metal fibers, including copper, nickel, aluminum, and silver; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0142] The negative electrode current collector may be selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and a combination thereof.

[0143]

[0144] separator

[0145] Depending on the type of lithium secondary battery, a separator may be present between the positive and negative electrodes. Such separators may include polyethylene, polypropylene, polyvinylidene fluoride, or multilayer films comprising two or more layers thereof. Furthermore, mixed multilayer films such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, or a polypropylene / polyethylene / polypropylene three-layer separator may also be used.

[0146] The above separator may include a porous substrate and a coating layer comprising an organic material, an inorganic material, or a combination thereof, positioned on one or both sides of the porous substrate.

[0147] The above porous substrate may be a polymer film formed of any one polymer selected from polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyacetal, polyamide, polyimide, polycarbonate, polyether ketone, polyarylether ketone, polyetherimide, polyamideimide, polybenzimidazole, polyethersulfone, polyphenylene oxide, cyclic olefin copolymer, polyphenylene sulfide, polyethylene naphthalate, glass fiber, Teflon, and polytetrafluoroethylene, or a copolymer or mixture of two or more thereof.

[0148] The above organic material may include a polyvinylidene fluoride-based antibody or a (meth)acrylic polymer.

[0149] The above inorganic materials are Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, It may include inorganic particles selected from, but not limited to, SrTiO3, BaTiO3, Mg(OH)2, boehmite, and combinations thereof.

[0150] The organic and inorganic substances may be mixed and present in one coating layer, or a coating layer including an organic substance and a coating layer including an inorganic substance may be present in a laminated form.

[0151]

[0152] lithium secondary battery

[0153] Lithium secondary batteries can be classified into cylindrical, square, pouch, coin, etc. types according to their shapes. FIGS. 1 to 4 are schematic diagrams illustrating lithium secondary batteries according to one embodiment, wherein FIG. 1 can be said to be a cylindrical battery, FIG. 2 a square battery, and FIGS. 3 and 4 a pouch battery. Referring to FIGS. 1 to 4, a lithium secondary battery (100) may include an electrode assembly (40) having a separator (30) interposed between a positive electrode (10) and a negative electrode (20), and a case (50) in which the electrode assembly (40) is built. The positive electrode (10), the negative electrode (20), and the separator (30) may be impregnated with an electrolyte (not shown). The lithium secondary battery (100) may include a sealing member (60) that seals the case (50) as shown in FIG. 1. In addition, in FIG. 2, the lithium secondary battery (100) may include a positive lead tab (11), a positive terminal (12), a negative lead tab (21), and a negative terminal (22). As in FIGS. 3 and 4, the lithium secondary battery (100) may include electrode tabs (70), i.e., a positive tab (71) and a negative tab (72), which serve as electrical paths for inducing current formed in the electrode assembly (40) to the outside.

[0154]

[0155] A lithium secondary battery according to one embodiment of the present invention can be applied to automobiles, mobile phones, and / or various types of electrical devices, but the present invention is not limited thereto.

[0156]

[0157] Hereinafter, examples and comparative examples of the present invention will be described. However, the following examples are merely examples of the present invention, and the present invention is not limited to the following examples.

[0158]

[0159] Examples and Comparative Examples

[0160] An electrolyte and a lithium secondary battery were manufactured using the following method.

[0161]

[0162] Example 1

[0163] (1) Preparation of electrolyte

[0164] An electrolyte was prepared by dissolving 1.3 M LiPF6 in a non-aqueous organic solvent containing ethylene carbonate (EC), propylene carbonate (PC), and a solvent represented by the following chemical formula 1-1 (propyl butyrate (PB); CAS No.: 105-66-8) in a 15:15:70 ratio, and adding 1 wt% of an additive represented by the following chemical formula 2-1 (lithium difluoro(oxalato)borate; CAS No.: 409071-16-5):

[0165] [Chemical Formula 1-1]

[0166]

[0167] [Chemical Formula 2-1]

[0168]

[0169] (2) Manufacturing of lithium secondary batteries

[0170] LiCoO2 as a positive electrode active material, polyvinylidene fluoride as a binder, and acetylene black as a conductive material were mixed in a weight ratio of 96:3:1, and dispersed in N-methyl pyrrolidone to prepare a positive electrode active material slurry.

[0171] The above positive electrode active material slurry was coated on a 15 μm thick Al foil, dried at 100°C, and then pressed to manufacture a positive electrode.

[0172] Artificial graphite was used as the negative active material, and the negative active material, styrene-butadiene rubber binder, and carboxymethyl cellulose were mixed in a weight ratio of 98:1:1, respectively, and dispersed in distilled water to prepare a negative active material slurry.

[0173] The above negative active material slurry was coated on a 10 μm thick Cu foil, dried at 100°C, and then pressed to manufacture a negative electrode.

[0174] An electrode assembly was manufactured by assembling the positive electrode and the negative electrode and a separator made of polyethylene material having a thickness of 10 μm, and the electrolyte was injected to manufacture a lithium secondary battery.

[0175]

[0176] Example 2

[0177] An electrolyte and a lithium secondary battery were manufactured in the same manner as in Example 1, except that a non-aqueous organic solvent containing ethylene carbonate (EC), propylene carbonate (PC), and a solvent represented by the chemical formula 1-1 in a 10:15:75 mixture was used in the manufacture of the electrolyte.

[0178]

[0179] Example 3

[0180] An electrolyte and a lithium secondary battery were manufactured in the same manner as in Example 1, except that a non-aqueous organic solvent containing ethylene carbonate (EC), propylene carbonate (PC), and a solvent represented by the chemical formula 1-1 in a 10:10:80 mixture was used in the manufacture of the electrolyte.

[0181]

[0182] Example 4

[0183] An electrolyte and a lithium secondary battery were manufactured in the same manner as in Example 2, except that 0.5 wt% of the additive represented by the chemical formula 2-1 was added during the manufacture of the electrolyte.

[0184]

[0185] Example 5

[0186] An electrolyte and a lithium secondary battery were manufactured in the same manner as in Example 2, except that 3 wt% of the additive represented by the chemical formula 2-1 was added during the manufacture of the electrolyte.

[0187]

[0188] Example 6

[0189] An electrolyte and a lithium secondary battery were manufactured in the same manner as in Example 2, except that 5 wt% of the additive represented by the chemical formula 2-1 was added during the manufacture of the electrolyte.

[0190]

[0191] Example 7

[0192] (1) Preparation of electrolyte

[0193] An electrolyte was prepared by dissolving 1.3 M LiPF6 in a non-aqueous organic solvent containing ethylene carbonate (EC), propylene carbonate (PC), a solvent represented by the above chemical formula 1-1, and a solvent represented by the following chemical formula 1-2 (ethyl pentanoate; CAS No.: 539-82-2) in a ratio of 10:15:40:35, and adding 1 wt% of an additive represented by the above chemical formula 2-1:

[0194] [Chemical Formula 1-2]

[0195]

[0196] (2) Manufacturing of lithium secondary batteries

[0197] An electrolyte and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the above electrolyte was used.

[0198]

[0199] Example 8

[0200] An electrolyte and a lithium secondary battery were manufactured in the same manner as in Example 1, except that a non-aqueous organic solvent containing ethylene carbonate (EC), propylene carbonate (PC), a solvent represented by the above chemical formula 1-1, and a solvent represented by the above chemical formula 1-2 mixed in a ratio of 10:15:45:30 was used in the manufacture of the electrolyte.

[0201]

[0202] Example 9

[0203] An electrolyte and a lithium secondary battery were manufactured in the same manner as in Example 1, except that a non-aqueous organic solvent containing ethylene carbonate (EC), propylene carbonate (PC), a solvent represented by the above chemical formula 1-1, and a solvent represented by the above chemical formula 1-2 mixed in a ratio of 10:15:50:25 was used when manufacturing the electrolyte.

[0204]

[0205] Comparative Example 1

[0206] (1) Preparation of electrolyte

[0207] An electrolyte was prepared by dissolving 1.3 M LiPF6 in a non-aqueous organic solvent containing ethylene carbonate (EC), propylene carbonate (PC), and a solvent represented by the following chemical formula 3 (propyl propionate; CAS No.: 106-36-5) in a ratio of 10:15:75:

[0208] [Chemical Formula 3]

[0209]

[0210] (2) Manufacturing of lithium secondary batteries

[0211] A lithium secondary battery was manufactured in the same manner as in Example 1, except that the above electrolyte was used.

[0212]

[0213] Comparative Example 2

[0214] (1) Preparation of electrolyte

[0215] An electrolyte was prepared by dissolving 1.3 M LiPF6 in a non-aqueous organic solvent containing ethylene carbonate (EC), propylene carbonate (PC), and a solvent represented by the above chemical formula 3 in a 10:15:75 mixture, and adding 1 wt% of an additive represented by the above chemical formula 2-1:

[0216] (2) Manufacturing of lithium secondary batteries

[0217] A lithium secondary battery was manufactured in the same manner as in Example 1, except that the above electrolyte was used.

[0218]

[0219] Each electrolyte according to Examples 1 to 9 and Comparative Examples 1 and 2 is summarized in Table 1 below.

[0220]

[0221] Non-aqueous organic solvent (vol%) Additive (wt%) ECPC Chemical formula 1-1 Chemical formula 1-2 Chemical formula 3 Chemical formula 2-1 Example 1 151570--1 Example 2 101575--1 Example 3 101080--1 Example 4 101575--0.5 Example 5 101575--3 Example 6 101575--5 Example 7 10154035-1 Example 8 10154530-1 Example 9 10155025-1 Comparative example 11015--75-Comparative example 2 1015--751

[0222] In the above Table 1, the solvent content represents the volume % occupied by each solvent among the volume of non-aqueous organic solvent (100 volume %), and the additive content represents the weight % occupied by the additive among the weight (100 weight %) of the total electrolyte solution including non-aqueous organic solvent + lithium salt + additive.

[0223]

[0224] Evaluation Example: Evaluation of high-temperature charge / discharge cycle characteristics

[0225] The cycle characteristics of the lithium secondary batteries according to Examples 1 to 9 and Comparative Examples 1 and 2 were evaluated after charge and discharge under the following conditions, and the results are shown in Table 2.

[0226] After 200 cycles of charge and discharge under conditions of 45℃, 0.33C charge (CC / CV, 4.53V, 0.025C Cut-off) / 1.0C discharge (CC, 2.5V Cut-off), the capacity retention rate and the thickness change rate of the battery were measured.

[0227] The capacity retention rate was calculated according to Equation 1 below, and the thickness change rate of the battery was calculated according to Equation 2 below.

[0228] [Formula 1]

[0229] Capacity retention rate = (discharge capacity after 200 cycles / discharge capacity after 1 cycle) * 100

[0230] [Formula 2]

[0231] Battery thickness change rate = [(battery thickness after 200 cycles) - (battery thickness after 1 cycle)] / (battery thickness after 1 cycle) * 100

[0232]

[0233] Capacity retention rate after 200 cycles (%) @45℃ Thickness change rate after 200 cycles (%) @45℃ Example 1787.5 Example 2837.0 Example 37910.1 Example 4809.6 Example 57710.2 Example 67912.3 Example 7815.8 Example 8866.0 Example 9834.5 Comparative example 16516.5 Comparative example 27217.0

[0234] According to Table 1 above, it can be seen that, in Examples 1 to 9, the thickness change of the lithium secondary battery was suppressed and the capacity retention rate (lifespan) was increased even under high voltage charging conditions of 4.5 V or higher, compared to Comparative Examples 1 and 2.

[0235] Although the preferred embodiments of the present invention have been described above, the present invention is not limited thereto, and various modifications can be made within the scope of the patent claims, the detailed description of the invention, and the attached drawings, and it is obvious that this also falls within the scope of the present invention.

[0236]

[0237] [Explanation of symbols]

[0238] 100: Lithium secondary battery 10: Cathode

[0239] 11: Positive lead tab 12: Positive terminal

[0240] 20: Negative lead tab 21: Negative lead tab

[0241] 22: Negative terminal 30: Separator

[0242] 40: Electrode assembly 50: Case

[0243] 60: Sealing member 70: Electrode tab

[0244] 71: Positive tab 72: Negative tab

Claims

1. Lithium salt; A non-aqueous organic solvent comprising a solvent represented by the following chemical formula 1; and Containing an additive represented by the following chemical formula 2, Electrolyte for lithium secondary batteries: [Chemical Formula 1] In the above chemical formula 1, R 1 is a substituted or unsubstituted alkyl group having 3 to 10 carbon atoms; R 2 is a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms; [Chemical formula 2] In the above chemical formula 2, R 3 and R 4 are each independently a halogen atom or a fluoroalkyl group having 1 to 10 carbon atoms.

2. In paragraph 1, R 1 An electrolyte for lithium secondary batteries, which is a silver propyl group or butyl group.

3. In paragraph 1, R 2 An electrolyte for lithium secondary batteries containing an ethyl or propyl group.

4. In paragraph 1, The solvent represented by the chemical formula 1 above is an electrolyte for a lithium secondary battery, which includes a solvent represented by the chemical formula 1-1 below, a solvent represented by the chemical formula 1-2 below, or a combination thereof: [Chemical Formula 1-1] [Chemical Formula 1-2] .

5. In paragraph 1, An electrolyte for a lithium secondary battery, wherein the solvent represented by the chemical formula 1 is contained in an amount of 40% by volume or more based on the total volume of the non-aqueous organic solvent.

6. In paragraph 1, An electrolyte for a lithium secondary battery, wherein the non-aqueous organic solvent further comprises a carbonate solvent.

7. In paragraph 6, The above carbonate solvent is an electrolyte for a lithium secondary battery including ethylene carbonate (EC) and propylene carbonate (PC).

8. In paragraph 7, An electrolyte for a lithium secondary battery, wherein the solvent represented by the chemical formula 1 is contained in an amount of 70 to 90 volume%, the ethylene carbonate (EC) is contained in an amount of 1 to 15 volume%, and the propylene carbonate (PC) is contained in an amount of 5 to 20 volume%, based on the total volume of the non-aqueous organic solvent.

9. In paragraph 1, The above chemical formula 2 is an electrolyte for a lithium secondary battery represented by the following chemical formula 2-1: [Chemical Formula 2-1] .

10. In paragraph 1, An electrolyte for a lithium secondary battery, wherein the additive is contained in an amount of 0.1 to 10 wt% based on the total amount of the electrolyte.

11. In paragraph 1, The above lithium salt is an electrolyte for a lithium secondary battery, which is LiPF6.

12. In paragraph 1, An electrolyte for a lithium secondary battery, wherein the concentration of the lithium salt is 0.1 M to 2.0 M.

13. A cathode comprising a cathode active material; A negative electrode comprising a negative active material; and Electrolyte according to any one of the provisions of paragraphs 1 to 12 A lithium secondary battery comprising:

14. In paragraph 13, A lithium secondary battery wherein the positive electrode active material comprises lithium nickel-based oxide, lithium cobalt-based oxide, lithium manganese-based oxide, lithium iron phosphate-based compound, cobalt-free nickel-manganese oxide, or a combination thereof.

15. In paragraph 13, A lithium secondary battery comprising the above negative electrode active material, a carbon-based negative electrode active material, a Si-based negative electrode active material, or a combination thereof.

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