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 including a solvent represented by chemical formula 1 below; and an additive represented by chemical formula 2 below. [Chemical formula 1] [Chemical formula 2] (The description of each of the chemical formulas is as set forth 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] However, as lithium secondary batteries are repeatedly charged and discharged, lithium dendrites form on the surface of the negative electrode, reducing its lifespan and / or increasing resistance, potentially leading to internal short circuits. This phenomenon becomes more severe as the charging voltage of the lithium secondary battery increases and / or the negative electrode composite density increases.

[0006]

[0007] One embodiment provides an electrolyte for a lithium secondary battery that improves the lifespan of the lithium secondary battery while suppressing an increase in resistance even when the charging voltage of the lithium secondary battery is increased and / or the composite density of the negative electrode is increased.

[0008] Another embodiment provides a lithium secondary battery comprising the electrolyte for the lithium secondary battery.

[0009]

[0010] 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:

[0011] [Chemical Formula 1]

[0012]

[0013] [Chemical Formula 2]

[0014] .

[0015] 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.

[0016]

[0017] An electrolyte for a lithium secondary battery according to one embodiment can improve the life of a lithium secondary battery while suppressing an increase in resistance even when the charging voltage of the lithium secondary battery is increased and / or the composite density of the negative electrode is increased.

[0018]

[0019] Figures 1 to 4 are schematic diagrams illustrating a lithium secondary battery according to one embodiment.

[0020]

[0021] 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.

[0022] 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 is another part in between.

[0023] 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."

[0024] As used herein, “combination thereof” may mean mixtures, laminates, composites, copolymers, alloys, blends, and reaction products of the components.

[0025] 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.

[0026] 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.

[0027] In this specification, the “composite density of the negative electrode” is a value calculated by dividing the weight of the components (active material, conductive material, binder, etc.) excluding the current collector in the negative electrode by the volume.

[0028]

[0029] (electrolyte)

[0030] 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:

[0031] [Chemical Formula 1]

[0032]

[0033] [Chemical Formula 2]

[0034] .

[0035]

[0036] In the above chemical formula 1, R 1 has 3 or more carbon atoms, and R 1 In contrast to the case where the carbon number is 2 or less, the oxidation resistance is high. Therefore, the solvent represented by the above chemical formula 1 is suitable for use in a high voltage environment of 4.5 V or higher.

[0037] Meanwhile, in the above chemical formula 2, R 3 and R 4 are each independently an aryl group, and R 3 and R 4 In contrast to the case where each independently represents an alkyl group or an alkenyl group, it is advantageous in suppressing the generation and growth of lithium dendrites. Accordingly, the additive represented by the above chemical formula 2 can suppress the generation and growth of lithium dendrites and enable lithium ions to enter the negative electrode evenly even if the composite density of the negative electrode is increased.

[0038] Therefore, an electrolyte 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 resistance while improving the life of a lithium secondary battery, even if the charging voltage of the lithium secondary battery is increased and / or the composite density of the negative electrode is increased.

[0039]

[0040] Hereinafter, an electrolyte for a lithium secondary battery according to an embodiment is described in more detail.

[0041]

[0042] non-aqueous organic solvent

[0043] The above non-aqueous organic solvent acts as a medium through which ions involved in the electrochemical reaction of the battery can move.

[0044]

[0045] An electrolyte for a lithium secondary battery according to one embodiment includes a solvent represented by the chemical formula 1, as described above. In the chemical formula 1, R 1 may be a substituted or unsubstituted alkyl group having 3 to 10 carbon atoms. For example, R 1 It may be a profiler.

[0046] In the above chemical formula 1, R 2 may be a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms. For example, R 2 may be an ethyl group.

[0047] Representative examples of the solvent represented by the above chemical formula 1 are as follows:

[0048] [Chemical Formula 1-1]

[0049]

[0050] The solvent represented by the above chemical formula 1 may be included in an amount of 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. Within this range, the electrolyte containing the solvent represented by the above chemical formula 1 may exhibit high oxidation resistance.

[0051]

[0052] The above non-aqueous organic solvent may further include a carbonate solvent.

[0053] 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).

[0054] The above carbonate solvents can be used alone or in combination of two or more.

[0055] For example, among the above carbonate solvents, cyclic carbonates such as ethylene carbonate (EC) and propylene carbonate (PC) can be mixed and used. The mixture of ethylene carbonate (EC) and propylene carbonate (PC) has a high dielectric constant, so it dissociates lithium salts to produce lithium ions and has the effect of moving lithium ions. However, the mixture of ethylene carbonate (EC) and propylene carbonate (PC) has a very high viscosity, so if applied in excess, the performance of the lithium secondary battery may deteriorate.

[0056] 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 85 vol%, or 75 to 80 vol%; the ethylene carbonate (EC) may be included in an amount of 1 to 15 vol%, or 5 to 10 vol%; and the propylene carbonate (PC) may be included in an amount of 5 to 20 vol%, or 15 to 20 vol%. In this range, the effects of the solvent represented by the chemical formula 1 and the effects of the mixture of the ethylene carbonate (EC) and the propylene carbonate (PC) may be harmonized.

[0057]

[0058] additives

[0059] An electrolyte for a lithium secondary battery according to one embodiment includes, as described above, an additive represented by the chemical formula 2.

[0060] In the above chemical formula 2, R 3 and R 4 Each independently may be a substituted or unsubstituted aryl group having 6 to 20 carbon atoms. For example, R 3 and R 4 At least one of them may be a phenyl group.

[0061] Representative examples of the additive represented by the above chemical formula 2 are as follows:

[0062] [Chemical Formula 2-1]

[0063]

[0064] 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.

[0065]

[0066] lithium salt

[0067] 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.

[0068] LiPF6 can be used as the above lithium salt.

[0069] The concentration of the lithium salt may be 0.1 M to 2.0 M.

[0070]

[0071] (lithium secondary battery)

[0072] 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.

[0073]

[0074] 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.

[0075]

[0076] Hereinafter, descriptions overlapping with the above will be omitted, and a lithium secondary battery according to an embodiment will be described in more detail.

[0077]

[0078] upper limit charging voltage

[0079] 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.

[0080] Specifically, the lithium secondary battery may have a charging upper limit voltage of 4.5 V or higher.

[0081]

[0082] positive electrode active material

[0083] 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.

[0084] 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.

[0085] 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 About 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 About 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 About 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).

[0086] 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.

[0087] 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 a 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.

[0088] 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.

[0089] [Chemical Formula 11]

[0090] Li a1 Ni x1 M 1 y1 M 2 z1 O 2-b1 X b1

[0091] 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 2are 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.

[0092] 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.

[0093] [Chemical Formula 12]

[0094] Li a2 Co x2 M 3 y2 O 2-b2 X b2

[0095] 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.

[0096] [Chemical Formula 13]

[0097] Li a3 Fe x3 M 4 y3 PO 4-b3 X b3

[0098] 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 4is 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.

[0099] [Chemical Formula 14]

[0100] Li a4 Ni x4 Mn y4 M 5 z4 O 2-b4 X b4

[0101] 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.

[0102] 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.

[0103]

[0104] anode

[0105] 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.

[0106] For example, the anode may further include an additive that can act as a sacrificial anode.

[0107] 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.

[0108] 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.

[0109] 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.

[0110] Al may be used as the above current collector, but is not limited thereto.

[0111]

[0112] Negative active material

[0113] 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.

[0114] 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.

[0115] 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.

[0116] 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.

[0117] 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.

[0118] 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.

[0119] 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.

[0120]

[0121] cathode

[0122] The composite density of the above-mentioned negative electrode may be 1.7 g / cc or more. Even if the composite density of the negative electrode is increased in this way, the electrolyte of one embodiment can suppress an increase in resistance while improving the lifespan of a lithium secondary battery.

[0123] 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.

[0124] 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.

[0125] 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.

[0126] 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.

[0127] 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.

[0128] 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.

[0129] 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.

[0130] 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.

[0131] 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.

[0132]

[0133] separator

[0134] 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.

[0135] 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.

[0136] 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.

[0137] The above organic material may include a polyvinylidene fluoride-based antibody or a (meth)acrylic polymer.

[0138] 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.

[0139] 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.

[0140]

[0141] lithium secondary battery

[0142] Lithium secondary batteries can be classified into cylindrical, square, pouch, coin, etc. shapes according to their form. FIGS. 1 to 4 are schematic diagrams illustrating lithium secondary batteries according to one embodiment, wherein FIG. 1 can be said to be a circular battery shape, FIG. 2 a square battery shape, and FIGS. 3 and 4 a pouch battery shape. 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.

[0143]

[0144] 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.

[0145]

[0146] 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.

[0147]

[0148] Examples and Comparative Examples

[0149] An electrolyte and a lithium secondary battery were manufactured using the following method.

[0150]

[0151] Example 1

[0152] (1) Preparation of electrolyte

[0153] 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 (EB) represented by the following chemical formula 1 in a 10:15:75 ratio, and adding 1 wt% of an additive (DPS) represented by the following chemical formula 2:

[0154] [Chemical Formula 1-1]

[0155]

[0156] ethyl butyrate (CAS No.: 105-54-4)

[0157] [Chemical Formula 2-1]

[0158]

[0159] diphenyl sulfone (CAS No.: 127-63-9)

[0160] (2) Manufacturing of lithium secondary batteries

[0161] 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.

[0162] 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.

[0163] 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.

[0164] The above-mentioned negative electrode active material slurry was coated on a 10 μm thick Cu foil, dried at 100°C, and pressed to manufacture a negative electrode. At this time, the composite density of the negative electrode was set to 1.7 g / cc. For reference, the composite density of the negative electrode can be calculated by dividing the weight of the negative electrode active material layer by the volume after removing the Cu foil (current collector) from the negative electrode.

[0165] 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.

[0166]

[0167] Example 2

[0168] An electrolyte and a lithium secondary battery were manufactured in the same manner as in Example 1, except that 3 wt% of an additive was added during the preparation of the electrolyte.

[0169]

[0170] Example 3

[0171] An electrolyte and a lithium secondary battery were manufactured in the same manner as in Example 1, except that 5 wt% of an additive was added during the preparation of the electrolyte.

[0172]

[0173] Example 4

[0174] An electrolyte and a lithium secondary battery were manufactured in the same manner as in Example 2, except that a non-aqueous organic solvent containing ethylene carbonate (EC), propylene carbonate (PC), and a solvent (EB) represented by the above chemical formula 1 in a 10:20:70 mixture was used in the manufacture of the electrolyte.

[0175]

[0176] Example 5

[0177] An electrolyte and a lithium secondary battery were manufactured in the same manner as in Example 2, except that a non-aqueous organic solvent containing ethylene carbonate (EC), propylene carbonate, and a solvent (EB) represented by the following chemical formula 1 in a 10:10:80 mixture was used in the manufacture of the electrolyte.

[0178]

[0179] Comparative Example 1

[0180] An electrolyte was prepared by dissolving 1.3 M LiPF6 in a non-aqueous organic solvent containing ethylene carbonate (EC), propylene carbonate, and a solvent (PP) represented by the following chemical formula A in a 10:15:75 ratio:

[0181] [Chemical Formula A]

[0182]

[0183] propyl propionate (CAS No.: 106-36-5)

[0184] An electrolyte and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the above electrolyte was used.

[0185]

[0186] Comparative Example 2

[0187] An electrolyte was prepared by dissolving 1.3 M LiPF6 in a non-aqueous organic solvent containing ethylene carbonate (EC), propylene carbonate, a solvent (EB) represented by the above chemical formula 1, and a solvent (PP) represented by the above chemical formula A mixed in a weight ratio of 10:15:30:45.

[0188] An electrolyte and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the above electrolyte was used.

[0189]

[0190] Comparative Example 3

[0191] An electrolyte was prepared by dissolving 1.3 M LiPF6 in a non-aqueous organic solvent containing ethylene carbonate (EC), propylene carbonate, a solvent (EB) represented by the above chemical formula 1, and a solvent (PP) represented by the above chemical formula A mixed in a weight ratio of 10:15:45:30.

[0192] An electrolyte and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the above electrolyte was used.

[0193]

[0194] Comparative Example 4

[0195] An electrolyte was prepared by dissolving 1.3 M LiPF6 in a non-aqueous organic solvent containing ethylene carbonate (EC), propylene carbonate, and a solvent (EB) represented by the above chemical formula 1 in a weight ratio of 10:15:75.

[0196] An electrolyte and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the above electrolyte was used.

[0197]

[0198] Comparative Example 5

[0199] An electrolyte and a lithium secondary battery were manufactured in the same manner as in Example 1, except that a solvent (PP) represented by the chemical formula A was used instead of the solvent (EB) represented by the chemical formula 1 in manufacturing the electrolyte.

[0200]

[0201] Comparative Example 6

[0202] An electrolyte and a lithium secondary battery were manufactured in the same manner as in Example 2, except that a solvent (PP) represented by the chemical formula A was used instead of the solvent (EB) represented by the chemical formula 1 in the manufacture of the electrolyte.

[0203]

[0204] Comparative Example 7

[0205] An electrolyte and a lithium secondary battery were manufactured in the same manner as in Example 3, except that a solvent (PP) represented by the chemical formula A was used instead of the solvent (EB) represented by the chemical formula 1 in the manufacture of the electrolyte.

[0206]

[0207] Comparative Example 8

[0208] An electrolyte and a lithium secondary battery were manufactured in the same manner as in Example 1, except that a solvent (MP) represented by the following chemical formula B was used instead of the solvent (EB) represented by the above chemical formula 1 when manufacturing the electrolyte:

[0209] [Chemical Formula B]

[0210]

[0211] methyl propionate (CAS No.: 554-12-1)

[0212]

[0213] Comparative Example 9

[0214] An electrolyte and a lithium secondary battery were manufactured in the same manner as in Example 1, except that a solvent (EP) represented by the following chemical formula C was used instead of the solvent (EB) represented by the above chemical formula 1 when manufacturing the electrolyte:

[0215] [Chemical Formula C]

[0216]

[0217] ethyl propionate (CAS No.: 105-37-3).

[0218]

[0219] Comparative Example 10

[0220] An electrolyte and a lithium secondary battery were manufactured in the same manner as in Example 1, except that an additive (DMS) represented by the following chemical formula D was used instead of the additive represented by the above chemical formula 2 when manufacturing the electrolyte:

[0221] [Chemical Formula D]

[0222]

[0223] dimethyl sulfone (CAS No.: 67-71-0)

[0224]

[0225] Each electrolyte according to Examples 1 to 5 and Comparative Examples 1 to 10 is summarized in Table 1 below.

[0226]

[0227] Solvent (vol%) Additive (wt%) ECPCEBPPMPEPDPSDMS Comparative Example 11015-75----Comparative Example 210153045----Comparative Example 310154530----Comparative Example 4101575----Comparative Example 51015-75--1-Comparative Example 61015-75--3-Comparative Example 71015-75--5-Comparative Example 81015--75-1-Comparative Example 91015---751-Comparative Example 10101575----1Example 1101575---1-Example 2101575---3-Example 3101575---5-Example 4102070---3-Example 5101080---3-

[0228] 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.

[0229]

[0230] Evaluation example

[0231] Lithium secondary batteries were evaluated using the following method.

[0232]

[0233] Evaluation 1: Evaluation of room-temperature charge-discharge cycle characteristics

[0234] The cycle characteristics of the lithium secondary batteries according to Examples 1 to 5 and Comparative Examples 1 to 10 were evaluated after charge and discharge under the following conditions, and the results are shown in Table 2.

[0235] After 200 cycles of charge and discharge under conditions of 25℃, 0.33C charge (CC / CV, 4.53V, 0.025C Cut-off) / 1.0C discharge (CC, 2.5V Cut-off), the capacity retention rate and changes in direct current internal resistance (DC-IR) were measured.

[0236] The capacity retention rate was calculated according to Equation 1 below, and the DC internal resistance change rate was calculated according to Equation 2 below using the value of △V / △I (change in voltage / change in current).

[0237] [Formula 1]

[0238] Capacity retention rate = (discharge capacity after 200 cycles / discharge capacity after 1 cycle) * 100

[0239] [Formula 2]

[0240] DC internal resistance change rate = [(DC-IR after 200 cycles) - (DC-IR after 1 cycle)] / (DC-IR after 1 cycle) * 100

[0241]

[0242] Capacity retention (@25℃, 200 cycles)DC-IR change rate after 200 cycles@25℃ (%)Comparative example 16738Comparative example 26935Comparative example 37532Comparative example 47831Comparative example 57928Comparative example 68225Comparative example 78026Comparative example 84758Comparative example 95849Comparative example 107141Example 18722Example 29019Example 38821Example 48524Example 58623

[0243] Each electrolyte according to Examples 1 to 5 and Comparative Examples 1 to 10 was evaluated under high voltage (4.53 V) and high negative electrode material density (1.7 g / cc). According to Table 2 above, when an electrolyte including the solvent represented by Chemical Formula 1 and the additive represented by Chemical Formula 2 were used at the same time as in the Examples of the present invention, it was confirmed that the lifespan of the lithium secondary battery was significantly improved compared to the Comparative Examples while effectively suppressing an increase in resistance.

[0244] 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.

[0245]

[0246] [Explanation of symbols]

[0247] 100: Lithium secondary battery 10: Cathode

[0248] 11: Positive lead tab 12: Positive terminal

[0249] 20: Negative lead tab 21: Negative lead tab

[0250] 22: Negative terminal 30: Separator

[0251] 40: Electrode assembly 50: Case

[0252] 60: Sealing member 70: Electrode tab

[0253] 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 substituted or unsubstituted aryl group having 6 to 20 carbon atoms.

2. In paragraph 1, R 1 A lithium secondary battery electrolyte that is a silver profiler.

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

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

5. In paragraph 1, An electrolyte for a lithium secondary battery, wherein the solvent represented by the above chemical formula 1 is contained in an amount of 70% by volume or more with respect to 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 85 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, R 3 and R 4 An electrolyte for a lithium secondary battery, wherein at least one of the groups is a phenyl group.

10. 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] .

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

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

13. 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.

14. A cathode containing a cathode active material; A negative electrode comprising a negative active material; and Electrolyte according to any one of claims 1 to 13 A lithium secondary battery comprising:

15. In paragraph 14, A lithium secondary battery having a composite density of the above negative electrode of 1.7 g / cc or more.

16. In paragraph 14, 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-based oxide, or a combination thereof.

17. In paragraph 14, 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.

18. In paragraph 14, A lithium secondary battery having an upper limit charging voltage of 4.5 V or higher.

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