Negative electrode and rechargeable lithium battery including same

Abstract

The invention relates to a negative electrode and a lithium secondary battery including the same, wherein the negative electrode comprises a current collector, a negative electrode active material layer, and a functional layer comprising a nanometal and a nanocarbon, and the functional layer is located between the current collector and the negative electrode active material layer or on the negative electrode active material layer.

Description

Technology Field

[0001] This invention relates to a negative electrode and a lithium secondary battery containing the same. Background Technology

[0002] With the recent rapid proliferation of electronic devices using batteries, such as mobile phones, laptop computers, and electric vehicles, the demand for small, lightweight, and relatively high-capacity rechargeable batteries is increasing rapidly. In particular, as there is a demand for lithium rechargeable batteries with high energy density and excellent efficiency, research is required to improve the composite density of the negative electrode. The problem to be solved

[0003] One embodiment provides a cathode that exhibits excellent cycle life characteristics and rate characteristics.

[0004] Another embodiment provides a lithium secondary battery comprising the above-mentioned cathode. means of solving the problem

[0005] One embodiment provides a cathode comprising a current collector; a negative electrode active material layer; and a functional layer comprising a nanometal and a nanocarbon with respect to the current collector, wherein the functional layer is located between the current collector and the negative electrode active material layer or on the negative electrode active material layer.

[0006] According to another embodiment, a lithium secondary battery comprising the cathode; the anode; and the electrolyte is provided. Effects of the invention

[0007] The cathode according to one embodiment can exhibit excellent lifespan characteristics and rate characteristics. Brief explanation of the drawing

[0008] FIG. 1 is a schematic diagram showing a cathode according to one embodiment. FIG. 2 is a schematic diagram showing a cathode according to another embodiment. FIG. 3 is a schematic diagram showing a lithium secondary battery according to one embodiment. Specific details for implementing the invention

[0009] 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, and the present invention is defined only by the scope of the claims set forth below.

[0010] The terms used herein are for describing exemplary embodiments only and are not intended to limit the invention. The singular expression includes the plural expression unless the context clearly indicates otherwise.

[0011] Here, "combinations of these" refers to mixtures of components, laminates, composites, copolymers, alloys, blends, reaction products, etc.

[0012] The terms "include," "equip," or "have" used herein are intended to specify the existence of the implemented features, numbers, steps, components, or combinations thereof, and should be understood as not excluding in advance the existence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0013] In the drawings, thicknesses have been enlarged to clearly represent various layers and regions, and the same reference numerals have been used for similar parts throughout the specification. When a part such as a layer, film, region, or plate is described as being "on" or "on" another part, this includes not only cases where it is "immediately on" another part, but also cases where there is another part in between. Conversely, when a part is described as being "immediately on" another part, it means that there is no other part in between.

[0014] In addition, the term "layer" here includes not only the shape formed on the entire surface when viewed in a plan view, but also the shape formed on some surfaces.

[0015] Here, "or" is not interpreted in an exclusive sense; for example, "A or B" is interpreted to include A, B, A+B, etc.

[0016] Unless otherwise defined in this specification, the particle size or size may be the average particle size. This average particle size refers to the average particle size (D50) which means the diameter of a particle whose cumulative volume in the particle size distribution is 50% by volume. The average particle size (D50) may be measured by methods widely known to those skilled in the art, for example, by measuring with a particle size analyzer, or by measuring with a transmission electron microscope (TEM) image or a scanning electron microscope (SEM) image. Alternatively, the average particle size (D50) value may be obtained by measuring using a measuring device utilizing dynamic light-scattering, performing data analysis to count the number of particles for each particle size range, and then calculating from this.

[0017] A negative electrode for a lithium secondary battery according to one embodiment includes a current collector, a negative electrode active material layer, and a functional layer. The functional layer may include nanometals and nanocarbons.

[0018] The above functional layer may be located between the current collector and the negative active material layer, or may be located on the negative active material layer.

[0019] Referring to FIG. 1, a cathode according to one embodiment may have a current collector (3), a functional layer (5), and a cathode active material layer (7) sequentially positioned on the cathode (1).

[0020] FIG. 2 shows a cathode according to another embodiment, wherein the functional layer (5) may be located on the cathode active material layer (7), and the cathode may have the current collector (3), the cathode active material layer (7), and the functional layer (5) sequentially located thereon.

[0021] As shown in FIGS. 1 and 2, the functional layer (5) includes nanometal (a) and nanocarbon (b).

[0022] Since a functional layer containing nanometals is included within the anode, conductivity can be improved. Furthermore, because the functional layer contains nanometals, additional capacity can be obtained due to these nanometals. This allows for appropriate capacity to be exhibited even with a low density of the active material layer. Therefore, to increase capacity, a high-composite anode must be manufactured, and this method can prevent problems associated with performing strong rolling for the manufacture of such anodes. If strong rolling is performed, the active material layer is excessively compressed, which can make the active material layer too dense. When lithium ions must pass through such a dense active material layer, they have difficulty moving toward the current collector, causing them to accumulate on the surface of the active material layer and form lithium dendrites, which can lead to problems such as degradation of rate characteristics and cycle life characteristics.

[0023] In addition, the metal included in the functional layer is a nanometal having a nanometer size, and reactivity is superior when it has a nanometer size. In a cathode according to one embodiment, the metal included in the functional layer has a lithium ion diffusion rate higher than that of lithium metal, and in particular, when it is a nanometal having a nanometer size, the lithium ion diffusion rate It is even better.

[0024] Since a functional layer containing nanometals with excellent lithium ion diffusion rates is included within the cathode, lithium ions that have moved to the cathode during charging and discharging can be effectively diffused.

[0025] When a functional layer containing nanometals is included in the cathode, the effect of increased lithium ion diffusion rate may be more effective when the functional layer containing nanometals is located between the current collector and the cathode active material layer.

[0026] When the functional layer is located between the current collector and the negative electrode active material layer, lithium ions that migrate to the negative electrode during charging and discharging do not accumulate (precipitate) on the surface of the negative electrode active material layer, but rather pass through the negative electrode active material layer and rapidly move to the functional layer. Furthermore, since lithium ions can rapidly pass through the functional layer, the phenomenon of short circuits occurring when they pass through the separator and come into contact with the positive electrode can be more effectively prevented, thereby improving lifespan characteristics. Additionally, lithium well accumulated between the current collector and the functional layer moves to the positive electrode during charging and discharging, contributing to the charge / discharge capacity and thus demonstrating an effect of increasing capacity.

[0027] The above nanometal is suitable for nanometer size as it can enhance reactivity, and for example, it may be several nm to several hundred nm. The specific size of the nanometal may be 1 nm to 100 nm, 20 nm to 100 nm, or 40 nm to 100 nm.

[0028] In the above nanometal, the metal may be Ag, Pt, Al, Zn, Au, Mg, Ge, Cu, In, Ni, Bi, or a combination thereof, or Ag, Al, or a combination thereof.

[0029] When Si is used as the metal of the above nanometal, it may not be suitable because Si practically has almost no metallic properties, has almost no conductivity, and has a low lithium ion diffusion rate, so it cannot perform the role of causing lithium precipitation between the current collector and the functional layer.

[0030] In addition, if the above-mentioned nanometal is used as a metal compound, for example, a metal oxide even if it has a nanoscale, such a metal compound is not conductive and may not be suitable because it cannot perform the role of causing lithium deposition between the current collector and the functional layer.

[0031] Carbon, particularly nanocarbon, included in the above functional layer can enable uniform charging and discharging. The nanocarbon may be carbon black, acetylene black, Ketjen black, Denka black, carbon nanotubes, canon nanofibers, graphite, or a combination thereof.

[0032] The above nanocarbon is suitable to be of nanometer size, for example, several nm to several hundred nm. The specific size of the nanocarbon may be 10 nm to 100 nm, or 20 nm to 60 nm.

[0033] In one embodiment, the content of the nanometal may be 1% to 50% by weight and 10% to 40% by weight with respect to 100% by weight of the functional layer. When the content of the nanometal falls within the above range, the capacity increase effect resulting from the use of the nanometal can be further enhanced without causing volume expansion problems during charging and discharging.

[0034] In one embodiment, the mixing ratio of the nanometal and the nanocarbon may be 10:90 to 40:60 by weight, and 15:85 to 40:60 by weight.

[0035] The above functional layer A binder may be further included. This binder may be a water-based binder, and examples include a cellulose-based compound, styrene-butadiene rubber, acrylated styrene-butadiene rubber, acrylonitrile-butadiene rubber, acrylic rubber, butyl rubber, a polymer containing ethylene oxide, polyvinylpyrrolidone, polypropylene, ethylene-propylene copolymer, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, polystyrene, ethylene-propylene-diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, polyacrylic acid, or a combination thereof. As the cellulose-based compound, one or more types such as carboxymethyl cellulose, hydroxypropylmethyl cellulose, methyl cellulose, or alkali metal salts thereof may be mixed and used. Na, K, or Li can be used as the above alkali metal.

[0036] Cellulose-based compounds can also serve as thickeners that impart viscosity.

[0037] The content of the nano carbon may be 1% to 50% by weight and 10% to 40% by weight with respect to 100% by weight of the functional layer. Additionally, the content of the binder may be 1% to 50% by weight and 10% to 40% by weight with respect to 100% by weight of the functional layer.

[0038] The thickness of the functional layer may be 50 nm or more, 50 nm to 20 µm, or 50 nm to 10 µm. When the thickness of the functional layer falls within the above range, the increase in capacity due to the inclusion of the functional layer can be obtained more appropriately, and the effects of rapid charging and improved capacity characteristics can be further enhanced.

[0039] In one embodiment, the thickness of the negative electrode active material layer can be appropriately adjusted and is not limited.

[0040] The above cathode active material layer includes a cathode active material.

[0041] The above-mentioned 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.

[0042] Carbon materials can be used as materials capable of reversibly intercalating / deintercalating the lithium ions. Any carbon-based negative electrode active material commonly used in lithium-ion secondary batteries can be used, and representative examples include crystalline carbon, amorphous carbon, or a combination thereof. Examples of crystalline carbon include graphite such as amorphous, plate-like, flake-like, spherical, or fibrous natural graphite or artificial graphite. Examples of amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, calcined coke, etc.

[0043] Materials capable of doping and dedoping the above lithium include Si, Si-C composites, and SiO₂. x(0 <x<2), Si-Q 합금(상기 Q는 알칼리 금속, 알칼리 토금속, 13족 원소, 14족 원소, 15족 원소, 16족 원소, 전이금속, 희토류 원소 및 이들의 조합으로 이루어진 군에서 선택되는 원소이며, Si은 아님), Sn, SnO2, Sn-R(상기 R은 알칼리 금속, 알칼리 토금속, 13족 원소, 14족 원소, 15족 원소, 16족 원소, 전이금속, 희토류 원소 및 이들의 조합으로 이루어진 군에서 선택되는 원소이며, Sn은 아님) 등을 들 수 있고, 또한 이들 중 적어도 하나와 SiO2를 혼합하여 사용할 수도 있다. 상기 원소 Q 및 R로는 Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ti, Ge, P, As, Sb, Bi, S, Se, Te, Po, 및 이들의 조합으로 이루어진 군에서 선택되는 것을 사용할 수 있다.

[0044] The above Si-C composite may include silicon particles and crystalline carbon. The above Si-C composite may further include an amorphous carbon layer formed in at least a portion. The above Si-C composite may include a secondary particle, i.e., an assembly, in which silicon primary particles and crystalline carbon are assembled, and may include an amorphous carbon coating layer located on the surface of the assembly. The amorphous carbon may be filled between the assemblies and positioned to surround the surface of the primary particles.

[0045] According to another embodiment, the Si-C composite may be a composite of silicon and amorphous carbon. According to one embodiment, the Si-C composite may be in the form of a silicon-based material and amorphous carbon coated on the surface of the silicon-based material. For example, the Si-C composite may include secondary particles assembled from silicon primary particles and an amorphous carbon coating layer located on the surface of the secondary particles. The amorphous carbon may also be located between the silicon primary particles, so that, for example, the silicon primary particles may be coated with amorphous carbon.

[0046] Since the above secondary particle is located at the center of the Si-C composite, it can be called the core or the center. In addition, the above amorphous carbon coating layer can be called the outer part or the shell.

[0047] The average particle size (D50) of the above silicon primary particles may be 10 nm to 30 µm, and according to one embodiment, may be 10 nm to 1,000 nm, and according to another embodiment, may be 20 nm to 150 nm. When the average particle size of the above silicon primary particles falls within the above range, volume expansion occurring during charging and discharging can be suppressed, and the interruption of the conductive path due to particle fragmentation during charging and discharging can be prevented.

[0048] When amorphous carbon is coated, the thickness of the amorphous carbon coating layer may be 5 nm to 100 nm.

[0049] The content of silicon particles, crystalline carbon, and amorphous carbon in the above Si-C composite can be appropriately controlled.

[0050] In one embodiment, the Si-C composite and crystalline carbon may be mixed and used as the cathode active material, and the mixing ratio can be appropriately adjusted.

[0051] In the above-mentioned negative electrode active material layer, the content of the negative electrode active material may be 95% to 98% by weight with respect to 100% by weight of the entire negative electrode active material layer.

[0052] The above negative electrode active material layer may include a binder and may further include a conductive material. The content of the binder may be 1% to 5% by weight with respect to 100% by weight of the entire negative electrode active material layer. The content of the conductive material may be 1% to 5% by weight with respect to 100% by weight of the entire negative electrode active material layer.

[0053] The above binder serves to effectively bond the negative electrode active material particles to each other and also to effectively bond the negative electrode active material to the current collector. As the binder, a non-aqueous binder, an aqueous binder, or a combination thereof may be used.

[0054] Examples of the above-mentioned non-aqueous binders include ethylene propylene copolymer, polyacrylonitrile, polystyrene, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or combinations thereof.

[0055] The above-mentioned water-based binder may be styrene-butadiene rubber (SBR), acrylated styrene-butadiene rubber (ABR), acrylonitrile-butadiene rubber, acrylic rubber, butyl rubber, fluororubber, a polymer containing ethylene oxide, polyvinylpyrrolidone, polypropylene, polyepichlorohydrin, polyphosphazene, ethylenepropylenediene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, or a combination thereof.

[0056] When a water-based binder is used as the above-mentioned cathode binder, a cellulose-based compound capable of imparting viscosity may be further included as a thickener. As this cellulose-based compound, one or more types such as carboxymethyl cellulose, hydroxypropylmethyl cellulose, methyl cellulose, or alkali metal salts thereof may be mixed and used. Na, K, or Li may be used as the alkali metal. The content of such a thickener may be 0.1 to 3 parts by weight per 100 parts by weight of the cathode active material.

[0057] The above conductive material is used to impart conductivity to the electrode, and any electronically conductive material that does not cause chemical changes can be used in the battery being constructed. Examples of conductive materials may include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, and carbon fibers; metal-based materials such as metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive polymers such as polyphenylene derivatives; or conductive materials comprising mixtures thereof.

[0058] As the above current collector, a material selected from the group consisting of copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof may be used.

[0059] Such a negative electrode for a lithium secondary battery can be manufactured by applying a functional layer composition to a current collector and drying to form a functional layer, then applying a negative electrode active material layer composition, and drying and rolling to form a negative electrode active material layer.

[0060] The above functional layer composition may include a nanometal, a nanocarbon, a binder, and a solvent. The solvent may be water.

[0061] The above-described negative electrode active material layer composition comprises a negative electrode active material, a binder, and a solvent, and may optionally further comprise a conductive material. The solvent may be an organic solvent such as N-methylpyrrolidone, and water may be used when an aqueous binder is used as the binder.

[0062] Another embodiment provides a lithium secondary battery comprising the above-mentioned cathode, a positive electrode, and an electrolyte.

[0063] The above anode includes a current collector and an anode active material layer formed on the current collector.

[0064] As the above-mentioned cathode active material, a compound capable of reversible intercalation and deintercalation of lithium (a rethated intercalation compound) may be used. Specifically, one or more composite oxides of lithium and a metal selected from cobalt, manganese, nickel, and combinations thereof may be used. As a more specific example, a compound represented by any one of the following chemical formulas may be used. Li a A 1-b X b D 1 2(0.90≤a≤1.8, 0 b≤0.5); Li a A 1-b X b O 2-c1 D 1 c1 (0.90≤a≤1.8, 0≤b≤0.5, 0≤c1≤0.05); Li a E 1-b X b O 2-c1 D 1 c1 (0.90≤a≤1.8, 0≤b≤0.5, 0≤c1≤0.05); Li a E 2-b X b O 4-c1 D 1 c1 (0.90≤a≤1.8, 0≤b≤0.5, 0≤c1≤0.05); Li a Ni 1-b-c Co b X c D1 α (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.5, 0<α≤2); Li a Ni 1-b-c Co b X c O 2-α T α (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.5, 0<α<2); Li a Ni 1-b-c Co b X c O 2-α T2(0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.5, 0<α<2); Li a Ni 1-b-c Mr b X c D 1 α (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.5, 0<α≤2); Li a Ni 1-b-c Mr b X c O 2-α T α (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.5, 0<α<2); Li a Ni 1-b-c Mr b X c O 2-α T2(0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.5, 0<α<2); Li a Ni b HAVE BEEN c G d O2(0.90≤a≤1.8, 0≤b≤0.9, 0≤c≤0.5, 0.001≤d≤0.1); 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, 0.001≤e≤0.1); Li a NiG b O2(0.90≤a≤1.8, 0.001≤b≤0.1) Li a CoGb 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); QO2; QS2; LiQS2; V2O5; LiV2O5; LiZO2; LiNiVO4; Li (3-f) J2(PO4)3(0≤f≤2); Li (3-f) Fe2(PO4)3(0≤f≤2); Li a FePO4(0.90≤a≤1.8)

[0065] In the above chemical formula, A is selected from the group consisting of Ni, Co, Mn, and combinations thereof; X is selected from the group consisting of Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, rare earth elements, and combinations thereof; and D 1 is selected from the group consisting of O, F, S, P, and combinations thereof; E is selected from the group consisting of Co, Mn, and combinations thereof; T is selected from the group consisting of F, S, P, and combinations thereof; G is selected from the group consisting of Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, and combinations thereof; Q is selected from the group consisting of Ti, Mo, Mn, and combinations thereof; Z is selected from the group consisting of Cr, V, Fe, Sc, Y, and combinations thereof; J is selected from the group consisting of V, Cr, Mn, Co, Ni, Cu, and combinations thereof; L 1 It is selected from the group consisting of Mn, Al, and combinations thereof.

[0066] Of course, a coating layer on the surface of this compound may be used, or a mixture of the compound and a compound having a coating layer may be used. This coating layer may include at least one coating element compound selected from the group consisting of oxides of coating elements, hydroxides of coating elements, oxyhydroxides of coating elements, oxycarbonates of coating elements, and hydroxycarbonates of coating elements. The compounds forming these coating layers may be amorphous or crystalline. As coating elements included in the coating layer, Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or mixtures thereof may be used. For the coating layer formation process, any coating method may be used as long as the compound can be coated using these elements in a way that does not adversely affect the physical properties of the cathode active material (e.g., spray coating, immersion method, etc.). Since this is a matter that is well understood by those skilled in the art, a detailed explanation will be omitted.

[0067] In the above anode, the content of the anode active material may be 90% to 98% by weight with respect to the total weight of the anode active material layer.

[0068] In one embodiment, the positive active material layer may further include a binder and a conductive material. In this case, the content of the binder and the conductive material may each be 1% to 5% by weight with respect to the total weight of the positive active material layer.

[0069] The above binder serves to adhere the positive active material particles well to each other and also to adhere the positive active material well to the current collector. Representative examples of binders include polyvinyl alcohol, carboxymethylcellulose, hydroxypropylcellulose, diacetylcellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc., but are not limited thereto.

[0070] The above conductive material is used to impart conductivity to the electrode, and any electronically conductive material that does not cause chemical changes can be used in the battery being constructed. Examples of conductive materials include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, and carbon fibers; metal-based materials such as metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive polymers such as polyphenylene derivatives; or conductive materials comprising mixtures thereof.

[0071] Al may be used as the current collector mentioned above, but is not limited thereto.

[0072] The above electrolyte includes a non-aqueous organic solvent and a lithium salt.

[0073] The above-mentioned non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move.

[0074] The above-mentioned non-aqueous organic solvent may be a carbonate-based, ester-based, ether-based, ketone-based, alcohol-based, or aprotic solvent.

[0075] The above carbonate-based solvents may include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), etc. The above ester-based solvents may include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methylpropionate, ethylpropionate, decanolide, mevalonolactone, caprolactone, etc. The above ether-based solvents may include dibutyl ether, tetraglame, deglame, dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, etc. Additionally, the above ketone-based solvents may include cyclohexanone, etc. In addition, the above alcohol-based solvent may include ethyl alcohol, isopropyl alcohol, etc., and the above aprotic solvent may include nitriles such as R-CN (where R is a straight-chain, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may include a double bond, directional ring, or ether bond), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, sulfolanes, etc.

[0076] The above organic solvents may be used alone or in a mixture of one or more. When used in a mixture of one or more, the mixing ratio can be appropriately adjusted according to the desired battery performance, which is widely understood by those engaged in the relevant field.

[0077] In addition, for the above carbonate-based solvent, it is preferable to use a mixture of cyclic carbonates and chain carbonates. In this case, using a mixture of cyclic carbonates and chain carbonates in a volume ratio of 1:1 to 1:9 can result in excellent performance of the electrolyte.

[0078] The above organic solvent may further include an aromatic hydrocarbon organic solvent in the carbonate-based solvent. In this case, the carbonate-based solvent and the aromatic hydrocarbon organic solvent may be mixed in a volume ratio of 1:1 to 30:1.

[0079] As the above aromatic hydrocarbon organic solvent, an aromatic hydrocarbon compound of the following chemical formula 1 may be used.

[0080] [Chemical Formula 1]

[0081]

[0082] (In the above Chemical Formula 1, R1 to R6 are identical or different from each other and are selected from the group consisting of hydrogen, halogen, alkyl groups having 1 to 10 carbon atoms, haloalkyl groups, and combinations thereof.)

[0083] Specific examples of the above aromatic hydrocarbon-based organic solvents include benzene, fluorobenzene, 1,2-difluorobenzene, 1,3-difluorobenzene, 1,4-difluorobenzene, 1,2,3-trifluorobenzene, 1,2,4-trifluorobenzene, chlorobenzene, 1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene, 1,2,3-trichlorobenzene, 1,2,4-trichlorobenzene, iodobenzene, 1,2-diiodobenzene, 1,3-diiodobenzene, 1,4-diiodobenzene, 1,2,3-triiodobenzene, 1,2,4-triiodobenzene, toluene, fluorotoluene, 2,3-difluorotoluene, 2,4-difluorotoluene. It is selected from the group consisting of 2,5-difluorotoluene, 2,3,4-trifluorotoluene, 2,3,5-trifluorotoluene, chlorotoluene, 2,3-dichlorotoluene, 2,4-dichlorotoluene, 2,5-dichlorotoluene, 2,3,4-trichlorotoluene, 2,3,5-trichlorotoluene, iodotoluene, 2,3-diiodotoluene, 2,4-diiodotoluene, 2,5-diiodotoluene, 2,3,4-triiodotoluene, 2,3,5-triiodotoluene, xylene, and combinations thereof.

[0084] The above electrolyte may further include vinyl ethyl carbonate, vinylene carbonate, or an ethylene carbonate-based compound of the following chemical formula 2 as a life-enhancing additive to improve battery life.

[0085] [Chemical Formula 2]

[0086]

[0087] (In the above chemical formula 2, R7 and R8 are identical or different from each other and are selected from the group consisting of hydrogen, a halogen group, a cyano group (CN), a nitro group (NO2), and a fluorinated alkyl group having 1 to 5 carbon atoms, and at least one of R7 and R8 is selected from the group consisting of a halogen group, a cyano group (CN), a nitro group (NO2), and a fluorinated alkyl group having 1 to 5 carbon atoms, provided that R7 and R8 are not both hydrogen.)

[0088] Representative examples of the above-mentioned ethylene carbonate-based compounds include difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate, or fluoroethylene carbonate. When using more of these lifespan-enhancing additives, the amount used can be appropriately controlled.

[0089] The above lithium salt is a material that dissolves 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 facilitating the movement of lithium ions between the anode and cathode. Representative examples of such lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiN(SO2C2F5)2, Li(CF3SO2)2N, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide (LiFSI), LiC4F9SO3, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, and LiN(C x F 2x+1 SO2)(C y F 2y+1 SO2)(where x and y are natural numbers, for example, integers from 1 to 20), lithium difluoro(bisoxolato) phosphate, LiCl, LiI, LiB(C2O4)2 (lithium bis(oxalato) borate (LiBOB)), and lithium difluoro(oxalato) borate (LiDFOB) are included as supporting electrolyte salts, one or more selected from the group consisting of lithium bis(oxalato) borate (LiBOB) and lithium difluoro(oxalato) borate (LiDFOB). It is preferable to use a lithium salt concentration within the range of 0.1 M to 2.0 M. When the lithium salt concentration falls within the above range, the electrolyte has appropriate conductivity and viscosity, so it can exhibit excellent electrolyte performance and lithium ions can move effectively.

[0090] Depending on the type of lithium secondary battery, a separator may be present between the positive and negative electrodes. As such a separator, polyethylene, polypropylene, polyvinylidene fluoride, or multilayer films of two or more layers thereof may be used, and of course, mixed multilayer films such as polyethylene / polypropylene two-layer separators, polyethylene / polypropylene / polyethylene three-layer separators, and polypropylene / polyethylene / polypropylene three-layer separators may be used.

[0091] FIG. 3 shows an exploded perspective view of a lithium secondary battery according to one embodiment of the present invention. Although the lithium secondary battery according to one embodiment is described as being prismatic, the present invention is not limited thereto and can be applied to various types of batteries such as cylindrical and pouch types.

[0092] Referring to FIG. 3, a lithium secondary battery (100) according to one embodiment may include an electrode assembly (40) wound with 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 housed. The positive electrode (10), the negative electrode (20), and the separator (30) may be impregnated with an electrolyte (not shown).

[0093] Examples and comparative examples of the present invention are described below. However, the following examples are merely one example of the present invention, and the present invention is not limited to the following examples.

[0094] (Example 1)

[0095] A functional layer slurry was prepared by mixing 30 wt% of Ag with an average particle size (D50) of 100 nm, 55 wt% of Denka Black with an average particle size (D50) of 50 nm, and 15 wt% of a carboxymethyl cellulose binder in a water solvent.

[0096] A negative electrode active material layer slurry was prepared by mixing 97.5 wt% of a negative electrode active material of artificial graphite and silicon-carbon composite (mixing ratio of artificial graphite and silicon-carbon composite = 89:11 weight ratio), 1 wt% of carboxymethyl cellulose, and 1.5 wt% of styrene butadiene rubber in a water solvent.

[0097] The silicon-carbon composite used above comprises a core containing silicon nanoparticles and a soft carbon coating layer formed on the surface of the core. At this time, the content of the silicon nanoparticles was 40 wt% with respect to the total weight of the silicon-carbon composite, and the content of the amorphous carbon was 60 wt%. The thickness of the soft carbon coating layer was 20 nm, and the average particle size (D50) of the silicon nanoparticles was 100 nm.

[0098] A functional layer is formed by coating and drying the functional layer slurry on a Cu foil current collector, and a negative active material layer is formed by coating, drying, and rolling the negative active material layer slurry on the functional layer to manufacture a negative electrode.

[0099] In the manufactured cathode, the thickness of the functional layer was 5 μm, and the thickness of the cathode active material layer was 35 μm. In addition, the composite density of the cathode active material layer was 1.5 g / cm³.

[0100] A half-cell was manufactured using the above-described cathode, lithium metal counter electrode, and electrolyte. As the electrolyte, a mixture of ethylene carbonate, ethylmethyl carbonate, and diethyl carbonate (volume ratio of 2:1:7) in which 1M LiPF6 was dissolved was used, to which 3.5% by weight of fluoroethylene carbonate was added relative to the total weight of the mixture.

[0101] In addition, the above cathode, LiNi 0.88 Co0. 11 Al 0.01 A coin full cell was manufactured using an O2 anode and the above electrolyte.

[0102] (Example 2)

[0103] A cathode was prepared in the same manner as in Example 1 using a functional layer slurry prepared by mixing 30 wt% of Ag with an average particle size (D50) of 50 nm, 55 wt% of Denka Black with an average particle size (D50) of 50 nm, and 15 wt% of a carboxymethyl cellulose binder in a water solvent. In the prepared cathode, the thickness of the functional layer was 5 μm, and the thickness of the cathode active material layer was 35 μm. In addition, the composite density of the cathode active material layer was 1.5 g / cm³.

[0104] Half batteries and coin-type batteries were manufactured by carrying out the same procedure as in Example 1 using the manufactured cathode.

[0105] (Example 3)

[0106] A cathode was prepared in the same manner as in Example 1 using a functional layer slurry prepared by mixing 15 wt% of Ag with an average particle size (D50) of 50 nm, 70 wt% of Denka Black with an average particle size (D50) of 50 nm, and 15 wt% of a carboxymethyl cellulose binder in a water solvent. In the prepared cathode, the thickness of the functional layer was 5 μm, and the thickness of the cathode active material layer was 35 μm. In addition, the composite density of the cathode active material layer was 1.5 g / cm³.

[0107] Half batteries and coin-type batteries were manufactured by carrying out the same procedure as in Example 1 using the manufactured cathode.

[0108] (Example 4)

[0109] A negative electrode active material layer slurry prepared in Example 2 above was coated and dried on a Cu foil current collector to form a negative electrode active material layer, and a functional layer slurry prepared in Example 1 above was coated, dried, and rolled on the negative electrode active material layer to form a functional layer, thereby manufacturing a negative electrode.

[0110] Half batteries and coin-type batteries were manufactured by carrying out the same procedure as in Example 1 using the manufactured cathode.

[0111] (Comparative Example 1)

[0112] A negative electrode active material layer slurry was prepared by mixing 97.5 wt% of a negative electrode active material of artificial graphite and silicon-carbon composite (mixing ratio of artificial graphite and silicon-carbon composite = 89:11 weight ratio), 1 wt% of carboxymethyl cellulose, and 1.5 wt% of styrene butadiene rubber in a water solvent.

[0113] A cathode was manufactured by forming a cathode active material layer by coating, drying, and rolling the above cathode active material layer slurry onto a Cu foil current collector. In the manufactured cathode, the thickness of the cathode active material layer was 43 μm. In addition, the composite density of the cathode active material layer was 1.6 g / cm³.

[0114] A half-cell was manufactured using the above-described cathode, lithium metal counter electrode, and electrolyte. As the electrolyte, a mixture of ethylene carbonate, ethylmethyl carbonate, and diethyl carbonate (volume ratio of 2:1:7) in which 1M LiPF6 was dissolved was used, to which 3.5% by weight of fluoroethylene carbonate was added relative to the total weight of the mixture.

[0115] In addition, the above cathode, LiNi 0.88 Co0. 11 Al 0.01 A coin full cell was manufactured using an O2 anode and the above electrolyte.

[0116] (Comparative Example 2)

[0117] A cathode was prepared in the same manner as in Example 1 using a functional layer slurry prepared by mixing 70 wt% of Denka black with an average particle size (D50) of 50 nm and 30 wt% of a carboxymethyl cellulose binder in a water solvent. In the prepared cathode, the thickness of the functional layer was 5 μm, and the thickness of the cathode active material layer was 35 μm. In addition, the composite density of the cathode active material layer was 1.5 g / cm³.

[0118] Half batteries and coin-type batteries were manufactured by carrying out the same procedure as in Example 1 using the manufactured cathode.

[0119] (Comparative Example 3)

[0120] A negative electrode active material layer slurry was prepared by mixing 77.5 wt% of a negative electrode active material of artificial graphite and silicon-carbon composite (mixing ratio of artificial graphite and silicon-carbon composite = 89:11 weight ratio), 1 wt% of carboxymethyl cellulose, 1.5 wt% of styrene butadiene rubber, 5 wt% of Ag with an average particle size (D50) of 50 nm, and 15 wt% of Denka Black with an average particle size (D50) of 50 nm in a water solvent.

[0121] A cathode was manufactured by carrying out the same procedure as in Example 1 using the above cathode active material layer slurry.

[0122] Half batteries and coin-type batteries were manufactured by carrying out the same procedure as in Example 1 using the manufactured cathode.

[0123] Experimental Example 1) Evaluation of Efficiency Characteristics

[0124] Half batteries prepared according to Examples 1 to 3 and Comparative Examples 1 to 3 were subjected to one charge and discharge cycle at 0.1C. The ratio of discharge capacity to charge capacity was calculated, and the results were shown as efficiency in Table 1 below.

[0125] Experimental Example 2) Evaluation of Rapid Charging Rate Characteristics

[0126] Half batteries prepared according to Examples 1 to 3 and Comparative Examples 1 to 3 were charged and discharged once at 0.2C and once at 1C. The ratio of the 1C charging capacity to the 0.2C charging capacity was calculated, and the results were shown as rapid charging rates in Table 1 below.

[0127] Experimental Example 3) Evaluation of Cycle Life Characteristics

[0128] Coin-type batteries prepared according to Examples 1 to 3 and Comparative Examples 1 to 3 were subjected to 100 charge-discharge cycles at 1C. The ratio of the 100-cycle discharge capacity to the 1-cycle discharge capacity was calculated, and the result was shown as the capacity retention rate in Table 1 below.

[0129] Experimental Example 4) Point of sharp drop in CFC (coin full cell)

[0130] The coin-type batteries prepared according to Examples 1 to 3 and Comparative Examples 1 to 3 were charged and discharged 500 times under the following charge and discharge conditions.

[0131] Charging: 1.0C / Cut-off: 4.0V-0.05C

[0132] Discharge: 1.0C / Cutoff: 2.5V

[0133] The ratio of the discharge capacity in each cycle to the discharge capacity in a single cycle was calculated. The number of cycles at which the ratio of discharge capacity drops to 85% or less is shown in Table 1 below.

[0134] Capacity (mAh / g) Efficiency (%) Rapid Charge / Discharge (%) Capacity retention rate (%) CFC sharp decline point (cyc.) Example 1 505 92 78 98 350 Example 2 505 92 78 98 400 Example 3 502 91 77 94 380 Example 4 481 86 75 98 210 Comparative Example 1 499 91 76 95 210 Comparative Example 2 497 90 75 94 210 Comparative Example 3 472 84 73 30 3

[0135] As shown in Table 1 above, the batteries of Examples 1 to 3 exhibited high specific capacity, efficiency, and rapid charge / discharge characteristics, while also demonstrating a very excellent capacity retention rate. In addition, the battery of Example 4 showed a very excellent capacity retention rate, although its specific capacity was somewhat lower. In particular, it can be seen that the discharge capacity of the batteries of Examples 1 to 3 is well maintained up to at least 350 charge / discharge cycles.

[0136] On the other hand, it can be seen that the battery of Comparative Example 1, which does not include a functional layer, and Comparative Example 2, which has a functional layer containing only nanocarbon, has a low specific capacity and the discharge capacity dropped sharply after 210 charge-discharge cycles.

[0137] In addition, the battery of Comparative Example 3, which used nano metal and nano carbon in the negative electrode active material layer, exhibited somewhat low rapid charge / discharge characteristics, very low specific capacity and efficiency, and a significantly degraded capacity retention rate. In particular, the discharge capacity of the battery of Comparative Example 3 dropped sharply after only three charge / discharge cycles.

[0138] Although preferred embodiments of the present invention have been described above, the present invention is not limited thereto and can be implemented with various modifications within the scope of the claims, the detailed description of the invention, and the attached drawings, and it is obvious that such modifications also fall within the scope of the present invention.

Claims

Claim 1 A cathode comprising a current collector; a negative electrode active material layer; and a functional layer comprising nanometal and nanocarbon, wherein the functional layer is located between the current collector and the negative electrode active material layer, and the negative electrode active material layer comprises a negative electrode active material of a Si-C composite and crystalline carbon. Claim 2 delete Claim 3 delete Claim 4 In claim 1, the nanometal is a cathode that is Ag, Pt, Al, Zn, Au, Mg, Ge, Cu, In, Ni, Bi, or a combination thereof. Claim 5 A cathode according to claim 1, wherein the content of the nanometal is 1% to 50% by weight with respect to 100% by weight of the functional layer. Claim 6 A cathode according to claim 1, wherein the mixing ratio of the nanometal and the nanocarbon is 10:90 to 40:60 by weight. Claim 7 In claim 1, the cathode having a functional layer thickness of 50 nm or more. Claim 8 In claim 7, the cathode having a functional layer thickness of 50 nm to 20 μm. Claim 9 In claim 1, the nanocarbon is a cathode that is carbon black, acetylene black, Ketjen black, Denka black, carbon nanotubes, carbon nanofibers, graphite, or a combination thereof. Claim 10 A cathode according to claim 1, wherein the functional layer further comprises a binder. Claim 11 A lithium secondary battery comprising the cathode; a positive electrode; and an electrolyte of claim 1.

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