Lithium secondary battery and method for manufacturing same

Abstract

To provide a lithium battery utilizing a composite current collector.SOLUTION: A lithium secondary battery according to an embodiment of the present invention includes a plurality of stacked unit cells and a separator interposed between the plurality of unit cells, wherein each of the plurality of unit cells includes a composite current collector including an upper surface and a lower surface facing each other, a first active material layer on the upper surface of the composite current collector, and a second active material layer on the lower surface of the composite current collector, and the composite current collectors of the unit cells adjacent to each other among the plurality of unit cells are in contact with each other.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present invention relates to a composite substrate for a lithium secondary battery and a lithium secondary battery including the same. [Background technology]

[0002] Recently, with the rapid spread of battery-powered electronic devices such as mobile phones, laptops, and electric vehicles, the demand for high-energy-density and high-capacity secondary batteries has been increasing rapidly. Accordingly, research and development efforts to improve the performance of lithium secondary batteries have been actively conducted.

[0003] A lithium secondary battery is a battery that includes a cathode and an anode, each containing an active material capable of intercalating and deintercalating lithium ions, and an electrolyte. Electrical energy is produced through oxidation and reduction reactions that occur when lithium ions are intercalated and deintercalated at the cathode and anode. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2004 / 023584 Summary of the Invention [Problem to be solved by the invention]

[0005] The problem to be solved by the present invention is to provide a lithium battery utilizing a composite current collector. [Means for solving the problem]

[0006] A lithium secondary battery according to an embodiment of the present invention includes a plurality of stacked unit cells and a separator interposed between the plurality of unit cells, wherein each of the plurality of unit cells includes a composite current collector having upper and lower surfaces facing each other, a first active material layer on the upper surface of the composite current collector, and a second active material layer on the lower surface of the composite current collector, and the composite current collectors of adjacent unit cells among the plurality of unit cells may be in contact with each other.

[0007] A lithium secondary battery according to some embodiments of the present invention includes a plurality of stacked unit cells, a separator interposed between the plurality of unit cells, and an electrolyte in contact with the separator, wherein each of the plurality of unit cells includes a composite current collector, a first active material layer on an upper surface of the composite current collector, and a second active material layer on a lower surface of the composite current collector, the electrolyte being in contact with the first active material layer, the second active material layer, and the separator, and the composite current collectors of adjacent unit cells among the plurality of unit cells may be in contact with each other.

[0008] A method for manufacturing a lithium secondary battery according to an embodiment of the present invention includes stacking a plurality of unit cells, each of the plurality of unit cells including a composite current collector, sealing the first, second, third, and fourth sides of each of the plurality of unit cells, the first and second sides facing each other, the third and fourth sides facing each other, and the first and second sides intersecting the third and fourth sides, injecting an electrolyte through the fourth side, and sealing the fourth side, wherein each of the plurality of unit cells includes a composite current collector having upper and lower sides facing each other, a first active material layer on the upper side of the composite current collector, and a second active material layer on the lower side of the composite current collector, and the composite current collectors of adjacent unit cells among the plurality of unit cells may be in contact with each other. [Effects of the Invention]

[0009] According to an embodiment of the present invention, each of the stacked unit cells may include a composite current collector including a support layer, a first active material layer on the upper surface of the composite current collector, and a second active material layer on the lower surface of the composite current collector. The support layers of adjacent unit cells among the plurality of unit cells may contact each other and be bonded together to form an integrated unit. This allows an electrolyte to fill the inside of the bonded support layers. This allows a lithium battery using the composite current collector to be provided. Furthermore, by using the composite current collector, a lithium secondary battery with reduced weight and excellent space utilization may be provided. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a conceptual diagram illustrating a lithium secondary battery according to an embodiment of the present invention; [Figure 2] 1 is a schematic diagram illustrating a lithium secondary battery according to an embodiment, the lithium secondary battery having a cylindrical battery shape. [Figure 3] 1 is a cross-sectional view showing a lithium secondary battery according to an embodiment. [Figure 4] 1 is a schematic diagram illustrating a lithium secondary battery according to an embodiment, the battery having a prismatic shape. [Figure 5] 1 is a schematic diagram illustrating a lithium secondary battery according to an embodiment, in the form of a pouch-shaped battery. [Figure 6] 1 is a perspective view of a lithium secondary battery according to an embodiment of the present invention; [Figure 7] FIG. 7 is a cross-sectional view taken along line AA' in FIG. [Figure 8] FIG. 7 is a cross-sectional view taken along line BB' in FIG. [Figure 9] FIG. 1 is a perspective view of a composite current collector according to an embodiment of the present invention. [Figure 10] FIG. 10 is a cross-sectional view taken along line AA' in FIG. [Figure 11] FIG. 1 is a perspective view of a unit cell according to an embodiment of the present invention. [Figure 12] FIG. 11 is a cross-sectional view taken along line AA' in FIG. [Figure 13]FIG. 2 is a perspective view of a plurality of stacked unit cells according to an embodiment of the present invention. [Figure 14] FIG. 14 is a cross-sectional view taken along line AA' in FIG. [Figure 15] FIG. 2 is a perspective view of a plurality of stacked unit cells according to an embodiment of the present invention. [Figure 16] FIG. 16 is a cross-sectional view taken along line AA' in FIG. [Figure 17] FIG. 16 is a cross-sectional view taken along line BB' in FIG. [Figure 18] FIG. 2 is a perspective view of a plurality of stacked unit cells according to an embodiment of the present invention. [Figure 19] FIG. 19 is a cross-sectional view taken along line AA' in FIG. [Figure 20] FIG. 19 is a cross-sectional view taken along line BB' in FIG. [Figure 21] FIG. 2 is a perspective view of a plurality of stacked unit cells according to an embodiment of the present invention. [Figure 22] FIG. 22 is a cross-sectional view taken along line BB' in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0011] In order to fully understand the configuration and effects of the present invention, preferred embodiments of the present invention will be described with reference to the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, and can be implemented in various forms and can be modified in various ways. However, the description of the present embodiments is provided to ensure a complete disclosure of the present invention and to fully convey the scope of the invention to those skilled in the art to which the present invention pertains.

[0012] In this specification, when a certain component is referred to as being on another component, it means that it can be formed directly on the other component, or a third component can be interposed therebetween. Also, in the drawings, the thickness of the components is exaggerated for the sake of efficient explanation of the technical content. Parts designated with the same reference numerals throughout the specification refer to the same components.

[0013] Unless otherwise specified herein, the singular can also include the plural. Furthermore, unless otherwise specified, "A or B" can mean "including A, including B, or including A and B." As used in the specification, "comprises" and / or "comprising" does not exclude the presence or addition of one or more other elements to the referenced element.

[0014] As used herein, "combinations thereof" can mean mixtures, laminates, composites, copolymers, alloys, blends, reaction products, and the like of compositions.

[0015] Unless otherwise defined herein, particle size refers to the average particle size. Furthermore, particle size refers to the average particle size (D50), which refers to the diameter of particles with a cumulative volume of 50% in a particle size distribution. The average particle size (D50) can be measured by methods well known to those skilled in the art, such as using a particle size analyzer or a transmission electron microscope (TEM) or scanning electron microscope (SEM) image. Alternatively, the average particle size (D50) can be measured using a measuring device that uses dynamic light scattering, and data analysis can be performed to count the number of particles in each particle size range, after which the average particle size (D50) can be calculated. Alternatively, the average particle size (D50) can be measured using a laser diffraction method. More specifically, when measuring by the laser diffraction method, the particles to be measured are dispersed in a dispersion medium, then introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000), and irradiated with ultrasonic waves of approximately 28 kHz at an output of 60 W. The average particle size (D50) based on 50% of the particle size distribution in the measuring device can then be calculated.

[0016] 1 is a schematic diagram illustrating a lithium secondary battery according to an embodiment of the present invention. Referring to FIG. 1, the lithium secondary battery may include a positive electrode 10, a negative electrode 20, a separator 30, and an electrolyte ELL.

[0017] The positive electrode 10 and the negative electrode 20 may be separated from each other by a separator 30. The separator 30 may be disposed between the positive electrode 10 and the negative electrode 20. The positive electrode 10, the negative electrode 20, and the separator 30 may be in contact with an electrolyte solution ELL. The positive electrode 10, the negative electrode 20, and the separator 30 may be impregnated in the electrolyte solution ELL.

[0018] The electrolyte ELL can be a medium for transferring lithium ions between the positive electrode 10 and the negative electrode 20. In the electrolyte ELL, the lithium ions can pass through the separator 30 and move toward the positive electrode 10 or the negative electrode 20.

[0019] positive electrode 10 The positive electrode 10 for a lithium secondary battery may include a current collector COL1 and a positive electrode active material layer AML1 formed on the current collector COL1. The positive electrode active material layer AML1 includes a positive electrode active material and may further include a binder and / or a conductive material.

[0020] In one embodiment, the positive electrode 10 can further include an additive that can act as a sacrificial positive electrode.

[0021] The content of the positive electrode active material in the positive electrode active material layer AML1 may be 90 wt % to 99.5 wt % relative to 100 wt % of the positive electrode active material layer AML1, and the contents of the binder and conductive material may be 0.5 wt % to 5 wt % each relative to 100 wt % of the positive electrode active material layer AML1.

[0022] The binder serves to firmly adhere the positive electrode active material particles to each other and to firmly adhere the positive electrode active material to the current collector COL1. Representative examples of binders 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, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylate styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, and nylon.

[0023] The conductive material is used to impart conductivity to the electrode, and any material that does not cause a chemical change in the constructed battery and is electronically conductive can be used. Examples of conductive materials 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; and mixtures thereof.

[0024] The current collector COL1 can be made of Al, but is not limited to this.

[0025] positive electrode active material The positive electrode active material in the positive electrode active material layer AML1 may be a compound capable of reversibly inserting and extracting lithium (lithiated intercalation compound). Specifically, one or more of composite oxides of lithium and a metal selected from cobalt, manganese, nickel, and combinations thereof may be used.

[0026] The composite oxide is a lithium transition metal composite oxide, and specific examples thereof include lithium nickel oxide, lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate compound, cobalt-nickel-manganese oxide, or a combination thereof.

[0027] For example, a compound represented by any one of the following chemical formulas can be used: Li a A 1-b X b O 2-c D c (0.90≦ a≦ 1.8, 0≦ b≦ 0.5, 0≦ c≦ 0.05);Li a Mn 2-b X b O 4-c D c (0.90≦ a≦ 1.8, 0≦ b≦ 0.5, 0≦ c≦ 0.05);Li a Ni 1-b-c Co b X c O 2-α D α (0.90≦ a≦ 1.8, 0≦ b≦ 0.5, 0≦ c≦ 0.5, 0<α<2);Li a Ni 1-b-c Mn b X c O 2-α D α (0.90≦ a≦ 1.8, 0≦ b≦ 0.5, 0≦ c≦ 0.5, 0<α<2);Li a Ni b Co c L 1 d G e O2(0.90≦ a≦ 1.8, 0≦ b≦ 0.9, 0≦ c≦ 0.5, 0≦ d≦ 0.5, 0≦ e≦ 0.1);Li a 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 bO2(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).

[0028] In the chemical formula, A is Ni, Co, Mn, or a combination thereof; X is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element, or a combination thereof; D is O, F, S, P, or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof; and L1 is Mn, Al, or a combination thereof.

[0029] For example, the positive electrode active material may be a high-nickel-based positive electrode 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 but 99 mol% or less relative to 100 mol% of metals excluding lithium in a lithium transition metal composite oxide. The high-nickel-based positive electrode active material can provide high capacity and therefore can be applied to high-capacity, high-density lithium secondary batteries.

[0030] negative electrode 20 The negative electrode 20 for a lithium secondary battery includes a current collector COL2 and a negative electrode active material layer AML2 located on the current collector COL2. The negative electrode active material layer AML2 includes a negative electrode active material and may further include a binder and / or a conductive material.

[0031] For example, the negative electrode active material layer AML2 may contain 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.

[0032] The binder serves to firmly adhere the negative electrode active material particles to each other and to firmly adhere the negative electrode active material to the current collector COL 2. The binder may be a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof.

[0033] Examples of non-aqueous binders include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or combinations thereof.

[0034] The water-based binder may be selected from styrene-styrene rubber, (meth)acrylate styrene-styrene rubber, (meth)acrylonitrile-styrene rubber, (meth)acrylic rubber, butyl rubber, fluororubber, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, poly(meth)acrylonitrile, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0035] When an aqueous binder is used as the negative electrode binder, it may further contain a cellulose-based compound that can impart viscosity. The cellulose-based compound may be a mixture of one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, or alkali metal salts thereof. The alkali metal may be sodium, potassium, or lithium.

[0036] The dry binder may be a fiberizable polymeric material such as polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0037] The conductive material is used to impart conductivity to the electrode, and any material that does not cause a chemical change in the constructed battery and is electronically conductive can be used. Specific examples 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 in the form of metal powder or metal fiber, including copper, nickel, aluminum, and silver; conductive polymers such as polyphenylene derivatives; and mixtures thereof.

[0038] The current collector COL2 may be made of a material selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof.

[0039] negative electrode active material The negative electrode active material in the negative electrode active material layer AML2 includes a material capable of reversibly inserting / extracting lithium ions, lithium metal, a lithium metal alloy, a material capable of being doped with and de-doped from lithium, or a transition metal oxide.

[0040] The carbon-based negative electrode active material capable of reversibly inserting / extracting lithium ions may include, for example, 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, hard carbon, mesophase pitch carbide, and calcined coke.

[0041] As the 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.

[0042] As a substance capable of being doped and undoped with lithium, a Si-based negative electrode active material or a Sn-based negative electrode active material can be used. The Si-based negative electrode active material can be silicon, a silicon-carbon composite, SiOx (0 < x < 2), a Si-Q alloy (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 combinations thereof. The Sn-based negative electrode active material can be Sn, SnO2, a Sn-based alloy, or combinations thereof.

[0043] The silicon-carbon composite can be a composite of silicon and amorphous carbon. According to one embodiment, the silicon-carbon composite can be in a form in which silicon particles are coated with amorphous carbon on the surface of the silicon particles. For example, it can include secondary particles (cores) assembled from primary silicon particles and an amorphous carbon coating layer (shell) located on the surface of the secondary particles. The amorphous carbon can also be located between the primary silicon particles, for example, the primary silicon particles can be coated with amorphous carbon. The secondary particles can be dispersed and present in an amorphous carbon matrix.

[0044] The silicon-carbon composite may further contain crystalline carbon. For example, the silicon-carbon composite can include a core containing crystalline carbon and silicon particles and an amorphous carbon coating layer located on the surface of the core.

[0045] The Si-based negative electrode active material or the Sn-based negative electrode active material can be used by mixing with a carbon-based negative electrode active material.

[0046] Separator 30 Depending on the type of lithium secondary battery, a separator 30 may be present between the positive electrode 10 and the negative electrode 20. As such separator 30, polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more layers thereof may be used, and it goes without saying that 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.

[0047] Separator 30 can include a porous substrate and a coating layer comprising an organic material, an inorganic material, or a combination thereof located on one or both sides of the porous substrate.

[0048] The porous substrate may be a polymer membrane 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, polyaryl ether ketone, polyetherimide, polyamide imide, polybenzimidazole, polyethersulfone, polyphenylene oxide, cyclic olefin copolymers, polyphenylene sulfide, polyethylene naphthalate, glass fiber, Teflon (registered trademark), and polytetrafluoroethylene, or a copolymer or mixture of two or more of these.

[0049] The organic material may include a polyvinylidene fluoride polymer or a (meth)acrylic polymer.

[0050] The inorganic material may include, but is not limited to, inorganic particles selected from Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, boehmite, and combinations thereof.

[0051] The organic material and the inorganic material may be mixed in one coating layer, or may be stacked in a form in which a coating layer containing an organic material and a coating layer containing an inorganic material are laminated.

[0052] Electrolyte ELL The electrolyte ELL for lithium secondary batteries contains a non-aqueous organic solvent and a lithium salt.

[0053] The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can migrate.

[0054] The non-aqueous organic solvent can be a carbonate, ester, ether, ketone, or alcohol solvent, an aprotic solvent, or a combination thereof.

[0055] Examples of carbonate solvents that can be used include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC).

[0056] Examples of ester solvents that can be used include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolide, mevalonolactone, valerolactone, and caprolactone.

[0057] Examples of ether solvents that can be used include dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, and tetrahydrofuran. Examples of ketone solvents that can be used include cyclohexanone. Examples of alcohol solvents that can be used include ethyl alcohol and isopropyl alcohol. Examples of aprotic solvents that can be used include nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, which may contain a double bond, an aromatic ring, or an ether group); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane and 1,4-dioxolane; and sulfolanes.

[0058] The non-aqueous organic solvents can be used alone or in combination of two or more.

[0059] When a carbonate-based solvent is used, a cyclic carbonate and a chain carbonate may be mixed together, and the cyclic carbonate and the chain carbonate may be mixed in a volume ratio of 1:1 to 1:9.

[0060] Lithium salts are dissolved in organic solvents and act as a source of lithium ions in the battery, enabling basic lithium secondary battery operation and facilitating the movement of lithium ions between the positive and negative electrodes. Representative examples of lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide (LiFSI), LiC4F9SO3, LiN(C x F 2x+1 SO2)(C y F 2y+1SO2) (x and y are integers from 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalato)phosphate (LiDFOB), and lithium bis(oxalato)borate (LiBOB).

[0061] Lithium secondary battery Lithium secondary batteries can be classified into cylindrical, prismatic, pouch, and coin types depending on their shape. FIGS. 2 to 5 are schematic diagrams showing lithium secondary batteries according to embodiments, with FIG. 2 being a cylindrical type, FIG. 3 being a cross-sectional view, FIG. 4 being a prismatic type, and FIG. 5 being a pouch type. Referring to FIGS. 2 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 housed. 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. 2. Also, as shown in FIG. 3, the lithium secondary battery 100 may include a positive electrode lead tab 11, a positive electrode terminal 12, a negative electrode lead tab 21, and a negative electrode terminal 22. As shown in FIGS. 4 and 5, the lithium secondary battery 100 may include electrode tabs 70, i.e., a positive electrode tab 71 and a negative electrode tab 72, which serve as electrical paths for conducting current generated in the electrode assembly 40 to the outside.

[0062] Figure 6 is a perspective view of a lithium secondary battery according to an embodiment of the present invention. Figure 7 is a cross-sectional view taken along line A-A' in Figure 6. Figure 8 is a cross-sectional view taken along line B-B' in Figure 6. For simplicity of explanation, descriptions that overlap with those of the lithium secondary battery described with reference to Figures 1 to 5 will be omitted.

[0063] 6 to 8, a lithium secondary battery according to an embodiment of the present invention includes a plurality of unit cells CEL1, CEL2, and CEL3 stacked one on another, a separator 30 interposed between the unit cells, and an electrolyte ELL. The separator 30 may correspond to the separator 30 described with reference to FIG.

[0064] A plurality of unit cells CEL1, CEL2, and CEL3 may be stacked on one another along a third direction D3. For example, the plurality of unit cells CEL1, CEL2, and CEL3 may include a first unit cell CEL1, a second unit cell CEL2 on the first unit cell CEL1, and a third unit cell CEL3 on the second unit cell CEL2. The first to third unit cells CEL1, CEL2, and CEL3 may be electrically connected to one another.

[0065] Referring to FIG. 6, only three unit cells CEL1, CEL2, and CEL3 are shown, but the present invention is not limited thereto, and three or more unit cells may be stacked.

[0066] Each of the plurality of unit cells CEL1, CEL2, and CEL3 may include a composite current collector CPS having upper and lower surfaces facing each other, a first active material layer AL1 on the upper surface of the composite current collector CPS, and a second active material layer AL2 on the lower surface of the composite current collector CPS.

[0067] The first active material layer AL1 may be any one of the positive electrode active material layer AML1 and the negative electrode active material layer AML2 previously described with reference to Fig. 1. The second active material layer AL2 may be the other one of the positive electrode active material layer AML1 and the negative electrode active material layer AML2 previously described with reference to Fig. 1. In one embodiment of the present invention, the first active material layer AL1 may be the positive electrode active material layer AML1, and the second active material layer AL2 may be the negative electrode active material layer AML2.

[0068] The composite current collector CPS may include a support layer SPL, a first metal layer ME1 on the upper surface of the support layer SPL, and a second metal layer ME2 on the lower surface of the support layer SPL. The thickness of each of the first metal layer ME1 and the second metal layer ME2 may be, for example, 200 nm to 5 μm. A first active material layer AL1 may be disposed on the first metal layer ME1, and a second active material layer AL2 may be disposed on the second metal layer ME2. Each of the first and second metal layers ME1 and ME2 of the composite current collector CPS may correspond to the current collector COL1 or COL2 described above with reference to FIG. 1.

[0069] The support layer SPL may be, for example, a porous film. The porosity of the support layer SPL may be, for example, 30% to 70%, 35% to 55%, 42% to 64%, 31% to 62%, or 48% to 65%. The thickness of the support layer may be, for example, 3 μm to 10 μm. When the porosity and / or thickness of the support layer SPL satisfy the above numerical ranges, the lithium secondary battery may have excellent mechanical stability and integration. The support layer SPL may, for example, include one or more of a polyethylene film, a polypropylene film, a polyvinylidene chloride film, and a multilayer film formed by combining these.

[0070] The composite current collectors CPS of adjacent unit cells CEL1, CEL2, and CEL3 may be in contact with each other. More specifically, the support layers SPL of adjacent unit cells CEL1, CEL2, and CEL3 may be in contact with each other and bonded to each other. The bonded support layers SPL may surround the first metal layer ME1, the first active material layer AL1, the separator 30, the second metal layer ME2, and the second active material layer AL2.

[0071] For example, the support layer SPL of the first unit cell CEL1 and the support layer SPL of the second unit cell CEL2 may be bonded together to form an integrated structure. The combined support layer SPL may surround the first metal layer ME1 and the first active material layer AL1 of the first unit cell CEL1 and the second metal layer ME2 and the second active material layer AL2 of the second unit cell CEL2, and the separator 30.

[0072] For example, the support layer SPL of the second unit cell CEL1 and the support layer SPL of the third unit cell CEL2 may be bonded together to form an integrated structure. The combined support layer SPL may surround the first metal layer ME1 and the first active material layer AL1 of the second unit cell CEL2 and the second metal layer ME2, the second active material layer AL2, and the separator 30 of the third unit cell CEL3.

[0073] That is, the support layer SPL according to an embodiment of the present invention can perform not only the role of a support layer for the composite substrate but also the role of packaging, thereby providing a lithium secondary battery with excellent space utilization.

[0074] An electrolyte solution ELL may be disposed inside the combined support layers SPL. For example, the support layer SPL of the first unit cell CEL1 and the support layer SPL of the second unit cell CEL2 may be combined together to form a single unit. The electrolyte solution ELL may fill the inside of the combined support layers SPL. For example, the support layer SPL of the second unit cell CEL2 and the support layer SPL of the third unit cell CEL3 may be combined together to form a single unit. The electrolyte solution ELL may fill the inside of the combined support layers SPL.

[0075] The electrolyte solution ELL may be in contact with the first metal layer ME1, the first active material layer AL1, the second metal layer ME2, the second active material layer AL2, and the separator 30. The first metal layer ME1, the first active material layer AL1, the second metal layer ME2, the second active material layer AL2, and the separator 30 may be impregnated with the electrolyte solution ELL. The electrolyte solution ELL may correspond to the electrolyte solution described with reference to FIG. 1.

[0076] The first unit cell CEL1, the second unit cell CEL2, the third unit cell CEL3, the electrolyte ELL, and the separator 30 in FIG. 6 may constitute the electrode assembly 40 described above with reference to FIGS.

[0077] 9 to 22 are views illustrating a manufacturing process of a lithium secondary battery according to an embodiment of the present invention. FIG. 9 is a perspective view of a composite current collector according to an embodiment of the present invention. FIG. 10 is a cross-sectional view taken along line A-A' of FIG. 9. FIG. 11 is a perspective view of a unit cell according to an embodiment of the present invention. FIG. 12 is a cross-sectional view taken along line A-A' of FIG. 11. FIG. 13 is a perspective view of a plurality of stacked unit cells according to an embodiment of the present invention. FIG. 14 is a cross-sectional view taken along line A-A' of FIG. 13. FIG. 15 is a perspective view of a plurality of stacked unit cells according to an embodiment of the present invention. FIG. 16 is a cross-sectional view taken along line A-A' of FIG. 15. FIG. 17 is a cross-sectional view taken along line B-B' of FIG. 15. FIG. 18 is a perspective view of a plurality of stacked unit cells according to an embodiment of the present invention. FIG. 19 is a cross-sectional view taken along line A-A' of FIG. 18. FIG. 20 is a cross-sectional view taken along line B-B' of FIG. 18. FIG. 21 is a perspective view of a plurality of stacked unit cells according to an embodiment of the present invention. FIG. 22 is a cross-sectional view taken along line B-B' of FIG. 21. For the sake of simplicity, the description overlapping with the lithium secondary battery described with reference to FIGS. 1 to 6 will be omitted.

[0078] 9 and 10, a composite current collector CPS can be provided, including a support layer SPL, a first metal layer ME1 on the upper surface of the support layer SPL, and a second metal layer ME2 on the lower surface of the support layer SPL. In one embodiment, the support layer SPL may be a porous film. In one embodiment, the porosity of the support layer SPL may be 30% to 70%, 35% to 55%, 42% to 64%, 31% to 62%, or 48% to 65%. In one embodiment, the thickness of the support layer SPL may be 3 μm to 10 μm. For example, the thickness of each of the first metal layer ME1 and the second metal layer ME2 may be 200 nm to 5 μm. Each of the first and second metal layers ME1 and ME2 may correspond to the current collector COL1 or COL2 described above with reference to FIG. 1.

[0079] 11 and 12, a first active material layer AL1 may be coated on a first metal layer ME1, and a second active material layer AL2 may be coated on a second metal layer ME2, forming a first unit cell CEL1.

[0080] The first active material layer AL1 may be any one of the positive electrode active material layer AML1 and the negative electrode active material layer AML2 previously described with reference to Fig. 1. The second active material layer AL2 may be the other one of the positive electrode active material layer AML1 and the negative electrode active material layer AML2 previously described with reference to Fig. 1. In one embodiment of the present invention, the first active material layer AL1 may be the positive electrode active material layer AML1, and the second active material layer AL2 may be the negative electrode active material layer AML2.

[0081] 13 and 14, a plurality of unit cells CEL1, CEL2, and CEL3 may be stacked on one another along a third direction D3. The plurality of unit cells CEL1, CEL2, and CEL3 may include a first unit cell CEL1, a second unit cell CEL2 on the first unit cell CEL1, and a third unit cell CEL3 on the second unit cell CEL2, as one embodiment. The second unit cell CEL2 and the third unit cell CEL3 may be manufactured using the same method as the first unit cell CEL1 described with reference to FIGS. 9 to 12.

[0082] A separator 30 may be interposed between the unit cells CEL1, CEL2, and CEL3. The separator 30 may correspond to the separator described with reference to FIG.

[0083] 15 and 16, among the first surface 1a, the second surface 2a, the third surface 3a, and the fourth surface 4a of each of the plurality of unit cells CEL1, CEL2, and CEL3, the first surface 1a, the second surface 2a, and the third surface 3a may be opposite surfaces, and the third surface 3a and the fourth surface 4a may be opposite surfaces. The first surface 1a and the second surface 2a may be surfaces that intersect with the third surface 3a and the fourth surface 4a.

[0084] In one embodiment, the sealing process may include bonding the support layers SPL of the unit cells CEL1, CEL2, and CEL3 to one another through thermocompression bonding. This allows the support layers SPL of the unit cells CEL1, CEL2, and CEL3 to be connected and / or contacted to one another. That is, the support layers SPL of the unit cells CEL1, CEL2, and CEL3 may be bonded together through the sealing process.

[0085] Referring to Figures 17 and 18, the first metal layer ME1, first active material layer AL1, second metal layer ME2, and second active material layer AL2 of each of the multiple unit cells CEL1, CEL2, and CEL3 can be exposed through the unsealed fourth surface 4a.

[0086] 19 and 20, an electrolyte solution ELL may be injected into the plurality of unit cells CEL1, CEL2, and CEL3 through the unsealed fourth surface 4a. The electrolyte solution ELL may correspond to the electrolyte solution ELL described with reference to FIG.

[0087] 21 and 22, the fourth surfaces 4a of the unit cells CEL1, CEL2, and CEL3 can be sealed. In one embodiment, the sealing process may include bonding the support layer SPL on the fourth surface 4a side of each of the unit cells CEL1, CEL2, and CEL3 by thermocompression bonding.

[0088] The sealing process can close all surfaces (first to fourth surfaces 1a, 2a, 3a, and 4a, in one embodiment) of each of the unit cells CEL1, CEL2, and CEL3. The sealing process can seal the electrolyte solution ELL inside the sealed support layer SPL. The sealing process can fill the inside of the combined support layer SPL. The first metal layer ME1, first active material layer AL1, second metal layer ME2, second active material layer AL2, and separator 30 can be impregnated with the electrolyte solution ELL.

[0089] Although the embodiments of the present invention have been described above with reference to the accompanying drawings, the present invention may be embodied in other specific forms without changing the technical spirit or essential features thereof. Therefore, it should be understood that the embodiments described above are illustrative in all respects and are not limiting. [Explanation of symbols]

[0090] 10 Positive electrode 10 20 Negative electrode 20 30 Separator 40 Electrode assembly AL1 1st active material layer AL2 2nd active material layer CEL1, CEL2, CEL3 unit cells CPS composite current collector ELL electrolyte ME1 1st metal layer ME2 2nd metal layer SPL support layer

Claims

1. a plurality of stacked unit cells; a separator interposed between the plurality of unit cells, Each of the plurality of unit cells comprises: a composite current collector including opposing upper and lower surfaces; a first active material layer on the top surface of the composite current collector; a second active material layer on the lower surface of the composite current collector, The composite current collectors of adjacent unit cells among the plurality of unit cells are in contact with each other.

2. The composite current collector is a support layer including opposing upper and lower surfaces; a first metal layer on the top surface of the support layer; a second metal layer on the lower surface of the support layer.

3. The lithium secondary battery according to claim 2 , wherein the support layers of adjacent unit cells among the plurality of unit cells are in contact with each other.

4. The lithium secondary battery according to claim 2 , wherein the support layer comprises at least one of a polyethylene film, a polypropylene film, a polyvinylidene chloride film, and a multilayer film formed by combining these films.

5. 3. The lithium secondary battery of claim 2, wherein each of the first metal layer and the second metal layer includes at least one of aluminum, an aluminum alloy, copper, a copper alloy, nickel, a nickel alloy, titanium, a titanium alloy, iron, an iron alloy, silver, and a silver alloy.

6. The thickness of each of the first metal layer and the second metal layer is 200 nm to 5 μm; 3. The lithium secondary battery according to claim 2, wherein the thickness of the support layer is 3 μm to 10 μm.

7. 3. The lithium secondary battery according to claim 2, wherein the porosity of the support layer is 30% to 70%.

8. The lithium secondary battery of claim 1 , wherein each of the plurality of unit cells further comprises an electrolyte in contact with the first active material layer, the second active material layer, and the separator.

9. The lithium secondary battery according to claim 2 , wherein the support layers of adjacent unit cells among the plurality of unit cells are integrally bonded to each other.

10. The lithium secondary battery of claim 1 , wherein the plurality of unit cells are electrically connected to each other.

11. a plurality of stacked unit cells; a separator interposed between the plurality of unit cells; an electrolyte in contact with the separator; Each of the plurality of unit cells comprises: a composite current collector; a first active material layer on an upper surface of the composite current collector; a second active material layer on the lower surface of the composite current collector, the electrolyte solution is in contact with the first active material layer, the second active material layer, and the separator; The composite current collectors of adjacent unit cells among the plurality of unit cells are in contact with each other.

12. the composite current collector includes a support layer, a first metal layer on an upper surface of the support layer, and a second metal layer on a lower surface of the support layer; the support layers of adjacent unit cells among the plurality of unit cells are bonded to each other to form an integral unit; The lithium secondary battery according to claim 11 , wherein the electrolyte fills the inside of the combined support layers.

13. The lithium secondary battery according to claim 12, wherein the support layer comprises at least one of a polyethylene film, a polypropylene film, a polyvinylidene chloride film, and a multilayer film formed by combining these films.

14. 13. The lithium secondary battery according to claim 12, wherein the porosity of the support layer is 30% to 70%.

15. stacking a plurality of unit cells; each of the plurality of unit cells includes a composite current collector; sealing the first surface, the second surface, the third surface, and the fourth surface of each of the plurality of unit cells; the first surface and the second surface are opposite to each other, the third surface and the fourth surface are opposite to each other, the first surface and the second surface intersect with the third surface and the fourth surface, injecting an electrolyte through the fourth surface; sealing the fourth surface; Each of the plurality of unit cells comprises: a composite current collector including opposing upper and lower surfaces; a first active material layer on the top surface of the composite current collector; a second active material layer on the lower surface of the composite current collector, The composite current collectors of adjacent unit cells among the plurality of unit cells are in contact with each other.

16. 16. The method of claim 15, wherein the composite current collector comprises a support layer, a first metal layer on an upper surface of the support layer, and a second metal layer on a lower surface of the support layer.

17. 17. The method of claim 16, wherein the support layer comprises at least one of a polyethylene film, a polypropylene film, a polyvinylidene chloride film, and a multilayer film formed by combining these films.

18. The method of claim 16, wherein the support layers of adjacent unit cells among the plurality of unit cells are bonded to each other to form an integral unit.

19. 17. The method of claim 16, wherein the porosity of the support layer is 30% to 70%.

20. The thickness of each of the first metal layer and the second metal layer is 200 nm to 5 μm; 17. The method of claim 16, wherein the support layer has a thickness of 3 μm to 10 μm.

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