Lithium secondary battery structure comprising composite conductive current collector

Abstract

The present invention relates to a lithium secondary battery structure having excellent safety by suppressing heat generation or ignition, while exhibiting improved output characteristics. The lithium secondary battery structure comprises a plurality of battery units including: a first electrode comprising a first conductive current collector having an active material layer formed on at least one surface; a second electrode comprising a second conductive current collector having an active material layer formed on at least one surface; and a separator formed between the active material layers of the first and second electrodes facing each other. The first or second conductive current collector is a metal current collector or a composite conductive current collector having a metal layer formed on a polymer substrate for each battery unit, and the metal current collector : the composite conductive current collector are included in the entire battery structure in a number ratio of 5 : 1 to 1 : 5.

Description

Technology Field

[0001] The present invention relates to a lithium secondary battery structure that exhibits enhanced output characteristics while having excellent safety by suppressing heat generation or ignition. Background Technology

[0002] Recently, with the increasing technological development and demand for mobile devices, the demand for rechargeable secondary batteries as an energy source has been rapidly rising, and consequently, extensive research is being conducted on secondary batteries capable of meeting various requirements. Furthermore, secondary batteries are also attracting attention as power sources for electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (Plug-in HEVs), which are being proposed as solutions to address air pollution caused by conventional gasoline and diesel vehicles that use fossil fuels.

[0003] Accordingly, electric vehicles (EVs) that can be operated solely on secondary batteries and hybrid electric vehicles (HEVs) that use secondary batteries in combination with conventional engines have been developed, and some have been commercialized. While nickel-metal hydride (Ni-MH) secondary batteries are mainly used as power sources for EVs and HEVs, research on the use of lithium secondary batteries, which have high energy density, high discharge voltage, and output stability, is currently being actively conducted and some have been commercialized.

[0004] Such a lithium secondary battery is manufactured by applying an electrode slurry containing an electrode active material to an electrode current collector, drying and rolling to produce an electrode, and then embedding an electrode assembly with a separator interposed between the electrodes in a battery case together with an electrolyte.

[0005] Meanwhile, although copper or aluminum is commonly used as the material for electrode current collectors, aluminum, which is conventionally used as an anode current collector, presents a problem in that it exhibits a dangerous mode leading to ignition by coming into contact with the cathode active material in the event of a short circuit.

[0006] To address this, an attempt was made to replace the conventional aluminum anode current collector with a current collector coated with aluminum on a PET substrate; however, while this increases the resistance of the current collector itself and thus raises the short-circuit resistance upon contact with the cathode active material—which is expected to reduce the risk of ignition during safety verification—it results in a problem where the overall cell resistance increases, degrading output characteristics.

[0007] Therefore, there is a continuous demand for the development of technology that can improve output characteristics and achieve high stability by applying organic / metal composites as metal current collectors. The problem to be solved

[0008] Accordingly, the present invention provides a lithium secondary battery structure that exhibits improved output characteristics while possessing excellent safety by suppressing heat generation or ignition caused by external impact, etc.

[0009] In addition, the present invention provides a lithium secondary battery structure comprising a metal current collector and a composite conductive current collector, exhibiting excellent stability and enhanced lifespan characteristics. means of solving the problem

[0010] Hereinafter, a lithium secondary battery structure, etc., according to a specific embodiment of the invention will be described.

[0011] Terms and words used in this specification and claims shall not be interpreted as being limited to their ordinary or dictionary meanings, but shall be interpreted in a meaning and concept consistent with the technical spirit of the invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe his invention.

[0012] The terms used in this specification are used merely to describe exemplary embodiments and are not intended to limit the invention. The singular expression includes the plural expression unless the context clearly indicates otherwise.

[0013] In this specification, terms such as “comprising,” “comprising,” or “having” are intended to specify the existence of the implemented features, numbers, steps, components, or combinations thereof, and should not be understood as precluding the existence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0015] According to one embodiment of the invention, a lithium secondary battery structure is provided comprising a plurality of battery units (A, B), each comprising: a first electrode (100) including a first conductive current collector (110) having an active material layer (120) formed on at least one surface; a second electrode (200) including a second conductive current collector (210) having an active material layer (220) formed on at least one surface; and a separator (300) formed between the active material layers (120, 220) of the first and second electrodes facing each other, wherein the first or second conductive current collector (110, 210) is a metal current collector or a composite conductive current collector (110') having a metal layer (112) formed on a polymer substrate (111) for each battery unit, and the metal current collector : the composite conductive current collector is included in the total battery structure in a number ratio of 5 : 1 to 1 : 5.

[0016] The inventors have been conducting research and experiments to develop a secondary battery that achieves high stability while simultaneously possessing improved output characteristics, unlike conventional secondary batteries using aluminum foil positive current collectors or composite current collectors in which aluminum is coated on a polymer such as PET.

[0017] As a result of these ongoing studies, it was confirmed that excellent performance can be obtained by combining a metal current collector with a composite conductive current collector, consisting of a metal layer coated on a polymer, as the current collector for each battery unit within a battery structure containing multiple battery units. In particular, it was confirmed that stability and cell characteristics can be simultaneously improved by adjusting the ratio of the metal current collector and the composite conductive current collector used in the entire battery structure.

[0018] In the case of aluminum, which is conventionally used as a positive current collector, it exhibits low resistance characteristics but has low stability because a short circuit leads to ignition upon contact with the negative active material. In the case of composite conductive current collectors, which are formed by coating a metal layer on a polymer, the inherent resistance increases, resulting in high short-circuit resistance even when in contact with the negative active material, thus providing excellent stability; however, this increases the overall cell resistance, leading to a deterioration in output characteristics. Thus, there is a trade-off relationship between the two in terms of stability and output characteristics. Accordingly, by adjusting the ratio of the metal current collector and the composite conductive current collector, or by regularly alternating the metal current collector and the composite conductive current collector, it is possible to obtain both stability and output characteristics at a good level.

[0019] These excellent output characteristics can be supported by the initial resistance measurement results of the experimental example described below, excellent stability can be supported by the low ignition and explosion rates in the impact test of the experimental example described below, and lifespan characteristics can be confirmed by the excellent capacity retention rate of 80% or more, or 90% or more, after 300 cycles, in the lifespan characteristic evaluation results according to the charging and discharging process at room temperature of the embodiment described below.

[0020] Meanwhile, in one embodiment of the present invention, the metal current collector supports the active material layer (120, 220) and is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, palladium, calcined carbon, a surface treated with carbon, nickel, silver, etc. on the surface of copper or stainless steel, an aluminum-cadmium alloy, etc. may be used.

[0021] In addition, the metal current collector (110, 210) can form fine irregularities on its surface to strengthen the bonding force with the active material layer, and can be used in various forms such as film, sheet, foil, mesh, net, porous body, foam, nonwoven fabric, etc. For example, the metal current collector may be aluminum foil.

[0022] In one embodiment, the composite conductive current collector (110') may have a structure in which a metal layer (112) is formed on a polymer substrate (111). Specifically, the composite conductive current collector (110') may have a three-layer stacked structure in which a metal layer (112) is formed on each side of the polymer substrate (111).

[0023] In the case of a positive current collector made of a metal material, flexibility is not excellent due to the metal, and it is difficult to achieve lightness of the battery. However, by using the polymer substrate (111), flexibility and lightness of the battery can be secured, and conductivity identical to that of a metal single-material current collector can be provided through the metal layer (112), thereby preventing a decrease in battery performance.

[0024] In one embodiment, the polymer substrate (111) may be a polyester resin substrate, and for example, the polyester resin may include a resin such as polyethylene terephthalate (PET), polytrimethylene terephthalate (PTT), polybutylene terephthalate (PBT), or polyethylene naphthalate (PEN). Preferably, the polymer substrate may be a polyethylene terephthalate (PET) substrate.

[0025] In addition, in one embodiment, the metal layer (112) may be a metal layer such as stainless steel, aluminum, copper, nickel, or titanium, or a surface treated with carbon, nickel, titanium, or silver on the surface of aluminum or stainless steel. In addition, the metal layer may have fine irregularities formed on its surface and may have various forms such as a film, sheet, foil, net, porous body, foam, or nonwoven fabric. For example, the metal layer may be an aluminum layer.

[0026] Meanwhile, processability and the electrochemical performance and stability of the cell can be improved by adjusting the ratio of the thickness of the polymer substrate (111) and the metal layer (112) included in the composite conductive current collector (110'). For example, in the composite conductive current collector (110'), the ratio of the total thickness of the polymer substrate to the total thickness of the metal layer may be 1:2 to 5:1. However, if the ratio of the thickness of the polymer substrate is excessively high, the resistance may increase and the cell performance may be degraded, and if the ratio of the thickness of the metal layer is high, it may result in a structure similar to a metal foil and there may be no difference in terms of stability.

[0027] In the lithium secondary battery structure according to the above embodiment, the first or second conductive current collector (110, 210) may be a metal current collector for each battery unit, or a composite conductive current collector (110') in which a metal layer (112) is formed on a polymer substrate (111). At this time, in at least one battery unit, the first or second conductive current collector (110, 210) may be a composite conductive current collector (110').

[0028] In one embodiment, the first electrode (100) is a positive electrode, and the first conductive current collector (110) may be the metal current collector or the composite conductive current collector (110') for each battery unit. At this time, the first conductive current collector (110) may have a thickness in the range of 6 μm to 20 μm. If the thickness range becomes excessively large or small, the R2R coating process may not be possible if it is less than 6 μm, and there may be a significant loss in the energy density per unit volume of the cell if it exceeds 20 μm.

[0029] In one embodiment, the first conductive current collector (110) is the metal current collector or the composite conductive current collector (110') for each of the battery units (A, B), and the metal current collector and the composite conductive current collector may be arranged alternately in a regular manner according to the stacking order of the first electrode (100).

[0030] Specifically, the metal current collector and the composite conductive current collector (100') may be arranged in a repeating order according to the stacking order of the first electrode (100), such that one composite conductive current collector (110') is arranged for every one to three metal current collectors, or one metal current collector is arranged in a repeating order for every one to three composite conductive current collectors (110').

[0031] For example, if a battery unit including a positive electrode with a metal current collector is denoted as A and a battery unit including a positive electrode with a composite conductive current collector is denoted as B, they may be repeatedly arranged in the order ABAB…ABAB, ABBABB…ABBABB, ABBBABBB…ABBBABBB, AABAAB…AABAAB, or AAAB…AAAB depending on the stacking order of each battery unit. For reference, FIG. 1 shows a schematic cross-sectional view of an example of a lithium secondary battery structure in which a battery unit (A) including a positive electrode and a negative electrode with a metal current collector, a battery unit (B) including a positive electrode with a composite conductive current collector and a negative electrode with a metal current collector, and a battery unit (A) including a positive electrode and a negative electrode with a metal current collector are alternately arranged.

[0032] In one embodiment, when the metal current collector and the composite conductive current collector are included in the entire battery structure in a number ratio of 5:1 to 1:5, excellent output characteristics and lifespan characteristics can be improved while ensuring a high level of stability. In particular, optimal results can be expected when the metal current collector and the composite conductive current collector are included in a number ratio of 3:1 to 1:3. However, if the ratio becomes excessively large or small, the stability characteristics or output characteristics may be degraded.

[0033] In the electrode of one embodiment, the active material layer (120, 220) is formed on both sides of the first and second conductive current collectors (110, 210), and the first and second electrodes (100, 200) may be alternately stacked with a separator (300) in between. For example, an active material layer (120, 220) comprising an active material, a conductive material, and a binder may be formed on the first or second conductive current collector (110, 210).

[0034] In these active material layers (120, 220), if the active material is a positive active material, it is not particularly limited as long as it is a material capable of reversible insertion and extraction of lithium ions, and for example, it may include a lithium metal composite oxide containing one or more metal elements selected from the group consisting of Co, Mn, Ni, W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg and Mo.

[0035] More specifically, as the positive electrode active material, a compound represented by any one of the following chemical formulas may be used. Li a A 1-b R b D2 (wherein 0.90 ≤ a ≤ 1.8 and 0 ≤ b ≤ 0.5); Li a E 1-b R b O 2-c D c (In the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, and 0 ≤ c ≤ 0.05); LiE 2-b R b O 4-c D c (In the above equation, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05); Li a Ni 1-b-c Co b R c D α (In the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05 and 0 < α ≤ 2); Li a Ni 1-b-c Co b R c O 2-α Z α (In the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, and 0 < α < 2); Li a Ni 1-b-c Co b R c O2-α Z2 (wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05 and 0 < α < 2); Li a Ni 1-b-c Mn b R c D α (In the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05 and 0 < α ≤ 2); Li a Ni 1-b-c Mn b R c O 2-α Z α (In the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, and 0 < α < 2); Li a Ni 1-b-c Mn b R c O 2-α Z2 (wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05 and 0 < α < 2); Li a Ni b E c G d O2(wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5 and 0.001 ≤ d ≤ 0.1); Li a Ni b Co c Mn d GeO2(wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0 ≤ d ≤ 0.5 and 0.001 ≤ e ≤ 0.1); Li a NiG b O2(wherein 0.90 ≤ a ≤ 1.8 and 0.001 ≤ b ≤ 0.1); Li a CoG b O2(wherein 0.90 ≤ a ≤ 1.8 and 0.001 ≤ b ≤ 0.1); Li a MnG bO2(wherein 0.90 ≤ a ≤ 1.8 and 0.001 ≤ b ≤ 0.1); Li a Mn2G b O4 (wherein 0.90 ≤ a ≤ 1.8 and 0.001 ≤ b ≤ 0.1); QO2; QS2; LiQS2; V2O5; LiV2O5; LiTO2; LiNiVO4; and Li (3-f) J2(PO4)3(0 ≤ f ≤ 2).

[0036] In the above chemical formula, A is Ni, Co, Mn or a combination thereof; R is Al, Ni, Co, Mn, Cr, Fe, Mg, V or a combination thereof; D is O, F, S, P or a combination thereof; E is Co, Mn or a combination thereof; Z is F, S, P or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, V or a combination thereof; Q is Ti, Mo, Mn or a combination thereof; T is Cr, V, Fe, Sc, Y or a combination thereof; and J is V, Cr, Mn, Co, Ni, Cu or a combination thereof.

[0037] In addition, the compound having a coating layer on its surface may be used, or the compound having a coating layer may be mixed with the compound. The coating layer may be a coating element compound and may include an oxide, hydroxide, oxyhydroxide, oxycarbonate, or hydroxycarbonate of a coating element. The compounds forming the coating layer may be amorphous or crystalline. The coating elements included in the coating layer may be Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or a mixture thereof.

[0038] In addition, the conductive material included in the positive active material layer (120) 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 include natural graphite, artificial graphite, carbon black-based conductive material, carbon fiber, carbon nanotube, metal powder such as copper, nickel, aluminum, silver, metal fiber, etc., and one or more types of conductive materials such as polyphenylene derivatives can be used in combination. Furthermore, the same or different from the carbon-based conductive material included in the safety protection layer described above can be used as such a conductive material.

[0039] The conductive material may be added in an amount of 1 to 50 weight% or 2 to 20 weight% based on the total weight of the positive electrode active material layer (120). By doing so, excellent electrical properties can be imparted to the positive electrode, while ensuring the desirable formation of the positive electrode.

[0040] The above binder serves to adhere the positive active material particles well to each other and also increases the adhesion of the positive active material layer (120). Representative examples include the above-mentioned halogenated polyolefin-based polymer binder, polyvinyl alcohol, carboxymethylcellulose, hydroxypropylcellulose, diacetylcellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polymer containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, or nylon.

[0041] The binder may be added in an amount of 1 to 50 weight% or 2 to 30 weight% based on the total weight of the positive active material layer (120). This enables the formation of a positive electrode with excellent durability without impairing the electrical characteristics and / or capacitance characteristics of the positive electrode.

[0042] The above-described positive active material layer (120) can be formed by dissolving or dispersing each component, such as the above-described positive active material, conductive material, and binder, in a medium such as an organic solvent to form a slurry composition, and then applying and drying it on a conductive current collector.

[0043] At this time, examples of the medium such as the organic solvent mentioned above include N-methyl-2-pyrrolidone (NMP), methoxypropyl acetate, butyl acetate, glycol acid, butyl ester, butyl glycol, methylalkylpolysiloxane, alkylbenzene, propylene glycol, xylene, or monophenyl glycol, and among these, NMP, etc. can be appropriately used.

[0044] However, since the formation process and conditions of the above-mentioned positive active material layer (120) may follow general positive formation processes and conditions, further explanation regarding this is omitted.

[0045] The above-described positive active material layer (120) can be formed with a thickness of, for example, 10 to 300 μm or 15 to 200 μm, and as a result, can exhibit excellent safety and electrical characteristics during charging and discharging.

[0046] Meanwhile, according to another embodiment of the invention, individual battery units (A, B) comprising a positive electrode (100), a negative electrode (200), and a separator (300) interposed between them are provided, and a lithium secondary battery structure may be formed by including a plurality of these battery units.

[0047] In a lithium secondary battery, which is a battery unit of this other embodiment, the negative electrode (200) is manufactured by applying, drying, and rolling a negative electrode active material on a negative electrode current collector (210), and may further include a conductive material and a binder as needed.

[0048] The above-mentioned cathode active material may include, for example, carbon and graphite materials such as graphite having a completely formed layered crystal structure like natural graphite, soft carbon having a low-crystallinity layered crystal structure (graphene structure; a structure in which hexagonal honeycomb-shaped planes of carbon are arranged in layers), hard carbon in which such structures are mixed with amorphous parts, artificial graphite, expanded graphite, carbon fiber, non-graphitized carbon, carbon black, carbon nanotubes, fullerene, and activated carbon; or LixFe2O3(0≤x≤1), LixWO2(0≤x≤1), SnxMe1-xMe'yOz (Me: Mn, Fe, Pb, Ge; Me', Al, B, P, Si, elements of Group 1, Group 2, and Group 3 of the periodic table, halogens; 0 <x≤1; 1≤y≤3; 1≤z≤8) 등의 금속 복합 산화물; 리튬 금속; 리튬 합금; 규소, 규소 산화물 또는 규소계 합금; 주석계 합금; 폴리아세틸렌 등의 도전성 고분자; Li-Co-Ni계 재료; 티타늄 산화물; 또는 리튬 티타늄 산화물 등을 사용할 수 있다.

[0049] In one example, the cathode active material may include graphite and silicon (Si)-containing particles together, and the graphite may include one or more of natural graphite having a layered crystal structure and artificial graphite having an isotropic structure, and the silicon (Si)-containing particles may include silicon (Si) particles, silicon oxide particles, or a mixture of silicon (Si) particles and silicon oxide particles as particles containing silicon (Si) as a main component as a metal component.

[0050] In addition, the conductive material and binder that can be used together with the above-mentioned negative electrode active material may have the same components as the conductive material and binder included in the positive electrode active material layer (120).

[0051] In addition, the cathode active material layer (220) including the cathode active material may have an average thickness of 100㎛ to 200㎛, and specifically, may have an average thickness of 100㎛ to 180㎛, 100㎛ to 150㎛, 120㎛ to 200㎛, 140㎛ to 200㎛, or 140㎛ to 160㎛.

[0052] In addition, the above-mentioned negative current collector (210) is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, nickel, titanium, calcined carbon, etc. may be used, and in the case of copper or stainless steel, a surface-treated one such as carbon, nickel, titanium, silver, etc. may be used.

[0053] In addition, the above-mentioned negative current collector (210), like the positive current collector (110), may form fine irregularities on its surface to strengthen the bonding force with the negative active material layer (220), and may take various forms such as a film, sheet, foil, net, porous body, foam, or nonwoven fabric. Furthermore, the average thickness of the above-mentioned negative current collector (210) can be appropriately applied in the range of 3 to 500 μm, taking into consideration the conductivity and total thickness of the negative being manufactured.

[0054] Additionally, the separator (300) is interposed between the anode (100) and the cathode (200), and an insulating thin film having high ion permeability and mechanical strength is used. The separator (300) is not particularly limited as long as it is commonly used in the industry, but specifically, a sheet or nonwoven fabric made of chemically resistant and hydrophobic polypropylene; glass fiber; or polyethylene may be used, and in some cases, a composite separator in which inorganic particles / organic particles are coated by an organic binder polymer on a porous polymer substrate such as the sheet or nonwoven fabric may be used. When a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte may also serve as the separator. Furthermore, the pore diameter of the separator may be an average of 0.01 to 10 μm, and the thickness may be an average of 5 to 300 μm.

[0055] The battery unit of the other embodiment described above may further include an electrolyte, and such electrolyte may be an electrolyte solution comprising a non-aqueous organic solvent and a lithium salt, or an electrolyte membrane comprising an organic or inorganic solid electrolyte, and these may be mixed together. However, the types of usable electrolytes are well known to those skilled in the art and are not particularly limited in the battery of the other embodiment, so further description regarding this is omitted. Effects of the invention

[0056] As described above, the lithium secondary battery structure of the present invention can achieve excellent safety of the lithium secondary battery structure and improve output characteristics, etc., by including a metal current collector and a composite conductive current collector in a certain ratio within the entire battery structure.

[0057] In addition, the above lithium secondary battery structure can exhibit excellent lifespan characteristics at room temperature. Brief explanation of the drawing

[0058] FIG. 1 illustrates a cross-sectional view of a lithium secondary battery structure according to one embodiment of the present invention. Specific details for implementing the invention

[0059] Hereinafter, embodiments of the present invention are described in detail so that those skilled in the art can easily practice the invention. However, the present invention may be embodied in various different forms and is not limited to the embodiments described herein.

[0061] Comparative Example 1: Secondary battery structure with metal current collector

[0062] First, a positive electrode slurry was prepared by mixing a positive electrode active material (LCO), a conductive material (carbon black), and a binder (PVdF) in a mass ratio of 97:1.2:1.8 in N-methylpyrrolidone (NMP) solvent, and then the slurry was coated onto a 10 μm aluminum foil metal current collector with a designed loading, dried, and then rolled to produce a double-sided positive electrode.

[0063] Then, a cathode slurry was prepared by mixing a cathode active material (graphite), a conductive material (carbon black), a binder (SBR), and CMC in a mass ratio of 95.35:0.5:3:1.15 as the counter cathode. The cathode was then manufactured by coating this slurry onto an 8 µm copper foil current collector with a designed loading, drying, and rolling. A monocell (metal current collector) was manufactured by applying a 10 µm thick separator coated with SRS onto a polyolefin substrate to the separator between the anode and the cathode.

[0064] A lithium secondary battery structure was manufactured by arranging 24 manufactured monocells.

[0066] Comparative Example 2: Secondary battery structure with composite conductive current collector

[0067] First, a positive electrode active material (LCO), a conductive material (carbon black), and a binder (PVdF) were mixed in a mass ratio of 97:1.2:1.8 in N-methylpyrrolidone (NMP) solvent to prepare a positive electrode slurry. Then, this slurry was coated onto a total 12 µm composite conductive current collector composed of 1 µm aluminum / 10 µm PET / 1 µm aluminum with a designed loading, dried, and then rolled to produce a double-sided positive electrode.

[0068] Then, a cathode slurry was prepared by mixing cathode active material (graphite), conductive material (carbon black), binder (SBR), and CMC in a mass ratio of 95.35:0.5:3:1.15 as the counter cathode. Afterward, this slurry was coated onto an 8 µm copper foil current collector with a designed loading, dried, and then rolled to manufacture the cathode. A monocell (composite conductive current collector) was manufactured by applying a 10 µm thick separator coated with SRS onto a polyolefin substrate as the separator between the anode and the cathode.

[0069] A lithium secondary battery structure was manufactured by arranging 24 manufactured monocells.

[0071] Example 1: Secondary battery structure with composite conductive current collector (Metal:Composite = 1:5)

[0072] A monocell (metal current collector, A) manufactured in the same manner as Comparative Example 1 and a monocell (composite conductive current collector, B) manufactured in the same manner as Comparative Example 2 were prepared.

[0073] A lithium secondary battery structure was manufactured by arranging 4 manufactured monocells A and 20 manufactured monocells B in the order ABBBBBABBBBB… ABBBBBABBBBB. At this time, the ratio of metal current collectors to composite conductive current collectors was set to 1:5.

[0075] Example 2: Secondary battery structure with composite conductive current collector (Metal:Composite=1:3)

[0076] A lithium secondary battery structure was manufactured in the same manner as in Example 1, except that 6 monocells A and 18 monocells B manufactured in Example 1 were arranged in the order ABBBABBB…ABBBABBB. At this time, the ratio of the number of metal current collectors to the number of composite conductive current collectors was set to 1:3.

[0078] Example 3: Secondary battery structure with composite conductive current collector (Metal:Composite=1:1)

[0079] A lithium secondary battery structure was manufactured in the same manner as in Example 1, except that 12 monocells A and 12 monocells B manufactured in Example 1 were arranged in the order ABAB…ABAB. At this time, the ratio of the number of metal current collectors to composite conductive current collectors was set to 1:1.

[0081] Example 4: Secondary battery structure with composite conductive current collector (Metal:Composite = 3:1)

[0082] A lithium secondary battery structure was manufactured in the same manner as in Example 1, except that 18 monocells A and 6 monocells B manufactured in Example 1 were arranged in the order AAABAAAB…AAABAAAB. At this time, the ratio of the number of metal current collectors to the number of composite conductive current collectors was set to 3:1.

[0084] Example 5: Secondary battery structure with composite conductive current collector (Metal:Composite = 5:1)

[0085] A lithium secondary battery structure was manufactured in the same manner as in Example 1, except that 20 monocells A and 4 monocells B manufactured in Example 1 were arranged in the order AAAAABAAAAAB… AAAAABAAAAAB. At this time, the ratio of the number of metal current collectors to the number of composite conductive current collectors was set to 5:1.

[0087] Experimental Example 1: Performance Evaluation According to the Ratio of Metal Current Collectors and Composite Conductive Current Collectors

[0088] To evaluate the performance of the lithium secondary battery structures of the above examples and comparative examples, the following experiments were performed.

[0090] 1) Initial resistance measurement

[0091] The AC impedance value of the manufactured lithium secondary battery structure was measured at a frequency of 10 kHz, and the results are shown in Table 1 below.

[0093] 2) Cycle Life Performance Evaluation

[0094] Initial (one) charge-discharge cycles were performed at room temperature on the lithium secondary battery structures of the Examples and Comparative Examples. During this process, charging was carried out to SOC 50 using a constant current (CC) of 1 C-rate, followed by charging to SOC 100 using a constant current-constant voltage (CC-CV) of 0.7 C-rate, and discharging was carried out to 3.0 V using a 0.7 C-rate. The capacity retention rate (Capacity Retention[%]) was measured while performing these charge-discharge cycles a total of 300 times. The capacity retention rate was calculated using Equation 1 below, and the results are shown in Table 1 below:

[0095] [Equation 1]

[0096] Capacity Retention Rate (%) = (Discharge capacity after 300 charge / discharge cycles / Discharge capacity after 1 charge / discharge cycle) × 100

[0098] 3) Stability test

[0099] An impact test was performed by placing a cylindrical bar with a diameter of 15.8 phi on the lithium secondary battery structures of the examples and comparative examples, and dropping a 9.1 kg weight from a height of 610 mm to impact the cell. The cell was judged to have passed if it satisfied the NF (no fire) and NE (no explosion) conditions. The number of passes was measured based on the total number of tests, and the pass rate (%) was evaluated from this. The evaluation results are shown in Table 1 below.

[0100] Comparative Example 1 Comparative Example 2 Example 1 Example 2 Example 3 Example 4 Example 5 Metal Current Collector: Composite Conductive Current Collector Ratio 10:0 0:10 1:5 1:3 1:1 3:1 5:1 Initial resistance (mOhm) 3.1 25.1 20.1 15.3 15.2 14.2 12.5 Battery life (%, 300 cycle @ RT) 93.2 80.4 89.2 92.7 93.5 94.6 95.6 Stability Test(%, Pass) 40 100 100 100 100 90 80

[0101] Referring to Table 1 above, it was confirmed that the lithium secondary battery structures of Examples 1 to 5 have low initial resistance values ​​and exhibit high capacity retention and excellent lifespan characteristics even after 300 charge-discharge cycles. In particular, it was confirmed that Examples 2 to 4, in which the ratio of metal current collector to composite conductive current collector is 1:3 to 3:1, exhibit superior characteristics.

[0102] In contrast, it was confirmed that the lithium secondary battery structure with a single metal current collector of Comparative Example 1 exhibited poor performance in terms of stability characteristics, and the lithium secondary battery structure with a composite conductive current collector of Comparative Example 2 exhibited poor performance in terms of initial resistance value and lifespan characteristics.

[0104] Experimental Example 2: Performance Evaluation According to the Thickness Ratio of the Composite Conductive Current Collector

[0105] First, a positive electrode active material (LCO), a conductive material (carbon black), and a binder (PVdF) were mixed in a mass ratio of 97:1.2:1.8 in N-methylpyrrolidone (NMP) solvent to prepare a positive electrode slurry. Then, this slurry was coated onto a composite conductive current collector with different thickness ratios of a polymer substrate (PET) and a metal layer (aluminum) as shown in Table 2 below, with a design loading, dried, and then rolled to produce a double-sided positive electrode.

[0106] Then, a cathode slurry was prepared by mixing cathode active material (graphite), conductive material (carbon black), binder (SBR), and CMC in a mass ratio of 95.35:0.5:3:1.15 as the counter-cathode. This slurry was then coated onto an 8 µm copper foil current collector with a designed loading, dried, and rolled to manufacture the cathode. Monocell samples of Examples 6-7 and Comparative Examples 3-5 were prepared by applying a 10 µm thick separator coated with SRS on a polyolefin substrate as the separator between the anode and cathode. The following experiments were performed to evaluate the performance of the prepared samples.

[0108] 1) Fairness evaluation

[0109] The monocell samples manufactured above were wound onto a cylindrical column with a diameter of 80 mm, and the occurrence of a break (or crack) on the electrode surface was measured, and the results are shown in Table 2 below.

[0111] 2) 2C Output Evaluation

[0112] Samples of Examples 6-7 and Comparative Examples 3-5, prepared with different thickness ratios of the polymer substrate (PET) and metal layer (aluminum) of the composite conductive current collector, were discharged once under current conditions of 2 C-rate, and the capacity ratio relative to the 0.1 C discharge capacity was calculated and the results are shown in Table 2 below.

[0114] 3) Nail penetration test

[0115] For the samples of Examples 6-7 and Comparative Examples 3-5 manufactured above, ignition was evaluated when a 3 mm diameter metal body was dropped at a speed of 80 mm / sec to penetrate the cell, identical to the PV8450 certification conditions. The number of times ignition occurred was measured based on the total number of tests, and the ignition rate (%) was evaluated from this. The results of this evaluation are shown in Table 2 below.

[0116] Metal layer / polymer substrate / metal layer Comparative Example 30.5um / 11um / 0.5um Example 61um / 10um / 1um Example 74um / 4um / 4um Comparative Example 45um / 2um / 5um Comparative Example 56um / 0um / 6um Total polymer thickness: Total metal layer thickness 11:1 5:1 1:2 1:5 0:1 fairness Disconnection occurred Good Good Good Good 2C Output Evaluation (%, relative to 0.1C discharge capacity) 61.2 90.1 92.4 94.4 96.9 Nail penetration test 100% 100% 90% 20% 20%

[0117] Referring to Table 2 above, it was confirmed that Examples 6 and 7, in which the ratio of the total thickness of the polymer substrate to the total thickness of the metal layer is in the range of 1:2 to 5:1, have excellent processability, output characteristics, and stability.

[0118] In contrast, Comparative Example 3, which has a high thickness ratio of the PET polymer substrate, showed that not only did a wire break occur, but cell performance was also degraded due to high resistance. On the other hand, Comparative Example 4, which has a high thickness ratio of the aluminum metal layer, showed excellent output characteristics, while it was confirmed that there was no significant difference in stability compared to Comparative Example 5, which consists only of an aluminum metal layer. Explanation of the symbols

[0119] 100: First electrode, positive electrode 100': First electrode with composite conductive current collector, anode with composite conductive current collector 110: First conductive current collector, positive conductive current collector 110': Composite conductive current collector 111: Polymer substrate 112: Metal layer 120: Positive active material layer 200: Second electrode, cathode 210: Second conductive current collector, negative conductive current collector 220: Cathode active material layer 300: Separator

Claims

Claim 1 A lithium secondary battery structure comprising a plurality of battery units, each comprising: a first electrode including a first conductive current collector having an active material layer formed on at least one surface; a second electrode including a second conductive current collector having an active material layer formed on at least one surface; and a separator formed between the active material layers of the first and second electrodes facing each other, wherein the first electrode is a positive electrode, and the first conductive current collector is composed of a metal current collector or a composite conductive current collector having a metal layer formed on a polymer substrate for each battery unit, and the second conductive current collector is composed of a metal current collector, and the metal current collector : the composite conductive current collector are included in the entire battery structure in a number ratio of 5 : 1 to 1 :

5. Claim 2 In claim 1, the metal current collector: the composite conductive current collector is included in the entire battery structure in a number ratio of 3:1 to 1:3, forming a lithium secondary battery structure. Claim 3 In claim 1, the first conductive current collector is a lithium secondary battery structure in which the metal current collector or the composite conductive current collector is formed for each battery unit. Claim 4 In claim 1, the first conductive current collector is the metal current collector or the composite conductive current collector for each battery unit, and the metal current collector and the composite conductive current collector are regularly alternately arranged according to the stacking order of the first electrodes, forming a lithium secondary battery structure. Claim 5 In claim 4, the metal current collector and the composite conductive current collector are a lithium secondary battery structure in which, according to the stacking order of the first electrode, one composite conductive current collector is repeatedly arranged for every one to three metal current collectors, or one metal current collector is repeatedly arranged for every one to three composite conductive current collectors. Claim 6 A lithium secondary battery structure according to claim 1, wherein in the composite conductive current collector, the ratio of the total thickness of the polymer substrate to the total thickness of the metal layer is 1:2 to 5:

1. Claim 7 A lithium secondary battery structure according to claim 3, wherein the polymer substrate is a polyester resin substrate and the metal layer is an aluminum layer. Claim 8 In claim 7, the above-mentioned polyester resin comprises one or more resins selected from the group consisting of polyethylene terephthalate (PET), polytrimethylene terephthalate (PTT), polybutylene terephthalate (PBT), and polyethylene naphthalate (PEN), forming a lithium secondary battery structure. Claim 9 In claim 1, the first conductive current collector is a lithium secondary battery structure having a thickness in the range of 6 μm to 20 μm. Claim 10 A lithium secondary battery structure according to claim 1, wherein the active material layer is formed on both sides of the first and second conductive current collectors, and the first and second electrodes are alternately stacked with a separator in between.

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