Lithium secondary battery structure including composite conductive current collector

Abstract

The present invention relates to a lithium secondary battery structure that exhibits excellent safety by suppressing heat generation or fire and improved output characteristics. The lithium secondary battery structure includes a plurality of battery units, each including a first electrode including a first conductive current collector having an active material layer formed on at least one surface thereof, a second electrode including a second conductive current collector having an active material layer formed on at least one surface thereof, 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 for each battery unit, or a composite conductive current collector having a metal layer formed on a polymer substrate, and the metal current collector:composite conductive current collector ratio within the entire battery structure is 5:1 to 1:5.

Description

[Technical Field]

[0001] The present invention relates to a lithium secondary battery structure that exhibits excellent safety due to suppressed heat generation or ignition, as well as improved output characteristics. [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 increasing, leading to a lot of research on secondary batteries that can meet diverse requirements. Secondary batteries are also attracting attention as a power source for electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (Plug-in HEVs), which have been proposed as solutions to address air pollution caused by existing gasoline and diesel vehicles that use fossil fuels.

[0003] Therefore, electric vehicles (EVs) that can run solely on secondary batteries, and hybrid electric vehicles (HEVs) that use secondary batteries in combination with existing engines, have been developed, and some are already in regular use. While nickel-metal hydride (Ni-MH) secondary batteries are mainly used as power sources for EVs and HEVs, research into lithium-ion batteries, which offer high energy density, high discharge voltage, and output stability, has recently been actively conducted, and some are already in regular use.

[0004] Such lithium secondary batteries are manufactured by applying an electrode slurry containing electrode active material to an electrode current collector, drying and rolling it to produce electrodes, and then assembling an electrode assembly with a separator membrane interposed between these electrodes into a battery case together with an electrolyte.

[0005] On the other hand, copper or aluminum are commonly used as materials for electrode current collectors, but the aluminum used in existing positive electrode current collectors has the problem of exhibiting a dangerous mode that can lead to ignition when it comes into contact with the negative electrode active material during a short circuit.

[0006] To solve this problem, attempts have been made to replace the existing aluminum positive electrode current collector with a current collector in which aluminum is coated on a PET substrate. In this case, the resistance of the current collector itself increases, and the short-circuit resistance also increases when in contact with the negative electrode active material, which is expected to reduce the possibility of ignition during safety verification. On the other hand, this causes the problem that the resistance of the entire cell increases and the output characteristics degrade.

[0007] Accordingly, there has been a continuous demand for the development of technology that can achieve high stability by applying an organic / metal composite as a metal current collector, while also improving output characteristics and other properties thereof. Summary of the Invention Problems to be Solved by the Invention

[0008] Therefore, an object of the present invention is to provide a lithium secondary battery structure that is suppressed from heat generation or ignition due to external impact or the like, has excellent safety, and exhibits improved output characteristics.

[0009] Another object of the present invention is to provide a lithium secondary battery structure that includes a metal current collector and a composite conductive current collector, and exhibits excellent stability and improved lifespan characteristics. Means for Solving the Problems

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

[0011] Terms and words used in the present specification and claims shall not be construed as being limited to ordinary or dictionary meanings, and based on the principle that an inventor can appropriately define the concept of terms to describe his / her own invention in the best way, they shall be interpreted with meanings and concepts consistent with the technical idea of the present invention.

[0012] The terms used herein are for illustrative purposes only and are not intended to limit the invention. Unless otherwise clearly indicated in the context, singular expressions include plural expressions.

[0013] In this specification, terms such as “includes,” “equip,” or “have” are intended to specify the presence of implemented features, figures, steps, components, or combinations thereof, and should not be understood to preemptively exclude the presence or possibility of adding one or more other features, figures, steps, components, or combinations thereof.

[0014] 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 separation membrane 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 collectors 110, 210 consist of a metal current collector or a composite conductive current collector 110' having a metal layer 112 formed on a polymer substrate 111, and the metal current collector:composite conductive current collector are included in the overall battery structure in a ratio of 5:1 to 1:5.

[0015] Unlike existing secondary batteries that use aluminum foil positive electrode current collectors or composite current collectors coated with aluminum on polymers such as PET, the inventors have continued research and experiments to develop a secondary battery that achieves high stability and has improved output characteristics.

[0016] Through these ongoing research findings, we confirmed that superior performance can be obtained when combining a metal current collector and a composite conductive current collector (a polymer coated with a metal layer) as current collectors for each battery unit within a battery structure containing multiple battery units. In particular, we confirmed that stability and cell characteristics can be simultaneously improved by adjusting the ratio of metal current collectors to composite conductive current collectors used in the overall battery structure.

[0017] In the case of aluminum, which is used as an existing positive electrode current collector, it has low resistance characteristics or low stability because it comes into contact with the negative electrode active material during a short circuit, leading to ignition. In the case of a composite conductive current collector, which has a metal layer coated on a polymer, its own resistance is high, and the short-circuit resistance is also high when it comes into contact with the negative electrode active material, resulting in excellent stability, but the resistance of the entire cell increases and the output characteristics decrease, so there is a trade-off relationship between stability characteristics and output characteristics. Therefore, by adjusting the ratio of metal current collectors to composite conductive current collectors, or by regularly alternating the metal current collectors and the composite conductive current collectors, it is possible to obtain good levels of both stability characteristics and output characteristics.

[0018] These excellent output characteristics are supported by the initial resistance measurement results in the experimental examples described later, the excellent stability is supported by the low ignition rate and explosion rate in the impact tests in the experimental examples described later, and the life characteristics can be confirmed by the evaluation results of the life characteristics by charging and discharging at room temperature in the examples described later, for example, by the excellent capacity retention rate of 80% or more, or 90% or more, after 300 cycles.

[0019] On the other hand, in one embodiment of the present invention, the metal current collector is not particularly limited as long as it supports the active material layers 120 and 220 and has high conductivity without inducing chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, palladium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, silver, etc., and aluminum-cadmium alloys can be used.

[0020] Furthermore, the metal current collectors 110 and 210 can have fine irregularities formed on their surfaces to strengthen their bonding force with the active material layer, and can be used in a variety of forms such as films, sheets, foils, meshes, nets, porous materials, foams, and nonwoven fabrics. For example, the metal current collector may be aluminum foil.

[0021] 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 laminated structure in which metal layers 112 are formed on both sides of the polymer substrate 111.

[0022] In the case of a positive electrode current collector made of metal, the metal makes it difficult to achieve a lightweight battery due to its lack of flexibility. However, the polymer substrate 111 ensures flexibility and lightweight battery properties, while the metal layer 112 provides the same conductivity as a current collector made of a single metal material, thus preventing a decrease in battery performance.

[0023] In one embodiment, the polymer substrate 111 may be a polyester resin substrate, for example, the polyester resin may include resins 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.

[0024] In one embodiment, the metal layer 112 may be a metal layer such as stainless steel, aluminum, copper, nickel, or titanium, or an aluminum or stainless steel surface treated with carbon, nickel, titanium, or silver. The metal layer may also have fine irregularities formed on its surface and can take 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.

[0025] On the other hand, processability, 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 contained 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 thickness ratio of the polymer substrate is excessively high, the resistance may increase and the cell performance may decrease, and if the thickness ratio of the metal layer is high, it may result in a structure similar to that of a metal foil, and there may be no difference in terms of stability.

[0026] In the lithium secondary battery structure according to the above embodiment, the first or second conductive current collectors 110, 210 may be a metal current collector or a composite conductive current collector 110' in which a metal layer 112 is formed on a polymer substrate 111, for each battery unit. In this case, the first or second conductive current collectors 110, 210 in at least one battery unit may be a composite conductive current collector 110'.

[0027] 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. In this case, the first conductive current collector 110 can have a thickness in the range of 6 μm to 20 μm. If the thickness range is excessively large or small, if it is less than 6 μm, the R2R coating process may not be possible, and if it exceeds 20 μm, the loss of energy density per unit volume of the cell may be significant.

[0028] In one embodiment, the first conductive current collector 110 consists of 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.

[0029] Specifically, the metal current collector and the composite conductive current collector 100' may be arranged such that one composite conductive current collector 110' 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 110', depending on the stacking order of the first electrode 100.

[0030] For example, if a battery unit including a positive electrode to which the metal current collector is applied is shown as A, and a battery unit including a positive electrode to which a composite conductive current collector is applied is shown as B, the order in which the battery units are stacked may be repeated in the order of ABAB...ABAB, ABBABB...ABBABB, ABBBABBB...ABBBABBB, AABAAB...AABAAB, or AAAB...AAAB. For reference, Figure 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 and negative electrode to which a metal current collector is applied, a battery unit (B) including a positive electrode to which a composite conductive current collector is applied and a negative electrode to which a metal current collector is applied, and a battery unit (A) including a positive and negative electrode to which a metal current collector is applied are arranged alternately.

[0031] In one embodiment, when the metal current collector and the composite conductive current collector are included in the overall battery structure in a ratio of 5:1 to 1:5, a high level of stability can be ensured, and excellent output characteristics and life characteristics can be improved. In particular, when the metal current collector and the composite conductive current collector are included in a ratio of 3:1 to 1:3, optimal results can be expected. However, if the ratio becomes excessively large or small, the stability characteristics or output characteristics may deteriorate.

[0032] In one embodiment of the electrodes, the active material layers 120 and 220 are formed on both sides of the first and second conductive current collectors 110 and 210, and the first and second electrodes 100 and 200 may be alternately stacked with a separation film 300 in between. For example, active material layers 120 and 220 containing an active material, a conductive material, and a binder may be formed on the first or second conductive current collectors 110 and 210.

[0033] In such active material layers 120 and 220, when the active material is a positive electrode active material, there is no particular limitation as long as it is a material capable of reversibly intercalating and deintercalating lithium ions. 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.

[0034] More specifically, as the positive electrode active material, a compound represented by any one of the following chemical formulas can be used. Li a A 1-b R b D2 (in the above formula, 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 formula, 0 ≤ b ≤ 0.5 and 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 O 2-α Z2 (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 Dα (In the above equation, 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 equation, 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 (In the above equation, 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(In the above equation, 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 (In the above formula, 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(In the above formula, 0.90≦a≦1.8 and 0.001≦b≦0.1);Li a CoG b O2(In the above formula, 0.90≦a≦1.8 and 0.001≦b≦0.1);Li a MnG b O2(In the above formula, 0.90≦a≦1.8 and 0.001≦b≦0.1);Li a Mn2G b O4 (In the above formula, 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).

[0035] 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; J is V, Cr, Mn, Co, Ni, Cu or a combination thereof.

[0036] Furthermore, compounds having a coating layer on their surface can also be used, or a mixture of the compound and a compound having a coating layer can be used. The coating layer may include, as a coating element compound, an oxide, a hydroxide, an oxyhydroxy, an oxycarbonate, or a hydroxycarbonate of the coating element. The compounds forming these coating layers 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 mixtures thereof.

[0037] Furthermore, the conductive material contained in the positive electrode 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 that is constructed. Examples include natural graphite, artificial graphite, carbon black-based conductive materials, carbon fibers, carbon nanotubes, metal powders and fibers such as copper, nickel, aluminum, and silver, and one or more conductive materials such as polyphenylene derivatives can be used. In addition, the conductive material used can be the same as or different from the carbon-based conductive material contained in the safety protective layer mentioned above.

[0038] The conductive material may be added in an amount of 1 to 50% by weight, or 2 to 20% by weight, based on the total weight of the positive electrode active material layer 120. Therefore, it is possible to ensure a favorable formation of the positive electrode while providing it with excellent electrical properties.

[0039] The binder plays a role in ensuring good adhesion between the positive electrode active material particles and enhancing the adhesion of the positive electrode active material layer 120. Typical examples of binders that can be used include halogenated polyolefin polymer binders, polyvinyl alcohol, carboxymethylcellulose, hydroxypropylcellulose, diacetylcellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polyethylene, polypropylene, styrene-butadiene rubber, acrylic styrene-butadiene rubber, epoxy resin, or nylon.

[0040] The binder may be added in an amount of 1 to 50% by weight, or 2 to 30% by weight, based on the total weight of the positive electrode active material layer 120. Therefore, it is possible to form a positive electrode with excellent durability without impairing the electrical properties and / or capacitance characteristics of the positive electrode.

[0041] The positive electrode active material layer 120 described above may be formed by dissolving or dispersing the components such as the positive electrode active material, conductive material, and binder described above in a medium such as an organic solvent to form a slurry composition, and then applying and drying this slurry composition onto a conductive current collector.

[0042] Examples of the organic solvent or other medium include N-methyl-2-pyrrolidone (NMP), methoxypropyl acetate, butyl acetate, glycolic acid, butyl ester, butyl glycol, methylalkylpolysiloxane, alkylbenzene, propylene glycol, xylene, or monophenyl glycol, and among these, NMP can be used appropriately.

[0043] However, since the process and conditions for forming the positive electrode active material layer 120 are those of a general positive electrode formation process and conditions, no further explanation regarding them will be provided.

[0044] The aforementioned positive electrode active material layer 120 can be formed to a thickness of, for example, 10 to 300 μm or 15 to 200 μm, and as a result, it can exhibit excellent safety and electrical characteristics during charging and discharging.

[0045] On the other hand, according to another embodiment of the present invention, individual battery units (A, B) are provided, each including a positive electrode 100, a negative electrode 200, and a separation membrane 300 interposed between them, as described in the above-described embodiment. A lithium secondary battery structure can be formed by including a plurality of these battery units.

[0046] In a lithium secondary battery, which is a battery unit of another embodiment, the negative electrode 200 is manufactured by coating, drying, and rolling a negative electrode active material onto a negative electrode current collector 210, and may further include a conductive material and a binder as needed.

[0047] Examples of the negative electrode active material include, for example, complete graphite with a layered crystalline structure like natural graphite, soft carbon having a low-crystalline layered crystalline structure (graphene structure; a structure in which hexagonal honeycomb-like planes of carbon are arranged in layers), hard carbon in which such a structure is mixed with amorphous parts, artificial graphite, expanded graphite, carbon fiber, non-graphitizable carbon, carbon black, carbon nanotubes, fullerenes, activated carbon, and other carbon and graphite materials; Li x Fe2O3(0≦x≦1, Li x WO2(0≦x≦1, Sn x Me 1-x Me' y O z(Me: Mn, Fe, Pb, Ge; Me': Al, B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, halogen; 0 < x ≦ 1; 1 ≦ y ≦ 3; 1 ≦ z ≦ 8; metal composite oxides of the like; lithium metal; lithium alloys; silicon, silicon oxide or silicon-based alloys; tin-based alloys; conductive polymers such as polyacencylene; Li-Co-Ni based materials; titanium oxides; or lithium titanium oxides, etc. can be used.

[0048] In one example, the negative electrode active material may contain both graphite and silicon (Si)-containing particles. The graphite may include at least one of natural graphite having a layered crystal structure and artificial graphite having an isotropic structure. The silicon (Si)-containing particles are particles containing silicon (Si) as a main component as a metal component, and may include silicon (Si) particles, silicon oxide particles, or a mixture of the silicon (Si) particles and silicon oxide particles.

[0049] As the conductive material and binder that can be used together with the negative electrode active material, the same components as the conductive material and binder contained in the positive electrode active material layer 120 can be used.

[0050] The negative electrode active material layer 220 containing the negative electrode active material may have an average thickness of 100 µm to 200 µm, specifically, may have an average thickness of 100 µm to 180 µm, 100 µm to 150 µm, 120 µm to 200 µm, 140 µm to 200 µm, or 140 µm to 160 µm.

[0051] The negative electrode current collector 210 is not particularly limited as long as it has high conductivity without inducing chemical changes in the battery. For example, copper, stainless steel, nickel, titanium, calcined carbon, etc. can be used; in the case of copper or stainless steel, those surface-treated with carbon, nickel, titanium, silver, etc. can also be used.

[0052] Furthermore, similar to the positive electrode current collector 110, the negative electrode current collector 210 can have fine irregularities formed on its surface to strengthen its bonding force with the negative electrode active material layer 220, and can take on a variety of forms such as film, sheet, foil, net, porous material, foam, and nonwoven fabric. In addition, the average thickness of the negative electrode current collector 210 can be appropriately applied from 3 to 500 μm, taking into consideration the conductivity and total thickness of the manufactured negative electrode.

[0053] Furthermore, the separation membrane 300 is interposed between the positive electrode 100 and the negative electrode 200, and a thin insulating film with high ion permeability and mechanical strength is used. The separation membrane 300 is not particularly limited as long as it is commonly used in the industry, but specifically, sheets or nonwoven fabrics made of chemically resistant and hydrophobic polypropylene; glass fiber; or polyethylene can be used, and in some cases, a composite separation membrane may be used in which inorganic particles / organic particles are coated with an organic binder polymer on a porous polymer substrate such as the sheet or nonwoven fabric. When a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte can also serve as the separation membrane. The pore diameter of the separation membrane may be an average of 0.01 to 10 μm, and the thickness may be an average of 5 to 300 μm.

[0054] The battery units of the other embodiments described above may further include an electrolyte, which may consist of 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 batteries of the other embodiments, so no further explanation thereto is provided. [Effects of the Invention]

[0055] As described above, the lithium secondary battery structure of the present invention achieves excellent safety and improves output characteristics, etc., by including a metal current collector and a composite conductive current collector in a certain ratio within the overall battery structure.

[0056] Furthermore, the lithium secondary battery structure can exhibit excellent lifespan characteristics at room temperature. [Brief explanation of the drawing]

[0057] [Figure 1] Figure 1 shows a cross-sectional view of a lithium secondary battery structure according to one embodiment of the present invention. [Modes for carrying out the invention]

[0058] The following describes in detail embodiments of the present invention so that those with ordinary skill in the art to which the invention pertains can easily implement it. However, the present invention can be embodied in a variety of different forms and is not limited to the embodiments described herein.

[0059] Comparative Example 1: Secondary battery structure using a metal current collector First, a positive electrode slurry was prepared by mixing the positive electrode active material (LCO), conductive material (carbon black), and binder (PVdF) in an N-methylpyrrolidone (NMP) solvent in a mass ratio of 97:1.2:1.8. Then, this slurry was coated onto a 10 μm aluminum foil metal current collector with a predetermined filling amount, dried, and rolled to produce a double-sided positive electrode.

[0060] Subsequently, a negative electrode slurry was manufactured by mixing negative electrode active material (graphite), conductive material (carbon black), binder (SBR), and CMC in a mass ratio of 95.35:0.5:3:1.15. This slurry was then coated onto an 8 μm copper foil current collector with a predetermined filling amount, dried, and then rolled to manufacture the negative electrode. For the separation membrane between the positive and negative electrodes, a 10 μm thick separation membrane coated with SRS was applied to a polyolefin base to manufacture a monocell (metal current collector).

[0061] A lithium secondary battery structure was manufactured by arranging 24 of the manufactured monocells.

[0062] Comparative Example 2: Secondary battery structure using a composite conductive current collector First, a positive electrode slurry was prepared by mixing positive electrode active material (LCO), conductive material (carbon black), and binder (PVdF) in N-methylpyrrolidone (NMP) solvent in a mass ratio of 97:1.2:1.8. Then, this slurry was coated onto a 12 μm composite conductive current collector composed of 1 μm aluminum / 10 μm PET / 1 μm aluminum in a predetermined amount, dried, and then rolled to produce a double-sided positive electrode.

[0063] Subsequently, a negative electrode slurry was manufactured by mixing negative electrode 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 relative negative electrode. This slurry was then coated onto an 8 μm copper foil current collector with a predetermined filling amount, dried, and then rolled to manufacture the negative electrode. For the separation membrane between the positive and negative electrodes, a 10 μm thick separation membrane coated with SRS was applied to a polyolefin base to manufacture a monocell (composite conductive current collector).

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

[0065] Example 1: Secondary battery structure using a composite conductive current collector (metal:composite = 1:5) A monocell (metal current collector, A) manufactured using the same method as in Comparative Example 1 and a monocell (composite conductive current collector, B) manufactured using the same method as in Comparative Example 2 were prepared.

[0066] Four monocells A and 20 monocells B were manufactured and arranged in the order ABBBBBABBBBB...ABBBBBABBBBB to create a lithium secondary battery structure. At this time, the ratio of metal current collectors to composite conductive current collectors was 1:5.

[0067] Example 2: Secondary battery structure using a composite conductive current collector (metal:composite = 1:3) A lithium secondary battery structure was manufactured in the same manner as in Example 1, except for six monocells A and eighteen monocells B manufactured in Example 1, arranged in the order ABBBABBB...ABBBABBB. In this case, the ratio of metal current collectors to composite conductive current collectors was set to 1:3.

[0068] Example 3: Secondary battery structure using a composite conductive current collector (metal:composite = 1:1) 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. In this case, the ratio of metal current collectors to composite conductive current collectors was 1:1.

[0069] Example 4: Secondary battery structure using a composite conductive current collector (metal:composite = 3:1) A lithium secondary battery structure was manufactured in the same manner as in Example 1, except for 18 monocells A and 6 monocells B manufactured in Example 1, arranged in the order AAABAAAB...AAABAAAB. In this case, the ratio of metal current collectors to composite conductive current collectors was set to 3:1.

[0070] Example 5: Secondary battery structure using a composite conductive current collector (metal:composite = 5:1) A lithium secondary battery structure was manufactured in the same manner as in Example 1, except for 20 monocells A and 4 monocells B manufactured in Example 1, arranged in the order AAAAABAAAAAB...AAAAABAAAAAB. In this case, the ratio of metal current collectors to composite conductive current collectors was 5:1.

[0071] Experimental Example 1: Performance evaluation based on the number ratio of metal current collectors and composite conductive current collectors. To evaluate the performance of the lithium secondary battery structures of the above-mentioned examples and comparative examples, the following experiments were conducted.

[0072] 1) Measurement of initial resistance The manufactured lithium secondary battery structures had their AC impedance measured at a frequency of 10 kHz, and the results are shown in Table 1 below.

[0073] 2) Cycle life performance evaluation Initial (single) charge-discharge cycles were performed on the lithium secondary battery structures of the examples and comparative examples at room temperature. During this process, charging was carried out at a constant current (CC) of 1C-rate up to SOC50, followed by a constant current-constant voltage (CC-CV) of 0.7C-rate up to SOC100. Discharging was performed at 0.7C-rate down to 3.0V. The capacity retention rate (%) was measured during a total of 300 such charge-discharge cycles. The capacity retention rate was calculated using Equation 1 below, and the results are shown in Table 1 below. [Formula 1] Capacity retention rate (%) = (discharge capacity after 300 charges / discharges / discharge capacity after 1 charge / discharge)×100

[0074] 3) Stability Test A cylindrical bar with a diameter of 15.8π was placed on the lithium secondary battery structures of the examples and comparative examples, and a 9.1 kg weight was dropped from a height of 610 mm to impact the cells in an impact test. If the cells satisfied the NF (no fire) and NE (no explosion) conditions, it was judged to have passed. The number of passes was measured based on the total number of tests, and the pass rate (%) was evaluated based on this, and the evaluation results are shown in Table 1 below.

[0075] [Table 1]

[0076] 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 life characteristics even after 300 charge-discharge cycles. In particular, Examples 2 to 4, in which the metal current collector:composite conductive current collector ratio was changed from 1:3 to 3:1, showed even better characteristics.

[0077] In contrast, the lithium secondary battery structure using a single metal current collector in Comparative Example 1 was found to have inferior stability characteristics, and the lithium secondary battery structure using a composite conductive current collector in Comparative Example 2 was found to have inferior performance in terms of initial resistance and lifespan characteristics.

[0078] Experimental Example 2: Performance Evaluation of Composite Conductive Current Collectors Based on Thickness Ratio First, a positive electrode slurry was prepared by mixing the positive electrode active material (LCO), conductive material (carbon black), and binder (PVdF) in an N-methylpyrrolidone (NMP) solvent in a mass ratio of 97:1.2:1.8. Then, this slurry was coated onto a composite conductive current collector, in which the thickness ratio of the polymer substrate (PET) and metal layer (aluminum) was varied as shown in Table 2 below, in a predetermined filling amount. After drying, the material was rolled to produce a double-sided positive electrode.

[0079] Subsequently, a negative electrode slurry was prepared by mixing negative electrode 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 relative negative electrode. This slurry was then coated onto an 8 μm copper foil current collector with a predetermined filling amount, dried, and rolled to produce the negative electrode. For the separation membrane between the positive and negative electrodes, a 10 μm thick separation membrane coated with SRS on a polyolefin base was applied to produce monocell samples for Examples 6-7 and Comparative Examples 3-5. The following experiments were conducted to evaluate the performance of the produced samples.

[0080] 1) Evaluation of processability The manufactured monocell samples were wound onto a cylinder with a diameter of 80 mm, and the presence or absence of wire breakage (or cracking) on ​​the electrode surface was measured. The results are shown in Table 2 below.

[0081] 2) 2C output evaluation Samples of Examples 6-7 and Comparative Examples 3-5, manufactured by varying the thickness ratio of the polymer substrate (PET) and metal layer (aluminum) of the composite conductive current collector, were subjected to one discharge under a 2C-rate current condition. The capacity ratio to the 0.1C discharge capacity was then calculated, and the results are shown in Table 2 below.

[0082] 3) Nail penetration test For the samples of Examples 6-7 and Comparative Examples 3-5 manufactured above, a 3mm diameter metal body was lowered at a speed of 80mm / sec and the presence or absence of ignition when it penetrated the cell was evaluated, similar 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 based on this. The evaluation results are shown in Table 2 below.

[0083] [Table 2]

[0084] 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 was in the range of 1:2 to 5:1, exhibited excellent processability, output characteristics, and stability.

[0085] In contrast, in Comparative Example 3, which had a higher thickness ratio of the PET polymer substrate, not only did wire breakage occur, but cell performance deteriorated due to high resistance. On the other hand, in Comparative Example 4, which had a higher thickness ratio of the aluminum metal layer, it was confirmed that while the output characteristics were excellent, there was no significant difference in terms of stability compared to Comparative Example 5, which consisted only of an aluminum metal layer. [Explanation of Symbols]

[0086] 100: First electrode, positive electrode 100': First electrode with composite conductive current collector, positive electrode with composite conductive current collector 110: First conductive current collector, positive electrode conductive current collector 110': Composite conductive current collector 111: Polymer base material 112: Metal layer 120: Positive electrode active material layer 200: 2nd electrode, negative electrode 210: Second conductive current collector, negative conductive current collector 220: Negative electrode active material layer 300: Separation membrane

Claims

1. A first electrode including 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 lithium secondary battery structure comprising a plurality of battery units, each including a separation membrane formed between the active material layers of first and second electrodes facing each other, 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 in which a metal layer is formed on a polymer substrate, for each battery unit, and the second conductive current collector is composed of a metal current collector. The aforementioned metal current collector: The aforementioned composite conductive current collector is included in the overall battery structure in a number ratio of 5:1 to 1:5, in a lithium secondary battery structure.

2. The lithium secondary battery structure according to claim 1, wherein the metal current collector: the composite conductive current collector is included in the overall battery structure in a number ratio of 3:1 to 1:

3.

3. The lithium secondary battery structure according to claim 1, wherein the first conductive current collector comprises the metal current collector or the composite conductive current collector for each of the battery units.

4. The first conductive current collector consists of the metal current collector or the composite conductive current collector for each of the battery units. The lithium secondary battery structure according to claim 1, wherein the metal current collector and the composite conductive current collector are arranged in a regular alternating pattern according to the stacking order of the first electrodes.

5. The lithium secondary battery structure according to claim 4, wherein, depending on the stacking order of the first electrodes, 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.

6. The lithium secondary battery structure according to claim 1, wherein the composite conductive current collector has a ratio of the total thickness of the polymer substrate to the total thickness of the metal layer of 1:2 to 5:

1.

7. The aforementioned polymer substrate is a polyester resin substrate. The lithium secondary battery structure according to claim 3, wherein the metal layer is an aluminum layer.

8. The lithium secondary battery structure according to claim 7, wherein the 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).

9. The lithium secondary battery structure according to claim 1, wherein the first conductive current collector has a thickness in the range of 6 μm to 20 μm.

10. The active material layer is formed on both sides of the first and second conductive current collectors. The lithium secondary battery structure according to any one of claims 1 to 9, wherein the first and second electrodes are alternately stacked with the separation film in between.

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