Electrode for lithium secondary battery and lithium secondary battery including the same

Abstract

To provide an electrode for a lithium secondary battery.SOLUTION: The present invention relates an electrode for a lithium secondary battery and a lithium secondary battery including the same, the electrode for lithium secondary battery includes an active material layer for lithium secondary battery and an organic layer integrated with the active material layer, the organic layer includes a sea-island region consisting of an island region and a sea region, and the area ratio of the island region to the sea-island region is 1 to 20%.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This application claims priority to and the benefit of Korean Patent Application No. 10-2024-0057506, filed with the Korean Intellectual Property Office on April 30, 2024, the entire disclosure of which is incorporated herein by reference.

[0002] The present invention relates to an electrode for a lithium secondary battery and a lithium secondary battery including the same. [Background technology]

[0003] In recent years, the rapid spread of battery-powered electronic devices such as mobile phones, laptops, and electric vehicles has led to a rapid increase in demand for high-energy-density, high-capacity secondary batteries, which has led to active research and development into improving the performance of lithium secondary batteries.

[0004] 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 document: KR2015-0088266

[0005] One embodiment provides an electrode for a lithium secondary battery, which includes an organic layer integrated with an active material layer, and the organic layer has high adhesive strength to the active material layer, a low thermal shrinkage rate, and can improve the lifespan of the battery.

[0006] Another embodiment provides a lithium secondary battery including the electrode for a lithium secondary battery. Summary of the Invention [Problem to be solved by the invention]

[0007] One embodiment provides an electrode for a lithium secondary battery. [Means for solving the problem]

[0008] The electrode for a lithium secondary battery includes an active material layer for a lithium secondary battery and an organic layer integrated with the active material layer, the organic layer including a sea-island region consisting of an island region and a sea region, and the area ratio of the island region to the sea-island region is 1 to 20%.

[0009] Another embodiment provides a lithium secondary battery.

[0010] The lithium secondary battery includes the electrode for a lithium secondary battery and another electrode facing the electrode for a lithium secondary battery.

[0011] In an electrode for a lithium secondary battery according to an embodiment, an organic layer that can replace a conventional separator is integrated with an active material layer, eliminating the need for a lamination process for bonding the separator and the active material layer, thereby enabling economical battery manufacture.

[0012] In the electrode for a lithium secondary battery according to one embodiment, the organic layer has high adhesive strength to the active material layer, low thermal shrinkage, and an improved battery life maintenance rate, thereby improving the stability and reliability of the lithium secondary battery. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a cross-sectional view of an electrode for a lithium secondary battery according to one embodiment. [Figure 2] FIG. 2 is a cross-sectional view of an electrode for a lithium secondary battery according to another embodiment. [Figure 3] FIG. 3 is a cross-sectional view schematically illustrating a lithium secondary battery according to an embodiment. [Figure 4] FIG. 4 is a cross-sectional view schematically illustrating a lithium secondary battery according to an embodiment. [Figure 5] FIG. 5 is a cross-sectional view schematically illustrating a lithium secondary battery according to an embodiment. [Figure 6] FIG. 6 is a cross-sectional view schematically illustrating a lithium secondary battery according to an embodiment. [Figure 7] 7 shows SEM results of the electrode for a lithium secondary battery according to Example 1. The result on the left is a photograph of the sea-island region of the organic layer, and the result on the right is an enlarged photograph of the sea region on the left. [Figure 8] 8 shows SEM results of the electrode for a lithium secondary battery according to Comparative Example 1. The result on the left is a photograph of the sea-island region of the organic layer, and the result on the right is an enlarged photograph of the sea region on the left. [Figure 9] 9 shows SEM results of the electrode for a lithium secondary battery according to Comparative Example 2. The result on the left is a photograph of the sea-island region of the organic layer, and the result on the right is an enlarged photograph of the sea region on the left. [Figure 10] FIG. 10 shows the results of evaluating the battery capacity depending on the number of cycles of the battery in Example 1 (solid line) and Comparative Example 1 (dotted line). DETAILED DESCRIPTION OF THE INVENTION

[0014] DETAILED DESCRIPTION OF THE INVENTION The following detailed description of the present invention is provided by way of example only and is not intended to limit the scope of the present invention, which is defined solely by the scope of the claims that follow.

[0015] Unless otherwise specified in this specification, when a layer, film, region, plate, or other part is said to be "on" another part, this includes not only the case where it is "directly on" the other part, but also the case where there is another part in between.

[0016] Unless otherwise specified herein, singular terms may also include plural terms. Also, unless otherwise specified, "A or B" means "including A, or including B, or including A and B."

[0017] As used herein, "combinations thereof" refers to mixtures, laminates, composites, copolymers, alloys, blends, reaction products, and the like of compositions.

[0018] An electrode for a lithium secondary battery (hereinafter also referred to as "electrode") according to one embodiment includes an active material layer for a lithium secondary battery and an organic layer integrated with the active material layer, the organic layer including a sea-island region consisting of an island region and a sea region, and the area ratio of the island region in the sea-island region is 1 to 20%.

[0019] [Organic layer] The organic layer is located between an electrode for a lithium secondary battery and an opposing electrode, and can serve as a separator to prevent short circuits.

[0020] A lithium secondary battery including an electrode according to an embodiment does not include a separate separator. Therefore, the electrode does not require a lamination process for bonding a separator and an electrode when manufacturing a battery such as a stack cell, and the battery may be manufactured using a simpler and more economical process.

[0021] The organic layer is integrated with the active material layer for a lithium secondary battery. Here, "integrated" means that the organic layer is formed directly on the active material layer without any other layer interposed therebetween, and the organic layer is more firmly bonded to the active material layer.

[0022] According to one embodiment, the organic layer may be formed by permeating the active material layer and drying, which can prevent an increase in resistance during lithium ion migration.

[0023] The integration of the active material layer and the organic layer can be confirmed by SEM, TEM, etc. According to one embodiment, the results of SEM or TEM clearly show that the active material layer and the organic layer are distinct from each other, but the interface (boundary) between the active material layer and the organic layer is not completely separated and is uneven (uneven or unflat).

[0024] The organic layer means a layer in which 90% by weight or more, for example 95% by weight to 100% by weight of all components forming the layer are organic components.

[0025] According to one embodiment, the organic layer may have a thickness of 1 to 20 μm, for example, 1 to 10 μm. In this specification, the "thickness of the organic layer" refers to the thickness of the region in the organic layer where the organic components are present in a layered form, and does not refer to the thickness where the organic components are present independently and separately. When the thickness of the organic layer falls within this range, it can exhibit an appropriately high density.

[0026] The organic layer includes nanofibers. According to one embodiment, the organic layer includes a plurality of nanofibers, and the organic layer may partially include a non-woven nanofiber structure, e.g., a network structure. An organic layer having a network structure has the advantage of minimizing resistance to lithium ion migration. The non-woven organic layer means that the organic layer is a porous layer in which voids are randomly formed between the nanofibers. If the organic layer is formed as a dense layer, the migration distance of lithium ions increases, which may result in a relatively increased resistance to lithium ion migration, which may be undesirable. According to one embodiment, the diameter of the voids may be 90 nm or less, e.g., 10 to 90 nm.

[0027] According to one embodiment, the average diameter of the nanofibers may be 300 nm or less, for example, 10 to 200 nm, or 10 to 100 nm. In this range, the formation of an organic layer is easy.

[0028] The organic layer includes a sea-island region consisting of an island region and a sea region. The sea-island region may occupy 95% or more, for example, 99 to 100%, or even 100%, of the total area of ​​the organic layer.

[0029] The sea region may be a region in which the nanofibers have a non-woven network structure. The sea region has voids formed by the nanofibers within the network structure, allowing lithium ions to easily move through them, thereby minimizing resistance to the movement of lithium ions. According to one embodiment, the sea region may be a porous region.

[0030] The island region may be an island-like region surrounded by the sea region, and may be a region having a predetermined area where nanofibers are aggregated and / or bonded to each other. According to one embodiment, the island region may be a non-void region that does not contain voids formed by nanofibers, or a region where the average diameter of the voids is significantly smaller than that of the sea region. According to one embodiment, the island region may be a film region made of nanofibers, in which nanofibers are formed into a film.

[0031] According to one embodiment, the island regions and the sea regions may be integrally formed and made of the same material, for example, the nanofibers forming the sea regions and the nanofibers forming the island regions may be of the same type.

[0032] According to one embodiment, the sea-island region may have a shape in which island regions are discontinuously arranged in a sea region, as shown in FIG. 7 below.

[0033] According to one embodiment, the island regions may be spaced apart in an irregular shape.

[0034] The area ratio of the island regions to the sea-island regions is 1 to 20%. An organic layer consisting only of sea regions may have low wet adhesion to the active material layer. In the present invention, the organic layer is composed of sea-island regions, but the area ratio of the island regions is controlled. When the area ratio of the island regions is 1% or more, not only is the adhesion between the organic layer and the active material layer high, but the thermal shrinkage rate is also low, thereby improving the stability and lifespan of the lithium secondary battery. When the area ratio of the island regions is 20% or less, resistance during lithium ion migration is not increased, preventing battery short circuits and improving the battery lifespan.

[0035] According to one embodiment, the area ratio of the island regions may be 10 to 20%, or 10 to 15%. The area ratio of the island regions in the sea-island region may be measured using an SEM image analyzer, for example, ImageJ (National Institutes of Health and the Laboratory for Optical and Computational Instrumentation (LOCI), University of Wisconsin).

[0036] According to one embodiment, the organic layer may have a MD / TD heat shrinkage of 0.1% or less, for example, 0 to 0.1%, and a wet adhesive strength of 0.15 gf / mm or more. The heat shrinkage and wet adhesive strength may be measured by the methods described below.

[0037] According to one embodiment, the area of ​​each of the island regions is 10 μm 2 ~800μm 2 , e.g., 50 μm 2 ~150μm 2 In this range, the area ratio can be easily achieved.

[0038] The area ratio of the island regions can be achieved by adjusting the electrospinning conditions when forming the organic layer using electrospinning, as will be described in more detail below.

[0039] The nanofibers may include a heat-resistant polymer, which can improve the reliability of the organic layer in the battery. Examples of heat-resistant polymers include polyester, polyamide, polyimide (PI), polyamideimide (PAI), polyetherimide, polyacrylonitrile (PAN), polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), polycarbonate (PC), polyvinyl chloride (PVC), polyvinylidene chloride, polyethylene glycol derivatives, polyoxide, polyvinyl acetate, polystyrene (PS), polyvinylpyrrolidone (PVP), copolymers thereof, and combinations thereof.

[0040] According to one embodiment, the heat-resistant polymer may include one or more of polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), and polyacrylonitrile (PAN).

[0041] The method for producing the organic layer will be described below.

[0042] The manufacturing method includes preparing an electrospinning solution containing a nanofiber polymer, and electrospinning the electrospinning solution onto one surface of an active material layer to form an organic layer. The ratio of island regions in the sea-island region can be controlled by adjusting the polymer concentration in the electrospinning solution, the gap between the nozzle pack and the collector roller, the internal temperature of the electrospinning space, and the air pressure inside the nozzle. That is, the lower the polymer concentration in the electrospinning solution, the lower the fraction of polymers with a large difference in solubility constant with the solvent, the stronger the electric field interference, the lower the internal temperature of the space, and the lower the air pressure inside the nozzle, the higher the ratio of island regions to sea regions due to the inhibition of volatilization of the solvent contained in the electrospinning solution.

[0043] According to one embodiment, electrospinning may be performed by wet spinning, which is a method of producing and solidifying fibers by extruding an electrospinning solution prepared by dissolving a polymer in a solvent through a nozzle in a solidification solution.

[0044] (1) Prepare an electrospinning solution. An electrospinning solution containing a polymer and a solvent is prepared. The solvent can facilitate the dispersion and dissolution of the polymer, thereby enabling good electrospinning. For example, a solvent having a boiling point of 200°C or less, e.g., 100 to 180°C, can be used. In this range, it is easy to form sea-island regions that fill the island regions. For example, the solvent may be methylformamide, dimethylacetamide, dimethylsulfoxide, methylpyrrolidone, etc., but is not limited thereto. To enhance the dispersion and dissolution of the polymer, stirring and / or heat treatment may be further performed.

[0045] For example, the concentration of the polymer in the electrospinning solution may be 5% to 20% by weight relative to 100% by weight of the entire electrospinning solution. Within this range, it is easy to produce an organic layer that satisfies the proportion of island regions.

[0046] (2) The electrospinning solution is electrospun onto one surface of the active material layer to form an organic layer.

[0047] Electrospinning is preferably carried out in a space with an internal temperature of 25° C. or lower, for example, above 18° C. and below 23° C. Within this range, the degree of volatilization of the solvent in the electrospinning solution decreases, and some residual solvent remains after electrospinning, making it easier to form island regions.

[0048] Electrospinning may be performed by positioning a nozzle pack having a tip with a needle size of 23G to 30G and a collector roller at a certain distance, adding an electrospinning solution to the tip, placing the active material layer on the collector roller, and then applying a voltage of 35kV to 90kV to the tip. The distance between the nozzle pack and the active material layer may be 10cm to 20cm. A tip needle size of 25G to 30G is appropriate because it allows the formation of an organic layer with the desired shape.

[0049] During the electrospinning process, the electrospinning solution is ejected and hangs down in the form of fibers, forming a layer containing nanofibers on the active material of the electrode plate. The electrospinning solution hangs in droplet form at the tip due to surface tension. When voltage is applied, charges accumulate on the surface of the solution, generating a charge repulsion force. When the critical voltage is reached, at which the repulsive force between the charges becomes greater than the surface tension of the solution, a conical Taylor cone is formed, and the electrospinning solution jet is ejected from the apex of the cone. The jet is highly elongated to form nanofibers, which are then collected on the electrode plate, forming an organic layer.

[0050] The air pressure inside the nozzle may be 1 MPa or less, for example, 0.05 to 0.8 MPa. Within this range, the degree of solvent volatilization decreases, and some residual solvent remains after electrospinning, making it easier to form island regions.

[0051] It is preferable to properly adjust the tip air pressure to minimize interference between tips and ensure uniform electrospinning. Tip air pressure may be adjusted by feeding compressed air at a pressure of 0.1 MPa to 0.3 MPa.

[0052] The roll speed of the collector roller may be adjusted to form an organic layer with an appropriate thickness, for example, 1 m / min to 3 m / min, and the flow rate of the electrospinning solution discharged from the tip may be adjusted to 20 μL / min to 200 μL / min.

[0053] In one specific example, after the electrospinning step, a drying step may be carried out at 20°C to 30°C.

[0054] In another specific example, after the electrospinning step, a drying step may be performed using hot air at 70°C to 110°C.

[0055] The electrode for a lithium secondary battery may further include an inorganic layer integrated with the organic layer.

[0056] [Inorganic layer] The inorganic layer may be integrated with the organic layer. Here, "integration" does not mean that the organic layer and the inorganic layer are formed as separate, independent layers, but rather that the inorganic layer is formed directly on the organic layer, with one component of the inorganic layer permeating into the organic layer. This is evident when the interface between the organic layer and the inorganic layer is not completely distinct and is not flat. This can be confirmed by SEM, TEM, or the like. Integration can improve the impregnation of the organic layer and the inorganic layer with the electrolyte.

[0057] According to an embodiment, the electrode may include an organic layer and an inorganic layer sequentially positioned on one side of the active material layer.

[0058] The inorganic layer may contain ceramic as the inorganic material. Ceramics are preferred in that they suppress the formation of lithium dendrites. For example, the ceramic may contain inorganic materials such as alumina (Al2O3), bohemite (aluminum oxide hydroxide), zirconia, titanium oxide (TiO2), and silica (SiO2), or a combination thereof. According to one embodiment, the ceramic is preferably one or more of alumina and bohemite. The average particle size (D50) of the inorganic material may be 100 to 500 nm, for example, 100 to 400 nm, or 100 to 200 nm. Within this range, the breathability of the organic-inorganic composite layer is also improved.

[0059] According to one embodiment, the inorganic layer may further contain an organic material in addition to the inorganic material. The organic material can facilitate the formation of the inorganic layer compared to a layer containing only the inorganic material. The organic material may be polyvinylidene fluoride, polyamideimide, polyvinylpyrrolidone, polyacrylonitrile, polyacrylic acid (PAA), polyvinyl alcohol (PVA), copolymers thereof, or combinations thereof. According to one embodiment, the inorganic material:organic material in the inorganic layer may be contained in a weight ratio of 10:1 to 30:1, for example, 15:1 to 25:1. Within this range, the effects of the inorganic layer can be provided.

[0060] According to one embodiment, the inorganic layer may be a dense layer. Here, the term "dense layer" refers to a layer in which the size of pores within the inorganic layer is minimized or the degree of pore formation is minimized. When the inorganic layer exists as a dense layer, the formation of lithium dendrites can be more effectively suppressed. However, when the inorganic layer exists as a porous layer, a short circuit may occur during charge and discharge, which is not suitable.

[0061] According to one embodiment, the inorganic layer may have a thickness of 1 to 20 μm, for example, 1 to 8 μm. In this specification, the "thickness of the inorganic layer" refers to the thickness of the region in which the inorganic components are present in a layered form within the organic-inorganic composite layer, and does not refer only to the thickness of the region in which the inorganic substances are present independently and separately. When the thickness of the inorganic layer falls within this range, the density of the inorganic layer is appropriately improved and the occurrence of lithium dendrites can be somewhat suppressed, which is appropriate.

[0062] The inorganic layer may be formed on the organic layer by electrospraying, as described below. The composition for forming the inorganic layer includes an inorganic substance and may further include one or more of a binder and a solvent. The electrospraying process may be performed by positioning a nozzle pack having a tip with a needle size of 23G to 30G and a collector roller at a predetermined distance, adding the composition for forming the inorganic layer to the tip, positioning the layer containing nanofibers on the collector roller, and then applying a voltage of 35kV to 90kV to the tip.

[0063] The distance between the nozzle pack and the nanofiber-containing layer may be 10 cm to 20 cm. A tip needle size of 25 G to 30 G is appropriate because it allows the formation of an inorganic layer with the desired shape. The inorganic layer may be formed by spraying the inorganic layer-forming layer composition onto the layer in a dot pattern by an electrical spraying process. The roll speed of the collector roller may be adjusted so that the inorganic layer is formed with an appropriate thickness, and may be, for example, 0.5 m / min to 3.0 m / min. The flow rate of the inorganic layer-forming composition discharged from the tip may be adjusted to a rate of 20 μl / min to 100 μl / min. The tip air may be adjusted by injecting compressed air at a pressure of 0.1 MPa to 0.3 MPa. After the electrical spraying process, a drying process may be performed using hot air at 90°C to 110°C.

[0064] In the composition for forming an inorganic layer, the inorganic substance is as described above. The solvent may be distilled water, alcohol such as ethanol, dimethyl acetate, N-methylpyrrolidone, dimethylformamide, acetone, or a combination thereof. The binder may be polyvinylidene fluoride, polyamideimide, polyvinylpyrrolidone, polyacrylonitrile, polyacrylic acid, polyvinyl alcohol, polyacrylic acid, carboxymethyl cellulose, or a copolymer or combination thereof. The content of the inorganic substance in the composition for forming an inorganic layer may be 85% by weight to 96% by weight, based on 100% by weight of the entire composition.

[0065] [Active material layer for lithium secondary batteries] The active material layer for a lithium secondary battery may be a positive electrode active material layer or a negative electrode active material layer. For example, the active material layer for a lithium secondary battery may be a negative electrode active material layer.

[0066] The positive electrode active material layer includes a positive electrode active material and may further include a binder and / or a conductive material. For example, the positive electrode active material layer may further include an additive that can function as a sacrificial positive electrode.

[0067] The content of the positive electrode active material may be 90% by weight to 99.5% by weight relative to 100% by weight of the positive electrode active material layer, and the contents of the binder and conductive material may be 0.5% by weight to 5% by weight each relative to 100% by weight of the positive electrode active material layer.

[0068] The positive electrode active material may be a compound capable of reversibly inserting and extracting lithium (lithiate 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.

[0069] The composite oxide may be a lithium transition metal composite oxide, and specific examples include lithium nickel oxide, lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate compound, cobalt-free nickel-manganese oxide, or a combination thereof.

[0070] As an example, a compound represented by any of the following chemical formulas may be used: Li a A 1-b X b O 2-c D c (0.90≦a≦1.8,0≦b≦0.5,0≦c≦0.05);Li a Mn 2-b X b 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 L1 d G e O2(0.90≦a≦1.8,0≦b≦0.9,0≦c≦0.5,0≦d≦0.5,0≦e≦0.1);Li a NiG b O2(0.90≦a≦1.8,0.001≦b≦0.1);Li a CoG b O2(0.90≦a≦1.8,0.001≦b≦0.1);Li a Mn 1-b G b O2(0.90≦a≦1.8,0.001≦b≦0.1);Li a Mn2G b O4(0.90≦a≦1.8,0.001≦b≦0.1);Li a Mn 1-g G g PO4(0.90≦a≦1.8,0≦g≦0.5);Li (3-f) Fe2(PO4)3(0≦f≦2);Li a FePO4(0.90≦a≦1.8).

[0071] In the 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; and G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof.

[0072] For example, the positive electrode active material may be a high-nickel 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 not more than 99 mol%, relative to 100 mol% of metals excluding lithium in a lithium transition metal composite oxide. The high-nickel positive electrode active material can provide high capacity and may be applied to high-capacity, high-density lithium secondary batteries.

[0073] 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. 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.

[0074] The conductive material is used to impart conductivity to the electrodes, and any material that is electron-conductive without undergoing chemical changes in the battery that is being constructed can be used. Examples of the conductive material include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, and carbon nanotube; metal-based materials in the form of metal powder or metal fiber, including copper, nickel, aluminum, and silver; conductive polymers such as polyphenylene derivatives; and mixtures thereof.

[0075] The negative electrode active material layer contains a negative electrode active material and may further contain a binder and / or a conductive material. For example, the negative electrode active material layer may contain 90% to 99% by weight of the negative electrode active material, 0.5% to 5% by weight of the binder, and 0% to 5% by weight of the conductive material.

[0076] The negative electrode active material includes a material capable of reversibly inserting / extracting lithium ions, lithium metal, a lithium metal alloy, a material capable of doping and dedoping lithium, or a transition metal oxide.

[0077] As a substance capable of reversibly inserting / desorbing lithium ions, a carbon-based negative electrode active material is used, and for example, it may contain crystalline carbon, amorphous carbon, or a combination thereof. Examples of crystalline carbon include graphite such as amorphous, plate-like, flaky, spherical or fibrous natural graphite or artificial graphite, and examples of amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, calcined coke, and the like.

[0078] As an alloy of lithium metal, 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 may be used.

[0079] As a substance capable of doping and undoping lithium, an Si-based negative electrode active material or an Sn-based negative electrode active material may be used. The Si-based negative electrode active material may be silicon, a silicon-carbon composite, SiOx (0 < x < 2), an 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 a combination thereof. The Sn-based negative electrode active material may be Sn, SnO2, an Sn-based alloy, or a combination thereof. <00003​​​​​The silicon-carbon composite may further comprise crystalline carbon. For example, the silicon-carbon composite may comprise a core comprising crystalline carbon and silicon particles and an amorphous carbon coating layer disposed on the core.

[0082] The Si-based negative electrode active material or the Sn-based negative electrode active material may be used in combination with a carbon-based negative electrode active material.

[0083] 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. The binder may be a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof.

[0084] 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.

[0085] The aqueous binder may be selected from styrene-butadiene rubber, (meth)acrylate styrene-butadiene rubber, (meth)acrylonitrile-butadiene 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.

[0086] 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.

[0087] The dry binder is a fiberizable polymeric material, which may be, for example, polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0088] The conductive material is used to impart conductivity to the electrodes, and any material that is electron-conductive without undergoing chemical changes in the battery that is being constructed 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.

[0089] The electrode for a lithium secondary battery may further include a current collector.

[0090] The current collector may be located on one side of the active material layer. According to one embodiment, the electrode may include an active material layer, a current collector located on one side of the active material layer, and an organic-inorganic composite layer located on the other side of the active material layer. According to one embodiment, the organic-inorganic composite layer may be formed on the other side of the current collector.

[0091] The current collector for the positive electrode active material layer may include an aluminum current collector, and the current collector for the negative electrode active material layer may be selected from the group consisting of copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof.

[0092] 1 and 2 are cross-sectional views of an electrode according to one embodiment.

[0093] Referring to FIG. 1, an electrode 1 includes an active material layer 2 for a lithium secondary battery and an organic layer 3 integrated with the active material layer 2 for a lithium secondary battery.

[0094] Referring to FIG. 2, the electrode 1 includes an active material layer 2 for a lithium secondary battery, an organic layer 3 integrated with the active material layer 2 for a lithium secondary battery, and an inorganic layer 4 integrated with the organic layer 3.

[0095] In Figures 1 and 2, the active material layer 2 for a lithium secondary battery and the organic layer 3 are shown as being formed as separate layers, but this is merely a notation for indicating the active material layer 2 for a lithium secondary battery and the organic layer 3, and the dotted line indicates that the active material layer 2 for a lithium secondary battery and the organic layer 3 are integrated together.

[0096] In FIG. 2, the organic layer 3 and the inorganic layer 4 are shown as being formed as separate layers, but this is merely a notation for illustrating the organic layer 3 and the inorganic layer 4, and the dotted lines indicate that the organic layer 3 and the inorganic layer 4 are integrated together.

[0097] Another embodiment provides an electrode assembly for a lithium secondary battery, and a lithium secondary battery including the electrode assembly for a lithium secondary battery.

[0098] In a lithium secondary battery, one electrode for the lithium secondary battery has different electrical characteristics from the other electrode for the lithium secondary battery. That is, when the electrode assembly for the lithium secondary battery includes a positive electrode for the lithium secondary battery, the electrode for the lithium secondary battery may be a negative electrode. Also, when the electrode assembly for the lithium secondary battery includes a negative electrode for the lithium secondary battery, the electrode for the lithium secondary battery may be a positive electrode.

[0099] The lithium secondary battery may further include electrodes for the lithium secondary battery and an electrolyte solution located between the electrodes for the lithium secondary battery.

[0100] The electrolyte for the lithium secondary battery includes a non-aqueous organic solvent and a lithium salt.

[0101] The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can migrate.

[0102] The non-aqueous organic solvent may be a carbonate, ester, ether, ketone, or alcohol solvent, an aprotic solvent, or a combination thereof.

[0103] Examples of carbonate solvents that may 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).

[0104] As the ester-based solvent, methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolide, mevalonolactone, valerolactone, caprolactone, and the like may be used.

[0105] Examples of ether solvents that may be used include dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, and tetrahydrofuran. Examples of ketone solvents that may be used include cyclohexanone. Examples of alcohol solvents that may be used include ethyl alcohol and isopropyl alcohol. Examples of aprotic solvents that may be used include nitriles such as R-CN (where R is a hydrocarbon group having a linear, branched, or cyclic structure and having 2 to 20 carbon atoms, and 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.

[0106] The non-aqueous organic solvents may be used alone or in combination of two or more.

[0107] When a carbonate-based solvent is used, a cyclic carbonate and a chain carbonate may be mixed and used, and the cyclic carbonate and the chain carbonate may be mixed in a volume ratio of 1:1 to 1:9.

[0108] Lithium salts are substances that dissolve in organic solvents and act as a source of lithium ions within 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, and LiN(C x F 2x+1 SO2)(C y F 2y+1SO2) (x and y are integers of 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethersulfonate, lithium difluorobis(oxalate)phosphate (LiDFOB), and lithium bis(oxalate)borate (LiBOB).

[0109] Lithium secondary batteries may be classified into cylindrical, prismatic, pouch-shaped, coin-shaped, and the like, depending on their shape.

[0110] 3 to 6 are schematic diagrams showing a lithium secondary battery according to an embodiment, in which FIG. 3 shows a cylindrical battery, FIG. 4 shows a prismatic battery, and FIGS. 5 and 6 show a pouch-shaped battery.

[0111] 3 to 6, a lithium secondary battery 100 may include an electrode assembly 40 including a positive electrode 10 for a lithium secondary battery and a negative electrode 20 including a negative electrode active material layer and an organic layer for a lithium secondary battery, and a case 50 in which the electrode assembly 40 is housed. The positive electrode 10 and the negative electrode 20 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. 3. Also, in FIG. 4, the lithium secondary battery 100 may include a positive electrode lead tab 11 and a positive electrode terminal 12, a negative electrode lead tab 21 and a negative electrode terminal 22. As shown in FIGS. 5 and 6, the lithium secondary battery 100 may include electrode tabs 70, i.e., a positive electrode tab 71 and a negative electrode tab 72, that function as electrical paths for conducting current generated in the electrode assembly 40 to the outside.

[0112] The lithium secondary battery according to an embodiment of the present invention may be applied to automobiles, mobile phones, and / or various types of electrical appliances, but the present invention is not limited thereto.

[0113] Examples of the present invention and comparative examples are described below. The following examples are merely examples of the present invention, and the present invention is not limited to the following examples.

[0114] Example 1 Anode active material slurry was prepared by mixing 97.5 wt% of artificial graphite, 1.0 wt% of carboxymethyl cellulose, and 1.5 wt% of styrene-butadiene rubber (SBR) in an aqueous solvent. The anode active material slurry was applied to a copper current collector, dried, and rolled to form a cathode active material layer.

[0115] An electrospinning solution was prepared by mixing polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) as a nanofiber polymer, polyacrylonitrile (PAN), and dimethylacetamide (boiling point: 165°C) as a solvent. The concentration of the PVDF-HFP / PAN polymer in the electrospinning solution was 15 wt%. The electrospinning solution was electrospun onto the negative electrode active material layer to form an organic layer (10 μm thick) containing nanofibers (average diameter: 90 nm).

[0116] The electrospinning process was carried out in the following manner.

[0117] Temperature of the internal space where electrospinning is performed: 22°C

[0118] A nozzle pack with a 25G needle was positioned 16 cm apart from the collector roller, and the electrospinning solution was added to the tip. A voltage of 40 to 75 kV was applied to perform electrospinning. The collector roller roll speed was 1 to 3 m / min, and the solids flow rate of the organic layer-forming composition discharged from the tip was 150 μl / min. Air pressure was 0.275 MPa while blowing in air. After electrospinning was completed, the sample was dried with hot air at 90°C.

[0119] In this process, a negative electrode was manufactured in which an organic layer (thickness: 10 μm) (area ratio of the island region: 15%) was integrated with the negative electrode active material layer.

[0120] A positive electrode active material slurry was prepared by mixing 96 wt% LiCoO2, 2 wt% Ketjen black, and 2 wt% polyvinylidene fluoride in N-methylpyrrolidone as a solvent. The positive electrode active material slurry was applied to an aluminum current collector, dried, and rolled to prepare a positive electrode active material layer.

[0121] The fabricated negative and positive electrodes were stacked together to fabricate an electrode assembly. The organic layer of the negative electrode and the positive electrode active material layer were positioned so that they were in contact with each other. A lithium secondary battery (without a separator) was fabricated using the electrode assembly and an electrolyte. The electrolyte used was a mixed solvent (50:50 volume ratio) of ethylene carbonate and ethyl methyl carbonate in which LiPF6 was dissolved.

[0122] Example 2 An organic layer (area ratio of island regions: 10%) and a battery were manufactured in the same manner as in Example 1, except that the air pressure was changed from 0.275 MPa to 0.3 MPa when manufacturing the organic layer in Example 1.

[0123] Example 3 An organic layer (area ratio of island regions was 20%) and a battery were manufactured in the same manner as in Example 1, except that the TCD (distance between the nozzle pack and the collector roller) was changed from 16 cm to 14 cm when manufacturing the organic layer in Example 1.

[0124] Comparative Example 1 A negative electrode active material layer was formed on a copper current collector in the same manner as in Example 1. A positive electrode active material layer was formed on an aluminum current collector in the same manner as in Example 1. A separator manufactured by Asahi Kasei Corporation (thickness: 13 μm, a polyethylene substrate film having an inorganic layer containing bohemite and an organic binder layer formed in that order) was used.

[0125] A separator was placed between the fabricated negative electrode and positive electrode, and they were stacked together to fabricate an electrode assembly. A lithium secondary battery was fabricated using the electrode assembly and an electrolyte. The electrolyte was the same as that used in Example 1.

[0126] Comparative Example 2 An organic layer (area ratio of island regions: 30%) and a battery were manufactured in the same manner as in Example 1, except that the temperature of the internal space where electrospinning was performed was changed from 22°C to 18°C ​​when manufacturing the organic layer in Example 1.

[0127] SEM photographs were taken of the negative electrodes containing the organic layers prepared in the examples and comparative examples, and the results are shown in Figure 7 (Example 1), Figure 8 (Comparative Example 1), and Figure 9 (Comparative Example 2).

[0128] Referring to FIG. 7, the island area of ​​the organic layer in Example 1 is 15%.

[0129] On the other hand, referring to FIG. 8, the adhesive layer of Comparative Example 1 is configured in the form of a dot arrangement with a diameter of 200 μm.

[0130] On the other hand, referring to FIG. 9, the island area of ​​the organic layer in Comparative Example 2 is 30%.

[0131] The negative electrodes and batteries including the negative electrodes prepared in the examples and comparative examples were evaluated for the following physical properties, and the results are shown in Table 1 below and FIG.

[0132] (1) Wet Adhesion Strength (unit: gf / mm): Electrode assemblies (cathode-negative electrode integrated with organic layer) prepared in the examples and comparative examples were cut into 2.5 cm x 8 cm samples. The prepared samples were placed in pouches. 2.5 g of a mixed solvent (50:50 volume ratio) of ethylene carbonate and ethyl methyl carbonate in which LiPF6 was dissolved was poured into the pouches, which were then sealed and left at 25°C for 12 hours. The pouches were then left in a 50°C chamber under a pressure of 200 kgf for 2 hours. After separating the organic layer from the negative electrode plate by 10–20 mm, the separator was attached to the upper grip and the negative electrode plate to the lower grip, with a 20 mm gap between the grips. The sample was then pulled 180° to separate the adhesive strength. The peel speed was 20 mm / min, and the force required to peel 40 mm after the start of peeling was measured three times and averaged. The average of the measured values ​​was used for calculation.

[0133] (2) Thermal shrinkage (unit: %): An organic layer was prepared in the same manner as in the Examples and Comparative Examples. The prepared organic layer-electrode plate was cut into a 5 cm x 5 cm sample. A 5 cm x 5 cm square was drawn on the surface of the sample, which was then sandwiched between paper or alumina powder and left in an oven at 180°C for 1 hour. The sample was then removed and the dimensions of the sides of the square were measured to calculate the thermal shrinkage in both the mechanical direction (MD) and the perpendicular direction (TD). The thermal shrinkage was calculated using the following equation: [Number 1] Heat shrinkage rate = (L0-L1) / L0 x 100 (L0 is the initial length of the organic layer, and L1 is the length of the organic layer after standing at 180°C for 1 hour).

[0134] (3) Battery life retention rate: Batteries were manufactured in the same manner as in the examples and comparative examples. The capacity efficiency (unit: %) of the manufactured batteries was evaluated after 1 cycle and 500 cycles at 55°C. The charge and discharge conditions were as follows: Charging: CC1.0C to 4.4V, CV to 0.01C Discharge: CC1.0C to 2.75V

[0135] [Table 1]

[0136] *ND: In Comparative Example 2, the cell could not be driven and the battery life could not be measured.

[0137] As shown in Table 1, the lithium secondary battery electrodes of the examples have high adhesive strength to the active material layer, low thermal shrinkage, and can increase the battery life retention rate even after 500 cycles.

[0138] On the other hand, the electrode of the comparative example with a conventional separator had a high thermal shrinkage of the separator. Also, the electrode of comparative example 2, which contained an organic layer with sea-island regions but with an island area ratio of 30%, was unable to operate the cell.

[0139] Although the preferred embodiments of the present invention have been described above, the present invention is not limited thereto and can be embodied in various modifications within the scope of the claims, the detailed description of the invention, and the accompanying drawings, and it is to be understood that these modifications also fall within the scope of the present invention. [Explanation of symbols]

[0140] 1 electrode 2. Active material layer for lithium secondary batteries 3 organic layer 3 4 Inorganic layer 10. Positive electrodes for lithium secondary batteries 11 Positive electrode lead tab 12 Positive terminal 20. Negative electrode for lithium secondary batteries 21 Negative electrode lead tab 22 Negative terminal 40 Electrode assembly 50 cases 60 Sealing member 70 Electrode tab 71 Positive electrode tab 72 Negative electrode tab

Claims

1. The present invention relates to a lithium secondary battery, and an organic layer integrated with the active material layer. the organic layer includes a sea-island region consisting of an island region and a sea region; The area ratio of the island regions to the sea-island regions is 1 to 20%.

2. 2. The electrode for a lithium secondary battery according to claim 1, wherein the sea region is a region in which the nanofibers are in a non-woven state, and the island region is a film region made of nanofibers.

3. 3. The electrode for a lithium secondary battery according to claim 2, wherein the sea-island region has the island regions discontinuously arranged in the sea region.

4. The electrode for a lithium secondary battery according to claim 2 , wherein the nanofibers in the sea region are of the same type as the nanofibers in the island region.

5. 3. The electrode for a lithium secondary battery according to claim 2, wherein the sea region is a porous region, and the island region is a non-void region or a region in which the average diameter of the voids is smaller than that of the sea region.

6. 3. The electrode for a lithium secondary battery according to claim 2, wherein the nanofibers comprise polyester, polyamide, polyimide (PI), polyamideimide (PAI), polyetherimide, polyacrylonitrile (PAN), polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), polycarbonate (PC), polyvinyl chloride (PVC), polyvinylidene chloride, polyethylene glycol derivatives, polyoxide, polyvinyl acetate, polystyrene (PS), polyvinylpyrrolidone (PVP), copolymers thereof, or combinations thereof.

7. The area of ​​each of the island regions is 10 μm 2 ~800μm 2 3. The electrode for a lithium secondary battery according to claim 2, wherein

8. 3. The electrode for a lithium secondary battery according to claim 2, wherein the nanofibers have an average diameter of 300 nm or less.

9. The electrode for a lithium secondary battery according to claim 1 , wherein the electrode further comprises an inorganic layer integrated with the organic layer.

10. 2. The electrode for a lithium secondary battery according to claim 1, wherein the active material layer for a lithium secondary battery is a negative electrode active material layer.

11. The electrode for a lithium secondary battery according to claim 10 , wherein the negative electrode active material layer contains a carbon-based negative electrode active material.

12. A lithium secondary battery comprising the electrode for a lithium secondary battery according to any one of claims 1 to 11 and an electrode for a lithium secondary battery facing the electrode for a lithium secondary battery.

13. The lithium secondary battery of claim 12 , wherein the lithium secondary battery is membrane-free.

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