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 to an electrode for a lithium secondary battery, and a lithium secondary battery including the same. The electrode for a lithium secondary battery includes an active material layer for a lithium secondary battery and an organic-inorganic composite layer integrated with the active material layer. The organic-inorganic composite layer includes nanofiber. The nanofiber includes an inorganic material and a matrix. The inorganic material includes one or more kinds of a boron nitride nanosheet and a boron nitride nanotube. The matrix includes one or more kinds of a polyimide polymer and a polyamic acid polymer. The inorganic material is contained by 0.1 to 7 wt% of the nanofiber.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This application claims priority to and the benefit of Korean Patent Application No. 10-2024-0057507, 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. Summary of the Invention [Problem to be solved by the invention]

[0005] In one embodiment, an electrode for a lithium secondary battery is provided, which includes an organic-inorganic composite layer integrated with an active material layer, the organic-inorganic composite layer having excellent puncture strength and low heat shrinkage, excellent dispersion of inorganic material within nanofibers in the organic-inorganic composite layer, and excellent adhesive strength between the organic-inorganic composite layer and the active material layer.

[0006] In another embodiment, a lithium secondary battery including the lithium secondary battery electrode is provided. [Means for solving the problem]

[0007] In one embodiment, an electrode for a lithium secondary battery is provided.

[0008] The electrode for a lithium secondary battery comprises an active material layer for a lithium secondary battery and an organic-inorganic composite layer integrated with the active material layer for a lithium secondary battery, the organic-inorganic composite layer comprising nanofibers, the nanofibers comprising an inorganic material and a matrix, the inorganic material comprising at least one of boron nitride nanosheets and boron nitride nanotubes, the matrix comprising at least one of polyimide (PI)-based polymers and polyamic acid (PAA)-based polymers, and the inorganic material comprising 0.1 to 7 wt % of the nanofibers.

[0009] In another embodiment, a lithium secondary battery is provided.

[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 one embodiment, an organic-inorganic composite layer, which 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-inorganic composite layer is a single layer, which can replace the conventional multi-layer structure of organic and inorganic layers, and allows for simple and economical battery fabrication.

[0013] In an electrode for a lithium secondary battery according to an embodiment, the organic-inorganic composite layer not only has excellent puncture strength and low thermal shrinkage, but also has excellent adhesion to the active material layer and excellent dispersibility of inorganic materials in the nanofibers, thereby improving the stability and lifespan of the lithium secondary battery. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a cross-sectional view of an electrode for a lithium secondary battery according to one embodiment. [Figure 2] The figure is a cross-sectional view schematically illustrating a lithium secondary battery according to an 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. DETAILED DESCRIPTION OF THE INVENTION

[0015] 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.

[0016] 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.

[0017] Unless otherwise specified herein, singular terms may also include plural terms. Furthermore, unless otherwise specified, "A or B" means "including A, or including B, or including A and B."

[0018] As used herein, "combinations thereof" refers to mixtures, laminates, composites, copolymers, alloys, blends, reaction products, and the like of compositions.

[0019] Unless otherwise defined herein, particle size may refer to the average particle size. Furthermore, particle size refers to the average particle size (D50), which refers to the diameter of particles with a cumulative volume of 50% by volume in the particle size distribution. The average particle size (D50) may be measured by methods well known to those skilled in the art, such as using a particle size analyzer or a transmission electron microscope (TEM) or scanning electron microscope (SEM) photograph. Alternatively, measurement may be performed using a measuring device using dynamic light scattering, and data analysis may be performed to count the number of particles in each particle size range, after which the average particle size (D50) value can be calculated. Alternatively, measurement may be performed using a laser diffraction method. When measuring by the laser diffraction method, more specifically, the particles to be measured may be dispersed in a dispersion medium, then introduced into a commercially available laser diffraction particle size measuring device (e.g., MT 3000 by Microtrac), and irradiated with ultrasonic waves of approximately 28 kHz at an output of 60 W, after which the average particle size D50 based on 50% of the particle size distribution measured by the measuring device may be calculated.

[0020] 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-inorganic composite layer integrated with the active material layer, the organic-inorganic composite layer including nanofibers, the nanofibers including an inorganic material and a matrix, the inorganic material including one or more of boron nitride nanosheets and boron nitride nanotubes, the matrix including one or more of polyimide (PI)-based polymers and polyamic acid (PAA)-based polymers, and the inorganic material being included in an amount of 0.1 to 7 wt % of the nanofibers.

[0021] [Organic-inorganic composite layer] The organic-inorganic composite layer is located between an electrode for a lithium secondary battery and an electrode facing it, and can function as a separator to prevent short circuits.

[0022] 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.

[0023] The organic-inorganic composite layer is integrated with the active material layer for a lithium secondary battery. Here, "integration" refers to the organic-inorganic composite layer being formed directly on the active material layer without the intervention of any other layer, and the organic-inorganic composite layer being more firmly bonded to the active material layer. Integration can prevent an increase in resistance during lithium ion migration.

[0024] According to one embodiment, the organic-inorganic composite layer may be formed by permeating the active material layer and drying, thereby being integrated with the active material layer.

[0025] The integration of the active material layer and the organic-inorganic composite layer can be confirmed by SEM, TEM, etc. According to one embodiment, the results of SEM or TEM clearly show that the integration is achieved when the active material layer and the organic-inorganic composite layer are distinct from each other, but the interface (boundary) between the active material layer and the organic-inorganic composite layer is not completely distinct and is in an uneven or unflat state.

[0026] The organic-inorganic composite layer may be a single layer. Here, "single layer" means that it consists of one layer, whereas conventional organic-inorganic composite layers consist of multiple layers including an organic layer and an inorganic layer. The organic-inorganic composite layer can replace multiple layers including an organic layer and an inorganic layer, allowing batteries to be manufactured using a simple and economical process. According to one embodiment, the electrode may not include an inorganic layer. Here, "inorganic layer" refers to a layer containing an inorganic component or inorganic material, for example, a ceramic, or a layer containing an inorganic component or inorganic material as the main component (e.g., 70% by weight or more).

[0027] According to one embodiment, the organic-inorganic composite layer may have a thickness of 1 to 20 μm, for example, 1 to 10 μm. In this specification, the "thickness of the organic-inorganic composite layer" refers to the thickness of the region in the organic-inorganic composite 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-inorganic composite layer falls within this range, it can exhibit an appropriately high density.

[0028] The organic-inorganic composite layer includes nanofibers. According to one embodiment, the organic-inorganic composite layer includes a plurality of nanofibers. The organic-inorganic composite layer may include a woven or non-woven nanofiber structure, e.g., a network structure. An organic-inorganic composite layer having a network structure has the advantage of minimizing resistance to lithium ion migration. The woven organic-inorganic composite layer is a porous layer with voids formed between the nanofibers. On the other hand, if the organic-inorganic composite layer is formed as a dense layer, the lithium ion migration distance 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.

[0029] According to one embodiment, the average diameter of the nanofibers may be 300 nm or less, for example, 10 to 200 nm, 10 to 100 nm, or 50 to 100 nm. In this range, it is easy to form an organic-inorganic composite layer.

[0030] The nanofibers include an inorganic material, and the inorganic material includes at least one of a boron nitride nanosheet and a boron nitride nanotube.

[0031] At least one of boron nitride nanosheets and boron nitride nanotubes can easily increase the puncture strength of the organic-inorganic composite layer and reduce the thermal shrinkage rate.

[0032] One or more of boron nitride nanosheets and boron nitride nanotubes are contained in the nanofibers at 0.1 to 7 wt %. When one or more of boron nitride nanosheets and boron nitride nanotubes are contained at 0.1 wt % or more, the puncture strength and thermal shrinkage can be increased relative to a layer containing nanofibers consisting of only a matrix, as described below. When one or more of boron nitride nanosheets and boron nitride nanotubes are contained at 7 wt % or less, electrospinning is improved, as described below, and the formation of an organic-inorganic composite layer is facilitated. The boron nitride nanosheets and boron nitride nanotubes are not exposed to the outside of the nanofibers, which facilitates reducing resistance during lithium ion migration. For example, one or more of boron nitride nanosheets and boron nitride nanotubes may be contained at 1 to 7 wt % or 3 to 7 wt % of the nanofibers.

[0033] According to one embodiment, one or more of boron nitride nanosheets and boron nitride nanotubes may be contained in the inorganic material in an amount of 95% by weight or more, for example, 99 to 100% by weight, or 100% by weight, which provides sufficient puncture strength and low thermal shrinkage.

[0034] Boron nitride nanosheets are made by mixing boron and nitrogen elements in a 1:1 molar ratio, and have a hexagonal structure similar to graphite, with boron nitride having a two-dimensional crystal structure.

[0035] According to one embodiment, the boron nitride nanosheet may have a thickness of 0.3 to 30 nm, e.g., 3 to 10 nm, and a maximum diameter of 10 to 200 nm, e.g., 10 to 100 nm. According to one embodiment, the boron nitride nanosheet comprises an upper surface, a lower surface, and side surfaces connecting the upper and lower surfaces, and at least one of the upper and lower surfaces may have a curved shape, such as a polygonal shape (e.g., a rectangle or a square), or a circular shape. According to one embodiment, the boron nitride nanosheet may have a ratio of maximum diameter to thickness of 10 to 300, e.g., 10 to 50.

[0036] Boron nitride nanotubes are composed of boron and nitrogen elements mixed in a 1:1 molar ratio, and have a tube structure similar to that of carbon nanotubes. According to one embodiment, the boron nitride nanotubes may have an average outer diameter of 10 to 100 nm, e.g., 10 to 50 nm, an average length of 1 to 50 μm, e.g., 10 to 50 μm, and an aspect ratio of 10 to 5000, e.g., 100 to 3000. Here, the "aspect ratio" refers to the ratio of the average length to the average outer diameter of the boron nitride nanotubes.

[0037] For example, the inorganic material may include boron nitride nanosheets, which, when contained in the nanofiber at the same content as boron nitride nanotubes, have higher puncture strength and better dispersibility.

[0038] Although boron nitride nanosheets and boron nitride nanotubes can easily increase the puncture strength and reduce the thermal shrinkage of organic-inorganic composite layers, their specific morphology can reduce their dispersibility within the nanofiber matrix during electrospinning. To improve the dispersibility of boron nitride nanosheets and boron nitride nanotubes, dispersing techniques such as ultrasound can be applied to the electrospinning solution containing the boron nitride nanosheets and boron nitride nanotubes. However, the use of such additional dispersing techniques can reduce the processability of the organic-inorganic composite layer. Furthermore, since the organic-inorganic composite layer is formed integrally with the active material layer, it must have excellent adhesion to the active material layer.

[0039] The nanofibers include a matrix in which the inorganic material is impregnated.

[0040] The matrix contains one or more of a polyimide (PI)-based polymer and a polyamic acid (PAA)-based polymer. In nanofibers containing one or more of a boron nitride nanosheet and a boron nitride nanotube, the polyimide-based polymer and the polyamic acid-based polymer enhance the dispersibility of the boron nitride nanosheet and the boron nitride nanotube, thereby facilitating increased adhesion to the active material layer, increased puncture strength of the organic-inorganic composite layer, and further reduced thermal shrinkage. The inventors of the present invention have confirmed that the aforementioned effects can be achieved by fabricating nanofibers containing one or more of a boron nitride nanosheet and a boron nitride nanotube in a matrix composed of one or more of a polyimide-based polymer and a polyamic acid-based polymer.

[0041] According to one embodiment, one or more of polyimide-based polymers and polyamic acid-based polymers may be included in the nanofibers in an amount excluding inorganic materials, for example, 90 to 99.9 wt %, or 93 to 99.9 wt %.

[0042] According to one embodiment, the matrix may contain at least one of a polyimide-based polymer and a polyamic acid-based polymer in an amount of 95% by weight or more, for example, 99 to 100% by weight, or 100% by weight.

[0043] According to one embodiment, the matrix may consist solely of a polyimide-based polymer or a polyamic acid-based polymer.

[0044] According to another embodiment, the polymer matrix is ​​made of a mixture of a polyimide polymer and a polyamic acid polymer, and the polyimide polymer and polyamic acid polymer may be contained in a ratio of 20-50 wt%:50-80 wt%, for example, 20-40 wt%:60-80 wt%, of the 100 wt% mixture. Within this range, the compatibility of the polyimide and polyamic acid in the polymer matrix is ​​excellent.

[0045] According to one embodiment, the polyimide-based polymer may include a repeating unit of the following formula:

[0046] [ka]

[0047] (In Chemical Formula 1, * denotes the linking site of the element, R 1 is a tetravalent organic group, R 2 is a divalent aliphatic, alicyclic, or aromatic organic group or a combination thereof having a total of 3 to 30 carbon atoms.

[0048] In one embodiment, R 2 may be an alkylene group, cycloalkylene group, or arylene group having 3 to 30 carbon atoms and having at least a linking group selected from the group consisting of -O-, -SO2-, -CO-, -CH2-, -C(CH3)2-, -OSi(CH3)2-, -C2H4O-, and -S-.

[0049] In one embodiment, R 1 may be selected from the group consisting of a portion of the following:

[0050] [ka]

[0051] [ka]

[0052] [ka]

[0053] (* indicates the linking site of the element)

[0054] Polyimide-based polymers may be prepared by conventional methods known to those skilled in the art.

[0055] According to one embodiment, the polyamic acid polymer may contain one or more repeating units of the following formulas (2) and (3).

[0056] [ka]

[0057] [ka]

[0058] (In Chemical Formula 2 and Chemical Formula 3, * denotes the linking site of the element, R 3 , R 4 are each independently a hydrogen atom or an alkyl group having 1 to 5 carbon atoms, R 5 represents a single bond, an alkylene group having 1 to 5 carbon atoms, an arylene group having 6 to 10 carbon atoms, or an arylalkylene group having 7 to 10 carbon atoms; R 6 represents an alkylene group having 1 to 5 carbon atoms, an arylene group having 6 to 10 carbon atoms, an aryl alkylene group having 7 to 10 carbon atoms, or an aryl ether group having 6 to 10 carbon atoms)

[0059] For example, the polyamic acid polymer may contain one or more units of the following formulas 2-1 and 2-2.

[0060] [ka]

[0061] [ka]

[0062] The polyamic acid polymer may be prepared by conventional methods known to those skilled in the art.

[0063] The method for producing the organic-inorganic composite layer will be described below.

[0064] The manufacturing method includes the steps of preparing an electrospinning solution containing at least one of a polyimide-based polymer and a polyamic acid-based polymer, and at least one of a boron nitride nanosheet and a boron nitride nanotube, and electrospinning the electrospinning solution onto one surface of an active material layer to form an organic-inorganic composite layer.

[0065] (1) Prepare an electrospinning solution.

[0066] An electrospinning solution is prepared containing at least one of a polyimide polymer and a polyamic acid polymer, and at least one of a boron nitride nanosheet and a boron nitride nanotube. The electrospinning solution contains at least one of a boron nitride nanosheet and a boron nitride nanotube in an amount of 0.1 to 7 wt % based on the solid content.

[0067] The electrospinning solution may further contain a solvent to improve dispersion of each component in the electrospinning solution, such as, but not limited to, dimethyl acetate, methyl formamide, dimethyl acetamide, N-methylpyrrolidone, etc.

[0068] The total content of each component in the electrospinning solution may be 5% by weight to 20% by weight, based on 100% by weight of the total electrospinning solution. Within this range, an organic-inorganic composite layer may be formed with an appropriate thickness.

[0069] During preparation of the electrospinning solution, stirring may be further performed to enhance dispersion of one or more of the boron nitride nanosheets and boron nitride nanotubes. In the present invention, one or more of the boron nitride nanosheets and boron nitride nanotubes can be easily dispersed without using ultrasound. However, the use of ultrasound can further enhance dispersion of the boron nitride nanosheets and boron nitride nanotubes.

[0070] (2) Form an organic-inorganic composite layer by electrospinning.

[0071] The electrospinning process may be performed by positioning a nozzle pack having a tip with a hole diameter of 23 to 30 g and a collector roller at a regular interval, adding the electrospinning solution to the tip, positioning the active material layer on the collector roller, and then applying a voltage of 35 to 50 kV, for example, 40 to 50 kV, to the tip. The number of tips may be adjusted appropriately depending on the content of one or more of the polyimide-based polymer and polyamic acid-based polymer in the electrospinning solution, and may be, for example, 20 to 60. The distance between the nozzle pack and the active material layer may be 10 to 20 cm. A tip hole diameter of 25 to 30 g is appropriate because it allows the formation of an organic-inorganic composite layer with a desired shape.

[0072] Through the electrospinning process, the electrospinning solution may be electrospun and hang down in the form of fibers, which are then spun into a cone-shaped active material layer, forming an organic-inorganic composite layer. The electrospinning solution hangs in the form of droplets at the tip due to surface tension. When a voltage is applied, a repulsive force of electric charge occurs, causing the solution to begin to distort in the opposite direction to the surface tension of the solution. When a critical voltage is reached, the polymer solution is sprayed from the apex of the droplet, and the spray, called a Taylor cone, is collected by a collector roller, forming an organic-inorganic composite layer.

[0073] According to one embodiment, the electrospinning process may be carried out under conditions of 20°C to 30°C and a relative humidity of 40% to 60%. When the electrospinning process is carried out under such temperature and relative humidity conditions, it has the advantage of maintaining a constant diameter of the nanofibers during spinning.

[0074] The roll speed of the collector roller may be adjusted to form an organic-inorganic composite layer with an appropriate thickness, for example, 1 m / min to 3 m / min, and may be adjusted to discharge the electrospinning solution from the tip at a solid content of 20 μL / min to 200 μL / min.

[0075] Tip air is appropriately adjusted to minimize interference between tips and ensure uniform electrospinning. Tip air may be adjusted by feeding compressed air at a pressure of 0.1 MPa to 0.2 MPa.

[0076] In one specific example, after the electrospinning step, a drying step may be performed at 20° C. to 30° C. In another specific example, after the electrospinning step, a drying step may be performed with hot air at 70° C. to 110° C.

[0077] [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.

[0078] 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.

[0079] 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.

[0080] 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.

[0081] 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.

[0082] 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 L 1 d G e O2(0.90≦a≦1.8,0≦b≦0.9,0≦c≦0.5,0≦d≦0.5,0≦e≦0.1);Li a NiG b O2(0.90≦a≦1.8,0.001≦b≦0.1);Li a CoG b O2(0.90≦a≦1.8,0.001≦b≦0.1);Li a Mn 1-b G 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);Lia FePO4(0.90≦a≦1.8).

[0083] In the chemical formula, A is Ni, Co, Mn, or a combination thereof; X is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element, or a combination thereof; D is O, F, S, P, or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof; and L 1 is Mn, Al, or a combination thereof.

[0084] 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.

[0085] The binder serves to firmly adhere the positive electrode active material particles to each other and 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.

[0086] 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.

[0087] 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.

[0088] 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.

[0089] The material capable of reversibly inserting / extracting lithium ions is a carbon-based negative electrode active material, and may include, for example, crystalline carbon, amorphous carbon, or a combination thereof. Examples of crystalline carbon include graphite such as amorphous, plate-like, flake-like, spherical, or fibrous natural graphite or artificial graphite, and examples of amorphous carbon include soft carbon, hard carbon, mesophase pitch carbide, and calcined coke.

[0090] As the lithium metal alloy, an alloy of lithium and a metal selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al and Sn may be used.

[0091] As the substance capable of being doped and undoped with lithium, a Si-based negative electrode active material or a 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), a Si-Q alloy (Q is selected from alkali metals, alkaline earth metals, group 13 elements, group 14 elements (excluding Si), group 15 elements, group 16 elements, transition metals, rare earth elements, and combinations thereof), or a combination of these. The Sn-based negative electrode active material may be Sn, SnO2, a Sn-based alloy, or a combination of these.

[0092] The silicon-carbon composite may be a composite of silicon and amorphous carbon. According to one embodiment, the silicon-carbon composite may be in a form in which silicon particles are coated with amorphous carbon on the surface of the silicon particles. For example, it may include secondary particles (cores) assembled from primary silicon particles and an amorphous carbon coating layer (shell) located on the surface of the secondary particles. Amorphous carbon may also be located between the primary silicon particles, and for example, the primary silicon particles may be coated with amorphous carbon. The secondary particles may be dispersed and present in an amorphous carbon matrix.

[0093] The silicon-carbon composite may further include crystalline carbon. For example, the silicon-carbon composite may include a core containing crystalline carbon and silicon particles and an amorphous carbon coating layer located on the surface of this core.

[0094] The Si-based negative electrode active material or the Sn-based negative electrode active material may be used in mixture with a carbon-based negative electrode active material.

[0095] The binder serves to make the negative electrode active material particles adhere well to each other and further make the negative electrode active material adhere well to the current collector. As the binder, a non-aqueous binder, an aqueous binder, a dry binder, or a combination of these may be used.

[0096] 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.

[0097] 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.

[0098] 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.

[0099] 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.

[0100] 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.

[0101] The electrode for a lithium secondary battery may further include a current collector.

[0102] 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.

[0103] 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.

[0104] FIG. 1 is a cross-sectional view of an electrode according to one embodiment.

[0105] Referring to FIG. 1, an electrode 1 includes an active material layer 2 for a lithium secondary battery and an organic-inorganic composite layer 3 integrated with the active material layer 2 for a lithium secondary battery.

[0106] In FIG. 1, the active material layer 2 for a lithium secondary battery and the organic-inorganic composite layer 3 are shown as being formed as separate layers, but this is merely a notation for illustrating the active material layer 2 for a lithium secondary battery and the organic-inorganic composite layer 3, and the dotted line indicates that the active material layer 2 for a lithium secondary battery and the organic-inorganic composite layer 3 are integrated together.

[0107] Another embodiment provides an electrode for a lithium secondary battery, and a lithium secondary battery including the electrode for the lithium secondary battery.

[0108] In a lithium secondary battery, the electrode for the lithium secondary battery and the electrode for the lithium secondary battery have different electrical characteristics. 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.

[0109] 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.

[0110] The electrolyte for the lithium secondary battery includes a non-aqueous organic solvent and a lithium salt.

[0111] The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can migrate.

[0112] The non-aqueous organic solvent may be a carbonate, ester, ether, ketone, or alcohol solvent, an aprotic solvent, or a combination thereof.

[0113] 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).

[0114] 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.

[0115] 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.

[0116] The non-aqueous organic solvents may be used alone or in combination of two or more.

[0117] 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.

[0118] 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+1 SO2) (x and y are integers of 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethersulfonate, lithium difluorobis(oxalate)phosphate (LiDFOB), and lithium bis(oxalate)borate (LiBOB).

[0119] Lithium secondary batteries may be classified into cylindrical, prismatic, pouch-shaped, coin-shaped, and the like, depending on their shape.

[0120] 2 to 5 are schematic diagrams showing a lithium secondary battery according to an embodiment, in which FIG. 2 shows a cylindrical battery, FIG. 3 shows a prismatic battery, and FIGS. 4 and 5 show a pouch-shaped battery.

[0121] 2 to 5, 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. 2. Also, in FIG. 3, 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. 4 and 5, the lithium secondary battery 100 may include electrode tabs 70, i.e., a positive electrode tab 71 and a negative electrode tab 72, that function as electrical paths for conducting current generated in the electrode assembly 40 to the outside.

[0122] 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.

[0123] 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.

[0124] Example 1 Anode active material slurry was prepared by mixing 97.5 wt% of a mixture of artificial graphite and natural graphite, 1.0 wt% of carboxymethyl cellulose, and 1.5 wt% of styrene-butadiene rubber (SBR) in an aqueous solvent. The anode active material layer was prepared by applying the anode active material slurry to a copper current collector, drying, and rolling.

[0125] A polyimide-based polymer (PI, P84, Evonik Industries) was dissolved in dimethyl acetate at 70°C to produce a polyimide solution. Boron nitride nanosheets (BNNS, thickness: 10 nm, maximum diameter: 0.1 μm) were added to the dimethyl acetate solvent and dispersed ultrasonically to produce a boron nitride nanosheet solution. The resulting polyimide solution and boron nitride nanosheet solution were mixed and stirred to produce an electrospinning solution. The electrospinning solution was electrospun onto the negative electrode active material layer and dried at 100°C to form a layer (thickness: 10 μm) containing nanofibers (containing polyimide and boron nitride nanosheets, average diameter: 90 nm). The electrospinning process was performed as follows.

[0126] A nozzle pack consisting of two tips with a 25G hole diameter and a collector roller were positioned 15 cm apart, and the electrospinning solution was added to the tips. A voltage of 40-50 kV was applied, and electrospinning was performed under conditions of 26°C and 50% relative humidity. The roll speed of the collector roller was 1-3 m / min, and the solid content of the electrospinning solution discharged from the tips was 150 μl / min.

[0127] In this process, a negative electrode was produced in which an organic-inorganic composite layer (thickness: 10 μm) was integrated with the negative electrode active material layer. Among the nanofibers that make up the organic-inorganic composite layer, boron nitride nanosheets were contained at 1 wt%.

[0128] 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.

[0129] The fabricated negative and positive electrodes were stacked together to fabricate an electrode assembly. The organic-inorganic composite layer of the negative electrode and the positive electrode active material layer of the positive electrode 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 was a mixed solvent (50:50 volume ratio) of ethylene carbonate and ethyl methyl carbonate in which LiPF6 was dissolved.

[0130] Example 2 The same method as in Example 1 was carried out, except that the content of boron nitride nanosheets in the electrospinning solution was changed so that the boron nitride nanosheets were contained in an amount of 3 wt% in the nanofibers forming the organic-inorganic composite layer.

[0131] Example 3 The same method as in Example 1 was carried out, except that the content of boron nitride nanosheets in the electrospinning solution was changed so that the boron nitride nanosheets were contained in an amount of 5 wt% in the nanofibers forming the organic-inorganic composite layer.

[0132] Example 4 The same method as in Example 1 was carried out, except that the content of boron nitride nanosheets in the electrospinning solution was changed so that the boron nitride nanosheets were contained in an amount of 7 wt% in the nanofibers forming the organic-inorganic composite layer.

[0133] Example 5 The same method as in Example 1 was carried out, except that the content of boron nitride nanosheets in the electrospinning solution was changed so that the boron nitride nanosheets were contained in the nanofibers forming the organic-inorganic composite layer at 0.1 wt%.

[0134] Example 6 The same method as in Example 1 was carried out, except that a polyamic acid polymer (PAA, Poly(amic acid), containing the following repeating unit) was used instead of polyimide in the electrospinning solution.

[0135] [ka]

[0136] Example 7 The same method as in Example 1 was carried out, except that boron nitride nanotubes (BNNTs) were used instead of boron nitride nanosheets in the electrospinning solution.

[0137] Comparative Example 1 The same method as in Example 1 was carried out, except that the boron nitride nanosheet was not used in the electrospinning solution.

[0138] Comparative Example 2 The same method as in Example 1 was carried out, except that a polypropylene-based separator was used between the positive electrode active material layer and the negative electrode active material layer instead of the organic-inorganic composite layer.

[0139] Comparative Example 3 The content of boron nitride nanosheets in the electrospinning solution was changed to 10 wt% in Example 1 to prepare an electrospinning solution. However, the electrospinning solution did not perform properly, and an organic-inorganic composite layer could not be prepared.

[0140] Comparative Examples 4 to 6 The same method as in Example 1 was carried out, except that the components in Table 1 below were used as the polymer instead of polyimide.

[0141] Comparative Example 7 The same method as in Example 1 was carried out, except that bohemite was used instead of the boron nitride nanosheets.

[0142] The negative electrodes including the organic-inorganic composite layers prepared in the Examples and Comparative Examples and the batteries including the same were evaluated for the following physical properties, and the results are shown in Table 1 below.

[0143] (1) Thermal shrinkage (unit: %): An organic-inorganic composite layer was prepared in the same manner as in the Examples and Comparative Examples. The prepared organic-inorganic composite layer was cut into a size of 8 cm x 8 cm to prepare a 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 each of the mechanical direction (MD) and the perpendicular direction (TD). The thermal shrinkage was calculated using the following equation.

[0144] [Number 1] Heat shrinkage rate = (L0-L1) / L0 x 100 (L0 is the initial length of the organic-inorganic composite layer, and L1 is the length of the organic layer after standing at 180°C for 1 hour).

[0145] (2) Puncture strength (unit: gf): Each organic-inorganic composite layer was cut at 10 different points along a 50mm x 50mm dimension to create 10 specimens. Using a KATO Tech G5 device, the specimens were placed over a 10cm hole and the punching force was measured by pressing a 1mm probe. The puncture strength of each specimen was measured three times and the average value was calculated.

[0146] [Table 1]

[0147] *PI: Polyimide (P84, Evonik) *PAA: Poly(amic acid)

[0148] [ka]

[0149] *PVDF: Polyvinylidene fluoride (Kynar 761A, Arkema) *PAN: Polyacrylonitrile (Polyscience, includes units of the chemical formula below)

[0150] [ka]

[0151] *In Comparative Example 6, PVDF:PAN is included in a weight ratio of 1:1.

[0152] As shown in Table 1, the organic-inorganic composite layers of the examples provided excellent puncture strength and low heat shrinkage.

[0153] 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]

[0154] 1 Electrode 1 is 2. Active material layer for lithium secondary batteries 3 Organic-inorganic composite layer 10. Positive electrodes for lithium secondary batteries 11 Positive electrode lead tab 12 Positive terminal 20 negative electrode 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 100 Lithium secondary battery

Claims

1. The present invention relates to a lithium secondary battery, and an organic-inorganic composite layer integrated with the active material layer. the organic-inorganic composite layer contains nanofibers, the nanofibers include an inorganic material and a matrix; the inorganic material includes at least one of a boron nitride nanosheet and a boron nitride nanotube; the matrix contains at least one of a polyimide-based polymer and a polyamic acid-based polymer, The inorganic material is contained in an amount of 0.1 to 7% by weight of the nanofibers in the electrode for a lithium secondary battery.

2. 2. The electrode for a lithium secondary battery according to claim 1, wherein the inorganic material contains at least one of the boron nitride nanosheets and the boron nitride nanotubes in an amount of 95% by weight or more.

3. 2. The electrode for a lithium secondary battery according to claim 1, wherein the boron nitride nanosheet has a thickness of 0.3 to 10 nm and a maximum diameter of 10 to 200 nm.

4. 2. The electrode for a lithium secondary battery according to claim 1, wherein the boron nitride nanotubes have an average outer diameter of 10 to 100 nm and an average length of 1 to 50 μm.

5. The electrode for a lithium secondary battery according to claim 1 , wherein the matrix is ​​impregnated with at least one of the boron nitride nanosheets and the boron nitride nanotubes.

6. 2. The electrode for a lithium secondary battery according to claim 1, wherein the polyimide-based polymer contains a repeating unit represented by the following formula 1: 【Chemistry 1】 (In the above Chemical Formula 1, * denotes the linking site of the element, R 1 is a tetravalent organic group, R 2 represents a divalent aliphatic, alicyclic, or aromatic organic group or a combination thereof having a total of 3 to 30 carbon atoms.

7. 2. The electrode for a lithium secondary battery according to claim 1, wherein the polyamic acid-based polymer contains one or more units selected from the group consisting of the following formulas 2 and 3: 【Chemistry 2】 【Transformation 3】 (In the above formulas 2 and 3, * denotes the linking site of the element, R 3 , R 4 are each independently hydrogen or an alkyl group having 1 to 5 carbon atoms, R 5 represents a single bond, an alkylene group having 1 to 5 carbon atoms, an arylene group having 6 to 10 carbon atoms, or an arylalkylene group having 7 to 10 carbon atoms; R 6 represents an alkylene group having 1 to 5 carbon atoms, an arylene group having 6 to 10 carbon atoms, an aryl alkylene group having 7 to 10 carbon atoms, or an aryl ether group having 6 to 10 carbon atoms)

8. 2. The electrode for a lithium secondary battery according to claim 1, wherein the matrix contains at least one of the polyimide polymer and the polyamic acid polymer in an amount of 95% by weight or more.

9. 2. The electrode for a lithium secondary battery according to claim 1, wherein the organic-inorganic composite layer is in a woven or non-woven state of the nanofibers.

10. 2. The electrode for a lithium secondary battery according to claim 1, wherein the organic-inorganic composite layer is a single layer.

11. 2. The electrode for a lithium secondary battery according to claim 1, wherein the organic-inorganic composite layer is a porous layer.

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

13. 13. The electrode for a lithium secondary battery according to claim 12, wherein the negative electrode active material layer comprises 90% by weight to 99% by weight of the negative electrode active material, 0.5% by weight to 5% by weight of the binder, and 0% by weight to 5% by weight of the conductive material.

14. A lithium secondary battery comprising the electrode for a lithium secondary battery according to any one of claims 1 to 13 and an electrode for a lithium secondary battery facing the electrode for a lithium secondary battery.

15. 15. The lithium secondary battery of claim 14, wherein the lithium secondary battery is membrane-free.

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