Electrodes for lithium secondary batteries and lithium secondary batteries containing the same

Abstract

To provide an electrode for a lithium secondary battery and a lithium secondary battery including the same that improves the battery's fast charging life characteristics by ensuring the reversibility of lithium deposition on a negative electrode during fast charging, and improves the battery's life stability by modifying a solid-electrolyte-interface (SEI).SOLUTION: The present invention relates to an electrode for a lithium secondary battery including a current collector, an electrode active material layer located on the current collector, and a functional layer, the functional layer includes a lithium-containing polyoxazoline, and also relates to a lithium secondary battery including the same.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This relates to electrodes for lithium secondary batteries and lithium secondary batteries. [Background technology]

[0002] Globally, the demand for lithium-ion batteries is rapidly increasing due to the rapid growth of electric vehicles, the efficient use of new renewable energy sources in response to climate change, and the widespread adoption of the Internet of Things (IoT). The demand for technologies that enable rapid charging while maintaining high energy density is also rapidly rising, and various related research projects are actively underway. Among these diverse attempts, research into creating thick-film electrodes by layering the active material on the current collector to increase energy storage per unit volume is a relatively simple approach. However, there remain challenges to be addressed, including how to fabricate such thick-film electrodes and the increased difficulty of ion and electron transport in the thickness direction when using thick-film electrodes. In particular, in rapid charging situations where fast lithium ion movement is required, the problem of lithium deposition on the negative electrode due to current concentration and overpotential inevitably arises, necessitating solutions to this problem. [Overview of the project] [Problems that the invention aims to solve]

[0003] The reversibility of lithium deposited on the negative electrode during rapid charging is ensured, improving the rapid charging life characteristics of the battery, and the battery's life stability is improved by modifying the solid electrolyte interface (SEI). [Means for solving the problem]

[0004] In one embodiment, the present invention provides an electrode for a lithium secondary battery comprising a current collector, an electrode active material layer located on the current collector, and a functional layer, wherein the functional layer contains lithium-containing polyoxazoline.

[0005] Another embodiment provides a lithium secondary battery including the aforementioned electrodes and electrolyte.

Advantages of the Invention

[0006] According to one embodiment, the reversibility of lithium deposited on the electrode during rapid charging is improved, the life characteristics of the lithium secondary battery under rapid charging conditions can be enhanced, and the life stability of the lithium secondary battery can be improved by modifying the SEI film.

Brief Description of the Drawings

[0007] [Figure 1] It is a cross-sectional view schematically showing a lithium secondary battery according to one embodiment. [Figure 2] It is a cross-sectional view schematically showing a lithium secondary battery according to one embodiment. [Figure 3] It is a cross-sectional view schematically showing a lithium secondary battery according to one embodiment. [Figure 4] It is a cross-sectional view schematically showing a lithium secondary battery according to one embodiment. [Figure 5] It is an infrared spectroscopy (IR) graph of the functional polymer (Li-POX) and POX manufactured in Example 1. [Figure 6] It is an infrared spectroscopy (IR) graph of the functional polymer (Li-POX) and POX manufactured in Example 1. [Figure 7] It is the ToF-SIMS Depth analysis result for the lithium secondary batteries of Example 1 and Comparative Example 1, and it is a graph showing the component change of the SEI film before and after formation. [Figure 8] It shows the life characteristics under rapid charging conditions of Example 1 and Comparative Example 1, and it is a graph showing the discharge specific capacity according to the number of cycles.

Modes for Carrying Out the Invention

[0008] The following describes specific embodiments in detail so that they can be easily implemented by those with ordinary skill in the art. However, the present invention can be realized in various different forms and is not limited to the embodiments described herein.

[0009] The terms used herein are used solely to describe exemplary embodiments and are not intended to limit the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise.

[0010] Here, "these combinations" refers to mixtures of components, laminates, composites, copolymers, alloys, blends, reaction products, etc.

[0011] Here, terms such as “include,” “equip,” or “possess” are intended to specify the presence of an implemented feature, figure, stage, component, or combination thereof, and should be understood not to preemptively exclude the possibility of the presence or addition of one or more other features, figures, stages, components, or combinations thereof.

[0012] In the drawings, thicknesses are shown enlarged to clearly represent various layers and regions, and similar parts are denoted by the same reference numerals throughout the specification. When a layer, film, region, plate, or other part is described as being "on top" of another part, this includes not only when it is "directly above" another part, but also when there is another part in between. Conversely, when a part is described as being "directly above" another part, it means that there is no other part in between.

[0013] Furthermore, here, "layer" includes not only the shapes formed on the entire surface when observed in a plan view, but also the shapes formed on some of the surfaces.

[0014] The average particle size can be measured by methods widely known to those skilled in the art, for example, by a particle size analyzer, or by transmission electron microscope images or scanning electron microscope images. Alternatively, it can be measured using dynamic light scattering, and the average particle size value can be calculated by performing data analysis to count the number of particles for each particle size range. Unless otherwise defined, the average particle size is the particle diameter (D) of the particle with a cumulative volume of 50% in the particle size distribution. 50 ) can mean. Also, unless otherwise defined, the average particle size is obtained by measuring the size (diameter or length of the major axis) of more than 20 random particles in a scanning electron microscope image to obtain a particle size distribution, and the particle size (D) of the particle with a cumulative volume of 50 volume% in the said particle size distribution. 50 This is taken as the average particle size.

[0015] Here, "or" is not interpreted in an exclusive sense; for example, "A or B" is interpreted as including A, B, A+B, etc.

[0016] The term "metal" is interpreted as a concept that includes general metals, transition metals, and metalloids.

[0017] Electrodes for lithium secondary batteries In one embodiment, the present invention provides an electrode for a lithium secondary battery comprising a current collector, an electrode active material layer located on the current collector, and a functional layer, wherein the functional layer contains lithium-containing polyoxazoline.

[0018] The functional layer can be located on the electrode active material layer and / or between the current collector and the electrode active material layer. As an example, an electrode may include a current collector, an electrode active material layer located on the current collector, and a functional layer located on the electrode active material layer. The functional layer can be described as a type of coating layer containing a functional polymer. By introducing the functional layer into the electrode, the physical strength can be improved, thereby inducing a uniform, non-dendritic film shape for the lithium deposition, and improving the reversibility of the deposited lithium, which is the ratio of desorbed lithium metal to electrodeposited lithium metal. Furthermore, the functional polymer in the functional layer can act as a captor for lithium salts and / or anions, thereby influencing the composition of SEI produced during the battery's chemical reaction. For example, it may be possible to induce LiF-rich SEI, thereby improving the battery's lifespan stability.

[0019] The thickness of the functional layer is not particularly limited, but in one embodiment, it can be as thin as a few micrometers or a few to several hundred nanometers, thereby increasing the reversibility of the deposited lithium without increasing the overall thickness and volume of the battery. The thickness of the functional layer may be, for example, 5 nm to 900 nm, 5 nm to 700 nm, 10 nm to 500 nm, or 20 nm to 300 nm. The thickness of the functional layer can be measured via SEM imaging of the cross-section of the electrode.

[0020] The functional layer can be introduced into the electrode in various ways; for example, it can be introduced by a general coating method, one example being by electrospinning. When the functional layer is coated by electrospinning, a very thin and strong functional layer can be introduced.

[0021] Lithium-containing polyoxazoline differs from general polyoxazoline in that it contains lithium ions. The polyoxazoline and lithium may be chemically bonded or physically bonded, or for example, the oxygen or nitrogen groups within the polyoxazoline may be bonded to the lithium cation. General polyoxazoline that does not contain lithium lacks lithium ion transport function, and when introduced as a functional layer in an electrode plate, it may act as a resistor. In contrast, lithium-containing polyoxazoline according to one embodiment has excellent lithium ion transport performance, and when introduced as a functional layer, it not only enhances the reversibility of lithium deposited during rapid charging but also improves lithium ion conductivity, thereby improving battery performance. Furthermore, the performance of the battery can be further improved by adjusting the SEI component to LiF-rich SEI.

[0022] Lithium-containing polyoxazolines may, for example, be polyoxazolines obtained by initiating polymerization with a lithium salt. For example, lithium-containing polyoxazolines may be obtained by dissolving a lithium salt in a monomer solution and then polymerizing it at approximately 30°C to 100°C for 24 to 72 hours.

[0023] Here, the lithium salt can include, for example, LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiFSI, LiTFSI, LiOTf, LiBOB, LiDFOB, or combinations thereof. The concentration of the lithium salt added to the monomer solution may be 1M to 5M, or 3M to 4M.

[0024] Lithium-containing polyoxazolines may specifically include lithium-containing poly(2-alkyl-2-oxazolines), lithium-containing poly(2-aryl-2-oxazolines), or combinations thereof. Here, alkyl may be a substituted or unsubstituted alkyl having 1 to 10 carbon atoms, or a substituted or unsubstituted alkyl having 1 to 5 carbon atoms. Aryl may be a substituted or unsubstituted aryl having 6 to 20 carbon atoms, or a substituted or unsubstituted aryl having 6 to 12 carbon atoms.

[0025] For example, lithium-containing polyoxazolines may be lithium-containing poly(2-methyl-2-oxazoline), lithium-containing poly(2-ethyl-2-oxazoline), lithium-containing poly(2-propyl-2-oxazoline), lithium-containing poly(2-isopropyl-2-oxazoline), lithium-containing poly(2-cyclopropyl-2-oxazoline), or a combination thereof.

[0026] Weight-average molecular weight (M) of lithium-containing polyoxazolines w The polydispersity (PDI;M) of lithium-containing polyoxazolines may be 500 g / mol to 500,000 g / mol, or more specifically, 10,000 g / mol to 70,000 g / mol. w / M n ) could be, for example, 1 to 4, or more specifically, 1.2 to 1.8 or 3 to 4.

[0027] An electrode for a lithium secondary battery according to one embodiment may be a positive electrode or a negative electrode, and for example, it may be a negative electrode. By introducing a functional layer into the negative electrode, the reversibility of lithium deposited during rapid charging is improved, thereby dramatically improving the lifespan characteristics under rapid charging conditions.

[0028] When the electrode is a negative electrode, the current collector is a negative electrode current collector, and the electrode active material layer may be a negative electrode active material layer, or, as another example, the electrode active material layer may be a negative electrode coating layer used for a deposition type negative electrode.

[0029] negative electrode current collector The negative electrode current collector may include, for example, indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), lithium (Li), or alloys thereof, and may be in the form of foil, sheet, or foam. The thickness of the negative electrode current collector may be, for example, 1 μm to 20 μm, 5 μm to 15 μm, or 7 μm to 10 μm.

[0030] Negative electrode active material layer The negative electrode active material layer comprises a negative electrode active material and may further selectively include a binder, a conductive material, or a combination thereof.

[0031] negative electrode active material The negative electrode active material includes a material into which lithium ions can be reversibly inserted / de-inserted, lithium metal, an alloy of lithium metal, a material that can be doped and de-doped with lithium, or a transition metal oxide.

[0032] Materials capable of reversibly inserting / deinserting lithium ions include carbon-based anode active materials, such as crystalline carbon, amorphous carbon, or combinations thereof. Examples of crystalline carbon include graphite such as amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite, while examples of amorphous carbon include soft or hard carbon, mesophase pitch carbide, and calcined coke.

[0033] As lithium metal alloys, alloys of lithium with metals selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn can be used.

[0034] As a substance that can be doped and undoped with lithium, a Si-based negative electrode active material or a Sn-based negative electrode active material can be used. As the Si-based negative electrode active material, silicon, a silicon-carbon composite, SiO x (0 < x < 2), a Si-Q alloy (Q is an element 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, for example, Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Tl, Ge, P, As, Sb, Bi, S, Se, Te, Po, and combinations thereof), or a combination thereof may also be used. As the Sn-based negative electrode active material, Sn, SnO2, a Sn alloy, or a combination thereof may also be used.

[0035] The silicon-carbon composite may be a composite of silicon and amorphous carbon. The average particle size (D 50 ) of the silicon-carbon composite particles may be, for example, 0.5 μm to 20 μm. According to one embodiment, the silicon-carbon composite may be in a form in which amorphous carbon is coated on the surface of silicon particles. For example, it may include secondary particles (cores) formed by granulating primary silicon particles and an amorphous carbon coating layer (shell) located on the surface of the secondary particles. Amorphous carbon is also located between the primary silicon particles, for example, the primary silicon particles are coated with amorphous carbon. The secondary particles can exist dispersed in the amorphous carbon matrix.

[0036] The silicon-carbon composite may further contain crystalline carbon. For example, the silicon-carbon composite can include a core containing crystalline carbon and silicon particles and an amorphous carbon coating layer located on the surface of the core. The crystalline carbon may be artificial graphite, natural graphite, or a combination thereof. Examples of the amorphous carbon include soft carbon, hard carbon, mesophase pitch carbide, and calcined coke.

[0037] When the silicon-carbon composite contains silicon and amorphous carbon, the content of silicon may be 10% to 50% by weight based on 100% by weight of the silicon-carbon composite, and the content of amorphous carbon may be 50% to 90% by weight. Also, when the silicon-carbon composite contains silicon, amorphous carbon, and crystalline carbon, the content of silicon may be 10% to 50% by weight based on 100% by weight of the silicon-carbon composite, the content of crystalline carbon may be 10% to 70% by weight, and the content of amorphous carbon may be 20% to 40% by weight.

[0038] Also, the thickness of the amorphous carbon coating layer may be 5 nm to 100 nm. The average particle size (D 50 ) of the silicon particles (primary particles) may be 10 nm to 1 μm, or 10 nm to 200 nm. The silicon particles may exist alone as silicon, in the form of a silicon alloy, or in an oxidized form. The oxidized form of silicon is represented by SiO x (0 < x < 2). At this time, the atomic content ratio of Si:O indicating the degree of oxidation may be 99:1 to 33:67. In this specification, unless otherwise defined, the average particle size (D 50 ) means the particle size at which the cumulative volume is 50% by volume in the particle size distribution.

[0039] The Si-based negative electrode active material or the Sn-based negative electrode active material can be used by mixing with the carbon-based negative electrode active material. When the Si-based negative electrode active material or the Sn-based negative electrode active material is mixed with the carbon-based negative electrode active material and used, the mixing ratio may be 1:99 to 90:10 by weight.

[0040] binder The binder plays a role in ensuring that the negative electrode active material particles adhere well to each other and that the negative electrode active material adheres well to the current collector. Non-aqueous binders, aqueous binders, dry binders, or combinations thereof can be used as binders.

[0041] Examples of non-aqueous binders include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyimide, or combinations thereof.

[0042] The aqueous binder may be selected from styrene-butadiene rubber, (meth)acrylicated 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.

[0043] When using an aqueous binder as the negative electrode binder, it may further contain a cellulosic compound capable of imparting viscosity. This cellulosic compound can be a mixture of one or more carboxymethylcellulose, hydroxypropylmethylcellulose, methylcellulose, or alkali metal salts thereof. As the alkali metal, Na, K, or Li can be used.

[0044] The dry binder may be a fiberizable polymer, such as polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0045] conductive material Conductive materials are used to impart conductivity to electrodes, and any electronically conductive material that does not cause chemical changes can be used in the battery that is constructed. Specific examples include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjenblack, carbon fibers, carbon nanofibers, and carbon nanotubes; metallic materials containing copper, nickel, aluminum, silver, etc., in the form of metal powders or metal fibers; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0046] The content of the negative electrode active material may be 95% to 99.5% by weight relative to 100% by weight of the negative electrode active material layer, and the content of the binder may be 0.1% to 5% by weight relative to 100% by weight of the negative electrode active material layer. For example, the negative electrode active material layer may contain 90% to 99% by weight of the negative electrode active material, 0.1% to 5% by weight of the binder, and 0.1% to 5% by weight of the conductive material.

[0047] Negative electrode coating layer A deposition-type negative electrode is one in which the battery does not contain negative electrode active material during assembly, but lithium metal or other materials are deposited or electrodeposited onto the negative electrode during battery charging, and this then acts as the negative electrode active material.

[0048] A deposition-type negative electrode can include a current collector and a negative electrode coating layer located on the current collector. In a lithium secondary battery having such a deposition-type negative electrode, initial charging is started without any negative electrode active material present. During charging, a high-density lithium metal layer is deposited or electrodeposited between the current collector and the negative electrode coating layer, or on the negative electrode coating layer, forming a lithium metal layer that can act as the negative electrode active material. Thus, in a lithium secondary battery that has undergone one or more charging cycles, the deposition-type negative electrode can include, for example, a current collector, a lithium metal layer located on the current collector, and a negative electrode coating layer located on the lithium metal layer.

[0049] The lithium metal layer refers to the layer formed when lithium metal or other materials are deposited during the battery charging process, and can be called a metal layer, lithium layer, lithium electrodeposited layer, or negative electrode active material layer.

[0050] The negative electrode coating layer, also known as the lithium electrodeposition induction layer or negative electrode catalyst layer, may contain metal, carbon material, or a combination thereof.

[0051] The metal may be a lithium-hydrophilic metal and may include, for example, gold, platinum, palladium, silicon, silver, aluminum, bismuth, tin, zinc, or a combination thereof, and may consist of one of these or an alloy of several of these. If the metal exists in particulate form, its average particle size (D 50 The thickness may be approximately 4 μm or less, for example, 10 nm to 4 μm.

[0052] The carbon material may be, for example, crystalline carbon, amorphous carbon, or a combination thereof. Crystalline carbon may be, for example, natural graphite, artificial graphite, mesophase carbon microbeads, or a combination thereof. Amorphous carbon may be, for example, carbon black, activated carbon, acetylene black, Denka black, Ketjen black, or a combination thereof.

[0053] When the negative electrode coating layer contains both metal and carbon material, the mixing ratio of metal to carbon material may be, for example, a weight ratio of 1:10 to 2:1. In this case, the deposition of lithium metal can be effectively promoted, improving the properties of the all-solid-state secondary battery. The negative electrode coating layer may, for example, contain carbon material on which a catalyst metal is supported, or it may contain a mixture of metal particles and carbon material particles.

[0054] The negative electrode coating layer may, for example, include the lithophilic metal and amorphous carbon, in which case the deposition of lithium metal can be effectively promoted. Specifically, the negative electrode coating layer may include a composite in which the lithophilic metal is supported on amorphous carbon.

[0055] The negative electrode coating layer may further contain a binder, which may, for example, be a conductive binder. The negative electrode coating layer may also further contain common additives such as fillers, dispersants, and ionic conductive agents.

[0056] The thickness of the negative electrode coating layer may be, for example, 100 nm to 20 μm, 500 nm to 10 μm, or 1 μm to 5 μm.

[0057] Cathode active material layer For example, the electrode for the lithium secondary battery mentioned above may be a positive electrode, in which case the current collector may be a positive electrode current collector, and the electrode active material layer may be a positive electrode active material layer.

[0058] The positive electrode active material layer may contain a positive electrode active material and selectively include a binder and / or a conductive material.

[0059] positive electrode active material As the positive electrode active material, a compound that allows for reversible insertion and removal of lithium (lithiated insertion compound) can be used. Specifically, one or more composite oxides of lithium with a metal selected from cobalt, manganese, nickel, and combinations thereof can be used.

[0060] The composite oxide may be a lithium transition metal composite oxide, and specific examples include lithium nickel oxides, lithium cobalt oxides, lithium manganese oxides, lithium iron phosphate compounds, cobalt-free nickel-manganese oxides, lithium-excess layered oxides, or combinations thereof.

[0061] As an 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 relative to 100 mol% of the metal excluding lithium in a lithium transition metal composite oxide. The nickel content in the high-nickel positive electrode active material may be 85 mol% or more, 90 mol% or more, 91 mol% or more, or 94 mol% or more, or 99 mol% or less, relative to 100 mol% of the metal excluding lithium. High-nickel positive electrode active materials can achieve high capacity and are applicable to high-capacity, high-density lithium secondary batteries.

[0062] As a more specific example, you can use a compound represented by any one of the following chemical formulas: 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 O(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)

[0063] In the above chemical formula, A is Ni, Co, Mn, or a combination thereof; X is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, rare earth elements, 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; Q is Ti, Mo, Mn, or a combination thereof; Z is Cr, V, Fe, Sc, Y, or a combination thereof; L 1 This is Mn, Al, or a combination of these.

[0064] The positive electrode active material may be in the form of secondary particles formed by the aggregation of multiple primary particles, or it may be in the form of single particles. Furthermore, the positive electrode active material may be spherical or nearly spherical in shape, or it may be polyhedral or irregular in shape.

[0065] On the other hand, the positive electrode active material may include a buffer layer on the surface of the particles. The buffer layer, represented as a coating layer, protective layer, etc., can play a role in reducing the interfacial resistance between the positive electrode active material and the sulfide-based solid electrolyte particles. As an example, the buffer layer may contain a lithium-metal-oxide, where the metal may be one or more elements selected from the group consisting of, for example, Al, B, Ca, Ce, Cr, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ta, V, W, and Zr. The lithium-metal-oxide contributes to reducing the interfacial resistance between the positive electrode active material and the solid electrolyte particles while improving the performance of the positive electrode active material by facilitating lithium ion movement and electron conduction.

[0066] The positive electrode active material is present in an amount of 55% to 99.5% by weight relative to 100% by weight of the positive electrode active material layer, for example, 65% to 95% by weight, or 75% to 91% by weight.

[0067] binder The binder plays a role in ensuring that the positive electrode active material particles adhere well to each other and that the positive electrode active material adheres well to the current collector. Typical examples of binders include, but are not limited to, polyvinyl alcohol, carboxymethylcellulose, hydroxypropylcellulose, diacetylcellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylicated styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, and nylon.

[0068] conductive material Conductive materials are used to impart conductivity to electrodes, and any electronically conductive material that does not cause chemical changes can be used in the battery that is constructed. Examples of conductive materials include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjenblack, carbon fibers, carbon nanofibers, and carbon nanotubes; metallic materials containing copper, nickel, aluminum, silver, etc., in the form of metal powders or metal fibers; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0069] The content of the binder and conductive material may be 0.1% to 5% by weight, respectively, based on 100% by weight of the positive electrode active material layer.

[0070] While materials such as Al and SUS can be used as the positive electrode current collector, it is not limited to these.

[0071] Lithium-ion rechargeable battery In one embodiment, a lithium secondary battery is provided that includes the electrodes and electrolyte described above. The lithium secondary battery may be a lithium-ion battery that uses an electrolyte, or, as another example, an all-solid-state secondary battery that uses a solid electrolyte. As an example, a lithium secondary battery using an electrolyte will be described.

[0072] Lithium-ion batteries are classified into cylindrical, prismatic, pouch-type, coin-type, and other types depending on their form. Figures 1 to 4 are schematic diagrams showing a lithium-ion battery according to one embodiment, with Figure 1 being circular, Figure 2 being prismatic, and Figures 3 and 4 being pouch-type batteries. Referring to Figures 1 to 4, the lithium-ion battery 100 can include an electrode assembly 40 with a separator 30 interposed between a positive electrode 10 and a negative electrode 20, and a case 50 in which the electrode assembly 40 is housed. The positive electrode 10, negative electrode 20, and separator 30 may be impregnated with an electrolyte (not shown). The lithium-ion battery 100 can include a sealing member 60 that seals the case 50, as shown in Figure 1. Also, in Figure 2, the lithium-ion battery 100 can include a positive electrode lead tab 11 and a positive electrode terminal 12, and a negative electrode lead tab 21 and a negative electrode terminal 22. As shown in Figures 3 and 4, the lithium secondary battery 100 may include electrode tabs 70, namely a positive electrode tab 71 and a negative electrode tab 72, which serve as electrical pathways for inducing the current formed in the electrode assembly 40 to the outside.

[0073] electrolyte The electrolyte for lithium secondary batteries may, for example, be an electrolyte solution, which may contain a non-aqueous organic solvent and a lithium salt.

[0074] Non-aqueous organic solvents serve as a medium through which ions involved in the electrochemical reactions of the battery can move. Non-aqueous organic solvents may be carbonate-based, ester-based, ether-based, ketone-based, or alcohol-based solvents, aprotic solvents, or combinations thereof.

[0075] Suitable carbonate solvents 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). Suitable ester solvents include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolide, mevalonolactone, valerolactone, and caprolactone. Suitable ether solvents include dibutyl ether, tetraglyceride, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, and tetrahydrofuran. Suitable ketone solvents include cyclohexanone. Suitable alcohol solvents include ethyl alcohol and isopropyl alcohol. Suitable aprotic solvents include nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group with 2 to 20 carbon atoms, and may include double bonds, aromatic rings, or ether groups); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane and 1,4-dioxolane; and sulfolanes.

[0076] Non-aqueous organic solvents can be used alone or in combination of two or more. When using a mixture of two or more, the mixing ratio can be appropriately adjusted according to the desired battery performance, and this is generally understood by those working in this field.

[0077] When using carbonate-based solvents, cyclic carbonates and linear carbonates can be mixed, and these can be mixed in a volume ratio of 1:1 to 1:9.

[0078] The non-aqueous organic solvent may further contain aromatic hydrocarbon organic solvents. For example, the carbonate solvent and the aromatic hydrocarbon organic solvent can be mixed and used in a volume ratio of 1:1 to 30:1.

[0079] The electrolyte may further contain vinyl ethyl carbonate, vinylene carbonate, or ethylene carbonate compounds to improve battery life.

[0080] Representative examples of the aforementioned ethylene carbonate compounds include fluoroethylene carbonate, difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, and cyanoethylene carbonate.

[0081] Lithium salts dissolve in organic solvents and act as a source of lithium ions within batteries, enabling the operation of basic lithium secondary batteries and facilitating the movement of lithium ions between the positive and negative electrodes. Typical 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 It may contain one or more selected from SO2) (where x and y are integers from 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalato)phosphate (LiDFBOP), and lithium bis(oxalato)borate (LiBOB).

[0082] The lithium salt concentration should ideally be within the range of 0.1 M to 2.0 M. When the lithium salt concentration falls within this range, the electrolyte has appropriate ionic conductivity and viscosity, resulting in excellent performance and effective lithium ion movement.

[0083] Separator Depending on the type of lithium secondary battery, a separator may be present between the positive and negative electrodes. Suitable separators include polyethylene, polypropylene, polyvinylidene fluoride, or multilayer films of two or more layers thereof. Mixed multilayer films such as polyethylene / polypropylene two-layer separators, polyethylene / polypropylene / polyethylene three-layer separators, and polypropylene / polyethylene / polypropylene three-layer separators can also be used.

[0084] The separator may include a porous substrate and a coating layer containing organic, inorganic, or a combination thereof located on one or both sides of the porous substrate.

[0085] The porous substrate may be a polymer film formed from one polymer selected from polyethylene, polyolefins such as polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyacetal, polyamide, polyimide, polycarbonate, polyetherketone, polyaryletherketone, polyetherimide, polyamideimide, polybenzimidazole, polyethersulfone, polyphenylene oxide, cyclic olefin copolymer, polyphenylene sulfide, polyethylene naphthalate, glass fiber, Teflon, and polytetrafluoroethylene, or from copolymers or mixtures of two or more of these polymers.

[0086] The porous substrate can have a thickness of approximately 1 μm to 40 μm, for example, 1 μm to 30 μm, 1 μm to 20 μm, 5 μm to 15 μm, or 10 μm to 15 μm.

[0087] The organic material may include a (meth)acrylic copolymer comprising a first structural unit derived from (meth)acrylamide and a second structural unit comprising at least one of a structural unit derived from (meth)acrylic acid or (meth)acrylate and a structural unit derived from (meth)acrylamide sulfonic acid or a salt thereof.

[0088] Inorganic materials may include, but are not limited to, inorganic particles selected from Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, boehmite, and combinations thereof. The average particle size (D) of the inorganic particles is... 50 The wavelength range may be 1 nm to 2000 nm, for example, 100 nm to 1000 nm or 100 nm to 700 nm.

[0089] Organic and inorganic materials can exist mixed together in a single coating layer, or in a form where a coating layer containing organic materials and a coating layer containing inorganic materials are stacked on top of each other.

[0090] The thickness of the coating layer may be 0.5 μm to 20 μm, or for example, 1 μm to 10 μm, or 1 μm to 5 μm.

[0091] Examples and comparative examples of the present invention are described below. The following examples are merely examples of the present invention, and the present invention is not limited to the following examples.

[0092] Example 1 1. Manufacturing of functional polymers A 3M LiFSI lithium salt was added to the liquid monomer 2-ethyl-2-oxazoline, and after complete dissolution, the mixture was heated at 60°C until polymerization was complete to polymerize lithium-containing poly-(2-ethyl-2-oxazoline) (Li-POX). The functional polymer (Li-POX) polymerized in this way, initiated with the lithium salt, was dissolved at a concentration of 0.5% by weight in a solvent consisting of acetone and IPA in a 5:5 volume ratio to prepare a polymer solution.

[0093] 2. Manufacturing of the negative electrode A negative electrode active material layer slurry was prepared by mixing 97% by weight of graphite negative electrode active material, 1.7% by weight of carboxymethylcellulose, 0.8% by weight of styrene-butadiene rubber, and 0.5% by weight of acetylene black in an aqueous solvent. The negative electrode active material layer slurry was coated onto a copper foil current collector, dried, and rolled to form a graphite-based negative electrode active material layer on the current collector.

[0094] A polymer solution prepared by electrospinning was coated onto the surface of the negative electrode active material layer. This was dried at 60°C for 12 hours to produce a negative electrode with a functional layer formed on the negative electrode active material layer. The electrospinning settings were as follows: TCD (Tip to collector distance) was 9 cm, Tip size was No. 21, applied voltage was 25 kV, flow rate was 4 mL / hr, and spinning time was 2 minutes.

[0095] 3. Manufacturing of lithium-ion batteries A lithium secondary battery (half-cell) was manufactured using lithium metal as the counter electrode and a polytetrafluoroethylene separator interposed between the negative electrode and the counter electrode. After inserting this into a case, an electrolyte solution containing 1.15 M LiPF6 dissolved in a solvent mixed with ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate in a volume ratio of 2:4:4 was injected to manufacture a lithium secondary battery (half-cell) using the conventional method.

[0096] Comparative Example 1 The negative electrode and lithium secondary battery were manufactured in substantially the same manner as in Example 1, except that a functional layer was not formed on the negative electrode active material layer.

[0097] Evaluation Example 1: IR Analysis of Functional Polymers To understand the properties of the functional polymer (Li-POX) produced by Example 1, which was polymerized starting with a lithium salt, infrared spectroscopy was performed on both Li-POX and poly-(2-ethyl-2-oxazoline)(POX) polymerized by a general method without a lithium salt. Figure 5 shows the peak corresponding to C=O stretching, and Figure 6 shows the peak corresponding to CN stretching.

[0098] Referring to Figure 5, it can be confirmed that the Li-POX from the example exhibits a red shift phenomenon at the peak corresponding to the C=O stretching relative to POX, which is understood to be due to the bonding between oxygen and lithium cations. Furthermore, referring to Figure 6, the Li-POX from the example exhibits a blue shift phenomenon at the peak corresponding to the CN stretching relative to POX, which is understood to be due to the bonding between nitrogen and lithium salt anions.

[0099] Evaluation Example 2: Analysis of SEI component changes after chemical conversion process The lithium secondary batteries of Example 1 and Comparative Example 1 were charged to 0.01V at 25°C with a constant current of 0.1C, and then discharged to 1.5V with a constant current of 0.2C to proceed with the initial charge-discharge process, i.e., the chemical conversion process. The surface of the negative electrode was analyzed using ToF-SIMS depth analysis before and after the chemical conversion process to analyze the change in SEI components, and the results are shown in Figure 7. All graphs in Figure 7 represent fluoride ions (F - ) shows strength. Example 1, in which a functional layer according to one embodiment is introduced on the surface of the negative electrode, shows strong F in SEI of the negative electrode surface after the chemical conversion process. - It can be seen that strength is revealed. This confirms that LiF-rich SEI is formed after the chemical conversion process by introducing a functional layer.

[0100] Evaluation Example 3: Evaluation of Rapid Charging Lifespan Characteristics In Example 1 and Comparative Example 1, instead of lithium metal as the positive electrode, a full cell was manufactured using a positive electrode produced as follows: LiNi 0.78 Co 0.2Al 0.02 A slurry of positive electrode active material layer was prepared by mixing 96% by weight of O2 positive electrode active material, 2.0% by weight of polyvinylidene fluoride binder, and 2.0% by weight of acetylene black conductive material. This slurry was then coated onto an aluminum foil current collector, dried, and rolled to produce the positive electrode.

[0101] The full cells of Example 1 and Comparative Example 1 were charged with a constant current at 25°C and 0.1C up to 4.25V, then charged at a constant voltage of 0.05C, and discharged to 2.8V at 0.1C to proceed with the initial charge and discharge cycle. Next, the charge and discharge cycle was performed at 25°C and 1C / 1C in the voltage range of 2.8V to 4.25V for more than 400 cycles to evaluate the life characteristics, and Figure 8 shows the change in specific capacity according to the number of cycles.

[0102] Referring to Figure 8, it can be confirmed that in Example 1, the long-term life characteristics are improved compared to Comparative Example 1. This confirms that the lithium secondary battery with the functional layer according to one embodiment shows improved life characteristics under rapid charging conditions. This is understood to be because rapid charging increases the reversibility of lithium deposited on the electrodes, changing the SEI composition and reducing side reactions between the electrodes and the electrolyte.

[0103] Although preferred embodiments have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements by those skilled in the art that utilize the basic concepts defined in the following claims also fall within the scope of the present invention. [Explanation of symbols]

[0104] 100: Lithium secondary battery, 10: Positive electrode 11: Positive lead tab, 12: Positive terminal 20: Negative electrode, 21: Negative electrode lead tab 22: Negative terminal, 30: Separator 40: Electrode assembly, 50: Case 60: Sealing member, 70: Electrode tab 71: Positive tab, 72: Negative tab

Claims

1. Current collector and, An electrode active material layer located on the current collector, Including functional layers, The functional layer comprises lithium-containing polyoxazoline, The lithium-containing polyoxazoline comprises lithium-containing poly(2-alkyl-2-oxazoline), lithium-containing poly(2-aryl-2-oxazoline), or a combination thereof. The alkyl is a substituted or unsubstituted alkyl having 1 to 10 carbon atoms, and the aryl is a substituted or unsubstituted aryl having 6 to 20 carbon atoms. The functional layer is located on the electrode active material layer, An electrode for lithium secondary batteries, which serves as the negative electrode.

2. The electrode for a lithium secondary battery according to claim 1, wherein the functional layer is also located between the current collector and the electrode active material layer.

3. The electrode for a lithium secondary battery according to claim 1, wherein the thickness of the functional layer is 5 nm to 900 nm.

4. The lithium-containing polyoxazoline is lithium-containing poly(2-methyl-2-oxazoline), lithium-containing poly(2-ethyl-2-oxazoline), lithium-containing poly(2-propyl-2-oxazoline), lithium-containing poly(2-isopropyl-2-oxazoline), lithium-containing poly(2-cyclopropyl-2-oxazoline), or a combination thereof, as described in claim 1, for a lithium secondary battery electrode.

5. The weight-average molecular weight (M) of the lithium-containing polyoxazoline. w The electrode for a lithium secondary battery according to claim 1, wherein the concentration is 500 g / mol to 500,000 g / mol.

6. The polydispersity (PDI; M) of the lithium-containing polyoxazoline w / M n The electrode for a lithium secondary battery according to claim 1, wherein ) is 1 to 4.

7. The electrode active material layer is either a negative electrode active material layer or a negative electrode coating layer. The electrode for a lithium secondary battery according to claim 1, wherein the negative electrode coating layer is located on the current collector of the deposition type negative electrode during battery assembly, and lithium metal is deposited or electrodeposited during the battery charging process.

8. The electrode for a lithium secondary battery according to claim 7, wherein the electrode active material layer is a negative electrode active material layer, and the negative electrode active material layer includes lithium metal, lithium alloy, carbon-based negative electrode active material, silicon-based negative electrode active material, or a combination thereof.

9. The electrode active material layer is a negative electrode coating layer, The negative electrode coating layer comprises a lithium-hydrophilic metal, a carbon material, or a combination thereof. The electrode for a lithium secondary battery according to claim 7, wherein a lithium metal layer is formed between the current collector and the negative electrode coating layer by charging.

10. A lithium secondary battery comprising an electrode and an electrolyte for a lithium secondary battery according to any one of claims 1 to 9.

11. The lithium secondary battery according to claim 10, further comprising a positive electrode.

12. A positive electrode and, A separation membrane located between the positive electrode and the lithium secondary battery electrode, A lithium secondary battery according to claim 10, further comprising an electrolyte.

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