Electrode for lithium secondary battery and lithium secondary battery including 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] Relates to an electrode for a lithium secondary battery and a lithium secondary battery.

Background Art

[0002] Worldwide, the demand for lithium secondary batteries is increasing rapidly due to the rapid growth of electric vehicles, the use of efficient renewable energy due to climate change, and the utilization of the Internet of Things (IoT) on a wide scale. The demand for technologies that enable rapid charging while having a high energy density is also increasing rapidly, and various corresponding studies are being actively carried out. Among such various attempts, the study of making a thick-film electrode in which the active material constituting the electrode is placed thicker on the current collector to increase the energy storage amount per unit volume can be said to be a relatively simple approach method. Along with how to fabricate such a thick-film electrode, there remains a problem to be solved together, which is that when it becomes a thick-film electrode, the movement of ions and electrons in the thickness direction becomes more difficult. In particular, in a rapid charging situation where fast movement of lithium ions is required, the problem of lithium precipitation on the negative electrode due to current concentration and overpotential inevitably occurs, so a solution to this is required.

Summary of the Invention

Problems to be Solved by the Invention

[0003] Ensure the reversibility of lithium deposited on the negative electrode during rapid charging, improve the rapid charging life characteristics of the battery, and improve the life stability of the battery by modifying the solid-electrolyte-interface (SEI).

Means for Solving the Problems

[0004] In one embodiment, there is provided 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, wherein the functional layer contains a lithium-containing polyoxazoline.

[0005] In another embodiment, there is provided a lithium secondary battery including the aforementioned electrode and an 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 improved, and the life stability of the lithium secondary battery can be improved by modifying the SEI film.

Brief Description of the Drawings

[0007]

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Modes for Carrying Out the Invention

[0008] Hereinafter, specific embodiments will be described in detail so that those with ordinary knowledge in this technical field can easily implement them. 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 merely used to describe exemplary embodiments and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise.

[0010] Here, "these combinations" means a mixture, laminate, composite, copolymer, alloy, blend, reaction product, etc. of components.

[0011] Here, terms such as "comprising", "including", or "having" are intended to specify that the implemented features, numbers, steps, components, or combinations thereof exist, and it should be understood that they do not preclude the possibility of the existence or addition of one or more other features, numbers, steps, components, or combinations thereof in advance.

[0012] In the drawings, the thickness is enlarged to clearly show various layers and regions, and the same reference numerals are given to similar parts throughout the specification. When a part such as a layer, film, region, or plate 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 are other parts in between. Conversely, when a part is said to be "directly on" another part, it means that there are no other parts in between.

[0013] Also, here, "layer" includes not only the shape formed on the entire surface but also the shape formed on a part of the surface when observed in a plan view.

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

[0015] Here, "or" is not construed in an exclusive sense. For example, "A or B" is construed to include A, B, A + B, etc.

[0016] "Metal" is construed as a concept including common metals, transition metals, and metalloids.

[0017] Electrode for lithium secondary battery In one embodiment, a lithium secondary battery electrode is provided that includes a current collector, an electrode active material layer located on the current collector, and a functional layer, and the functional layer includes a 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, the electrode can 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 said to be a kind of coating layer containing a functional polymer. By introducing the functional layer into the electrode, the physical strength can be improved, and thereby the shape of lithium precipitation can be induced into a uniform film shape rather than dendritic, and the reversibility of the deposited lithium, which is the ratio of the desorbed lithium metal to the electrodeposited lithium metal, can be improved. Furthermore, the functional polymer of the functional layer can act as a captor of lithium salts and / or anions, and thereby may affect the components of the SEI generated during the formation process of the battery. For example, it can induce an LiF-rich SEI, thereby improving the life stability of the battery.

[0019] The thickness of the functional layer is not particularly limited. However, in one embodiment, it is thin at the level of several micrometers or several 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, or may be 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 through a SEM image 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. As an example, it is coated by an electrospinning method. When the functional layer is coated by the electrospinning method, a very thin and strong functional layer can be introduced.

[0021] Lithium-containing polyoxazoline is characterized by containing lithium ions, which is different from general polyoxazoline. Polyoxazoline and lithium may be chemically bonded or physically bound. For example, oxygen groups or nitrogen groups in polyoxazoline may be bonded to lithium cations. General polyoxazoline without lithium does not have a lithium ion conduction function and may act as a resistance when introduced as a functional layer into the electrode plate. In contrast, lithium-containing polyoxazoline according to one embodiment, when introduced as a functional layer with excellent lithium ion conduction performance, not only enhances the reversibility of lithium deposited during rapid charging, but also improves the lithium ion conductivity to improve the battery performance. In addition, the components of SEI can be adjusted to Lif-rich (LiF-rich) SEI to further improve the battery performance.

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

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

[0024] The lithium-containing polyoxazoline can specifically include lithium-containing poly(2-alkyl-2-oxazoline), lithium-containing poly(2-aryl-2-oxazoline), or a combination thereof. Here, the alkyl can be a substituted or unsubstituted alkyl having 1 to 10 carbon atoms, or a substituted or unsubstituted alkyl having 1 to 5 carbon atoms. The aryl can 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] As an example, the lithium-containing polyoxazoline can 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] The weight average molecular weight (M w ) of the lithium-containing polyoxazoline can be 500 g / mol to 500,000 g / mol, and specifically can also be 10,000 g / mol to 70,000 g / mol. Also, the polydispersity (PDI; M w / M n ) of the lithium-containing polyoxazoline can be, for example, 1 to 4, and specifically can be 1.2 to 1.8 or 3 to 4.

[0027] The electrode for a lithium secondary battery according to one embodiment is a positive electrode or a negative electrode, and as an example, it can be a negative electrode. By introducing a functional layer into the negative electrode, the reversibility of lithium deposited during rapid charging can be improved, and thereby the life characteristics under rapid charging conditions can be remarkably improved.

[0028] When the electrode is a negative electrode, the current collector is a negative electrode current collector, and the electrode active material layer can be a negative electrode active material layer, or as another example, the electrode active material layer can 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 a foil, sheet, or foam. The thickness of the negative electrode current collector may be, for example, 1 μm to 20 μm, or may be 5 μm to 15 μm, or 7 μm to 10 μm.

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

[0031] Negative electrode active material The negative electrode active material includes a material capable of reversibly inserting / desorbing lithium ions, lithium metal, an alloy of lithium metal, a material capable of doping and dedoping with lithium, or a transition metal oxide.

[0032] Examples of the material capable of reversibly inserting / desorbing lithium ions include carbon-based negative electrode active materials, which may include, for example, crystalline carbon, amorphous carbon, or a combination thereof. Examples of crystalline carbon include graphite such as amorphous, plate-like, flaky, spherical, or fibrous natural graphite or artificial graphite, and examples of amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, calcined coke, and the like.

[0033] Examples of the alloy of lithium metal include alloys of lithium and metals selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn.

[0034] As a substance capable of being 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 be used. As the Sn-based negative electrode active material, Sn, SnO2, a Sn alloy, or a combination thereof may 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 be dispersed and present 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. When the silicon-carbon composite contains silicon, amorphous carbon, and crystalline carbon, based on 100% by weight of the silicon-carbon composite, the content of silicon may be 10% to 50% by weight, 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 serves to make the negative electrode active material particles adhere well to each other and also 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 thereof can be used.

[0041] Examples of the non-aqueous binder include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene-propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or a combination thereof.

[0042] Examples of the aqueous binder may be selected from styrene-butadiene rubber, (meth)acrylated 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, phenol resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0043] When an aqueous binder is used as the negative electrode binder, a cellulose-based compound capable of imparting viscosity can be further included. As this cellulose-based compound, one or more of carboxymethyl cellulose, hydroxypropylmethyl cellulose, methyl cellulose, or alkali metal salts thereof can be mixed and used. As the alkali metal, Na, K, or Li can be used.

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

[0045] Conductive material The conductive material is used to impart conductivity to the electrode, and in the battery being configured, any electron - conductive material can be used as long as it does not cause a chemical change. Specific examples include carbon - based substances such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, carbon nanotube; metal - based substances containing copper, nickel, aluminum, silver, etc. in the form of metal powder or metal fiber; 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 based on 100% by weight of the negative electrode active material layer, and the content of the binder may be 0.1% to 5% by weight based on 100% by weight of the negative electrode active material layer. For example, the negative electrode active material layer can contain 90% to 99% of the negative electrode active material, 0.1% to 5% of the binder, and 0.1% to 5% of the conductive material.

[0047] Negative electrode coating layer The deposited - type negative electrode means a negative electrode that does not contain a negative electrode active material during battery assembly, but lithium metal or the like is deposited or electrodeposited on the negative electrode during battery charging, and this serves as the negative electrode active material.

[0048] The deposited-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 deposited-type negative electrode, initial charging is started in a state where no negative electrode active material exists. During charging, high-density lithium metal is deposited or electrodeposited between the current collector and the negative electrode coating layer, or on the negative electrode coating layer to form a lithium metal layer, which can serve as the negative electrode active material. As a result, in a lithium secondary battery that has been charged one or more times, the deposited-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 means a layer in which lithium metal or the like is deposited during the charging process of the battery, and can be referred to as a metal layer, a lithium layer, a lithium electrodeposited layer, or a negative electrode active material layer, etc.

[0050] The negative electrode coating layer can also be referred to as a lithium electrodeposition induction layer or a negative electrode catalyst layer, and can include a metal, a carbon material, or a combination thereof.

[0051] The metal may be a lithiumophilic metal, for example, it can include gold, platinum, palladium, silicon, silver, aluminum, bismuth, tin, zinc, or a combination thereof, and may be composed of one of these or a plurality of alloys. When the metal exists in a particulate state, its average particle size (D 50 ) may be about 4 μm or less, for example, it may be 10 nm to 4 μm.

[0052] The carbon material may be, for example, crystalline carbon, amorphous carbon, or a combination thereof. The crystalline carbon may be, for example, natural graphite, artificial graphite, mesophase carbon microbeads, or a combination thereof. The 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 a metal and a carbon material, the mixing ratio of the metal and the carbon material may be, for example, a weight ratio of 1:10 to 2:1. In this case, the precipitation of lithium metal can be effectively promoted, and the characteristics of the all-solid-state secondary battery can be improved. The negative electrode coating layer can include, for example, a carbon material supporting a catalytic metal, or can include a mixture of metal particles and carbon material particles.

[0054] As an example, the negative electrode coating layer can include the lithiophilic metal and amorphous carbon, and in this case, the precipitation of lithium metal can be effectively promoted. As a specific example, the negative electrode coating layer can include a composite in which a lithiophilic metal is supported on amorphous carbon.

[0055] The negative electrode coating layer can further include a binder, and the binder can be, for example, a conductive binder. Also, the negative electrode coating layer can further include common additives such as fillers, dispersants, and ion conductive agents.

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

[0057] Positive electrode active material layer As an example, the electrode for the lithium secondary battery described above can be a positive electrode, and in this case, the current collector is a positive electrode current collector, and the electrode active material layer can be a positive electrode active material layer.

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

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

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

[0061] As an example, the positive electrode active material may be a high-nickel-based positive electrode active material in which the nickel content is 80 mol% or more with respect to 100 mol% of the metal excluding lithium in the lithium transition metal composite oxide. The nickel content in the high-nickel-based positive electrode active material may be 85 mol% or more, 90 mol% or more, 91 mol% or more, or 94 mol% or more with respect to 100 mol% of the metal excluding lithium, and may be 99 mol% or less. The high-nickel-based positive electrode active material can achieve a high capacity and is applicable to high-capacity, high-density lithium secondary batteries.

[0062] As a more specific example, a compound represented by any one of the following chemical formulas can 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 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 is Mn, Al, or a combination thereof.

[0064] The positive electrode active material may be in the form of secondary particles formed by aggregation of a plurality of primary particles, or may be in the form of single particles. Further, the positive electrode active material may have a spherical shape or a shape close to spherical, or may be a polyhedron or an irregular shape.

[0065] On the other hand, the positive electrode active material can include a buffer layer on the surface of the particles. The buffer layer is represented by a coating layer, a protective layer, etc., and 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 can include a lithium-metal-oxide, where the metal may be, for example, one or more elements selected from the group consisting of 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 smoothing the movement of lithium ions and electron conduction to improve the performance of the positive electrode active material.

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

[0067] Binder The binder plays a role in well adhering the positive electrode active material particles to each other and also well adhering the positive electrode active material to the current collector. Representative examples of the binder 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, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, nylon, etc.

[0068] Conductive material The conductive material is used to impart conductivity to the electrode, and in the battery being configured, any material can be used as long as it is an electron conductive material without causing a chemical change. Examples of the conductive material include carbon-based substances such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, and carbon nanotube; metal-based substances in the form of metal powder or metal fiber containing copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

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

[0070] As the positive electrode current collector, Al, SUS, etc. can be used, but it is not limited thereto.

[0071] Lithium secondary battery In one embodiment, a lithium secondary battery including the above-described electrode and electrolyte is provided. The lithium secondary battery may be a lithium ion battery to which an electrolytic solution is applied, and as another example, it may be an all-solid-state secondary battery to which a solid electrolyte is applied. As an example, a lithium secondary battery to which an electrolytic solution is applied will be described.

[0072] Lithium secondary batteries are classified into cylindrical, prismatic, pouch, coin, etc. according to their form. Figures 1 to 4 are schematic views showing a lithium secondary battery according to an embodiment. Figure 1 shows a circular shape, Figure 2 shows a prismatic shape, and Figures 3 and 4 show a pouch-type battery form. Referring to Figures 1 to 4, the lithium secondary 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 incorporated. The positive electrode 10, negative electrode 20, and separator 30 may be impregnated with an electrolytic solution (not shown). The lithium secondary battery 100 can include a sealing member 60 for sealing the case 50 as shown in Figure 1. Also, in Figure 2, the lithium secondary 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 can include electrode tabs 70, that is, a positive electrode tab 71 and a negative electrode tab 72, which serve as an electrical path for guiding the current formed by the electrode assembly 40 to the outside.

[0073] Electrolyte As an example, the electrolyte for a lithium secondary battery may be an electrolytic solution, which can include a non-aqueous organic solvent and a lithium salt.

[0074] The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move. The non-aqueous organic solvent may be a carbonate-based, ester-based, ether-based, ketone-based, or alcohol-based solvent, an aprotic solvent, or a combination thereof.

[0075] As carbonate solvents, 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), butylene carbonate (BC), etc. can be used. As ester solvents, methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolide, mevalonolactone, valerolactone, caprolactone, etc. can be used. As ether solvents, dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, tetrahydrofuran, etc. can be used. Further, as ketone solvents, cyclohexanone, etc. can be used. As alcohol solvents, ethyl alcohol, isopropyl alcohol, etc. can be used, and as aprotic solvents, nitriles such as R-CN (R is a linear, branched, or cyclic hydrocarbon group 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, 1,4-dioxolane, sulfolane, etc. can be used.

[0076] The non-aqueous organic solvent can be used alone or in a mixture of two or more. When used in a mixture of two or more, the mixing ratio can be appropriately adjusted according to the intended battery performance, which can be widely understood by those skilled in the art.

[0077] When using a carbonate solvent, a cyclic carbonate and a chain carbonate can be mixed and used, and the cyclic carbonate and the chain carbonate can be mixed at a volume ratio of 1:1 to 1:9.

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

[0079] The electrolytic solution may further contain vinyl ethyl carbonate, vinylene carbonate or an ethylene carbonate-based compound in order to improve the battery life.

[0080] Typical examples of the ethylene carbonate-based compound include fluoroethylene carbonate, difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate and the like.

[0081] The lithium salt is dissolved in an organic solvent, acts as a source of lithium ions in the battery to enable the operation of a basic lithium secondary battery, and plays a role in promoting the movement of lithium ions between the positive electrode and the negative electrode. Typical examples of the lithium salt include LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide; LiFSI), LiC4F9SO3, LiN(C x F 2x+1 SO2)(C y F 2y+1 SO2)(where x and y are integers from 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalato)phosphate (LiDFBOP), lithium bis(oxalato)borate (LiBOB), and one or more selected therefrom can be included.

[0082] The concentration of the lithium salt is preferably used within the range of 0.1 M to 2.0 M. When the concentration of the lithium salt is within the above range, the electrolyte has appropriate ionic conductivity and viscosity, so it can exhibit excellent performance and lithium ions can move effectively.

[0083] Separator Depending on the type of lithium secondary battery, a separator may be present between the positive electrode and the negative electrode. As such a separator, polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more layers thereof can be used, and it goes without saying that mixed multilayer films such as a two-layer separator of polyethylene / polypropylene, a three-layer separator of polyethylene / polypropylene / polyethylene, and a three-layer separator of polypropylene / polyethylene / polypropylene can be used.

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

[0085] The porous substrate can be a polymer selected from any one of polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyacetal, polyamide, polyimide, polycarbonate, polyether ketone, polyaryl ether ketone, polyether imide, polyamide imide, polybenzimidazole, polyether sulfone, polyphenylene oxide, cyclic olefin copolymer, polyphenylene sulfide, polyethylene naphthalate, glass fiber, Teflon, and polytetrafluoroethylene, or a polymer film formed from a copolymer or mixture of two or more of these.

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

[0087] The organic matter can include a (meth)acrylic copolymer containing a first structural unit derived from (meth)acrylamide and a second structural unit including at least one of a structural unit derived from (meth)acrylic acid or (meth)acrylate and a structural unit derived from (meth)acrylamidosulfonic acid or a salt thereof.

[0088] The inorganic matter can include, but is 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 50 ) can be 1 nm to 2000 nm, for example, 100 nm to 1000 nm, or 100 nm to 700 nm.

[0089] The organic matter and the inorganic matter can be mixed and present in one coating layer, or can be present in a form in which a coating layer containing the organic matter and a coating layer containing the inorganic matter are laminated.

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

[0091] Hereinafter, examples and comparative examples of the present invention will be described. The following examples are only examples of the present invention, and the present invention is not limited to the following examples.

[0092] Example 1 1. Production of functional polymer 3M lithium salt LiFSI was added to liquid monomer 2-ethyl-2-oxazoline and completely dissolved. Then, it was heated at 60 °C until the polymerization was completed to polymerize lithium-containing poly-(2-ethyl-2-oxazoline) (Li-POX). The functional polymer (Li-POX) polymerized starting with the lithium salt was dissolved in a solvent in which acetone and IPA were mixed at a volume ratio of 5:5 to 0.5 wt% to prepare a polymer solution.

[0093] 2. Production of negative electrode 97 wt% of graphite negative electrode active material, 1.7 wt% of carboxymethyl cellulose, 0.8 wt% of styrene butadiene rubber, and 0.5 wt% of acetylene black were mixed in an aqueous solvent to produce a negative electrode active material layer slurry. The negative electrode active material layer slurry was coated on a copper foil current collector, dried and rolled to form a graphite-based negative electrode active material layer on the current collector.

[0094] The polymer solution prepared by the electrospinning method was coated on 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 are specifically as follows. TCD (Tip to collector distance) is 9 cm, Tip size is 21 gauge, the applied voltage is 25 kV, the flow rate is 4 mL / hr, and the spinning time is 2 minutes.

[0095] 3. Production of lithium secondary battery Lithium metal was used as the counter electrode, and a unit cell was manufactured with a polytetrafluoroethylene separator interposed between the negative electrode and the counter electrode. After inserting this into a case, an electrolyte solution in which 1.15 M LiPF6 was dissolved in a solvent in which ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate were mixed at a volume ratio of 2:4:4 was injected to manufacture a lithium secondary battery (half cell) by a normal method.

[0096] Comparative Example 1 A negative electrode and a 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 polymer To understand the characteristics of the functional polymer (Li-POX) according to Example 1, which was initiated with a lithium salt and polymerized, infrared spectroscopic analysis was performed on each of Li-POX and poly-(2-ethyl-2-oxazoline) (POX) polymerized by a general method without a lithium salt. The peak corresponding to the C=O stretch is shown in Figure 5, and the peak corresponding to the C-N stretch is shown in Figure 6.

[0098] Referring to Figure 5, it can be confirmed that for Li-POX according to the example, a red shift phenomenon appears in the peak corresponding to the C=O stretch compared to POX, which is understood to be due to the bond between oxygen and lithium cations. Also, referring to Figure 6, for Li-POX according to the example, a blue shift phenomenon appears in the peak corresponding to the C-N stretch compared to POX, which is understood to be due to the bond between nitrogen and the anion of the lithium salt.

[0099] Evaluation Example 2: Analysis of SEI component change after formation process The lithium secondary batteries of Example 1 and Comparative Example 1 were charged to 0.01 V at a constant current of 0.1 C at 25 °C, and then discharged at a constant current of 0.2 C to 1.5 V to carry out the initial charge and discharge, that is, the formation process. The surface of the negative electrode was subjected to ToF-SIMS Depth analysis before and after the formation process to analyze the component change of the SEI, and the results are shown in Figure 7. All the graphs in Figure 7 show the intensity of fluorine ions (F - ). It can be seen that for Example 1 in which a functional layer according to one embodiment was introduced on the surface of the negative electrode, a strong F - intensity appears in the SEI on the surface of the negative electrode after the formation process. Thus, it is confirmed that a LiF-rich SEI is formed after the formation process by introducing the functional layer.

[0100] Evaluation Example 3: Rapid charge life characteristic evaluation In Example 1 and Comparative Example 1, instead of lithium metal as the positive electrode, a full cell was manufactured using the positive electrode manufactured as follows. LiNi 0.78 Co 0.2Al 0.02 A positive electrode active material layer slurry was prepared by mixing 96 wt% O2 positive electrode active material, 2.0 wt% polyvinylidene fluoride binder, and 2.0 wt% acetylene black conductive material, and the positive electrode active material layer slurry was coated on an aluminum foil current collector, dried, and rolled to prepare a positive electrode.

[0101] The full cells of Example 1 and Comparative Example 1 were charged at a constant current of 0.1C at 25°C up to 4.25V, charged at a constant voltage of 0.05C, and then discharged at 0.1C down to 2.8V to carry out initial charge / discharge. Next, they were charged / discharged at 25°C at 1C / 1C in the voltage range of 2.8V to 4.25V for more than 400 times to evaluate the life characteristics. The change in specific capacity according to the number of cycles is shown in FIG. 8.

[0102] 8, it can be seen that the long-term life characteristics are improved in Example 1 compared to Comparative Example 1. As a result, it can be seen that the lithium secondary battery incorporating the functional layer according to an embodiment has improved life characteristics under fast charging conditions, which is understood to be because the reversibility of lithium deposited on the electrode due to fast charging is increased, and the composition of the SEI is changed, thereby reducing side reactions between the electrode and the electrolyte.

[0103] Although the preferred embodiments have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements made by those skilled in the art using 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 electrode lead tab, 12: Positive electrode terminal 20: negative electrode, 21: negative electrode lead tab 22: negative electrode terminal, 30: separator 40: electrode assembly, 50: case 60: sealing member, 70: electrode tab 71: Positive electrode tab, 72: Negative electrode tab

Claims

1. A current collector; an electrode active material layer located on the current collector; A functional layer, The functional layer is an electrode for a lithium secondary battery that contains a lithium-containing polyoxazoline.

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

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

4. The electrode for a lithium secondary battery according to claim 1 , wherein the functional layer is coated by electrospinning.

5. 2. The electrode for a lithium secondary battery according to claim 1, wherein the lithium-containing polyoxazoline is a polyoxazoline obtained by initiating polymerization with a lithium salt.

6. The lithium salt is LiPF 6 , LiBF 4 , LiSbF 6 , LiAsF 6 , LiClO 4 , LiAlO 2 , LiAlCl 4 , LiPO 2 F 2 6. The electrode for a lithium secondary battery according to claim 5, comprising LiCl, LiI, LiFSI, LiTFSI, LiOTf, LiBOB, LiDFOB, or a combination thereof.

7. the lithium-containing polyoxazoline comprises a lithium-containing poly(2-alkyl-2-oxazoline), a lithium-containing poly(2-aryl-2-oxazoline), or a combination thereof; 2. The electrode for a lithium secondary battery according to claim 1, wherein 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.

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

9. The weight average molecular weight (M w 2. The electrode for a lithium secondary battery according to claim 1, wherein the molecular weight of the polymer is 500 g / mol to 500,000 g / mol.

10. The polydispersity index (PDI; M w / M n 2. The electrode for a lithium secondary battery according to claim 1, wherein R is an integer of 1 to 4.

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

12. 12. The electrode for a lithium secondary battery according to claim 11, wherein the electrode active material layer is a negative electrode active material layer, and the negative electrode active material layer includes lithium metal, a lithium alloy, a carbon-based negative electrode active material, a silicon-based negative electrode active material, or a combination thereof.

13. the electrode active material layer is a negative electrode coating layer, the negative electrode coating layer comprises a lithophilic metal, a carbon material, or a combination thereof; 12. The electrode for a lithium secondary battery according to claim 11, wherein a lithium metal layer is formed between the current collector and the negative electrode coating layer by charging.

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

15. Further comprising a positive electrode, The lithium secondary battery according to claim 14, wherein the electrode for a lithium secondary battery according to any one of claims 1 to 13 is a negative electrode.

16. The electrode for a lithium secondary battery according to any one of claims 1 to 13 is a negative electrode, A positive electrode and a separator disposed between the positive electrode and the lithium secondary battery electrode; The lithium secondary battery according to claim 14, further comprising an electrolyte.

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