Electrode and lithium secondary battery including same

Abstract

The present invention provides an electrode including a current collector and an electrode active material layer disposed on the current collector, wherein the electrode active material layer includes an electrode active material, a conductive material, and a binder. The conductive material includes multi-walled carbon nanotubes, and the multi-walled carbon nanotubes have a ratio of a content of C=O bonds to a content of C–O bonds, as measured by X-ray photoelectron spectroscopy (XPS), in a range of 1.05 to 2.00.

Description

Electrode and lithium secondary battery including the same

[0001] The present application claims the benefit of priority based on Korean Patent Application No. 10-2024-0191956 dated December 19, 2024 and Korean Patent Application No. 10-2025-0198130 dated December 12, 2025, the entire contents of which are incorporated herein.

[0002] The present invention relates to an electrode with improved electrode adhesion and a lithium secondary battery including the same.

[0003] Due to the rapid increase in the use of fossil fuels, there is a growing demand for alternative or clean energy. As part of this effort, the fields of power generation and energy storage utilizing electrochemical reactions are the most actively researched.

[0004] Currently, a representative example of an electrochemical device utilizing such electrochemical energy is the secondary battery, and its scope of application is increasingly expanding. Recently, with the technological development and growing demand for portable devices such as portable computers, mobile phones, and cameras, the demand for secondary batteries as an energy source has been rapidly increasing. Among these secondary batteries, much research has been conducted on lithium secondary batteries, which have high energy density—that is, high capacity—and have been commercialized and are widely used.

[0005] Meanwhile, while applying cathode active materials with high capacity is important for manufacturing high-energy-density batteries, the materials included in the cathode also play a crucial role. To this end, research is being conducted to maximize the proportion of active materials while minimizing the content of conductive agents and binders; however, applying this to actual mass production is difficult because the increase in cell unit costs is significantly disproportionate to the performance improvement when the amount of active material used increases.

[0006] Accordingly, increasing price competitiveness while satisfying a specific energy density or higher has become a recent research trend.

[0007] Meanwhile, carbon nanotubes (CNTs) are widely used as conductive materials because they offer superior conductivity and length characteristics compared to carbon black, making them advantageous for forming conductive networks. Among these, while single-walled carbon nanotubes (SWCNTs) are advantageous for forming conductive networks, they are difficult to disperse and expensive; consequently, multi-walled carbon nanotubes (MWCNTs) are used. However, there has been a problem with reduced electrode adhesion due to binder migration.

[0008] Accordingly, there is a need for multi-walled carbon nanotubes (MWCNTs) with excellent electrode adhesion.

[0009] The present invention aims to provide an electrode with improved electrode adhesion and a lithium secondary battery including the same by using multi-walled carbon nanotubes as a conductive material in which the ratio of the content of C=O bonds to the content of CO bonds measured by X-ray photoelectron spectroscopy (XPS) is controlled.

[0010] [1] According to one embodiment of the present invention, an electrode is provided comprising a current collector and an electrode active material layer disposed on the current collector, wherein the electrode active material layer comprises an electrode active material, a conductive material and a binder, wherein the conductive material comprises multi-walled carbon nanotubes, and the ratio of the content of C=O bonds to the content of CO bonds measured by X-ray photoelectron spectroscopy (XPS) is 1.05 to 2.00.

[0011] [2] In the above [1], the multi-walled carbon nanotube may have a C=O bond content of 0.4 atomic% to 2.0 atomic% as measured by X-ray photoelectron spectroscopy (XPS).

[0012] [3] In the above [1] or [2], the multiwalled carbon nanotube may have a CO bond content of 0.35 atomic% to 1.2 atomic% as measured by X-ray photoelectron spectroscopy (XPS).

[0013] [4] In at least one of [1] to [3] above, the multi-walled carbon nanotube may have an oxygen (O) content of 0.8 atomic% to 3.0 atomic% as measured by X-ray photoelectron spectroscopy (XPS).

[0014] [5] In at least one of [1] to [4] above, the multi-walled carbon nanotube may have a carbon (C) content of 96 atomic% to 99.5 atomic% as measured by X-ray photoelectron spectroscopy (XPS).

[0015] [6] In at least one of [1] to [5] above, the multi-walled carbon nanotube may have an aluminum (Al) content of 0.1 atomic% to 0.5 atomic% as measured by X-ray photoelectron spectroscopy (XPS).

[0016] [7] In at least one of [1] to [6] above, the multiwalled carbon nanotube may have a chlorine (Cl) content of 0.05 atomic% to 0.2 atomic% as measured by X-ray photoelectron spectroscopy (XPS).

[0017] [8] In at least one of [1] to [7] above, the multiwalled carbon nanotube has a BET specific surface area of ​​200 m² 2 / g to 350m 2 It can be / g.

[0018] [9] In at least one of [1] to [8] above, the multi-walled carbon nanotube may be included in an amount of 0.5% to 2.0% by weight based on the total weight of the electrode active material layer.

[0019]

[0010] In at least one of [1] to [9] above, the electrode active material may be a positive electrode active material.

[0020]

[0011] In at least one of [1] to

[0010] above, the electrode active material may be a negative electrode active material.

[0021]

[0012] According to another embodiment of the present invention, a lithium secondary battery comprising an electrode according to at least one of [1] to

[0011] is provided.

[0022] The electrode according to the present invention uses a multi-walled carbon nanotube as a conductive material, comprising a CO bond capable of forming hydrogen bonds with a dispersant and a binder, and a C=O bond capable of inducing strong ionic interactions with the dispersant and the binder, and can improve the adhesion between the current collector and the electrode active material layer by controlling the ratio of the content of C=O bonds to the content of CO bonds within the multi-walled carbon nanotube.

[0023] In addition, the lithium secondary battery according to the present invention can have an excellent capacity retention rate because, by applying an electrode with excellent electrode adhesion, the current collector and the electrode active material layer are strongly adhered during the charging and discharging process, so the electrode active material is not lost.

[0024] Terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted in a meaning and concept consistent with the technical spirit of the invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe his invention.

[0025] In this specification, terms such as “comprising,” “comprising,” or “having” are intended to specify the existence of the implemented features, numbers, steps, components, or combinations thereof, and do not exclude the existence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0026] In this specification, "specific surface area" is measured by the BET method, and specifically, can be calculated from the amount of nitrogen gas adsorbed at a liquid nitrogen temperature (77K) using BEL SORP-mino II of BEL Japan.

[0027] In this specification, X-ray photoelectron spectroscopy (XPS) is a method for analyzing the constituent elements of a sample and their electronic states by irradiating a sample, particularly the surface of the sample, with X-rays and measuring the energy of the photoelectrons generated. In particular, since X-ray photoelectron spectroscopy can analyze a region from the surface of the sample to a depth of about 2 nm to 8 nm (usually about 5 nm), the concentration of elements in about half of the surface area can be analyzed quantitatively and qualitatively. In this invention, analysis was performed using a Thermo Fisher Scientific (ESCA-02) under the following conditions: light source: Al-Kα (1486.6 eV); acceleration voltage: 1 Kv, 300 W; energy resolution: about 1.0 eV; minimum analysis area: 400 micro; sputter rate: 0.13 nm / min).

[0028]

[0029] The present invention will be described in detail below.

[0030] The electrode according to the present invention and the lithium secondary battery including the same comprise at least one of the configurations described below, and may comprise any combination of technically feasible configurations among the following configurations.

[0031]

[0032] electrode

[0033] The electrode according to the present invention comprises a current collector and an electrode active material layer disposed on the current collector, wherein the electrode active material layer comprises an electrode active material, a conductive material, and a binder, wherein the conductive material comprises multi-walled carbon nanotubes, and the ratio of the content of C=O bonds to the content of CO bonds measured by X-ray photoelectron spectroscopy (XPS) of the multi-walled carbon nanotubes is 1.05 or more and 2.00 or less.

[0034]

[0035] (1) The whole house

[0036] The above current collector may be a positive current collector or a negative current collector having conductivity without causing chemical changes in the battery, and its type is not particularly limited.

[0037] For example, the above-mentioned positive current collector may be stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc.

[0038] The above positive current collector can typically have a thickness of 3 μm to 500 μm, and preferably can have a thickness of 300 μm or less, 200 μm or less, 100 μm or less, or 80 μm or less. Fine irregularities may be formed on the surface of the current collector to strengthen the bonding force with the positive active material. For example, it can be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0039] The above-mentioned negative current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, heat-treated carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy may be used.

[0040] The above-mentioned negative current collector can typically have a thickness of 3 μm to 500 μm, and preferably can have a thickness of 300 μm or less, 200 μm or less, 100 μm or less, or 80 μm or less. Fine irregularities may be formed on the surface of the current collector to strengthen the bonding force with the negative active material. For example, it can be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0041]

[0042] (2) Electrode active material layer

[0043] 1) Challenge material

[0044] The conductive material according to the present invention comprises multi-walled carbon nanotubes, wherein the ratio of the content of C=O bonds to the content of CO bonds measured by X-ray photoelectron spectroscopy (XPS) is 1.05 or higher.

[0045] The CO bonds and C=O bonds of the multiwalled carbon nanotubes described above originate from highly polar functional groups containing oxygen atoms, such as carboxyl groups (-COOH), ester bonds (-C(=O)-O-), ether bonds (COC), and carbonyl groups (-C(=O)-). These functional groups are generated during the process of surface treatment of multiwalled carbon nanotubes with a strong acid such as sulfuric acid (H2SO4). During this process, the content of CO bonds and C=O bonds can be controlled by adjusting the degree of oxidation and content. Specifically, the oxygen content can be increased as the amount of surface treatment agent having acidic groups increases.

[0046] The above C=O bond is a double bond consisting of one sigma (σ) bond and one pi (π) bond. Due to the difference in electronegativity between carbon and oxygen, oxygen attracts electrons more strongly, resulting in a large dipole moment with electron density shifted more toward oxygen, thus possessing very strong polarity. Therefore, the C=O bond within the conductive material induces ionic interactions with polar substances within the electrode active material, dispersant, and binder, thereby increasing interfacial bonding strength. Consequently, the binder is uniformly distributed without aggregation, which can improve the adhesion between the current collector and the electrode active material layer.

[0047] Since the above CO bonds form hydrogen bonds to strengthen intermolecular bonding, they form hydrogen bonds with hydrogen provided by functional groups such as hydroxyl groups (-OH), ether groups (-COC-) and carboxyl groups (-COOH) in the dispersant, and fluoro groups (-CF₂-), hydroxyl groups (-OH), carboxyl groups (-COOH) and nitrile groups (-CN) in the binder, thereby increasing interfacial bonding strength. Consequently, stress is generated between the electrode active material, binder, and conductive material, so the electrode active material layer is maintained despite repeated expansion and contraction due to the insertion / extraction of lithium ions during the charging / discharging process, thereby improving the adhesion between the current collector and the electrode active material layer.

[0048] The inventors completed the present invention by confirming that when the ratio of the content of C=O bonds to the content of CO bonds measured by X-ray photoelectron spectroscopy (XPS) of the multi-walled carbon nanotube is 1.05 or higher, the content of CO bonds and the content of C=O bonds are optimized, thereby increasing the interfacial bonding strength of the conductive material with the dispersant and binder, and consequently improving electrode adhesion.

[0049] When the ratio of the content of C=O bonds to the content of CO bonds measured by X-ray photoelectron spectroscopy (XPS) of the above multi-walled carbon nanotubes is less than 1.05, it means that the content of C=O bonds is excessively low compared to the content of CO bonds. When the content of C=O bonds, which have high polarity, is low, ionic interactions decrease, and the interfacial bonding force between the electrode active material, dispersant, and binder weakens, causing the binder to aggregate and thus reducing the electrode adhesion force between the current collector and the electrode active material layer.

[0050] In addition, if the ratio of the content of C=O bonds to the content of CO bonds in the multi-walled carbon nanotubes exceeds 2.00, it means that the content of C=O bonds is excessively high compared to the content of CO bonds. When the content of C=O bonds, which have high polarity, is excessive in this way, strong interactions such as hydrogen bonding and van der Waals forces occur between the conductive material particles, which can lead to aggregation. As a result, the conductive material particles clump together and fail to disperse uniformly within the electrode. This reduces the contact area with the active material, which not only hinders electron transfer but can also lead to a decrease in adhesion between the current collector and the electrode active material layer.

[0051] Specifically, the ratio of the content of C=O bonds to the content of CO bonds measured by X-ray photoelectron spectroscopy (XPS) of the multi-walled carbon nanotube may be 1.05 or more, 1.06 or more, 1.07 or more, 1.08 or more, 1.09 or more, 1.10 or more, 1.11 or more, or 1.12 or more, and may be 2.00 or less, 1.80 or less, 1.70 or less, 1.60 or less, 1.50 or less, 1.40 or less, 1.30 or less, 1.25 or less, 1.23 or less, or 1.20 or less. The ratio of the content of C=O bonds to the content of CO bonds in the multi-walled carbon nanotubes may be, for example, 1.05 to 1.50, preferably 1.10 to 1.30, more preferably 1.10 to 1.23, and even more preferably 1.10 to 1.20. When the above range is satisfied, the highly polar C=O bonds induce ionic interactions with polar substances in the dispersant and binder, thereby increasing the interfacial bonding strength between the electrode active material, the dispersant, and the binder, while the CO bonds, which are relatively less polar than the C=O bonds, provide hydrogen bonding with hydrogen provided by functional groups in the dispersant and binder, thereby complementing the ionic interactions of the C=O bonds. Accordingly, the electrode active material layer is maintained despite repeated expansion and contraction due to the insertion / extraction of lithium ions during the charging / discharging process, and the binder is uniformly distributed without aggregation, thereby improving the adhesion between the current collector and the electrode active material layer.

[0052] The above multi-walled carbon nanotube may have a CO bond content of 0.35 atomic% to 1.2 atomic%, preferably 0.6 atomic% to 1.1 atomic%, and more preferably 0.75 atomic% to 0.85 atomic% as measured by X-ray photoelectron spectroscopy (XPS). When the above range is satisfied, hydrogen bonding of the CO bond is appropriately provided, increasing the bonding strength with the binder and dispersant, thereby maintaining a balance of dispersibility and conductivity to improve electrode adhesion.

[0053] The above multi-walled carbon nanotubes may have a C=O bond content of 0.4 atomic% to 2.0 atomic%, preferably 0.6 atomic% to 1.5 atomic%, and more preferably 0.8 atomic% to 1.0 atomic% as measured by X-ray photoelectron spectroscopy (XPS). When the above range is satisfied, the ionic interaction with the binder of the conductive material is increased due to the strong polarity of the C=O bonds, thereby strengthening interfacial adhesion and improving electrode adhesion.

[0054] The above multi-walled carbon nanotubes may have an oxygen (O) content of 0.8 atomic% to 3.0 atomic%, preferably 1.5 atomic% to 2.5 atomic%, and more preferably 1.8 atomic% to 2.2 atomic% as measured by X-ray photoelectron spectroscopy (XPS). These oxygen functional groups may be generated from a grinding or disintegration process when the multi-walled carbon nanotubes are debundled from large-micron scale bundles, and may be bonded to nodes or cut surfaces present in the multi-walled carbon nanotubes. These oxygen functional groups can help to achieve more effective dispersion during the dispersion process of the multi-walled carbon nanotubes. When the above range is satisfied, the oxygen functional groups can increase hydrophilicity on the surface of the multi-walled carbon nanotubes to exhibit uniform dispersibility and provide an appropriate content of CO bonds and C=O bonds. At this time, the oxygen (O) content includes both the CO bond and the C=O bond content, and may additionally include the oxygen ionically bonded with aluminum (Al).

[0055] The ratio of the content of C=O bonds to the content of oxygen (O) measured by X-ray photoelectron spectroscopy (XPS) in the above multi-walled carbon nanotubes may be 0.46 or more, 0.465 or more, or 0.468 or more, and may be 0.52 or less, 0.50 or less, 0.49 or less, 0.485 or less, 0.48 or less, or 0.475 or less, preferably 0.46 to 0.52, more preferably 0.465 to 0.485, and even more preferably 0.465 to 0.475. When the above range is satisfied, the C=O bonds having strong polarity induce ionic interactions with polar substances in the electrode active material, dispersant, and binder, thereby increasing interfacial bonding strength and preventing the binder from aggregating, which can improve the adhesion between the current collector and the electrode active material layer.

[0056] The ratio of the CO bond content to the oxygen (O) content measured by X-ray photoelectron spectroscopy (XPS) of the above multi-walled carbon nanotube may be 0.30 or more, 0.35 or more, 0.37 or more, 0.39 or more, or 0.40 or more, and may be 0.44 or less or 0.43 or less, preferably 0.30 to 0.44, more preferably 0.35 to 0.44, and even more preferably 0.40 to 0.44. When the above range is satisfied, the ionic interaction of the C=O bond is complemented to provide hydrogen bonding with hydrogen provided by functional groups in the dispersant and binder, thereby maintaining the electrode active material layer despite repeated expansion and contraction due to the insertion / extraction of lithium ions during the charging / discharging process, and thus improving the adhesion between the current collector and the electrode active material layer.

[0057] The above multi-walled carbon nanotubes may have a carbon (C) content of 96 atomic% to 99.5 atomic%, preferably 96 atomic% to 98 atomic%, and more preferably 97 atomic% to 98 atomic% as measured by X-ray photoelectron spectroscopy (XPS). When the above range is satisfied, the conductive network can be improved, and the durability of the electrode can be enhanced by maintaining the mechanical strength of the multi-walled carbon nanotubes to improve electrode adhesion.

[0058] The above multi-walled carbon nanotubes may have an aluminum (Al) content of 0.1 atomic% to 0.5 atomic%, preferably 0.1 atomic% to 0.4 atomic%, and more preferably 0.1 atomic% to 0.3 atomic% as measured by X-ray photoelectron spectroscopy (XPS). The aluminum (Al) may be a byproduct of the catalyst used in the manufacturing process of the multi-walled carbon nanotubes.

[0059] The above multi-walled carbon nanotubes may have a chlorine (Cl) content of 0.05 atomic% to 0.2 atomic%, preferably 0.05 atomic% to 0.15 atomic%, and more preferably 0.08 atomic% to 0.12 atomic% as measured by X-ray photoelectron spectroscopy (XPS). The chlorine (Cl) plays a role in maintaining a stable interface between the electrode and the electrolyte by helping to form a Solid Electrolyte Interphase (SEI) film during the initial charging process, and satisfying the above range can improve the capacity retention rate.

[0060] The above multi-walled carbon nanotube has a BET specific surface area of ​​200 m² 2 / g to 350m 2 / g, preferably 250m 2 / g to 300m 2 / g, more preferably 270m2 / g to 280m 2 It can be / g. If the above range is satisfied, the contact area between the electrode active material and the electrolyte is increased, and the capacity retention rate can be improved.

[0061] The above multi-walled carbon nanotubes may be included in an amount of 0.5% to 2.0% by weight, preferably 0.8% to 1.5% by weight, and more preferably 1.1% to 1.3% by weight, based on the total weight of the electrode active material layer. When the above range is satisfied, the solid content of the electrode slurry being manufactured does not become excessively low, so binder migration occurs during electrode drying, thereby improving electrode adhesion.

[0062]

[0063] 2) Electrode active material

[0064] The above electrode active material may be a positive or negative active material commonly used in the relevant technical field, and its type is not particularly limited.

[0065]

[0066] For example, as the positive electrode active material, a lithium transition metal oxide or a lithium transition metal phosphate-based compound containing lithium and one or more transition metals such as cobalt, manganese, nickel, or aluminum may be used. More specifically, the lithium transition metal oxide is a lithium-manganese-based oxide (e.g., LiMnO2, LiMn2O4, etc.), a lithium-cobalt-based oxide (e.g., LiCoO2, etc.), a lithium-nickel-based oxide (e.g., LiNiO2, etc.), or a lithium-nickel-manganese-based oxide (e.g., LiNi 1-Y1 Mn Y1 O2(here, 0 <Y1<1), LiNi Z1 Mn 2-Z1 O4 (where 0 < Z1 < 2), etc.), lithium-nickel-cobalt oxides (e.g., LiNi 1-Y2 Co Y2O2(here, 0 <Y2<1) 등), 리튬-망간-코발트계 산화물(예를 들면, LiCo 1-Y3 Mn Y3 O2(here, 0 <Y3<1), LiMn 2-Z2 Co Z2 O4 (where 0 < Z2 < 2), etc.), lithium-nickel-cobalt-manganese oxides (e.g., Li(Ni P1 Co Q1 Mn R1 )O2(where, 0<P1<1, 0<Q1<1, 0<R1<1, P1+Q1+R1=1) or Li(Ni P2 Co Q2 Mn R2 ) O4 (where 0 < P2 < 2, 0 < Q2 < 2, 0 < R2 < 2, P2+Q2+R2=2), etc.), or lithium-nickel-cobalt-manganese-other metal (M) oxide (e.g., Li(Ni P3 Co Q3 Mn R3 M 1S )O2(wherein M1 is selected from the group consisting of Al, Cu, Fe, V, Cr, Ti, Zr, Zn, Ta, Nb, Mg, B, W and Mo, and P3, Q3, R3 and S are each atomic fractions of independent elements, such that 0<P3<1, 0<Q3<1, 0<R3<1, 0<S<1, P3+Q3+R3+S=1), etc.), any one or more of these compounds may be included.

[0067] In addition, the above lithium transition metal phosphate-based compound is an olivine-based lithium metal phosphate (e.g., Li 1+x [M3 1-q M4 q ]PO 4-r X r(Here, M3 is at least one selected from the group consisting of Fe, Mn, Co, and Ni, M4 is at least one selected from the group consisting of Al, Mg, and Ti, X is at least one selected from the group consisting of F, S, and N, and -0.5≤x≤0.5, 0≤q≤0.5, 0≤r≤0.1) etc.) may be included.

[0068] Preferably, the positive electrode active material may include a lithium-nickel-cobalt-manganese oxide or a lithium phosphate compound, and the lithium-nickel-cobalt-manganese oxide may be in the form of a single particle or a secondary particle, and if the chemical formula exemplified above is expressed more specifically, it may have a composition such as Chemical Formula 1 below.

[0069] [Chemical Formula 1]

[0070] Li 1+x Ni a Co b M 1 c M 2 d O 2-e X e

[0071] In the above chemical formula 1, M 1 ... comprises one or more selected from Mn and Al, and M 2 comprises 1 or more selected from the group consisting of W, Zr, Y, Ba, Ca, Ti, V, Mg, Ta, and Nb, and X comprises 1 or more selected from the group consisting of N, P, S, F, and Cl, where 0≤x≤0.1, 0.5≤a<1, 0 <b≤0.35, 0<c≤0.35, 0≤d≤0.05 및 0≤e≤0.05 이다.

[0072] In the above chemical formula 1, M 1 is Mn, Al, or a combination thereof, preferably Mn or a combination of Mn and Al, and M 2is one or more selected from the group consisting of Zr, W, Y, Ba, Ca, Ti, Mg, Ta, and Nb, preferably one or more selected from the group consisting of Zr, Y, Mg, and Ti, and more preferably Zr, Y, or a combination thereof. 2 The element is not necessarily included, but if included in an appropriate amount, it can play a role in promoting grain growth during sintering or improving crystal structure stability. In addition, the above X is an anion substituted at the oxygen site and may include N, P, S, F, or Cl.

[0073] The above 1+x represents the molar ratio of lithium in the lithium nickel-based oxide, and may be 0≤x≤0.1, 0≤x≤0.08, 0≤x≤0.05, 0≤x≤0.03, or 0≤x≤0.02.

[0074] The above a represents the molar ratio of nickel among the total metals excluding lithium in the lithium nickel-based oxide, and may be 0.50≤a<1.00, 0.60≤a≤0.99, 0.70≤a≤0.99 or 0.75≤a≤0.99, 0.80≤a≤0.99, 0.82≤a≤0.99, 0.84≤a≤0.99, or 0.86≤a≤0.99.

[0075] The above b represents the molar ratio of cobalt among the total metals excluding lithium in the lithium nickel-based oxide, where 0 <b≤0.35, 0.01≤b≤0.34, 0.01≤b≤0.30, 0.01≤b≤0.25, 0.01≤b≤0.20, 또는 0.01≤b≤0.15일 수 있다.

[0076] The above c is M among the total metals excluding lithium in the lithium nickel-based oxide. 1 Representing the molar ratio of, 0 <c≤0.35, 0.01≤c≤0.34, 0.01≤c≤0.30, 0.01≤c≤0.25, 0.01≤c≤0.20, 또는 0.01≤c≤0.15일 수 있다.

[0077] The above d is M among the total metals excluding lithium in the lithium nickel-based oxide. 2 It represents the molar ratio of the elements, which can be 0≤d≤0.05, 0≤d≤0.02, or 0≤d≤0.01.

[0078] The above e represents the molar ratio of element X among all nonmetals excluding oxygen in the lithium nickel-based oxide, and may be 0≤e≤0.05, 0≤e≤0.02, or 0≤e≤0.01.

[0079] Meanwhile, the lithium nickel-based oxide may further include a coating layer on the particle surface comprising one or more coating elements selected from the group consisting of Al, Ti, W, B, F, P, Mg, Ni, Co, Fe, Cr, V, Cu, Ca, Zn, Zr, Nb, Mo, Sr, Sb, Bi, Si, and S.

[0080] The above positive active material includes a lithium transition metal phosphate-based compound and may be represented by the following chemical formula 2.

[0081] [Chemical Formula 2]

[0082] Li 1+x [Fe 1-y M y ]PO4

[0083] In the above chemical formula 2, M comprises one or more selected from the group consisting of Mn, Co, Ni, Al, Mg, and Ti, and -0.5≤x≤0.5, 0≤y<1.

[0084] The above lithium transition metal phosphate-based compound can be doped with M. In this case, the lattice structure and distance within the olivine crystal structure, which is the crystal structure, are changed, thereby increasing the diffusivity of lithium ions, and consequently, the electrochemical properties of the battery containing the positive electrode active material can be improved.

[0085] The above x may be -0.5 to 0.5, preferably -0.3 or more, -0.1 or more, or 0 or more, and may be 0.5 or less, 0.4 or less, 0.3 or less, 0.2 or less, or 0.1 or less.

[0086] The above y may be 0 or greater, less than 1, or 0.90 or less, 0.80 or less, 0.70 or less, 0.60 or less, 0.50 or less, 0.40 or less, 0.30 or less, 0.20 or less, 0.10 or less, or 0.05 or less.

[0087] The above lithium transition metal phosphate-based compound may be, for example, LiFePO4.

[0088] The lithium transition metal phosphate-based compound according to the present invention may be in the form of a single particle consisting of only one primary particle, or in the form of an irregular secondary particle consisting of 2 to 50 primary particles. Furthermore, the lithium transition metal phosphate-based compound may include an olivine structure, and specifically, may consist solely of an olivine structure. The coating layer according to the present invention may be formed not only on the secondary particle but also on the primary particle. That is, the coating layer according to the present invention may be uniformly present on the surface of the primary particle existing inside the secondary particle.

[0089]

[0090] In addition, as the negative electrode active material, a material capable of reversibly inserting / extracting lithium ions may be applied, and may include at least one selected from the group consisting of, for example, lithium metal; carbon-based active material; metalloid-based active material including Si or Sn; metal-based active material including a metal or an alloy of these metals and lithium; metal composite oxide; and transition metal oxide.

[0091] The above carbon-based active material may be used without particular limitation as long as it is commonly used in lithium-ion secondary batteries, and representative examples include crystalline carbon, amorphous carbon, or a combination thereof. Examples of the above crystalline carbon include graphite such as amorphous, plate-like, flake-like, spherical, or fibrous natural graphite or artificial graphite, and examples of the above amorphous (or low-crystallinity) carbon include soft carbon (low-temperature calcined carbon) or hard carbon, mesophase pitch carbide, calcined coke, etc.

[0092] The above metalloid active material may include silicon-based active materials and / or tin-based active materials, and silicon-based active materials include Si and SiO x (0 <x≤2), Si-Y 합금(상기 Y는 알칼리 금속, 알칼리 토금속, 13족 원소, 14족 원소, 전이금속, 희토류 원소 및 이들의 조합으로 이루어진 군에서 선택되는 원소이며, Si은 아님)으로 이루어진 군에서 선택될 수 있다. 또한 주석계 활물질은, Sn, SnO2, Sn-Y(상기 Y는 알칼리 금속, 알칼리 토금속, 13족 원소, 14족 원소, 전이금속, 희토류 원소 및 이들의 조합으로 이루어진 군에서 선택되는 원소이며, Sn은 아님) 등을 들 수 있고, 또한 이들 중 적어도 하나와 SiO2를 혼합하여 사용할 수도 있다. 상기 원소 Y로는 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, Ge, P, As, Sb, Bi, S, Se, Te, Po 및 이들의 조합으로 이루어진 군에서 선택될 수 있다.

[0093] As the above-mentioned metal-based active material, a metal selected from the group consisting of Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn, or an alloy of these metals and lithium may be used.

[0094] The above metal composite oxides include PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, Bi2O5, Li x Fe2O3(0≤x≤1), Li x WO2(0≤x≤1) and Sn x Me 1-x Me y O z (Me: Mn, Fe, Pb, Ge; Me': Al, B, P, Si, Group 1, 2, and 3 elements of the periodic table, halogens; 0 <x≤1; 1≤y≤3; 1≤z≤8) 로 이루어진 군에서 선택되는 것이 사용될 수 있다.

[0095] Examples of the above transition metal oxides include lithium-containing titanium composite oxide (LTO), vanadium oxide, and lithium vanadium oxide.

[0096]

[0097] According to one embodiment of the present invention, the positive active material may be 90% to 99% by weight, more specifically 93% or more, 95% or more, 96% or more, or 97% or more by weight, based on the total weight of the positive active material layer, and may be included in an amount of 98.5% or less, or 98% or less by weight, and excellent energy density, electrode adhesion, and electrical conductivity can be achieved when included within the above content range.

[0098] In addition, the above-mentioned negative electrode active material may be included in an amount of 70% to 99.5% by weight, preferably 80% to 99% by weight, based on the total weight of the negative electrode active material layer. When the content of the electrode active material satisfies the above range, excellent energy density, electrode adhesion, and electrical conductivity can be achieved.

[0099]

[0100] 3) Binder

[0101] The above binder serves to improve adhesion between electrode active material particles and adhesion between the electrode active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, polymethyl methacrylate, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, polyacrylic acid, and polymers in which hydrogens thereof are substituted with Li, Na, or Ca, or various copolymers thereof, and one of these alone or a mixture of two or more may be used.

[0102] The binder may be included in an amount of 0.1% to 10% by weight based on the total weight of the electrode active material layer, preferably 0.3% or more, 0.5% or more, 0.7% or more, or 1.0% or more by weight, and may also be 9.0% or less by weight, 8.5% or less by weight, 8.0% or less by weight, 7.5% or less by weight, 7.0% or less by weight, or 6.5% or less by weight.

[0103]

[0104] The above electrode can be manufactured according to a conventional electrode manufacturing method, except for using the above-described electrode active material powder. Specifically, it can be manufactured by applying an electrode slurry composition, prepared by dissolving or dispersing the above-described electrode active material powder and, optionally as needed, a binder, a conductive material (here, including carbon nanocables), and a dispersant in a solvent, onto an electrode current collector, and then drying and rolling.

[0105] The above solvent may be a solvent generally used in the relevant technical field, and may include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), dimethyl formamide (DMF), acetone, or water, and one of these alone or a mixture of two or more may be used. The amount of the above solvent used is sufficient if it is sufficient to dissolve or disperse the anode active material, conductive material, binder, and dispersant, taking into account the coating thickness of the slurry and the manufacturing yield, and to have a viscosity that can exhibit excellent thickness uniformity when coated for electrode manufacturing thereafter.

[0106] In addition, the electrode may also be manufactured by casting the electrode slurry composition onto a separate support and then laminating the film obtained by peeling off from the support onto an electrode current collector.

[0107]

[0108] lithium secondary battery

[0109] A lithium secondary battery according to one embodiment of the present invention will be described. The lithium secondary battery according to one embodiment of the present invention comprises the electrode of the present invention described above.

[0110] Specifically, the above lithium secondary battery comprises a positive electrode, a negative electrode positioned opposite the positive electrode, and a separator and an electrolyte interposed between the positive electrode and the negative electrode. Since the positive electrode and the negative electrode are identical to those previously described, a detailed description is omitted, and only the remaining components are described in detail below.

[0111] In addition, the lithium secondary battery may optionally further include a battery container that accommodates the electrode assembly of the positive electrode, negative electrode, and separator, and a sealing member that seals the battery container.

[0112]

[0113] In the above lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a pathway for the movement of lithium ions. Any separator typically used in lithium secondary batteries can be used without special limitations, and it is particularly desirable that it has low resistance to the movement of electrolyte ions and excellent electrolyte moisture retention capacity. Specifically, a porous polymer film, such as a porous polymer film made of a polyolefin-based polymer like ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof may be used. In addition, a conventional porous nonwoven fabric, such as a nonwoven fabric made of high-melting-point glass fiber or polyethylene terephthalate fiber, may be used. Furthermore, a coated separator containing ceramic components or polymer materials may be used to ensure heat resistance or mechanical strength, and it may optionally be used in a single-layer or multi-layer structure.

[0114]

[0115] In addition, the electrolytes used in the present invention may include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, etc., which are usable when manufacturing lithium secondary batteries, but are not limited to these.

[0116] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0117] The above organic solvent may be used without special restrictions as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the above organic solvent may include ester-based solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether-based solvents such as dibutyl ether or tetrahydrofuran; ketone-based solvents such as cyclohexanone; aromatic hydrocarbon-based solvents such as benzene and fluorobenzene; and carbonate-based solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethylmethyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC). Alcohol-based solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a straight-chain, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may include a double bond-directing ring or ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes may be used. Among these, carbonate-based solvents are preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of the battery, and a low-viscosity linear carbonate-based compound (e.g., ethylmethyl carbonate, dimethyl carbonate or diethyl carbonate, etc.) is more preferred.

[0118] The above lithium salt may be used without special restrictions as long as it is a compound capable of providing lithium ions used in lithium secondary batteries. Specifically, as the anion of the above lithium salt, F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - The lithium salt may be at least one selected from the group consisting of LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO2, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. It is preferable to use the lithium salt within the range of 0.1 to 2.0 M. When the concentration of the lithium salt falls within the above range, the electrolyte has appropriate conductivity and viscosity, so it can exhibit excellent electrolyte performance and lithium ions can move effectively.

[0119] In addition to the above electrolyte components, the above electrolyte may further include one or more additives for the purpose of improving the lifespan characteristics of the battery, suppressing the decrease in battery capacity, and improving the discharge capacity of the battery, such as, for example, haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, triamide hexaphosphate, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride. In this case, the above additives may be included in an amount of 0.1 to 5 weight% based on the total weight of the electrolyte.

[0120]

[0121]

[0122] The present invention will be explained in more detail below through examples. However, the following examples are intended to illustrate the present invention and do not limit the scope of the present invention.

[0123] Examples and Comparative Examples

[0124] Multiwalled carbon nanotubes were surface-treated with sulfuric acid (H2SO4) to prepare multiwalled carbon nanotubes A to F having functional group content as described in Table 1 below.

[0125] The functional group content of each of the multiwalled carbon nanotubes A to F was analyzed using X-ray photoelectron spectroscopy (XPS) (manufactured by Thermo Fisher Scientific (ESCA-02)), and after obtaining the O 1s spectrum under conditions of light source: Al-Kα (1486.6 eV), acceleration voltage: 1 Kv, 300 W, energy resolution: approximately 1.0 eV, minimum analysis area: 400 micro, and sputter rate 0.13 nm / min, the peak intensity values ​​for each peak are listed in Table 1 below.

[0126] Unit: Atomic % Multi-walled Carbon Nanotube A Multi-walled Carbon Nanotube B Multi-walled Carbon Nanotube C Multi-walled Carbon Nanotube D Multi-walled Carbon Nanotube E Multi-walled Carbon Nanotube FC-O Bond Content 0.8 0.9 0.3 0.9 0.4 0.5 C=O Bond Content 0.9 1.1 0.3 0.9 0.5 1.1 C=O Bond Content / CO Bond Content 1.1 3 1.2 2 1.0 1.0 1.2 5 2.2 Oxygen (O) Content 1.9 2.3 0.6 2.0 1.0 2.4 Carbon (C) Content 97.8 97.4 99.3 97.9 99.0 97.5 Aluminum (Al) Content 0.2 0.2 ---- Chlorine (Cl) Content 0.1 0.1 - 0.1 - 0.1

[0127]

[0128] Example 1: Preparation of anode

[0129] LiNi as the positive active material 0.6 Co 0.2 Mn 0.2 A cathode slurry was prepared by mixing a lithium nickel-based oxide having an O2 composition, the multi-walled carbon nanotube A as a conductive material, and PVdF as a binder in an N-methylpyrrolidone solvent in a weight ratio of 96.4:1.2:2.4.

[0130] Subsequently, the anode slurry was applied to one side of an aluminum current collector, dried at 130°C, and rolled once using a roll-to-roll rolling machine at a linear pressure of 1.6 ton / cm to manufacture an anode having an anode active material layer disposed on an aluminum current collector.

[0131]

[0132] Example 2: Preparation of Anode

[0133] A cathode was prepared in the same manner as in Example 1, except that the above-mentioned multi-walled carbon nanotube B was used as the conductive material.

[0134]

[0135] Example 3: Preparation of Anode

[0136] A cathode was prepared in the same manner as in Example 1, except that multi-walled carbon nanotube E was used as the conductive material.

[0137]

[0138] Comparative Example 1: Preparation of Anode

[0139] A cathode was prepared in the same manner as in Example 1, except that multi-walled carbon nanotube C was used as the conductive material.

[0140]

[0141] Comparative Example 2: Preparation of Anode

[0142] A cathode was prepared in the same manner as in Example 1, except that multi-walled carbon nanotube D was used as the conductive material.

[0143]

[0144] Comparative Example 3: Preparation of Anode

[0145] A cathode was prepared in the same manner as in Example 1, except that multi-walled carbon nanotube F was used as the conductive material.

[0146]

[0147] Experimental Example: Evaluation of Electrode Adhesion

[0148] For the anodes prepared according to Examples 1 and 2 and Comparative Examples 1 and 2 above, the 90° peel strength of the aluminum current collector and the anode active material layer was measured.

[0149] Specifically, each manufactured anode was cut to a width of 20 mm. Then, the adhesion was evaluated by measuring the average value of the 90° peel strength in the displacement range of 20 to 60 mm by peeling off the anode active material layer from the current collector using a UTM device.

[0150] The measurement results are shown in Table 2 below.

[0151] Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Adhesion [gf / 20mm] 61.78 40.22 35.13 27.32 17.71 19.40

[0152] Referring to Table 2 above, it can be seen that the anodes of Examples 1 to 3, which are manufactured by including multi-walled carbon nanotubes according to the present invention as a conductive material, have superior adhesion compared to the anodes of Comparative Examples 1 to 3.

Claims

1. The entire house; and It includes an electrode active material layer disposed on the above current collector; and The above electrode active material layer comprises an electrode active material, a conductive material, and a binder, and The above conductive material includes multi-walled carbon nanotubes, and The above multiwalled carbon nanotube is an electrode having a ratio of the content of C=O bonds to the content of CO bonds measured by X-ray photoelectron spectroscopy (XPS) of 1.05 to 2.

00.

2. In Claim 1, The above multi-walled carbon nanotube is an electrode having a C=O bond content of 0.4 atomic% to 2.0 atomic% as measured by X-ray photoelectron spectroscopy (XPS).

3. In Claim 1, The above multiwalled carbon nanotube is an electrode having a CO bond content of 0.35 atomic% to 1.2 atomic% as measured by X-ray photoelectron spectroscopy (XPS).

4. In Claim 1, The above multi-walled carbon nanotube is an electrode having an oxygen (O) content of 0.8 atomic% to 3.0 atomic% as measured by X-ray photoelectron spectroscopy (XPS).

5. In Claim 1, The above multi-walled carbon nanotube is an electrode having a carbon (C) content of 96 atomic% to 99.5 atomic% as measured by X-ray photoelectron spectroscopy (XPS).

6. In Claim 1, The above multi-walled carbon nanotube is an electrode having an aluminum (Al) content of 0.1 atomic% to 0.5 atomic% as measured by X-ray photoelectron spectroscopy (XPS).

7. In Claim 1, The above multi-walled carbon nanotube is an electrode having a chlorine (Cl) content of 0.05 atomic% to 0.2 atomic% as measured by X-ray photoelectron spectroscopy (XPS).

8. In Claim 1, The above multi-walled carbon nanotube has a BET specific surface area of ​​200 m² 2 / g to 350m 2 / g electrode.

9. In Claim 1, The electrode comprising the above multi-walled carbon nanotubes in an amount of 0.5% to 2.0% by weight based on the total weight of the electrode active material layer.

10. In Claim 1, The above electrode active material is an electrode that is a positive active material.

11. In Claim 1, The above electrode active material is an electrode that is a negative electrode active material.

12. A lithium secondary battery comprising the electrode of claim 1.