Negative electrode for lithium secondary battery, method for manufacturing the same, and lithium secondary battery comprising the same

Abstract

The present invention relates to a negative electrode for a lithium secondary battery, a manufacturing method thereof, and a lithium secondary battery including the same, the negative electrode including: a crystalline carbon layer; an amorphous carbon layer having a network structure formed on the crystalline carbon layer, and formed of disordered and non-crystalline carbon atoms; and lithium ions or lithium carbide compounds embedded in the amorphous carbon layer, and lithium metal electrodeposited around the lithium ions or lithium carbide compounds, wherein the amorphous carbon layer includes a carbon defect structure formed of electron-deficient carbon atoms, the crystalline carbon layer includes a plurality of carbon fibers, and when the amorphous carbon layer is analyzed by XPS, a ratio of a peak intensity originating from the carbon defect structure to a peak intensity originating from carbon having an sp 2 hybrid structure is 0.3 or more. The negative electrode of the present invention can provide a lithium secondary battery having a higher energy density, and can fundamentally prevent an electrolyte decomposition reaction and lithium dendrite formation.

Description

[0001] This application is a divisional application of PCT / KR2021 / 009356, an international PCT application filed on July 20, 2021. The original application was an invention patent application, which entered the Chinese national phase with application number 202180021644.7 and was entitled "Negative electrode for lithium secondary batteries, method of manufacturing the same and lithium secondary batteries comprising the same".

[0002] Cross-references to related applications

[0003] This application claims the benefits of Korean Patent Application No. 10-2020-0091886 filed with the Korean Intellectual Property Office on July 23, 2020, and Korean Patent Application No. 10-2020-0128634 filed with the Korean Intellectual Property Office on October 6, 2020, the disclosures of which are incorporated herein by reference in their entirety. Technical Field

[0004] This invention relates to a negative electrode for lithium secondary batteries, a method for manufacturing the same, and a lithium secondary battery comprising the same, wherein the negative electrode provides a lithium secondary battery with higher energy density and fundamentally prevents electrolyte decomposition reactions and lithium dendrite formation. Background Technology

[0005] Lithium-ion batteries have excellent performance characteristics (such as high energy density and long lifespan) and are currently used in most portable electronic devices. In addition, their applications are rapidly expanding to electric vehicles and high-capacity energy storage devices.

[0006] As the application fields of lithium-ion batteries expand, there is a growing need to develop next-generation lithium-ion batteries with higher energy densities than conventional lithium-ion batteries. As a next-generation lithium-ion battery with such high capacity and high energy characteristics, there has been a significant increase in interest in next-generation batteries such as lithium metal batteries, lithium-sulfur batteries, or lithium-air batteries using lithium metal anodes. For reference, lithium metal anodes have a high theoretical capacity (3860 mAh / g) and a low standard reduction potential (–3.040 V vs. SHE), thus enabling the achievement of high capacity and high energy density per unit volume / weight.

[0007] However, for next-generation batteries that use lithium metal anodes (such as lithium metal batteries), a solid electrolyte interface (SEI) is formed and consumed at the interface between the anode and the electrolyte according to the principles described below. This leads to electrolyte reduction and decomposition reactions and the formation of lithium dendrites in the form of dendrite protrusions, which causes the problem of low coulombic efficiency in the battery.

[0008] More specifically, during the electrochemical cycling process of a battery, dendritic lithium dendrites and dead lithium in the lithium metal anode grow and form three-dimensionally (e.g., in the form of protrusions) from the surface of the anode (e.g., the lithium metal active material layer formed as an additional thin film), which can lead to a significant loss of active material. Furthermore, due to its high reactivity, lithium metal reacts with the electrolyte solution and residual moisture to form a solid electrolyte interface (SEI) on the surface of the anode, and the process of increasing electrode surface area due to the formation of lithium dendrites and dead lithium, and thus the breaking and reforming of the SEI, repeats itself. Therefore, due to the electrolytic reduction decomposition reaction occurring in this process, continuous consumption of lithium metal and electrolyte occurs, which can lead to low coulombic efficiency and short cycle life of the lithium metal anode. Additionally, when protruding lithium dendrites penetrate the separator and grow, internal short circuits can occur, potentially leading to fire or explosion problems.

[0009] Furthermore, if the lithium metal film with a thickness of tens to hundreds of micrometers, which is typically embedded in the cell assembly process, is not used, the stable source of lithium disappears, and thus the aforementioned electrolyte decomposition reaction and dendrite formation reaction can be further aggravated.

[0010] Therefore, there is a continued need to develop next-generation lithium secondary batteries that exhibit higher energy density and associated high capacity and high energy characteristics, while effectively suppressing electrolyte decomposition reactions and lithium dendrite growth caused by the three-dimensional formation of lithium metal thin films as active material layers. Summary of the Invention

[0011] [Technical Issues]

[0012] One object of the present invention is to provide a negative electrode for lithium secondary batteries and a method for manufacturing the same, which can provide lithium secondary batteries with higher energy density and can fundamentally prevent electrolyte decomposition reactions and lithium dendrite formation.

[0013] Another object of the present invention is to provide a lithium secondary battery including the negative electrode, which not only has the same or higher level of high capacity and high energy characteristics as conventional lithium metal batteries, but also fundamentally suppresses electrolyte decomposition reactions and lithium dendrite formation caused by applying lithium metal thin film to the negative electrode.

[0014] [Technical Solution]

[0015] According to one aspect of the present invention, a negative electrode for a lithium secondary battery is provided, comprising: a crystalline carbon layer; an amorphous carbon layer having a network structure formed on the crystalline carbon layer; lithium ions or lithium carbide compounds embedded in the amorphous carbon layer; and lithium metal electrodeposited around the lithium ions or lithium carbide compounds.

[0016] According to another aspect of the present invention, a method for manufacturing the negative electrode of the present invention is provided, the method comprising: The step of subjecting a crystalline carbon fabric containing multiple carbon fibers to oxygen plasma treatment to oxidize the surface; The step of reacting the crystalline carbon fabric, nitrogen precursor, and metal precursor with the surface oxidized to form a carbon fabric coated with a metal-organic framework (MOF); The step of calcining the carbon fabric coated with a metal-organic framework at a temperature above 700°C to carbonize the carbon fabric; and The steps include electrochemically reacting the carbonized carbon fabric in an electrolyte containing lithium salt to bind lithium ions or lithium carbide compounds to the carbonized carbon fabric and electrodepositing lithium metal around the lithium ions or lithium carbide compounds.

[0017] According to another aspect of the present invention, a lithium secondary battery is provided, comprising: a positive electrode having a positive electrode current collector and a lithium composite oxide-type positive electrode active material layer formed on the positive electrode current collector; a negative electrode of the present invention; a separator between the positive electrode and the negative electrode; and an electrolyte.

[0018] [Beneficial Effects]

[0019] The negative electrode of the present invention not only excludes or minimizes the three-dimensionally formed individual active material layers (e.g., individual lithium metal films), but also forms and includes an amorphous carbon layer with a network structure, which includes carbon defect structures formed by electron-deficient carbon atoms through a predetermined process of chemically treating a crystalline carbon layer.

[0020] By forming an amorphous carbon layer containing such carbon defect structures, the active material layer (e.g., lithium metal thin film) formed in the form of a three-dimensional attached thin film in existing lithium metal batteries can be eliminated or reduced. Therefore, the formation and growth of lithium dendrites and dead lithium from such lithium metal thin films can be fundamentally suppressed. Furthermore, since the carbon defect structure in the amorphous carbon layer used as the active material layer is formed by multiple electron-deficient carbon atoms, the Fermi level is lowered to the valence band, thus fundamentally suppressing electrolytic reduction decomposition reactions.

[0021] Furthermore, in the amorphous carbon layer, because the carbon defect structure contains multiple electron-deficient carbon atoms, multiple lithium ions and / or lithium compounds containing them can be inserted, while simultaneously donating electrons to these carbon atoms. Moreover, by using such lithium ions as nuclei, lithium metal can be uniformly electrodeposited around them. Therefore, this amorphous carbon layer can induce uniform lithium electrodeposition formed two-dimensionally on the same plane, resulting in its usability as an active material layer with a lithium-ion source.

[0022] Therefore, when the negative electrode of this invention is applied, a battery can be provided that has the same or higher levels of high capacity and high energy characteristics as conventional lithium metal batteries, while fundamentally suppressing the electrolytic reduction decomposition reaction and lithium dendrite growth caused by the lithium metal thin film in the form of an additional three-dimensional thin film. This battery exhibits excellent cell performance and lifespan characteristics and is well-suited for use as a next-generation battery for applications such as electric vehicles. Attached Figure Description

[0023] Figure 1 This is a diagram illustrating an example of a negative electrode for a lithium secondary battery according to one embodiment; Figure 2a and 2b These are figures showing the SEM and TEM analysis results of the surfaces of the negative electrodes for lithium secondary batteries manufactured in Comparative Example 1 and Example 1, respectively; Figures 3a to 3c This is a figure showing the analysis results of elemental analysis of carbon paper and negative electrode by EDS and the corresponding SEM images for each manufacturing step of Example 1. Figure 4 This is a graph showing the XPS analysis results of the negative electrodes formed in Comparative Example 1 and Example 1, respectively; Figure 5 This is a graph showing the Raman spectral analysis results of the negative electrodes formed in Comparative Example 1 and Example 1, respectively; Figure 6 This is a graph showing the BET analysis results of the electrode surfaces of Example 1 and Comparative Example 1; Figure 7 This is a graph showing the results of evaluating the extent of electrolyte decomposition reaction using lithium secondary batteries from Comparative Example 2 and Examples 2 and 4; Figure 8a and 8b The graphs show the TEM-EDX analysis results of the electrode surface after the first cycle in Experimental Example 4, respectively, in order to evaluate the degree of electrolyte decomposition reaction in the batteries of Comparative Example 2 and Example 2. Figure 9a and 9b This is a graph showing the SEM analysis results of the electrode surface states of Comparative Example 1 and Example 1 after lithium-ion intercalation and lithium metal electrodeposition in the batteries of Comparative Example 2 and Example 2; and Figure 10a and 10b This is a graph showing the cell performance evaluation results of the lithium secondary batteries of Example 2 and Comparative Example 2. Detailed Implementation

[0024] Throughout this specification, when a component is referred to as "comprising" a certain component, it means that the component may further include other components without excluding them, unless otherwise stated. The terms "about or approximately" or "substantially" are intended to have a meaning close to a value or range specified by permissible error and are intended to prevent any unreasonable or unfair use by any third party of the precise or absolute values ​​disclosed for the purpose of understanding the invention. The terms "steps to do something" or "steps of something" as used in this specification do not imply steps for doing something.

[0025] Throughout the specification, the term "combination" as used in the description of the Markush type refers to a mixture or combination of one or more components selected from the group of components described in the Markush type, and thus means that the invention includes one or more components selected from the Markush group.

[0026] Based on the above definitions, embodiments of the present invention will be described in detail. However, these embodiments are presented for illustrative purposes only, and the present invention is not limited thereto, and is defined only by the claims described below.

[0027] Negative electrode for lithium secondary batteries

[0028] According to one embodiment of the present invention, a negative electrode for a lithium secondary battery is provided, comprising: a crystalline carbon layer; an amorphous carbon layer having a network structure formed on the crystalline carbon layer; lithium ions or lithium carbide compounds embedded in the amorphous carbon layer; and lithium metal electrodeposited around the lithium ions or lithium carbide compounds.

[0029] The negative electrode of this embodiment is similar to the method described below, and is manufactured by the following process: plasma oxidation treatment of the surface of the crystalline carbon fabric providing the crystalline carbon layer, and surface coating and carbonization of the metal-organic framework (MOF).

[0030] As a result of this chemical treatment, a large number of electron-deficient carbon atoms are formed on the crystalline carbon layer, and an amorphous carbon layer with a network structure can also be formed, which includes carbon defect structures containing these electron-deficient carbon atoms.

[0031] Furthermore, in the amorphous carbon layer, while the metal-organic framework is carbonized, a large number of nanopores (vacancies) with sizes of 0.5 to 2 nm, or 0.8 to 1.5 nm, or 1.0 to 1.2 nm can be formed in the carbon defect structure.

[0032] For reference, the amorphous properties of the amorphous carbon layer, the formation of carbon defect structures (formation of electron-deficient carbon atoms), and the formation of multiple nanopores can be confirmed by TEM analysis, XPS analysis, Raman spectroscopy, and BET analysis, which will be described later.

[0033] As described above, due to the formation of a high-density carbon defect structure comprising multiple electron-deficient carbon atoms in the amorphous carbon layer, the Fermi level of the electrode can be reduced to the valence band. As a result, electrolytic reduction decomposition reactions on the electrode surface can be fundamentally suppressed.

[0034] Furthermore, in the amorphous carbon layer, a large number of electron-deficient carbon atoms are contained in the carbon defect structure, forming numerous nanopores with sizes ranging from 0.5 to 2 nm, more specifically from 1.0 to 1.2 nm. Therefore, in the amorphous carbon layer, electrons are supplied from the conduction band of lithium (which is used to donate electrons to carbon atoms) to the valence band of the carbon defect structure, and lithium originating from a large number of lithium ions and / or lithium-ion-containing lithium compounds (e.g., lithium carbide compounds in the form of Li3C8) can be well adsorbed and bound to the electron-deficient carbon atoms and intercalated. Additionally, the lithium ions intercalated in this way act as a nucleus, and lithium metal can be uniformly electrodeposited around the carbon defect structure centered on the lithium ions.

[0035] In one example, lithium ions and the lithium metal electrodeposited around them can be two-dimensionally embedded and formed into multiple nanopores, and can be used as a lithium-ion source for the negative electrode. Therefore, in the negative electrode of one embodiment, the lithium-ion source can be two-dimensionally contained in the same plane (or inside) as the amorphous carbon layer. Thus, the amorphous carbon layer itself can be used as an active material layer having a lithium-ion source contained in a two-dimensional plane, resulting in the elimination or significant reduction of the addition of a lithium metal film formed in the form of a three-dimensional additional thin film.

[0036] As described above, while reducing the addition of lithium metal films in the form of three-dimensional additional thin films, a lithium-ion source can be formed in two dimensions in the carbon defect structure in the amorphous carbon layer. This makes it possible to fundamentally suppress the formation and growth of lithium dendrites and dead lithium from individual lithium metal films additionally formed on the negative electrode.

[0037] It has been confirmed that, through the above-described technical principles, the negative electrode of one embodiment can fundamentally suppress electrolyte decomposition reactions and lithium dendrite growth, and lithium secondary batteries including such a negative electrode can have the same or higher levels of high capacity and high energy characteristics as conventional lithium metal batteries.

[0038] Therefore, when the negative electrode of one embodiment is applied, the problems caused by electrolyte decomposition reaction and lithium dendrite growth can be fundamentally suppressed, and higher capacity and high energy characteristics can be achieved. Therefore, it is very suitable for use as a next-generation battery for electric vehicles and the like.

[0039] On the other hand, the various properties of the aforementioned amorphous carbon layer (e.g., non-crystalline), the formation of carbon defect structures (formation of electron-deficient carbon atoms), and the formation of multiple nanopores can be confirmed by TEM analysis, XPS analysis, Raman spectroscopy analysis, and BET analysis of the surface of the negative electrode (e.g., the amorphous carbon layer).

[0040] First, TEM analysis confirmed that the amorphous carbon layer is formed from disordered and non-crystalline carbon atoms. Furthermore, TEM images confirmed that it forms as multiple graphene layers with thicknesses of approximately 1 to 100 nm or approximately 2 to 70 nm, and that it forms as multiple defect layers.

[0041] Furthermore, XPS analysis of the amorphous carbon layer confirmed the formation of numerous nanopores (vacancies) due to the carbonization process following the formation of the metal-organic framework during manufacturing. Additionally, the XPS analysis revealed individual peaks originating from carbon defect structures containing electron-deficient carbon atoms, such as nanopores. In particular, the intensity ratio of these individual peaks to peaks originating from carbon with sp2 orbital hybridization (normal carbon in an electron-deficient state) was greater than 0.3, or 0.35 to 0.50, or 0.4 to 0.45, confirming the formation of electron-deficient carbon atoms and the carbon defect structures they encompass at a considerable proportion and high density.

[0042] Furthermore, Raman spectroscopy analysis of the amorphous carbon layer confirmed that the 1500 cm⁻¹ region originated from carbon defect structures. -1 Below, or 1100 to 1500 cm -1 The peak (D band; the peak originating from electron-deficient carbon in carbon defect structures) shows a value equal to or greater than 1500 cm⁻¹. -1 And 2000 cm -1 The intensity of the peaks observed below (G band; peaks originating from normal carbon with a graphite structure). More specifically, the intensity ratio of the peaks in the D band to the peaks in the G band can be greater than 1, or 1 to 1.5, or 1.1 to 1.3.

[0043] Even through Raman spectroscopy analysis, it can be confirmed that electron-deficient carbon atoms and carbon defect structures including them are formed in a considerable proportion and at a high density on the amorphous carbon layer contained in the negative electrode of one embodiment.

[0044] In addition, based on the Raman spectral analysis results of the amorphous carbon layer, at 2500 cm⁻¹ -1 Above, or 2500 to 2900 cm -1 or 2600 to 2800 cm -1 Additional broad peaks can be identified in the region. This confirms that amorphous carbon layers can have shapes comprising multiple carbon layers.

[0045] Furthermore, the formation of multiple nanopores contained in the amorphous carbon layer can be confirmed even by using BET surface analysis with nitrogen adsorption, and the specific analytical results are described in the test examples described below.

[0046] As described above, in the negative electrode of one embodiment, lithium ions and / or lithium compounds are two-dimensionally embedded through the carbon defect structure and nanopores due to the high-density formation of carbon defect structures comprising multiple nanopores and electron-deficient carbon atoms. Furthermore, lithium metal electrodeposited around these lithium ions can be two-dimensionally contained on the amorphous carbon layer. The lithium ions and lithium metal can be used as the lithium-ion source for the negative electrode.

[0047] As described above, while avoiding or significantly reducing the application of lithium metal films formed as separate three-dimensional films on the negative electrode, an amorphous carbon layer includes a high-density lithium-ion source grown and formed therein in a two-dimensional manner, and it can itself be used as an active material layer. Therefore, a lithium secondary battery including a negative electrode according to one embodiment can exhibit high capacity and high energy characteristics comparable to or higher than conventional lithium metal batteries. Furthermore, it can fundamentally suppress the problem of lithium dendrites growing three-dimensionally from a lithium metal film formed as a separate film to the outside of the electrode, or the reduction and decomposition reaction of the electrolyte caused by the addition of a lithium metal film. Thus, a lithium secondary battery including a negative electrode according to one embodiment is very suitable as a next-generation battery that fundamentally solves the problems involved in existing lithium metal batteries, etc.

[0048] On the other hand, in the negative electrode of one of the above embodiments, since the crystalline carbon layer supporting the amorphous carbon layer is formed by crystalline carbon fabric or the like, it includes multiple carbon fibers and can have a thickness of 1 to 50 μm, 2 to 30 μm, or 1 to 10 μm. Therefore, the negative electrode can exhibit suitable mechanical and electrochemical properties.

[0049] The crystalline carbon layer can be used as a negative electrode current collector, while supporting the amorphous carbon layer used as an active material layer. Thus, in one embodiment of the negative electrode, a separate metal current collector can be omitted.

[0050] However, in one embodiment, the negative electrode may consist only of a crystalline carbon layer serving as a current collector and an amorphous carbon layer serving as an active material layer including the aforementioned lithium-ion source. It may further include a metal current collector, such as a copper current collector, a nickel current collector, or a stainless steel (SUS) current collector, to support the crystalline carbon layer. Since this additional metal current collector follows the construction of metal current collectors in the electrodes of a typical lithium-ion secondary battery, its additional description will be omitted.

[0051] at the same time, Figure 1 This is a diagram illustrating an example of a negative electrode for a lithium secondary battery according to one embodiment described above. (See reference) Figure 1 One embodiment of the negative electrode includes a negative electrode plate comprising a crystalline carbon layer, an amorphous carbon layer, lithium ions or lithium carbide compounds, and lithium metal, and may include a negative electrode tab protruding from the negative electrode plate. In this case, the negative electrode tab is integrally formed with the negative electrode plate, and may be formed to include the same crystalline carbon layer and amorphous carbon layer as the negative electrode plate.

[0052] However, according to this embodiment of the negative electrode, since the negative electrode plate and the negative electrode tab protruding from it are composed only of the aforementioned carbon layer, the bonding strength with conventional metal leads may be deteriorated. That is, in the past, welding methods were mainly used to join the negative electrode tab and the metal leads, but in one embodiment of the negative electrode, since the negative electrode tab is based on a carbon material that is a non-metallic component, it is difficult to apply such welding methods, and thus insufficient bonding strength cannot be obtained.

[0053] However, similar to the specific embodiments described above, since the negative electrode tab made of carbon layer is bonded to the metal lead by a conductive epoxy resin that exhibits excellent bonding properties to both metal and carbon materials, it has been confirmed that it can exhibit excellent bonding properties between the two.

[0054] At this point, there are no particular limitations on the type of conductive epoxy resin that can be used for bonding between the negative electrode tab and the metal lead, and any resin or composition thereof previously known to exhibit excellent conductivity and electrolyte resistance and suitable for bonding conductive components to batteries, capacitors, and devices can be used. One embodiment of such a conductive epoxy resin may include a resin composition comprising an epoxy resin that cures at room temperature (e.g., 20 to 30°C) and exhibits bonding properties, and a conductive metal filler (e.g., silver microparticles). Furthermore, it goes without saying that various epoxy resins or compositions thereof known to exhibit conductivity and electrolyte resistance can be used.

[0055] On the other hand, according to the general battery structure, the metal leads connected to the aforementioned negative electrode tab, specifically its carbon layer, can be made of copper and / or nickel, or suitably an alloy of copper and nickel.

[0056] Methods for manufacturing lithium metal anodes

[0057] On the other hand, according to another embodiment of the present invention, a method for manufacturing a negative electrode for a lithium secondary battery as described above can be provided. This method for manufacturing a negative electrode for a lithium secondary battery may include: Oxygen plasma treatment was applied to crystalline carbon fabric containing multiple carbon fibers to oxidize the surface. The crystalline carbon fabric, nitrogen precursor, and metal precursor are reacted to oxidize the surface to form a carbon fabric coated with a metal-organic framework (MOF). The carbon fabric coated with a metal-organic framework is calcined and carbonized at a temperature above 700°C; and The carbonized carbon fabric is electrochemically reacted in an electrolyte containing lithium salt to bind lithium ions or lithium carbide compounds to the carbonized carbon fabric and to electrodeposit lithium metal around the lithium ions or lithium carbide compounds.

[0058] According to other manufacturing methods, the crystalline carbon fabric corresponding to the crystalline carbon layer can be subjected to oxygen plasma treatment to oxidize the surface, and the oxidized crystalline carbon fabric, nitrogen precursor, and metal precursor can be reacted to form a carbon fabric coated with a metal-organic framework (MOF). Then, by calcining and carbonizing it at high temperature to remove the metal-organic framework, a carbon defect structure formed by electron-deficient carbon atoms and an amorphous carbon layer including it can be formed in the corresponding portion of the formed metal-organic framework.

[0059] Then, the carbonized carbon fabric is electrochemically reacted in an electrolyte containing lithium salt, embedding lithium ions or lithium carbide compounds into the carbonized carbon fabric and electrodepositing lithium metal around it, thus forming a two-dimensional lithium ion source in the amorphous carbon layer, which makes it possible to manufacture an anode exhibiting the above-mentioned excellent properties.

[0060] In particular, as described above, lithium ions or lithium metal can be embedded and formed in two dimensions around carbon defect structures in the amorphous carbon layer. Therefore, unlike active material layers such as lithium metal films that are added separately in three dimensions, the amorphous carbon layer itself can be used as an active material layer, serving as a lithium ion source for the negative electrode without causing the growth of three-dimensional protruding lithium dendrites.

[0061] In other manufacturing methods, carbon paper formed from carbon fibers with a diameter of 1 to 8 μm or 3 to 5 μm can be used as the crystalline carbon fabric, for example, and any other equivalent crystalline carbon fabric can be used without particular limitation.

[0062] Furthermore, in the oxygen plasma treatment step, one or both surfaces of the crystalline carbon fabric can be surface-treated with oxygen plasma or a mixed gas plasma containing oxygen and an inert gas (e.g., argon) to perform surface oxidation, which allows for the definition of portions that subsequently form metal-organic frameworks and carbon defect structures.

[0063] Furthermore, in the step of forming the carbon fabric coated with a metal-organic framework, there are no particular limitations on the type of metal-organic framework or the types of nitrogen and metal precursors used to form it. This is because, in another embodiment of the manufacturing method, the metal-organic framework is carbonized in a subsequent step to remove all remaining metals and organic components other than carbon, and the carbon components only contribute to the formation of carbon defect structures.

[0064] However, specific examples of metal-organic frameworks that can be formed in the above steps may include at least one compound selected from the group consisting of: Zn2DOT (MOF-74), Cu2(BDC-Br)2(H2O)2 (MOF-101), Zn4O(BTB)2 (MOF-177), [Fe3O(BDC)3(DMF)3][FeCl4].(DMF)3 (MOF-235), Al(OH)(BPYDC) (MOF-253), Zn4O(BDC)3.7DEF.3H2O (IRMOF-1 (MOF-5)), Zn4O(TPDC)3.17DEF.2H2O (IRMOF-16), Zr6O6(BDC)6 (UiO-66), Zr6O6(BPDC)6 (UiO-67), Zr6O6(TPDC)6 (UiO-68), Al(OH)(BDC)(MIL-53), Al(OH)(BDC-NH2) (MIL-53(Al)-NH2), Fe3O(MeOH)3(O2CCH=CHCO2)3.MeCO2.nH2O(MIL-88A), Fe3O(MeOH)3(O2C(CH2)2CO2)3.AcO.(MeOH) 4.5 (MIL-88-Fe), 2Fe3O(OH)(H2O)2(BDC-Me2)3 (MIL-88B-4CH3), Fe III 3O(H2O)2F.(BTC)2.nH2O (MIL-100-Fe), Cr3O(H2O)2F.(BDC)3. nH2O (MIL-101), Cu3(BTC)2 (HKUST-1 (MOF-199)), Gd2(BDC-NH2)3(DMF)4 (LIC-10), Zn(MIM)2 (ZIF-8), Zn(FIM)2 (ZIF-90), Cu2(PZDC)2(4,4'-BPY) (CPL-2), [Cu(HFBBA)(phen)2](H2HFBBA)2(H2O)(HCO2) (F-MOF-1) and Cu 24 (m-BDC) 24 (DMF) 14 (H2O) 10 (MOP-1). In addition, it can form all kinds of metal-organic frameworks that can be formed on carbon layers without any particular limitation.

[0065] However, in order to properly form carbon defect structures through the formation and carbonization of such metal-organic frameworks, it is preferable to form metal-organic frameworks in the form of metal zeolite-imidazolium structures, such as ZIF-8.

[0066] Furthermore, those skilled in the art can appropriately select and use the corresponding nitrogen precursor and metal precursor according to the type of metal-organic framework. For example, when forming a metal-organic framework in the form of a metal zeolite-imidazolium structure, imidazolium compounds (e.g., methylimidazolium) are preferably used as the nitrogen precursor, and in addition, various nitrogen precursors can be selected and used according to the type of metal-organic framework.

[0067] Furthermore, those skilled in the art can obviously select and use appropriate metal-containing compounds based on the type of metal-organic framework described above, regarding the types of metal precursors that react with nitrogen precursors.

[0068] Examples of metal precursors include compounds containing at least one metal selected from the group consisting of zinc (Zn), aluminum (Al), copper (Cu), zirconium (Zr), iron (Fe), chromium (Cr), and gadolinium (Gd), and various salts of these metals (e.g., nitrates, hydroxides, or sulfates), or compounds in the form of hydrates and / or solvates thereof, without particular limitation.

[0069] On the other hand, in the step of forming the carbon fabric coated with the above-mentioned metal-organic framework, the surface-oxidized crystalline carbon fabric, nitrogen precursor, and metal precursor can be reacted in water or a polar organic solvent (e.g., methanol) under stirring, and after the reaction, a washing and drying step using a polar organic solvent can be further performed. The specific conditions for performing these washing and drying steps are described in detail in the examples described below.

[0070] On the other hand, after forming a carbon fabric coated with a metal-organic framework, the carbon fabric can be calcined and carbonized at a temperature of 700°C or higher, or 700 to 1300°C, or 800 to 1200°C. When this carbonization step is performed, the metal-organic framework is carbonized and removed, and an amorphous carbon layer containing the aforementioned carbon defect structure can be formed.

[0071] Optionally thereafter, an inorganic impurity removal step using hydrochloric acid, a washing step, and a drying step may be added, the result may be electrochemically reacted in an electrolyte containing lithium salt, and lithium ions or lithium carbide compounds may be combined and embedded into the carbonized carbon fabric, and lithium metal may be electrodeposited around it by using lithium ions as a core, thereby creating a negative electrode of one embodiment.

[0072] This electrochemical reaction can occur as a separate lithium-ion intercalation reaction or lithium metal electrodeposition reaction during the manufacture of the negative electrode, but it can be replaced by the initial charge / discharge step after the manufacture of the lithium secondary battery. For example, lithium ions or lithium carbide compounds combine through an electrochemical reaction that occurs naturally during the initial charge / discharge step, thereby allowing the intercalation of lithium ions, etc.

[0073] On the other hand, after forming a negative electrode layer including a crystalline carbon layer and an amorphous carbon layer by the above method, the negative electrode layer can be cut into a shape including a desired negative electrode plate and a negative electrode tab protruding from it according to the general method for forming a negative electrode.

[0074] Subsequently, conductive epoxy resin is coated onto the bonding portion of the negative electrode tab, and a metal lead is placed on the epoxy resin. Drying and curing then follow, thereby bonding the negative electrode tab to the metal lead. During this curing process, the epoxy resin can be cured at room temperature (20 to 30°C), or alternatively, it can be cured under heat or pressure at temperatures above 50°C or between 50 and 100°C. This allows for the fabrication of a negative electrode with a good bond between the non-metallic negative electrode tab and the metal lead.

[0075] Lithium secondary batteries

[0076] According to another embodiment of the present invention, a lithium secondary battery including the above-described negative electrode is provided. The lithium secondary battery of another embodiment includes: a positive electrode containing a positive electrode current collector and a lithium composite oxide-based positive electrode active material layer formed on the positive electrode current collector; the negative electrode of the above-described embodiment; a separator between the positive electrode and the negative electrode; and an electrolyte.

[0077] The lithium secondary battery of the other embodiment described above includes the negative electrode of the first embodiment described above, and thus can exhibit the characteristics of fundamentally suppressing the growth of lithium dendrites and electrolyte decomposition reaction, while having excellent high capacity and high energy characteristics.

[0078] The negative electrode used in lithium secondary batteries is described above, and the battery components other than the negative electrode will be described in detail below.

[0079] The electrolyte in a lithium secondary battery can be a liquid electrolyte (i.e., an electrolyte solution).

[0080] Electrolyte solutions may include non-aqueous organic solvents and lithium salts.

[0081] Non-aqueous organic solvents act as a medium through which ions participating in the electrochemical reactions of the battery can move.

[0082] As non-aqueous organic solvents, carbonate solvents, ester solvents, ether solvents, ketone solvents, alcohol solvents, or aprotic solvents can be used. Carbonate solvents may include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), and butyl carbonate (BC), etc., and ester solvents may include methyl acetate, ethyl acetate, n-propyl acetate, ethyl 1,1-dimethylacetate, methyl propionate, ethyl propionate, γ-butyrolactone, decanolactone, valproic acid, methylhydroxyvalproic acid, and caprolactone, etc. Ether solvents may include dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, dimethoxyethane, 2-methyltetrahydrofuran, and tetrahydrofuran, etc., and ketone solvents may include cyclohexanone, etc. In addition, alcohol solvents may include ethanol and isopropanol, and aprotic solvents may include nitriles such as R-CN (where R is a straight-chain, branched or cyclic hydrocarbon group from C2 to C20, which may include double bonds, aromatic rings or ether bonds), amides such as dimethylformamide, dioxolane such as 1,3-dioxolane and sulfolane, etc.

[0083] Non-aqueous organic solvents may be used alone or in combination of one or more. When one or more solvents are used in combination, the mixing ratio may be appropriately adjusted according to the required battery performance, as will be widely understood by those skilled in the art.

[0084] Furthermore, when using carbonate solvents, it is advantageous to use a mixture of cyclic and chain carbonates. In this case, the cyclic and chain carbonates are mixed in a volume ratio of about 1:1 to about 1:9, thereby exhibiting excellent performance characteristics of the electrolyte solution.

[0085] The electrolyte solution may further contain vinylene carbonate and / or ethylene carbonate compounds of formula 2 below to improve battery life: [Chemical Formula 2]

[0086] In formula 2, R7 and R8 are each independently hydrogen, halogen group, cyano (CN), nitro (NO2) or C1-C5 fluoroalkyl, and at least one of R7 and R8 is halogen group, cyano (CN), nitro (NO2) or C1-C5 fluoroalkyl.

[0087] Representative examples of ethylene carbonate compounds include difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate, and fluoroethylene carbonate. When further using ethylene carbonate or ethylene carbonate compounds, their lifespan can be improved by appropriately controlling their usage.

[0088] In the electrolyte solution of a lithium secondary battery, lithium salts are dissolved in an organic solvent to serve as a lithium-ion source in the battery, thereby enabling the lithium secondary battery of one embodiment to operate substantially and facilitating the movement of lithium ions between the positive and negative electrodes.

[0089] As lithium salts, lithium salts widely used in electrolyte solutions are typically used. For example, LiPF6, LiBF4, LiSbF6, LiAsF6, LiC4F9SO3, LiClO4, LiAlO2, LiAlCl4, and LiN(C) can be used. x F 2x+1 SO2)(C y F 2y+1 SO2 (where x and y are natural numbers), LiCl, LiI, LiB(C2O4)2 (lithium bis(oxalate)borate; LiBOB) or combinations thereof.

[0090] Furthermore, the concentration of lithium salt in the electrolyte solution can be controlled within the range of 0.1 to 5.0 M. Within this range, the electrolyte solution can have suitable conductivity and viscosity, and lithium ions can move efficiently within the lithium secondary battery. However, this is merely an example, and the invention is not limited thereto.

[0091] The electrolyte solution can be in the form of an impregnation within a porous membrane positioned between the negative and positive electrodes. Here, the membrane separates the positive and negative electrodes and provides a pathway for lithium ion movement; any membrane can be used without limitation, as long as it is commonly used as a membrane in lithium-ion secondary batteries. That is, a membrane with excellent electrolyte solution retention capabilities while exhibiting low resistance to the movement of electrolyte ions can be used.

[0092] The separator can be selected from materials such as glass fiber, polyester, Teflon, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), or combinations thereof, and can be nonwoven or woven fabric. For example, in lithium secondary batteries, polyolefin polymer separators, such as polyethylene and polypropylene, are mainly used, and to ensure heat resistance or mechanical strength, coated separators including ceramic components or polymer materials can be used, and optionally, single-layer or multi-layer structures can be used.

[0093] Regardless of the electrolyte (electrolyte solution) of the lithium secondary battery, the positive electrode may include a positive current collector and a layer of positive active material located on the positive current collector.

[0094] The positive electrode is manufactured by mixing active materials and binders, optionally conductive materials and fillers, in a solvent to prepare an electrode slurry, and then coating the electrode slurry onto each positive electrode current collector. Since the above electrode manufacturing method is well known in the art, its detailed description will be omitted herein.

[0095] There are no particular restrictions on the positive electrode active material, as long as it is a lithium composite oxide material capable of reversibly inserting and deintercalating lithium ions. For example, it may include one or more composite oxides of cobalt, manganese, nickel, or combinations of these metals and lithium.

[0096] In a more specific instance, as a positive electrode active material, any compound represented by any of the following chemical formulas can be used. Li a A 1-b R b D2 (where 0.90 ≤ a ≤ 1.8 and 0 ≤ b ≤ 0.5); Li a E 1-b R b O 2-c D c (where 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5 and 0 ≤ c ≤ 0.05); LiE 2-b R b O 4-c D c (where 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05); Li a Ni 1-b-c Co b R c D α (where 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05 and 0 < α ≤ 2); Li a Ni 1-b-c Co b R c O 2-α Z α (where 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05 and 0 < α < 2); Li a Ni 1-b-c Co b R c O 2-α Z2 (where 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05 and 0 < α < 2); Li a Ni 1-b-c Mn b R c D α (where 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05 and 0 < α ≤ 2); Li a Ni 1-b-c Mn bR c O 2-α Z α (where 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05 and 0 < α < 2); Li a Ni 1-b-c Mn b R c O 2-α Z2 (where 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05 and 0 < α < 2); Li a Ni b E c G d O2 (where 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5 and 0.001 ≤ d ≤ 0.1); Li a Ni b Co c Mn d G e O2 (where 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0 ≤ d ≤ 0.5 and 0 ≤ e ≤ 0.1); Li a NiG b O2 (where 0.90 ≤ a ≤ 1.8 and 0.001 ≤ b ≤ 0.1); Li a CoG b O2 (where 0.90 ≤ a ≤ 1.8 and 0.001 ≤ b ≤ 0.1); Li a MnG b O2 (where 0.90 ≤ a ≤ 1.8 and 0.001 ≤ b ≤ 0.1); Li a Mn2G b O4 (where 0.90 ≤ a ≤ 1.8 and 0.001 ≤ b ≤ 0.1); QO2; QS2; LiQS2; V2O5; LiV2O5; LiTO2; LiNiVO4; Li (3-f) J2(PO4)3 (0 ≤ f ≤ 2); Li (3-f) Fe2(PO4)3 (0 ≤ f ≤ 2); and LiFePO4.

[0097] In the above chemical formulas, A is Ni, Co, Mn or a combination thereof; R 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; E is Co, Mn or a combination thereof; Z is 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; T is Cr, V, Fe, Sc, Y or a combination thereof; J is V, Cr, Mn, Co, Ni, Cu or a combination thereof.

[0098] Of course, compounds with a coating on their surface can also be used, or mixtures of the above-mentioned compounds with a coating compound can be used. The coating may include a coating element compound, such as a coating element oxide, hydroxide, coating element hydroxyl oxide, coating element oxycarbonate, or coating element basic carbonate. The compounds forming these coatings can be amorphous or crystalline. As coating elements included in the coating, Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or mixtures thereof can be used. As for the coating formation process, any coating method can be used, as long as it allows coating by means that the use of these elements in the compound will not adversely affect the physical properties of the positive electrode active material (e.g., spraying or dipping). Since this is something that will be widely understood by those skilled in the art, its detailed description will be omitted.

[0099] Positive electrode current collectors are typically manufactured to a thickness of 3 to 500 μm. There are no particular limitations on the positive electrode current collector, as long as it possesses high conductivity without causing chemical changes in the corresponding battery, and it can be formed from materials such as stainless steel, aluminum, nickel, titanium, calcined carbon, or materials formed by surface treatment of aluminum or stainless steel with carbon, nickel, titanium, or silver. The current collector can have micro-protrusions and depressions formed on its surface to enhance the adhesion of the positive electrode active material, and it can be formed in various forms, such as films, sheets, foils, meshes, porous bodies, foams, and nonwoven structures.

[0100] There are no particular restrictions on conductive materials, as long as they are conductive and do not cause chemical changes in the corresponding battery. For example, graphite, such as natural graphite and artificial graphite; carbon black, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black and thermal cracking carbon black; conductive fibers, such as carbon fibers and metal fibers; metal powders such as fluorinated carbon powder, aluminum powder and nickel powder; conductive whiskers, such as zinc oxide and potassium titanate; conductive metal oxides, such as titanium oxide; conductive materials such as polyphenylene derivatives.

[0101] One embodiment of the lithium secondary battery can be used not only as a unit cell for powering small devices, but also as a unit cell in medium to large-sized battery modules comprising multiple battery cells. Furthermore, it can be used to construct battery packs including this battery module.

[0102] Preferred embodiments, comparative examples, and test examples for evaluating the present invention are described below. However, the following embodiments are merely preferred embodiments of the present invention, and the present invention is not limited to the following embodiments.

[0103] Example 1: Manufacturing of the negative electrode for lithium secondary batteries

[0104] Purchase carbon paper (HCP010N, Shanghai Hesen Electric Co. Ltd. CN) and perform surface oxidation on both the front and back sides of the carbon paper using oxygen plasma treatment. The plasma treatment is performed as follows: plasma treatment is applied to both the front and back sides for 15 minutes each while a mixed gas of oxygen and argon is flowing through the paper.

[0105] Next, at room temperature, the surface-oxidized carbon paper was placed in 100 mL of methanol containing 13.136 g (8 eq) of 2-methylimidazole, and the mixture was stirred for 6 hours. Then, 100 mL of methanol containing 5.95 g (1 eq) of zinc nitrate hexahydrate was added to the solution, and the mixture was stirred for 12 hours. This resulted in carbon paper coated with a zinc-organic framework (ZLF-8).

[0106] After stirring, remove the carbon paper coated with the zinc-organic framework and wash it with pure methane 3 to 5 times.

[0107] The carbon paper was then held and dried in an oven at approximately 80°C under vacuum for 12 hours. The process before drying was set as one, and the zinc-organic framework coating was repeated a total of two times.

[0108] To carbonize the dry carbon paper, heat the carbon paper at 5°C for 5 minutes. -1 The temperature was increased to 1000℃ at a certain rate, and then calcined and carbonized in a nitrogen atmosphere for 5 hours.

[0109] The carbonized carbon paper was stirred in a 2M hydrochloric acid solution for 6 hours to remove impurity minerals (Zn). The carbon paper was then removed from the hydrochloric acid, immersed in deionized water (DI), washed three times for 20 minutes each time, and finally dried in a vacuum oven at 70°C for 7 hours.

[0110] The carbon paper thus prepared was subjected to an electrochemical reaction in a lithium salt-containing electrolyte under the conditions of the experimental example described below to prepare a negative electrode layer.

[0111] The negative electrode layer was cut to make it 4 cm thick. A rectangular negative electrode plate with a specification of 3.4 cm and a 1 cm protrusion from one side of the negative electrode plate. The shape of the 0.5 cm rectangular negative electrode tab is as follows: Figure 1 As shown.

[0112] On the negative electrode tab cut in this manner, a commercially available conductive silver epoxy paste (trade name: EPO-TEK H21D) is uniformly coated to a thickness of approximately 5 μm. Before the coated paste dries, a copper / nickel alloy metal lead with a thickness of 100 μm is placed over the coated portion, and then the portion is rolled at room temperature (approximately 25°C) under a pressure of 1 MPa, and finally heated in a vacuum oven at 80°C for 1 hour. This bonding of the negative electrode tab and the metal lead produces the negative electrode of Example 1.

[0113] Example 2: Manufacturing of a lithium secondary battery including the negative electrode of Example 1

[0114] A separator (polypropylene porous polymer substrate) was inserted between the negative electrode and the lithium metal reference electrode of Example 1 to manufacture a button cell. An electrolyte solution containing 1M LiPF6, dissolved in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) / fluoroethylene carbonate (FEC) / vinyl carbonate (VC) in a volume ratio of 89:10:1, was injected into the button cell to manufacture a semi-cell.

[0115] Examples 3 and 4: Negative electrode for lithium secondary batteries and manufacturing of lithium secondary batteries

[0116] The process prior to zinc-organic framework coating was carried out under the same methods and conditions as in Example 1.

[0117] Subsequently, in order to carbonize the dried carbon paper, the carbon paper was heated to 5°C for 5 minutes. -1 The temperature was increased to 700°C at a certain rate, and then calcined and carbonized in a nitrogen atmosphere for 5 hours.

[0118] The carbonized carbon paper was stirred in a 2M hydrochloric acid solution for 6 hours to remove impurity minerals (Zn). The carbon paper was then removed from the hydrochloric acid, immersed in deionized water (DI), washed three times for 20 minutes each time, and finally dried in a vacuum oven at 70°C for 7 hours.

[0119] The carbon paper thus prepared was subjected to an electrochemical reaction in a lithium salt-containing electrolyte under the conditions of the experimental examples described below to prepare a negative electrode layer. This negative electrode layer was then subjected to cutting and bonding steps in the same manner as in Example 1 to manufacture the negative electrode of Example 3.

[0120] The half-cell of Example 4 was manufactured in the same manner as in Example 2, except that the negative electrode of Example 3 was used instead of the negative electrode of Example 1.

[0121] Comparative Examples 1 and 2: Manufacturing of Anodes and Lithium-ion Secondary Batteries

[0122] The carbon paper used as the initial raw material in Example 1 was used as the negative electrode of Comparative Example 1, and was cut and bonded to metal leads. A lithium secondary battery containing the carbon paper instead of the negative electrode of Example 1 was manufactured in the same manner as in Example 2, and was used as the lithium secondary battery of Comparative Example 2.

[0123] Experimental Example 1: SEM and TEM Analysis of the Negative Electrode Surface

[0124] The surfaces of the negative electrodes for lithium secondary batteries manufactured in Comparative Example 1 and Example 1 were analyzed by SEM and TEM, respectively, and the SEM and TEM images are shown in the figures. Figure 2a and 2b .

[0125] First, refer to Figure 2a SEM images confirmed that the negative electrode of Comparative Example 1 was an electrode composed of fibers with a diameter of 3–5 μm. In contrast, the reference electrode… Figure 2b It was confirmed that the negative electrode of Example 1 was formed by a network of defective carbon layers on the fiber surface of the crystalline carbon layer.

[0126] In addition, refer to Figure 2a The TEM image shows that in the electrode of Comparative Example 1, the 100 crystal plane is observed, which is a regular carbon crystal plane (the lattice spacing of the 100 crystal plane is 0.341 nm). FFT analysis reveals that the electrode consists of a crystalline carbon layer with a very regular arrangement of carbon atoms. In contrast, the reference... Figure 2b The TEM images show that multiple defect layers with a thickness of about 1.03 nm were generated on the electrode surface of Example 1, and unlike Comparative Example 1, FFT analysis shows that disordered and amorphous carbon was generated.

[0127] Experimental Example 2: EDS Analysis of the Negative Electrode

[0128] For each manufacturing step in Example 1, elemental analysis of the carbon paper and negative electrode was performed using EDS, and the analysis results are shown together with their corresponding SEM images. Figures 3a to 3c The elemental contents of each manufacturing step based on the analysis results are summarized in Table 1 below. During the EDS elemental analysis, the contents of four elements—carbon, oxygen, nitrogen, and zinc—were analyzed to confirm whether the zinc-organic framework (ZLF-8) was formed and removed through carbonization during the manufacturing process.

[0129] Specifically, the elemental analysis results of (a) the carbon paper in its initial raw material state ( Figure 3a (b) Elemental analysis results before carbonization Figure 3b (c) Elemental analysis results after carbonization to form the final anode. Figure 3c They were distinguished and summarized separately.

[0130] [Table 1]

[0131] Refer to Table 1 and Figures 3a to 3c Elemental analysis confirmed that the reaction of the zinc and nitrogen precursors (methylimidazole) before the carbonization step formed and coated a zinc-organic framework on the carbon paper, which was then completely removed by carbonization and calcination, leaving no residue in the final negative electrode.

[0132] Therefore, it was confirmed that the characteristics of the negative electrode finally formed in Example 1 depended only on the formation of carbon defect structures, and not on the zinc-organic framework.

[0133] Experimental Example 3: Analysis of carbon defect structure and nanopores in the negative electrode (XPS, Raman spectroscopy and BET surface analysis)

[0134] First, the negative electrodes formed in Comparative Example 1 and Example 1 were analyzed by XPS, and the analysis results are shown in... Figure 4 . refer to Figure 4 It was confirmed that in Example 1, a large number of nanopores (vacancies) were formed on the electrode due to the process of zinc-organic framework formation and coating, followed by carbonization and removal.

[0135] Furthermore, based on the XPS analysis results of Comparative Example 1 and Example 1, carbon defect structures including electron-deficient carbon atoms were confirmed, particularly the individual peaks (non-conjugated C peaks) originating from nanopores. In particular, the analysis results of Example 1 showed that the intensity ratio of the individual peak originating from this carbon defect structure to the peak originating from carbon with sp2 orbital hybridization (normal carbon without electron-deficient states) was 0.403, which was stronger than the intensity ratio of 0.175 in Comparative Example 1.

[0136] Thus, it was confirmed that a carbon defect structure, including nanopores and electron-deficient carbon atoms, was formed at a high density in the electrode of Example 1.

[0137] Meanwhile, Raman spectroscopy analysis was performed on the negative electrodes formed in Comparative Example 1 and Example 1, and the analysis results are shown in... Figure 5 .

[0138] refer to Figure 5 It was confirmed that in the electrode of Example 1, the 1100 to 1500 cm⁻¹ region originated from carbon defect structures. -1The peak (D band; the peak originating from electron-deficient carbon in carbon defect structures) is greater than or equal to that at a depth greater than 1500 cm⁻¹. -1 and less than 2000 cm -1 The intensity of the peak observed at (G band; the peak originating from normal carbon with a graphite structure) is defined as I. D / I G Its strength ratio is as high as 1.124. In contrast, in the electrode of Comparative Example 1, it was confirmed that the strength ratio was determined by I. D / I G The intensity of the peak is as low as 0.788 compared to the defined peak.

[0139] Based on the results of Raman spectroscopy analysis, it was confirmed that in the negative electrode of Example 1, electron-deficient carbon atoms and carbon defect structures including them were formed on the amorphous carbon layer in a considerable proportion and at a high density.

[0140] Furthermore, based on the Raman spectroscopy analysis results of Example 1, at approximately 2700 cm⁻¹ -1 Nearby, the 2D peak used to determine the number of graphene layers was further confirmed with considerable intensity. This peak was not observed in Comparative Example 1. The point where the intensity ratio of the 2D peak to the G peak was approximately 0.34 confirmed that the amorphous carbon layer included in the electrode of Example 1 was formed into a shape comprising multiple graphene layers. For reference, a 2D / G ratio of approximately 4 is generally known to represent monolayer graphene, and values ​​below 1 represent multilayer graphene.

[0141] Finally, BET analysis was performed on the electrode surfaces of Example 1 and Comparative Example 1, and the results are shown in... Figure 6 More specifically, nitrogen adsorption was used for BET porosity analysis. (Reference) Figure 6 It was confirmed that pores of 20–120 nm were developed in the electrode of Comparative Example 1, while nanopores of approximately 1.1 nm were mainly developed in the electrode of Example 1. The nanopores of Example 1 were confirmed to correspond to the high-density carbon defect structure identified by XPS and Raman spectroscopy analysis.

[0142] Experimental Example 4: Evaluation of the Degree of Electrolyte Decomposition Reaction

[0143] First, the batteries from Examples 2, 4, and Comparative Example 2 were used at 1.0 mA cm⁻¹. -2 Electrochemical reactions were carried out under 0V voltage cutoff conditions. Lithium ions were inserted into the negative electrodes of Examples 1, 3, and Comparative Example 1, followed by deintercalation. The results are shown in... Figure 7 . refer to Figure 7It was confirmed that in Examples 2 and 4, the lithium-ion insertion-extraction coulombic efficiencies in the first cycle were approximately 85% and 73.2%, respectively, which appeared to be higher than the 69.7% in Comparative Example 2. This confirmed that the electrolyte decomposition reaction consumed in the formation of the solid electrolyte interface (SEI) initially accumulated on the negative electrode surface could be greatly suppressed in the examples.

[0144] In addition, the electrode surfaces after the first cycle were analyzed by TEM-EDS, and the results are shown in the figure. Figure 8a (Comparative Example 2) and Figure 8b (Example 2). Reference Figure 8a and 8b It was confirmed that in Comparative Example 2, the solid electrolyte interface caused by the electrolyte decomposition reaction had a thickness of about 40-55 nm, while in Example 2, the solid electrolyte interface was confirmed to be about 10-25 nm, thus confirming that the electrolyte decomposition reaction was greatly reduced.

[0145] Experimental Example 5: Evaluation of Electrode Surface Condition after Lithium Metal Electrodeposition

[0146] First, the batteries from Example 2 and Comparative Example 2 were used at 5 μAh cm⁻¹. -2 3mAh cm -2 and 9mAh cm -2 1.0mA cm -2 An electrochemical reaction was carried out under the conditions of [condition missing], in which lithium ions were embedded into the negative electrodes of Example 1 and Comparative Example 1, and lithium metal electrodeposition was performed. After this reaction, the electrode surface state of Comparative Example 2 and Example 2 was analyzed by SEM, and the results are shown in [figure missing]. Figure 9a and 9b For reference, the first image in each figure shows the embedding and electrodeposition reactions at 5 μAh cm⁻¹. -2 SEM images were taken at 3 mAh cm⁻¹, and the second image was taken at 3 mAh cm⁻¹. -2 The following images were taken at 9 mAh cm⁻¹. -2 The following will proceed.

[0147] refer to Figure 9a The first and second images show that, in the comparative example, lithium aggregates vertically on each carbon fiber and grows in a dendritic pattern. Referring to the third and fourth images, it can be seen that at 9 mAh cm⁻¹... -2 At this capacity, the grown lithium dendrites block the entire upper surface of the electrode, and lithium with a thickness of about 17 μm accumulates in areas where lithium ions frequently move (where mass transfer often occurs), rather than filling the interior of the electrode one after another.

[0148] In comparison, reference Figure 9bAs can be seen in the embodiments, the lithium core is uniformly grown in two dimensions over the entire area of ​​the electrode (first to second images), and even at 9 mAh cm⁻¹ -2 The interior of the electrode is also densely filled, but it does not actually block the top surface of the electrode.

[0149] Experiment Example 6: Performance Evaluation of Lithium Secondary Batteries

[0150] The cell performance of the lithium secondary batteries of Example 2 and Comparative Example 2 was evaluated, and the results are shown in the figures below. Figure 10a and 10b For reference, Figure 10a The results of full-cell testing under 100 μl excess electrolyte conditions are shown. Figure 10b It showed 17 μl (4.0 μl mAh) -1 The results of the full cell test under low electrolyte conditions are shown. For reference, the results of each evaluation are compared with and shown in a reference example where only copper current collectors are used to form the negative electrode.

[0151] refer to Figure 10a It was confirmed that even under conditions of excess electrolyte, Reference Example and Comparative Example 2 experienced continuous lithium source consumption due to uneven electrodeposition morphology and the formation of dead lithium, and exhibited a rapid decline in discharge capacity. In contrast, the battery of Example 2 was confirmed to have excellent discharge capacity retention in the initial stage.

[0152] Additionally, refer to Figure 10b Because the batteries in Reference Example and Comparative Example 2 consumed a large amount of initial electrolyte used for the current collector, they exhibited unstable discharge capacity curves from the beginning of the initial cycle. However, because the battery in Example 2 did not consume a large amount of initial electrolyte used for the current collector, it exhibited stable cycle characteristics. Furthermore, it was confirmed that due to its electrodeposition morphology, which makes it difficult to form dead lithium, it exhibited excellent discharge capacity even under lean conditions.

[0153] Experiment Example 7: Evaluating the bonding strength between the negative electrode tab and the metal lead

[0154] In the negative electrode of Example 1, a sample of the joint between the negative electrode tab and the metal lead was prepared. An increased load was applied at a speed of 200 mm / min using an adhesive strength testing device (SHIMADZU AGS-1kNX model, Japan), and the adhesive strength of the joint was measured. Based on these measurements, a good joint between the negative electrode tab and the metal lead was evaluated when an adhesive strength of 1.3 kgf / 5 mm or higher was observed.

[0155] The evaluation results of the negative electrode in Example 1 confirmed that the bonding strength was greater than 1.3 kgf / 5 mm, and the bonding between the negative electrode tab and the metal lead was excellent.

Claims

1. A negative electrode for a lithium secondary battery, comprising: Crystalline carbon layer; An amorphous carbon layer with a network structure is formed on the crystalline carbon layer, and the amorphous carbon layer is formed of disordered and non-crystalline carbon atoms; as well as Lithium ions or lithium carbide compounds embedded in the amorphous carbon layer, and lithium metal electrodeposited around the lithium ions or lithium carbide compounds. The amorphous carbon layer includes carbon defect structures formed by electron-deficient carbon atoms, and The crystalline carbon layer comprises multiple carbon fibers, and When the amorphous carbon layer is analyzed by XPS, the peak intensity originating from the carbon defect structure / originating from the sp 2 The peak intensity ratio of carbons in the orbital hybrid structure is above 0.

3.

2. The negative electrode for a lithium secondary battery as described in claim 1, wherein: Nanopores with a size of 0.5 to 2 nm are formed in the carbon defect structure.

3. The negative electrode for a lithium secondary battery as described in claim 1, wherein: When the amorphous carbon layer was subjected to Raman spectroscopy analysis, the 1100 to 1500 cm⁻¹ region originating from the carbon defect structure... -1 The peak (D band) shows a value equal to or greater than 1500 cm⁻¹. -1 And 2000 cm -1 The intensity of the peak observed below (G band).

4. The negative electrode for a lithium secondary battery as described in claim 3, wherein: The intensity ratio of the peak in the D band to the peak in the G band is defined as 1 to 1.

5.

5. The negative electrode for a lithium secondary battery as described in claim 3, wherein: The amorphous carbon layer comprises multiple graphene layers, and The Raman spectroscopy analysis results showed that at 2500 cm⁻¹, originating from the multiple graphene layers... -1 There are additional peaks in the above regions.

6. The negative electrode for a lithium secondary battery as described in claim 1, wherein: The crystalline carbon layer has a thickness of 1 to 50 μm.

7. The negative electrode for a lithium secondary battery as described in claim 1, wherein: The amorphous carbon layer has a thickness of 1 to 100 nm.

8. The negative electrode for a lithium secondary battery as described in claim 1, wherein: The lithium ions or lithium carbide compounds are bonded to the lithium metal in a two-dimensional plane on the same plane as the amorphous carbon layer.

9. The negative electrode for a lithium secondary battery as described in claim 1, wherein: Lithium, derived from the lithium ion or lithium carbide compound, donates electrons to the electron-deficient carbon atom and binds to the carbon defect structure.

10. The negative electrode for a lithium secondary battery as described in claim 9, wherein: The lithium carbide compound is in the form of Li3C8.

11. The negative electrode for a lithium secondary battery as described in claim 1, It also includes a metal current collector that supports the crystalline carbon layer.

12. A method for manufacturing the negative electrode according to claim 1, the method comprising: Oxygen plasma treatment was applied to crystalline carbon fabric containing multiple carbon fibers to oxidize the surface. The crystalline carbon fabric, nitrogen precursor, and metal precursor are reacted to oxidize the surface to form a carbon fabric coated with a metal-organic framework. The carbon fabric coated with a metal-organic framework is calcined and carbonized at a temperature above 700°C; and The carbonized carbon fabric is electrochemically reacted in an electrolyte containing lithium salt to bind lithium ions or lithium carbide compounds to the carbonized carbon fabric and to electrodeposit lithium metal around the lithium ions or lithium carbide compounds.

13. The method for manufacturing the negative electrode as described in claim 12, wherein, The metal precursor comprises a compound containing at least one metal selected from the group consisting of zinc (Zn), aluminum (Al), copper (Cu), zirconium (Zr), iron (Fe), chromium (Cr), and gadolinium (Gd).

14. The method for manufacturing the negative electrode as described in claim 12, wherein, The metal-organic framework is selected from Zn2DOT, Cu2(BDC-Br)2(H2O)2, Zn4O(BTB)2, [Fe3O(BDC)3(DMF)3][FeCl4].(DMF)3, Al(OH)(BPYDC), Zn4O(BDC)3.7DEF.3H2O, Zn4O(TPDC)3.17DEF.2H2O, Zr6O6(BDC)6, Zr6O6(BPDC)6, Zr6O6(TPDC)6, Al(OH)(BDC), Al(OH)(BDC-NH2), Fe3O(MeOH)3(O2CCH=CHCO2)3.MeCO2.nH2O, Fe3O(MeOH)3(O2C(CH2)2CO2)3.AcO.(MeOH) 4.5 , 2Fe3O(OH)(H2O)2(BDC-Me2)3, Fe III 3O(H2O)2F.(BTC)2.nH2O, Cr3O(H2O)2F.(BDC)3.nH2O, Cu3(BTC)2, Gd2(BDC-NH2)3(DMF)4, Zn (MIM)2, Zn(FIM)2, Cu2(PZDC)2(4,4'-BPY), [Cu(HFBBA)(phen)2](H2HFBBA)2(H2O)(HCO2) and Cu 24 (m-BDC) 24 (DMF) 14 (H2O) 10 At least one compound from the group consisting of.

15. The method for manufacturing the negative electrode as described in claim 12, further comprising: Perform the step of removing inorganic impurities using hydrochloric acid.

16. A lithium secondary battery, comprising: The positive electrode includes a positive electrode current collector and a lithium composite oxide positive electrode active material layer formed on the positive electrode current collector; The negative electrode according to any one of claims 1 to 11; and A membrane between the positive and negative electrodes; and an electrolyte.

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