Fiber Matrix Electrode, Method for Manufacturing the Same, and Secondary Battery Including the Same

Abstract

The present invention relates to an electrode for a secondary battery using a fiber matrix composed of conductive fibers as an electrode substrate, and a secondary battery including the same. The electrode comprises an electrode active material formed on the surface of the fiber matrix, wherein the electrode active material comprises secondary particles or single-crystal particles and may be covalently bonded to the fiber surface via an interface layer or grown directly on the fiber surface. The fiber matrix may include metal fibers, carbon fibers, metal-coated fibers, etc., and a metal plating layer such as nickel, copper, or tin may be formed on a portion of the surface. When the electrode is a positive electrode, it may include various positive active materials such as NCM, LFP, or NCA, and when the electrode is a negative electrode, it may include graphite or a mixture of graphite and silicon. Furthermore, the active material may be formed into a multilayer structure in which the type, particle size, shape, or composition differs from layer to layer. The secondary battery including the electrode may include a non-aqueous electrolyte or a sulfide-based, oxide-based, or polymer-based solid electrolyte, and may not substantially include a current collector.

Description

Technology Field

[0001] The present invention relates to the field of secondary battery technology, and more specifically, to an electrode for a secondary battery comprising a structure in which a fiber matrix made of conductive fibers is utilized as an electrode substrate and an electrode active material is covalently bonded or directly grown on the surface of the fiber matrix, and a secondary battery comprising the same. Background Technology

[0002] Rechargeable batteries are used as core power sources in various applications, such as portable electronic devices, electric vehicles, and energy storage systems, and the stability of the electrode structure and interfacial characteristics are considered important to ensure high energy density and long lifespan.

[0003] Conventional electrodes are manufactured by applying a slurry of active material, conductive material, and binder onto a metal current collector, followed by drying and rolling. While this process is suitable for mass production, it is prone to low adhesion between the active material and the current collector and a decrease in conductivity caused by the binder. In particular, when increasing electrode thickness or applying high-capacity electrodes, problems such as electrochemical performance degradation and shortened cycle life due to non-uniformity of internal electrode density and increased interfacial resistance are exacerbated.

[0004] Furthermore, the occurrence of microcracks and active material detachment in electrodes due to repeated charge-discharge cycles exacerbate interfacial resistance and act as a major cause of impaired long-term stability. Accordingly, there is a growing need for new electrode design technologies capable of securing the mechanical stability of the electrode structure, strengthening the bonding force between the active material and the electrode substrate, and improving the internal conductive network of the electrode.

[0005] Furthermore, the interfacial characteristics between the electrolyte and the electrode also significantly affect battery performance. Poor contact or adverse reactions occurring at the electrolyte-electrode interface lead to increased interfacial resistance and degradation, which in turn degrades long-term cycle stability and output characteristics. Therefore, electrode technology capable of enhancing the bonding strength of the electrolyte-electrode interface, along with electrode structural stability, is required. The problem to be solved

[0006] The present invention aims to solve problems such as reduced electrode density, detachment of active material particles, and increased interfacial resistance caused by the limitations of conventional slurry-coated electrodes. Since existing electrodes rely on binders and conductive materials to attach particles, the inactive volume increases, and particle detachment and interfacial instability occur due to repeated charge-discharge cycles, making it difficult to implement high-load electrodes and secure long-life characteristics. In addition, there were technical limitations in forming stable interfaces with current collector-free structures or with single-crystal and secondary particle-based active materials.

[0007] Accordingly, the present invention aims to suppress interfacial resistance and improve stability by integrating the interface between the electrode and the active material through the direct growth of the active material on the fiber surface or the formation of covalent bonds based on a conductive fiber matrix, and by implementing a covalent bond or direct growth structure with a solid electrolyte as needed. Through this, a lightweight electrode structure capable of collecting current without a current collector can be realized, and high energy density and long lifespan characteristics can be achieved simultaneously. means of solving the problem

[0008] An electrode for a secondary battery according to one embodiment of the present invention comprises a fiber matrix substrate made of conductive fibers and an electrode active material formed on the surface of the fiber matrix substrate, wherein the electrode active material comprises at least one of a secondary particle covalently bonded to the fiber matrix substrate and a primary particle directly formed on the surface of the fiber matrix substrate.

[0009] The conductive fiber may be one or more of pitch-based carbon fibers, PAN-based carbon fibers, metal fibers, conductive polymer fibers, and metal-coated fibers in which metal is coated on the surface of insulating fibers.

[0010] The fiber matrix may be at least one of a plain weave structure, a woven fabric, a nonwoven fabric, a knitted structure, a quasi-woven structure, a laminated structure, a three-dimensional structure, or an integral structure.

[0011] The fiber matrix may include a metal plating layer comprising at least one of nickel, copper, cobalt, iron, tin, or aluminum on at least a portion of its surface.

[0012] When the above electrode is an anode, the metal plating layer may include one or more of nickel, aluminum, and iron, and when the above electrode is a cathode, the metal plating layer may include one or more of tin and copper.

[0013] The above electrode is a positive electrode, and the electrode active material may include at least one of NCM, high-nickel NCM, NCA, LFP, manganese-rich NCM, LMO, HVBM (High-volume Blended Manganese), lithium-excess layered oxide or LFMP, layered oxide for sodium-ion batteries, Prussian blue compound, polyanion compound or high-voltage spinel compound.

[0014] The above electrode active material includes secondary particles and is covalently bonded to the surface of the fiber matrix via an interfacial layer existing at the boundary between the primary particles of the secondary particles, and the covalent bond may be one or more of silane coupling, electrochemical bonding, carboxyl group-metal oxide bonding, or crosslinking agent reaction-based bonding.

[0015] The above electrode active material includes single-crystal particles, and the single-crystal particles can be directly formed on the surface of the fiber matrix by heat treatment or electrochemical crystallization reaction after deposition of the metal precursor and the lithium precursor and fixed at the interface.

[0016] The above electrode is a negative electrode, and the electrode active material comprises graphite or a mixture of graphite and silicon, and the graphite or the mixture of graphite and silicon may be electrochemically bonded via an interfacial layer formed on the surface of a fiber matrix or after surface modification, or may be coated on the surface of a fiber matrix.

[0017] The above electrode active material is formed in two or more layers, and each layer may differ in at least one of the type of active material, particle size, mixing ratio of secondary particles and single crystals, or mixing ratio of heterogeneous active materials.

[0018] Another embodiment of the present invention is a method for manufacturing an electrode for a secondary battery, comprising the steps of: preparing a fiber matrix composed of conductive fibers (S1); preparing a secondary particle active material (S2); pre-treating the surface of the fiber matrix to introduce at least one functional group among -OH, -COOH, and -NH2 (S3); pre-treating the surface of the secondary particle active material to introduce at least one functional group among -OH, -COOH, and -NH2 into an interface layer existing at the boundary between primary particles constituting the secondary particles (S4); coating the secondary particle active material onto the surface of the fiber matrix (S5); and forming a covalent bond with the fiber matrix through coupling or electrochemical bonding via an interface layer existing at the boundary between primary particles of the secondary particles (S6).

[0019] After the fiber matrix preparation step, the method may additionally include a step (S11) of plating metal on the surface of the fiber matrix.

[0020] The above secondary particle active material may include at least one of NCM, high-nickel NCM, NCA, LFP, manganese-rich NCM, LMO, HVBM, lithium-excess layered oxide, LFMP, layered oxide for sodium-ion batteries, Prussian blue compound, polyanion compound, or high-voltage spinel compound.

[0021] A method for manufacturing an electrode for a secondary battery according to another embodiment of the present invention may include the steps of: preparing a fiber matrix composed of conductive metal fibers (S1); pre-treating the surface of the fiber matrix to introduce at least one functional group among -OH, -COOH, and -NH2 (S3); depositing at least one metal precursor and a lithium precursor on the surface of the fiber matrix (H3); growing a single-crystal active material on the surface of the fiber matrix by sintering or heat-treating the metal precursor and the lithium precursor (H4); and heat-treating the fiber matrix on which the single-crystal active material has grown to improve interfacial stability, crystallinity, and mechanical strength of the electrode structure (H5).

[0022] The above single-crystal active material comprises at least one of NCM, NCA, or lithium-excess layered oxide, and the sintering can be performed in an oxygen atmosphere of 700°C or higher and 850°C or lower.

[0023] The fiber matrix above may be nickel fiber or stainless steel fiber.

[0024] The above single-crystal active material is LFP or LMFP (LiM 1-x Fe x PO4, 0 < x ≤ 1, where M is at least one of Mn, Co, and Ni), and the sintering can be performed under an inert atmosphere or a weak reducing atmosphere at 500 ℃ or higher and 650 ℃ or lower.

[0025] The metal precursor comprises at least one of nickel, cobalt, manganese, and iron, and the lithium precursor may be LiOH or Li2CO3.

[0026] Another embodiment of the present invention relates to a method for manufacturing an electrode for a secondary battery, comprising the steps of: preparing a fiber matrix composed of conductive fibers (S1); pre-treating the surface of the fiber matrix to introduce at least one functional group among -OH, -COOH, and -NH2 (S3); preparing graphite and introducing -OH or -COOH functional groups to the surface by oxidation treatment, plasma treatment, or electrochemical oxidation (G1); coating the surface-treated graphite onto the surface of the fiber matrix (G2); and forming a covalent bond or chemical adhesion between the graphite and the fiber matrix through electrochemical interface activation or a coupling agent reaction (G3).

[0027] The present invention provides a secondary battery comprising the electrode described above.

[0028] The above secondary battery may include a non-aqueous liquid electrolyte.

[0029] The above secondary battery may include at least one of a sulfide-based, oxide-based, or polymer-based solid electrolyte.

[0030] The above solid electrolyte may be a polymer-based solid electrolyte that is covalently or electrochemically bonded to -OH, -COOH, and -NH2 functional groups formed on the electrode surface, or is grown directly on the electrode surface through the deposition and heat treatment of a solid electrolyte precursor.

[0031] The above electrode can perform the current collection function itself, with the fiber matrix substrate.

[0032] The above secondary battery may not substantially include a current collector. Effects of the invention

[0033] According to the present invention, by fixing an electrode active material via a covalent bonding method using a fiber matrix composed of conductive fibers, the detachment of the active material within the electrode can be prevented and interfacial stability can be significantly improved. Accordingly, structural collapse during repeated charge and discharge cycles can be minimized, and the amount of binder used can be reduced, thereby simultaneously improving electrode density and energy density.

[0034] Furthermore, by directly growing the active material on the fiber surface or fixing it in a single-crystal form, the conductive path and interfacial resistance can be optimized, thereby simultaneously securing high power characteristics and long lifespan characteristics. In addition, since the fiber matrix functions as a current collector, a lightweight structure can be realized by eliminating the current collector; moreover, by directly growing the solid electrolyte on the electrode surface or covalently bonding it, interfacial contact resistance can be reduced, and the stability of the solid electrolyte-based battery can be improved.

[0035] Therefore, the present invention can provide a secondary battery electrode and a battery that simultaneously satisfy high energy density, high power output, lightweight, and long lifespan characteristics, and can be effectively utilized in various applications such as solid electrolyte batteries, current collector-free structures, and flexible electrodes. Brief explanation of the drawing

[0036] FIG. 1 is a cross-sectional view and a plan view illustrating an electrode for a secondary battery according to one embodiment of the present invention. FIG. 2 is a figure illustrating an electrode active material of secondary particles according to one embodiment of the present invention. FIG. 3 is a flowchart illustrating a method for manufacturing an electrode for a secondary battery according to another embodiment of the present invention. FIG. 4 is a flowchart illustrating a method for manufacturing an electrode for a secondary battery according to another embodiment of the present invention. FIG. 5 is a flowchart illustrating a method for manufacturing an electrode for a secondary battery according to another embodiment of the present invention. FIG. 6 is a diagram showing the cross-sectional structure of an electrode laminate (100) according to one embodiment of the present invention. FIG. 7 is a top view of an anode and a cathode according to an embodiment of the present invention. Specific details for implementing the invention

[0037] Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings. Although the present invention may be subject to various modifications and embodied in various forms, the embodiments described below are merely examples to aid in understanding the present invention and are not limited thereto.

[0038] FIG. 1 is a cross-sectional view and a plan view illustrating an electrode for a secondary battery according to one embodiment of the present invention.

[0039] An electrode (1) for a secondary battery according to one embodiment of the present invention comprises a fiber matrix substrate (10) made of conductive fibers and an electrode active material (20) formed on the surface of the fiber matrix substrate, wherein the electrode active material comprises at least one of a secondary particle covalently bonded to the fiber matrix substrate and a primary particle directly formed on the surface of the fiber matrix substrate.

[0040] The conductive fiber may be one or more of pitch-based carbon fibers, PAN-based carbon fibers, metal fibers, conductive polymer fibers, and metal-coated fibers in which metal is coated on the surface of insulating fibers.

[0041] The conductive fibers described above may include pitch-based or PAN-based carbon fibers, metal fibers, conductive polymer fibers, or metal-coated fibers in which a metal plating layer is formed on an insulating fiber, and each fiber provides various characteristics depending on the purpose. For example, pitch-based carbon fibers provide high electrical conductivity and structural strength, making them suitable for high-power electrodes, while PAN-based carbon fibers offer excellent flexibility and mechanical stability. Metal fibers provide conductivity sufficient to replace current collectors, and conductive polymer fibers are suitable for implementing flexible electrode structures. Additionally, metal-coated fibers can ensure a balance between the flexibility and conductivity of the substrate, thereby increasing the degree of freedom in structural design.

[0042] In the present invention, pitch-based carbon fibers may preferably be used as the conductive fibers. Pitch-based carbon fibers possess high crystallinity and excellent electrical conductivity, and when utilized as a fiber matrix substrate, they exhibit excellent interfacial reactivity with active materials, making them suitable for realizing covalent bonds and direct growth structures. Furthermore, based on high thermal stability and mechanical strength, they can maintain their structure even during high-temperature sintering processes and can be effectively applied to lightweight electrode structures that do not include current collectors.

[0043] The fiber matrix (10) may be at least one of a plain weave structure, a woven fabric, a nonwoven fabric, a knitted structure, a quasi-woven structure, a laminated structure, a three-dimensional structure, or an integral structure.

[0044] The fiber matrix (10) can be implemented in various shapes and structures, and each structure can be classified according to the arrangement method of the fibers, mechanical properties, conductivity, ease of manufacturing, etc.

[0045] First, the plain weave structure is the most basic type of fabric, formed by the intersecting of warp and weft threads in a 1:1 ratio, and provides a dense and uniform surface, which is advantageous for the uniform distribution and fixation of electrode active materials. The fabric is a fiber structure woven by regularly intersecting warp and weft threads, encompassing all general fabric forms, and is effective in ensuring excellent mechanical strength and conductivity.

[0046] Nonwoven fabrics are sheet-shaped materials produced by physically or chemically bonding fibers without weaving threads. They possess excellent porosity and flexibility, and are suitable for improving electrolyte permeability and large-area processing. Knitted structures are formed by creating loops with a single thread and are advantageous for applications such as wearable electrodes due to their high elasticity and flexibility.

[0047] Semi-woven structures possess warp and weft directions like fabrics but are partially fixed without a complete weave through methods such as heat fusion, bonding, or compression; they can be described as structures that strike a balance between the strength of fabrics and the processing convenience of non-woven fabrics. Laminated structures are composed of multiple fiber layers or functional layers stacked in a vertical direction and are suitable for integrating multi-layer functions, such as electrode active material layers and electrolyte layers.

[0048] The three-dimensional structure is a structure in which fibers are arranged three-dimensionally in the vertical, horizontal, and depth directions, offering high space utilization and excellent electrolyte absorption and diffusion characteristics through its internal porous structure. The integrated structure is a structure formed by integrating the fiber substrate and the electrode functional layer without separation; it is a simplified structure capable of performing current collection and electrode functions without a current collector or binder, and can contribute to weight reduction and process miniaturization.

[0049] Among these, semi-woven structures or laminated structures are more desirable. Semi-woven structures have a geometric arrangement similar to fabric as fibers are aligned in the warp and weft directions; however, since the fibers are not actually woven but are fixed only at their intersections through methods such as heat fusion, bonding, or compression, they offer superior flexibility compared to fabrics, a simpler manufacturing process, and the advantage of allowing the fiber surface to be well exposed during active material deposition or growth processes. Meanwhile, laminated structures are structures that allow for vertical stacking of functional layers such as conductive fiber layers, active material layers, and electrolyte layers. They offer high flexibility in integrating different materials and functions at each interface and are advantageous for realizing high-performance electrode platforms.

[0050] The conductive fibers preferably have an average diameter of 5 μm to 50 μm, and more preferably 10 μm to 30 μm. This fiber diameter range provides a sufficient surface area for fixing the active material at the interface, while effectively suppressing the shedding of the active material during repeated charging and discharging without excessively reducing the electrode density, thereby improving the lifespan and structural stability of the electrode.

[0051] The fiber matrix (10) comprises a grid structure formed by arranging conductive fibers in warp and weft directions. The grid size between the fibers formed therein, i.e., the average spacing between fibers, is preferably 20 μm to 500 μm, and more preferably 50 μm to 200 μm. This grid spacing range is suitable for forming a three-dimensional structure in which the active material can penetrate or be fixed by sufficiently securing space between fibers during the deposition or growth of the electrode active material, while simultaneously satisfying both mechanical flexibility and electrical continuity of the electrode. In addition, it can prevent problems such as weakening of the active material's support strength due to excessive spacing, or conversely, a decrease in the active material coating efficiency due to an excessively dense structure.

[0052] The fiber matrix (10) may include a metal plating layer comprising at least one of nickel, copper, cobalt, iron, tin, or aluminum on at least a portion of its surface. This metal plating layer serves to improve the electrical conductivity of the fiber matrix, increase the interfacial bonding strength with the electrode active material and electrolyte, and improve the mechanical strength and durability of the electrode structure.

[0053] When the electrode is an anode, the metal plating layer may include one or more of nickel, aluminum, and iron. Nickel and iron exhibit excellent corrosion resistance in high-voltage oxidation environments and enhance interfacial bonding with the anode active material, thereby increasing the mechanical stability and electrochemical lifespan of the electrode. Aluminum possesses lightweight properties and excellent electrical conductivity, and provides long-term stable current collection capabilities by improving corrosion resistance through the oxide film formed on its surface. Meanwhile, when the electrode is a cathode, the metal plating layer may include one or more of tin and copper. Copper provides very low electrical resistance and excellent current distribution characteristics, thereby suppressing lithium plating and peeling, while tin improves electrochemical reactivity and enhances capacitance characteristics through alloying reactions with lithium. The selection of metal plating layers according to polarity optimizes the electrical and mechanical stability of the electrode and provides the effect of simultaneously improving electrode performance and lifespan.

[0054] The metal plating layer must be continuously formed on the front surface of the fiber matrix to uniformly attach and fix the positive active material and secure a current collection path.

[0055] During the plating process, current may concentrate at structural intersections, which can result in a relatively thicker plating thickness in those areas; this has the secondary effect of improving the electrical conductivity and mechanical strength of the intersections.

[0056] To ensure a plating layer of sufficient thickness even on straight sections, the plating conditions can be adjusted, or electroless plating can be performed in parallel to ensure uniformity across the entire surface.

[0057] The above electrode is a positive electrode, and the electrode active material may include at least one of NCM, high-nickel NCM, NCA, LFP, manganese-rich NCM, LMO, HVBM, lithium-excess layered oxide, or LFMP.

[0058] NCM, high-nickel NCM, and NCA are representative layered cathode materials that provide high energy density and good cycle characteristics in lithium secondary batteries, and output characteristics and lifespan characteristics can be adjusted by controlling the ratio of nickel (Ni), cobalt (Co), and manganese (Mn). In particular, high-nickel NCM has a nickel content of 80% or more, providing high discharge capacity and energy density, but has the problem of relatively weak interfacial stability and structural stability. When high-nickel NCM is applied to the fiber matrix (10) lattice structure of the present invention, the particle-electrode interface is stabilized through covalent or electrochemical bonding with the metal plating layer and surface functional groups, and particle cracking and electrode delamination occurring during the charging and discharging process are suppressed. In addition, multiple lattice-shaped conductive paths are formed, improving the electrical conductivity of the entire electrode, and the current distribution becomes uniform during high-speed charging and discharging, resulting in the effect of suppressing heat generation and improving output characteristics.

[0059] LFP (LiFePO4) and LMFP (LiMn x Fe 1-xP(PO4) is an iron phosphate-based cathode material with an olivine structure that provides excellent thermal stability and long cycle life. It is highly safe, with minimal structural collapse or oxygen release even in high-temperature and overcharge environments. LFP has an operating voltage of approximately 3.4V and offers high stability, while LMFP can improve energy density by increasing the operating voltage through the substitution of some iron (Fe) with manganese (Mn) in the LFP structure. However, with LMFP, there is a possibility of manganese leaching in high-temperature environments as the manganese content increases.

[0060] When LFP or LMFP is applied to the lattice structure of the fiber matrix (10) of the present invention, low electrical conductivity is compensated by the formation of a metal plating layer and multiple conduction paths, and the current distribution becomes uniform, thereby improving high-rate charge / discharge performance. In addition, manganese leaching is suppressed by the interfacial stabilization effect of surface functional groups, and particle detachment and electrode structure collapse are prevented by mechanical support of the lattice structure, thereby simultaneously improving long-term lifespan and stability.

[0061] Despite the improved structural stability and safety of manganese-rich NCMs due to increased manganese content, manganese leaching may occur during the charge-discharge process due to reactions with the electrolyte. In particular, HF generated in LiPF6-based electrolytes [leaks] to the Mn on the anode surface 3+ Reduce Mn 2+ Manganese ions are leached into the electrolyte in this form, and the leached manganese ions are deposited on the cathode surface, inhibiting lithium ion diffusion and increasing internal resistance. This leads to a problem where long-term cycle life is shortened and performance degradation intensifies in high-temperature environments.

[0062] When manganese-rich NCM is applied to the lattice structure of the fiber matrix (10) of the present invention, the direct reaction between HF and the surface of the cathode material is suppressed due to the interfacial stabilization effect by the metal plating layer and surface functional groups, and the manganese leaching rate is reduced. In addition, due to the mechanical support of the lattice structure and the strong bonding of the particle-electrode interface, particle cracking and the formation of new reaction surfaces occurring during charging and discharging are suppressed, thereby minimizing performance degradation caused by manganese leaching. Accordingly, long-term cycle characteristics and output characteristics can be simultaneously improved while maintaining the economic efficiency and safety of the manganese-rich NCM.

[0063] LMO (LiMn2O4) is a lithium manganese oxide cathode material with a spinel structure that provides excellent high-rate charge / discharge characteristics through a three-dimensional lithium ion diffusion pathway. It also offers low raw material costs and excellent safety due to its manganese-based composition. Due to these characteristics, LMO can be widely used in applications requiring high power performance, such as power tools, hybrid vehicles, and electric buses. However, LMO has the disadvantage of shortened long-term cycle life due to accelerated manganese leaching and electrolyte decomposition in high-temperature environments.

[0064] When LMO is applied to the lattice structure of the fiber matrix (10) of the present invention, output characteristics can be maximized through a metal plating layer and multiple conduction paths, and manganese leaching in high-temperature environments can be suppressed through the interface stabilization effect based on surface functional groups. In addition, particle detachment and electrode structure collapse are suppressed by the mechanical support of the lattice structure, so that long-term lifespan and stability are improved while maintaining the high output characteristics, which are the advantages of LMO.

[0065] HVBM (High Voltage Blended Manganese) is a manganese-based cathode material that combines a high-voltage spinel structure and a layered structure. It has a high operating voltage of approximately 4.7V, thereby providing high energy density and excellent output characteristics simultaneously. Based on a manganese-based composition, it is possible to minimize cobalt content, which enables cost reduction in raw materials, and it offers excellent high-speed charge / discharge performance due to the three-dimensional lithium diffusion pathways of the spinel structure. However, in high-voltage environments, electrolyte oxidation and decomposition are accelerated, and long-term cycle stability is reduced due to manganese leaching and increased interfacial resistance.

[0066] When HVBM is applied to the lattice structure of the fiber matrix (10) of the present invention, the oxidation reaction of the electrolyte in the high voltage range is suppressed due to the interfacial stabilization effect by the metal plating layer and surface functional groups, and the manganese leaching and increase in interfacial resistance are mitigated. In addition, by preventing particle detachment and structural collapse through the mechanical support effect of the lattice structure and the formation of multiple conduction paths, it is possible to simultaneously improve long-term cycle life and stability while maintaining the high voltage and high output characteristics of HVBM.

[0067] Lithium excess layer oxide is Li 1+x M 1-x It has a composition of O2 (M = Ni, Co, Mn, etc.) and includes a structure in which Li2MnO3 components are mixed into a layered LiMO2 series. During the initial charging process, the Li2MnO3 portion is activated, causing an oxygen oxidation reaction, which can provide a high initial discharge capacity of over 250 mAh / g. These ultra-high capacity characteristics enable the realization of high-energy-density batteries and can be utilized to replace or complement high-nickel cathode materials. However, problems exist such as electrolyte decomposition due to oxygen release, increased interfacial resistance, voltage drop during long-term cycles, and particle structure collapse.

[0068] When a lithium-excess layered oxide is applied to the lattice structure of the fiber matrix (10) of the present invention, oxygen release and the resulting electrolyte decomposition reaction can be suppressed due to the interfacial stabilization effect caused by the metal plating layer and surface functional groups. In addition, multiple electron and lithium ion conduction paths are formed by the lattice structure, thereby mitigating the voltage drop rate and suppressing particle cracking and electrode structure collapse, thereby simultaneously improving long-term cycle life and high-power characteristics.

[0069] Layered oxide for sodium-ion batteries is NaNi 1 / 3 Mn 1 / 3 Co 1 / 3 O2, NaFe 1 / 2 Mn 1 / 2 Sodium-based metal oxides having a layered structure, such as O2, exhibit electrochemical behavior similar to that of layered cathode materials in lithium-ion batteries. These provide relatively high capacity and good cycle characteristics, and are suitable for large batteries or energy storage systems (ESS) due to their excellent raw material supply stability. When applied to the fiber matrix structure of the present invention, interfacial bonding strength and conductivity are improved, thereby stabilizing the diffusion path of sodium ions and improving output characteristics.

[0070] Prussian blue compounds are metal hexacyano complexes such as Na2Fe[Fe(CN)6] and Na2Mn[Fe(CN)6], which possess open three-dimensional ion diffusion pathways, enabling rapid sodium insertion and extraction. The raw materials are inexpensive, the synthesis process is simple, and they possess characteristics advantageous for low temperature and high-speed charging and discharging. However, since the structure water content and stability can affect performance, the interface stabilization technology of the present invention can be applied to simultaneously improve long-term cycle stability and output characteristics.

[0071] Polyanionic compounds are polyvalent anions (PO4) such as Na3V2(PO4)3 and NaFePO4. 3- , SO4 2-It has a crystal structure including (etc.) and is characterized by high structural stability and excellent thermal safety. Although it has a relatively high potential and excellent long-term lifespan, its low electrical conductivity makes the design of conductive materials important; however, by applying the fiber matrix lattice structure and metal plating layer of the present invention, conductivity can be supplemented and high-rate charge / discharge characteristics improved.

[0072] High-voltage spinel-based compounds are LiNi 0.5 Mn 1.5 It has a spinel structure similar to O4 (LNMO) and provides a high operating voltage of approximately 4.7V. It offers high cost competitiveness due to its cobalt-free composition and excellent high-power characteristics due to its three-dimensional lithium diffusion pathway; however, lifespan degradation may occur in high-voltage environments due to electrolyte decomposition and manganese leaching. By applying the interface stabilization and mechanical support structure of the present invention, structural stability can be maintained even in high-voltage environments, while simultaneously ensuring long-term cycle life and power characteristics.

[0073] The electrode active material (20) comprises secondary particles and is covalently bonded to the surface of the fiber matrix via an interfacial layer existing at the boundary between the primary particles of the secondary particles, and the covalent bond may be one or more of silane coupling, electrochemical bonding, carboxyl group-metal oxide bonding, or crosslinking agent reaction-based bonding.

[0074] Metal oxide-based cathode active materials (NCM, LFP, LMO, etc.) have crystal surfaces that are mostly saturated with metal-oxygen (MO) bonds, making it difficult to form direct covalent bonds with the surface of conductive fibers. Since reactive groups such as -OH, -COOH, and -NH2 are not sufficiently present on the surface of conductive carbon or metal fibers, or do not possess high chemical affinity with the metal oxide crystal lattice, active material particles exist on the fiber surface primarily in the form of physical adhesion due to van der Waals forces or electrostatic attraction. Such physical adhesion can cause delamination or separation during repeated charge-discharge cycles, leading to performance degradation and a shortened lifespan of the electrode.

[0075] FIG. 2 is a figure illustrating an electrode active material of secondary particles according to one embodiment of the present invention.

[0076] The secondary particles are a structure formed by the aggregation of multiple primary particles, and an intergranular phase (21) exists between the primary particles. This intergranular phase may include Li2CO3, LiOH, metal oxides / hydroxides, amorphous oxides, etc. formed during the synthesis process, and has relatively high chemical reactivity. Therefore, the intergranular phase is a favorable region for introducing reactive groups such as -OH, -COOH, and -NH2 through surface modification, and the imparting of such reactive groups enables the formation of a chemical bond between the active material and the conductive fiber through the intergranular phase.

[0077] In the present invention, a reactor introduced into the interface layer (21) and a reactor introduced into the surface of the conductive fiber are configured to form a covalent bond through silane coupling, electrochemical bonding, carboxyl group-metal oxide bonding, or crosslinking agent reaction. For example, the -COOH of the interface layer reacts with the metal-hydroxyl group (M-OH) on the fiber surface to form an MOC=O bond, thereby chemically fixing the active material particles to the surface of the conductive fiber. This covalent bond structure suppresses the delamination of the active material particles and stabilizes the electron and lithium ion transport pathways, thereby simultaneously improving the mechanical strength and electrochemical performance of the electrode.

[0078] Although not specifically limited, the above secondary particles may be designed to have an average particle size in the range of, for example, 1 μm to 20 μm, and the primary particles (including single crystals) constituting them may be controlled to have an average particle size in the range of 0.1 μm to 5 μm. Optimizing the particle size in this way maximizes the surface area of ​​the interfacial layer in contact with the fiber surface, facilitating the formation of chemical bonds and improving the diffusion paths of electrons and lithium ions within the electrode. In particular, single crystal particles with an average diameter of several microns or more minimize the lithium ion diffusion path at the particle boundary, thereby lowering interfacial resistance and providing the effect of suppressing particle breakage during repeated charge and discharge cycles.

[0079] The above electrode active material (20) includes single crystal particles, and the single crystal particles can be directly formed on the surface of the fiber matrix by heat treatment or electrochemical crystallization reaction after deposition of the metal precursor and lithium precursor and fixed at the interface.

[0080] The electrode active material (20) with a single crystal structure is generally attached to the electrode current collector by slurry coating after powder synthesis, but since this method is a structure in which the active material particles are physically attached to the conductive substrate, it is prone to peeling during long-term charging and discharging processes and has the problem of increased interfacial resistance. In the present invention, these limitations are solved by adopting a method of growing the active material directly on the surface of the substrate.

[0081] First, metal precursors such as nickel, cobalt, manganese, and iron, and lithium precursors such as LiOH and Li2CO3 are uniformly deposited on the surface of the fiber matrix. Deposition methods such as sputtering, atomic layer deposition (ALD), chemical vapor deposition (CVD), electroplating, and solution immersion coating may be used, ensuring that the precursors are stably attached through the plating layer or surface functional groups (-OH, -COOH, etc.) on the fiber surface.

[0082] Subsequently, the deposited precursor is heat-treated or subjected to an electrochemical crystallization reaction to grow a single-crystal active material directly on the fiber surface. The single-crystal particles formed in this way form chemical bonds and crystallographic bonds with the substrate, becoming strongly fixed at the interface. This minimizes the transport pathways for electrons and lithium ions, thereby lowering the internal resistance of the electrode. Furthermore, the high mechanical stability simultaneously improves long-term cycle life and output characteristics.

[0083] The above electrode is a negative electrode, and the electrode active material (20) comprises graphite or a mixture of graphite and silicon, and the graphite or the mixture of graphite and silicon may be electrochemically bonded via an interfacial layer formed on the surface of a fiber matrix or after surface modification, or may be coated on the surface of a fiber matrix.

[0084] Graphite-based anode active materials are widely used as anode materials for lithium-ion batteries due to their excellent electrical conductivity and stable lithium insertion and extraction characteristics, and mixing them with silicon enables improved initial capacity and increased energy density. However, simply physically attaching graphite or graphite-silicon mixed particles to the surface of a conductive fiber matrix can lead to problems such as particle delamination or increased interfacial resistance caused by volume changes and interfacial stress during the charge-discharge process.

[0085] In the present invention, an interface layer having reactive groups such as -OH, -COOH is formed on the surface of a fiber matrix (10) through a metal plating layer or chemical pretreatment, and this is utilized as a bonding medium with graphite or graphite-silicon mixed particles. The particles introduce reactive groups to the surface through oxidation treatment, plasma treatment, or electrochemical oxidation, and are strongly fixed to the fiber surface by forming covalent or electrochemical bonds with the reactive groups of the interface layer.

[0086] In addition, by applying an electrochemical bonding method, the surface reactors of graphite or mixed particles and the interfacial layer reactors can be induced to react selectively. This method lowers interfacial resistance compared to simple physical coatings and effectively suppresses particle exfoliation and structural collapse even during long-term cycles.

[0087] Furthermore, it is also possible to directly coat the surface of a fiber matrix with graphite or mixed particles in a slurry state containing a binder. In this case, the coating layer penetrates into the irregularities and pores of the fiber surface to provide mechanical fixation and maintains electrical conductivity through adhesion to a metal plating layer or an interface layer. Combining surface modification with the coating method improves both initial adhesion and long-term durability, while increasing manufacturing process flexibility and maximizing electrode performance and reliability.

[0088] The above electrode active material is formed in two or more layers, and each layer may differ in at least one of the type of active material, particle size, mixing ratio of secondary particles and single crystals, or mixing ratio of heterogeneous active materials.

[0089] The electrode according to the present invention may form the electrode active material into two or more layers as needed. In this case, each layer may be designed such that at least one of the type of active material, particle size, particle shape (secondary particle or single crystal), or composition ratio differs. For example, an active material such as low-nickel NCM, LFP, or LMFP may be applied to the lower layer to ensure structural stability and long life characteristics, and an active material such as high-nickel NCM, NCA, or lithium-excess layered oxide may be applied to the upper layer to ensure high energy density. Alternatively, fine particles with a large reaction surface area may be placed in the lower layer to increase initial reactivity, and particles with a relatively large particle size may be placed in the upper layer to mitigate volume change and interfacial stress during the charge / discharge process.

[0090] In addition, it is possible to configure the electrode by applying secondary particles to the lower layer to form high tap density and conduction paths, and by applying a single crystal to the upper layer to improve interfacial stability and long-term lifespan. Such a multilayer structure allows for balanced optimization of the electrochemical properties of the entire electrode by differentiating the type, particle size, shape, and composition of the active material for each layer. In particular, by utilizing the structural support and interfacial bonding characteristics of the fiber matrix substrate, each layer can be stably stacked and fixed, enabling stable operation for a long period without interlayer delamination.

[0091] In addition, even when the negative electrode active material is graphite or a mixture of graphite and silicon, by forming a structure of two or more layers with different particle sizes, crystallinity, degree of surface modification, or composition ratios for each layer, it is possible to simultaneously improve initial lithium insertion characteristics, suppress electrode expansion, secure electrical conductivity, and long-term cycle stability.

[0092] Therefore, the multilayer electrode structure according to the present invention is advantageous for simultaneously realizing high power, high energy density, and long lifespan characteristics.

[0093] FIG. 3 is a flowchart illustrating a method for manufacturing an electrode for a secondary battery according to another embodiment of the present invention.

[0094] Another embodiment of the present invention is a method for manufacturing an electrode for a secondary battery, comprising the steps of: preparing a fiber matrix composed of conductive fibers (S1); preparing a secondary particle active material (S2); pre-treating the surface of the fiber matrix to introduce at least one functional group among -OH, -COOH, and -NH2 (S3); pre-treating the surface of the secondary particle active material to introduce at least one functional group among -OH, -COOH, and -NH2 into an interface layer existing at the boundary between primary particles constituting the secondary particles (S4); coating the secondary particle active material onto the surface of the fiber matrix (S5); and forming a covalent bond with the fiber matrix through coupling or electrochemical bonding via an interface layer existing at the boundary between primary particles of the secondary particles (S6).

[0095] A method for manufacturing an electrode for a secondary battery according to one embodiment of the present invention begins with the step (S1) of preparing a fiber matrix composed of conductive fibers. The fiber matrix may be composed of metal fibers, carbon fibers, or composite fibers thereof, and can secure excellent electrical conductivity by providing a three-dimensional structure and a large specific surface area to maximize the contact surface with the active material and multiplexing the electron transfer path within the electrode. In addition, through a flexible structure, resistance to mechanical stress during the electrode manufacturing and modularization process is improved.

[0096] After the fiber matrix preparation step described above, a step (S11) of plating a metal on the surface of the fiber matrix may be added. A metal plating layer may be formed on the surface of the fiber matrix by coating a metal such as nickel, copper, aluminum, silver, or gold using methods such as electroplating, electroless plating, sputtering, or deposition. The metal plating layer improves the electrical conductivity of the fiber surface and, at the same time, significantly improves the interfacial bonding strength and electron transfer efficiency of the active material formed thereafter. In particular, the plating layer may be formed relatively thickly due to electric field concentration at the fiber intersections, which improves current distribution at the intersections and lowers the resistance of the entire electrode.

[0097] The metal plating layer described above is not limited to a single metal component and may include a composite metal phase (a homoalloy phase or a micro-coexistence phase of different metals) formed during the plating process. Such a composite metal phase forms a through-thickness gradient in the thickness direction through the coexistence of metal species having different work functions and surface diffusion coefficients, thereby providing the effect of converging the electric field distribution to a quasi-uniform state at the micro-domain level. As a result, local overcurrent phenomena at specific intersections or protrusions tend to transition to electrochemically inactive regions (passive regions). This mechanism is not limited to specific metal combinations or process conditions, and all variations governed by the relative dominance of phase fractions and surface energies are included within the scope of the present invention.

[0098] Furthermore, coupled thickness-composition modulation of the plating layer is difficult to regard as a manufacturing deviation; rather, it offers the potential advantage of inducing charge distribution in a self-alignment manner during electrode operation. That is, the interface between the micro-heterogeneous phases formed during the initial plating stage causes constriction relief in the electron transfer pathway, thereby resolving current bottlenecks and expanding the effective active area to prevent excessive concentration of nucleation active sites when the active material is coated or crystallized in subsequent stages. This behavior is not limited to a specific numerical range and can be understood as spontaneous equilibration under normal conditions.

[0099] In addition, if necessary, a small amount of sub-oxide / hydroxylated interlayer may be formed on the surface of the plating layer through low-temperature heat treatment or a wet curing process, which acts as a precursor bonding site with coupling systems (silanes, crosslinking agents, etc.) applied in subsequent steps. At this time, the degree of sublayer formation is indirectly controlled by the composition of the process medium, residual moisture, substrate potential history, etc., and as a result, the interfacial energy barrier between the active material, the plating layer, and the fiber matrix is ​​softened, showing a tendency for the initiation overpotential of bond formation to be lowered. The present invention includes various variations utilizing the series of interdependent phenomena described above, but does not limit specific process variables to numerical values.

[0100] In the next step, a secondary particle active material is prepared. The secondary particles have a structure in which a plurality of primary particles are aggregated, and provide high tap density and uniform electrochemical reactivity simultaneously within the bulk electrode. The secondary particle structure forms a lithium ion diffusion pathway through the primary particle interface within the particles and has the effect of improving the uniformity of the electrode reaction. In particular, in the present invention, by utilizing the interfacial layer of the secondary particles to induce a strong bond with the fiber matrix, the detachment of particles during long-term cycles can be prevented.

[0101] The above secondary particle active material may include at least one of NCM, high-nickel NCM, NCA, LFP, manganese-rich NCM, LMO, HVBM, lithium-excess layered oxide, LFMP, layered oxide for sodium-ion batteries, Prussian blue compound, polyanion compound, or high-voltage spinel compound as described above.

[0102] Subsequently, the surface of the fiber matrix is ​​pretreated to introduce at least one functional group selected from -OH, -COOH, and -NH2. These surface functional groups provide chemical reaction sites that enhance binding affinity with metal oxide-based or carbon-based active materials and can be introduced by methods such as plasma treatment, wet oxidation treatment, or chemical modification. Surface pretreatment not only activates the surface but also serves as a precursor for coupling reactions or electrochemical bonding reactions in subsequent steps.

[0103] Next, the surface of the secondary particle active material is pretreated to introduce at least one functional group among -OH, -COOH, and -NH2 into the interfacial layer existing at the boundary between the primary particles constituting the secondary particle. This process imparts reactive groups to the interfacial layer within the secondary particle, thereby enabling the interfacial layer to act as a chemical bridge that can directly bond with the reactive groups of the fiber matrix. Through this, the bonding strength between the active material particles and the fiber is significantly improved, and the stability of the bonding interface can be maintained even with volume changes occurring during the charging and discharging process.

[0104] Next, the pretreated secondary particle active material is coated onto the surface of the fiber matrix. This coating step can be performed using various processes, such as slurry-based wet coating, powder spray dry coating, or electrophoretic coating, and enhances initial adhesion strength by combining simple physical adhesion with interfacial reactions. The coating thickness and distribution can be optimized considering the electrochemical performance and mechanical stability of the electrode.

[0105] In this coating step, when applying a wet coating, a slurry composition may be prepared comprising a pretreated secondary particle active material, a binder, a conductivity aid, a solvent, and optionally a coupling agent. The binder may consist of PVdF, SBR, CMC, PTFE, PAA, PVA, etc., and the conductivity aid may include carbon black, acetylene black, graphene, CNT, etc. The solvent may include NMP, water, alcohol, ketones, etc. The coupling agent may include silane-based, titanate-based, zirconate-based, etc., and promotes the formation of covalent bonds between the interfacial layer reactor of the pretreated active material and the fiber surface reactor. The viscosity and solid content of the slurry are controlled through stirring, dispersion, and degassing steps, and a coating layer is formed by uniformly applying it to the surface of the fiber matrix and then drying and heat treating it.

[0106] Finally, covalent bonds can be formed between the fiber matrix and the active material through a coupling agent (e.g., silane-based, titanate-based, zirconate-based, etc.) treatment or an electrochemical bond induction step mediated by the pre-treated interface layer and the reactor of the active material.

[0107] Here, the coupling agent treatment is a method of directly forming metal-oxygen-carbon bonds with -OH, -COOH, -NH2, etc. through chemical reactions, and the electrochemical bonding is a method of inducing rearrangement, reduction, and precipitation reactions of metal-oxygen, metal-carbon, metal-sulfur bonds, etc. at the interface by applying a potential. This covalent bond structure minimizes interfacial resistance inside the electrode, suppresses the exfoliation of active material particles and the collapse of the electrode structure even during long-term cycles, and stabilizes electron-ion transport pathways.

[0108] Consequently, the manufacturing method according to the present invention simultaneously improves the bonding stability and electrochemical performance of the active material-fiber interface, thereby contributing to the realization of high energy density and long-life secondary batteries.

[0109] FIG. 4 is a flowchart illustrating a method for manufacturing an electrode for a secondary battery according to another embodiment of the present invention.

[0110] Another embodiment of the present invention relates to a method for manufacturing an electrode for a secondary battery, comprising the steps of: preparing a fiber matrix composed of conductive metal fibers (S1); pre-treating the surface of the fiber matrix to introduce at least one functional group selected from -OH, -COOH, and -NH2 (S3); depositing at least one metal precursor and a lithium precursor on the surface of the fiber matrix (H3); growing a single-crystal active material on the surface of the fiber matrix by sintering or heat-treating the metal precursor and the lithium precursor (H4); and heat-treating the fiber matrix on which the single-crystal active material has grown to improve interfacial stability, crystallinity, and mechanical strength of the electrode structure (H5).

[0111] Steps S1 and S3 above are identical to other embodiments of the present invention described above, and may additionally include the metal plating step of Step S11 described above as necessary.

[0112] In the H1 step, a metal precursor and a lithium precursor are deposited on the surface of a conductive metal fiber matrix to form a compositional and structural basis for the subsequent growth of a single-crystal active material. The metal precursor can be supplied with metal elements such as nickel, cobalt, manganese, iron, vanadium, titanium, silicon, tin, and aluminum, and can be provided in the form of sulfates, nitrates, acetates, metal alkoxides, metal-organic complexes, etc. As a lithium precursor, lithium carbonate, lithium hydroxide, lithium nitrate, lithium acetate, etc. can be used. Deposition can be performed through wet coating methods such as immersion, spraying, or drop casting using a precursor solution or slurry, vapor phase deposition methods such as atomic layer deposition (ALD), chemical vapor deposition (CVD), and physical vapor deposition (PVD), or electrochemical deposition methods. In this process, the concentration, solvent composition, pH, viscosity, and polarity of the metal and lithium precursors are controlled to ensure uniform distribution on the fiber surface; in particular, concentration variations at fiber intersections or areas of surface roughness are minimized to induce uniform nucleation. The precursor layer formed through this process provides conditions for growth into a single-crystal active material during subsequent sintering or heat treatment steps, while simultaneously serving to strengthen interfacial bonding with the fiber surface.

[0113] The above metal precursor can be selected from at least one of nickel, cobalt, manganese, and iron, and LiOH or Li2CO3 can be applied as a lithium precursor to provide a composition necessary for forming a single-crystal active material.

[0114] In the H2 step, the metal precursor and lithium precursor deposited on the surface of the fiber matrix in the H1 step are sintered or heat-treated to grow into a single-crystal active material.

[0115] Sintering or heat treatment promotes atomic diffusion and phase transitions within precursor particles to induce grain growth, thereby forming a single-crystal structure with uniform crystal orientation rather than a polycrystalline state. In this process, the heat treatment temperature, heating rate, holding time, and atmospheric gas (oxygen, argon, nitrogen, mixed gas, etc.) act as key factors determining the size and crystallinity of the grown single crystal. For example, heat treatment in an oxygen or oxygen-containing atmosphere can ensure structural stability by minimizing oxygen defects in metal oxide-based active materials (NCM, NCA, LFP, etc.), while in an inert gas atmosphere, stable crystal growth can be induced by maintaining the reduced state of specific metal ions.

[0116] Furthermore, the fiber intersection regions exhibit relatively high local precursor concentrations and surface energies, which lead to rapid initiation of single-crystal nucleation during heat treatment and a tendency for growth directions to be consistently aligned. The single-crystal active material formed at this stage has a low interfacial defect density and continuously connected lithium ion diffusion pathways, resulting in significantly improved electrochemical performance (rate characteristics, lifespan, and high-temperature stability). Therefore, the H4 stage can be considered a key process that simultaneously maximizes the electrochemical properties and mechanical durability of the electrode.

[0117] Although not specifically limited, the temperature (T), holding time (t), heating rate, and atmosphere (oxygen / inert) can be controlled during the H2 stage sintering or heat treatment to promote the phase decomposition and diffusion of the precursor and to grow the single-crystal active material. Generally, the single-crystal size increases with higher temperatures and longer holding times; however, since excessive conditions may induce compositional segregation and granular sintering, the process is optimized to meet the target size.

[0118] Layered NCM / NCA (lithium-ion): Oxygen or oxygen-containing atmosphere, 700–850 ℃, 1–10 h → Single crystal average size 0.5–5 μm (preferably 1–4 μm).

[0119] LFP / LMFP (olivine): inert (Ar / N2) or weakly reducing atmosphere, 500–650 ℃, 1–8 h → 0.5–3 μm (preferably 0.8–2.5 μm).

[0120] LMO (Spinel, LiMn2O4): Oxygen atmosphere, 650–800 ℃, 1–6 h → 0.5–4 μm.

[0121] High voltage spinel (LNMO, etc.): oxygen / dry air, 750–900 ℃, 1–6 h → 1–5 μm (preferably 2–4 μm).

[0122] Lithium excess layered oxide (Li-rich): Oxygen (including active), 700–900 ℃, 2–12 h → 1–6 μm (2–5 μm recommended to suppress voltage drop).

[0123] Sodium layered oxide (SIB): Oxygen / air, 700–900 ℃, 2–10 h → 1–5 μm.

[0124] General process guidelines (example): It is desirable to increase the temperature by 1 to 5 ℃ / min and to cool slowly (0.5 to 3 ℃ / min) to prevent cracking. If the target single crystal is at the level of ~5 μm, the upper limit temperature and sufficient holding time of each series are applied, and to suppress overgrowth and ensure uniformity, it is effective to increase the time at a temperature 20 to 40 ℃ lower than the upper limit.

[0125] In one embodiment of the present invention, when the single crystal active material is NCM, NCA, or a lithium excess layered oxide, it is preferable to perform sintering or heat treatment in an oxygen atmosphere of 700°C or higher and 850°C or lower.

[0126] The fiber matrix above may be nickel fiber or stainless steel fiber.

[0127] When nickel fibers or stainless steel fibers are used as the fiber matrix substrate, high electrical conductivity and mechanical strength characteristic of metals can be secured simultaneously. Nickel fibers have excellent conductivity and high interfacial affinity with transition metal oxide-based active materials, which can improve electrochemical reaction efficiency and, in particular, maintain relative stability even during high-temperature heat treatment. Stainless steel fibers have excellent corrosion resistance and exhibit durability in various electrolyte compositions, making them advantageous for batteries requiring long-term cycle characteristics. Both materials can be manufactured in the form of a porous fiber matrix, which is advantageous for the uniform attachment of active materials and the formation of electrolyte penetration pathways. However, since a surface oxide layer may form during high-temperature heat treatment in an oxygen atmosphere, it is desirable to perform inert atmosphere heat treatment or oxide layer removal treatment in parallel as needed.

[0128] When the substrate is a carbon fiber or a metal fiber sensitive to oxidation, oxidation and damage to the substrate may occur at high temperatures in an oxygen atmosphere, so it is desirable to perform heat treatment only under an inert atmosphere (Ar, N2, etc.). If oxygen is required, it is desirable to proceed after applying low-temperature reoxidation (e.g., 300~450 ℃, O2≤ 1000 ppm) separately or forming a surface protective film.

[0129] The H3 step is a process that finally heat-treats the fiber matrix on which the single-crystal active material has been grown to simultaneously improve interfacial stability, crystallinity, and mechanical strength.

[0130] In this stage, unreacted precursors, residual bound water, and organic matter present at the interface between the single-crystal particles formed in the H2 stage and the fiber surface are removed, the defect density of the crystal lattice is reduced, and the composition of the particle surface is stabilized. During the heat treatment process, ① ion rearrangement within the crystal structure is completed, ② structural defects such as non-uniform oxygen vacancies or Li / Ni incorporation on the particle surface are mitigated, and ③ covalent and electrochemical bonds between the fiber and the active material are strengthened.

[0131] In addition, a stable film (e.g., a thin layer of Li2O, LiF, or metal oxide) is formed on the surface of the active material particles, which suppresses adverse reactions with the electrolyte and reduces structural collapse and particle delamination during long-term cycles. In the case of carbon fiber substrates, heat treatment is performed under an inert atmosphere (Ar, N2), and if necessary, the surface oxygen bonding state can be controlled through post-treatment in a low-temperature oxygen atmosphere.

[0132] Consequently, the H5 stage improves mechanical durability, electrical conductivity, interfacial adhesion, and the electrochemical stability of the electrode, playing a role in securing the final quality necessary for realizing high-energy-density, long-life secondary batteries.

[0133] The heat treatment in the H3 stage is a process designed to enhance interfacial stability between the single-crystal active material grown in the H2 stage and the conductive metal fiber substrate, improve crystallinity, and strengthen the mechanical strength of the electrode structure. This stage improves the long-term cycle characteristics and electrochemical stability of the electrode by inducing microcrystal rearrangement, healing of in-lattice defects, removal of surface impurities, and stress relaxation. Generally, it is performed at a slightly lower temperature than the H4 stage, with the heating rate set to 1 to 3 ℃ / min and the cooling rate to 0.5 to 2 ℃ / min to prevent thermal shock and crack formation. Depending on the type of active material, such as lamellar, olivine, or spinel types, it is preferable to maintain the temperature in the range of 400 to 750 ℃ ​​for 0.5 to 6 hours, which allows for the simultaneous achievement of improved interfacial bonding strength and grain stress relaxation. In particular, when the substrate is carbon fiber, it is essential to perform the heat treatment in the H3 stage exclusively in an inert atmosphere (Ar, N2) to prevent damage caused by oxidation.

[0134] FIG. 5 is a flowchart illustrating a method for manufacturing an electrode for a secondary battery according to another embodiment of the present invention.

[0135] Another embodiment of the present invention relates to a method for manufacturing an electrode for a secondary battery, comprising the steps of: preparing a fiber matrix composed of conductive fibers (S1); pre-treating the surface of the fiber matrix to introduce at least one functional group among -OH, -COOH, and -NH2 (S3); preparing graphite and introducing -OH or -COOH functional groups to the surface by oxidation treatment, plasma treatment, or electrochemical oxidation (G1); coating the surface-treated graphite onto the surface of the fiber matrix (G2); and forming a covalent bond or chemical adhesion between the graphite and the fiber matrix through electrochemical interface activation or a coupling agent reaction (G3).

[0136] Here, the fiber matrix in step S1 can be composed of various electrically conductive materials such as carbon fibers, metal fibers, and conductive composite fibers, and the surface pretreatment in step S3 is performed through oxidation treatment, plasma treatment, wet chemical treatment, etc., to introduce active functional groups for interfacial bonding. The surface-functionalized graphite prepared in step G1 is treated to have affinity functional groups capable of interacting with the fiber surface, and the coating in step G2 is performed through various wet or dry methods such as slurry application, spraying, electrodeposition, electrophoresis, and vacuum filtration. Finally, in step G3, strong covalent bonds or chemical adhesion are formed between the fiber matrix and graphite particles through coupling agent reactions such as silane-based, titanate-based, and zirconate-based agents or electrochemical interfacial activation, thereby suppressing interfacial delamination and increased electrode resistance, and improving long-term cycle life and electrical stability.

[0137] The present invention provides a secondary battery comprising the electrode described above.

[0138] When such electrodes are introduced into secondary batteries, delamination and structural collapse occurring during repeated charge and discharge cycles are suppressed due to strong interfacial bonding between the electrode active material and the fiber matrix, and electrical conductivity is improved as interfacial resistance is reduced. Furthermore, the mechanical strength and thermal stability of the electrode structure are enhanced, leading to improved long-term cycle life and high-output characteristics, and enabling stable capacity maintenance even during high-current operation.

[0139] The above secondary battery may include a non-aqueous liquid electrolyte. When a non-aqueous liquid electrolyte is used, the electrochemical stability window of the electrode is widened, enabling high-voltage operation, and high power characteristics can be secured due to higher electrical conductivity and ionic conductivity compared to an aqueous electrolyte. In addition, electrolyte decomposition or hydrogen generation reactions at the electrode interface are suppressed, thereby improving long-term cycle life. The liquid electrolyte is based on, for example, a carbonate-based solvent (EC, EMC, DEC, etc.) and a lithium salt (LiPF6, LiFSI, etc.), but may further include a sulfone / nitrile-based auxiliary solvent depending on the target voltage range.

[0140] However, when applying a fiber matrix with a nickel plating layer, nickel corrosion may occur due to specific additives in the non-aqueous electrolyte (fluorinated solvents, lithium salt decomposition byproducts, etc.). Therefore, to suppress this, a suitable combination of phosphate-based film-forming agents (LiDFP / LiPO2F2), fluorinated film-forming agents (VC, FEC), sulfide / sulfone-based additives (PES / ES), and corrosion-inhibiting phosphorus-based additives (TMP, TEP) is used, or a thin inert oxide / nitride film (e.g., ALD-Al2O3, TiO2, SiN) is applied to the surface. x It is desirable to form an electroless alloy layer of ) or Ni-P / Ni-WP. In addition, maintaining low moisture and HF content (e.g., H2O ≤ 20 ppm) can further suppress corrosion and degradation reactions. These compositions and surface treatments form a stable protective film on the nickel surface to block corrosion reactions and contribute to maintaining electrode structural stability during long-term operation.

[0141] The above secondary battery may include at least one of a sulfide-based, oxide-based, or polymer-based solid electrolyte. The sulfide-based solid electrolyte has high ionic conductivity (≥10 -3 Oxide-based solid electrolytes possess excellent interparticle sinterability and S / cm, resulting in superior adhesion to electrodes and the ability to maintain high conductivity characteristics even at low temperatures. Oxide-based solid electrolytes offer chemical stability and a wide electrochemical stability window, enabling high-voltage operation, while their high stability against moisture and oxygen makes them easy to handle. Polymer-based solid electrolytes exhibit excellent processability and flexibility, and their good interfacial compatibility with electrodes allows them to suppress the increase in interfacial resistance during charging and discharging. These solid electrolytes can be used alone or combined with different series to simultaneously ensure high conductivity and stability, and long-term cycle life and safety can be improved through covalent bonding or chemical immobilization on the electrode surface.

[0142] The above solid electrolyte may be a polymer-based solid electrolyte that is covalently or electrochemically bonded to -OH, -COOH, or -NH2 functional groups formed on the electrode surface, or is directly self-polymerized and grown on the electrode surface through the deposition and heat treatment of a solid electrolyte precursor.

[0143] The polymer-based solid electrolyte precursor composition used in the present invention may comprise, based on 100 weight% of the composition excluding the structure, 30 to 70 weight% of a self-polymerizable monomer, 5 to 40 weight% of an ion-conducting lithium salt, 1 to 10 weight% of a coupling agent, 5 to 20 weight% of a gelling-capable organic solvent, 0 to 20 weight% of a crosslinking agent, 0 to 20 weight% of a heat-sensitive polymer, 0 to 15 weight% of a low-temperature flexible polymer, 0 to 30 weight% of an inorganic filler, 0 to 5 weight% of a photoinitiator, 0 to 10 weight% of a gas adsorbent, and 0 to 10 weight% of a moisture adsorbent.

[0144] The bonding between the active functional groups on the electrode surface and the solid electrolyte induces chemical immobilization at the interface, thereby suppressing electrolyte peeling or an increase in interfacial resistance during repeated charge and discharge cycles. Furthermore, long-term interfacial stability can be secured by maintaining the functional groups semi-permanently through silane coupling, copolymerization, or crosslinking treatments. In addition, the solid electrolyte formed by directly depositing and polymerizing a precursor on the electrode surface penetrates and bonds deeply into the micro-irregularities and functional groups on the electrode surface, thereby simultaneously achieving effects such as reduced interfacial resistance, improved mechanical durability, secure electrolyte immobilization, and increased thermal stability.

[0145] Furthermore, by including temperature-responsive polymers having LCST, such as PNIPAM, PVCL, PDEAAm, and Pluronic block copolymers, the orientation or swelling state of the polymer chains changes according to the heat (e.g., 30–60°C) generated during battery operation, thereby relieving structural stress and significantly improving interfacial stability and lifespan even under repeated charge and discharge conditions. This temperature-responsive behavior simultaneously achieves suppression of swelling at high temperatures and interfacial adhesion at low temperatures, effectively preventing separation, cracking, and increased resistance at the electrode-electrolyte interface even during long-term cycling.

[0146] The electrode described above is based on a fiber matrix composed of conductive metal fibers, carbon fibers, or composite fibers thereof, and can perform the current collection function without a separate current collector by providing excellent electrical conductivity through the fibers themselves. In this structure, the electrode active material is directly bonded to the fiber surface, resulting in low interfacial resistance, and the current path is formed three-dimensionally along the fiber network, enabling the maintenance of high power characteristics. Therefore, it is possible to realize an electrode structure that substantially does not include a current collector (such as aluminum foil or copper foil), which reduces the weight of the battery, improves energy density relative to weight, and expands mechanical flexibility and design freedom. Furthermore, it eliminates electrochemical side reactions and potential drops that may occur at the current collector interface, thereby enhancing long-term cycle stability and providing cost reduction effects by simplifying the manufacturing process.

[0147] FIG. 6 is a diagram showing the cross-sectional structure of an electrode laminate (100) according to one embodiment of the present invention.

[0148] The electrode laminate (100) includes an anode layer (200) in which an anode active material (210) is attached to the surface of a first fiber matrix substrate (11) made of conductive fibers, and a cathode layer (300) in which a cathode active material (310) containing graphite is attached to the surface of a second fiber matrix substrate (12) made of conductive fibers.

[0149] An intermediate layer (30) composed of at least one of a separator, a non-conductive fiber matrix, or a sulfide-based / oxide-based compressed film is disposed between the anode layer (200) and the cathode layer (300), and a solid electrolyte layer or a liquid electrolyte layer (40) may be interposed between the intermediate layer (30) and the electrode layer.

[0150] The electrode stack (100) configured in this way can be directly connected to an external circuit through positive and negative terminals without a current collector, and contributes to electrode weight reduction and energy density improvement.

[0151] FIG. 7 is a top view of an anode (200) and a cathode (300) according to one embodiment of the present invention.

[0152] The above electrodes (200, 300) can perform the current collection function of the fiber matrix substrate (11, 12) itself.

[0153] The positive electrode (200) includes a first fiber matrix substrate (11) made of conductive fibers and a positive electrode terminal (220) formed at the bottom. The positive electrode terminal (210) is designed to be directly electrically connected to an external circuit without a current collector, and the entire first fiber matrix substrate (11) acts as a current transmission path.

[0154] The cathode (300) includes a second fiber matrix substrate (12) made of conductive fibers and a cathode terminal (320) formed at the bottom. The cathode terminal (320) can also be directly connected to an external circuit without a current collector, and the second fiber matrix substrate (12) is responsible for current transmission.

[0155] A secondary battery (100) according to one embodiment of the present invention may not substantially include a current collector.

[0156] The terminal structure of the positive electrode (200) and negative electrode (300) provided electrical connection and mechanical support for the electrodes simultaneously without using a separate metal foil current collector, thereby contributing to the reduction of the electrode weight and improvement of energy density.

[0157] In addition, the manufacturing process can be simplified by removing the current collector, and manufacturing costs can be significantly reduced by replacing the current collector coating and drying processes that are essential in conventional slurry electrode manufacturing.

[0158] Furthermore, reducing the current collector material increases resource efficiency by reducing the use of rare metals, and provides the effect of improving the cell's capacity and output characteristics by maximizing the active material content relative to the electrode thickness. However, if necessary, the current collector may be used as an auxiliary material to ensure uniform current distribution, mechanical reinforcement, or stability during the manufacturing process; even in this case, the specific gravity of the current collector can be minimized to maintain the lightweighting effect of the present invention.

[0159] [Preparation Example]

[0160] [Preparation of Fiber Matrix Structure]

[0161] A polyethylene terephthalate (PET)-based nonwoven fabric (average pore size approximately 10 μm) was prepared. To chemically activate the surface of the nonwoven fabric, O2 plasma treatment was performed at 100 W output for 3 minutes to form -OH and -COOH hydrophilic functional groups. Subsequently, a 2 wt% solution of glycyrrhizoxypropyltrimethoxysilane (GPTMS) was applied, and the surface was functionalized by drying at 60°C for 10 minutes. Through this treatment, the surface of the nonwoven fabric acquired epoxy groups capable of covalently bonding with the monomers of the solid electrolyte precursor, thereby securing a structure capable of forming interfacial immobilization with the solid electrolyte matrix.

[0162] [Grid Anode Manufacturing]

[0163] S1. Preparation of fiber matrix

[0164] A conductive fiber matrix composed of carbon fibers with an average diameter of about 10 μm was prepared.

[0165] S11. Metal plating on fiber surface

[0166] To improve electrochemical conductivity and interfacial bonding, a 50 nm thick layer of nickel (Ni) was electroplated on the fiber surface.

[0167] S2. Preparation of secondary particle active material

[0168] High-nickel NCM (88:6:6) secondary particles were prepared.

[0169] S3. Fiber Matrix Surface Pretreatment

[0170] After O₂ plasma treatment, a 3-aminopropyltrimethoxysilane (APTMS, 1 wt%) solution was applied to introduce -NH2 functional groups.

[0171] S4. Active material surface pretreatment

[0172] A 1 wt% LiNbO3 coating layer was formed on the surface of the secondary particle active material, and the surface was wet-treated with a diluted aqueous H2O2 solution and then dried to expose -OH functional groups. This introduced -OH functional groups to the primary particle boundaries of the secondary active material particles.

[0173] S5. Active material coating

[0174] The pretreated high-nickel active material was dry-spray coated onto the surface of the fiber matrix. Before coating, the fiber matrix was preheated at 70°C for 5 minutes to increase particle adhesion.

[0175] S6. Formation of covalent bonds

[0176] The coated structure was heat-treated at 120°C for 30 minutes to form a silane coupling-based covalent bond between the -NH2 functional groups on the fiber surface and the -OH functional groups on the active material surface.

[0177] [Grid Cathode Manufacturing]

[0178] S1. Preparation of fiber matrix

[0179] A conductive fiber matrix composed of carbon fibers with an average diameter of about 10 μm was prepared.

[0180] S3. Fiber Matrix Surface Pretreatment

[0181] After O₂ plasma treatment, a 3-aminopropyltrimethoxysilane (APTMS, 1 wt%) solution was applied to introduce -NH₂ functional groups.

[0182] G1. Graphite Surface Treatment

[0183] Natural graphite and artificial graphite were mixed in an 8:2 ratio, and then oxidized in an aqueous solution of nitric acid (HNO3) (2 M) at 80°C for 2 hours to introduce -OH and -COOH functional groups to the surface. After drying, Ar plasma treatment (30 W, 1 min) was performed.

[0184] G2. Graphite coating

[0185] Surface-treated graphite was coated onto the surface of a fiber matrix using a dry spray coating method. Before coating, the fiber matrix was preheated at 70°C for 5 minutes to improve particle adhesion.

[0186] G3. Formation of covalent bonds or chemical adhesions

[0187] While heat-treating the coated structure in a vacuum oven at 120°C for 30 minutes, γ-glycisidoxypropyltrimethoxysilane (GPTMS, 1 wt%) vapor treatment was performed in parallel to form silane coupling-based covalent bonds between the -NH2 functional groups on the fiber surface and the -OH / -COOH functional groups on the graphite surface.

[0188] [Preparation of Solid Electrolyte Precursor]

[0189] A composition was prepared comprising a self-polymerizable monomer (PEGDA, 60 wt%), a gelling-capable organic solvent (EC / PC mixture, 10 wt%), a lithium salt (LiTFSI, 10 wt%), a coupling agent (GPTMS, 2 wt%), a crosslinking agent (TMPTA, 5 wt%), a photoinitiator (Irgacure 184, 1 wt%), a gas adsorbent (mesoporous silica, 1 wt%), and a moisture adsorbent (silica gel, 1 wt%). All components were mixed under anhydrous conditions and stirred at 200 rpm for 30 minutes to ensure homogeneous mixing.

[0190] [Secondary Battery Assembly]

[0191] The prepared solid electrolyte precursor was applied to the surfaces of the anode and cathode structures and treated under vacuum (-0.08 MPa) for 5 minutes to penetrate into the fibers and the inter-particle spaces of the active material. Subsequently, a photoinitiation reaction was induced by irradiating with UV light of 365 nm wavelength for 60 seconds, and self-polymerization and cross-linking were completed at room temperature for 10 minutes. The anode-solid electrolyte-cathode structure was aligned and stacked, and final curing was performed under an applied pressure of approximately 5 kPa. The fabricated battery substantially does not contain a current collector, and the electrodes and electrolytes form covalent bonds and mechanical interlocking structures to suppress interfacial resistance and improve mechanical durability. Explanation of the symbols

[0192] 1: Electrode for secondary battery 10: Fiber matrix substrate 11: First fiber matrix substrate 12: Second fiber matrix substrate 20: Electrode active material 21: Interface layer 30: Intermediate layer 40: Electrolyte layer 100: Secondary battery 200: Cathode layer 210: Positive active material 220: Positive terminal 300: Cathode layer 310: Cathode active material 320: Negative terminal

Claims

Claim 1 An electrode for a secondary battery comprising: a fiber matrix substrate made of conductive fibers; and an electrode active material formed on the surface of the fiber matrix substrate, wherein the electrode active material comprises at least one of a secondary particle covalently bonded to the fiber matrix substrate and a primary particle formed directly on the surface of the fiber matrix substrate by heat treatment or electrochemical crystallization reaction after deposition of a precursor including a metal precursor and fixed at an interface. Claim 2 An electrode for a secondary battery according to claim 1, characterized in that the conductive fiber is one or more of pitch-based carbon fiber, PAN-based carbon fiber, metal fiber, conductive polymer fiber, and metal-coated fiber in which a metal is coated on the surface of an insulating fiber. Claim 3 An electrode for a secondary battery according to claim 1, wherein the fiber matrix is ​​at least one of a plain weave structure, a woven fabric, a nonwoven fabric, a knitted structure, a quasi-woven structure, a laminated structure, a three-dimensional structure, or an integral structure. Claim 4 An electrode for a secondary battery according to claim 1, wherein the fiber matrix comprises a metal plating layer comprising at least one of nickel, copper, cobalt, iron, tin, or aluminum on at least a portion of its surface. Claim 5 An electrode for a secondary battery according to claim 4, wherein, when the electrode is a positive electrode, the metal plating layer comprises one or more of nickel, aluminum, and iron, and when the electrode is a negative electrode, the metal plating layer comprises one or more of tin and copper. Claim 6 An electrode for a secondary battery according to claim 1, wherein the electrode is a positive electrode, and the electrode active material comprises at least one of NCM, high-nickel NCM, NCA, LFP, manganese-rich NCM, LMO, HVBM (High-volume Blended Manganese), lithium-excess layered oxide, LFMP, layered oxide for sodium-ion batteries, Prussian blue compound, polyanion compound, or high-voltage spinel compound. Claim 7 An electrode for a secondary battery according to claim 6, wherein the electrode active material comprises secondary particles and is covalently bonded to the surface of the fiber matrix via an interfacial layer existing at the boundary between the primary particles of the secondary particles, and the covalent bond is one or more of silane coupling, electrochemical bonding, carboxyl group-metal oxide bonding, or crosslinking agent reaction-based bonding. Claim 8 An electrode for a secondary battery according to claim 6, wherein the electrode active material comprises single-crystal particles, and the single-crystal particles are formed directly on the surface of the fiber matrix by heat treatment or electrochemical crystallization reaction after deposition of a metal precursor and a lithium precursor and are fixed at the interface. Claim 9 An electrode for a secondary battery according to claim 1, wherein the electrode is a negative electrode, the electrode active material comprises graphite or a mixture of graphite and silicon, and the graphite or the mixture of graphite and silicon is integrated by forming a covalent bond through an interfacial layer formed on the surface of a fiber matrix. Claim 10 An electrode for a secondary battery according to any one of claims 1 to 9, wherein the electrode active material is formed of two or more layers, and each layer is characterized in that at least one of the active material type, particle size, mixing ratio of secondary particles and single crystals, or mixing ratio of heterogeneous active materials is different. Claim 11 A method for manufacturing an electrode for a secondary battery, characterized by comprising: a step of preparing a fiber matrix composed of conductive fibers (S1); a step of preparing a secondary particle active material (S2); a step of pre-treating the surface of the fiber matrix to introduce at least one functional group among -OH, -COOH, and -NH2 (S3); a step of pre-treating the surface of the secondary particle active material to introduce at least one functional group among -OH, -COOH, and -NH2 into an interface layer existing at the boundary between primary particles constituting the secondary particles (S4); a step of coating the secondary particle active material onto the surface of the fiber matrix (S5); and a step of forming a covalent bond with the fiber matrix by coupling or electrochemical bonding through the interface layer existing at the boundary between primary particles of the secondary particles (S6). Claim 12 A method for manufacturing an electrode for a secondary battery, characterized in that, in claim 11, after the fiber matrix preparation step, the method further includes a step (S11) of plating a metal on the surface of the fiber matrix. Claim 13 A method for manufacturing an electrode for a secondary battery according to claim 11, wherein the secondary particle active material comprises at least one of NCM, high-nickel NCM, NCA, LFP, manganese-rich NCM, LMO, HVBM, lithium-excess layered oxide, LFMP, layered oxide for sodium-ion batteries, Prussian blue-based compounds, polyanion-based compounds, or high-voltage spinel-based compounds. Claim 14 A method for manufacturing an electrode for a secondary battery, characterized by comprising: a step of preparing a fiber matrix composed of conductive metal fibers (S1); a step of pre-treating the surface of the fiber matrix to introduce at least one functional group among -OH, -COOH, and -NH2 (S3); a step of depositing at least one metal precursor and a lithium precursor on the surface of the fiber matrix (H3); a step of growing a single-crystal active material on the surface of the fiber matrix by sintering or heat-treating the metal precursor and the lithium precursor (H4); and a step of heat-treating the fiber matrix on which the single-crystal active material has grown to improve interfacial stability, crystallinity, and mechanical strength of the electrode structure (H5). Claim 15 A method for manufacturing an electrode for a secondary battery according to claim 14, wherein the single-crystal active material comprises at least one of NCM, NCA, or lithium-excess layered oxide, and the sintering or heat treatment is performed in an oxygen atmosphere of 700°C or higher and 850°C or lower. Claim 16 A method for manufacturing an electrode for a secondary battery, characterized in that, in either claim 14 or 15, the fiber matrix is ​​nickel fiber or stainless steel fiber. Claim 17 In claim 14, the single-crystal active material is LFP or LMFP (LiM 1-x Fe x A method for manufacturing an electrode for a secondary battery, characterized in that PO₄, 0 < x ≤ 1, where M is at least one of Mn, Co, and Ni, and the sintering is performed in an inert atmosphere or a weak reducing atmosphere at 500 ℃ or higher and 650 ℃ or lower. Claim 18 A method for manufacturing an electrode for a secondary battery according to claim 14, wherein the metal precursor comprises at least one of nickel, cobalt, manganese, and iron, and the lithium precursor is LiOH or Li2CO3. Claim 19 A method for manufacturing an electrode for a secondary battery, characterized by comprising: a step of preparing a fiber matrix composed of conductive fibers (S1); a step of pre-treating the surface of the fiber matrix to introduce at least one functional group among -OH, -COOH, and -NH2 (S3); a step of preparing graphite and introducing -OH or -COOH functional groups to the surface by oxidation treatment, plasma treatment, or electrochemical oxidation (G1); a step of coating the surface-treated graphite onto the surface of the fiber matrix (G2); and a step of forming a covalent bond between the graphite and the fiber matrix through electrochemical interface activation or coupling agent reaction to integrate them (G3). Claim 20 A secondary battery characterized by including an electrode according to claim 1. Claim 21 In claim 20, the secondary battery is characterized by comprising a non-aqueous liquid electrolyte. Claim 22 In claim 20, the secondary battery is characterized by comprising at least one of a sulfide-based, oxide-based, or polymer-based solid electrolyte. Claim 23 A secondary battery according to claim 22, wherein the solid electrolyte is covalently or electrochemically bonded to -OH, -COOH, and -NH2 functional groups formed on the electrode surface, or is a polymer-based solid electrolyte grown directly on the electrode surface through deposition and heat treatment of a solid electrolyte precursor. Claim 24 A secondary battery according to claim 20, wherein the electrode is characterized in that the fiber matrix substrate itself performs the current collection function and does not include a separate current collector within the electrode. Claim 25 delete

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