Negative active material, lithium secondary battery containing the same, and method for manufacturing the negative active material

Abstract

A negative electrode active material according to one embodiment may be provided by including a composite material composed of a silicon-based active material and a nanoribbon surrounding the silicon-based active material.

Description

Technology Field

[0001] The present invention relates to a negative electrode active material comprising a silicon-based active material having improved electrical capacity, electrochemical properties, structural stability, and electrical conductivity, a lithium secondary battery comprising the same, and a method for manufacturing the negative electrode active material. Background Technology

[0002] Recently, due to the rapid growth of the electric vehicle, energy storage system (ESS), and mobile device markets, there is an increasing demand for high energy density, high power output, and long lifespan characteristics for lithium secondary batteries. While existing lithium secondary batteries have achieved a certain level of performance in terms of energy density, lifespan, and stability, high-performance applications such as electric vehicles require an energy density of over 1000 Wh / L. Consequently, increasing the capacity of the anode active material, a key component of lithium secondary batteries, has emerged as an important technological challenge.

[0003] Graphite is a commercially available anode material for lithium-ion batteries that possesses a stable structure and long lifespan characteristics, but its theoretical capacity is only about 374 mAh / g, which limits its ability to realize high-energy density cells. For this reason, research on high-capacity anode materials such as silicon (Si) and silicon oxide (SiOx) is actively underway. Silicon has a very high theoretical capacity of up to 3579 mAh / g, and SiOx is attracting attention as a candidate for next-generation anode materials as it exhibits a lower expansion rate and superior cycle characteristics compared to silicon.

[0004] However, silicon-based anode materials undergo volume expansion of over 300% during charging and discharging, leading to structural and electrochemical instability such as particle fragmentation, electrode separation, and the repeated formation of SEI layers. In particular, SiO undergoes irreversible Li2 and Li2 during the lithiation process. xThe formation of byproducts such as SiO₂ causes a decrease in initial efficiency and lithium loss, and this instability leads to a rapid reduction in capacity and a short cycle life. Furthermore, due to low electrical conductivity, it is difficult to secure high-speed charge and discharge characteristics, making the incorporation of conductive materials essential to secure electron transport pathways.

[0005] To address these issues, designing composite structures capable of controlling the volume expansion of silicon-based active materials, enhancing electrical conductivity, and ensuring structural stability is emerging as a critical technical challenge. In particular, graphene-based carbon materials are known to be effective in suppressing the expansion of silicon-based particles and stabilizing SEI, based on their excellent conductivity and mechanical strength. The problem to be solved

[0006] The disclosed embodiment relates to a silicon-based active material composite comprising a silicon-based active material having excellent electrochemical performance and superior structural stability, and a nanoribbon forming a network of silicon-based active materials. means of solving the problem

[0007] A negative electrode active material according to one embodiment comprises a silicon-based active material and a composite of a nanoribbon surrounding the silicon-based active material.

[0008] The above composite is provided with a core containing the silicon-based active material and a shell surrounding the core and containing the nanoribbon.

[0009] The above shell is provided with a thickness of 5 nm to 50 nm.

[0010] The above composite is provided with a porous structure.

[0011] The above composite is prepared with an average particle size of 50 nm to 5 μm.

[0012] The above silicon-based active material is Si and SiOx(0 <x≤2) 중 적어도 하나 이상을 포함한다.

[0013] The above silicon-based active material consists of a single-crystal structure.

[0014] The above complex is characterized by the observation of characteristic peaks on the (111), (220), and (311) crystal planes during XRD pattern analysis.

[0015] The above nanoribbon is composed of graphene.

[0016] The above nanoribbon is formed with a thickness of 5 to 50 nm.

[0017] A lithium secondary battery according to another embodiment comprises a negative electrode including a negative electrode active material; a positive electrode including a positive electrode active material; and an electrolyte that delivers lithium ions to the positive electrode and the negative electrode.

[0018] The above lithium secondary battery exhibits a capacity retention rate of 97% or more after 500 or more charge-discharge cycles at a current density of 0.2 A / g.

[0019] The above lithium secondary battery exhibits a capacity of 1500 mAh / g or more at a current density of 0.1 A / g.

[0020] A method for manufacturing a negative electrode active material according to another embodiment includes a pretreatment step for manufacturing and purifying a silicon-based active material; and a composite manufacturing step for manufacturing a core-shell structured composite using the pretreated silicon-based active material and a graphene nanoribbon precursor.

[0021] The above pretreatment step includes a step of melting a silicon-based precursor; and a step of condensing the molten silicon-based particles, and the composite manufacturing step includes a step of forming a carbon nanoribbon shell on the outside of the heat-treated particles. Effects of the invention

[0022] A negative electrode active material according to one embodiment of the present invention comprises a silicon-based active material and a silicon-based active material complex comprising a nanoribbon forming a network of silicon-based active materials, and has the effect of having excellent electrochemical performance and excellent structural stability.

[0023] The negative electrode active material according to one embodiment of the present invention includes a silicon-based active material and has a high capacity, while also having excellent cycle characteristics due to structural stability.

[0024] A negative electrode active material according to one embodiment of the present invention has the effect of providing high electrical conductivity by including a silicon-based active material core and a shell containing nanoribbons on the surface of the core.

[0025] The negative electrode active material according to one embodiment of the present invention has the effect of ensuring initial Coulomb efficiency by uniformly forming SEI through a single-crystal GNR shell and suppressing irreversible lithium loss. Brief explanation of the drawing

[0026] FIG. 1 is a schematic cross-section of a composite consisting of a silicon-based active material and a carbon nanoribbon according to one embodiment of the present invention. FIG. 2 is a schematic diagram illustrating the surface of a negative electrode active material comprising a plurality of composites according to one embodiment of the present invention. FIG. 3 is an FE-SEM image showing a cathode active material including a composite prepared according to one embodiment of the present invention. FIG. 4 is an FE-SEM image showing a cathode active material including a composite prepared according to one embodiment of the present invention. Figure 5 is an HR-TEM image of a cathode active material containing a composite prepared according to one embodiment of the present invention. FIGS. 6(a) and (b) are graphs showing X-ray photoelectron spectroscopy (XPS) results for analyzing the surface chemical composition of a composite according to one embodiment of the present invention. Figure 7 is an X-ray diffraction (XRD) pattern result for analyzing the crystal structure of a composite according to one embodiment of the present invention. Figure 8 is a graph showing the results of Raman spectroscopy analysis of a complex according to one embodiment of the present invention. Figures 9(a) and (b) are graphs showing the initial charge-discharge voltage-capacity curve and the CV (Cyclic Voltammetry) curve of a composite-based battery according to one embodiment of the present invention. FIGS. 10(a) and (b) are graphs showing the evaluation results of the rate capability, long-term cycle characteristics, and Coulombic efficiency of a GNR / Si composite-based battery according to one embodiment of the present invention. Specific details for implementing the invention

[0027] Throughout the specification, the same reference numerals refer to the same components. This specification does not describe all elements of the embodiments, and general content in the art to which the invention pertains or content that overlaps between embodiments is omitted.

[0028] Throughout the specification, when a part is described as being "connected" to another part, this includes not only cases where they are directly connected but also cases where they are indirectly connected, and indirect connections include connections made via a wireless communication network.

[0029] Furthermore, when it is stated that a part "includes" a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but may include additional components.

[0030] Singular expressions include plural expressions unless there is an obvious exception in the context.

[0031] In addition, terms such as "~part," "~unit," "~block," "~part," and "~module" may refer to a unit that processes at least one function or operation. For example, the above terms may refer to at least one piece of hardware such as an FPGA (field-programmable gate array) or ASIC (application specific integrated circuit), at least one piece of software stored in memory, or at least one process processed by a processor.

[0032] The symbols attached to each step are used to identify each step and do not indicate the order of the steps relative to one another; the steps may be performed differently from the specified order unless a specific order is clearly indicated in the context.

[0033] Hereinafter, embodiments relating to a solid electrolyte according to one aspect and a secondary battery including the same will be described in detail with reference to the attached drawings. The embodiments described in this specification and the configurations illustrated in the drawings are merely the most preferred embodiments of the present invention, and various equivalents and modifications that can replace them may exist at the time of filing this application.

[0034] Cathode active material

[0035] The negative electrode active material is a compound capable of reversibly intercalating and deintercalating lithium ions.

[0036] FIG. 1 is a schematic diagram showing a cross-section of a composite material composed of a silicon-based active material and a carbon nanoribbon according to one embodiment of the present invention, and FIG. 2 is a schematic diagram showing the surface of a negative electrode active material comprising a plurality of composite materials.

[0037] Referring to FIGS. 1 and 2, the negative electrode active material comprises a silicon-based active material and a composite (10) consisting of a nanoribbon surrounding the silicon-based active material.

[0038] The composite (10) may be formed in a core-shell structure. Specifically, the composite (10) may include a core (11) containing a silicon-based active material and a shell (12) that surrounds the core (11) and contains a nanoribbon.

[0039] The core (11) is located at the center of the composite (10) and may contain a silicon-based active material, and the silicon-based active material is Si and SiOx (0 <x≤2) 중 적어도 하나 이상을 포함하여 리튬이온을 가역적으로 인터칼레이션(intercalation) 및 디인터칼레이션(deintercalation)시킬 수 있다. 코어(11)는 다공성 실리콘 입자로 마련될 수 있으며, 이를 통해 리튬 이온의 확산 경로를 확보하고 충방전 시 발생하는 부피 팽창을 완충하는 역할을 할 수 있다. 코어(11)는 입자 크기가 50nm 내지 5 μm 이하로 마련될 수 있다.

[0040] The shell (12) may be formed on the outer surface of the core (11) to surround the core (11) and may include a nanoribbon. The shell (12) may be formed to surround all or part of the surface of the core (11). The shell (12) serves to improve the structural stability and electrochemical properties of the composite (10) by absorbing mechanical stress due to volume expansion of the core (11) and providing an electrical conduction path. The shell (12) may be formed with a thickness of 5 nm to 50 nm or less, preferably 10 nm or less, and configured to uniformly surround the core (11).

[0041] A nanoribbon is a carbon-based one-dimensional structure formed in a ribbon shape along its length, having an average thickness at the nanometer (nm) level and a structure that maintains single-crystal crystallinity. Specifically, the nanoribbon may have a ribbon-shaped nanostructure with a width of 1 nm to 999 nm and a length of 1 nm to 999 nm. Preferably, the nanoribbon may be provided as a graphene nanoribbon (GNR) or a carbon nanoribbon. The nanoribbon can additionally secure structural flexibility in a ribbon shape while maintaining excellent electrical conductivity and mechanical strength, and can contribute to the improvement of electrochemical and mechanical properties when formed into a composite (10) with a silicon-based active material. In addition to graphene, the nanoribbon may also be provided as Cu, Al, etc.

[0042] This composite (10) has a core-shell structure, which has advantages such as improved electrical conductivity, control of volume expansion of silicon active material, SEI stabilization, and improved structural stability through a uniform shell structure.

[0043] The composite (10) may contain a silicon-based active material in a weight ratio of 50 to 90 relative to the total weight of the composite, and a nanoribbon in a weight ratio of 10 to 50 relative to the total weight of the composite.

[0044] Silicon-based material (wt%) Nanoribbon (wt%) Key Features and Purpose of Use 90 10 High capacity orientation, minimal expansion inhibition effect 80 20 Practical high capacity (>2500 mAh / g), improved mechanical stability 70 30 Achieving a balance of cycle life and stability, aiming for commercialization 60 40 Advantageous for high stability and fast charge / discharge conditions 50 50 Low expansion, high stability design, all-solid-state batteries, and applications in systems requiring high stability

[0045] As shown in Table 1, the balance between stability and capacity can be adjusted by controlling the weight ratio of the silicon-based active material and the weight ratio of the nanoribbon. Specifically, when the weight ratio of the silicon-based active material is higher than the weight ratio of the nanoribbon, for example, when the weight ratio of the silicon-based active material is 90 wt% and the weight ratio of the nanoribbon is 10 wt%, high capacity can be achieved, but the expansion inhibition effect is low. On the other hand, when the weight ratio of the silicon-based active material is higher than the weight ratio of the nanoribbon, for example, when the weight ratio of the silicon-based active material is 50 wt% and the weight ratio of the nanoribbon is 50 wt%, a low-expansion, high-stability design is possible.

[0046] <Cathode>

[0047] The cathode comprises a current collector and a cathode layer provided on the current collector, the layer comprising a cathode active material, a conductive material, a binder, etc. For example, the cathode of the present invention can be obtained by preparing a coating solution by mixing a cathode active material, a binder, a conductive material, a thickener, a solvent such as a solvent or water, applying (coating) the coating solution onto the current collector, drying the solvent or water, and then pressure-molding to form a cathode layer. The current collector may be made of, for example, copper.

[0048] The negative electrode active material may be composed of the negative electrode active material described above, and may be included in an amount of 50% to 95% by weight based on 100 parts by weight of the negative electrode layer, and preferably may be composed of 85% by weight of the negative electrode layer.

[0049] The conductive material may include a carbon-based material with excellent electrical conductivity, and preferably may be provided as carbon black. The conductive material may be included in an amount of 1% to 15% by weight based on 100 parts by weight of the negative electrode layer of the negative electrode active material, and preferably may consist of 10% by weight of the negative electrode layer.

[0050] The binder is not particularly limited, but may include, for example, a styrene-butadiene copolymer; a (meth)acrylic copolymer obtained by copolymerizing an ethylenically unsaturated carboxylic acid ester such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, (meth)acrylonitrile, hydroxyethyl (meth)acrylate, and an ethylenically unsaturated carboxylic acid such as acrylic acid, methacrylic acid, itaconic acid, fumaric acid, maleic acid; and polymer compounds such as polyvinylidene fluoride, polyethylene oxide, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, polyimide, and polyamideimide.

[0051] The binder may be included in the cathode layer in an amount of 0.1% to 20% by weight, preferably 5% by weight. When the binder content is 0.1% by weight or more, the adhesion is good, and the destruction of the cathode due to expansion and contraction during charging and discharging tends to be suppressed. On the other hand, when the content is 20% by weight or less, the increase in electrode resistance tends to be suppressed.

[0052] Lithium secondary battery

[0053] The lithium secondary battery of the present invention comprises a positive electrode, the negative electrode, and an electrolyte.

[0054] The negative electrode can be made into a lithium-ion secondary battery by, for example, positioning it opposite the positive electrode through a separator and injecting an electrolyte containing an electrolyte.

[0055] The positive electrode can be obtained by forming a positive material layer on the surface of a current collector in the same manner as the above-mentioned negative electrode. The positive current collector may be made of, for example, aluminum.

[0056] The positive active material of the positive layer of the lithium secondary battery of the present invention is a compound capable of reversibly intercalating and deintercalating lithium ions. Specifically, it may include a lithium metal oxide containing lithium and one or more metals such as cobalt, manganese, nickel, or aluminum. For example, the lithium metal oxide may include a lithium-manganese-based oxide, a lithium-cobalt-based oxide, a lithium-nickel-based oxide, a lithium-cobalt-nickel-based oxide, a lithium-nickel-manganese-cobalt-based oxide, and a lithium iron phosphate.

[0057] The electrolyte is not particularly limited and known electrolytes may be used. For example, a non-aqueous lithium-ion secondary battery can be manufactured by using a solution in which the electrolyte is dissolved in an organic solvent as the liquid electrolyte. Examples of electrolytes include LiPF6, LiClO4, LiBF4, LiClF4, LiAsF6, LiSbF6, LiAlO4, LiAlCl4, LiN(CF3SO2)2, LiN(C2F5SO2)2, LiC(CF3SO2)3, LiCl, and LiI. As for the organic solvent, it is sufficient if it can dissolve the above electrolyte, and examples include propylene carbonate, ethylene carbonate, diethyl carbonate, ethylmethyl carbonate, vinyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, and 2-methyltetrahydrofuran.

[0058] On the other hand, the electrolyte is not limited to liquid electrolytes and solid electrolytes may also be used.

[0059] Various known separators may also be used as separators. Specifically, examples include paper separators, polypropylene separators, polyethylene separators, glass fiber separators, etc.

[0060] However, if a solid electrolyte is used, the separator may not be included in the lithium secondary battery.

[0061] [Example 1]

[0062] Preparation of cathode active material

[0063] In this embodiment, a negative electrode active material in the form of a composite containing a silicon-based active material and a graphene nanoribbon (GNR) was prepared.

[0064] The particle size and dispersion characteristics of the silicon precursor were controlled by pre-treating it using a ball milling method. The pre-treated silicon precursor was fed into an induction melting heating device and subjected to evaporation, cooling, and condensation processes to synthesize micrometer-sized porous silicon particles.

[0065] Subsequently, a copper thin film was deposited on the surface of silicon particles, and then graphene nanoribbons (GNRs) were grown by thermally decomposing a carbon precursor (e.g., acetylene, methane, etc.) to form single-crystal GNRs on the surface of the silicon particles. Then, surface defects were removed in a mixed atmosphere of O2 and Ar gases.

[0066] The formed GNR / Si composite was heat-treated (annealed) at 680°C for 3 hours under a nitrogen atmosphere, then dispersed in an ethanol solvent and stirred at room temperature for 6 hours. Subsequently, the pH was adjusted to pH 9 with an aqueous ammonia solution, stirred for 4 hours, and sonication was performed for 2 hours.

[0067] The stirred slurry was dried in an oven at 90°C and then calcined for 4 hours at a heating rate of 5°C in an argon atmosphere at 450°C to finally obtain a cathode active material in the form of a GNR / Si composite.

[0068] Manufacturing of electrodes (half cell)

[0069] A cathode was manufactured based on a cathode active material containing the manufactured composite. The cathode slurry was composed of a composition including a cathode active material, a binder (CMC and SBR), and a conductive material (Super P), and the weight ratio of the cathode active material : binder : conductive material was set to 85 : 5 : 10.

[0070] The slurry was uniformly mixed using a Synkey mixer (2500 rpm, 2 minutes), applied onto a copper current collector, and then dried in a vacuum oven at 120°C for 8 hours to manufacture the electrode. The dried electrode was then subjected to a rolling process using a roll press to improve electrode density.

[0071] Subsequently, a half-cell was constructed inside a glove box by combining the manufactured cathode and lithium metal. Standard separators and electrolytes were used for cell assembly, and electrochemical characteristics were evaluated using a WBCS-3000 battery cycler (Won A Tech). <Physical Property Evaluation>

[0072] FIGS. 3 and 4 are FE-SEM images showing a negative electrode active material including a composite prepared according to Example 1 of the present invention, and FIG. 5 is an HR-TEM image showing a negative electrode active material including a composite prepared according to Example 1 of the present invention.

[0073] Referring to FIGS. 3 to 5, the composite comprises a core composed of silicon microparticles of approximately 4 μm in size and has a spherical composite structure in which graphene nanoribbons (GNRs) are uniformly formed on the surface of the particles.

[0074] The composite according to the present invention is synthesized by controlling the thermal decomposition reaction of a carbon gas precursor (e.g., acetylene, methane, etc.), and during the thermal decomposition reaction, single-crystal graphene nanoribbons are grown on the surface of silicon particles to form the composite. The GNR has an average thickness of less than 10 nanometers (nm) and is formed as a shell structure surrounding the core, and a uniform graphene layer maintaining a single-crystal structure is confirmed when observed from the outside.

[0075] The composite of the present invention is formed in a composite form of a porous structure of silicon microparticles and a thin, continuous outer shell structure of GNR, and it is determined that this composite is formed by an in-out diffusion reaction between the constituent components that occurs during the pyrolysis process.

[0076] In addition, according to TEM analysis results, no separate defect structures were observed inside the silicon particles, which means that the silicon particles were manufactured based on a single-crystal structure. On the other hand, the carbon-based GNR layer constituting the composite shell was observed to have a highly crystalline single-crystal structure.

[0077] Figures 6 (a) and (b) are graphs showing the results of X-ray Photoelectron Spectroscopy (XPS) for analyzing the surface chemical composition of a composite according to Example 1 of the present invention.

[0078] FIG. 6 (a) is an XPS graph showing the Si 2p bond energy of a composite according to one embodiment 1 of the present invention, and FIG. 6 (b) is an XPS graph showing the C 1s bond energy of a composite according to one embodiment 1 of the present invention.

[0079] Referring to Figures 6 (a) and (b), the XPS full-area scan of the composite revealed characteristic peaks corresponding to Si 2p, Si 2s, C 1s, and O 1s at 103.0 eV, 156.0 eV, 287.0 eV, and 532.0 eV, respectively. This confirmed that the composite does not contain any impurity elements other than Si, C, and O, which is consistent with the previous XRD analysis results.

[0080] Referring to Fig. 6 (a), the results of the Si 2p core level scan analysis in the range of 96–110 eV show that the broad peaks are Si 2+ , Si 3+ , Si 4+ Peaks were observed at 101.9 eV, 103.1 eV, and 103.8 eV, corresponding to each, respectively. This is interpreted as a result of the formation of various Si chemical species depending on the surface oxidation state of silicon particles during the manufacturing process, demonstrating that silicon in a stable oxidation state predominates. On the other hand, Si° or Si + No peak was observed, suggesting that the instability of Si particles was suppressed during the composite manufacturing process.

[0081] In contrast, in the case of a typical simple Si / C synthesis, a thick SiOx layer is formed and the carbon shell is unevenly coated, which can cause problems such as weakening or loss of the Si° signal in the core.

[0082] Referring to Fig. 6 (b), in a C 1s core level scan performed in the binding energy range of 280–288 eV, peaks corresponding to Si-C bonds (284.0 eV), CC bonds (284.2 eV), and C-OH bonds (284.9 eV) were detected, respectively. While typical CNT (carbon nanotube) based structures are formed mainly through CC bonds, it was confirmed that the single-crystal carbon shell formed through a direct growth pyrolysis process on a copper substrate in the GNR / Si nanocomposite of the present invention exists mainly in the form of Si-C bonds.

[0083] On the other hand, simple Si / C composites tend to have a relatively higher proportion of C-OH bonds due to the adsorption of -OH groups during the hydrothermal synthesis process, which is a characteristic that distinguishes them from GNR composites.

[0084] Consequently, the GNR / Si nanocomposite of the present invention provides abundant active sites for lithium ions, while the defect-free outer GNR shell provides stable Li + By providing a storage structure and an excellent electron conduction pathway, it enables the realization of fast reaction rates and high electrochemical performance.

[0085] Figure 7 shows the X-ray diffraction (XRD) pattern results for analyzing the crystal structure of the composite according to Example 1 of the present invention. In the embodiment of the present invention, X-ray diffraction (XRD) analysis was performed to analyze the crystal structure of the manufactured composite and raw materials. The measurement range was set to 2θ = 20˚ ~ 80˚, the step length to 0.02˚, and the step time to 2 s, while the acceleration voltage was 40 kV and the current was 100 mA. Through the XRD analysis results, the crystallinity of the composite raw materials and the coating layer of the composite were confirmed.

[0086] Referring to FIG. 7, the composite according to one embodiment 1 of the present invention exhibits distinct diffraction peaks at 2θ = 28.7°, 41.4°, and 56.1°, which are analyzed as characteristic peaks corresponding to the (111), (220), and (311) crystal planes of crystalline silicon, respectively.

[0087] The above results indicate that the silicon particles are incorporated within the composite structure while maintaining their crystallinity, suggesting that the silicon's crystal structure was not damaged by thermal or chemical treatment during the manufacturing process.

[0088] Meanwhile, the carbon nanotubes (CNT) analyzed for comparison showed diffraction peaks at 2θ = 25.8° and 43.7°, respectively, which correspond to the (002) and (101) crystal planes of the graphite structure and reflect the characteristic structure of the CNT.

[0089] In the GNR / Si nanocomposite of the present invention, silicon crystal peaks and diffraction characteristics according to the carbon-based structure of graphene nanoribbons (GNR) are simultaneously confirmed, thereby proving that the two components were composited in a structurally aligned state and that the crystallinity of the components was maintained throughout the entire synthesis process.

[0090] Figure 8 shows the results of Raman spectroscopy analysis to confirm the structural characteristics of the composite according to Example 1 of the present invention.

[0091] Referring to Figure 8, this analysis was performed at room temperature for the 10 nm GNR / Si composite and the 5 nm GNR / Si composite, respectively, and the Raman spectral characteristics of the two samples were compared.

[0092] Generally, in the Raman spectrum of carbonaceous materials, at approximately 1356 cm⁻¹ -1 The D band observed at approximately 1582 cm⁻¹ corresponds to a disordered or defective amorphous carbon structure. -1 The G band corresponds to a highly crystalline graphitized carbon structure.

[0093] In the case of the GNR / Si nanocomposite, the I_D / I_G ratio was found to be approximately 1.25, which implies the presence of a certain proportion of amorphous carbon within the composite, and the main cause is analyzed to be due to mesoporous carbon formed during the pyrolysis process on the copper substrate.

[0094] On the other hand, the single-crystal graphene nanoribbon (GNR) structure included in the complex is Li + It is evaluated to contribute to the improvement of diffusion speed and interfacial permeability.

[0095] Also, about 523 cm -1 The characteristic Raman peak of silicon was identified, and in the GNR / Si nanocomposite of the present invention, this peak is **524 cm⁻¹ -1 A blue shift** phenomenon was observed. This peak shift is interpreted as a masking effect caused by the amorphous silicon structure and the GNR layer coated on the surface of the silicon particles, which structurally proves that the GNR shell effectively surrounds the Si core.

[0096] Consequently, the Raman peak positions and intensities of the GNR / Si composites show variations depending on the GNR thickness and structure, which is considered to reflect the crystallinity, amorphousness, and interaction with silicon of the carbon structure within the composite.

[0097] Electrochemical Analysis

[0098] Figures 9(a) and (b) respectively show the initial charge / discharge voltage-capacity profile measured at a current density of 0.2 A / g to confirm the initial charge / discharge characteristics of the GNR / Si nanocomposite structure according to Example 1 of the present invention, and the results of performing Cyclic Voltammetry (CV) analysis on a unit cell using the GNR / Si nanocomposite.

[0099] Referring to Fig. 9 (a), the initial charge / discharge capacities were measured to be 1114 mAh / g and 1257 mAh / g, respectively, and the initial Coulomb efficiency was confirmed to be approximately 88.6%.

[0100] The decrease in initial Coulomb efficiency is interpreted as the result of a significant amount of Li ions being consumed due to the formation of a Solid Electrolyte Interphase (SEI) thin film layer and irreversible reactions with silicon oxide and heterogeneous materials during the initial charge-discharge cycle.

[0101] The GNR / Si nanocomposite-based cathode stably exhibited high capacity, which is attributed to the enhanced specific surface area and structural stability of the electrode resulting from the high-density structure of the GNR / Si composite and the mesoporous carbon-based matrix structure. Furthermore, an additional increase in capacity was induced by the alloying reaction between Si and Li during the charge-discharge process.

[0102] In particular, silicon microparticles and the GNR shell structure effectively buffer the volume expansion of Si during charging and discharging, and by maintaining the stability of the nano-micro composite structure, they enable excellent electrochemical cycle performance.

[0103] GNR suppresses the non-uniform aggregation of Si particles while simultaneously reducing the internal resistance of the electrode by providing a rapid electron transfer pathway, and the porous structure of the composite provides a diffusion pathway for lithium ions, thereby also enabling high-speed charge / discharge performance.

[0104] Referring to Fig. 9(b), the test was performed in a voltage range of 0.01–3 V, and two reduction peaks were identified at 0.31 V and 0.38 V during the discharge process of the first cycle. This indicates that the SEI film was successfully formed through the large surface area of ​​the GNR / Si composite.

[0105] In addition, during the oxidation process, an oxidation peak was observed at 0.58 V, and as the cycle was repeated, the intensity of the peak gradually decreased, which is interpreted as a result of the electrode surface being modified and the electrochemical stability being improved.

[0106] Figures 10(a) and (b) show the results of evaluating the rate capability of a lithium secondary battery containing a GNR / Si nanocomposite according to Example 1 of the present invention as a negative electrode active material, and the results of evaluating the long-term cycle performance and Coulombic efficiency of a battery with the GNR / Si nanocomposite applied.

[0107] Referring to FIG. 10 (a), a battery incorporating the negative electrode active material of the present invention exhibited excellent cycle characteristics, showing a capacity retention rate of 98.5% or more for more than 100 cycles under various charge / discharge rate conditions of 0.1, 0.2, 0.5, and 1 C-rate.

[0108] In addition, it was confirmed that it maintains a relatively high capacity compared to batteries using conventional silicon / graphite composite anodes even at high-speed charge / discharge conditions of 0.5, 1, and 2 C-rates, and in particular, showed high cycle stability of over 97% under the condition of 0.1 C.

[0109] These characteristics are attributed to the fact that the consistent formation of graphene nanoribbon (GNR) structures on the surface of silicon microparticles leads to the formation of a stable and uniform Solid Electrolyte Interphase (SEI) layer, which in turn reduces heterointerface resistance and facilitates the smooth transfer of electrons and ions within the electrode. Consequently, the GNR / Si composite was able to simultaneously achieve high capacity and a long lifespan, even under high-speed charge and discharge conditions.

[0110] Referring to Fig. 10 (b), the GNR / Si nanocomposite-based battery exhibited a capacity retention rate of approximately 97% after 500 cycles under a current density of 0.2 A / g, with a reversible capacity of 1114 mAh / g, maintaining high irreversible capacity characteristics.

[0111] In addition, even under conditions of a higher current density of 5 A / g, a reversible capacity of >1110 mAh / g was maintained after 500 cycles, and the Coulomb efficiency was also maintained stably at approximately 97% after 500 cycles.

[0112] These results indicate that the GNR / Si nanocomposite possesses excellent structural stability, and that the high electrical conductivity and porous matrix structure provided by GNR contribute to Li +This indicates that it significantly contributed to the long-term life characteristics of the battery by maintaining smooth diffusion and electron transport pathways.

[0113] [Example 2]

[0114] Example 2 is identical to Example 1 in all respects except for the preparation of the negative electrode active material.

[0115] Preparation of cathode active material

[0116] Silicon nano or microparticles were prepared, and copper or nickel was deposited within 20 nm on the silicon particles. Then, a dry etching process, such as using a shadow mask and ICP-RIE (Inductively Coupled Plasma Reactive Ion Etching), was performed to fabricate metal, namely copper or nickel, microribbons. Subsequently, by applying the ICP-RIE method, carbon undergoes repeated in-diffusion and out-diffusion into the metal structure, restructuring and forming nanoribbons through direct growth on the silicon particles.

[0117] Example 2 utilizes a dry etching process called ICP-RIE, which is used in semiconductor manufacturing, to increase the ion density with a high plasma density to accelerate the etching speed. Additionally, by controlling the ion energy with a separate RF power source, precise anisotropic etching is enabled while minimizing damage. In other words, high linearity, etch selectivity, and low damage characteristics are simultaneously realized, making it suitable for use in nanoribbon manufacturing.

[0118] [Example 3]

[0119] Example 3 is identical to Example 1 in all respects except for the preparation of the negative electrode active material.

[0120] Preparation of cathode active material

[0121] Silicon oxide (SiOx, 0 <x≤2)를 1000도 이상에서 10초 이내 펄스 에너지를 통한 순간 열처리를 반복하여 산소를 제거한다. 이후 실리콘의 표면에 구리 또는 니켈을 10nm 이내로 증착한 후, 쉐도우 마스크와 ICP-RIE(유도 결합 플라즈마 반응성 이온 식각) 등 드라이 에칭 공정을 진행하여 메탈 즉 구리 또는 니켈의 마이크로 리본을 제작했다. 이후 ICP-RIE 공법을 적용하여 탄소가 메탈구조에 In-diffusion, Out-diffusion을 반복하며 재구조화되면서 실리콘 입자에 나노리본이 직성장(Direct growth)하여 형성된다.

[0122] As described above, the disclosed embodiments have been explained with reference to the attached drawings. Those skilled in the art will understand that the present invention may be practiced in forms different from the disclosed embodiments without changing the technical spirit or essential features of the invention. The disclosed embodiments are illustrative and should not be interpreted restrictively. Explanation of the symbols

[0123] 10: Complex 11: Core 12: Shell

Claims

Claim 1 A composite comprising a silicon-based active material and a nanoribbon surrounding the silicon-based active material, wherein the composite is provided with a core containing the silicon-based active material and a shell surrounding the core and containing the nanoribbon, wherein the shell is formed into a single crystal structure by growing directly on the surface of the core, and wherein the composite is a cathode active material in which a Si-C bond (284.0 eV) peak is observed in a C 1s core level scan during X-ray photoelectron spectroscopy (XPS) analysis. Claim 2 delete Claim 3 In claim 1, the shell is a negative electrode active material having a thickness of 5 nm to 50 nm. Claim 4 In claim 1, the cathode active material provided with the above-mentioned composite having a porous structure. Claim 5 In claim 4, the above composite is a negative electrode active material having an average particle size of 50 nm to 5 μm. Claim 6 In claim 5, the silicon-based active material is Si and SiOx(0 <x≤2) 중 적어도 하나 이상을 포함하는 음극 활물질. Claim 7 In claim 6, the silicon-based active material is a negative electrode active material composed of a single crystal structure. Claim 8 In claim 6, the above composite is a negative active material in which characteristic peaks are observed at the crystal planes (111), (220), and (311) during XRD pattern analysis. Claim 9 In claim 1, the nanoribbon is a negative electrode active material composed of graphene. Claim 10 In claim 9, the nanoribbon is a negative electrode active material formed with a thickness of 5 to 50 nm. Claim 11 A lithium secondary battery comprising: a negative electrode comprising a negative electrode active material according to any one of claims 1, 3 to 10; a positive electrode comprising a positive electrode active material; and an electrolyte that delivers lithium ions to the positive electrode and the negative electrode. Claim 12 In claim 11, the lithium secondary battery is a lithium secondary battery that exhibits a capacity retention rate of 97% or more after 500 or more charge-discharge cycles at a current density of 0.2 A / g. Claim 13 In claim 11, the lithium secondary battery is a lithium secondary battery having a capacity of 1500 mAh / g or more at a current density of 0.1 A / g. Claim 14 A method for manufacturing a negative electrode active material comprising: a pretreatment step for manufacturing and purifying a silicon-based active material; a step of depositing a copper or nickel thin film on the surface of the pretreated silicon-based active material; and a composite manufacturing step for manufacturing a core-shell structured composite by directly growing a single-crystal carbon nanoribbon shell on the surface of the silicon-based active material using a carbon precursor pyrolysis or an ICP-RIE (inductively coupled plasma reactive ion etching) process. Claim 15 A method for manufacturing a cathode active material according to claim 14, wherein the pretreatment step comprises a step of melting a silicon-based precursor; and a step of condensing molten silicon-based particles, and the composite manufacturing step comprises a step of forming a carbon nanoribbon shell on the outside of the condensed silicon-based particles.

Images