A kind of Nb2O5-based confined fiber electrode material related to lithium energy storage field

Abstract

The application belongs to the technical field of electrode materials, and particularly relates to a Nb2O5-based confined fiber electrode material in the field of lithium energy storage, wherein spinning sol is prepared by electrospinning of carbon tubes, a self-sacrificial template, a polymer carbon source and a niobium source through regulation of electrospinning parameters, and then a membrane material is obtained through pre-oxidation-carbonization. The electrode material uses capillary carbon tubes as an effective mechanical enhancement framework of a fiber cage, improves the overall mechanical strength of the fiber material under the cage structure, and limits T-Nb2O5-x rich in oxygen vacancy defects in the fiber cage, so that a membrane electrode material with both porosity and flexibility is prepared, and the membrane electrode material has excellent electronic conductivity.

Description

Technical Field

[0001] This invention belongs to the field of electrode material technology, specifically relating to a method for developing Nb2O5-based confined fiber electrode materials for lithium energy storage. Background Technology

[0002] Cage structures built around pores are increasingly demonstrating their importance in the field of energy storage materials. In energy storage, a cage is defined as a porous structure that confines space, like a cage, allowing high-strain energy storage materials to be contained within a limited space while maintaining sufficient pores to facilitate the transfer of electrolyte between the internal space and the material. Sufficient buffer space within the cage suppresses strain forces during energy storage. Furthermore, the relatively independent micro-reaction chambers can provide higher reaction efficiency and reduce the impact of the external environment. Combining cage structures with one-dimensional fibers enhances charge correlation between cage structures, promoting charge transfer and storage. However, since mechanical strength is generally inversely proportional to pore volume, simultaneously balancing porosity and flexibility is a key research focus.

[0003] The advantages of the cage structure can be further leveraged by carrying high-efficiency energy storage materials within the fiber cage. Orthorhombic niobium pentoxide (T-Nb2O5) exhibits excellent intercalation pseudocapacitive behavior due to its high chemical stability and open lattice framework, demonstrating high rate performance in the Li / Na ion storage system; the large lattice spacing (3.9 Å) of Nb2O5 corresponding to the (001) crystal plane is much larger than that of Li. + (1.18 Å) and Na + The (2.04 Å) diameter facilitates rapid transport and embedding of both electrolytes. Simultaneously, its safe operating voltage window effectively avoids problems such as electrolyte decomposition and dendrite growth, resulting in higher safety and longer lifespan. However, Nb₂O₅ inherently has low conductivity (~3 × 10⁻⁶ Å). -6 The limited S / cm ratio restricts its practical application in energy storage materials. Constructing a three-dimensional conductive network is an effective strategy to alleviate this problem, such as preparing carbon fiber networks by electrospinning. However, Nb2O5 particles are often randomly distributed inside the fiber and are not easily activated by the electrolyte. Therefore, combining the cage structure with the fiber conductive network is necessary. At the same time, ensuring rapid electrolyte wetting of the fiber structure is also one of the optimization directions. Summary of the Invention

[0004] This invention mainly provides a Nb2O5-based confined fiber electrode material for lithium energy storage, and a method for preparing the material, to solve the problems in the prior art where the mechanical strength and high porosity of electrode materials cannot be simultaneously achieved, ion transport efficiency is low, and oxygen vacancies cause lattice imbalance. The technical solution is as follows:

[0005] A Nb2O5-based confined fiber electrode material relating to lithium energy storage includes a fiber cage formed by carbon nanotubes as a framework and Nb2O5 particles encapsulated within the fiber cage; the fiber cage has pores evenly distributed on it.

[0006] Furthermore, the diameter of the carbon nanotubes is 20~100nm; the particle size of the Nb2O5 particles is 2~50nm.

[0007] Furthermore, the pores include macropores with a diameter of not less than 60 nm, mesopores with a diameter of 60-5 nm, and micropores with a diameter of 5-0.3 nm.

[0008] A method for preparing the above-mentioned Nb2O5-based confined fiber electrode material related to lithium energy storage includes the following steps:

[0009] (1) Mix carbon nanotubes with self-sacrificing template emulsion to form reaction solution A; mix polymer carbon source and niobium source in water, add boric acid to form solution B; mix reaction solution A and solution B evenly to prepare spinning sol;

[0010] (2) Electrospin the spinning sol and dry it;

[0011] (3) Pre-oxidize the dried spun membrane; then, in a protective atmosphere, heat it to 600-1200℃ at a rate of 3-8℃ / min to obtain a fiber membrane precursor after carbonization.

[0012] Excessive heating rate leads to rapid pyrolysis of polyvinyl alcohol and polytetrafluoroethylene, causing fiber structure cracking and reducing structural stability. Insufficient heating rate results in incomplete degradation and removal of polytetrafluoroethylene, leading to incomplete development of the pore structure. Excessively high or low carbonization temperatures can alter the Nb₂O₅ lattice, hindering the formation of orthorhombic crystals. Orthorhombic crystals are the most favorable crystal form for lithium storage in Nb₂O₅, while the formation of impurities is detrimental to lithium storage. Furthermore, excessively low temperatures also hinder complete template removal. Excessively high temperatures reduce the structural stability of the carbon fiber.

[0013] (4) The fiber membrane precursor is heated to 600-800℃ for 1-3h in a mixed atmosphere of argon and hydrogen at a rate of 1-4℃ / min. The main purpose of this step is to use H2 to capture some oxygen atoms in Nb2O5 and build a certain number of oxygen vacancies. If the heating rate is too high, the reaction will be violent and insufficient to make H2 completely and uniformly distributed in the bulk phase of the material, thus reducing the uniformity of oxygen vacancies. If the heating rate is too slow, the time cost will increase, which is not conducive to the efficient preparation of the material. In addition, if the isothermal time is too long, too many oxygen vacancies will be built, which will destroy the long-term stability of the crystal structure and aggravate the irreversible structural collapse during repeated lithium ion insertion / extraction, resulting in rapid capacity decay. At the same time, it may expose more unstable surface active sites and aggravate the side reactions with the electrolyte. If the isothermal time is too short, it is not conducive to the generation of oxygen vacancies, and too few oxygen vacancies are insufficient to optimize the material.

[0014] Furthermore, the self-sacrificing template is polytetrafluoroethylene; the polymer carbon source is polyvinyl alcohol; and the niobium source is ammonium oxalate niobate.

[0015] Furthermore, the mass ratio of carbon nanotubes to self-sacrificing templates is 1:50~150; if the proportion of carbon nanotubes is too low, it will directly affect the structural stability of the final fiber and be detrimental to the cycle stability of the electrode material; if the proportion of carbon nanotubes is too high, it will inhibit the generation of pore structure, resulting in too few pores, which is not conducive to the improvement of specific surface area and the occurrence of cage confinement effect, thus reducing specific capacity.

[0016] The molar ratio of carbon atoms in the carbon source to niobium atoms in the niobium source is 290~730:1. Excessive content of ammonium oxalate hydrate will lead to excessive Nb2O5 derivatives and agglomeration, which is detrimental to lithium storage behavior and reduces specific capacity. Insufficient content of ammonium oxalate hydrate will result in insufficient lithium storage sites, which is also detrimental to high specific capacity performance.

[0017] The mass ratio of carbon nanotubes to carbon source is 0.01~0.02:1.

[0018] Furthermore, the needle-collector distance in the electrospinning process is 10~30cm; if the distance is too short, the spun fibers will show obvious agglomeration and clumping, which will reduce the effective specific surface area; if the distance is too long, the spun fibers will break, which is not conducive to structural stability.

[0019] Furthermore, the feeding rate is 0.5~1.5mL / h; if the feeding rate is too fast, the fibers will be too coarse and there will be problems such as agglomeration and uneven composition; if the feeding rate is too slow, the fibers will be too fine and there will be problems such as breakage and uneven thickness, which will reduce the conductivity and performance uniformity of the material.

[0020] Furthermore, the temperature should be 15~30℃ and the humidity should be 40~60%. Temperature and humidity mainly interfere with the fiber curing speed. If the temperature is too low or the humidity is too high, the fiber will not cure in time and will agglomerate and clump together.

[0021] Furthermore, after electrospinning, the spun film is peeled off and dried at 60~80℃ until all residual solvent is completely removed.

[0022] Furthermore, the pre-oxidation is carried out in an oxidizing atmosphere at 180~380℃ for 1.5~3 hours.

[0023] A battery made using the aforementioned Nb2O5-based confined fiber electrode material related to lithium energy storage.

[0024] By adopting the above scheme, the method of the present invention has the following advantages:

[0025] 1. In the electrode material of this invention, carbon nanotubes, aided by capillary effect, penetrate the fiber like blood vessels, rapidly delivering electrolyte to all parts of the bulk phase, thus enhancing the material's space utilization and ion transport rate. Secondly, as a cage-like framework, carbon nanotubes ensure that the electrode material maintains good structural toughness and stability while possessing a porous structure with numerous interconnected macropores (>60 nm), mesopores (~5 nm), and micropores (0.3 nm). Simultaneously, carbon nanotubes provide a robust conductive framework for the active material, effectively buffering drastic volume changes during charge and discharge, suppressing material pulverization and structural collapse, thereby significantly improving the electrode's cycle stability and lifespan. Furthermore, their excellent conductivity constructs high-speed electron transport channels, accelerating the diffusion kinetics of lithium ions and electrons, and significantly improving the material's rate performance.

[0026] 2. The preparation method of this invention introduces oxygen vacancy defects into T-Nb2O5, which can improve intrinsic conductivity and reduce ion transport barriers, ensuring good electron transfer rate and ion storage capacity. Oxygen vacancy defects also enhance the ion adsorption tendency of Nb2O5, thereby increasing the material's capacitance. Simultaneously, Nb2O... 5-x The near-quantum dot size of the particles, combined with the high permeability of the nanocage, ensures high exposure and utilization of active defect sites.

[0027] 3. This invention utilizes high-defect T-Nb2O 5-x Encapsulated within a fiber cage formed by a carbon skeleton, the Nb2O5 is protected by the carbon fiber cage. This robust physical barrier effectively suppresses the volume expansion and structural pulverization of the Nb2O5 core during cycling. Furthermore, the small-diameter pores that allow ions to enter and exit prevent direct contact between the electrolyte and Nb2O5, thus ensuring the full progress of the electrochemical process while suppressing side reactions, including electrolyte decomposition, initiated by highly reactive oxygen vacancies.

[0028] 4. In the electrode material of this invention, the fiber cage formed by carbon nanotubes as the framework has high permeability and confinement effect: the confinement effect and void structure of the constructed large number of cage structures effectively mitigate the volume expansion strain of the material during energy storage. The fibers constituting the cages in the electrode material have small diameters, and the highly porous structure of the cages is more conducive to electrolyte wetting of the bulk phase, shortening the ion transport path. At the same time, under the action of highly conductive carbon nanotubes and doped ions, the fiber cages have excellent electronic conductivity, constructing an excellent electron transport network.

[0029] 5. The preparation method of this invention utilizes a self-sacrificing template to construct an interpenetrating porous structure in electrospun fibers, overcoming the disadvantage of insufficient specific surface area in traditional fiber materials. Secondly, the cage-like confinement effect brought about by the porous structure can effectively alleviate problems such as volumetric strain in Nb₂O₅ energy storage. Furthermore, using carbon nanotubes as a framework to maintain the structural stability of the porous fibers solves the problem that while numerous self-sacrificing templates can construct more porous structures, they also reduce the structural stability of the fibers. This method effectively combines the structural stability and high porosity of the fiber material, corresponding to the dual performance advantages of high specific capacitance and high stability.

[0030] 6. In the electrode material of this invention, Nb2O5 is in the form of small particles close to quantum dots, which is beneficial for exposing more active sites. Nb2O5 further utilizes H2 to capture some oxygen to construct oxygen vacancies, which can effectively improve its lithium storage performance. The introduction of oxygen vacancies leads to a decrease in the valence state of some niobium ions, which significantly enhances the electronic conductivity of the material and thus reduces the internal resistance of the electrode. At the same time, the vacancy defects in the lattice can expand the lithium ion transport channel and reduce the diffusion barrier, accelerate the ion migration rate, and improve the rate performance. In addition, oxygen vacancies, as active sites, can also provide an additional pseudocapacitive lithium storage mechanism, which can generate higher specific capacity and better electrochemical kinetics. Attached Figure Description

[0031] Figure 1 This is a scanning electron microscope image of the electrode material synthesized in Example 1.

[0032] Figure 2 This is a transmission electron microscope (TEM) image of the electrode material synthesized in Example 1.

[0033] Figure 3 This is a high-magnification transmission electron microscope image of the electrode material synthesized in Example 1.

[0034] Figure 4 This is an electron microscope image of the lattice fringes of the electrode material synthesized in Example 1.

[0035] Figure 5 This is a scanning electron microscope image of the electrode material synthesized in Example 2.

[0036] Figure 6 This is a scanning electron microscope image of the electrode material synthesized in Example 3.

[0037] Figure 7 This is a scanning electron microscope image of the electrode material synthesized in Example 4.

[0038] Figure 8 This is a scanning electron microscope image of the electrode material synthesized in Example 5.

[0039] Figure 9 This is a scanning electron microscope image of the electrode material synthesized in Example 6.

[0040] Figure 10 The image shows the electron paramagnetic resonance spectrum of the electrode material synthesized in Example 1.

[0041] Figure 11 The image shows the XRD pattern of the electrode material synthesized in Example 1.

[0042] Figure 12 The image shows the XRD pattern of the electrode material synthesized in Example 3.

[0043] Figure 13 The image shows the XPS-Nb spectrum of the electrode material synthesized in Example 1.

[0044] Figure 14 The image shows the XPS-C spectrum of the electrode material synthesized in Example 1.

[0045] Figure 15 The image shows the XPS-N spectrum of the electrode material synthesized in Example 1.

[0046] Figure 16 The image shows the electron paramagnetic resonance spectrum of the electrode material synthesized in Example 3.

[0047] Figure 17 The cyclic voltammetry curves are for the lithium-ion half-cell prepared in Example 1.

[0048] Figure 18 The cyclic voltammetry curves for the first three cycles of the lithium-ion half-cell prepared in Example 1 are shown.

[0049] Figure 19 This is a comparison of the cyclic voltammetry curves of the lithium-ion half-cells prepared in Example 1 and Example 3.

[0050] Figure 20 This is a constant current charge-discharge curve of the lithium-ion half-cell prepared in Example 1.

[0051] Figure 21 This is a comparison chart of the specific capacity of the lithium-ion half-cells prepared in Example 1 and Example 3.

[0052] Figure 22The cycling curve of the lithium-ion half-cell prepared in Example 1 is shown.

[0053] Figure 23 The constant current charge-discharge curves of the lithium-ion half-cells prepared for comparison are shown. Detailed Implementation

[0054] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0055] Example 1: (1) 0.015 g of carbon nanotubes were immersed in 1.5 g of polytetrafluoroethylene emulsion (60 wt% aqueous solution) and mixed by ultrasonic stirring to form reaction solution A; 1 g of polyvinyl alcohol, 0.001 mg of boric acid (4 wt% aqueous solution) and 0.04 g of ammonium niobate oxalate hydrate were mixed in water to form solution B; reaction solution A and solution B were mixed and stirred evenly to prepare a stable spinning sol;

[0056] (2) The electrospinning parameters were set as follows: needle-collector distance, feed rate, temperature and humidity were 15 cm, 1 mL / h, 25℃ and 50%, respectively. After electrospinning, the spun membrane was peeled off from the collector. It was dried in a vacuum oven at 70℃ for 12 h to completely remove the residual solvent. Then, the spun membrane was oxidized in an air atmosphere at 250℃ for 2 h, and then carbonized in an N2 atmosphere at a heating rate of 5℃ / min to 900℃ for 2 h to obtain the fiber membrane precursor.

[0057] (3) The fiber membrane precursor was heated to 700℃ in a H2 / Ar mixture (5%) at a rate of 2.5℃ / min and held at that temperature for 2h to obtain the electrode material.

[0058] Figure 1 The image shows a scanning electron microscope (SEM) image of the electrode material obtained in Example 1. As can be seen from the image, the obtained sample consists of long and uniform carbon fibers forming an intertwined structure. The fiber surface is distributed with macroporous structures that penetrate the entire fiber, which facilitates rapid electrolyte wetting of the bulk phase of the material, improves the space utilization of the fiber, and also alleviates the volumetric strain effect during energy storage.

[0059] Figure 2 The transmission electron microscopy (TEM) images show that the fiber has a large number of pores that penetrate the bulk phase, and that the fiber is a large fiber composed of multiple small fibers with carbon nanotubes as the backbone, which forms a fiber cage structure. At the same time, Nb2O5 nanoparticles can be observed distributed in the fiber and protected by the fiber cage structure.

[0060] Figure 3 The high-magnification transmission electron microscopy (TEM) images show that the Nb₂O₅ nanoparticles in the prepared sample fibers have a diameter of approximately 20 nm, close to the size of quantum dots. Smaller nanoparticles facilitate the exposure of more active sites, resulting in high specific capacity.

[0061] Figure 4 The electron microscopy images of the lattice fringes show that the Nb₂O₅ nanoparticles exhibit distinct and uniform bright and dark fringes, indicating that they possess a unified lattice type. The lattice interstices are 0.39 nm, corresponding to an orthorhombic crystal structure, and this interstices perfectly satisfy the Li… + The transport and embedding of ions are used to construct a better ion transport channel.

[0062] Figure 10 The electron paramagnetic resonance spectrum shows that a strong signal was generated at the position of g≈2.0 by electron capture at the defect site, which verifies the existence of oxygen vacancies.

[0063] Figure 11 The XRD patterns show that the XRD response peaks of the samples prepared in the examples are consistent with the standard card (JCPDS#27-1003) of T-Nb2O5, with obvious response peaks at 22.6°, 28.3°, and 36.5°, corresponding to the (001), (180), and (181) crystal planes, respectively, and corresponding to the orthorhombic crystal system (T-, pbam space group lattice constants: a = 6.19, b = 3.625, c = 3.94 Å; εr = 78). Firstly, the lattice voids of the orthorhombic T-Nb2O5 satisfy the Li... + Na + The insertion / extraction behavior occurs; secondly, no obvious impurity peaks appear in the XRD after oxygen vacancy construction, which indicates that vacancy construction does not introduce new low-valence niobium oxides, and the construction of oxygen vacancy does not fundamentally destroy the T-Nb2O5 lattice, but maintains its lattice system unchanged.

[0064] Figure 13 The XPS-Nb spectrum shows that the Nb 3d spectrum of Example 1 can be resolved to be located at 207.5 eV (Nb 3d). 5 / 2 ) and 210.2 eV (Nb 3d 3 / 2 The double peak corresponds to Nb 5+ The energy level was [value missing]; no other low-valence peaks appeared in its spectrum, which is consistent with the conclusion from XRD analysis that oxygen vacancy construction did not introduce low-valence oxides into Nb2O5.

[0065] Figure 14The XPS-C spectrum shows that the fine spectrum of C 1s in the electrode material synthesized in Example 1 has four sub-peaks: 284.4 eV for CC, 285.5 eV for CN, 286.5 eV for CO, and 288.6 eV for C=O. Among them, CN (285.5 eV) is due to the doping of carbon material by nitrogen element during the pyrolysis of niobium source.

[0066] Figure 15 The XPS-N spectrum shows that the fine N 1s spectrum can be interpreted as four sub-peaks. The Nb-N peak at 397.7 eV proves that nitrogen has successfully entered the Nb2O5 lattice and formed a stable valence bond relationship. The appearance of the other three peaks is due to the doping defects formed by nitrogen in the carbon fiber.

[0067] Example 2: The difference from Example 1 is as follows:

[0068] In step (2), the electrospinning parameters are set as follows: needle-collector distance is 10 cm, feed rate is 2 mL / h, temperature is 25℃, and humidity is 50%.

[0069] Figure 5 The scanning electron microscope images show that, due to the spinning parameters being set outside the protection range, the fibrous structure of the electrode material synthesized in Example 2 exhibits problems such as uneven thickness and incomplete curing, resulting in the fibers in the membrane structure sticking together and failing to show a uniform and reliable porous structure.

[0070] Example 3: The difference from Example 1 is as follows:

[0071] In step (3), the fiber membrane precursor is heated to 700℃ in a H2 / Ar mixture (5%) at a rate of 5℃ / min and held at that temperature for 0.5h to obtain the electrode material.

[0072] contrast Figure 6 and Figure 1 The scanning electron microscope images show that, in terms of morphology, the structure of Example 3 is basically the same as that of Example 1. This indicates that the formation of oxygen vacancies has little impact on the material morphology.

[0073] Figure 16 As can be seen from the electron paramagnetic resonance (EPR) spectrum, due to the short oxygen vacancy construction time in Example 3, insufficient oxygen vacancies were formed. The absence of a significant response peak in the EPR spectrum indicates that oxygen vacancy construction failed.

[0074] Example 4: The difference from Example 1 is as follows:

[0075] In step (1), 0.015 g of carbon nanotubes are immersed in 0.5 g of polytetrafluoroethylene emulsion (60 wt% aqueous solution) and mixed by ultrasonic stirring to form reaction solution A.

[0076] Figure 7 The scanning electron microscope images show that, due to the insufficient content of polytetrafluoroethylene as a self-sacrificing template in Example 4, the pore structure on the fibers of the final synthesized electrode material was not fully developed. Only micropores were formed, and macropores and mesopores of various sizes were not formed. This is not conducive to the activation and utilization of bulk components, especially the Nb2O5 particles wrapped inside the fibers, which are difficult to participate in electrochemical reactions.

[0077] Example 5: The difference from Example 1 is as follows:

[0078] In step (1), 0.005 g of carbon nanotubes are immersed in 0.5 g of polytetrafluoroethylene emulsion (60 wt% aqueous solution) and mixed by ultrasonic stirring to form reaction solution A.

[0079] Figure 8 The scanning electron microscope (SEM) images show that, due to the insufficient number of carbon nanotubes serving as the framework in Example 5, the synthesized electrode material suffers from severe fragmentation and aggregation, leading to instability in its electrochemical performance during energy storage. This also demonstrates that the carbon nanotubes in the electrode material of this invention can effectively improve electrochemical performance by acting as a framework.

[0080] Example 6: The difference from Example 1 is as follows:

[0081] In step (2), the fiber membrane precursor is obtained by heating to 900℃ for 2 hours in a N2 atmosphere at a heating rate of 5℃ / min.

[0082] Figure 9 The scanning electron microscope images show that the carbonization temperature and heating rate in Example 6 were too high, resulting in excessively intense pyrolysis. This prevented the effective release of dissolved gases, causing the fibers of the synthesized electrode material to exhibit a large number of irregular pore structures, which is detrimental to the stability of the material properties and the continuous charge-discharge reaction.

[0083] Comparative Example: The difference from Example 1 is that:

[0084] Step (1) does not contain ammonium niobate oxalate.

[0085] Electrochemical performance testing:

[0086] The electrode materials, conductive graphite, and binder polytetrafluoroethylene (PTFE) prepared in each example and comparative example were mixed with an appropriate amount of ethanol in a mass ratio of 85:10:5 and coated onto copper foil (1.6 cm in diameter) to obtain the working electrode. The working electrode was dried to constant weight in a vacuum drying oven at 60°C. Lithium metal sheets, glass fiber membranes, spring sheets, gaskets, and button cell casings were prepared in a glove box, and lithium-ion half-cells were assembled. Experiments were conducted using lithium-ion half-cells in an electrochemical workstation.

[0087] Figure 17 The cyclic voltammetry (CV) curves of the lithium-ion half-cell prepared in Example 1 are shown in the scan rate range of 0.2–1.0 mV / s. Figure 17 As can be seen, all CV curves exhibit highly similar and broadened redox peak shapes, indicating excellent reversibility of the lithium-ion insertion / extraction process. With the scan rate increasing stepwise from 0.2 mV / s to 1.0 mV / s, the overall shape of the curves remained well-maintained without significant distortion, and the potential difference between the oxidation and reduction peaks did not change significantly, revealing that the electrode possesses extremely low polarization and rapid charge transfer kinetics. In summary, the battery prepared using the electrode material of Example 1 demonstrates high reversibility, low polarization, and excellent rate retention over a wide scan rate range, confirming the great potential of the electrode material of this invention as a high-performance lithium-ion battery anode material.

[0088] Figure 18 The figures show the cyclic voltammetry curves of the lithium-ion half-cell prepared in Example 1 at 0.2 mV / s for the first three cycles. Figure 18 It can be seen that the small irreversible reduction peak caused by the formation of the solid electrolyte interface in the first cycle rapidly weakens and disappears completely in subsequent cycles. From the second cycle onwards, the curves highly overlap, indicating that the irreversible capacity loss caused by side reactions is extremely low, and the coulombic efficiency rapidly increases to nearly 100%. This phenomenon shows that the Nb2O5 particles are encapsulated in carbon fibers, effectively isolating the active material from direct erosion by the electrolyte. This allows the highly active oxygen vacancies to enhance the material's conductivity and capacitance contribution without triggering additional irreversible consumption such as continuous side reactions or structural dissolution. Simultaneously, the synergistic effect of the highly efficient electron conduction network constructed by the carbon fibers and the abundant ion adsorption sites provided by the oxygen vacancies contributes to improving the overall conductivity of the material. This synergistic design not only reduces the initial irreversible capacity loss to an extremely low level but also endows the material with excellent rate performance and cycle reversibility, verifying the great potential of the electrode material of this invention in constructing high-performance lithium-ion battery anode materials.

[0089] Figure 19 This is a comparison of the CV curves of the lithium-ion half-cells prepared in Examples 1 and 3. Figure 19It can be seen that the main difference between Example 1 and Example 3 lies in the oxygen vacancies. The CV curve of Example 1 shows a larger closed integral area, which directly corresponds to its higher reversible lithium storage capacity. This is mainly due to the positive effects brought about by the introduction of oxygen vacancies: First, oxygen vacancies, as active sites, significantly enhance the chemisorption capacity of lithium ions on the material surface, contributing additional pseudocapacitive capacity; second, oxygen vacancies effectively regulate the local electronic structure, improve intrinsic electronic conductivity, and promote rapid charge transport; more importantly, oxygen vacancies may broaden the lithium ion diffusion channels, reduce the energy barrier for ion insertion / extraction, and enable more bulk active materials to be efficiently utilized. Therefore, compared with Example 3, the sample of Example 1 containing oxygen vacancies exhibits superior electrochemical activity and energy storage capacity under the same test conditions.

[0090] Figure 20 The image shows the galvanostatic charge-discharge (GCD) curves of the lithium-ion half-cell prepared in Example 1 at current densities of 0.05–1.0 A / g. Figure 20 As can be seen, the GCD curves of Example 1 exhibit highly similar charge-discharge curves over a wide current density range, indicating that the charge-discharge process is highly reversible and has extremely low polarization. This superior electrochemical performance is directly attributed to the successful introduction of oxygen vacancies: First, oxygen vacancies, as active sites, enhance the intrinsic electronic conductivity and ion diffusion rate of the material, thereby reducing internal resistance and polarization; second, the pseudocapacitive behavior induced by oxygen vacancies enhances the rapid storage capacity of surface charge, contributing additional capacity and optimizing rate response; third, oxygen vacancies may alleviate lattice stress during lithium-ion insertion / extraction, thus maintaining structural integrity during cycling.

[0091] Figure 21 This is a comparison chart of the specific capacity of Example 1 and Example 3. (From...) Figure 21 It can be seen that, within a wide current density range of 0.05 to 1.0 A / g, the specific capacity of Example 1 is significantly higher than that of Example 3. This comprehensive performance improvement can be attributed to the multiple synergistic effects generated by the introduction of oxygen vacancies: First, oxygen vacancies, as additional active sites, directly enhance the lithium-ion adsorption capacity on the electrode surface, contributing additional pseudocapacitive capacity; second, oxygen vacancies effectively modulate the local electronic structure of the material, improving intrinsic electronic conductivity, thereby improving charge transport dynamics at high rates; finally, oxygen vacancies may broaden lithium-ion diffusion channels and lower the bulk diffusion barrier, allowing more bulk active material to be effectively utilized, which is related to... Figure 19 The conclusions are consistent with those of the CV test.

[0092] Figure 22 This is a cycle curve of the lithium-ion half-cell prepared in Example 1. Figure 22As can be seen, during 4000 charge-discharge cycles, the electrode not only exhibited extremely high capacity retention, but its coulombic efficiency remained close to 100%. This demonstrates that the carbon fiber acts as a physical and chemical barrier for Nb₂O₅, effectively isolating the electrolyte from direct contact with the Nb₂O₅ particles. This suppresses potential side reactions induced by highly reactive oxygen vacancies during cycling (such as irreversible electrolyte decomposition and dissolution of active materials), ensuring that oxygen vacancies, while enhancing the material's conductivity and ion diffusion capabilities, do not become failure points due to cycle degradation. Simultaneously, the robust carbon shell structure buffers the volume changes during repeated lithium-ion insertion / extraction, maintaining the electrode's structural integrity. Therefore, the synergistic design of carbon shell protection and oxygen vacancies successfully transforms the high activity of oxygen vacancies into a lasting electrochemical advantage, achieving ultra-long cycle life and near-ideal reversibility, demonstrating the enormous potential of this material system for next-generation long-life lithium-ion batteries.

[0093] Figure 23 The GCD curve of the lithium-ion half-cell prepared in Comparative Example 1 is shown. Figure 23 It can be seen that the specific capacitance of the sample in Comparative Example 1 is only 45.7 mAh / g, which indicates that Nb2O5 is the main energy storage active material in this application and plays the main role in the occurrence of lithium storage behavior, reflecting the importance of adding niobium salt in this application.

[0094] For those skilled in the art, various other corresponding changes and modifications can be made based on the technical solutions and concepts described above, and all such changes and modifications should fall within the protection scope of the claims of this invention.

Claims

1. A Nb₂O₅-based confined fiber electrode material relating to lithium energy storage, characterized in that, It includes a fiber cage formed by carbon nanotubes as a framework, Nb2O5 particles encapsulated within the fiber cage, and pores evenly distributed on the fiber cage.

2. The Nb₂O₅-based confined fiber electrode material relating to lithium energy storage according to claim 1, characterized in that, The diameter of the carbon nanotubes is 20~100nm; the particle size of the Nb2O5 particles is 2~50nm.

3. The Nb₂O₅-based confined fiber electrode material relating to lithium energy storage according to claim 1, characterized in that, The pores include macropores with a diameter of not less than 60 nm, mesopores with a diameter of 60-5 nm, and micropores with a diameter of 5-0.3 nm.

4. A method for preparing an Nb₂O₅-based confined fiber electrode material relating to lithium energy storage as described in any one of claims 1 to 3, characterized in that, Includes the following steps: (1) Mix carbon nanotubes with self-sacrificing template emulsion to form reaction solution A; mix polymer carbon source and niobium source in water, add boric acid to form solution B; mix reaction solution A and solution B evenly to prepare spinning sol; (2) Electrospin the spinning sol and dry it; (3) Pre-oxidize the dried spun film; Then, in a protective atmosphere, the temperature is increased to 600-1200℃ at a rate of 3-8℃ / min, and carbonization is performed to obtain the fiber membrane precursor; (4) The fiber membrane precursor is heated to 600-800℃ for 1-3h in a mixed atmosphere of argon and hydrogen at a rate of 1-4℃ / min.

5. The method for preparing Nb₂O₅-based confined fiber electrode material in the field of lithium energy storage according to claim 4, characterized in that, The self-sacrificing template is polytetrafluoroethylene; the polymer carbon source is polyvinyl alcohol; and the niobium source is ammonium oxalate niobate.

6. The method for preparing Nb₂O₅-based confined fiber electrode material in the field of lithium energy storage according to claim 4, characterized in that, The mass ratio of carbon nanotubes to the self-sacrificing template is 1:50~150; the molar ratio of carbon atoms in the carbon source to niobium atoms in the niobium source is 290~730:1; and the mass ratio of carbon nanotubes to the carbon source is 0.01~0.02:

1.

7. The method for preparing Nb₂O₅-based confined fiber electrode material in the field of lithium energy storage according to claim 4, characterized in that, The needle-collector distance of the electrospinning process is 10~30cm, the feed rate is 0.5~1.5mL / h, the temperature is 15~30℃, and the humidity is 40~60%.

8. The method for preparing Nb2O5-based confined fiber electrode material in the field of lithium energy storage according to claim 4, characterized in that, After electrospinning, the spun film is peeled off and dried at 60~80℃ until all residual solvent is removed.

9. The method for preparing Nb2O5-based confined fiber electrode material in the field of lithium energy storage according to claim 4, characterized in that, The pre-oxidation is carried out in an oxidizing atmosphere at 180~380℃ for 1.5~3 hours.

10. A battery made using the Nb2O5-based confined fiber electrode material relating to lithium energy storage as described in any one of claims 1 to 3.

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