Nanoengineering of Ultrathin Carbon-Coated T-Nb₂O₅ Nanosheets for High-Performance Lithium Storage

Abstract

Niobium pentoxide (Nb₂O₅) is a promising anode candidate for lithium-ion batteries due to its high theoretical capacity, excellent rate capability, and safe working potential. However, its inherent low conductivity limits its practical application in fast-charging scenarios. In this work, we develop an ultrathin carbon-coated two-dimensional T-Nb₂O₅ nanosheet composite (T-Nb₂O₅@UTC) through a facile solvothermal reaction and subsequent CVD acetylene decomposition. This unique design integrates a two-dimensional nanosheet structure with an ultrathin carbon layer, significantly enhancing electronic conductivity, reducing ion diffusion pathways, and preserving structural integrity during cycling. The T-Nb₂O₅@UTC electrode demonstrates an impressive specific capacity of 214.7 mAh g⁻¹ at a current density of 0.1 A g⁻¹, maintaining 117.9 mAh g⁻¹ at 5 A g⁻¹, much outperforming the bare T-Nb₂O₅ (179.6 mAh g⁻¹ at 0.1 A g⁻¹ and 62.9 mAh g⁻¹ at 5 A g⁻¹). It exhibits outstanding cyclic stability, retaining a capacity of 87.9% after 200 cycles at 0.1 A g⁻¹ and 83.7% after 1000 cycles at 1 A g⁻¹. In a full-cell configuration, the assembled T-Nb₂O₅@UTC||LiFePO₄ battery exhibits a desirable specific capacity of 186.2 mAh g⁻¹ at 0.1 A g⁻¹ and only a 1.5% capacity decay after 120 cycles. This work underscores a nanostructure engineering strategy for enhancing the electrochemical performance of Nb₂O₅-based anodes toward high-energy-density and fast-charging applications.

1. Introduction

With the increasing demand for high-energy-density and fast-charging energy storage devices in modern society, the development of advanced anode materials with superior rate performance and cycling stability has become a research hotspot for lithium-ion batteries (LIBs)s [1,2,3]. Traditional graphite anode materials are widely used due to their relatively high specific capacity (372 mAh g⁻¹) and excellent electrical conductivity, but their limited lithium-ion diffusion kinetics and poor rate performance restrict their application in fast-charging batteries [4,5]. Silicon-based anodes have an extremely high theoretical specific capacity (~4200 mAh g⁻¹), but they typically suffer severe volume expansion (~300%) during the Li-ion insertion and extraction processes, resulting in electrode structure collapse and rapid capacity degradation. This volume effect limits the practicality of silicon-based anodes in high-energy-density and long-cycle-life applications. Therefore, there is a pressing need to explore novel anode materials that can maintain excellent cycling stability while achieving higher rate performance. Among the emerging candidates, niobium pentoxide (Nb₂O₅) has attracted considerable attention as an intercalation-type transition metal oxide anode with fast pseudocapacitive Li⁺ storage, high structural stability, and a safe working potential (above 1.0 V vs. Li/Li⁺) that avoids lithium dendrite growth and solid electrolyte interphase formation [6,7,8,9,10]. Especially, the layered open framework structures of orthorhombic T-phase Nb₂O₅ provide rapid ion transport channels along the (001) plane during lithium insertion/extraction [11,12]. However, the unoccupied d⁰ electronic configuration of Nb⁵⁺ in Nb₂O₅ renders it a semiconductor with a wide bandgap (4 eV). Its relatively poor electrical conductivity (3 × 10⁻⁶ S cm⁻¹ at 300 K) still limits its practical application in high-energy-density and fast-charging scenarios [13,14,15].

To address this challenge, nanostructure engineering has been considered a promising approach to improve the electrical conductivity and enhance the electrochemical performance of T-Nb₂O₅ [16,17]. In particular, the two-dimensional (2D) nanosheet structure design exhibits several key advantages for electrode materials. It can significantly shorten the electron and ion diffusion pathways and offer a larger surface area for lithium-ion insertion [18,19]. Not only that, it facilitates better contact with conductive additives, which further improves the electrical conductivity of the material [20]. By leveraging these benefits, 2D T-Nb₂O₅ nanosheets can effectively mitigate the limitations of traditional bulk materials in electrochemical applications. In addition, carbon coating has been demonstrated to be an effective surface engineering scheme that can simultaneously enhance bulk electron transport and mitigate structural degradation throughout electrochemical cycling, thereby achieving a synergistic enhancement of capacity retention and initial coulombic efficiency [21]. Therefore, the choice of coating technology is crucial to the uniformity, thickness control, and interfacial bonding of the carbon layer, factors that are particularly critical for 2D nano systems. Traditional methods such as hydrothermal carbonization and sol–gel coating usually result in uneven carbon deposition (thickness variation > 5 nm) or pore blockage caused by precursor infiltration [22,23], which significantly reduces the accessible surface area of 2D nanosheets. In contrast, chemical vapor deposition (CVD) can precisely control the carbon layer at the nanoscale, achieving ultra-thin thickness-controlled conformal coating while retaining the 2D morphology, which is particularly suitable for composite material design [24,25,26]. Hence, combining the nanostructure design and surface modification is expected to synergistically improve the electrochemical performance of T-Nb₂O₅, providing a pathway to achieving high energy density, excellent rate capability, and enhanced cycling stability in LIBs.

In this study, we present the synthesis of a two-dimensional T-Nb₂O₅ nanosheet coated with an ultrathin carbon (UTC) layer (thickness < 5 nm) composite (T-Nb₂O₅@UTC) through a straightforward solvothermal reaction followed by CVD acetylene decomposition. The artful combination of the two-dimensional nanosheet structure and UTC coating aims to address the inherent limitations of T-Nb₂O₅ in terms of electrical conductivity and specific capacity, thereby significantly improving its electrochemical performance in LIBs. As a result, the T-Nb₂O₅@UTC electrode achieves remarkable pseudocapacitive lithium storage of 96.8% at 1.1 mV s⁻¹. The initial specific capacity can reach 214.7 mAh g⁻¹ at 0.1 A g⁻¹ and retain 117.9 mAh g⁻¹ at 5 A g⁻¹, much better than that of the bare T-Nb₂O₅ (179.6 mAh g⁻¹ at 0.1 A g⁻¹ and 62.9 mAh g⁻¹ at 5 A g⁻¹). Moreover, the T-Nb₂O₅@UTC exhibits outstanding cyclic stability, with 87.9% capacity retention after 200 cycles at 0.1 A g⁻¹ and 83.7% capacity retention after 1000 cycles at 1 A g⁻¹. When assembled with LiFePO₄, the full cell delivers a specific capacity of 186.2 mAh g⁻¹ at 0.1 A g⁻¹ and 98.5% capacity retention after 120 cycles. This work demonstrates a successful strategy for improving the electrochemical performance of T-Nb₂O₅ and provides valuable insights for developing advanced anode materials with high energy density and excellent rate capability for next-generation LIBs.

2. Results and Discussion

2.1. Preparation and Structural Characterization of T-Nb₂O₅@UTC

The general preparation process of T-Nb₂O₅@UTC is illustrated in Figure 1a. Initially, a flake-like T-Nb₂O₅ precursor is synthesized using an isopropanol-based solvothermal reaction. The obtained precursor is then transferred to a muffle furnace and subjected to high-temperature annealing in an air atmosphere to convert it into T-Nb₂O₅. Subsequently, utilizing acetylene decomposition of chemical vapor deposition (CVD) achieves a uniform carbon coating on the T-Nb₂O₅ nanosheets. More synthesis details are reflected in the supporting information. Scanning electron microscopy (SEM) captures the real morphological changes of the T-Nb₂O₅ precursor, T-Nb₂O₅, and T-Nb₂O₅@UTC. As shown in Figure 1b, the T-Nb₂O₅ precursor presents a smooth two-dimensional sheet-like structure. After air calcination, the acquired T-Nb₂O₅ inherits this two-dimensional nanosheet structure of precursor well (Figure 1c). Moreover, it is noteworthy that a porous architecture develops between primary particles through the volatilization of organic constituents during high-temperature calcination processes. After the CVD process, no significant morphological changes are observed except for a slight decrease in pore size. This indicates that the carbon coating on the nanosheets has been successfully achieved (Figure 1d). The detailed structure of T-Nb₂O₅@UTC was investigated by means of transmission electron microscopy (TEM). Figure 1e shows a single T-Nb₂O₅@UTC sheet assembled from many primary nanoparticles. Figure 1f presents a further high-magnification TEM image of a single primary particle, where an UTC layer (less than 5 nm thick) is clearly visible on the particle surface. In addition, lattice fringes with a spacing of approximately 0.481 nm were obtained by fast Fourier transform (FFT), corresponding to the (060) crystal plane of T-Nb₂O₅ (Figure 1g). The elemental distribution mapping in Figure 1h further manifests that carbon (C) is uniformly distributed across the primary particles. These results verify the successful carbon encapsulation via the acetylene decomposition of CVD.

2.2. Crystal Structure and Vibrational Analysis of T-Nb₂O₅ and T-Nb₂O₅@UTC

XRD was utilized to detect the crystal structure of T-Nb₂O₅ and T-Nb₂O₅@UTC. As shown in Figure 2a, the diffraction peaks of these two samples are consistent with the standard card of T-Nb₂O₅ (JCPDS No. 27-1003), and the three strong peaks at 22.6°, 28.4°, and 36.6° correspond to the (001), (180), and (181) crystal planes of T-Nb₂O₅ [27], respectively. Notably, the lattice parameters of T-Nb₂O₅@UTC are a = 6.1784 Å, B = 29.2867 Å, c = 3.9286 Å, while the parameters of T-Nb₂O₅ are a = 6.1757 Å, B = 29.2966 Å, c = 3.9282 Å, respectively. This indicates that the carbon coating does not alter the crystal structure of T-Nb₂O₅ (Figure S1). The additional peaks at 22.5°, 31°, and 40° may be caused by the preferred orientation of the crystal plane during sample preparation or by weak signal interference or structural defects related to experimental conditions [28,29,30]. Since all the main diffraction peaks match the T-Nb₂O₅ standard card, the unassigned peaks do not affect the core conclusions of this article. Moreover, the XRD results indicate UTC coating does not alter the crystal structure of T-Nb₂O₅. The bonding vibrations between metal and oxygen were analyzed by means of Raman spectroscopy (Figure 2b). The characteristic peaks observed at 230 cm⁻¹ and 312 cm⁻¹ are associated with the bending vibrations of the Nb–O–Nb bond, whereas the peak at 690 cm⁻¹ is attributed to the symmetric stretching vibrations of NbO₆ and NbO₇ octahedra [31,32], respectively. The characteristic vibrational modes at 1350 and 1610 cm⁻¹ are attributed to the D and G bands, respectively, which are associated with disorder-induced carbon and the graphitic sp² carbon structure. The intensity ratio of these two bands (about 0.8) suggests that the carbon is partially graphitized while retaining some structural disorder [33]. Fourier transform infrared (FTIR) spectra were also recorded for these two samples (Figure 2c). The vibrational signatures observed at 1639 and 3452 cm⁻¹ are characteristic of O–H stretching modes, arising from surface-adsorbed atmospheric water molecules. Furthermore, the spectral features below 1000 cm⁻¹ originate from symmetric and asymmetric stretching vibrations within the Nb–O coordination framework [34].

2.3. Carbon Content and Surface Area Analysis of T-Nb₂O₅ and T-Nb₂O₅@UTC

To determine the carbon coating content, thermogravimetric analysis (TGA) was conducted under an air atmosphere with a linear temperature ramp (10 °C min⁻¹) up to 600 °C to achieve controlled calcination (Figure 2d). The TG curve revealed that the weight content of carbon was 5.27%. Surface area measurements of T-Nb₂O₅@UTC and T-Nb₂O₅ were conducted using N₂ adsorption–desorption. As shown in Figure 2e, The Brunauer–Emmett–Teller (BET) surface areas were calculated as 8.3679 m² g⁻¹ for T-Nb₂O₅@UTC and 9.6568 m² g⁻¹ for T-Nb₂O₅. The slight decrease in specific surface area may be due to the filling of the mesoporous structure between nanoparticles by the ultrathin carbon layer (UTC), which makes some pores unable to be effectively adsorbed by N₂ molecules. These two samples exhibit abundant mesopores on their surfaces, and the pore size values are summarized in Table S1. Pore size distribution analysis indicates a predominant mesoporous range of 3–5 nm for both materials (Figure 2e, inset), in agreement with the morphological features observed by SEM. This porous structure facilitates the formation of multiple lithium-ion transport pathways, thereby enhancing ion mobility during electrochemical processes.

2.4. Elemental Composition and Chemical State Analysis by XPS

X-ray photoelectron spectroscopy (XPS) analysis was performed to determine the elemental composition and chemical bonding states, with the corresponding survey spectra presented in Figure 2f. The enhancement of the C signal in T-Nb₂O₅@UTC is caused by surface carbon coating. The spin–orbit splitting resulted in the splitting of the Nb 3d peak into two components at about 207 and 210 eV with a peak area ratio of 3:2 (Figure 2g), confirming that Nb⁵⁺ is the dominant oxidation state [35]. It is noteworthy that in T-Nb₂O₅@UTC, the Nb⁵⁺ peak shifts 0.2 eV toward lower binding energy. This can be attributed to the electron transfer between the Nb, O, and C. The peak at 205.4 eV belongs to Nb⁴⁺. This may be due to the fact that H₂ produced by the cracking of acetylene at high temperature reduces a small amount of Nb₂O₅ [36]. The O 1s peaks shown in Figure 2h appear at 530.22 and 531.82 eV, which can be attributed to Nb–O and C–O bonds [37,38], respectively. Additionally, the C 1s spectrum can be deconvoluted into two distinct peaks (Figure 2i), corresponding to C=C and C=O bonds [22]. These C-related bonds likely originate from the surface carbon layer. Both T-Nb₂O₅ and T-Nb₂O₅@UTC exhibit similar Nb and O atomic ratios, indicating that the UTC coating does not significantly alter the structural integrity of T-Nb₂O₅. Furthermore, a substantial increase in surface carbon content observed in T-Nb₂O₅@UTC confirms the success of the UTC coating (Table S2).

2.5. Electrochemical Performance Test

We tested T-Nb₂O₅@UTC||Li and T-Nb₂O₅||Li cells to explore how the nanosheet structure and UTC coating influence lithium-ion storage capacity. Compared with T-Nb₂O₅, the first three cyclic voltammetry (CV) curves of T-Nb₂O₅@UTC remain almost unchanged (Figure 3a,d), confirming that the UTC coating can significantly enhance the electrochemical stability of T-Nb₂O₅ and inhibit the occurrence of side reactions. Furthermore, as the scan rate increased from 0.2 to 1.1 mV s⁻¹, the oxidation potential of T-Nb₂O₅@UTC shifted positively by 0.06 V, clearly superior to that of T-Nb₂O₅ (0.24 V) (Figure 3b,e). Compared with T-Nb₂O₅, the CV curve of T-Nb₂O₅@UTC features a larger area, suggesting a bigger energy storage capacity and fast reaction kinetics. This illustrates that UTC modification and a 2D nanosheet structure can effectively improve electrochemical reaction kinetics and reduce polarization effects.

To further investigate the effects of the 2D nanosheet structure and carbon encapsulation on electrochemical energy storage behavior, the relationship between the peak current (i_p) and the square root of the scan rate (v^0.5) in the CV curves of T-Nb₂O₅ and T-Nb₂O₅@UTC was analyzed (Figure 3c,f). The i_p corresponding to the redox reactions of T-Nb₂O₅ and T-Nb₂O₅@UTC show a linear relationship with v^0.5 (Figure S2). Therefore, the electrochemical reactions of T-Nb₂O₅ and T-Nb₂O₅@UTC are diffusion-limited [39,40,41]. The reaction kinetics of T-Nb₂O₅ and T-Nb₂O₅@UTC were further studied by fitting the slope of the peak current (b value) with the scan rate using Equation (S1). The b value theoretically lies between 0.5 and 1 and can serve as a quantitative indicator of the charge storage mechanism: values close to 1 indicate a predominantly capacitive behavior, whereas values close to 0.5 reflect a diffusion-controlled process. Specifically, the b-values for the oxidation reactions of T-Nb₂O₅@UTC and T-Nb₂O₅ are 0.976 and 0.936, and the b-values for the reduction reactions are 0.904 and 0.902, respectively. These values range from 0.5 to 1, indicating that the redox reactions of T-Nb₂O₅ and T-Nb₂O₅@UTC are synergistically controlled by surface capacitance and surface diffusion. We calculated the percentage contribution of capacitance to the total electrode capacity by Equation (S2). The capacitance contribution of T-Nb₂O₅@UTC increases from 92.7% to 96.8% as the scan rate rises from 0.2 to 1.1 mV s⁻¹. Moreover, T-Nb₂O₅@UTC demonstrates a higher capacitance contribution than T-Nb₂O₅, which should be attributed to the enhanced reaction kinetics induced by UTC modification and the 2D nanosheet structure (Figure 3g–i).

The electrochemical energy storage behavior of T-Nb₂O₅@UTC and T-Nb₂O₅ was investigated by galvanostatic charge/discharge (GCD) tests. T-Nb₂O₅ is used as the working electrode (WE) and a lithium sheet is used as the counter electrode (CE). The electrode loading is about 1.5 mg/cm². As shown in Figure 4a,b, the GCD curves of T-Nb₂O₅@UTC and T-Nb₂O₅ at different current densities have similar shapes, indicating excellent electrochemical reversibility. Furthermore, the distinct voltage plateau observed between 1.5–1.9 V corresponds to the reversible Nb⁵⁺/Nb⁴⁺ redox couple, as confirmed by CV analysis showing corresponding oxidation/reduction peaks. The rate performance data of T-Nb₂O₅@UTC and T-Nb₂O₅ were obtained through three independent experiments of the same batch (Figure 4c). The error bars represent the standard deviation of the three experiments (mean ± 5 mAh g⁻¹, n = 3), and the relative error is about 6% (Figure S3). The average discharge capacities of T-Nb₂O₅ at 0.1, 0.2, 0.5, 1, 2, and 5 A g⁻¹ are 179.6, 165.3, 149.2, 133.9, 112.1, and 62.9 mAh g⁻¹, respectively. In contrast, T-Nb₂O₅@UTC shows higher discharge capacities of 214.7, 202.4, 184.4, 168.0, 149.7, and 117.9 mAh g⁻¹ at the same current densities. When the current density is reduced back to 0.1 A g⁻¹ again, the discharge capacities of T-Nb₂O₅@UTC and T-Nb₂O₅ return to 213.2 and 166.5 mAh g⁻¹, respectively. Overall, T-Nb₂O₅@UTC exhibits superior rate performance and cycling stability. Benefiting from the synergistic effect of the 2D porous nanosheet structure and UTC coating, the rate performance of the T-Nb₂O₅@UTC anode surpasses that of most previously reported T-Nb₂O₅ materials (such as TT-Nb₂O₅@C, H-Nb₂O₅, T-Nb₂O₅, H-Nb₂O₅/rGO, etc.) (Figure 4d and Table S3) [10,16,42,43,44,45,46].

Electrochemical impedance spectroscopy (EIS) measurements were conducted to investigate the charge transfer kinetics and interfacial properties of both T-Nb₂O₅@UTC and pristine T-Nb₂O₅ electrodes. In the Nyquist plot of EIS (Figure 4e), the first half of the curve typically appears as a semicircle, with its diameter representing the charge transfer resistance (R_ct) associated with the charge transfer process in the electrochemical reaction. The second half of the curve usually manifests as a straight line with a slope, corresponding to the Warburg impedance (R_w), which reflects the ion diffusion process in the electrolyte [47]. According to the equivalent circuit diagram fitting results, the R_ct of T-Nb₂O₅@UTC is 83.4 Ω, significantly lower than that of T-Nb₂O₅ (128.3 Ω). Meanwhile, the R_w of T-Nb₂O₅@UTC is also markedly lower than that of T-Nb₂O₅. This can be attributed to the structure of the 2D porous nanosheets and the coating of UTC, which effectively increases the contact area of T-Nb₂O₅@UTC with the electrolyte and reduces the interfacial resistance between them. Additionally, T-Nb₂O₅@UTC exhibits superior electrochemical stability, maintaining 87.9% of the initial specific capacity (184.8 mAh g⁻¹) after 200 cycles at 0.1 A g⁻¹ (Figure 4f). Even after 1000 cycles at 1 A g⁻¹, it still retains at 83.7% of the initial specific capacity (Figure 4g). In contrast, T-Nb₂O₅ maintains only 77.2% and 71.9% of the initial specific capacity at 0.1 and 1 A g⁻¹, respectively. The SEM images before and after 1000 cycles demonstrate that T-Nb₂O₅@UTC maintains its structural integrity (Figure S4), while T-Nb2O5 exhibits significant structural damage. This indicates that the UTC layer effectively alleviates the structural degradation of T-Nb₂O₅ caused by volume expansion and contraction during high-current cycling. In addition, the charge transfer resistance of T-Nb₂O₅@UTC does not increase significantly before and after cycling compared with T-Nb₂O₅ (Figure S5), which further suggests that UTC still maintains the structural stability of T-Nb₂O₅@UTC [48].

The lithium-ion diffusion behavior of T-Nb₂O₅@UTC and T-Nb₂O₅ was further examined using the galvanostatic intermittent titration technique (GITT) (Figure 5a,d). The diffusion coefficient (D_Li⁺) of lithium ions in the electrode material can be calculated according to Formula (1) as follows:

$$D_{{Li}^{+}}={\displaystyle \frac{4}{\pi }}{\left({\displaystyle \frac{m_B{V}_m}{M_{B}A}}\right)}^2{\left({\displaystyle \frac{∆E_s}{\tau \left(\frac{d{E}_{\tau }}{d\sqrt{\tau }}\right)}}\right)}^2\left(\tau \ll L^2/D_{{Li}^{+}}\right)$$

(1)

where A represents the actual contact area of the electrode, Molar mass can be expressed as M_B, and m_B denotes the mass of the active material. The symbol τ represents the current pulse time, ∆E_s represents the change in stable voltage, and the voltage change caused by the current pulse during the entire test can be expressed as ΔE_τ. Figure S6 illustrates that the single-step GITT consists of constant current and relaxation phases. Furthermore, the potential is proportional to τ^0.5 (Figure 5b,e), simplifying the above in the form of Equation (2) as follows:

$$D_{{Li}^{+}}={\displaystyle \frac{4}{\pi \tau }}{\left({\displaystyle \frac{m_B{V}_m}{M_{B}A}}\right)}^2{\left({\displaystyle \frac{∆E_s}{∆E_{\tau }}}\right)}^2$$

(2)

Using the above formula, the average D_Li⁺ values during lithium-ion insertion and extraction in T-Nb₂O₅ were calculated to be 4.72 × 10⁻¹² cm² s⁻¹ and 4.78 × 10⁻¹² cm² s⁻¹, respectively (Figure 5c). Under the same conditions, the average D_Li⁺ values for T-Nb₂O₅@UTC are 1.07 × 10⁻¹¹ cm² s⁻¹ and 1.09 × 10⁻¹¹ cm² s⁻¹ (Figure 5f). Notably, the D_Li⁺ of T-Nb₂O₅@UTC is about twice that of T-Nb₂O₅, indicating that UTC coating effectively enhances the lithium-ion diffusion capability. The enhanced lithium-ion diffusion kinetics of T-Nb₂O₅@UTC significantly optimize the concentration gradient of Li⁺ at the electrolyte–electrode interface during high-rate electrochemical reactions. This improvement effectively reduces the concentration polarization and minimizes the overpotential related to Li⁺ transport, thereby enhancing electrochemical energy storage performance.

3. Electrochemical Performance of Full Cells

To evaluate the practical application potential of T-Nb₂O₅@UTC, a T-Nb₂O₅@UTC||LiFePO₄ (T-Nb₂O₅@UTC||LFP) full cell was assembled.

As shown in Figure 6a, the Nyquist plot of the T-Nb₂O₅@UTC||LFP full cell shows the low R_ct and R_w, indicating superior electrochemical reaction kinetics. The charge/discharge curves of T-Nb₂O₅@UTC||LFP exhibit voltage plateaus at 1.89 V and 3.5 V (Figure 6b), corresponding to the redox reactions of T-Nb₂O₅ and LiFePO₄, respectively. The discharge-specific capacities of T-Nb₂O₅@UTC||LFP were calculated to be 186.2, 147.8, 123.1, 105.6, 86.8, and 67.4 mAh g⁻¹ at 0.1, 0.2, 0.5, 1, 2, and 5 A g⁻¹, respectively. As shown in Figure 6c, when the current density is reduced back to 0.1 A g⁻¹, the discharge capacity of T-Nb₂O₅@UTC||LFP recovers to 177.6 mAh g⁻¹, indicating the superior rate performance of T-Nb₂O₅@UTC||LFP. In Figure S7, the assembled T-Nb₂O₅@UTC||LFP full cell successfully powered an LED panel, further highlighting its practical application potential. More importantly, the T-Nb₂O₅@UTC||LFP full battery exhibits excellent cycling stability, with the specific capacity decreasing by only 1.5% after 120 cycles at 0.1 A g⁻¹ (Figure 6d). Capacity decay may be attributed to the continuous thickening of the solid electrolyte interface (SEI) film on the negative electrode surface during battery cycling. The formation of the SEI film consumes active lithium and increases the internal resistance of the battery, leading to capacity degradation. Additionally, the cycling performance of T-Nb₂O₅@UTC||LFP at 1 A g⁻¹ was tested, as shown in Figure 6e. After 300 cycles, a capacity retention rate of 76.3% was maintained, demonstrating the favorable electrochemical stability of T-Nb₂O₅@UTC||LFP even at high rates.

4. Conclusions

In this work, we successfully prepared a two-dimensional T-Nb₂O₅ nanosheet decorated with an ultrathin carbon coating as a fast-charging LIB anode material. The porous nanosheet structure facilitates rapid lithium-ion transport through multiple channels, significantly shortening the ion migration distance. The ultrathin carbon layer, prepared via a facile acetylene pyrolysis process, further enhances the conductive network between primary particles while effectively mitigating particle fragmentation during long-term cycling. As a result, the T-Nb₂O₅@UTC demonstrates outstanding electrochemical performance in half-cell tests, achieving a capacitive contribution of 96.8% at a scan rate of 1.1 mV s⁻¹ and retaining approximately 87.9% of its initial capacity after 200 cycles at 0.1 A g⁻¹. In full-cell tests, the T-Nb₂O₅@UTC||LFP delivers an impressive specific capacity of 186.2 mAh g⁻¹ at 0.1 A g⁻¹, with a minimal decay rate of only 1.5% after 120 cycles. This exceptional performance is ascribed to the synergistic effect of its two-dimensional architecture and ultrathin carbon surface modification, offering valuable insights for the development of high-performance fast-charging LIB anodes.