Plasma-engineered sandwich-structured N-doped carbon@TiNb₂O₇ with vertical graphene skeletons for ultrahigh-rate and long-cycling lithium storage

INTRODUCTION

Lithium-ion batteries (LIBs) have expanded beyond portable electronics to power a diverse range of applications, including electric vehicles and grid-scale energy storage systems^[1-3]. This rapid diversification has concurrently heightened demands for enhanced safety and ultrafast charge/discharge capabilities^[4-6]. Among promising alternative anode materials, titanium niobium oxide (TiNb₂O₇, TNO), with a shear ReO₃-type crystal structure that provides open tunnels to enable rapid lithium-ion diffusion pathways, offers significant advantages such as superior rate performance and minimal volume variation during cycling^[7,8]. Its theoretical capacity reaches up to 387.6 mAh g^-1, achieved via multi-electron transfer involving the Nb⁵⁺/Nb³⁺ (2e^-) and Ti⁴⁺/Ti³⁺ (1e^-) redox couples^[9,10]. Crucially, its relatively high operating voltage plateau (~1.6 V vs. Li/Li⁺) effectively mitigates lithium plating risks and associated hazards, such as internal short circuits and thermal runaway^[11-13]. Notably, TNO also exhibits superior low-temperature performance compared to commercial graphite anodes, maintaining significant capacity even at ultralow temperatures down to -40 °C^[14,15]. This combination of high-rate capability, intrinsic safety, long cycle life, and exceptional low-temperature performance positions TNO as a transformative anode material^[16]. Nevertheless, its commercial adoption is impeded by intrinsically low electronic conductivity and sluggish Li⁺ diffusion kinetics.

To overcome these limitations, strategies including heteroatom doping, conductive compositing, and morphology engineering have been implemented^[17-22]. Heteroatom doping enhances intrinsic electronic conductivity through band structure modulation, as demonstrated by Tian et al. in La-doped TNO, where doping induces localized energy levels via hybridization among O 2p, Ti 3d, and Nb 4d orbitals^[23]. However, excessive doping may compromise structural integrity^[24]. Conductive compositing effectively augments electronic conductivity without perturbing the host crystal structure^[25]. For example, Wu et al. reported significantly enhanced electrical transport in MXene-coated TNO microspheres, and Yang et al. achieved comparable improvements using solvothermal synthesized carbon-coated porous TNO microspheres^[26,27]. Ho et al. highlight the value of three-dimensional (3D) graphene macrostructures for building conductive, robust electrode frameworks, which supports our VG skeleton strategy^[28]. In parallel, Folorunso et al. demonstrate that graphene coating serves as a universal strategy for interfacial engineering, enhancing cycling stability^[29]. These conductive matrices establish extrinsic pathways, effectively mitigating limitations in electron transfer^[30]. Critically, while both heteroatom doping and conductive compositing significantly enhance electronic conductivity, their capacity to improve ion diffusion kinetics remains constrained. Morphology engineering, particularly reducing active material particle size, shortens diffusion pathways for both ions and electrons, thereby enhancing kinetics^[31]. Building on the work of Xu et al., who systematically investigated how the morphological dimensions (1D, 2D, 3D) of TNO anodes influence lithium-ion storage kinetics and identified the advantages of 2D structures for shorter Li⁺ diffusion paths^[32]. Nonetheless, the concomitant increase in specific surface area amplifies susceptibility to extensive interfacial side reactions, potentially degrading coulombic efficiency and cycle life^[33]. Consequently, developing TNO electrode materials with superior electrochemical performance requires a synergistic strategy that integrates morphological control with the design of conductive scaffolds^[34-36].

In this study, we design a sandwich-structured N-doped carbon (N-C)@TNO integrated with vertical graphene (VG) skeletons. The fabrication involves three sequential steps: First, the 2D graphene nanosheets are deposited on carbon cloth vertically via plasma-enhanced chemical vapor deposition (PECVD) to form a 3D conductive scaffold. Subsequently, TNO nanoparticles were grown on VG nanosheets via a simple solvothermal process with the preserved 2D morphology [Supplementary Figure 1]. The porous structure of VG nanosheets provides TNO with faster electronic/ionic transport channels. Finally, an ultrathin N-C shell (~3 nm) is uniformly in situ coated on TNO via PECVD again. This synergistic configuration establishes rapid 3D electron transport channels while the N-C shell acts as a physical barrier to minimize the direct contact between the electrodes and the electrolyte to prolong the cycle life. The resultant self-supporting electrode delivers outstanding performance: 300.1 mAh g^-1 at 0.2 C, 214.4 mAh g^-1 at 40 C, and 95.38% capacity retention after 5,000 cycles at 20 C. Post-cycling Scanning Electron Microscope (SEM) confirms structural integrity following rigorous electrochemical testing. This work establishes a novel paradigm for designing high-rate, durable energy storage devices through the integration of morphological and conductive engineering.

EXPERIMENTAL

RESULTS AND DISCUSSION

Figure 1A illustrates the fabrication schemes of the sandwich electrode with a triple-layered “conductive skeleton || active core || protective shell” architecture. First, the VG arrays are deposited on carbon cloth via a facile PECVD method. Supplementary Figure 2A and B shows that after the deposition, a thin layer of interconnected VG nanosheets grows on the carbon fibers with a ~200-500 nm porous structure, which acts as the high-conductivity 3D scaffold. Then, TNO nanoparticles are uniformly anchored onto the VG skeleton to form a coral-like composite structure using the simple solvothermal method. Finally, an N-C shell layer was in situ capped on the TNO surface by PECVD using EDA as the carbon precursor. This process resulted in the formation of a uniform and continuous N-C protective layer on the TNO surface. SEM images clearly revealed the morphological evolution across synthesis stages. On the one hand, high-quality VG arrays are a prerequisite for synthesizing sandwich electrodes; on the other hand, carbon cloth has high electrical conductivity and mechanical strength, with fast electron and ion transport speeds, making it an excellent conductive current collector for high-performance active materials^[37]. It can be seen that VG arrays completely and uniformly cover the surface of the carbon cloth, and VG nanosheets are cross-linked with each other to form an open pore structure, which is conducive to the rapid diffusion of Li⁺ [Supplementary Figure 2B].

Figure 1. Plasma-engineered synthesis and multi-scale characterization of the N-C@TiNb₂O₇ composite. (A) Schematic of the fabrication process; SEM images of (B) TNO array and (C) N-C@TNO array; HRTEM images of (D) TNO and (E) N-C@TNO; (F) EDX mapping of N-C@TNO showing elemental distribution. TNO: TiNb₂O₇, titanium niobium oxide; HRTEM: high-resolution transmission electron microscopy; EDX: energy-dispersive X-ray spectroscopy; PECVD: plasma-enhanced chemical vapor deposition; N-C: N-doped carbon; SEM: scanning electron microscope.

After TNO was synthesized on VG, the porous structure of VG remained intact, and the TNO array exhibited a coral-like morphology. TNO nanoparticles facilitate the reduction of the ions/electrons transport path, thereby accelerating the reaction kinetics [Figure 1B and Supplementary Figure 3A]. The thickness of the TNO nanosheets (about 40 nm) increased further after the N-C layer coating on the TNO surface; however, the N-C@TNO array could maintain an excellent 3D pore structure, indicating that the N-C layer has good compatibility with TNO [Figure 1C and Supplementary Figure 3B]. The detailed microstructure of the TNO and N-C@TNO composites was examined using TEM and HRTEM. The TEM image [Supplementary Figure 4A] shows that the particle size of TNO is about 30-60 nm. HRTEM images [Figure 1D] reveal lattice fringes with interplanar spacings of 0.20 nm and 0.19 nm, corresponding to the (-515) and (020) planes of TiNb₂O₇, respectively^[38]. A uniform N-C coating layer can be observed in the TEM image of N-C@TNO [Supplementary Figure 4B], and the HRTEM image shows that the thickness of the N-C layer on the surface is approximately 3.0 nm [Figure 1E]. Similarly, the crystal fringe within the particle exhibits a spacing of approximately 0.18 nm and 0.26 nm, which is attributed to the (205) and (510) crystal planes of TiNb₂O₇^[39]. In addition, energy-dispersive X-ray spectroscopy (EDX) mapping [Figure 1F] shows that C, N, Ti, Nb, and O are uniformly distributed in the N-C@TNO composites, further confirming the successful introduction of the N-C layer and its uniform encapsulation on the TNO surface. The above multiscale characterization results demonstrate the successful construction of the N-C@TNO sandwiched composite electrode, providing a structural basis for understanding the optimization of electrode performance. In this unique sandwich structure, an all-around conductive network is formed on the surface of TNO through the combined introduction of the VG conductive skeleton and the N-C layer shell.

The phases and crystal structures of the samples at different stages were analyzed using XRD. As shown in Figure 2A, TNO powder is the precipitate obtained after centrifugation of the solvothermal product, and its diffraction peaks match the standard pattern of TiNb₂O₇ (PDF#04-007-0513). Both TNO and N-C@TNO show peaks at 26.2° and 44.4° corresponding to the (002) and (101) planes of graphite. The remaining major peaks are observed at 17.3°, 23.9°, 26.0°, 32.5°, 44.5°, and 47.0°, corresponding to the (002), (110), (003), (203), (005), and (020) planes of TiNb₂O₇. The absence of impurity peaks also confirms the successful fabrication of TNO, and there was no shift in the peak position after the introduction of the N-C coating layer, indicating the good compatibility of the N-C shell layer with TNO. The Raman spectra analysis, plotted in Supplementary Figure 5, provides further insights into the phase evolution of TNO and N-C@TNO composite. Several remarkable characteristic peaks appear in the Raman spectra. Among them, the peak at 996 cm^-1 corresponds to edge-shared NbO₆ octahedra, while the peaks at 535 and 641 cm^-1 are attributed to vibrational modes of TiO₆ octahedra, and the peak at 261 cm^-1 is related to O-Ti-O and O-Nb-O modes^[40,41]. The Raman spectra show that the introduction of the N-C coating layer did not produce any new peaks. To quantitatively evaluate the graphitization degree, we performed Raman spectroscopy on the N-C@TNO sample. As shown in Supplementary Figure 6 (spectral range 1,200-2,000 cm^-1), the spectrum clearly exhibits the characteristic D and G bands of carbon materials at ~1,350 and ~1,600 cm^-1, respectively, indicating that the N-C layer is composed of highly defective graphitic carbon.

Figure 2. Structure and composition of the samples. (A) XRD patterns comparing the TNO array and N-C@TNO array; (B) Survey XPS spectra, and high-resolution XPS spectra of (C) C 1s, (D) N 1s, (E) Nb 3d, and (F) O 1s. TNO: TiNb₂O₇, titanium niobium oxide; N-C: N-doped carbon; XRD: X-ray diffraction; XPS: X-ray photoelectron spectroscopy.

Furthermore, the elemental composition and valence distribution on the surface of TNO and N-C@TNO are characterized by XPS. The survey spectra of N-C@TNO demonstrate the main elements (C, N, Ti, Nb, and O) in the composite arrays [Figure 2B]. Deconvolution of the C1s spectra reveals four peaks at 284.8 eV (C-C), 285.7 eV (C-O), 286.4 eV (C-N), and 287.6 eV (C=O), whereas no C-N signal is detected in TNO [Figure 2C]. The N 1s spectra can be deconvoluted into pyridine-N (397.1 eV), pyrrole-N (398.8 eV), and graphitic-N (400.4 eV), respectively [Figure 2D]. It is believed that N-C materials enhance electronic conductivity through the higher electronegativity of N atoms^[42]. There was no N signal observed in TNO, proving that the N-C layer was successfully coated on the surface of TNO nanoparticles. On the one hand, the higher electronegativity of nitrogen relative to carbon enhances the electrical conductivity of the N-C layer; on the other hand, the comparable atomic radii of N and C minimize structural distortion during substitution, thereby preserving the structural integrity of the carbon framework. As for the Ti 2p spectra [Supplementary Figure 7], two characteristic peaks of Ti 2p_1/2 and Ti 2p_3/2 are detected at 465.2 and 459.4 eV, associated with the state of Ti⁴⁺ in TiNb₂O₇. Note that, as shown in Figure 2E, the two characteristic peaks attributed to Nb 3d_5/2 and Nb 3d_3/2 of Nb⁴⁺ for TNO occur at 208.0 and 210.7 eV, respectively. In contrast, the N-C@TNO exhibits lower binding energy compared with TNO, possibly due to the change of the chemical environment in the lattice caused by the N-doping carbon layer^[15]. Figure 2F displays the O 1s spectra, which could be deconvoluted into the bonds of metal-O (531.0 eV) and C-O (533.2 eV). The intensified C-O signal in N-C@TNO is likely due to enhanced C-O bond formation within the carbon coating, while the attenuated M-O intensity suggests partial surface coverage of the metal oxides by the N-C layer, thereby reducing their signals. Together, these results demonstrate that the TNO nanoparticles are successfully sandwiched between the VG skeleton and the N-C shell.

To systematically evaluate the reaction kinetics of the N-C@TNO composite electrode, CV tests were conducted within a voltage window of 1.2-2.5 V (vs. Li/Li⁺) at a scan rate of 1.0 mV s^-1 [Figure 3A]. The redox peaks observed at approximately 1.3 V, 1.6-1.7 V, and 1.9 V correspond to the redox reactions of Nb⁴⁺/Nb³⁺, Nb⁵⁺/Nb⁴⁺, and Ti⁴⁺/Ti³⁺, respectively. The shape of the CV curves remains unchanged after the introduction of the N-C coating layer; however, the peak current density increases and the redox peak separation decreases, indicating that the N-C coating layer not only does not alter the reaction mechanism but also accelerates the electrochemical reaction kinetics and enhances reversibility. This kinetic superiority is directly manifested in the improved polarization behavior of the electrode. In CV tests at different scan rates, the redox peak potential difference (ΔE) of the N-C@TNO electrode remains consistently smaller than that of the TNO electrode, indicating reduced electrochemical polarization [Figure 3B]. The voltage-capacity profiles at 5 C further validate this conclusion; the N-C@TNO electrode demonstrates a higher discharge voltage plateau and a lower charge voltage plateau, with significantly reduced polarization [Figure 3C, 173.85 mV vs. 506.22 mV]. Notably, both electrodes exhibit similar charge/discharge plateaus at 5 C, which aligns consistently with the CV test results. The significant improvement in polarization behavior of N-C@TNO can be attributed to the synergistic effects of its unique conductive network architecture. The VG skeleton and N-C shell collaboratively establish a continuous 3D conductive network, which drastically reduces polarization voltage by providing integrated pathways for rapid electron transport. The fast-charging capability of electrode materials is a critical indicator for evaluating their potential in high-power applications. As shown in Figure 3D, the specific capacities of N-C@TNO and TNO electrodes are almost the same at low current (0.2 C to 2 C). However, at higher current densities of 20 C and 40 C, the N-C@TNO electrode demonstrates remarkable performance, delivering specific capacities of 246.2 and 214.4 mAh g^-1, respectively, compared to 178.7 mAh g^-1 and 109.1 mAh g^-1 for TNO. When the current density is reset to 0.2 C, the capacity nearly recovers to its initial level, demonstrating high kinetic reversibility. This enhanced rate performance is attributed to the efficient charge transport channels established by the N-C layer coating, which enables N-C@TNO to maintain exceptional capacity retention even under high current densities, surpassing most reported TNO-based electrodes in the literature [Figure 3E]^{[23,38,43-47]}. Additionally, we conducted low-temperature performance testing at 0 °C. As Supplementary Figure 8 illustrates, TNO exhibits virtually no capacity at a current density of 10 C under low-temperature conditions, whereas N-C@TNO retains some capacity (92.3 mAh g^-1). In a 200-cycle test at a current density of 5 C, N-C@TNO exhibited a capacity retention of 72.8%, compared to only 54.9% for TNO. This indicates that even at a low temperature of 0 °C, N-C@TNO maintains a favorable capacity retention, owing to the protective and conductive properties of the N-C shell.

Figure 3. Electrochemical properties of TNO and N-C@TNO electrodes in lithium-ion batteries (LIBs): (A) Comparison of CV curves at a scan rate of 1.0 mV s^-1; (B) Voltage gap (|ΔEp|) between the redox peaks at different scan rates; (C) Galvanostatic charge-discharge profiles at 5 C; (D) High-rate capability; (E) Comparison of the rate capability of TNO-based electrodes in the literature; (F) UV-vis absorption spectra; (G) Cycling performance at 20 C. TNO: TiNb₂O₇, titanium niobium oxide; N-C: N-doped carbon; CV: cyclic voltammetry; UV-vis: ultraviolet–visible spectroscopy.

To further elucidate the conductivity enhancement mechanism of the material’s electron transport properties. The optical bandgap energy (E_g) of the synthesized materials was determined using UV-Visible absorption spectroscopy, with the corresponding data presented in Figure 3F, expressed as

where α denotes the absorption coefficient, hν is the photon energy, and C represents a proportionality constant. Notably, the N-C@TNO composite exhibits a reduced bandgap of 2.57 eV compared to 2.83 eV for pristine TNO, indicating that the N-C coating effectively enhances electronic conductivity. This facilitation of charge transport promotes improved kinetics for Li⁺ insertion/extraction, which is particularly advantageous for high-rate battery applications. More importantly, the N-C@TNO electrode exhibits superior cyclic stability, with a capacity retention of 95.38% at 20 C and a nearly 100% Coulombic efficiency after 5,000 cycles. This performance is superior to that of the TNO electrodes, which exhibit a capacity retention of 83.37% [Figure 3G].

Multiple electrochemical methods, including the galvanostatic intermittent titration technique (GITT), EIS, and pseudocapacitive contribution obtained by CV, have been implemented in order to gain deeper insights into the diffusion kinetics. Supplementary Figure 9 exhibits the GITT curves of TNO and N-C@TNO. Based on Fick’s second law of diffusion, the Li⁺ diffusion coefficients ($$ D_{L i^{+}} $$) of N-C@TNO and TNO can be calculated using

where ΔE_s represents the steady state voltage change induced by the current pulse; ΔE_t denotes the total voltage variation during the pulse; τ represents the constant current pulse time; m_B is the quality of the active material, S refers to the electrode-electrolyte contact area, and ρ indicates the compacted density. As derived from the GITT data, N-C@TNO exhibits a higher $$ D_{L i^{+}} $$ value compared to TNO, demonstrating that the N-C coating effectively enhances the $$ D_{L i^{+}} $$ [Figure 4A]. Nyquist plots of N-C@TNO and TNO are presented in Figure 4B to further explain the electrochemical behavior. All Nyquist plots consist of a semicircle in the high frequency range and a linear slope in the mid/low frequency region. Specifically, the high frequency semicircle involves resistance including ohmic resistance (R_s), while the mid/low frequency linear region is associated with lithium-ion diffusion. Notably, N-C@TNO exhibits a smaller semicircle in the high frequency range and a steeper linear slope in the mid/low frequency range, indicating lower charge transfer resistance and faster Li⁺ diffusion kinetics. The electrochemical reaction kinetics and pseudocapacitive characteristics of the N-C@TNO and TNO electrodes were thoroughly investigated through CV measurements conducted across a range of scan rates, as illustrated in Supplementary Figure 10A and B. The analysis revealed that the N-C@TNO composite demonstrates minimal shift in peak positions relative to the pristine TNO, indicating reduced electrochemical polarization and enhanced reaction reversibility. This improvement is largely due to the incorporation of the N-C layer, which facilitates superior electronic conductivity by providing efficient charge transport pathways. The quantitative correlation between the peak current and the scan rate is a fundamental aspect of analyzing charge storage mechanisms, which can be determined by the power-law relationship:

Figure 4. The calculated $$ D_{L i^{+}} $$ for (A) TNO and N-C@TNO; (B) Nyquist plot. (C) Logarithmic relationships between the peak current and the scan rate; (D and E) Capacitive behavior of TNO and N-C@TNO at 0.1mv s^-1; (F) Capacitive contribution ratios at different scan rates. TNO: TiNb₂O₇, titanium niobium oxide; N-C: N-doped carbon.

Here, a is an adjustable parameter, while the magnitude of b serves to distinguish between different types of charge storage mechanisms. A b-value of 0.5 indicates that the lithium-ion intercalation/deintercalation process is predominantly governed by diffusion-controlled behavior, whereas a b-value of 1.0 is characteristic of surface-controlled capacitive processes. As shown in Figure 4C, the b-values derived from the analysis of the oxidation peaks are 0.915 for N-C@TNO and 0.870 for TNO, indicating that the electrochemical reactions of both electrodes involve a combination of pseudocapacitive and diffusion-controlled processes. To further quantify and distinguish between the capacitive and diffusion-controlled contributions, the expression can be reformulated as follows:

where k₁v and k₂v correspond to the current contributions from capacitive-controlled and diffusion-controlled processes, respectively. The pseudocapacitive contribution of the electrodes can be calculated for different sweep speeds, which can be written as follows:

Figure 4D and E displays the capacitive contribution of TNO with the value of 79.79% at a scan rate of 0.1 mv s^-1. In the same way, the pseudocapacitive contributions of N-C@TNO are 94.01% at 0.1 mv s^-1. As shown in Figure 4F, the pseudocapacitive contribution of N-C@TNO increases gradually (94.01%, 94.40%, 96.20%, 97.73%) with the scan rate increasing from low to high (0.1, 0.2, 0.5, 1.0 mV s^-1), which is higher than that of TNO (79.79%, 83.23%, 87.76%, 92.57%). The remarkably high pseudocapacitive contribution is attributed to the unique “conductive skeleton || active core || protective shell” structure, which synergistically enhances both electron and ion transport kinetics. Specifically, our structural advantages include (1) VG 3D Conductive Skeleton, (2) Nanoscale TNO core, and (3) N-Doped Carbon Shell. This synergistic design collectively optimizes both electron and ion transport, enabling the observed dominant pseudocapacitive behavior.

To verify the enhancement of N-C@TNO stability, we captured SEM, TEM, and HRTEM images after rate cycling and long cycling processes. Following the cycling process, the N-C@TNO electrode almost maintains its original architecture, still preserving a well-defined 3D porous framework without visible cracks or delamination [Figure 5A and B]. In contrast, the TNO electrode suffers severe particle agglomeration, extensive cracking, and complete collapse of its porous network [Supplementary Figure 11A and B]. These structural degradations directly account for its electrochemical performance decay, consistent with its inferior long-term cycling performance. TEM and HRTEM images show that the N-C coating layer on the surface maintains its intact morphology without degradation during the cycling process [Figure 5C and D]. EDX analysis of the images showed that the C and N signals are uniformly overlapped with Ti and Nb signals, indicating that the N-C layer remained tightly bound to TNO after rate cycling and long cycling processes [Supplementary Figure 12]. Furthermore, the high-resolution XPS spectra of the cycled N-C@TNO electrode reveal persistent C-N bonding states, with the N 1s spectrum showing stable pyridinic-N, pyrrolic-N, and graphitic-N species, and the C 1s spectrum maintaining a distinct C-N peak [Supplementary Figure 13A and B]. The appearance of the C-F peak is attributed to the decomposition of the electrolyte during cycling. This confirms the chemical stability of the N-C layer after 5,000 cycles, as the C-N bonds remain intact without degradation. Combined with the physical stability observed in TEM and HRTEM images, where the N-C coating prevents particle cracking, these results demonstrate that the N-C layer provides robust protection against electrochemical degradation, contributing to the material’s exceptional cycling performance. Such exceptional cycling stability can be attributed to the protection of the N-C coating layer.

Figure 5. Morphology of the N-C@TNO array after rate and long-term cycling. (A and B) SEM images, (C) TEM image, and (D) HRTEM image. TNO: TiNb₂O₇, titanium niobium oxide; N-C: N-doped carbon; TEM: transmission electron microscopy; HRTEM: high-resolution TEM; SEM: scanning electron microscope.

The excellent electrochemical performance of our N-C@TNO electrode can be attributed to the following factors: Firstly, the VG skeleton and the N-C layer form a 3D continuous conductive network, which can accelerate electron transfer and provide a sandwiched structure to enhance the reaction kinetics and high-rate performance. Secondly, the N-C layer also protects the electrode structure and maintains the structural stability of the electrode. Finally, nitrogen as an electron donor provides more free electrons and lowers the band gap, thus realizing the enhancement of material conductivity. The synergistic effect of conductive VG arrays and the N-C coating layer can endow the well-designed N-C@TNO electrode with superior high-rate capability and cycling stability.

CONCLUSIONS

In summary, we constructed a sandwich-structured electrode through a combined PECVD strategy. TNO nanoparticles were uniformly anchored on a VG skeleton and coated by a N-C shell, establishing a distinctive “conductive skeleton || active core || protective shell” architecture. The synergistic coupling between the highly conductive VG framework and the N-C coating significantly enhanced the electronic/ionic conductivity and cycling stability of electrodes. Compared to pristine TNO, the N-C@TNO composite exhibited markedly reduced polarization and charge transfer resistance, accelerated Li⁺ diffusion kinetics, and predominantly pseudocapacitive charge storage behavior. Consequently, the N-C@TNO electrode delivered exceptionally high-rate capability and ultralong cycle life.