English

• To date, lithium-ion batteries (LIBs) stand out as one of the most dependable and practical devices owing to their high energy/power density and eco-friendliness [1]. However, the graphite anode utilized by LIBs suffers from low capacity, which brings new challenges in meeting the increasing demand for high-performance energy storage in rapidly evolving electronic devices [2]. Therefore, it is necessary to further develop high-performance LIBs anode materials with high capacity and long cycling life.

  Of these anode materials, titanium dioxide (TiO₂) has been regarded as a promising anode material for LIBs, owing to its good structural stability and small volume changes (-5%) [3], in contrast to other metal oxides such as Nb₂O₅ [4], and MoO₃ [5]. These features can effectually improve the cycling stability of the TiO₂ electrode and prolong its operational lifespan. However, its inherent low conductivity and slow electrochemical reaction kinetics remain obstacles for achieving the high lithium storage performance. To address these issues, various approaches have been developed. For example, nanostructured engineering of TiO₂ materials is one of the most effective strategies. To date, nanosheet [6,7], nanowire [3], and nanotube [8] structured TiO₂ have been successfully prepared, demonstrating an improved electrochemical performance [9]. On the other hand, the conductivity of TiO₂ can be markedly enhanced by combining it with some two-dimensional (2D) conductive matrix. Specifically, Ti₃C₂T_x MXene exhibits distinct advantages in lithium-ion storage owing to exceptional conductivity and unique 2D structure [10,11]. Consequently, incorporating TiO₂ nanoparticles onto Ti₃C₂T_x holds significant promise for boosting their lithium storage performance. For instance, Shakoor et al. [12] loaded TiO₂ particles onto the Ti₃C₂T_x surface, resulting in a specific discharge capacity of 200 mAh/g at 0.1 C. Additionally, Li et al. [13] prepared the Ti₃C₂@TiO₂ MXene hybrid and exhibited a capacity of 302 mAh/g after 500 cycles at 200 mA/g. Nevertheless, the obtained TiO₂ particles generally have large size and unstable combination between TiO₂ and Ti₃C₂T_x, leading to the dissatisfactory electrochemical performance. As a unique nanostructure, zero-dimensional (0D) quantum dots (QDs) have garnered growing attention in LIBs due to their maximized surface area exposure and minimized charge diffusion distance [14,15]. More importantly, QDs can effectively buffer large volume expansion during ion insertion/extraction. Besides, the SiO₂ with excellent rigidity has been demonstrated to be an effective stabilizer for the composite materials in previous study [16]. Therefore, exploring the facile method for robust assembly of TiO₂ QDs onto Ti₃C₂T_x nanosheets by the incorporation of SiO₂ particles is anticipated to significantly enhance the lithium storage performance of the composite, especially its cycling stability.

  In this work, we design a new 0D/2D heterostructure (namely, A-TiO₂/Ti₃C₂T_x) through a scalable hydrothermal process induced by (3-aminopropyl)triethoxysilane (APTES). The results indicate that the SiO₂ nanoparticles produced by the hydrolysis of APTES contribute to a strong coupling effect between TiO₂ QDs and Ti₃C₂T_x nanosheets. Such a unique configuration endows the A-TiO₂/Ti₃C₂T_x anode with an extremely high capacity and long-term cycling life for lithium storage. Furthermore, in-situ electrochemical impedance spectroscopy (EIS) indicates that the remarkable structural stability of A-TiO₂/Ti₃C₂T_x plays a crucial role in enabling the electrochemical performance. In addition, the theoretical calculation indicates that the in-situ N-doping derived from APTES into the composite also enhances the adsorption of Li ions.

  Fig. 1a illustrates the synthesis process of A-TiO₂/Ti₃C₂T_x. Initially, Ti₃C₂T_x nanosheets were synthesized according to our recent work [10]. Then, positive APTES was adsorbed onto the negative Ti₃C₂T_x surface via electrostatic interactions between them. As confirmed by the zeta potential (Fig. S1 in Supporting information), the potential changes from −23 mV for pure Ti₃C₂T_x to 10 mV after the APTES modification. Along with the hydrolysis of APTES, an ultrathin SiO₂ layer was deposited onto the Ti₃C₂T_x surface, which was further validated by the XRD pattern (Fig. S2 in Supporting information). The broad peak around 23° is ascribed to the SiO₂ characteristic [17]. Moreover, the TEM images also clearly observe the presence of SiO₂ layer (Fig. S3a in Supporting information) compared to pristine Ti₃C₂T_x (Fig. S3b in Supporting information). Subsequently, in a mixed ethanol-glycerol solvent, Ti⁴⁺ underwent gradual hydrolysis and subsequent hydrothermal treatment, forming a uniform TiO₂ QDs structure onto Ti₃C₂T_x (Fig. S4 in Supporting information). Ultimately, after heat treatment at 600 ℃, the A-TiO₂/Ti₃C₂T_x composite with a well-defined morphology is obtained.

  Figure 1

  

  Figure 1.  (a) The fabrication process of A-TiO₂/Ti₃C₂T_x. (b, c) SEM images, (d) TEM image, (e, f) HRTEM images (insert is the SAED pattern), (g) particle size distribution profile, and (h) STEM image and corresponding elemental mappings of A-TiO₂/Ti₃C₂T_x.

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  Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) technique were used to observe the morphology and structure of A-TiO₂/Ti₃C₂T_x. Seen from SEM images (Figs. 1b and c), the composite maintains the lamellar structure of Ti₃C₂T_x, and a lot of TiO₂ nanoparticles are uniformly anchored onto the Ti₃C₂T_x surface. The TEM image further confirms the formation of this composite (Fig. 1d). In contrast, the TiO₂/Ti₃C₂T_x sample exhibits a uniform morphology before heat treatment (Fig. S5a in Supporting information). However, after calcination, its whole structure is obviously damaged (Fig. S5b in Supporting information), indicating a poor structural stability. This result indicates that the formed SiO₂ layer serves as a "glue" for tightly coupling the TiO₂ QDs with Ti₃C₂T_x. That further enhances the structural stability of A-TiO₂/Ti₃C₂T_x, suggesting a superior cycling stability for lithium storage. Figs. 1e and f show the HRTEM images of A-TiO₂/Ti₃C₂T_x. Clearly, the TiO₂ nanoparticles are highly dispersed into Ti₃C₂T_x. Fig. 1f displays the lattice spacing of 0.352 nm, aligning with the anatase (100) crystal face of TiO₂ [18]. The particle size distribution in Fig. 1g indicates that the TiO₂ QDs size predominantly fell within the range of 1.5–3.5 nm. Additionally, STEM image and energy dispersive spectroscopy (EDS) mapping manifest the uniform distribution of Ti, O, Si, C, and N elements in the composite (Fig. 1h).

  Fig. 2a presents the X-ray diffraction (XRD) patterns of two composites. A-TiO₂/Ti₃C₂T_x shows the broad peak around 23°, corresponding to the characteristic peaks of SiO₂ [17], while peaks at 25.3° and 62.7° are assigned to the crystal faces (100) and (204) of anatase TiO₂, indicating the formation of TiO₂ onto the Ti₃C₂T_x. Differently, no characteristic peaks of SiO₂ can be observed in TiO₂/Ti₃C₂T_x, in accordance with the experimental observations [19]. In Raman spectrum (Fig. 2b), the characteristic peaks at 200 cm⁻¹ derived from Ti₃C₂T_x can be visible in three samples. Moreover, the characteristic peaks of TiO₂ at 394, 513 and 635 cm⁻¹ are well-indexed in A-TiO₂/Ti₃C₂T_x and TiO₂/Ti₃C₂T_x [12]. Besides, the chemical bonds of two composites were further analyzed via FT-IR spectra (Fig. 2c). A-TiO₂/Ti₃C₂T_x and TiO₂/Ti₃C₂T_x both displays the absorption vibration peaks C—F (1097 cm⁻¹) and Ti—O (620 cm⁻¹) belonging to Ti₃C₂T_x. However, the absorption vibration peaks of C—N (1050 cm⁻¹) and Si—O (809 cm⁻¹) bonds are observed in A-TiO₂/Ti₃C₂T_x [20], suggesting the existence of SiO₂ originated from the hydrolysis of APTES, which is crucial for the formation of TiO₂ QDs. Additionally, the appearance of C—N (1670 cm⁻¹) and Si—O—Si (459 cm⁻¹) bonds on the SiO₂/Ti₃C₂T_x surface also confirms the point (Fig. S6 in Supporting information) [21]. Based on the N₂ sorption isotherms in Fig. 2d and Fig. S7a (Supporting information), the BET specific surface areas are about 110.1 m²/g and 100.2 m²/g for A-TiO₂/Ti₃C₂T_x and TiO₂/Ti₃C₂T_x, respectively. The larger surface areas of A-TiO₂/Ti₃C₂T_x can provide the more active sites for lithium storage, suggesting a better performance. Furtherly, two composites both illustrate the mesoporous characteristics (inset of Fig. 2d and Fig. S7b in Supporting information).

  Figure 2

  

  Figure 2.  (a) XRD patterns, (b) Raman spectra, and (c) FT-IR spectra of A-TiO₂/Ti₃C₂T_x and TiO₂/Ti₃C₂T_x. (d) N₂ sorption isotherm and corresponding pore size distribution curve, and high-resolution XPS spectra of A-TiO₂/Ti₃C₂T_x for (e) Ti 2p, (f) O 1s, (g) C 1s, (h) Si 2p and (i) N 1s.

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  X-ray photoelectron spectrometer (XPS) technique was applied to analyze the chemical states of A-TiO₂/Ti₃C₂T_x. The survey XPS spectrum confirms the existence of Ti, Si, O, C, and N (Fig. S8a in Supporting information), consistent with the above EDS analysis. And the N atomic content is 1.29% (Fig. S8b in Supporting information), which mainly comes from the containg-NH₂ APTES. Fig. 2e shows the high-resolution spectrum of Ti 2p, the peaks at 459.33 and 465.28 eV are attributed to Ti⁴⁺, while the doublet peaks at 456.49 and 464.29 eV are associated with the Ti-C bond. Meanwhile, the Ti-O bond at 459.05 eV is also observed. This further verifies the strong coupling of TiO₂ QDs with Ti₃C₂T_x. In the O 1s region, Si—O, Ti—O—C and Ti—O—Ti bonds can be well identified at the binding energy of 530.5, 531.09 and 532.41 eV (Fig. 2f) [6]. Two peaks at 284.72 eV and 286.08 eV in the C 1s spectrum (Fig. 2g) are ascribed to C—C (284.72 eV) and C-Ti/C—N/C—O [22]. The Si 2p spectrum in Fig. 2h displays distinct Si⁴⁺ (103 eV) and Si-O (102.19 eV) peaks [21], corresponding to the spectral analysis of O 1s. The N 1s high-resolution spectrum in Fig. 2i shows the presence of pyridinic N (398.3 eV), pyrrolic N (399.8 eV), and graphitic N (401 eV) [23], which can effectively enhance the adsorption of Li ions by heterostructure, thereby promoting the lithium storage capacity of the composite electrode.

  To evaluate the lithium storage performance of two composites, a half cell was assembled using lithium metal as the counter electrode. Fig. 3a illustrates the cyclic voltammetry (CV) curves for the first three cycles of the A-TiO₂/Ti₃C₂T_x electrode at a scan rate of 0.1 mV/s. In the first cycle, a cathodic peak appears around 0.75 V, and an anodic peak is observed near 0.95 V, indicating the Li⁺ insertion/extraction in the composite [24]. Additionally, an irreversible cathode peak at around 1.75 V and an anode peak at approximately 2.02 V are seen, attributing to the electrochemical activities of TiO₂. The irreversible cathodic peak is related to the formation of a solid electrolyte interface (SEI) [25]. In the following two cycles, the irreversible peaks are significantly reduced, and the curves almost completely overlap. Furthermore, in comparison to TiO₂/Ti₃C₂T_x (Fig. S9a in Supporting information), the CV curve of the A-TiO₂/Ti₃C₂T_x electrode exhibits a more rectangular shape, indicating a superior reversibility during cycling process [26].

  Figure 3

  

  Figure 3.  (a) CV curves of initial three cycles at a scan rate of 0.1 mV/s, and (b) charge-discharge profiles of the A-TiO₂/Ti₃C₂T_x electrode at 100 mA/g. (c) Rate capabilities, (d) cycling performances at 100 mA/g, and (e) comparison of cycle performances between the A-TiO₂/Ti₃C₂T_x electrode and other TiO₂-based anodes for LIBs. (f) Long cycling performances of A-TiO₂/Ti₃C₂T_x and TiO₂/Ti₃C₂T_x electrodes at a high current density of 1000 mA/g.

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  The galvanostatic charge/discharge (GDC) curves for the first three cycles of A-TiO₂/Ti₃C₂T_x and TiO₂/Ti₃C₂T_x electrodes are presented in Fig. 3b and Fig. S9b (Supporting information). In the first cycle, the discharge and charge capacities of the A-TiO₂/Ti₃C₂T_x electrode are 820.9 mAh/g and 376.9 mAh/g, respectively, while the TiO₂/Ti₃C₂T_x electrode exhibits a lower initial discharge capacity of only 662.4 mAh/g. Moreover, in subsequent cycles, the A-TiO₂/Ti₃C₂T_x electrode remains a higher capacity, demonstrating an enhanced lithium-storage performance.

  The rate performance of two electrodes was shown in Fig. 3c. At the current densities of 0.05, 0.1, 0.2, 0.5, 1.0, and 2.0 A/g, the A-TiO₂/Ti₃C₂T_x electrode delivers the specific capacities of 415.2, 375.8, 348.1, 315.5, 278.9, and 224.3 mAh/g, respectively. Furtherly, when the current density is returned to 0.1 A/g, the capacity increases to 420.4 mAh/g. In contrast, the TiO₂/Ti₃C₂T_x electrode has lower capacities of 370.9, 332.7, 298.3, 213.2, 123.6, and 54.1 mAh/g at the same current densities. Upon returning to 0.1 A/g, only 308 mAh/g of the capacity can be maintained. These results indicate that such a unique heterostructure can promote the lithium ion transport in the electrochemical reaction.

  Fig. 3d illustrates the cycle performances of A-TiO₂/Ti₃C₂T_x and TiO₂/Ti₃C₂T_x electrodes at a current density of 0.1 A/g. Clearly, the A-TiO₂/Ti₃C₂T_x electrode has a better cycle performance than that TiO₂/Ti₃C₂T_x electrode. More importantly, it maintains a high specific capacity of 424.7 mAh/g, corresponding to 126% of the theoretical capacity of TiO₂ (335 mAh/g) after 400 cycles. In comparison, the TiO₂/Ti₃C₂T_x electrode only sustains a capacity of 176 mAh/g mAh/g under the same conditions. The outstanding cycling performance of A-TiO₂/Ti₃C₂T_x can be related to its superior structural stability facilitated by the presence of SiO₂ during cycling. Moreover, as listed in Fig. 3e and Table S1 (Supporting information), the newly-developed A-TiO₂/Ti₃C₂T_x electrode in our work is comparable to those TiO₂-based anodes reported [3,27-34].

  Impressively, the A-TiO₂/Ti₃C₂T_x anode demonstrates an exceptional long cycling performance. As shown in Fig. 3f, after 2500 cycles, it maintains a specific capacity of 170 mAh/g at a high current density of 1000 mA/g, achieving an average coulombic efficiency of nearly 99.99%. The rate of capacity loss per cycle was a mere 0.009%. In stark contrast, the TiO₂/Ti₃C₂T_x electrode preserves a capacity of only 100 mAh/g after 2500 cycles at the same current density. This contrast underscores the enhanced durability and performance of the A-TiO₂/Ti₃C₂T_x electrode, attributed to the strong coupling effect of TiO₂ QDs and Ti₃C₂T_x nanosheets.

  To further demonstrate the N-doping advantages, the contact angles of two electrodes in the electrolytes were tested (Fig. S10 in Supporting information). Obviously, the wettability of the A-TiO₂/Ti₃C₂T_x electrode is superior to that of the TiO₂/Ti₃C₂T_x electrode, suggesting that A-TiO₂/Ti₃C₂T_x has more fully contact with the electrolyte during the electrochemical reaction. This enhanced wettability can be ascribed to the nitrogen introduction. Moreover, the TEM images after cycles of two electrodes (Fig. S11 in Supporting information) further demonstrate that the existence of thin SiO₂ layer in the heterostructure can ensure the stability of A-TiO₂/Ti₃C₂T_x during the long-term cycles, so as to obtain the superior long cycle life.

  A series of CV tests were carried out at various scan rates to investigate the transfer behavior of two electrodes. As illustrated in Fig. 4a and Fig. S12a (Supporting information), their curves display comparable profiles and trends. Furthermore, the presence of redox peaks points to rapid electrochemical reactions occurring within the materials. The relationship between the peak current and the scanning rate (ν) determine the material's capacitance and diffusion contributions [35], and the two obey the following relationship:

  (1)

  (2)

  where a and b are constants, and the fitted value of b () can indicate whether the electrode dynamic process is primarily governed by capacitance control (b-1.0) or diffusion control (b-0.5) [36]. In Fig. 4b, the fitting b values for the cathode and anode peaks of A-TiO₂/Ti₃C₂T_x are 0.90 and 0.84, respectively, suggesting a capacitance-controlled electrochemical process. Conversely, for TiO₂/Ti₃C₂T_x electrode, the fitted b values for the cathode and anode peaks are 0.61 and 0.56, respectively, indicating a diffusion-dominated behavior (Fig. S12b in Supporting information). The contribution of capacitance and diffusion control to capacity is analyzed by using the following formula [37]:

  (3)

  Figure 4

  

  Figure 4.  (a) CV curves at various scan rates, (b) the calculated b values at six redox peaks, (c) surface capacitive contribution at 1.0 mV/s, and (d) the percentage of capacitive contribution of the A-TiO₂/Ti₃C₂T_x electrode at diverse scan rates. (e) GITT curves of A-TiO₂/Ti₃C₂T_x and TiO₂/Ti₃C₂T_x electrodes and their (f) Li⁺ diffusion coefficients. In-situ EIS diagram of (g) discharge and (h) charge of A-TiO₂/Ti₃C₂T_x, and calculated R_ct resistance values for (i) discharge and (j) charge.

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  where k₁ν and k₂ν represent non-Faraday reactions and Faraday reactions, respectively. As depicted in Fig. 4c and Fig. S13a (Supporting information), at a scan rate of 1.0 mV/s, the capacitance contribution ratio is found to be 74.8% for A-TiO₂/Ti₃C₂T_x and 66.2% for TiO₂/Ti₃C₂T_x, respectively. Moreover, the capacitance contribution values were computed for multiple sweep speeds simultaneously. As illustrated in Fig. 4d and Fig. S13b (Supporting information), the A-TiO₂/Ti₃C₂T_x electrode exhibits a higher capacitance contribution rate across all scanning rates than TiO₂/Ti₃C₂T_x. That indicates its better transport dynamics, thereby improving the rate performance of A-TiO₂/Ti₃C₂T_x.

  Fig. 4e presents the galvanostatic intermittent titration technique (GITT) curves of A-TiO₂/Ti₃C₂T_x and TiO₂/Ti₃C₂T_x electrodes. The Li⁺ diffusion coefficients of two electrodes were calculated based on Fick's second law and the following equation [38]:

  (4)

  As shown in Fig. 4f, the D_Li⁺ values of two electrodes are relatively similar [39]. However, the overall D_Li⁺ levels of the A-TiO₂/Ti₃C₂T_x electrode is higher than those of TiO₂/Ti₃C₂T_x. These results further confirm that the A-TiO₂/Ti₃C₂T_x electrode exhibits an enhanced Li⁺ diffusion ability, thus effectively improving the energy storage performance.

  In-situ electrochemical impedance spectroscopy (EIS) was also conducted to analysis the impedance changes of A-TiO₂/Ti₃C₂T_x electrodes during the first cycle. The data was fitted with a suitable circuit, yielding the 2D Nyquist diagram, as depicted in Figs. 4g and h (where the line graph represents the fitted data). With the discharge to 1.7–1.0 V, the SEI film gradually forms, Nyquist curve in the intermediate frequency region is semicircular, indicating the resistance value of the SEI film [40]. The semicircle of the R_ct resistance region at this point also tends to stabilize (Fig. 4g). In the final process, two semicircular resistors are stabilized as R_SEI and R_ct, indicating the complete formation of the SEI film. In the subsequent charging process (Fig. 4h), the R_SEI resistance tends to stabilize, and only the R_ct resistance region gradually increases until it appears as a straight line. This change indicates the formation of the stable SEI film on the material's surface [41]. Additionally, based on the fitting results, the changes in R_ct during the charge and discharge processes were plotted (Figs. 4i and j), in line with the changes observed in the Nyquist curve and confirmed the above changes in R_ct.

  Then, we calculate the adsorption energy and surface charge density difference to show the enhancement of the Li adsorption and surface electron redistribution in the TiO₂/Ti₃C₂N₂ heterostructure compared to TiO₂/Ti₃C₂, Ti₃C₂N₂ and TiO₂ surface. Two adsorption sites at the TiO₂ (Ⅰ for Ti-top and Ⅱ for O-top) and Ti₃C₂ surface (Ⅰ for C-hollow, Ⅱ for Ti-hollow) were choose, respectively, to identity the more stable one for Li adsorption. As presented in Fig. 5a, the Li adsorption energy on the TiO₂/Ti₃C₂N₂ reaches −6.73 eV at the C-hollow site (Ⅰ), significantly lower than those on TiO₂/Ti₃C₂ (−1.06 eV), Ti₃C₂N₂ (−4.04 eV) and TiO₂ surface (−3.21 eV), manifesting the enhanced Li adsorption stability in the TiO₂/Ti₃C₂N₂. Besides, the charge density difference shows that the electrons preferred to deplete from the Li-ion and accumulate at the surface of the substrate, suggesting the electron transfer from the Li to the Ti₃C₂ or TiO₂ surface. The Bader analysis exhibits the 0.38e, 0.07e, 0.35e and 0.26e electrons transfer from the Li to the TiO₂/Ti₃C₂N₂, TiO₂/Ti₃C₂, Ti₃C₂N₂ and TiO₂ surface, respectively (Fig. 5b). Herein, the TiO₂/Ti₃C₂N₂ heterostructure attracts more electrons from the Li-ion, rendering it a stronger interaction on Li adsorption. Therefore, the enhanced adsorption of Li ions makes the TiO₂/Ti₃C₂N₂ heterostructure a promising electrode material for LIBs.

  Figure 5

  

  Figure 5.  (a) Lithium adsorption energies (E_ads) at different sites (Ⅰ and Ⅱ) for TiO₂/Ti₃C₂N₂, TiO₂/Ti₃C₂, Ti₃C₂N₂ and TiO₂ surface, respectively. (b) Corresponding charge density difference (iso-value of 0.002 e/ų) for each surface at their most stable site. (c) Schematic diagram of lithium storage merits of A-TiO₂/Ti₃C₂T_x.

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  Based on the above results, the outstanding lithium storage performance of the A-TiO₂/Ti₃C₂T_x electrode is mainly due to the following reasons (Fig. 5c): Firstly, the construction of 0D/2D heterostructure shortens the ion transport path, thus promoting the rapid transfer dynamics during cycles. Secondly, Ti₃C₂T_x nanosheets as the substrate establishes an excellent conductive network, effectively enhancing the conductivity of the whole electrode, and ultrasmall TiO₂ QDs provide the exposure of more active sites for lithium-ion storage, thereby boosting the reversible capacity. Furthermore, the N atoms derived from APTES enhance the adsorption of lithium ions, leading to increased lithium storage. More importantly, the SiO₂ layer ensures the tight attachment of TiO₂ QDs onto the Ti₃C₂T_x surface, significantly enhancing the structural integrity of the overall composite during the long cycling.

  In summary, a new type of 0D TiO₂ quantum dots/2D Ti₃C₂T_x composite with exceptional lithium storage performance has been constructed using the APTES-induced assembly route. The results indicate that the SiO₂ layer formed from the APTES hydrolysis significantly improves the structural stability of the whole electrode. The prepared A-TiO₂/Ti₃C₂T_x anode maintains a high capacity of 425.4 mAh/g after 400 cycles at 100 mA/g, surpassing the theoretical capacity of original TiO₂ by 126%. Furthermore, it has an impressive long-cycling performance, retaining a capacity of 170 mAh/g after 2500 cycles at 1000 mA/g. Through electrochemical kinetics analysis combining with DFT calculation, the excellent lithium storage performance of A-TiO₂/Ti₃C₂T_x is attributed to its unique heterostructure and in-situ N doping derived from APTES, which not only reduces the Li⁺ adsorption energy, but also gives the fast charge transfer dynamics. The strategy proposed in our work offers a promising approach towards high-performance nanocomposites with enhanced structural stability.

  Declaration of competing interest

  The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

  CRediT authorship contribution statement

  Xinlin Zhang: Investigation, Methodology, Writing – original draft. Cheng Tang: Software. Haitao Li: Validation. Jie Sun: Data curation. Aijun Du: Validation. Minghong Wu: Funding acquisition. Haijiao Zhang: Conceptualization, Project administration, Supervision, Writing – review & editing.

  Acknowledgments

  We appreciate the support from the Natural Science Foundation of Shanghai (No. 23ZR1423800), and Key Laboratory of Advanced Energy Materials Chemistry (Ministry of Education), Nankai University.

  Supplementary materials

  Supplementary material associated with this article can be found, in the online version, at doi:10.1016/j.cclet.2024.110088.

  
  
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  Figure 1  (a) The fabrication process of A-TiO₂/Ti₃C₂T_x. (b, c) SEM images, (d) TEM image, (e, f) HRTEM images (insert is the SAED pattern), (g) particle size distribution profile, and (h) STEM image and corresponding elemental mappings of A-TiO₂/Ti₃C₂T_x.

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  Figure 2  (a) XRD patterns, (b) Raman spectra, and (c) FT-IR spectra of A-TiO₂/Ti₃C₂T_x and TiO₂/Ti₃C₂T_x. (d) N₂ sorption isotherm and corresponding pore size distribution curve, and high-resolution XPS spectra of A-TiO₂/Ti₃C₂T_x for (e) Ti 2p, (f) O 1s, (g) C 1s, (h) Si 2p and (i) N 1s.

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  Figure 3  (a) CV curves of initial three cycles at a scan rate of 0.1 mV/s, and (b) charge-discharge profiles of the A-TiO₂/Ti₃C₂T_x electrode at 100 mA/g. (c) Rate capabilities, (d) cycling performances at 100 mA/g, and (e) comparison of cycle performances between the A-TiO₂/Ti₃C₂T_x electrode and other TiO₂-based anodes for LIBs. (f) Long cycling performances of A-TiO₂/Ti₃C₂T_x and TiO₂/Ti₃C₂T_x electrodes at a high current density of 1000 mA/g.

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  Figure 4  (a) CV curves at various scan rates, (b) the calculated b values at six redox peaks, (c) surface capacitive contribution at 1.0 mV/s, and (d) the percentage of capacitive contribution of the A-TiO₂/Ti₃C₂T_x electrode at diverse scan rates. (e) GITT curves of A-TiO₂/Ti₃C₂T_x and TiO₂/Ti₃C₂T_x electrodes and their (f) Li⁺ diffusion coefficients. In-situ EIS diagram of (g) discharge and (h) charge of A-TiO₂/Ti₃C₂T_x, and calculated R_ct resistance values for (i) discharge and (j) charge.

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  Figure 5  (a) Lithium adsorption energies (E_ads) at different sites (Ⅰ and Ⅱ) for TiO₂/Ti₃C₂N₂, TiO₂/Ti₃C₂, Ti₃C₂N₂ and TiO₂ surface, respectively. (b) Corresponding charge density difference (iso-value of 0.002 e/ų) for each surface at their most stable site. (c) Schematic diagram of lithium storage merits of A-TiO₂/Ti₃C₂T_x.

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