Search

Na 2 Ti 3 O 7 , a titanium-based compound for sodium ion batteries (SIBs), stands out among anode materials because of its ultralow voltage plateau which leads to advanced energy density. However, the poor electronic conductivity and mediocre sodium ion storage capability are the main bottlenecks for its large-scale development. In this regard, self-supported Se doped Na 2 Ti 3 O 7 arrays are innovatively proposed and different Se doping amounts are designed. It is concluded that the appropriate Se doping (Na 2 Ti 3 O 6 Se) could significantly enlarge the interlayer spacing, narrow the bandgap and decrease Na+ diffusion barrier, leading to enhanced reaction kinetics, which is also validated by the theoretical calculations in this work. As expected, the 0 anode exhibits a reversible capacity of 207 mAh g−1 after 100 cycles at 0.2 A g−1 in the voltage range of 0.01–3 V. A capacity of 155 mAh g−1 can be achieved after 1000 cycles at 1 A g−1. The experimental findings combined with theoretical calculations state that the Se doping protocol is an effective mean to modify the electrode materials. • A self supported Na 2 Ti 3 O 7 arrays with Se doping is designed. • The appropriate content Se doping into Na 2 Ti 3 O 7 improves the performance. • Se doping induces charge accumulation and stronger Na + adsorption capability. • Se doping improves the electronic conductivity. [ABSTRACT FROM AUTHOR]

Insertion‐type layered Na2Ti3O7 has attracted the attention of the researchers and is considered to be one of the promising low‐voltage anode materiasl for sodium‐ion batteries. In spite of its fascinating electrochemical properties, the low electronic conductivity and structural instability of Na2Ti3O7 are major drawbacks that restrict its practical application. Surface modification with pyrolytic carbon is one of the effective ways to reduce irreversible capacity loss caused by electrolytic degradation. In this work, attempts have been made to investigate the effects of different carbon coating approaches on the electrochemical properties of sol‐gel‐synthesized Na2Ti3O7 microrods. The as‐synthesized Na2Ti3O7 rods are coated with a uniform carbon layer both by in‐situ and ex‐situ methods using citric acid and polyvinyl alcohol as carbon source, respectively. Ex‐situ carbon‐coated Na2Ti3O7 (Na2Ti3O7@C), due to better coating uniformity and higher graphitized carbon percentage, shows enhanced cyclability and rate performance compared to bare material and in‐situ carbon composite (Na2Ti3O7/C). Following the ex‐situ carbonization method using PVA as carbon source, it is found that increase of carbon content from 5wt% to 10wt% significantly improves its electrochemical properties. However, further increase in PVA amount has adverse effect on the cycling as well as rate performance of Na2Ti3O7@C. Surface modified Na2Ti3O7@C with optimum carbon content (10wt% C) shows improved cycling capacity (capacity retention ∼74.75% after100 cycle) and rate performance (∼67 mAhg‐1 at 1.5 Ag‐1). Both excess and inadequate carbon content have detrimental effect on the electrochemical properties of Na2Ti3O7 anode. [ABSTRACT FROM AUTHOR]

Highlights: NTO heat-treated 48 h displays more ordered structure and less surface contamination. Sodium insertion involves formation of two phases Na4-xTi3O7 and Na4Ti3O7 as evidenced by Operando XRD. The increase in the calcination time leads to better reversibility of sodiation/desodiation and higher capacity. The growing interest in Na-ion batteries as a "beyond lithium" technologies for energy storage drives the research for high-performance and environment-friendly materials. Na2Ti3O7 (NTO) as an eco-friendly, low-cost anode material shows a very low working potential of 0.3 V vs. Na+/Na but suffers from poor cycling stability, which properties can be significantly influenced by materials synthesis and treatment. Thus, in this work, the influence of the calcination time on the electrochemical performance and the reaction mechanism during cycling were investigated. NTO heat-treated for 48 h at 800 °C (NTO-48h) demonstrated enhanced cycling performance in comparison to NTO heat-treated for only 8 h (NTO-8h). The pristine material was thoroughly characterized by X-ray diffraction, laser granulometry, X-ray photoelectron spectroscopy, and specific surface area measurements. The reaction mechanisms induced by sodiation/desodiation and cycling were investigated by operando XRD. Electrochemical impedance spectroscopy was used to evidence the evolution of the solid electrolyte interface layer (SEI) and modification of charge transfer resistances as well as the influence of cycling on capacity decay. The evolution of the crystallographic structure of NTO-48h revealed a more ordered structure and lower surface contamination compared to NTO-8h. Moreover, the residual Na4Ti3O7 phase detected after the sodium extraction step in NTO-8h seems correlated to the lower electrochemical performance of NTO-8h compared to NTO-48h. [ABSTRACT FROM AUTHOR]

Abstract Insertion‐type layered Na2Ti3O7 has attracted the attention of the researchers and is considered to be one of the promising low‐voltage anode materiasl for sodium‐ion batteries. In spite of its fascinating electrochemical properties, the low electronic conductivity and structural instability of Na2Ti3O7 are major drawbacks that restrict its practical application. Surface modification with pyrolytic carbon is one of the effective ways to reduce irreversible capacity loss caused by electrolytic degradation. In this work, attempts have been made to investigate the effects of different carbon coating approaches on the electrochemical properties of sol‐gel‐synthesized Na2Ti3O7 microrods. The as‐synthesized Na2Ti3O7 rods are coated with a uniform carbon layer both by in‐situ and ex‐situ methods using citric acid and polyvinyl alcohol as carbon source, respectively. Ex‐situ carbon‐coated Na2Ti3O7 (Na2Ti3O7@C), due to better coating uniformity and higher graphitized carbon percentage, shows enhanced cyclability and rate performance compared to bare material and in‐situ carbon composite (Na2Ti3O7/C). Following the ex‐situ carbonization method using PVA as carbon source, it is found that increase of carbon content from 5wt% to 10wt% significantly improves its electrochemical properties. However, further increase in PVA amount has adverse effect on the cycling as well as rate performance of Na2Ti3O7@C. Surface modified Na2Ti3O7@C with optimum carbon content (10wt% C) shows improved cycling capacity (capacity retention ∼74.75% after100 cycle) and rate performance (∼67 mAhg‐1 at 1.5 Ag‐1). Both excess and inadequate carbon content have detrimental effect on the electrochemical properties of Na2Ti3O7 anode.

Sodium titanate is considered as one of the most promising anode materials for sodium-ion batteries without any serious safety concerns due to its high theoretical capacity at sufficiently low voltage. However, its low electrical conductivity severely restricts the electrochemical performances as an anode for sodium-ion batteries. Because suitable doping is always found to be a trump card strategy to especially enhance the conductivity, a molybdenum-doped sodium titanate nanostructured anode was successfully synthesized for the first time using the solvothermal method. Molybdenum-doped sodium titanate electrode materials showed superior electrochemical performances than the pristine sample. On more precise consideration, the sodium titanate electrode doped with 15 wt % molybdenum not only delivers ∼24% high reversible capacity at a high current density of 1 A g–1 in comparison to the pure sodium titanate electrode but also maintains it until 2500 cycles. It is believed that the improved electrochemical performances are mainly contributed by the combination of enhanced electrical conductivity and oxygen vacancy generated in the sodium titanate framework as a result of molybdenum doping. Molybdenum doping may also allow Na+ ion diffusion through multiple pathways within the sodium titanate crystal lattice and increase the transport rate of Na+ ions. [ABSTRACT FROM AUTHOR]

The growing interest in Na-ion batteries as a “beyond lithium” technologies for energy storage drives the research for high-performance and environment-friendly materials. Na2Ti3O7 (NTO) as an eco-friendly, low-cost anode material shows a very low working potential of 0.3 V vs. Na+/Na but suffers from poor cycling stability, which properties can be significantly influenced by materials synthesis and treatment. Thus, in this work, the influence of the calcination time on the electrochemical performance and the reaction mechanism during cycling were investigated. NTO heat-treated for 48 h at 800 °C (NTO-48h) demonstrated enhanced cycling performance in comparison to NTO heat-treated for only 8 h (NTO-8h). The pristine material was thoroughly characterized by X-ray diffraction, laser granulometry, X-ray photoelectron spectroscopy, and specific surface area measurements. The reaction mechanisms induced by sodiation/desodiation and cycling were investigated by operando XRD. Electrochemical impedance spectroscopy was used to evidence the evolution of the solid electrolyte interface layer (SEI) and modification of charge transfer resistances as well as the influence of cycling on capacity decay. The evolution of the crystallographic structure of NTO-48h revealed a more ordered structure and lower surface contamination compared to NTO-8h. Moreover, the residual Na4Ti3O7 phase detected after the sodium extraction step in NTO-8h seems correlated to the lower electrochemical performance of NTO-8h compared to NTO-48h.

[Display omitted] We here demonstrate the controlled synthesis of BiOBr quantum dots (QDs) decorated Na 2 Ti 3 O 7 necklaces via a hydrothermal transformation of sodium titanate nanotubes. The BiOBr QDs are deposited on the surface of Na 2 Ti 3 O 7 necklaces, forming a heterogeneous interface of BiOBr(2 0 0) and Na 2 Ti 3 O 7 (1 1 0), which promotes the separation efficiency of photogenerated charges, thus resulting in its superior catalytic performance in the photo-oxidation of benzyl alcohol. The BiOBr/Na 2 Ti 3 O 7 -1.0 exhibiting highest oxygen defect population gives best photocatalytic activity with a promising conversion rate of 3.32 mmol reacted BA g catal. −1h−1, which is substantially higher than the corresponding reported photocatalysts. DFT results corroborate the superior performance of BiOBr/Na 2 Ti 3 O 7 is mainly due to the formation of a built-in electric field and given efficiently the charge transfer between BiOBr(2 0 0) and Na 2 Ti 3 O 7 (1 1 0). In all, this study reports a simple in-situ hydrothermal growth protocol to efficiently construct BiOBr/Na 2 Ti 3 O 7 heterojunction composites and offers guidelines for design of a new synthetic strategy to prepare efficient photocatalysts. [ABSTRACT FROM AUTHOR]

Na 2 Ti 3 O 7 -based anodes show great promise for Na + storage in sodium-ion batteries (SIBs), though the effect of Na 2 Ti 3 O 7 morphology on battery performance remains poorly understood. Herein, hydrothermal syntheses is used to prepare free-standing Na 2 Ti 3 O 7 nanosheets or Na 2 Ti 3 O 7 nanotubes on Ti foil substrates, with the structural and electrochemical properties of the resulting electrodes explored in detail. Results show that the Na 2 Ti 3 O 7 nanosheet electrode (NTO NSs) delivered superior performance in terms of reversible capacity, rate capability, and especially long-term durability in SIBs compared to its nanotube counterpart (NTO NTs). Electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM) investigations, combined with density functional theory calculations, demonstrated that the flexible 2D Na 2 Ti 3 O 7 nanosheets are mechanically more robust than the rigid Na 2 Ti 3 O 7 nanotube arrays during prolonged battery cycling, explaining the superior durability of the NTO NSs electrode. This work prompts the use of anodes based on Na 2 Ti 3 O 7 nanosheets in the future development of high-performance SIBs., (© 2024 Wiley‐VCH GmbH.)

Calcium ion batteries (CIBs) are a promising energy storage device due to the low redox potential of the Ca metal and the abundant reserves of the Ca element. However, the large radius and divalent nature of Ca 2+ lead to its slow ion diffusion kinetics and the lack of suitable electrode materials for Ca storage. Here, a layered structure of Na 2 Ti 3 O 7 (NTO) is presented as an anode material for nonaqueous CIBs. This NTO anode demonstrates a high discharge capacity of 165 mA h g -1 at 100 mA g -1 and a remarkable capacity retention rate of 80%, even after 2000 cycles at 500 mA g -1 , surpassing the performance of all reported intercalation-type anode materials for CIBs. The NTO transfers to layered Ca VII Na IX Ti 3 O 7 (CNTO) with intercalation of Ca 2+ and extraction of Na + during the first discharge process. Then, the CNTO undergoes the reversible insertion/extraction of Ca 2+ during subsequent cycling. Additionally, density functional theory calculations reveal that NTO possesses a rapid two-dimensional diffusion pathway for Ca 2+ . Moreover, the full CIBs based on NTO as the anode further underscore its potential for CIBs. This work presents promising anode materials for CIBs, offering opportunities to promote the development of high-performance CIBs.

Sodium‐ion batteries (SIBs), as next‐generation energy storage devices, can be made by a similar production process to lithium‐ion batteries (LIBs). The key to accelerating their commercialization is to discover appropriate high‐performance electrode materials with low cost, nontoxicity, and simple synthetic features. Herein, layered‐structure Na2Ti3O7, with the advantages of appropriate charge/discharge plateaus, superior stability, environmental friendliness, and ease of preparation using cheap raw materials, is selected for assembly in full‐cell battery packs to evaluate its suitability for practical application. When evaluated in a coin cell, it has a capacity of 77.2 mAh g−1 at 1 A g−1 after 10 000 cycles with capacity retention of 99.9%, demonstrating its excellent stability. In the case of a soft‐pack battery, it retains 22.3 mAh g−1 at 0.1 A g−1 and 18.1 mAh g−1 at 0.05 A g−1 after 50 cycles. After cycling, there is no sodium dendrite formation or active material shedding, further confirming its safety in practical application. Therefore, Na2Ti3O7 as another intercalation/deintercalation mechanism material has application potential in the future.

Hybrid storage systems require electrode materials with efficient capacitance and long cycle life. Their development is garnering increasing attention, with numerous efforts having been undertaken. Sodium titanate (Na 2 Ti 3 O 7) has significant potential as an appropriate electrode material candidate for progressive energy storage. However, the application of Na 2 Ti 3 O 7 is limited by its low electrical conductivity and cycling strength. Herein, a novel Na 2 Ti 3 O 7 /single-walled carbon nanotubes i.e NT/CNT nanostructure was fabricated via an in-situ hydrothermal method. Owing to the 1D/1D morphological features, high surface area, enriched interfacial conductivity, abundant active edge sites, and mesoporous nature of the Na 2 Ti 3 O 7 /SWCNTs nanostructure electrode, a remarkable capacity of 576.01 F g−1 at 0.8 A g−1 was obtained, with cycling stability featuring 91.43% retaining of capacitance after 5000 cycles. Importantly, a split-cell-type asymmetric supercapacitor was fabricated, demonstrating an energy density of 8.75 Wh kg−1 at a power density of 4500 W kg−1. A significant improvement in the electrochemical behavior of the novel 1D/1D NT/CNT nanostructure was primarily ascribed to the robust and intimate interfacial contact between the constituent Na 2 Ti 3 O 7 and SWCNTs, acting as an optimal reservoir for electrolyte ions. These outcomes indicate that the NT/CNT nanostructure is a remarkable electrode material for electroactive energy storage devices. [ABSTRACT FROM AUTHOR]

Na2Ti3O7 (NTO) is a potential anode material with low discharge voltage for room‐temperature sodium‐ion batteries. In this work, NTO nanotubes were prepared by a hydrothermal method. XRD, SEM, TEM, and HRTEM studies are performed to investigate the composition, morphology, and structure. As anodes for sodium‐ion batteries, NTO nanotubes show a reversible capacity of 126.2 mAh g−1 at 100 mA g−1. The discharge capacity can still reach 109 mAh g−1 even for 2000 cycles. Solid‐state sodium‐ion batteries containing NTO‐nanotube anodes and an Na3Zr2Si2PO12 solid electrolyte display a comparable performance to batteries with a liquid electrolyte. Moreover, the prepared solid‐state sodium battery is also demonstrated to store mechanical energy harvested by triboelectric nanogenerators (TENGs). The discharge capacity reaches 121 mAh g−1 at 5 mA g−1. [ABSTRACT FROM AUTHOR]

Abstract Sodium titanate nanopowder (nominal formula Na 1.5 H 0.5 Ti 3 O 7) was directly synthesized using a continuous hydrothermal flow synthesis process using a relatively low base concentration (4 M NaOH) in process. The as-made titanate nanomaterials were characterised using powder X-ray diffraction, X-ray photoelectron spectroscopy, energy-dispersive X-ray spectroscopy, Raman spectroscopy, Brunauer–Emmett–Teller analysis and transmission electron microscopy, and evaluated as potential electrode materials for Li-ion and Na-ion batteries. Cyclic voltammetry studies on half-cells revealed that the sodium titanate nanomaterial stored charge primarily through a combination of pseudocapacitive and diffusion-limited processes in both systems. Electrochemical cycling tests at a high specific current of 1000 mA g−1, revealed that the Li-ion and Na-ion cells retained relatively high specific capacities after 400 cycles of 131 and 87 mAh g−1, respectively. This study demonstrates the potential of CHFS-made sodium titanate nanopower as an anode material for both Li- and Na-ion cell chemistries. Graphical abstract Image 1 Highlights • Na 1.5 H 0.5 Ti 3 O 7 is synthesized via Continuous Hydrothermal Flow Synthesis. • The nanoparticles are examined as Li-ion and Na-ion battery anode materials. • Na 1.5 H 0.5 Ti 3 O 7 performs excellently in half-cells at current rates of up 2 A g−1. • A greater fast faradaic charge storage contribution was observed in Na-ion. [ABSTRACT FROM AUTHOR]

Abstract As a safe, low-voltage anode material, in recent years, Na 2 Ti 3 O 7 has become regarded as a highly alternative negative material for high energy room-temperature sodium ion batteries. However, its poor ion and electron conductivity produces very poor electrochemical performance of Na 2 Ti 3 O 7 , therefore greatly limiting its practical application in future scalable utilization. We report here a self-doping of Ti3+ into the Na 2 Ti 3 O 7 electrode material, through a very simple post heat-treatment process, that is, annealing the Na 2 Ti 3 O 7 precursor at an argon atmosphere containing 5% H 2. By XPS characterization, it is confirmed that Ti3+ is successfully doped into Na 2 Ti 3 O 7. Benefiting from this self-doped Ti3+ with larger ionic radius and better electronic conductivity, the obtained Na 2 Ti 3 O 7 demonstrates improved electron conductivity and ion diffusion properties. Combined with a carbon coating, this self-doped Na 2 Ti 3 O 7 electrode material exhibits superior electrochemical performance to that of non-doped electrode, e.g., this Na 2 Ti 3 O 7 sample could delivers a specific capacity of 187.8 and 51.9 mAh g−1 from 0.1C to 10C at various rate of discharge, respectively. When recycled back to 0.1C, it can still reach 153 mAh g−1. Compared with numerous reported nanoscale means, we believe this approach is practical and productive, and may extend to other ti-based electrode materials. Highlights • A self-doped Ti3+ of Na 2 Ti 3 O 7 anode is synthesized by a facile sol-gel process. • The Ti3+ enhances the electronic conductivity of Na 2 Ti 3 O 7. • The Ti3+ in crystal lattice of Na 2 Ti 3 O 7 enhances the Na+ diffusion coefficient. • This self-doped Na 2 Ti 3 O 7 material exhibits improved electrochemical performance. [ABSTRACT FROM AUTHOR]

Nanocrystalline Na2Ti3O7 material is prepared by a newly developed sol-gel procedure. The sol-gel made Na2Ti3O7 calcined at 500 °C possesses mesoporous structure and BET surface area of 89 m2 g−1. X-ray diffraction and scanning electron microscopy confirm the presence of sintered nanosheets or very small crystals of the size of 10-20 nm with short-range ordering. Electrochemical behavior of nanocrystalline Na2Ti3O7 is evaluated by cyclic voltammetry of Na insertion and by galvanostatic chronopotentiometry at different charging rates. The sol-gel made Na2Ti3O7 exhibits improved performance as compared to that of the microcrystalline Na2Ti3O7 prepared by solid-state synthesis. Discharge capacities of optimized material at charging rates 1, 2, and 5C reach 109, 86, and 63 mAh g−1, respectively, with 100% coulombic efficiency and zero capacity drop over 50 cycles after initial conditioning. Excellent performance of Na2Ti3O7_500 is obviously an effect of its large surface area giving rise to predominantly capacitive mechanism of charge storage. Hence, sol-gel made nanocrystalline Na2Ti3O7 represents promising anode material for Na-ion batteries due to its charge capacity and outstanding cycling stability.ᅟ [ABSTRACT FROM AUTHOR]

Na2Ti3O7 ceramic materials have been widely used in sodium-ion battery applications with relative good results; however, there are still several studies that might be carried out in the improvement of the Na2Ti3O7 properties and the overall batteries’ performance. In this direction, we used sonochemical method following a thermal treatment in order to synthetized pure phase Na2Ti3O7 nanopowders. X-ray diffraction characterization revealed that Na2Ti3O7 is the primary phase in nanopowders and ceramic sample; although, a high level of amorphization was observed in the sonicated nanopowder without heat treatment process. Nanopowder-prepared ceramic sample showed a crystallite size of 50 nm after sintering at 900 °C for 1 h. The specific surface area, pore volume, and pore size were obtained from the B.E.T. measurements, being 51 m2 g−1, 0.07 cm3 g−1, and 55 Å, respectively. The capacitance values of the nanopowder-prepared ceramic sample were in the order of microfarad. The total energy of the system was used to determine relaxation time of the sample (τ0 = 31 ms). [ABSTRACT FROM AUTHOR]

Abstract: Despite being a promising anode material for the Na‐ion battery system, Na‐titanate (viz., Na2Ti3O7) lacks in terms of cyclic stability; the cause(s) for which are under debate. Against this backdrop, through electrochemical measurements and in situ synchrotron X‐ray diffraction studies, the present work develops insights into the aspects concerning electrochemical reversibility of the fully sodiated phase (i.e., Na4Ti3O7), possible occurrence of irreversible reactions in Na‐ion cells, influences of the same towards cyclic instability, and a strategy towards alleviating this problem. The in situ studies rule out (in)stability/(ir)reversibility of Na4Ti3O7 as being a major cause for the capacity fade; rather they indicate the formation of ‘impurity’ phase(s) due to reaction with the electrolyte. Incorporation of multi‐walled carbon nanotubes (MWCNTs; uniformly ‘wrapping’ the rod‐shaped Na2Ti3O7 particles) significantly improved the cyclic stability (ca. 78 % reversible capacity retention after 50 cycles, as compared to ca. 6 % without MWCNTs) and rate capability (with nearly flat potential plateaus at 5C). The same suppressed the increase in charge‐transfer resistance upon cycling by an order of magnitude and also changed the sodiation reaction from being primarily surface to diffusion controlled. Correlation of the results/analysis indicate that, in the absence of a stable conducting network, loss in electrical connectivity owing to the formation of insulating/passivating (surface) phase(s) is the major cause for capacity fade of Na2Ti3O7. [ABSTRACT FROM AUTHOR]

Photocatalytic water splitting technologies are currently being considered for alternative energy sources. However, the strong demand for a high H2 production rate will present conflicting requirements of excellent photoactivity and low-cost photocatalysts. The first alternative may be abundant nanostructured titanate-related materials as a photocatalyst. Here, we report highly dispersed Na2Ti3O7 nanotubes synthesized via a facile hydrothermal route for photocatalytic degradation of Rhodamine B (RhB) and the water splitting under UV-visible light irradiation. Compared with commercial TiO2, the nanostructured Na2Ti3O7 demonstrated excellent photodegradation and water splitting performance, thus addressing the need for low-cost photocatalysts. The as-synthesized Na2Ti3O7 nanotubes exhibited desirable photodegradation, and rate of H2 production was 1,755 μmol·g−1·h−1 and 1,130 μmol·g−1·h−1 under UV and simulated solar light irradiation, respectively; the resulting as-synthesized Na2Ti3O7 nanotubes are active in UV light than that of visible light response. [ABSTRACT FROM AUTHOR]

Photocatalytic hydrogen production through ethanol photo-reforming using Na2Ti3O7 whiskers increases if the sodium titanate is decorated with well-known metallic catalysts such as Ni and Pt. Whereas wet impregnation with nickel gives only a slight increase in the activity, photo-deposition of Pt increased the H2 production by more than one order of magnitude. Through the combination of both co-catalysts (Ni and Pt) a superior performance in terms of H2 production is further observed. However, hydrogen yield is largely enhanced (almost three-fold), up to 778 μmol·g−1·h−1, if the Pt is photo-deposited on the surface of the catalyst before wet impregnation with Ni species (NTO/Pt/Ni) compared to H2 yield (283 μmol·g−1·h−1) achieved with the catalyst prepared in the reverse order (NTO/Ni/Pt). Structural, morphological, optical, and chemical characterization was carried out in order to correlate physicochemical properties with their photocatalytic activity. The X-ray photoelectron spectroscopy (XPS) results show a higher concentration of Pt2+ species if this metallic layer is under the nickel oxide layer. Moreover, X-ray diffraction patterns (XRD) show that Na2Ti3O7 surface is modified for both metal decoration processes.

Due to its special Z-shaped layered structure, Na 2 Ti 3 O 7 has great potential as an anode material for lithium-ion battery application. However, the poor electrical conductivity and cycle life have seriously affected its application in practice. In this paper, we prepared a sea urchin shaped Na 2 Ti 3 O 7 material by a simple hydrothermal method. This special morphology allows the material to have a large specific surface area, which can better contact with the electrolyte and increase the active site number. The half-cells assembled with sea urchin-like Na 2 Ti 3 O 7 show excellent cycling performance and good rate performance. After 1000 cycles at a 1 C rate, the specific capacity of NTO maintains at 70%. Even at a 5 C rate, NTO-2 delivers a discharge capacity of 71 mAh g−1 after 1000 cycles. The method proposed can be extended to other new anode materials to boost their electrochemical performances. [Display omitted] • Na 2 Ti 3 O 7 with a large specific surface area was prepared by a one-step hydrothermal method. • Morphology of the materials was optimized by regulating the PH of the solution. • The effect of morphology on the electrochemical properties of the materials was revealed. [ABSTRACT FROM AUTHOR]

Titanates have been widely reported as anode materials for sodium-ion batteries (SIBs). However, their wide temperature suitability and cycle life remain fundamental issues that hinder their practical application. Herein, a novel hollow Na 2 Ti 3 O 7 microsphere (H-NTO) with a unique chemically bonded NTO/C(N) interface is reported. Theoretical calculations demonstrated that the NTO/C(N) interface stabilizes the crystal structure, and the optimized interface enables the H-NTO anode to stably operate for 80 000 cycles in a conventional ester electrolyte with negligible capacity loss. Optimizing the electrolyte allows the H-NTO electrode to cycle stably for 200 calendar days without capacity degradation at -40 °C. The excellent cycling stability is attributed to the NTO/C(N) interface and the stable solid electrolyte interphase formed by the highly adaptable electrolyte/electrode interface. Titanate exhibits solvent co-intercalation behavior in ether-based electrolytes, and its robust structure ensures that it can adapt to large volume changes at low temperatures. This study provides a unique perspective on the long-cycle mechanism of titanate anodes and highlights the critical importance of manipulating the interfacial chemistry in SIBs, including the material and electrode/electrolyte interfaces., (© 2023 Wiley-VCH GmbH.)

The effects of fluorine (F) doping on the phase, crystal structure, and electrochemical performance of Na2Ti3O7 are studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), and electrochemical measurements. F-doping does not change the crystal structure of NTO, although it has an effect on the morphology of the resultant product. As an anode material for sodium-ion batteries, the specific capacity of Na2Ti3O7 exhibits a 30% increase with F-doping owing to the improved sodium ion diffusion coefficient. F-doped Na2Ti3O7 also displays an enhanced rate capability and favourable cycling performance for more than 800 cycles.

[Display omitted] • Ti 3 C 2 T x MQDs were first used for microwave absorption to prepare composites. • The chrysanthemum-like Na 2 Ti 3 O 7 /MQDs exhibits strong microwave absorption capacity. • The excellent microwave absorption property benefits from multiple loss mechanisms. As an outstanding representative of two-dimensional materials, newly emerged Ti 3 C 2 T x MXene has aroused widespread attention in the field of microwave absorption (MA). However, the high conductivity of Ti 3 C 2 T x MXene is prone to lead to impedance mismatch, and the attenuation performance of incident electromagnetic waves in the Ti 3 C 2 T x matrix needs to be further improved. To address these issues, Ti 3 C 2 T x MXene quantum dots (MQDs) were applied in the field of MA for the first time, and combined with Ti 3 C 2 T x derivative chrysanthemum-like Na 2 Ti 3 O 7 to prepare Na 2 Ti 3 O 7 /MQDs composites with 3D/0D heterostructure. Compared with Ti 3 C 2 T x MXene bulks and nanosheets, Ti 3 C 2 T x MQDs possess larger specific surface area and richer surface-active groups and defects, which are more favorable for interfacial polarization and dipole polarization, while the moderate conductivity of Ti 3 C 2 T x MQDs is conducive to impedance matching. The unique chrysanthemum-like Na 2 Ti 3 O 7 /MQDs with 3D/0D heterostructure generates abundant heterointerfaces to promote the increase of interfacial polarization, achieves a rational combination of different conductive materials to optimize impedance matching, and facilitates multiple reflections of electromagnetic waves among numerous nanowires in the chrysanthemum-like structure. Benefiting from the good impedance matching and the synergistic effect of multiple loss mechanisms, Na 2 Ti 3 O 7 /MQDs composites show excellent MA performance with a minimum reflection loss of −48.28 dB at a thickness of 2.6 mm. Simultaneously, the effective absorption bandwidth comes up to 6.38 GHz at 2.5 mm thickness. This study demonstrates the potential of MQDs as efficient microwave absorbers and points out the direction for a wide application of various MQDs in the field of MA. [ABSTRACT FROM AUTHOR]

A flexible humidity sensor with wide sensing range, superior sensitivity, high linearity, and advanced response/recovery capabilities is extremely desirable for practical applications in human body-related (HBR) monitoring and human-machine interaction (HMI). However, the practical sensor lacks a versatile nanomaterial integrated with sensing capabilities and mechanical flexibility to meet the criteria. Herein, a comprehensive flexible humidity sensor with ultralong Na 2 Ti 3 O 7 nanowires (>120 μm) is subtly constructed for the first time. Owing to the distinguish nanowires network structure, the sensor exhibits wide sensing range (11-95% RH), high sensitivity (>10 3 ), high linearity (R 2 > 0.98), and fast response/recovery capability (8.9/2.1 s), as well as excellent respiratory stability (>5000 s). In addition, the Na 2 Ti 3 O 7 -based humidity sensor demonstrates superior flexibility and antibacteria capabilities, and exhibits diverse applications in respiration monitoring, noncontact detection, as well as dynamic interactive display. This work provides a multifunctional humidity sensor with excellent practicability, suggesting the great potential in next-generation human-related flexible/wearable devices.

We have successfully prepared H2Ti12O25 by soft chemical synthetic technique using Na2Ti6O13 as a starting compound for the first time. In this synthetic route, we first prepared Li2Ti6O13 by Na+/Li+ ion-exchange reaction. Then, H2Ti6O13 was prepared by Li+/H+ ion-exchange reaction using HCl solution, and H2Ti12O25 was synthesized by heating the obtained H2Ti6O13 at 260 °C. The XRD pattern and 1H-MAS NMR spectrum of the H2Ti12O25 sample thus obtained were well consistent with those for the H2Ti12O25 sample prepared from Na2Ti3O7 as a starting compound. The H2Ti12O25 sample prepared from Na2Ti6O13 exhibited superior cycling performance with the initial discharge capacity of 229 mAh g−1 in the voltage range between 1.0 and 3.0 V with a fixed current density of 10 mA g−1 at 25 °C, which was higher than that (213 mAh g−1) for the H2Ti12O25 sample from Na2Ti3O7. The improvement of the discharge capacity may be explained by the smaller particle size for the present H2Ti12O25 sample. Accordingly, the initial coulombic efficiency for the H2Ti12O25 sample was improved from 86% to 92%. These facts suggest that H2Ti12O25 is one of the promising high-voltage oxide negative electrodes in advanced lithium ion batteries. [ABSTRACT FROM AUTHOR]

Layered sodium titanium oxide, Na2Ti3O7, is synthesized by a solid-state reaction method as a potential anode for sodium-ion batteries. Through optimization of the electrolyte and binder, the microsized Na2Ti3O7 electrode delivers a reversible capacity of 188 mA h g−1 in 1 M NaFSI/PC electrolyte at a current rate of 0.1C in a voltage range of 0.0-3.0 V, with sodium alginate as binder. The average Na storage voltage plateau is found at ca. 0.3 V vs. Na+/Na, in good agreement with a first-principles prediction of 0.35 V. The Na storage properties in Na2Ti3O7 are investigated from thermodynamic and kinetic aspects. By reducing particle size, the nanosized Na2Ti3O7 exhibits much higher capacity, but still with unsatisfied cyclic properties. The solid-state interphase layer on Na2Ti3O7 electrode is analyzed. A zero-current overpotential related to thermodynamic factors is observed for both nano- and microsized Na2Ti3O7. The electronic structure, Na+ ion transport and conductivity are investigated by the combination of first-principles calculation and electrochemical characterizations. On the basis of the vacancy-hopping mechanism, a quasi-3D energy favorable trajectory is proposed for Na2Ti3O7. The Na+ ions diffuse between the TiO6 octahedron layers with pretty low activation energy of 0.186 eV. [ABSTRACT FROM AUTHOR]

Mixtures of Na2Ti3O7/Na2Ti6O13 and Na2Ti6O13/TiO2 were synthesised by the sol-gel method using alkoxide precursors. XRD and SEM characterisations were performed. Semi-quantitative chemical analyses were carried out and the mixture ratio of Na2Ti3O7/Na2Ti6O13 was 3:1 wt. A qualitative estimation on the mixture Na2Ti6O13/TiO2 gives also a higher ratio. Such composites are well suited to be used directly as oxygen electrode materials in potentiometric gas sensor devices exchanging sodium and oxygen with the surrounding phases. Electrochemical impedance spectroscopy (EIS) was used to measure the total conductivity. A part of electronic conductivity depending on the partial oxygen pressure was observed in the mixture Na2Ti6O13/TiO2 due to the presence of rutile TiO2. [Copyright &y& Elsevier]

• Low voltage Na 2 Ti 3 O 7 coated with zirconia and carbon. • ZrO 2 surface coating by impregnation method is found beneficial. • Carbon coating using liquid carbon source impart additional stability. Surface modification by a thin layer of inert carbon or zirconia obtained by simple impregnation method are found to beneficial to improve the cycleability and rate capability of Na 2 Ti 3 O 7 , a promising low voltage anode for sodium ion battery. X-ray diffraction analysis confirms that the structure of Na 2 Ti 3 O 7 remains unaltered after the surface modification. Both carbon and zirconia coated samples show improved electrochemical properties compared to the bare Na 2 Ti 3 O 7 as both the thin coating layer helps to control unwanted solid electrolyte interface (SEI) growth at electrode–electrolyte interface. After 100 cycles, the modified materials are able to retain ~75% (for Na 2 Ti 3 O 7 @C) and ~68% (for Na 2 Ti 3 O 7 @ZrO 2) of their initial capacity whereas the bare material retains only ~21% of its initial capacity. [ABSTRACT FROM AUTHOR]

In this work, uniform Fe 3 O 4 @Na 2 Ti 3 O 7 (FNTO) nanoleafs coated with N-doped C (FNTO-CN) were synthesized through the hydrothermal reaction of Fe nanoparticles and TiO 2 powders in concentrated NaOH solution. FNTO exhibited a wider layer spacing and a more fluent Na-ion exchange effect than pure Na 2 Ti 3 O 7 (NTO). Afterwards, FNTO-CN composites were prepared via a facile solid-state method, with folic acid as C and N sources, as coated C could increase the overall conductivity. When FNTO or FNTO-CN was tested as a working electrode in a half-cell versus Na metal, they exhibited high-capacity densities of 142 and 175 mAh g−1 ​at 5C, respectively. They also showed stability of 1000 cycles owing to the high Na-ion diffusion rate and electron transport capability. Besides, a full cell assembled using the FNTO-CN anode with Na 2/3 (Ni 1/3 Mn 2/3)O 2 cathode afforded an energy density of ~117 ​Wh kg−1 (based on the mass of both electrodes). This interlayer engineering may provide a useful tool to develop high-performance anode materials, and folic acid is a promising dual C and N source for modifying the properties of anode/cathode materials. [Display omitted] • A ternary composite (FNTO-CN) consisting of Fe 3 O 4 nanoparticles, N doped carbon, and Na 2 Ti 3 O 7 nanoleafs was prepared. • FNTO-CN composite showed much better electrochemical performance than bare Na 2 Ti 3 O 7. • A full cell consisting of FNTO-CN anode displays high energy density and cycling performance. • FNTO-CN composite is a promising anode material for sodium ion batteries. [ABSTRACT FROM AUTHOR]

• Hierarchical flower-like particles are synthesized by the solvothermal method. • The sodium titanates are obtained under mildly alkaline conditions (2 M NaOH). • A Short time of solvothermal reaction (8 h) is enough to obtain the sodium titanates. • The adsorption equilibrium was achieved in a short time of 10 min. This work reports a facile solvothermal synthesis of hierarchical flower-like Na 2 Ti 3 O 7 structures with fast and high methylene blue adsorption capacity. A mesoporous architecture of Na 2 Ti 3 O 7 with a surface area of 159.63 m2-g-1 was produced under mild alkaline conditions (2 M NaOH) and a short reaction time (8 h). Interestingly, methylene blue adsorption equilibrium on the Na 2 Ti 3 O 7 powders was achieved in a short time of 10 min. The pseudo-second-order kinetic model and the Langmuir isotherm model described the adsorption mechanism. The synthesized Na 2 Ti 3 O 7 powders have interesting features that highlight their suitability for environmental applications. [ABSTRACT FROM AUTHOR]

• Pompon-like Na 2 Ti 3 O 7 @C constructed from MXene-Derivative was synthesized. • The cross-linked nanoribbon increases the contact area and the reactive site. • Proper interlayer spacing and the open pore structure promote the storage of sodium. • The carbon coating improves the electrical conductivity and cycling stability. Sodium-ion batteries are considered as the next generation of attractive promising batteries on account of their ample raw materials and low-cost. Two-dimensional MXene materials have been deemed to be potential anode material for sodium ion batteries. Nevertheless, multilayer Ti 3 C 2 T x material suffers from low specific capacity, limiting its commercial applications. Here, a pompon-like MXene-derivative sodium titanate with carbon-encapsulated has been fabricated. The Na 2 Ti 3 O 7 @C possesses crosslinked nanoribbon structure with suitable interlayer spacing and open porosity, which are beneficial to ions diffusion and electrolyte infiltration. More importantly, the thin carbon layer outside can significantly improve the electron transmission efficiency and maintain structural stability. When applied to anode material of sodium ion batteries, the Na 2 Ti 3 O 7 @C delivers a high reversible capacity of 173 mA h g−1 at 200 mA g−1 and exceptional stable cycling life up to 200 cycles with only 0.026% attenuation per cycle at 2 A g−1. [ABSTRACT FROM AUTHOR]

Photocatalytic hydrogen production through ethanol photo-reforming using Na2Ti3O7 whiskers increases if the sodium titanate is decorated with well-known metallic catalysts such as Ni and Pt. Whereas wet impregnation with nickel gives only a slight increase in the activity, photo-deposition of Pt increased the H2 production by more than one order of magnitude. Through the combination of both co-catalysts (Ni and Pt) a superior performance in terms of H2 production is further observed. However, hydrogen yield is largely enhanced (almost three-fold), up to 778 μmol·g−1·h−1, if the Pt is photo-deposited on the surface of the catalyst before wet impregnation with Ni species (NTO/Pt/Ni) compared to H2 yield (283 μmol·g−1·h−1) achieved with the catalyst prepared in the reverse order (NTO/Ni/Pt). Structural, morphological, optical, and chemical characterization was carried out in order to correlate physicochemical properties with their photocatalytic activity. The X-ray photoelectron spectroscopy (XPS) results show a higher concentration of Pt2+ species if this metallic layer is under the nickel oxide layer. Moreover, X-ray diffraction patterns (XRD) show that Na2Ti3O7 surface is modified for both metal decoration processes. [ABSTRACT FROM AUTHOR]

The effects of fluorine (F) doping on the phase, crystal structure, and electrochemical performance of Na2Ti3O7 are studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), and electrochemical measurements. F-doping does not change the crystal structure of NTO, although it has an effect on the morphology of the resultant product. As an anode material for sodium-ion batteries, the specific capacity of Na2Ti3O7 exhibits a 30% increase with F-doping owing to the improved sodium ion diffusion coefficient. F-doped Na2Ti3O7 also displays an enhanced rate capability and favourable cycling performance for more than 800 cycles. [ABSTRACT FROM AUTHOR]

With its inherent zig-zag layered structure and open framework, Na 2 Ti 3 O 7 (NTO) is a promising anode material for potassium-ion batteries (KIBs). However, its poor electronic conductivity caused by large band gap (∼3.7 eV) usually leads to low-performance KIBs. In this work, we synthesize the fluff-like hydrogenated Na 2 Ti 3 O 7 (HNTO) nanowires grown on N-doped carbon sponge (CS) as a binder-free and current-collector-free flexible anode for KIBs (denoted as HNTO/CS). High-resolution X-ray photoelectron spectroscopy (XPS) and electron spin-resonance spectroscopy (ESR) confirm the existence of Ti-OHs and O vacancies in HNTO. The first-principles calculation discloses that both Ti-OHs and O vacancies are equivalent to n-type doping because they can shift the Fermi level up to the conduction band, thus leading to a higher electronic conductivity and better performance for KIBs. In addition, the N-doped CS can further reinforce the conductivity and avoid the aggregation of HNTO nanowires during cycling. As a result, the as-made HNTO/CS can deliver a capacity of 107.8 mAh g -1 at 100 mA g -1 after 20 cycles, and keep the capacity of 90.9% and 82.5% after 200 and 1555 cycles, respectively, much better than the samples without hydrogenation treatment or N-doped CS and reported KTi x O y -based materials. Our work highlights the importance of hydrogenation treatment and N-doped CS in enhancing the electrochemical property for KIBs.

Sodium-ion batteries have increasingly been considered as an attractive alternative to lithium-ion batteries for large-scale applications. High specific capacity and suitable working potential anode materials are one of the keys to search for future developments. Here, a novel and stable sodium titanate/carbon-black phosphorus (NTO/C-BP) hybrids are first fabricated as a promising anode material for advanced sodium-ion batteries. Under the protection of argon (Ar) atmosphere, the direct high-energy mechanical milling of the BP nanoparticle and NTO/C results in the formation of NTO/C-BP hybrids. In other words, the BP nanoparticle can be interconnected with bare NTO by P-O-Ti bonds and/or form stable P-C bonds with the carbon coating layer on the surface of NTO. The NTO/C-BP hybrids are not only beneficial for enhancing specific capacity but also have a great protective effect on the exposure of BP to air by the synergistic effect between BP and NTO/C. The results show that the NTO/C-BP hybrids can deliver very high specific capacity (∼225 mA h g -1 after 55 cycles at 20 mA g -1 , ∼183 mA h g -1 after 100 cycles at 100 mA g -1 ). It is expected from these scientific findings that forming stable P-C bonds and P-O-Ti bonds in this work can serve as a guidance to other Ti-based and P-based electrode materials for practical large-scale application of sodium-ion batteries.

Na2Ti3O7 is considered a promising negative electrode for Na-ion batteries; however, poor capacity retention has been reported and the stability of the solid-electrolyte interphase (SEI) could be one of the main actors of this underperformance. The composition and evolution of the SEI in Na2Ti3O7 electrodes is hereby studied by means of X-ray photoelectron spectroscopy (XPS). To overcome typical XPS limitations in the photoelectron energy assignments, the analysis of the Auger parameter is here proposed for the first time in battery materials characterization. We have found that the electrode/electrolyte interface formed upon discharge, mostly composed by carbonates and semicarbonates (Na2CO3, NaCO3R), fluorides (NaF), chlorides (NaCl) and poly(ethylene oxide)s, is unstable upon electrochemical cycling. Additionally, solid state nuclear magnetic resonance (NMR) studies prove the reaction of the polyvinylidene difluoride (PVdF) binder with sodium. The powerful approach used in this work, namely Auger parameter study, enables us to correctly determine the composition of the electrode surface layer without any interference from surface charging or absolute binding energy calibration effects. As a result, the suitability for Na-ion batteries of binders and electrolytes widely used for Li-ion batteries is questioned here.