N-doped carbon coated anatase TiO2 nanoparticles as superior Na-ion battery anodes

Waxberry-like TiO2 with Synergistic Surface Modification of Pyrolytic Carbon Coating and Carbon Nanotubes as an Anode for Li-Ion Battery

Titanium dioxide (TiO2) as an anode material for lithium-ion batteries (LIBs) has the advantages of tiny volume expansion, high operating voltage, and outstanding safety performance. However, due to the low conductivity of TiO2 and the slow diffusion rate of lithium ions (Li+), it is limited in the application of LIBs. Therefore, waxberry-like TiO2 comodified by pyrolytic carbon coating and carbon nanotubes was prepared in this work. The waxberry-like TiO2 with nanorods on its surface shortens the diffusion distance of Li+. Carbon nanotubes and waxberry-like TiO2 are tightly combined through electrostatic assembly and form a cross-linked conductive network to provide more electron transmission paths. A thin layer of pyrolytic carbon wraps carbon nanotubes and waxberry-like TiO2, which enhance the conductivity of the composites and ensure the structural integrity of the materials throughout the cycling process. The experimental data revealed that the discharge-specific capacity of TiO2@CNT@C is 170.5 mAh g-1 after 3000 cycles at a large current density of 5 A g-1, and the discharge-specific capacity is still 143 mAh g-1 at the superhigh rate of 10 A g-1, which provides excellent rate performance and cyclic stability. The efficient dual-carbon modification strategy could potentially be extended to other materials.

Interfacial Mo-S-C Bond with High Reversibility for Advanced Alkali-Ion Capacitors: Strategies for High-Throughput Production

The high-throughput scalable production of low-cost and high-performance electrode materials that work well under high power densities required in industrial application is full of challenges for the large-scale implementation of electrochemical technologies. Here, motivated by theoretical calculation that Mo-S-C heterojunction and sulfur vacancies can reduce the energy band gap, decrease the migration energy barrier, and improve the mechanical stability of MoS2 , the scalable preparation of inexpensive MoS2-x @CN is contrived by employing natural molybdenite as precursor, which is characteristic of high efficiency in synthesis process and energy conservation and the calculated costs are four orders of magnitude lower than MoS2 /C in previous work. More importantly, MoS2- x @CN electrode is endowed with impressive rate capability even at 5 A g-1 , and ultrastable cycling stability during almost 5000 cycles, which far outperform chemosynthesis MoS2 materials. Obtaining the full SIC cell assembled by MoS2- x @CN anode and carbon cathode, the energy/power output is high up to 265.3 W h kg-1 at 250 W kg-1 . These advantages indicate the huge potentials of the designed MoS2- x @CN and of mineral-based cost-effective and abundant resources as anode materials in high-performance AICs.

Trapping Lithium Selenides with Evolving Heterogeneous Interfaces for High-Power Lithium-Ion Capacitors

Transition metal selenides anodes with fast reaction kinetics and high theoretical specific capacity are expected to solve mismatched kinetics between cathode and anode in Li-ion capacitors. However, transition metal selenides face great challenges in the dissolution and shuttle problem of lithium selenides, which is the same as Li-Se batteries. Herein, inspired by the density functional theory calculations, heterogeneous can enhance the adsorption of Li₂ Se relative to single component selenide electrodes, thus inhibiting the dissolution and shuttle effect of Li₂ Se. A heterostructure material (denoted as CoSe₂ /SnSe) with the ability to evolve continuously (CoSe₂ /SnSe→Co/Sn→Co/Li₁₃ Sn₅ ) is successfully designed by employing CoSnO₃ -MOF as a precursor. Impressively, CoSe₂ /SnSe heterostructure material delivers the ultrahigh reversible specific capacity of 510 mAh g^-1 after 1000 cycles at the high current density of 4 A g^-1 . In situ XRD reveals the continuous evolution of the interface based on the transformation and alloying reactions during the charging and discharging process. Visualizations of in situ disassembly experiments demonstrate that the continuously evolving interface inhibits the shuttle of Li₂ Se. This research proposes an innovative approach to inhibit the dissolution and shuttling of discharge intermediates (Li₂ Se) of metal selenides, which is expected to be applied to metal sulfides or Li-Se and Li-S energy storage systems.

Altering the Alkaline Metal Ions in Lepidocrocite-Type Layered Titanate for Sodium-Ion Batteries

The relatively large ionic radius of the Na ion is one of the primary reasons for the slow diffusion of Na ions compared to that of Li ions in de/intercalation processes in sodium-ion batteries (SIBs). Interlayer expansion of intercalation hosts is one of the effective techniques for facilitating Na-ion diffusion. For most ionic layered compounds, interlayer expansion relies on intercalation of guest ions. It is important to investigate the role of these ions for material development of SIBs. In this study, alkali-metal ions (Li⁺, Na⁺, K⁺, and Cs⁺) with different sizes were intercalated into lepidocrocite-type layered titanate by a simple ion-exchange technique to achieve interlayer modulation and those were then evaluated as anode materials for SIBs. By controlling the intercalated alkaline ion species, basal spacings of layered titanates (LTs) in the range of 0.68 to 0.85 nm were obtained. Interestingly, the largest interlayer spacing induced by the large size of Cs did not yield the best performance, while the Na intercalated layered titanate (Na-ILT) demonstrated a superior performance with a specific capacity of 153 mAh g^-1 at a current density of 0.1 A g^-1. We found that the phenomena can be explained by the high alkaline metal ion concentration and the efficient utilization of the active sites in Na-ILT. The detailed analysis indicates that large intercalating ions like Cs can hamper sodium-ion diffusion although the interlayer spacing is large. Our work suggests that adopting an appropriate interlayer ion species is key to developing highly efficient layered electrode materials for SIBs.

Recent Advances on Heterojunction-Type Anode Materials for Lithium-/Sodium-Ion Batteries

Rechargeable batteries are key in the field of electrochemical energy storage, and the development of advanced electrode materials is essential to meet the increasing demand of electrochemical energy storage devices with higher density of energy and power. Anode materials are the key components of batteries. However, the anode materials still suffer from several challenges such as low rate capability and poor cycling stability, limiting the development of high-energy and high-power batteries. In recent years, heterojunctions have received increasing attention from researchers as an emerging material, because the constructed heterostructures can significantly improve the rate capability and cycling stability of the materials. Although many research progress has been made in this field, it still lacks review articles that summarize this field in detail. Herein, this review presents the recent research progress of heterojunction-type anode materials, focusing on the application of various types of heterojunctions in lithium/sodium-ion batteries. Finally, the heterojunctions introduced in this review are summarized, and their future development is anticipated.

Metal-Organic Framework Materials for Electrochemical Supercapacitors

Exploring new materials with high stability and capacity is full of challenges in sustainable energy conversion and storage systems. Metal-organic frameworks (MOFs), as a new type of porous material, show the advantages of large specific surface area, high porosity, low density, and adjustable pore size, exhibiting a broad application prospect in the field of electrocatalytic reactions, batteries, particularly in the field of supercapacitors. This comprehensive review outlines the recent progress in synthetic methods and electrochemical performances of MOF materials, as well as their applications in supercapacitors. Additionally, the superiorities of MOFs-related materials are highlighted, while major challenges or opportunities for future research on them for electrochemical supercapacitors have been discussed and displayed, along with extensive experimental experiences.

Pseudocapacitance-boosted ultrafast and stable Na-storage in NiTe2 coupled with N-doped carbon nanosheets for advanced sodium-ion half/full batteries

Developing high-rate and durable anode materials for sodium-ion batteries (SIBs) is still a challenge because of the larger ion radius of sodium compared with the lithium ion during charge-discharge processes. Herein, NiTe₂ coupled with N-doped carbon (NiTe₂/NC) hexagonal nanosheets has been fabricated through a solvothermal and subsequent carbonisation strategy. This unique hexagonal nanosheet structure offers abundant active sites and contact area to the electrolyte, which could shorten the Na⁺ diffusion path. The heterostructured N-doping carbon improves the electrochemical conductivity and accelerates the kinetics of Na⁺ transportation. Electrochemical analysis shows that the charge-discharge process is controlled by the pseudocapacitive behavior thus leading to high-rate capability and long lifespan in half batteries. As expected, high capacities of 311 mA h g^-1 to 217 mA h g^-1 at 5 A g^-1 to 10 A g^-1 are maintained after 800 and 1200 cycles, respectively. Furthermore, a full battery equipped with a Na₃V₂(PO₄)₂O₂F cathode and a NiTe₂/NC anode offers a maximum energy density of 104 W h kg^-1 and a maximum power density of 9116 W kg^-1. The results clearly show that the NiTe₂/NC hexagonal nanosheet with superior Na storage properties is an advanced new material for energy storage systems.

A pre-oxidation strategy to improve architecture stability and electrochemical performance of Na2MnPO4F particles-embedded carbon nanofibers

The rational design of an excellent architecture for active materials combined with carbon matrix is of particular importanceto obtain flexible electrode material with high electrochemical properties. Well-designed nanofibers possess unique 3D network structure, which can significantly improve the electron/ion transportation and supplies sufficient active sites for Li⁺/Na⁺ insertion. Electrospinning-carbonization technology is a popular strategy to prepare nanofibers with active material embedded in carbon. It is found that the architecture of nanofibers tended to be wrecked and destroyed during the carbonization process without pre-oxidation treatment. In this study, we prepared Na₂MnPO₄F particles embedded in carbon nanofibers (Na₂MnPO₄F/C) using PVP as carbon source and investigated the strengthen mechanism of pre-oxidation on their architecture. The experiment and simulation results demonstrate that, without pre-oxidation, the main chain of PVP is severely ruptured during the carbonization procedure, consequently leads to fractured architecture of Na₂MnPO₄F/C nanofibers. In contrast, with pre-oxidation treatment, a long-chain and heat-resistance structured carbon matrix formed, and Na₂MnPO₄F/C nanofibers with stable architecture and improved electrochemical performance can be achieved. This study demonstrates a promising guide to construct carbon based nanofiber electrodes with stable architecture and high electrochemical performance.

Highly compacted TiO2/C micospheres via in-situ surface-confined intergrowth with ultra-long life for reversible Na-ion storage

TiO₂ as the promising anode material candidate of sodium-ion battery suffers from poor conductivity and slow ion diffusion rate, which severely hampers its development. Highly compacted TiO₂/C microspheres without inner pores/tunnels are synthesized by a very facile one-pot rapid processing method based on novel in-situ surface-confined inter-growth mechanism. This highly compacted TiO₂/C microspheres exhibit an excellent electrochemical performance of reversible Na⁺ storage despite with relatively large particle/aggregation size from submicrometer to micrometer. An outstanding cycling stability extending to 10,000 cycles is gained with a high retention capacity of 140.5 mAh g^-1 at a current rate of 2 A g^-1. An ultra-high reversible capacity of 362 mAh g^-1 close to its theoretic specific capacity is obtained at a current rate of 0.05 A g^-1. The successful combination of highly compacted structure with large particle size, excellent electrochemical performance as well as rapid cost-effective preparing process might provide a potential industrial approach for efficiently synthesizing electrode materials for Na ion batteries.

Oxygen Vacancy Engineering in Titanium Dioxide for Sodium Storage

Titanium dioxide (TiO₂ ) is a promising anode material for sodium-ion batteries (SIBs) due to its low cost, natural abundance, nontoxicity, and excellent electrochemical stability. Oxygen vacancies, the most common point defects in TiO₂ , can dramatically influence the physical and chemical properties of TiO₂ , including band structure, crystal structure and adsorption properties. Recent studies have demonstrated that oxygen-deficient TiO₂ can significantly enhance sodium storage performance. Considering the importance of oxygen vacancies in modifying the properties of TiO₂ , the structural properties, common synthesis strategies, characterization techniques, as well as the contribution of oxygen-deficient TiO₂ on initial Coulombic efficiency, cyclic stability, rate performance for sodium storage are comprehensively described in this review. Finally, some perspectives on the challenge and future opportunities for the development of oxygen-deficient TiO₂ are proposed.

Hydrogen-nitrogen plasma assisted synthesis of titanium dioxide with enhanced performance as anode for sodium ion batteries

Sodium ion batteries are considered as one of the most promising energy storage devices as lithium ion batteries due to the natural abundance of sodium. TiO2 is very popular as anode materials for both lithium and sodium ion batteries because of the nontoxicity, safety and great stabilities. However, the low electronic conductivities and inferior sodium ion diffusion make it becoming a great challenge to develop advanced TiO2 anodes. Doping heteroatoms and incorporation of defects are believed to be great ways to improve the electrochemical performance of TiO2 anodes. In this work, commercial TiO2 (P25) nanoparticles was modified by hydrogen and nitrogen high-power plasma resulting in a disordered surface layer formation and nitrogen doping as well. The electrochemical performances of the samples as anode materials for sodium ion batteries was measured and the results indicated that after the hydrogen-nitrogen plasma treatment, H-N-TiO2 electrode shows a 43.5% of capacity higher than the P-TiO2 after 400 cycles long-term discharge/charge process, and the samples show a good long cycling stability as well, the Coulombic efficiencies of all samples are nearly 99% after 50 cycles which could be sustained to the end of long cycling. In addition, hydrogen-nitrogen plasma treated TiO2 electrode reached the stable high Coulombic efficiency earlier than the pristine material. High resolution TEM images and XPS results indicate that there is a disordered surface layer formed after the plasma treatment, by which defects (oxygen vacancies) and N-doping are also introduced into the crystalline structure. All these contribute to the enhancement of the electrochemical performance.

Flexible Freestanding Carbon Nanofiber-Embedded TiO2 Nanoparticles as Anode Material for Sodium-Ion Batteries

Sodium-ion batteries (SIBs), owning to the low cost, abundant resources, and similar physicochemical properties with lithium-ion batteries (LIBs), have earned much attention for large-scale energy storage systems. In this article, we successfully synthesize flexible freestanding carbon nanofiber-embedded TiO₂ nanoparticles (CNF-TiO₂) and then apply it directly as anode in SIBs without binder or current collector. Taking the advantage of flexible CNF and high structural stability, this anode exhibits high reversible capacity of 614 mAh·g^-1 (0.27 mAh·cm^-2) after almost 400 cycles and excellent capacity retention ability of ~100.

Nitrogen-Doped TiO2-C Composite Nanofibers with High-Capacity and Long-Cycle Life as Anode Materials for Sodium-Ion Batteries

Nitrogen-doped TiO₂-C composite nanofibers (TiO₂/N-C NFs) were manufactured by a convenient and green electrospinning technique in which urea acted as both the nitrogen source and a pore-forming agent. The TiO₂/N-C NFs exhibit a large specific surface area (213.04 m² g^-1) and a suitable nitrogen content (5.37 wt%). The large specific surface area can increase the contribution of the extrinsic pseudocapacitance, which greatly enhances the rate capability. Further, the diffusion coefficient of sodium ions (D _Na+) could be greatly improved by the incorporation of nitrogen atoms. Thus, the TiO₂/N-C NFs display excellent electrochemical properties in Na-ion batteries. A TiO₂/N-C NF anode delivers a high reversible discharge capacity of 265.8 mAh g^-1 at 0.05 A g^-1 and an outstanding long cycling performance even at a high current density (118.1 mAh g^-1) with almost no capacity decay at 5 A g^-1 over 2000 cycles. Therefore, this work sheds light on the application of TiO₂-based materials in sodium-ion batteries.

Nitrogen-Doped TiO2-C Composite Nanofibers with High-Capacity and Long-Cycle Life as Anode Materials for Sodium-Ion Batteries

Nitrogen-doped TiO₂-C composite nanofibers (TiO₂/N-C NFs) were manufactured by a convenient and green electrospinning technique in which urea acted as both the nitrogen source and a pore-forming agent. The TiO₂/N-C NFs exhibit a large specific surface area (213.04 m² g^-1) and a suitable nitrogen content (5.37 wt%). The large specific surface area can increase the contribution of the extrinsic pseudocapacitance, which greatly enhances the rate capability. Further, the diffusion coefficient of sodium ions (D _Na+) could be greatly improved by the incorporation of nitrogen atoms. Thus, the TiO₂/N-C NFs display excellent electrochemical properties in Na-ion batteries. A TiO₂/N-C NF anode delivers a high reversible discharge capacity of 265.8 mAh g^-1 at 0.05 A g^-1 and an outstanding long cycling performance even at a high current density (118.1 mAh g^-1) with almost no capacity decay at 5 A g^-1 over 2000 cycles. Therefore, this work sheds light on the application of TiO₂-based materials in sodium-ion batteries.