A New Concept for Obtaining SnO2 Fiber‐in‐Tube Nanostructures with Superior Electrochemical Properties

Tin oxide (SnO₂) nanotubes with a fiber‐in‐tube structure have been prepared by electrospinning and the mechanism of their formation has been investigated. Tin oxide‐carbon composite nanofibers with a filled structure were formed as an intermediate product, which were then transformed into SnO₂ nanotubes with a fiber‐in‐tube structure during heat treatment at 500 °C. Nanofibers with a diameter of 85 nm were found to be located inside hollow nanotubes with an outer diameter of 260 nm. The prepared SnO₂ nanotubes had well‐developed mesopores. The discharge capacities of the SnO₂ nanotubes at the 2nd and 300th cycles at a current density of 1 A g^?1 were measured as 720 and 640 mA h g^?1, respectively, and the corresponding capacity retention measured from the 2nd cycle was 88 %. The discharge capacities of the SnO₂ nanotubes at incrementally increased current densities of 0.5, 1.5, 3, and 5 A g^?1 were 774, 711, 652, and 591 mA h g^?1, respectively. The SnO₂ nanotubes with a fiber‐in‐tube structure showed superior cycling and rate performances compared to those of SnO₂ nanopowder. The unique structure of the SnO₂ nanotubes with a fiber@void@tube configuration improves their electrochemical properties by reducing the diffusion length of the lithium ions, and also imparts greater stability during electrochemical cycling.     

Reduced Graphene Oxide‐Supported TiO2 Fiber Bundles with Mesostructures as Anode Materials for Lithium‐Ion Batteries

Although the synthesis of mesoporous materials is well established, the preparation of TiO₂ fiber bundles with mesostructures, highly crystalline walls, and good thermal stability on the RGO nanosheets remains a challenge. Herein, a low‐cost and environmentally friendly hydrothermal route for the synthesis of RGO nanosheet‐supported anatase TiO₂ fiber bundles with dense mesostructures is used. These mesostructured TiO₂‐RGO materials are used for investigation of Li‐ion insertion properties, which show a reversible capacity of 235 mA h g^?1 at 200 mA g^?1 and 150 mA h g^?1 at 1000 mA g^?1 after 1000 cycles. The higher specific surface area of the new mesostructures and high conductive substrate (RGO nanosheets) result in excellent lithium storage performance, high‐rate performance, and strong cycling stability of the TiO₂‐RGO composites.     

A Multi‐Wall Sn/SnO2@Carbon Hollow Nanofiber Anode Material for High‐Rate and Long‐Life Lithium‐Ion Batteries

Multi‐wall Sn/SnO₂@carbon hollow nanofibers evolved from SnO₂ nanofibers are designed and programable synthesized by electrospinning, polypyrrole coating, and annealing reduction. The synthesized hollow nanofibers have a special wire‐in‐double‐wall‐tube structure with larger specific surface area and abundant inner spaces, which can provide effective contacting area of electrolyte with electrode materials and more active sites for redox reaction. It shows excellent cycling stability by virtue of effectively alleviating pulverization of tin‐based electrode materials caused by volume expansion. Even after 2000 cycles, the wire‐in‐double‐wall‐tube Sn/SnO₂@carbon nanofibers exhibit a high specific capacity of 986.3 mAh g^?1 (1 A g^?1) and still maintains 508.2 mAh g^?1 at high current density of 5 A g^?1. This outstanding electrochemical performance suggests the multi‐wall Sn/SnO₂@ carbon hollow nanofibers are great promising for high performance energy storage systems.     

Flame Spray Pyrolysis for Finding Multicomponent Nanomaterials with Superior Electrochemical Properties in the CoOx‐FeOx System for Use in Lithium‐Ion Batteries

High‐temperature flame spray pyrolysis is employed for finding highly efficient nanomaterials for use in lithium‐ion batteries. CoO_x‐FeO_x nanopowders with various compositions are prepared by one‐pot high‐temperature flame spray pyrolysis. The Co and Fe components are uniformly distributed over the CoO_x‐FeO_x composite powders, irrespective of the Co/Fe mole ratio. The Co‐rich CoO_x‐FeO_x composite powders with Co/Fe mole ratios of 3:1 and 2:1 have mixed crystal structures with CoFe₂O₄ and Co₃O₄ phases. However, Co‐substituted magnetite composite powders prepared from spray solutions with Co and Fe components in mole ratios of 1:3, 1:2, and 1:1 have a single phase. Multicomponent CoO_x‐FeO_x powders with a Co/Fe mole ratio of 2:1 and a mixed crystal structure with Co₃O₄ and CoFe₂O₄ phases show high initial capacities and good cycling performance. The stable reversible discharge capacities of the composite powders with a Co/Fe mole ratio of 2:1 decrease from 1165 to 820 mA h g^?1 as the current density is increased from 500 to 5000 mA g^?1; however, the discharge capacity again increases to 1310 mA h g^?1 as the current density is restored to 500 mA g^?1.     

Compositing Amorphous TiO2 with N‐Doped Carbon as High‐Rate Anode Materials for Lithium‐Ion Batteries

Compositing amorphous TiO₂ with nitrogen‐doped carbon through Ti? N bonding to form an amorphous TiO₂/N‐doped carbon hybrid (denoted a‐TiO₂/C? N) has been achieved by a two‐step hydrothermal–calcining method with hydrazine hydrate as an inhibitor and nitrogen source. The resultant a‐TiO₂/C? N hybrid has a surface area as high as 108 m² g^?1 and, when used as an anode material, exhibits a capacity as high as 290.0 mA h g^?1 at a current rate of 1 C and a reversible capacity over 156 mA h g^?1 at a current rate of 10 C after 100 cycles; these results are better than those found in most reports on crystalline TiO₂. This superior electrochemical performance could be ascribed to a combined effect of several factors, including the amorphous nature, porous structure, high surface area, and N‐doped carbon.     

Preparation of Yolk‐Shell and Filled Co9S8 Microspheres and Comparison of their Electrochemical Properties

In this study, we report the first preparation of phase‐pure Co₉S₈ yolk–shell microspheres in a facile two‐step process and their improved electrochemical properties. Yolk–shell Co₃O₄ precursor microspheres are initially obtained by spray pyrolysis and are subsequently transformed into Co₉S₈ yolk–shell microspheres by simple sulfidation in the presence of thiourea as a sulfur source at 350 °C under a reducing atmosphere. For comparison, filled Co₉S₈ microspheres were also prepared using the same procedure but in the absence of sucrose during the spray pyrolysis. The prepared yolk–shell Co₉S₈ microspheres exhibited a Brunauer–Emmett–Teller (BET) specific surface area of 18 m² g^?1 with a mean pore size of 16 nm. The yolk–shell Co₉S₈ microspheres have initial discharge and charge capacities of 1008 and 767 mA h g^?1 at a current density of 1000 mA g^?1, respectively, while the filled Co₉S₈ microspheres have initial discharge and charge capacities of 838 and 638 mA h g^?1, respectively. After 100 cycles, the discharge capacities of the yolk–shell and filled microspheres are 634 and 434 mA h g^?1, respectively, and the corresponding capacity retentions after the first cycle are 82 % and 66 %.     

One‐Pot Fabrication of Hierarchical Nanosheet‐Based TiO2–Carbon Hollow Microspheres for Anode Materials of High‐Rate Lithium‐Ion Batteries

Hierarchical and hollow nanostructures have recently attracted considerable attention because of their fantastic architectures and tunable property for facile lithium ion insertion and good cycling stability. In this study, a one‐pot and unusual carving protocol is demonstrated for engineering hollow structures with a porous shell. Hierarchical TiO₂ hollow spheres with nanosheet‐assembled shells (TiO₂ NHS) were synthesized by the sequestration between the titanium source and 2,2′‐bipyridine‐5,5′‐dicarboxylic acid, and kinetically controlled etching in trifluoroacetic acid medium. In addition, annealing such porous nanostructures presents the advantage of imparting carbon‐doped functional performance to its counterpart under different atmospheres. Such highly porous structures endow very large specifics surface area of 404 m² g^?1 and 336 m² g^?1 for the as‐prepared and calcination under nitrogen gas. C/TiO₂ NHS has high capacity of 204 mA h g^?1 at 1 C and a reversible capacity of 105 mA h g^?1 at a high rate of 20 C, and exhibits good cycling stability and superior rate capability as an anode material for lithium‐ion batteries.     

Zinc‐Reduced Mesoporous TiOx Li‐Ion Battery Anodes with Exceptional Rate Capability and Cycling Stability

We demonstrate a unique synthetic route for oxygen‐deficient mesoporous TiO_x by a redox–transmetalation process by using Zn metal as the reducing agent. The as‐obtained materials have significantly enhanced electronic conductivity; 20 times higher than that of as‐synthesized TiO₂ material. Moreover, electrochemical impedance spectroscopy (EIS) and galvanostatic intermittent titration technique (GITT) measurements are performed to validate the low charge carrier resistance of the oxygen‐deficient TiO_x. The resulting oxygen‐deficient TiO_x battery anode exhibits a high reversible capacity (～180 mA h g^?1 at a discharge/charge rate of 1 C/1 C after 400 cycles) and an excellent rate capability (～90 mA h g^?1 even at a rate of 10 C). Also, the full cell, which is coupled with a LiCoO₂ cathode material, exhibits an outstanding rate capability (>75 mA h g^?1 at a rate of 3.0 C) and maintains a reversible capacity of over 100 mA h g^?1 at a discharge/charge of 1 C/1 C for 300 cycles.     

Sodium‐Ion Storage Properties of FeS–Reduced Graphene Oxide Composite Powder with a Crumpled Structure

The sodium‐ion storage properties of FeS–reduced graphene oxide (rGO) and Fe₃O₄‐rGO composite powders with crumpled structures have been studied. The Fe₃O₄‐rGO composite powder, prepared by one‐pot spray pyrolysis, could be transformed to an FeS‐rGO composite powder through a simple sulfidation treatment. The mean size of the Fe₃O₄ nanocrystals in the Fe₃O₄‐rGO composite powder was 4.4 nm. After sulfidation, FeS nanocrystals of size several hundred nanometers were confined within the crumpled structure of the rGO matrix. The initial discharge capacities of the FeS‐rGO and Fe₃O₄‐rGO composite powders were 740 and 442 mA h g^?1, and their initial charge capacities were 530 and 165 mA h g^?1, respectively. The discharge capacities of the FeS‐rGO and Fe₃O₄‐rGO composite powders at the 50th cycle were 547 and 150 mA h g^?1, respectively. The FeS‐rGO composite powder showed superior sodium‐ion storage performance compared to the Fe₃O₄‐rGO composite powder.     

Superior Electrochemical Properties of Nanofibers Composed of Hollow CoFe2O4 Nanospheres Covered with Onion‐Like Graphitic Carbon

Nanofibers composed of hollow CoFe₂O₄ nanospheres covered with onion‐like carbon are prepared by applying nanoscale Kirkendall diffusion to the electrospinning process. Amorphous carbon nanofibers embedded with CoFe₂@onion‐like carbon nanospheres are prepared by reduction of the electrospun nanofibers. Oxidation of the CoFe₂‐C nanofibers at 300 °C under a normal atmosphere produces porous nanofibers composed of hollow CoFe₂O₄ nanospheres covered with onion‐like carbon. CoFe₂ nanocrystals are transformed into the hollow CoFe₂O₄ nanospheres during oxidation through a well‐known nanoscale Kirkendall diffusion process. The discharge capacities of the carbon‐free CoFe₂O₄ nanofibers composed of hollow nanospheres and the nanofibers composed of hollow CoFe₂O₄ nanospheres covered with onion‐like carbon are 340 and 930 mA h g^?1, respectively, for the 1000th cycle at a current density of 1 A g^?1. The nanofibers composed of hollow CoFe₂O₄ nanospheres covered with onion‐like carbon exhibit an excellent rate performance even in the absence of conductive materials.     

Photovoltaic activity of Ti/MCM‐41

Ti/MCM‐41 is a well‐known heterogeneous catalyst for alkene epoxidation with organic peroxides. This titanosilicate contains isolated titanium atoms forming part of a framework of mesoporous silica whose structure is formed by parallel hexagonal channels 3.2 nm in diameter. The surface area and porosity of Ti/MCM‐41 are about 880 m² g^?1 and 0.70 cm³ g^?1, respectively. These values are among the highest for any material. Herein, we show that Ti/MCM‐41 exhibits photovoltaic activity. Dye‐sensitized solar cells using mesoporous Ti/MCM‐41 (2.8–5.7 % Ti content) as active layer, black dye N3 as photosensitizer and I₃^?/I^? in methoxyacetonitrile as electrolyte exhibit a V_OC, J_SC and FF of 0.44 V, 0.045 mA cm^?2 and 0.33, respectively. These values compare well against 0.75 V, 4.1 mA cm^?2 and 0.64, respectively, measured for analogous solar cells using conventional P‐25 TiO₂. However, the specific current density (J_SC/Ti atom) for the Ti/MCM‐41 is very similar to that of P25 TiO₂.     

Electrochemical Properties of Yolk–Shell‐Structured Zn–Fe–S Multicomponent Sulfide Materials with a 1:2 Zn/Fe Molar Ratio

Yolk–shell‐structured Zn–Fe–S multicomponent sulfide materials with a 1:2 Zn/Fe molar ratio were prepared applying a sulfidation process to ZnFe₂O₄ yolk–shell powders. The Zn–Fe–S powders had mixed sphalerite (Zn,Fe)S and hexagonal FeS crystal structures. The discharge capacities of the Zn–Fe–S powders sulfidated at 350 °C at a constant current density of 500 mA g^?1 for the first, second, and fiftieth cycles were 1098, 912, and 913 mA h g^?1, respectively. The powders exhibited a high discharge capacity of 602 mA h g^?1 even at the high current density of 10 A g^?1. The synergistic effect of yolk–shell structure and multicomponent composition improved the electrochemical properties of Zn–Fe–S powders.     

Preparation of Li4Ti5O12 Yolk–Shell Powders by Spray Pyrolysis and their Electrochemical Properties

We have reported for the first time the preparation of yolk–shell‐structured Li₄Ti₅O₁₂ powders for use as anode materials in lithium‐ion batteries. One Li₄Ti₅O₁₂ yolk–shell‐particle powder is directly formed from each droplet containing lithium, titanium, and carbon components inside the hot wall reactor maintained at 900 °C. The precursor Li₄Ti₅O₁₂ yolk–shell‐particle powders, which are directly prepared by spray pyrolysis, have initial discharge and charge capacities of 155 and 122 mA h g^?1, respectively, at a current density of 175 mA g^?1. Post‐treatment of the yolk–shell‐particle powders at temperatures of 700 and 800 °C improves the initial discharge and charge capacities. The initial discharge capacities of the Li₄Ti₅O₁₂ powders with a yolk–shell structure and a dense structure post‐treated at 800 °C are 189 and 168 mA h g^?1, respectively. After 100 cycles, the corresponding capacities are 172 and 152 mA h g^?1, respectively (retentions of 91 and 90 %).     

Nafion/Titanium Dioxide‐Coated Lithium Anode for Stable Lithium–Sulfur Batteries

Lithium–sulfur (Li–S) batteries have shown great potential as high energy‐storage devices. However, the stability of the Li metal anode is still a major concern. This is due to the formation of lithium dendrites and severe side reactions with polysulfide intermediates. We herein develop an anode protection method by coating a Nafion/TiO₂ composite layer on the Li anode to solve these problems. In this architecture, Nafion suppresses the growth of Li dendrites, protects the Li anode, and prevents side reactions between polysulfides and the Li anode. Moreover, doped TiO₂ further improves the ionic conductivity and mechanical properties of the Nafion membrane. Li–S batteries with a Nafion/TiO₂‐coated Li anode exhibit better cycling stability (776 mA h g^?1 after 100 cycles at 0.2 C, 1 C=1672 mA g^?1) and higher rate performance (787 mA h g^?1 at 2 C) than those with a pristine Li anode. This work provides an alternative way to construct stable Li anodes for high‐performance Li–S batteries.     

One‐Step Pyro‐Synthesis of a Nanostructured Mn3O4/C Electrode with Long Cycle Stability for Rechargeable Lithium‐Ion Batteries

A nanostructured Mn₃O₄/C electrode was prepared by a one‐step polyol‐assisted pyro‐synthesis without any post‐heat treatments. The as‐prepared Mn₃O₄/C revealed nanostructured morphology comprised of secondary aggregates formed from carbon‐coated primary particles of average diameters ranging between 20 and 40 nm, as evidenced from the electron microscopy studies. The N₂ adsorption studies reveal a hierarchical porous feature in the nanostructured electrode. The nanostructured morphology appears to be related to the present rapid combustion strategy. The nanostructured porous Mn₃O₄/C electrode demonstrated impressive electrode properties with reversible capacities of 666 mAh g^?1 at a current density of 33 mA g^?1, good capacity retentions (1141 mAh g^?1 with 100 % Coulombic efficiencies at the 100^th cycle), and rate capabilities (307 and 202 mAh g^?1 at 528 and 1056 mA g^?1, respectively) when tested as an anode for lithium‐ion battery applications.     

Dual‐Confined Sulfur Nanoparticles Encapsulated in Hollow TiO2 Spheres Wrapped with Graphene for Lithium–Sulfur Batteries

Lithium–sulfur (Li?S) batteries are attractive owing to their higher energy density and lower cost compared with the universally used lithium‐ion batteries (LIBs), but there are some problems that stop their practical use, such as low utilization and rapid capacity‐fading of the sulfur cathode, which is mainly caused by the shuttle effect, and the uncontrollable deposition of lithium sulfide species. Herein, we report the design and fabrication of dual‐confined sulfur nanoparticles that were encapsulated inside hollow TiO₂ spheres; the encapsulated nanoparticles were prepared by a facile hydrolysis process combined with acid etching, followed by “wrapping” with graphene (G?TiO₂@S). In this unique composite architecture, the hollow TiO₂ spheres acted as effective sulfur carriers by confining the polysulfides and buffering volume changes during the charge‐discharge processes by means of physical force from the hollow spheres and chemical binding between TiO₂ and the polysulfides. Moreover, the graphene‐wrapped skin provided an effective 3D conductive network to improve the electronic conductivity of the sulfur cathode and, at the same time, to further suppress the dissolution of the polysulfides. As results, the G?TiO₂@S hybrids exhibited a high and stable discharge capacity of up to 853.4 mA h g^?1 over 200 cycles at 0.5 C (1 C=1675 mA g^?1) and an excellent rate capability of 675 mA h g^?1 at a current rate of 2 C; thus, G?TiO₂@S holds great promise as a cathode material for Li?S batteries.     

Preparation and electrochemical properties of graphene‐supported Si‐TiO2 nanospheres as anode material for Li‐ion batteries

Graphene‐supported Si‐TiO₂ (Si‐Ti‐GE) composites have been synthesized by a simple polymerization and sintering method. In the Si‐Ti‐GE composites, many small Si‐TiO₂ particles are scattered on the graphene sheet, which can mitigate the agglomeration of the material and further reduce the particle size. The initial discharge capacities of Si‐TiO₂, Si‐Ti‐GE‐1, Si‐Ti‐GE‐2, and Si‐Ti‐GE‐3 are 336.9, 337.2, 339.8, and 356.6 mAh g⁻¹ at the current density of 200 mA g⁻¹, respectively. The discharge rate capacities of TiO₂, Si‐TiO₂, and Si‐Ti‐GE‐3 composites retain 57.5%, 41.7%, and 82.1% at the current density from 100 to 400 mA g⁻¹, respectively. Therefore, the introduction of graphene not only could facilitate the Li⁺ diffusion and electron transport but also could make better electrical conductivity.     

Mesoporous Carbon Nanofibers Embedded with MoS2 Nanocrystals for Extraordinary Li‐Ion Storage

MoS₂ nanocrystals embedded in mesoporous carbon nanofibers are synthesized through an electrospinning process followed by calcination. The resultant nanofibers are 100–150 nm in diameter and constructed from MoS₂ nanocrystals with a lateral diameter of around 7 nm with specific surface areas of 135.9 m² g^?1. The MoS₂@C nanofibers are treated at 450 °C in H₂ and comparison samples annealed at 800 °C in N₂. The heat treatments are designed to achieve good crystallinity and desired mesoporous microstructure, resulting in enhanced electrochemical performance. The small amount of oxygen in the nanofibers annealed in H₂ contributes to obtaining a lower internal resistance, and thus, improving the conductivity. The results show that the nanofibers obtained at 450 °C in H₂ deliver an extraordinary capacity of 1022 mA h g^?1 and improved cyclic stability, with only 2.3 % capacity loss after 165 cycles at a current density of 100 mA g^?1, as well as an outstanding rate capability. The greatly improved kinetics and cycling stability of the mesoporous MoS₂@C nanofibers can be attributed to the crosslinked conductive carbon nanofibers, the large specific surface area, the good crystallinity of MoS₂, and the robust mesoporous microstructure. The resulting nanofiber electrodes, with short mass‐ and charge‐transport pathways, improved electrical conductivity, and large contact area exposed to electrolyte, permitting fast diffusional flux of Li ions, explains the improved kinetics of the interfacial charge‐transfer reaction and the diffusivity of the MoS₂@C mesoporous nanofibers. It is believed that the integration of MoS₂ nanocrystals and mesoporous carbon nanofibers may have a synergistic effect, giving a promising anode, and widening the applicability range into high performance and mass production in the Li‐ion battery market.     

TiO2–B Nanosheets/Anatase Nanocrystals Co‐Anchored on Nanoporous Graphene: In Situ Reduction–Hydrolysis Synthesis and Their Superior Rate Performance as an Anode Material

A unique hybrid, TiO₂–B nanosheets/anatase nanocrystals co‐anchored on nanoporous graphene sheets, can be synthesized by a facile microwave‐induced in situ reduction–hydrolysis route. The as‐formed nanohybrid has a hierarchically porous structure, involving both mesopores of approximately 4 nm and meso‐/macropores of 30–60 nm in the graphene sheets, and a large surface area. Importantly, electrodes composed of the nanohybrid exhibit superior rate capability (160 mA h g^?1 at ca. 36 C; 154 mA h g^?1 at ca. 72 C) and excellent cyclability. The synergistic effects of conductive graphene with numerous nanopores and the pseudocapacitive effect of ultrafine TiO₂–B nanosheets and anatase nanocrystals endow the hybrid a superior rate capability.     

One‐Pot Method for Synthesizing Spherical‐Like Metal Sulfide–Reduced Graphene Oxide Composite Powders with Superior Electrochemical Properties for Lithium‐Ion Batteries

A facile, one‐pot method for synthesizing spherical‐like metal sulfide–reduced graphene oxide (RGO) composite powders by spray pyrolysis is reported. The direct sulfidation of ZnO nanocrystals decorated on spherical‐like RGO powders resulted in ZnS–RGO composite powders. ZnS nanocrystals with a size below 20 nm were uniformly dispersed on spherical‐like RGO balls. The discharge capacities of the ZnS–RGO, ZnO–RGO, bare ZnS, and bare ZnO powders at a current density of 1000 mA g^?1 after 300 cycles were 628, 476, 230, and 168 mA h g^?1, respectively, and the corresponding capacity retentions measured after the first cycles were 93, 70, 40, and 21 %, respectively. The discharge capacity of the ZnS–RGO composite powders at a high current density of 4000 mA g^?1 after 700 cycles was 437 mA h g^?1. The structural stability of the highly conductive ZnS–RGO composite powders with ultrafine crystals during cycling resulted in excellent electrochemical properties.