High‐Performance Lithium‐Ion Anodes with Hierarchically Assembled Single‐Crystal SnO2 Nanoflake Spheres

A large‐scale hierarchical assembly route is reported for the formation of SnO₂ on the nanoscale that contains rigid and robust spheres with irregular channels for rapid access of Li ions into the hierarchically structured interiors. Large volume changes during the process of Li insertion and extraction are accommodated by the SnO₂ nanoflake spheres’ internal porosity. The hierarchical SnO₂ nanoflake spheres exhibit good lithium storage properties with high capacity and long‐lasting performance when used as lithium‐ion anodes. A reversible capacity of 517 mA h g^?1, still greater than the theoretical capacity of graphite (372 mA h g^?1), after 50 charge–discharge cycles is attained. Meanwhile, the synthesis process is simple, inexpensive, safe, and broadly applicable, providing new avenues for the rational engineering of electrode materials with enhanced conductivity and power.     

Boron‐Doped,Carbon‐Coated SnO2/Graphene Nanosheets for Enhanced Lithium Storage

Heteroatom doping is an effective method to adjust the electrochemical behavior of carbonaceous materials. In this work, boron‐doped, carbon‐coated SnO₂/graphene hybrids (BCTGs) were fabricated by hydrothermal carbonization of sucrose in the presence of SnO₂/graphene nanosheets and phenylboronic acid or boric acid as dopant source and subsequent thermal treatment. Owing to their unique 2D core–shell architecture and B‐doped carbon shells, BCTGs have enhanced conductivity and extra active sites for lithium storage. With phenylboronic acid as B source, the resulting hybrid shows outstanding electrochemical performance as the anode in lithium‐ion batteries with a highly stable capacity of 1165 mA h g^?1 at 0.1 A g^?1 after 360 cycles and an excellent rate capability of 600 mA h g^?1 at 3.2 A g^?1, and thus outperforms most of the previously reported SnO₂‐based anode materials.     

Mesoporous MnCo2O4 with a Flake‐Like Structure as Advanced Electrode Materials for Lithium‐Ion Batteries and Supercapacitors

A mesoporous flake‐like manganese‐cobalt composite oxide (MnCo₂O₄) is synthesized successfully through the hydrothermal method. The crystalline phase and morphology of the materials are characterized by X‐ray diffraction, field‐emission scanning electron microscopy, transmission electron microscopy, and Brunauer–Emmett–Teller methods. The flake‐like MnCo₂O₄ is evaluated as the anode material for lithium‐ion batteries. Owing to its mesoporous nature, it exhibits a high reversible capacity of 1066 mA h g^?1, good rate capability, and superior cycling stability. As an electrode material for supercapacitors, the flake‐like MnCo₂O₄ also demonstrates a high supercapacitance of 1487 F g^?1 at a current density of 1 A g^?1, and an exceptional cycling performance over 2000 charge/discharge cycles.     

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.     

Multiple Ambient Hydrolysis Deposition of Tin Oxide into Nanoporous Carbon To Give a Stable Anode for Lithium‐Ion Batteries

A novel ambient hydrolysis deposition (AHD) methodology that employs sequential water adsorption followed by a hydrolysis reaction to infiltrate SnO₂ nanoparticles into the nanopores of mesoporous carbon in a conformal and controllable manner is introduced. The empty space in the SnO₂/C composites can be adjusted by varying the number of AHD cycles. An SnO₂/C composite with an intermediate SnO₂ loading exhibited an initial specific delithiation capacity of 1054 mAh g^?1 as an anode for Li‐ion batteries. The capacity contribution from SnO₂ in the composite electrode approaches the theoretical capacity of SnO₂ (1494 mAh g^?1) if both Sn alloying and SnO₂ conversion reactions are considered to be reversible. The composite shows a specific capacity of 573 mAh g^?1 after 300 cycles, that is, one of the most stable cycling performances for SnO₂/mesoporous carbon composites. The results demonstrated the importance of well‐tuned empty space in nanostructured composites to accommodate expansion of the electrode active mass during alloying/dealloying and conversion reactions.     

A Self‐Standing and Flexible Electrode of Yolk–Shell CoS2 Spheres Encapsulated with Nitrogen‐Doped Graphene for High‐Performance Lithium‐Ion Batteries

Flexible lithium‐ion batteries (LIBs) have recently attracted increasing attention with the fast development of bendable electronic systems. Herein, a facile and template‐free solvothermal method is presented for the fabrication of hybrid yolk–shell CoS₂ and nitrogen‐doped graphene (NG) sheets. The yolk–shell architecture of CoS₂ encapsulated with NG coating is designed for the dual protection of CoS₂ to address the structural and interfacial stability concerns facing the CoS₂ anode. The as‐prepared composite can be assembled into a film, which can be used as a binder‐free and flexible electrode for LIBs that does not require any carbon black conducting additives or current collectors. When evaluating lithium‐storage properties, such a flexible electrode exhibits a high specific capacity of 992 mAh g^?1 in the first reversible discharge capacity at a current rate of 100 mA g^?1 and high reversible capacity of 882 mAh g^?1 after 150 cycles with excellent capacity retention of 89.91 %. Furthermore, a reversible capacity as high as 655 mAh g^?1 is still achieved after 50 cycles even at a high rate of 5 C due to the yolk–shell structure and NG coating, which not only provide short Li‐ion and electron pathways, but also accommodate large volume variation.     

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.     

General Approach to Single and Hybrid Metal Oxide Fiber Structures for High‐Performance Lithium‐Ion Batteries

Owing to the high specific capacity and energy density, metal oxides have become very promising electrodes for lithium‐ion batteries (LIBs). However, poor electrical conductivity accompanied with inferior cycling stability resulting from large volume changes are the main obstacles to achieve a high reversible capacity and stable cyclability. Herein, a facile and general approach to fabricate SnO₂, Fe₂O₃ and Fe₂O₃/SnO₂ fibers is proposed. The appealing structural features are favorable for offering a shortened lithium‐ion diffusion length, easy access for the electrolyte and reduced volume variation when used as anodes in LIBs. As a consequence, both single and hybrid oxides show satisfactory reversible capacities (1206 mAh g^?1 for Fe₂O₃ and 1481 mAh g^?1 for Fe₂O₃/SnO₂ after 200 cycles at 200 mA g^?1) and long lifespans.     

Supercritical Carbon Dioxide Assisted Deposition of Fe3O4 Nanoparticles on Hierarchical Porous Carbon and Their Lithium‐Storage Performance

A composite of highly dispersed Fe₃O₄ nanoparticles (NPs) anchored in three‐dimensional hierarchical porous carbon networks (Fe₃O₄/3DHPC) as an anode material for lithium‐ion batteries (LIBs) was prepared by means of a deposition technique assisted by a supercritical carbon dioxide (scCO₂)‐expanded ethanol solution. The as‐synthesized Fe₃O₄/3DHPC composite exhibits a bimodal porous 3D architecture with mutually connected 3.7 nm mesopores defined in the macroporous wall on which a layer of small and uniform Fe₃O₄ NPs was closely coated. As an anode material for LIBs, the Fe₃O₄/3DHPC composite with 79 wt % Fe₃O₄ (Fe₃O₄/3DHPC‐79) delivered a high reversible capacity of 1462 mA h g^?1 after 100 cycles at a current density of 100 mA g^?1, and maintained good high‐rate performance (728, 507, and 239 mA h g^?1 at 1, 2, and 5 C, respectively). Moreover, it showed excellent long‐term cycling performance at high current densities, 1 and 2 A g^?1. The enhanced lithium‐storage behavior can be attributed to the synergistic effect of the porous support and the homogeneous Fe₃O₄ NPs. More importantly, this straightforward, highly efficient, and green synthetic route will definitely enrich the methodologies for the fabrication of carbon‐based transition‐metal oxide composites, and provide great potential materials for additional applications in supercapacitors, sensors, and catalyses.     

Sulfur‐Impregnated Core–Shell Hierarchical Porous Carbon for Lithium–Sulfur Batteries

Core–shell hierarchical porous carbon spheres (HPCs) were synthesized by a facile hydrothermal method and used as host to incorporate sulfur. The microstructure, morphology, and specific surface areas of the resultant samples have been systematically characterized. The results indicate that most of sulfur is well dispersed over the core area of HPCs after the impregnation of sulfur. Meanwhile, the shell of HPCs with void pores is serving as a retard against the dissolution of lithium polysulfides. This structure can enhance the transport of electron and lithium ions as well as alleviate the stress caused by volume change during the charge–discharge process. The as‐prepared HPC‐sulfur (HPC‐S) composite with 65.3 wt % sulfur delivers a high specific capacity of 1397.9 mA h g^?1 at a current density of 335 mA g^?1 (0.2 C) as a cathode material for lithium–sulfur (Li‐S) batteries, and the discharge capacity of the electrode could still reach 753.2 mA h g^?1 at 6700 mA g^?1 (4 C). Moreover, the composite electrode exhibited an excellent cycling capacity of 830.5 mA h g^?1 after 200 cycles.     

Facile Synthesis of Nitrogen‐Containing Mesoporous Carbon for High‐Performance Energy Storage Applications

Porous carbon with high specific surface area (SSA), a reasonable pore size distribution, and modified surface chemistry is highly desirable for application in energy storage devices. Herein, we report the synthesis of nitrogen‐containing mesoporous carbon with high SSA (1390 m² g^?1), a suitable pore size distribution (1.5–8.1 nm), and a nitrogen content of 4.7 wt % through a facile one‐step self‐assembly process. Owing to its unique physical characteristics and nitrogen doping, this material demonstrates great promise for application in both supercapacitors and encapsulating sulfur as a superior cathode material for lithium–sulfur batteries. When deployed as a supercapacitor electrode, it exhibited a high specific capacitance of 238.4 F g^?1 at 1 A g^?1 and an excellent rate capability (180 F g^?1, 10 A g^?1). Furthermore, when an NMC/S electrode was evaluated as the cathode material for lithium–sulfur batteries, it showed a high initial discharge capacity of 1143.6 mA h g^?1 at 837.5 mA g^?1 and an extraordinary cycling stability with 70.3 % capacity retention after 100 cycles.     

Preparation of Li2SnO3 and its application in lithium‐ion batteries

Tin‐based oxide Li₂SnO₃ has been synthesized by a hydrothermal route as negative material for lithium‐ion batteries. The microstructure and electrochemical properties of the as‐synthesized materials were investigated by some characterizations means and electrochemical measurements. The as‐synthesized Li₂SnO₃ is a porous rod, which is composed of many uniform and regular nano‐flakes with a size of 50–60 nm. Li₂SnO₃ also displays an electrochemical performance with high capacity and good cycling stability (510.2 mAh g^?1 after 50 cycles at a current density of 60 mA g^?1 between 0.0 V and 2.0 V verusus Li/Li⁺). Copyright © 2013 John Wiley & Sons, Ltd.     

Cu3V2O8 Nanoparticles as Intercalation‐Type Anode Material for Lithium‐Ion Batteries

Cu₃V₂O₈ nanoparticles with particle sizes of 40–50 nm have been prepared by the co‐precipitation method. The Cu₃V₂O₈ electrode delivers a discharge capacity of 462 mA h g^?1 for the first 10 cycles and then the specific capacity, surprisingly, increases to 773 mA h g^?1 after 50 cycles, possibly as a result of extra lithium interfacial storage through the reversible formation/decomposition of a solid electrolyte interface (SEI) film. In addition, the electrode shows good rate capability with discharge capacities of 218 mA h g^?1 under current densities of 1000 mA g^?1. Moreover, the lithium storage mechanism for Cu₃V₂O₈ nanoparticles is explained on the basis of ex situ X‐ray diffraction data and high‐resolution transmission electron microscopy analyses at different charge/discharge depths. It was evidenced that Cu₃V₂O₈ decomposes into copper metal and Li₃VO₄ on being initially discharged to 0.01 V, and the Li₃VO₄ is then likely to act as the host for lithium ions in subsequent cycles by means of the intercalation mechanism. Such an “in situ” compositing phenomenon during the electrochemical processes is novel and provides a very useful insight into the design of new anode materials for application in lithium‐ion batteries.     

Kilogram‐Scale Production of SnO2 Yolk–Shell Powders by a Spray‐Drying Process Using Dextrin as Carbon Source and Drying Additive

A simple and general method for the large‐scale production of yolk–shell powders with various compositions by a spray‐drying process is reported. Metal salt/dextrin composite powders with a spherical and dense structure were obtained by spray drying and transformed into yolk–shell powders by simple combustion in air. Dextrin plays a key role in the preparation of precursor powders for fabricating yolk–shell powders by spray drying. Droplets containing metal salts and dextrin show good drying characteristics even in a severe environment of high humidity. Sucrose, glucose, and polyvinylpyrrolidone are widely used as carbon sources in the preparation of metal oxide/carbon composite powders; however, they are not appropriate for large‐scale spray‐drying processes because of their caramelization properties and adherence to the surface of the spray dryer. SnO₂ yolk–shell powders were studied as the first target material in the spray‐drying process. Combustion of tin oxalate/dextrin composite powders at 600 °C in air produced single‐shelled SnO₂ yolk–shell powders with the configuration SnO₂@void@SnO₂. The SnO₂ yolk–shell powders prepared by the simple spray‐drying process showed superior electrochemical properties, even at high current densities. The discharge capacities of the SnO₂ yolk–shell powders at a current density of 2000 mA g^?1 were 645 and 570 mA h g^?1 for the second and 100th cycles, respectively; the corresponding capacity retention measured for the second cycle was 88 %.     

Green Template‐Free Synthesis of Hierarchical Shuttle‐Shaped Mesoporous ZnFe2O4 Microrods with Enhanced Lithium Storage for Advanced Li‐Ion Batteries

In the work, a facile and green two‐step synthetic strategy was purposefully developed to efficiently fabricate hierarchical shuttle‐shaped mesoporous ZnFe₂O₄ microrods (MRs) with a high tap density of ～0.85 g cm³, which were assembled by 1D nanofiber (NF) subunits, and further utilized as a long‐life anode for advanced Li‐ion batteries. The significant role of the mixed solvent of glycerin and water in the formation of such hierarchical mesoporous MRs was systematically investigated. After 488 cycles at a large current rate of 1000 mA g^?1, the resulting ZnFe₂O₄ MRs with high loading of ～1.4 mg per electrode still preserved a reversible capacity as large as ～542 mAh g^?1. Furthermore, an initial charge capacity of ～1150 mAh g^?1 is delivered by the ZnFe₂O₄ anode at 100 mA g^?1, resulting in a high Coulombic efficiency of ～76 % for the first cycle. The superior Li‐storage properties of the as‐obtained ZnFe₂O₄ were rationally associated with its mesoprous micro‐/nanostructures and 1D nanoscaled building blocks, which accelerated the electron transportation, facilitated Li⁺ transfer rate, buffered the large volume variations during repeated discharge/charge processes, and provided rich electrode–electrolyte sur‐/interfaces for efficient lithium storage, particularly at high rates.     

Mesoporous Spherical Li4Ti5O12 as High‐Performance Anodes for Lithium‐Ion Batteries

Porous microspherical Li₄Ti₅O₁₂ aggregates (LTO‐PSA) can be successfully prepared by using porous spherical TiO₂ as a titanium source and lithium acetate as a lithium source followed by calcinations. The synthesized LTO‐PSA possess outstanding morphology, with nanosized, porous, and spherical distributions, that allow good electrochemical performances, including high reversible capacity, good cycling stability, and impressive rate capacity, to be achieved. The specific capacity of the LTO‐PSA at 30 C is as high as 141 mA h g^?1, whereas that of normal Li₄Ti₅O₁₂ powders prepared by a sol–gel method can only achieve 100 mA h g^?1. This improved rate performance can be ascribed to small Li₄Ti₅O₁₂ nanocrystallites, a three‐dimensional mesoporous structure, and enhanced ionic conductivity.     

Biomass‐Derived Porous Carbon with Micropores and Small Mesopores for High‐Performance Lithium–Sulfur Batteries

Biomass‐derived porous carbon BPC‐700, incorporating micropores and small mesopores, was prepared through pyrolysis of banana peel followed by activation with KOH. A high specific BET surface area (2741 m² g^?1), large specific pore volume (1.23 cm³ g^?1), and well‐controlled pore size distribution (0.6–5.0 nm) were obtained and up to 65 wt % sulfur content could be loaded into the pores of the BPC‐700 sample. When the resultant C/S composite, BPC‐700‐S65, was used as the cathode of a Li–S battery, a large initial discharge capacity (ca. 1200 mAh g^?1) was obtained, indicating a good sulfur utilization rate. An excellent discharge capacity (590 mAh g^?1) was also achieved for BPC‐700‐S65 at the high current rate of 4 C (12.72 mA cm^?2), showing its extremely high rate capability. A reversible capacity of about 570 mAh g^?1 was achieved for BPC‐700‐S65 after 500 cycles at 1 C (3.18 mA cm^?2), indicating an outstanding cycling stability.     

Highly Ordered Mesoporous Few‐Layer Graphene Frameworks Enabled by Fe3O4 Nanocrystal Superlattices

While great progress has been achieved in the synthesis of ordered mesoporous carbons in the past decade, it still remains a challenge to prepare highly graphitic frameworks with ordered mesoporosity and high surface area. Reported herein is a simple synthetic methodology, based on the conversion of self‐assembled superlattices of Fe₃O₄ nanocrystals, to fabricate highly ordered mesoporous graphene frameworks (MGFs) with ultrathin pore walls consisting of three to six stacking graphene layers. The MGFs possess face‐centered‐cubic symmetry with interconnected mesoporosity, tunable pore width, and high surface area. Because of their unique architectures and superior structural durability, the MGFs exhibit excellent cycling stability and rate performance when used as anode materials for lithium‐ion batteries, thus retaining a specific capacity of 520 mAh g^?1 at a current density of 300 mA g^?1 after 400 cycles.     

Two‐Dimensional Cobalt‐/Nickel‐Based Oxide Nanosheets for High‐Performance Sodium and Lithium Storage

Two‐dimensional (2D) nanomaterials are one of the most promising types of candidates for energy‐storage applications due to confined thicknesses and high surface areas, which would play an essential role in enhanced reaction kinetics. Herein, a universal process that can be extended for scale up is developed to synthesise ultrathin cobalt‐/nickel‐based hydroxides and oxides. The sodium and lithium storage capabilities of Co₃O₄ nanosheets are evaluated in detail. For sodium storage, the Co₃O₄ nanosheets exhibit excellent rate capability (e.g., 179 mA h g^?1 at 7.0 A g^?1 and 150 mA h g^?1 at 10.0 A g^?1) and promising cycling performance (404 mA h g^?1 after 100 cycles at 0.1 A g^?1). Meanwhile, very impressive lithium storage performance is also achieved, which is maintained at 1029 mA h g^?1 after 100 cycles at 0.2 A g^?1. NiO and NiCo₂O₄ nanosheets are also successfully prepared through the same synthetic approach, and both deliver very encouraging lithium storage performances. In addition to rechargeable batteries, 2D cobalt‐/nickel‐based hydroxides and oxides are also anticipated to have great potential applications in supercapacitors, electrocatalysis and other energy‐storage‐/‐conversion‐related fields.     

Nitrogen‐Doped Mesoporous Carbon‐Encapsulated MoO2 Nanobelts as a High‐Capacity and Stable Host for Lithium‐Ion Storage

N‐doped mesoporous carbon‐capped MoO₂ nanobelts (designated as MoO₂@NC) were synthesized and applied to lithium‐ion storage. Owing to the stable core–shell structural framework and conductive mesoporous carbon matrix, the as‐prepared MoO₂@NC shows a high specific capacity of around 700 mA h g⁻¹ at a current of 0.5 A g⁻¹, excellent cycling stability up to 100 cycles, and superior rate performance. The N‐doped mesoporous carbon can greatly improve the conductivity and provide uninhibited conducting pathways for fast charge transfer and transport. Moreover, the core–shell structure improved the structural integrity, leading to a high stability during the cycling process. All of these merits make the MoO₂@NC to be a suitable and promising material for lithium ion battery.