Hydrothermal Synthesis of SnO2 Embedded MoO3-x Nanocomposites and Their Synergistic Effects on Lithium Storage

Electrospun cobalt Prussian blue analogue-derived nanofibers for oxygen reduction reaction and lithium-ion batteries

Electrospinning is an effective technique to fabricate one-dimensional materials. In this study, cobalt-embedded carbon nanofibers (Co@CNFs) are obtained via carbonization of electrospun cobalt Prussian blue analogue (Co-Co PBA) under nitrogen atmosphere. The Co@CNFs have metallic cobalt surrounded by graphitic carbon shells and possess high specific surface area, rich porosity, high graphitic degree, and rational nitrogen doping. The structure merits endow them with excellent electrocatalytic performances for oxygen reduction reaction (ORR): an onset potential of 0.867 V vs. RHE and 0.784 V vs. RHE at j =  - 3 mA cm^-2 with a four-electron transfer process. Through a further mild oxidation process, we obtain Co₃O₄ nanoparticles-embedded nitrogen-doped carbon (Co₃O₄@CNFs) with spindle-like morphology. When working as the anode materials for lithium-ion batteries (LIBs), Co₃O₄@CNFs show high specific capacity, good stability, and excellent rate capability. The Co₃O₄@CNFs anode delivers a discharge specific capacity of 1404 mA h g^-1 after 100 cycles at a current density of 100 mA g^-1 and about 500 mA h g^-1 after 500 cycles at 2000 mA g^-1. The diffusion- and capacitive-controlled processes both contribute to the charge storage of the Co₃O₄@CNFs electrode. This study provides a new strategy to fabricate the excellent electrocatalysts for ORR and anode materials for LIBs via facile electrospinning.

Porous nanotube networks of SnO2/MoO3@Graphene as anodes for rechargeable lithium-ion batteries

We successfully fabricated composite porous nanotube networks of SnO₂/MoO₃@Graphene through electrospinning and used it as lithium-ion battery anodes. When the ratio of SnO₂ to MoO₃ is 1:1, the composite of SnO₂/MoO₃ delivers a high capacity of 560 mAh g^-1 at 1 A g^-1 after 300 cycles. The excellent electrochemical performance was attributed to the unique 3D porous nanotube network structure which could provide more transmission channels for Li⁺ ions and electrons, and provide more electrochemical reaction sites. The hybrid nanostructure can also weaken local stress and relieve volume expansion which contributes to the attractive cycling stability. Moreover, we added a small amount of graphene in the composite to improve the electrical conductivity, and the SnO₂/MoO₃@Graphene composite showed favorable electrochemical performance (798 mAh g^-1 at 1 A g^-1 after 300 cycles). Finally, electrospinning technology is a simple and efficient synthesis strategy, which can promote the preparation of different types of metal oxide composite materials and has good application prospects.

Tin dioxide-based nanomaterials as anodes for lithium-ion batteries

The development of new electrode materials for lithium-ion batteries (LIBs) has attracted significant attention because commercial anode materials in LIBs, like graphite, may not be able to meet the increasing energy demand of new electronic devices. Tin dioxide (SnO2) is considered as a promising alternative to graphite due to its high specific capacity. However, the large volume changes of SnO2 during the lithiation/delithiation process lead to capacity fading and poor cycling performance. In this review, we have summarized the synthesis of SnO2-based nanomaterials with various structures and chemical compositions, and their electrochemical performance as LIB anodes. This review addresses pure SnO2 nanomaterials, the composites of SnO2 and carbonaceous materials, the composites of SnO2 and transition metal oxides, and other hybrid SnO2-based materials. By providing a discussion on the synthesis methods and electrochemistry of some representative SnO2-based nanomaterials, we aim to demonstrate that electrochemical properties can be significantly improved by modifying chemical composition and morphology. By analyzing and summarizing the recent progress in SnO2 anode materials, we hope to show that there is still a long way to go for SnO2 to become a commercial LIB electrode and more research has to be focused on how to enhance the cycling stability.

Embedding amorphous lithium vanadate into carbon nanofibers by electrospinning as a high-performance anode material for lithium-ion batteries

We design and fabricate a novel hybrid with amorphous lithium vanadate (LiV₃O_x, LVO for short) uniformly encapsulated into carbon nanofibers (denoted as LVO@CNFs) via an easy electrospinning strategy followed by proper postannealing. When examined for use as anode materials for lithium-ion batteries (LIBs), the optimized LVO@CNFs present a high discharge capacity of 603 mAh g^-1 with a capacity retention as high as 90% after 200 cycles at 0.5 A g^-1 and a high rate capacity of 326 mAh g^-1 after 400 cycles even at a high rate of 5 A g^-1. The superior electrochemical performance with excellent cycling stability and rate capability is attributed to the full encapsulation of the amorphous LVO into the conductive carbon nanofibers, which hold enlarged electrochemically active sites for lithium storage, facilitate the charge transfer, and efficiently alleviate the volume changes upon lithium insertion/extraction. More importantly, the current synthesis can be a general strategy to fabricate various alkaline earth metal vanadates, which is promising for developing advanced electrochemical energy storage devices.

Casting amorphorized SnO2/MoO3 hybrid into foam-like carbon nanoflakes towards high-performance pseudocapacitive lithium storage

We report an amorphorization-hybridization strategy to enhance lithium storage by casting atomically mixed amorphorized SnO₂/MoO₃ into porous foam-like carbon nanoflakes (denote as SnO₂/MoO₃@CNFs, or SMC in short), which are simply prepared by annealing tin(II)/molybdenum(IV) 2-ethylhexanoate within CNFs under ambient atmosphere at a low temperature (300 °C). The SnO₂/MoO₃ loading amount within CNFs can be easily adjusted by controlling the Sn/Mo/C precursors. When examined as lithium ion battery (LIB) anode materials, the amorphorized SnO₂/MoO₃@CNFs with carbon content of 32 wt% (also denote as SMC-32, in which the number represents the carbon content) deliver a high reversible capacity of 1120.5 mA h/g after 200 cycles at 200 mA/g and then 651.5 mA h/g after another 300 cycles at 2000 mA/g, which is much better than that of the crystalline SnO₂/CNFs (carbon content of 34 wt%), MoO₃/CNFs (carbon content of 22.7 wt%), or SnO₂/MoO₃@CNFs (with lower carbon contents of 11 and 25 wt%). The electrochemical measurements as well as the ex situ structure characterization clearly suggest that combination of amorphorization and hybridization of SnO₂/MoO₃ with CNFs synergistically contributes to the superior lithium storage performance with high pseudocapacitive contribution.

Template synthesis of graphitic hollow carbon nanoballs as supports for SnOx nanoparticles towards enhanced lithium storage performance

To address the volume change-induced pulverization problem of tin-based anodes, a concept using hollow carbon nanoballs (HCNBs) as buffering supports is herein proposed. HCNBs with hollow interior, flexibility and graphitic crystallization are first prepared by a combined method of chemical vapor deposition (CVD) and template-synthesis using CH4 as the carbon source and CaCO3 as the conformal template. The ultrafine SnO2 nanoparticles are loaded onto the HCNBs (denoted as SnO2@HCNBs) via pyrolysis of tin(ii) 2-ethylhexanoate at 300 °C in air. On further annealing SnO2@HCNBs in Ar, SnO2 is partially reduced to SnOx by consuming a part of carbon of HCNBs as the reducing agent, and thus SnOx@HCNBs are obtained (note that SnOx represents a composite consisting of SnO2, SnO and Sn phases). When applied as anode materials for lithium ion batteries (LIBs), HCNBs deliver high reversible capacities of 841 mA h g-1 after 125 cycles at 200 mA g-1, and 726 mA h g-1 after 400 cycles even at 1000 mA g-1, while SnO2@HCNBs and SnOx@HCNBs exhibit discharge capacities of 1042 and 1299 mA h g-1 after 400 cycles at 200 mA g-1, respectively. Notably, all of them display gradually increased capacity with retention over 100% even after long-term cycling, which is attributed to the novel robust characteristic of the HCNBs as revealed by the ex situ TEM analysis. The flexible hollow HCNBs with high graphitic crystallization not only efficiently tolerate the volume changes of the Li-Sn alloying-dealloying but also facilitate the electrolyte/charge transfer owing to the hollow structure and high conductivity of the HCNBs.

Large-Scale Fabrication of Core-Shell Structured C/SnO2 Hollow Spheres as Anode Materials with Improved Lithium Storage Performance

Due to the high theoretical capacity as high as 1494 mAh g^-1 , SnO₂ is considered as a potential anode material for high-capacity lithium-ion batteries (LIBs). Therefore, the simple but effective method focused on fabrication of SnO₂ is imperative. To meet this, a facile and efficient strategy to fabricate core-shell structured C/SnO₂ hollow spheres by a solvothermal method is reported. Herein, the solid and hollow structure as well as the carbon content can be controlled. Very importantly, high-yield C/SnO₂ spheres can be produced by this method, which suggest potential business applications in LIBs field. Owing to the dual buffer effect of the carbon layer and hollow structures, the core-shell structured C/SnO₂ hollow spheres deliver a high reversible discharge capacity of 1007 mAh g^-1 at a current density of 100 mA g^-1 after 300 cycles and a superior discharge capacity of 915 mAh g^-1 at 500 mA g^-1 after 500 cycles. Even at a high current density of 1 and 2 A g^-1 , the core-shell structured C/SnO₂ hollow spheres electrode still exhibits excellent discharge capacity in the long life cycles. Consideration of the superior performance and high yield, the core-shell structured C/SnO₂ hollow spheres are of great interest for the next-generation LIBs.