Dongbin Xiong

Superior sodium storage of novel VO2 nano-microspheres encapsulated into crumpled reduced graphene oxide

To uniformly encapsulate electrode materials with reduced graphene oxide (rGO) has been a considerable challenge due to the lack of appropriate synthetic methods and/or effective reaction systems. In this study, we present a one-step rapid and scalable solvothermal approach to achieve a crumpled reduced graphene oxide encapsulated VO2 material. As a demonstration of this promising configuration, for the first time, we systematically studied its Na+ storage behavior in the voltage range of 3.0 to 0.01 V (versus Na/Na+). It turned out that the as-prepared anode material exhibits high reversible capacities of 383 mA h g−1 at 0.1 A g−1 and 214 mA h g−1 at 4 A g−1, and can stably operate for as long as 2000 cycles at 4 A g−1 with a capacity fade of 0.013% per cycle, resulting from the improved electronic conductivity, structural stability, and electrode wettability. Furthermore, the formation mechanism and structural features of the desired crumpled reduced graphene oxide encapsulated VO2 material are discreetly expounded. More interestingly, a chain of cogent evidence is provided by coating on various electrode materials to confirm the scalability of this facile and rapid solvothermal synthesis method, which would open up a novel avenue to create more fascinating graphene-based functional materials for the multitudinous application domain.

Controllable oxygenic functional groups of metal-free cathodes for high performance lithium ion batteries

The poriferous reduced graphene oxide (rGO) with abundant oxygen-containing functional groups synthesized by a one-step hydrothermal method was successfully employed as a high performance cathode in lithium-ion batteries. The electrochemical results show that the rGO exhibits a remarkable lithium storage capacity (up to 270 mA h g−1 after 100 cycles). Further analysis shows that the rGO can exhibit a significantly high rate capacity, good reversibility, and excellent cycling stability, which clearly reveals the potential use of the rGO as the cathode material to boost both energy and power densities of LIBs. Furthermore, by controlling the oxygenic functional groups of the rGO, it was demonstrated that the capacity of rGO increased with the increase of the number of oxygenic functional groups, which illustrates that the excellent electrochemical performance of rGO could be attributed to its specific poriferous structure and the oxygen-containing functional groups.

Novel understanding of carbothermal reduction enhancing electronic and ionic conductivity of Li4Ti5O12 anode

Spinel Li4Ti5O12 performance highly depends on both the electronic and ionic conductivity, however, developing a low-cost strategy to improve its electronic and ionic conductivity still remains challenging. In this study, a facile cost-saving carbothermal reduction method is introduced to synthesize the microscaled spinel Li4Ti5O12 particles with the surface modification of Ti(III) using anatase–TiO2, Li2CO3, and acetylene black (AB) as precursors. Remarkably, this ingenious design can easily eliminate the influence of the residual carbon, and thus makes it possible to individually study the effect of the Ti(III) on the bulk Li4Ti5O12. To reveal the role of the Ti(III), the electronic conductivity and lithium-ion diffusion coefficient of the as-prepared materials were measured using a direct volt-ampere method, electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV). The results indicate that the carbothermal reduction leads to the increased electronic and ionic conductivity of the spinel Li4Ti5O12. As a result, the modified Li4Ti5O12 exhibits an enhanced cyclic stability, improved rate capability, and high Coulombic efficiency. The carbothermal reduction mechanism discreetly clarified in this study is beneficial to improving Li4Ti5O12 performance for further commercial applications.

Superior Cathode Performance of Nitrogen-Doped Graphene Frameworks for Lithium Ion Batteries

Development of alternative cathode materials is of highly desirable for sustainable and cost-efficient lithium-ion batteries (LIBs) in energy storage fields. In this study, for the first time, we report tunable nitrogen-doped graphene with active functional groups for cathode utilization of LIBs. When employed as cathode materials, the functionalized graphene frameworks with a nitrogen content of 9.26 at% retain a reversible capacity of 344 mAh g-1 after 200 cycles at a current density of 50 mA g-1. More surprisingly, when conducted at a high current density of 1 A g-1, this cathode delivers a high reversible capacity of 146 mAh g-1 after 1000 cycles. Our current research demonstrates the effective significance of nitrogen doping on enhancing cathode performance of functionalized graphene for LIBs.

Promising Dual-Doped Graphene Aerogel/SnS2 Nanocrystal Building High Performance Sodium Ion Batteries

We report the effort in designing layered SnS2 nanocrystals decorated on nitrogen and sulfur dual-doped graphene aerogels (SnS2@N,S-GA) as anode material of SIBs. The optimized mass loading of SnS2 along with the addition of nitrogen and sulfur on the surface of GAs results in enhanced electrochemical performance of SnS2@N,S-GA composite. In particular, the introduction of nitrogen and sulfur heteroatoms could provide more active sites and good accessibility for Na ions. Moreover, the incorporation of the stable SnS2 crystal structure within the anode results in the superior discharge capacity of 527 mAh g-1 under a current density of 20 mA g-1 upon 50 cycles. It maintains 340 mAh g-1 even the current density is increased to 800 mA g-1. Aiming to further systematically study mechanism of composite with improved SIB performance, we construct the corresponding models based on experimental data and conduct first-principles calculations. The calculated results indicate the sulfur atoms doped in GAs show a strong bridging effect with the SnS2 nanocrystals, contributing to build robust architecture for electrode. Simultaneously, heteroatom dual doping of GAs shows the imperative function for improved electrical conductivity. Herein, first-principles calculations present a theoretical explanation for outstanding cycling properties of SnS2@N,S-GA composite.

PVP-derived carbon nanofibers harvesting enhanced anode performance for lithium ion batteries

Co-embedded carbon nanofibers were synthesized using electrospinning with polyvinylpyrrolidone (PVP) instead of high cost polyacrylonitrile (PAN). The obtained composite nanofibers as an anode material for lithium ion batteries deliver a reversible capacity of 542.6 mA h g−1 in the 100th cycle at a current density of 100 mA g−1. Moreover, the anode material shows better cycle performance and rate capability in comparison to the resultant product without Co additive. It is believed that the significant improvement is attributed to the nanofiber morphology with high surface-to-volume ratio as well as the existence of Co nanoparticles that enhance the electrical conductivity of the nanocomposites.

SnO2/Reduced Graphene Oxide Interlayer Mitigating the Shuttle Effect of Li–S Batteries

The short cycle life of lithium-sulfur batteries (LSBs) plagues its practical application. In this study, a uniform SnO2/reduced graphene oxide (denoted as SnO2/rGO) composite is successfully designed onto the commercial polypropylene separator for use of interlayer of LSBs to decrease the charge-transfer resistance and trap the soluble lithium polysulfides (LPSs). As a result, the assembled devices using the separator modified with the functional interlayer (SnO2/rGO) exhibit improved cycle performance; for instance, over 200 cycles at 1C, the discharge capacity of the cells reaches 734 mAh g-1. The cells also display high rate capability, with the average discharge capacity of 541.9 mAh g-1 at 5C. Additionally, the mechanism of anchoring behavior of the SnO2/rGO interlayer was systematically investigated using density functional theory calculations. The results demonstrate that the improved performance is related to the ability of SnO2/rGO to effectively absorb S8 cluster and LPS. The strong Li-O/Sn-S/O-S bonds and tight chemical adsorption between LPS and SnO2 mitigate the shuttle effect of LSBs. This study demonstrates that engineering the functional interlayer of metal oxide and carbon materials in LSBs may be an easy way to improve their rate capacity and cycling life.

Design of a flower-like CuS nanostructure via a facile hydrothermal route

For the first time, a flower-like nanostructured CuS material was synthesised through a facile hydrothermal route using copper foil and brenstone as Cu and S sources, respectively. The obtained CuS was characterised by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy and transmission electron microscopy. The effects of the concentrations of the brenstone, reaction time, reaction temperature and NH4F additive on the morphologies of CuS nanostructures were studied in detail. It was found that morphological adjustment of the samples could be easily realised by optimising the amount of NH4F. However, the thickness of the CuS nanoplates highly depends on the combination of reaction time, reaction temperature and the concentrations of the brenstone and NH4F.

Novel iodine-doped reduced graphene oxide anode for sodium ion batteries

It is reported for the first time that iodine-doped reduced graphene oxide (I-rGO) has been designed as an anode material for sodium ion batteries (SIBs). In comparison to rGO, I-rGO with a high specific surface area exhibits a high reversible capacity (270 mA h g−1 at 50 mA g−1), good long-term cycling performance, with a high capacity of 212 mA h g−1 after 100 cycles, and excellent rate capability. The enhanced performance is due to defect evolution and enlarged layer distance by the doping of iodine atoms.