Dezhi Kong

Nontopotactic Reaction in Highly Reversible Sodium Storage of Ultrathin Co9Se8/rGO Hybrid Nanosheets

Transition metal chalcogenide with tailored nanosheet architectures with reduced graphene oxide (rGO) for high performance electrochemical sodium ion batteries (SIBs) are presented. Via one-step oriented attachment growth, a facile synthesis of Co9 Se8 nanosheets anchored on rGO matrix nanocomposites is demonstrated. As effective anode materials of SIBs, Co9 Se8 /rGO nanocomposites can deliver a highly reversible capacity of 406 mA h g-1 at a current density of 50 mA g-1 with long cycle stability. It can also deliver a high specific capacity of 295 mA h g-1 at a high current density of 5 A g-1 indicating its high rate capability. Furthermore, ex situ transmission electron microscopy observations provide insight into the reaction path of nontopotactic conversion in the hybrid anode, revealing the highly reversible conversion directly between the hybrid Co9 Se8 /rGO and Co nanoparticles/Na2 Se matrix during the sodiation/desodiation process. In addition, it is experimentally demonstrated that rGO plays significant roles in both controllable growth and electrochemical conversion processes, which can not only modulate the morphology of the product but also tune the sodium storage performance. The investigation on hybrid Co9 Se8 /rGO nanosheets as SIBs anode may shed light on designing new metal chalcogenide materials for high energy storage system.

Cubic-shaped WS2 nanopetals on a Prussian blue derived nitrogen-doped carbon nanoporous framework for high performance sodium-ion batteries

Despite the cost-effectiveness of sodium sources, sodium-ion based electrochemical energy storage devices still have a few challenges in competing with lithium-ion based batteries (LIBs) for commercialization and practical applications. In particular, the high rate performance and long cycling lifetimes are very difficult to be achieved in sodium-ion batteries (SIBs). Herein, we report a simple solvothermal method to prepare cubic-shaped nanostructures with vertical rose petal-like layers, which are used as anode materials in SIBs. The well-designed WS2@NC structures consist of WS2 nanosheets and Prussian blue-derived nitrogen doped carbon nanocubic framework, which possess unique 2D WS2 nanosheets and are vertically grown on the well-defined 3D porous carbon hierarchical structures. As anode materials for SIBs, this structure displayed high rate capacity at 384 and 151 mA h g−1 at 100 and 5000 mA g−1, respectively. More importantly, the performance of the electrode materials can be maintained at more than 200 cycles with coulombic efficiency not less than 99%. The excellent electrochemical performance is attributed to the synergistic effect of the composites that enhances the electrochemical transport properties of the WS2 due to the well-defined, nano-structured hierarchical scaffolding and the highly conductive nature of the framework. From the results shown, this unique design method provides unexplored insights into new and simple methods in improving the electrochemical performance of the 2D-TMDs based SIBs electrode materials.

3D carbon foam-supported WS2 nanosheets for cable-shaped flexible sodium ion batteries

Sodium ion batteries (SIBs) are proposed as alternatives to the current widely used lithium ion batteries (LIBs) due to the abundance of battery-grade sodium sources in nature. However, the search for suitable high-performance electrode materials for SIBs continues to remain a significant challenge. Herein, we report a hybrid nanoarchitecture with nitrogen-doped graphene quantum dots (NGQDs)-decorated WS2 nanosheets anchored on a porous three-dimensional carbon foam (NGQDs-WS2/3DCF) scaffold as the anode that enables long-term cycling and high rate capability for SIBs. Benefiting from the 3D robust porous interpenetrating framework and the NGQDs decoration, the NGQDs-WS2/3DCF nanoarchitecture exhibits a high rate capability with a capacity of 268.4 mA h g−1 at 2000 mA g−1, and a long lifetime with an extraordinary capacity retention of 97.1% over 1000 cycles. Furthermore, the pseudocapacitance contributions of the NGQDs-WS2/3DCF nanoarchitecture are quantified by an in-depth kinetics analysis, which provides a better understanding of the excellent electrochemical performances. Remarkably, a cable-shaped flexible full SIB was also demonstrated using NGQDs-WS2/3DCF as the anode electrode, which exhibits high capacity and excellent flexibility. The nanoarchitecture fabrication approach and the surface engineering strategy as well as the demonstrated cable-shaped configuration may open an avenue for the development of wearable SIBs with high performance.

Efficient Sodium Storage in Rolled-Up Amorphous Si Nanomembranes

Alloying-type materials are promising anodes for high-performance sodium-ion batteries (SIBs) because of their high capacities and low Na-ion insertion potentials. However, the typical candidates, such as P, Sn, Sb, and Pb, suffer from severe volume changes (≈293-487%) during the electrochemical reactions, leading to inferior cycling performances. Here, a high-rate and ultrastable alloying-type anode based on the rolled-up amorphous Si nanomembranes is demonstrated. The rolled-up amorphous Si nanomembranes show a very small volume change during the sodiation/desodiation processes and deliver an excellent rate capability and ultralong cycle life up to 2000 cycles with 85% capacity retention. The structural evolution and pseudocapacitance contribution are investigated by using the ex situ characterization techniques combined with kinetics analysis. Furthermore, the mechanism of efficient sodium-ion storage in amorphous Si is kinetically analyzed through an illustrative atomic structure with dangling bonds, offering a new perspective on understanding the sodium storage behavior. These results suggest that nanostructured amorphous Si is a promising anode material for high-performance SIBs.