Hierarchical MnV2O4 double-layer hollow sandwich nanosheets confined by N-doped carbon layer as anode for high performance lithium-ion batteries.

Binary transition metal oxides, especially vanadate metal oxides, are highly desirable for lithium-ion batteries (LIBs) anode materials due to their low-budget and high theoretical lithium storage capacity. However, low conductivity and poor cycle stability caused by volume changes during charge and discharge limit their grid-scale applications. Herein, a novel spinel MnV2O4 double-layer hollow sandwich nanosheets enclosed in N-doped porous carbon layer (MnV2O4/NC) was efficiently synthesized in 5 min by microwave-assisted and in-situ pyrolysis the coated polydopamine. MnV2O4/NC shows the superior performance as anode for LIBs with a specific capacities of 760 mA h g-1 at 1000 mA g-1 and outstanding of cycling stability with a specific capacities of 525.5 mA h g-1 after 1000 cycles even at 5000 mA g-1, respectively, which due to its unique double-layer hollow sandwich microstructure, mixed lithium storage mechanism and in-situ coating of nitrogen-doped carbon layer.

Enhancing Co/Co2VO4 Li-ion battery anode performances via 2D-2D heterostructure engineering.

High-capacity Co2VO4 has become a potential anode material for lithium-ion batteries (LIBs), benefiting from its lower output voltage during cycling than other cobalt vanadates. However, the application of this new conversion-type electrode is still hampered by its inherent large volume variation and poor kinetics. Here, a 2D-2D heterostructure building strategy has been developed to enhance the electrode performance of Co2VO4 through construction of Co/Co2VO4 nanocomposites converted from the in situ phase separation of Co2V2O7·3.3H2O nanosheets. Co/Co2VO4 based on face-to-face contact exhibits the optimized stacking configuration, where Co nanocrystals give gaps of several nanometers between stacked Co2VO4 nanosheets, enabling full contact with the electrolyte, a shorter transport path of lithium ions and more reactive sites. With this design, Co/Co2VO4 anodes deliver outstanding reversible capacity (750 mA h g-1 at 1 A g-1) with ultrahigh capacity retention rate, and excellent cycle stability at high rate (520 mA h g-1 at 5 A g-1 retained after 400 cycles). An "active center's charge transfer-capacity compensation" model was proposed based on capacity analysis, XPS depth analysis and HRTEM observation to uncover the fundamental reason of the excellent cycle performance. This in situ 2D-2D heterostructure constructing strategy may open up the possibility for designing high-performance LIBs.

A 1D Honeycomb-Like Amorphous Zincic Vanadate for Stable and Fast Sodium-Ion Storage.

Developing nanomaterials with synergistic effects of various structural merits is considered to be an effective strategy to improve the sluggish ion kinetics and severe structural degradation of sodium-ion battery (SIB) anodes. Herein, honeycomb-like amorphous Zn2 V2 O7 (ZVO-AH) nanofibers as SIBs anode material with plentiful defective sites, complex cavities, and good mechanical flexibility are reported. The fabrication strategy relies on the expansive and volatile nature of the organic vanadium source, based on a simple electrospinning with subsequent calcination. Originating from the synergies of amorphous nature and honeycomb-like cavities, ZVO-AH shows increased electrochemical activity, accelerated Na-ion diffusion, and robust structure. Impressively, the ZVO-AH anode delivers superior cycle stability (112% retention at 5 A g-1 after 5000 cycles) and high rate capability (150 mAh g-1 at 10 A g-1 ). The synthetic versatility is able to synergistically promote the practical application of more potential materials in sodium-ion storage.