Nitrogen-doped carbon decorated 3D NiCoSe2 micro-flowers as high-performance anode materials for lithium-ion batteries.

Compared with monometallic selenides, bimetallic selenides have better synergistic effects and more abundant active sites for electrochemical reactions. As an important member of the transition metal oxide family, NiCoSe2 has been widely used in energy storage devices and has shown excellent electrochemical performance. So in this paper, nitrogen-doped carbon decorated NiCoSe2 composites (NiCoSe2/NC-700, NiCoSe2/NC-800, and NiCoSe2/NC-900) with a microflower structure were synthesized by calcining nickel-cobalt bimetallic organic skeleton materials at different temperatures, and were used as anode materials for rechargeable lithium-ion batteries. Because the MOF precursor has many advantages such as structural controllability, and a bimetal synergistic effect, the test results showed that the prepared NiCoSe2/NC composites have a special morphology, outstanding electrical conductivity, excellent lithium storage performance and electrochemical cycling performance in the process of being used as anode materials for lithium-ion batteries. The NiCoSe2/NC-800 materials displayed a high initial capacity (2099.8/1084.3 mA h g-1), and still maintained a high capacity (1041.2/989.9 mA h g-1) after 100 cycles at a current density of 0.1 A g-1 and in the voltage range of 0.01-3.0 V. In addition, at high current densities of 0.5 A g-1 and 1.0 A g-1, the increased capacity of NiCoSe2/NC composites may be due to the activation of electrodes and the pseudocapacitance during cycling. Through ex situ XRD experiments, the lithium storage mechanism of the NiCoSe2/NC-800 electrode material during cycling was further studied, and NiCoSe2/NC-800 was continuously converted into Ni, Co, and Li2Se during cycling.

Enhancing Lithium Storage Performances of the Li4Ti5O12 Anode by Introducing the CuV2O6 Phase.

The low electronic conductivity of spinel-structured Li4Ti5O12 could be improved by introducing CuV2O6. Herein, several Li4Ti5O12/CuV2O6 composites with different CuV2O6 contents have been successfully prepared by a facile liquid-phase dispersion technique. The amount of CuV2O6 in composites is shown to affect the particle size and electrochemical performances of Li4Ti5O12. The Li4Ti5O12/CuV2O6 composite prepared with a 5 wt % CuV2O6 content (referred to as 5 wt % Li4Ti5O12/CuV2O6) exhibits the best electrochemical performances among all the Li4Ti5O12/CuV2O6 composites. The initial discharge/charge capacities of the 5 wt % Li4Ti5O12/CuV2O6 composite reach 241.1/199.8 mAh g-1 and retain at 136.8/135.7 mAh g-1 over 500 cycles at 30 mA g-1 between 1.0 and 3.0 V. In addition, initial discharge/charge capacities of the 5 wt % Li4Ti5O12/CuV2O6 composite amount to 129.8/90.5 mAh g-1 even at 1200 mA g-1 with maintained discharge/charge capacities of 71.1/71.1 mAh g-1 over 2500 cycles, which are superior to the pristine Li4Ti5O12 in all cases. The detailed electrode kinetic analysis reveals that the introduction of the CuV2O6 phase can enhance the lithium-ion transferring rate and cycling stability of Li4Ti5O12. The enhanced lithium-storage mechanism of the 5 wt % Li4Ti5O12/CuV2O6 composite is clarified by in situ X-ray diffraction (XRD) analysis. The acquired data confirms that in situ formation of small amounts of metallic Cu during discharge/charge processes highly enhance the electronic conductivity and decreases the charge-transfer resistance of Li4Ti5O12. In sum, the as-obtained 5 wt % Li4Ti5O12/CuV2O6 composite has potential for future construction of high-rate and long-lifespan anode materials for Li-ion batteries. The work also provides an innovative route to improve electrochemical performances of Li4Ti5O12.

Modification Effects of B2O3 on The Structure and Catalytic Activity of WO3-UiO-66 Catalyst.

Tungsten oxide (WO3) and boron oxide (B2O3) were irreversibly encapsulated into the nanocages of the Zr-based metal organic framework UiO-66, affording a hybrid material B2O3-WO3/UiO-66 by a simple microwave-assisted deposition method. The novel B2O3-WO3/UiO-66 material was systematically characterized by X-ray diffraction, Fourier transform infrared spectroscopy, N2 adsorption, ultraviolet⁻visible diffuse reflectance spectroscopy, scanning electron microscopy, transmission electron microscopy, X-ray phosphorescence, and Fourier transform infrared (FTIR)-CO adsorption methods. It was found that WO3 and B2O3 were highly dispersed in the nanocages of UiO-66, and the morphology and crystal structure of UiO-66 were well preserved. The B2O3 species are wrapped by WO3 species, thus increasing the polymeric degree of the WO3 species, which are mainly located in low-condensed oligomeric environments. Moreover, when compared with WO3/UiO-66, the B2O3-WO3/UiO-66 material has a little weaker acidity, which decreased by 10% upon the B2O3 introduction. The as-obtained novel material exhibits higher catalytic performance in the cyclopentene selective oxidation to glutaraldehyde than WO3/UiO-66. The high catalytic performance was attributed to a proper amount of B2O3 and WO3 with an appropriate acidity, their high dispersion, and the synergistic effects between them. In addition, these oxide species hardly leached in the reaction solution, endowing the catalyst with a good stability. The catalyst could be used for six reaction cycles without an obvious loss of catalytic activity.