Nanoporous Composites of CoO x Quantum Dots and ZIF-Derived Carbon as High-Performance Anodes for Lithium-Ion Batteries.

Transition-metal oxides are attracting considerable attention as anodes for lithium-ion batteries because of their high reversible capacities. However, the drastic volume change and inferior electrical conductivity greatly retard their widespread applications in lithium-ion batteries. Herein, three-dimensional nanoporous composites of CoO x (CoO and Co3O4) quantum dots and zeolitic imidazolate framework-67-derived carbon are fabricated by a precipitation method. The carbon prepared by carbonization of zeolitic imidazolate framework-67 can greatly enhance the electrical conductivity of the composite anodes. CoO x quantum dots anchored firmly on zeolitic imidazolate framework-67-derived carbon can effectively inhibit the aggregation and volume change of CoO x quantum dots during lithiation/delithiation processes. The nanoporous structure can shorten the ion diffusion paths and maintain the structural integrity upon cycling. Meanwhile, kinetics analysis reveals that a capacitance mechanism dominates the lithium storage capacity, which can greatly enhance the electrochemical performance. The composite anodes show a high discharge capacity of 1873 mAh g-1 after 200 cycles at 200 mA g-1, ultralong cycle life (1246 mAh g-1 after 900 cycles at 1000 mA g-1), and improved rate performance. This work may provide guidelines for preparing cobalt oxide-based anodes for LIBs.

3D Hollow Porous Spherical Architecture Packed by Iron-Borate Amorphous Nanoparticles as High-Performance Anode for Lithium-Ion Batteries.

Three-dimensional hollow porous spherical architecture packed by iron-borate amorphous nanoparticles as an anode for lithium-ion batteries is first prepared through a simple method. The anode exhibits a high Coulombic efficiency and an ultralong cycle life under high rate, delivering outstanding reversible capacity of 1170 mAh g-1 after 360 cycles at 100 mA g-1 and 1160 mAh g-1 after 750 cycles at 200 mA g-1. The iron-borate anode has a prominent ultralong cycle life. The reversible capacity can still remain at about 600 mAh g-1 even after 3500 cycles at 2000 mA g-1, which maintains an outstanding capacity and delivers a much longer cycle life than that of the reported iron-based oxide anodes measured at same current density only within 1000 cycles. The hollow porous structure offers efficient electron-transport and Li+-diffusion paths and buffers the structural strains to alleviate excessive pulverization of the anode materials. Large specific surface area of the hollow porous structure increases the contact area between the anode and electrolyte, providing more reaction sites. More importantly, the amorphous characteristics of the iron-borate anode possess higher density of active sites and improved faster reaction kinetics. This work demonstrates that the hollow porous iron-borate particle anode allows mass production and is one of the most attractive anodes in energy-storage applications.

Magnetoviscous Property and Hyperthermia Effect of Amorphous Nanoparticle Aqueous Ferrofluids.

Magnetic Fe-B, Fe-Ni-B, and Co-B nanoparticles were successfully synthesized and introduced to water to prepare aqueous ferrofluids. The Fe-B, Fe-Ni-B, and Co-B particles are homogeneous amorphous nanoparticles with an average particle size 15 nm. The shape of the amorphous nanoparticles is regular. The Fe-B, Fe-Ni-B, and Co-B amorphous nanoparticles are superparamagnetic. Moreover, the saturation magnetizations of Fe-B and Fe-Ni-B amorphous nanoparticles are 75 emu/g and 51 emu/g. These are approximately 2.8 and 1.9-fold larger than Co-B nanoparticles, respectively. The viscosity of the amorphous ferrofluids has a strong response to external magnetic field. The yield stress increases with increasing magnetic field. The hyperthermia research of amorphous ferrofluids was firstly investigated. The experimental results indicate that the heating temperature of Fe-B ferrofluid and Fe-Ni-B ferrofluid could increase to 42 °C in 750 s and 960 s, respectively, when the output current is 300 A. The temperature could reach 61.6 °C for a Fe-B ferrofluid. The heating efficiencies of the amorphous ferrofluids demonstrate that the Fe-B ferrofluid and Fe-Ni-B ferrofluid may have great potential for biomedical applications.

Metal-based magnetic fluids with core-shell structure FeB@SiO2 amorphous particles.

FeB@SiO2 amorphous particles were firstly introduced into Ga85.8In14.2 alloys to prepare metal-based magnetic fluids. The morphology of the FeB amorphous particles is spherical with an average particle size of about 190 nm. The shape of the particles is regular and the particle size is homogeneous. Stable core-shell structure SiO2 modified FeB amorphous particles are obtained and the thickness of the SiO2 coatings is observed to be about 40 nm. The results of VSM confirm that the saturation magnetization of the FeB amorphous particles is 131.5 emu g-1, which is almost two times higher than that of the Fe3O4 particles. The saturation magnetization of the FeB@SiO2 amorphous particles is 106.9 emu g-1, an approximate decrease of 18.7% due to the non-magnetic SiO2 coatings. The results from the torsional oscillation viscometer show that the metal-based magnetic fluids with FeB amorphous particles exhibit a desirable high temperature performance and are ideal candidates for high temperature use.