Self-assembly of hierarchical star-like Co3O4 micro/nanostructures and their application in lithium ion batteries

A novel hierarchical star-like Co3O4 was successfully synthesized from self-assembled hierarchical Co(OH)F precursors via a facile hydrothermal method and subsequent annealing in air. The morphological evolution process of the Co(OH)F precursors was investigated by examining the different reaction times during synthesis. First, hexagonal plates are formed, and then nanodiscs grow on the surface of the plates. Subsequently, dissolution and regrowth of Co(OH)F occur to form the star-like hierarchical structures. Co3O4 obtained from thermal decomposition of the Co(OH)F precursor in air at 350 °C exhibited high reversible capacity as an anode material in lithium ion batteries. The specific charge capacity of 1036 mA h g−1 was obtained in the first cycle at a current density of 50 mA g−1, and after 100 cycles, the capacity retention was nearly 100%. When the current density was increased to 500 mA g−1 and 2 A g−1, the capacities were 995 and 641 mA h g−1, respectively, after 100 cycles. In addition, a capacity of 460 mA h g−1 was recorded at a current density of 10 A g−1 in the rate capability test. The excellent electrochemical performance of the Co3O4 electrodes can be attributed to the porous interconnected hierarchical nanostructures, which protect the small particles from agglomeration and buffer the volume change during the discharge-charge process

SnSb/graphene composite as anode materials for lithium ion batteries

SnSb/graphene porous three dimensional (3-D) composite with dual buffering capability was prepared by an in situ chemical reduction of SnCl2, SbCl3, and graphene oxide prepared using a modified Hummers\u27 method. Field emission scanning electron microscope and transmission electron microscope images shows that the SnSb nanoparticles were distributed homogenously across the surface of the graphene sheets, and some were also found trapped in the corrugated graphene structure. The electrochemical performances of the SnSb/graphene composite was investigated by cyclic voltammetry and galvanostatic charge/discharge testing. The SnSb/graphene composite delivered 688 mAh/g at the 2nd cycle (compared to a calculated theoretical value of 768 mAh/g) and shows good capacity retention of 420 mAh/g after 100 cycles. A reaction model to explain the dual buffering effects of SnSb/graphene composite as anode material for lithium insertion and extraction has been proposed

Synthesis of Mn3O4-encapsulated graphene sheet nanocomposites via a facile, fast microwave hydrothermal method and their supercapacitive behaviour

Well-crystallized Mn3O4-anchored reduced graphene oxide (rGO) nanocomposites have been successfully synthesized via a facile, effective, energy-saving, and scalable microwave hydrothermal technique for potential application as supercapacitor material. Integrating these nanostructures resulted in a strong synergistic effect between the two materials, consequently leading to a hybrid composite with higher specific capacitance compared to the bare Mn3O4 nanoparticles. The results from different sorts of characterization indicate that the Mn3O4 particles were deposited and anchored on graphene sheets. The capacitance value of the rGO(31.6%)–Mn3O4 nanocomposite reached 153 F/g, much higher than that of the bare Mn3O4 (87 F/g) at a scan rate of 5 mV/s in the potential range from −0.1 V to 0.8 V. More importantly, a 200% increase in capacitance was observed for the nanocomposite with cycling at 10 mV/s due to electrochemical activation and the oxidization of Mn(II,III) to Mn(IV) during cycling, as verified by Xray photoelectron spectroscopy. There is no observable capacitance fading up to 1000 cycles. The facile synthesis method and good electrochemical properties indicate that the nanocomposite could be an electrode candidate for supercapacitors

Electrospun P2-type Na 2/3 (Fe 1/2 Mn 1/2 )O 2 hierarchical nano fibers as cathode material for sodium-ion batteries

Sodium-ion batteries can be the best alternative to lithium-ion batteries, because of their similar electrochemistry, nontoxicity, and elemental abundance and the low cost of sodium. They still stand in need of better cathodes in terms of their structural and electrochemical aspects

Free-standing V2O5 electrode for flexible lithium ion batteries

Free-standing and flexible V2O5 films have been prepared by filtration of ultra-long nanowires synthesised via the hydrothermal technique. In order to improve the conductivity of the films, multiwalled carbon nanotubes (MWCNTs) were added to the V2O5 nanowires to form an integrated web-like structure. The structure of the V2O5 nanowires was investigated with X-ray diffraction and transmission electron microscopy. The possible use of these films as cathode for lithium ion batteries was also investigated. The free-standing and flexible film electrodes exhibited good rate capability and excellent cycling performance, with capacity of 140 mAh/g, even after 50 cycles at 1.7 C in the voltage range of 2.5-4.0 V. The superior reversible lithium storage capability can be attributed to the fully reversible phase transitions of α-V2O5 through to δ-LiV2O5, good lithium diffusion in V2O5, and increased electronic conductivity and electrolyte diffusion from the incorporated MWCNT web

Sodium and lithium storage properties of spray-dried molybdenum disulfide-graphene hierarchical microspheres

Developing nano/micro-structures which can effectively upgrade the intriguing properties of electrode materials for energy storage devices is always a key research topic. Ultrathin nanosheets were proved to be one of the potential nanostructures due to their high specific surface area, good active contact areas and porous channels. Herein, we report a unique hierarchical micro-spherical morphology of well-stacked and completely miscible molybdenum disulfide (MoS2) nanosheets and graphene sheets, were successfully synthesized via a simple and industrial scale spray-drying technique to take the advantages of both MoS2 and graphene in terms of their high practical capacity values and high electronic conductivity, respectively. Computational studies were performed to understand the interfacial behaviour of MoS2 and graphene, which proves high stability of the composite with high interfacial binding energy (−2.02 eV) among them. Further, the lithium and sodium storage properties have been tested and reveal excellent cyclic stability over 250 and 500 cycles, respectively, with the highest initial capacity values of 1300 mAh g−1 and 640 mAh g−1 at 0.1 A g−1

V2O5/mesoporous carbon composite as a cathode material for lithium-ion batteries

V2O5/mesoporous carbon composite has been prepared by an ultrasonically assisted method followed by a sintering process. The as-prepared V2O5/mesoporous carbon material containing 90 wt% V2O5 shows better electrochemical performance, with capacity of 163 mA h g-1 after 100 cycles at the current density of 500 mA g-1, as well as better charge/discharge rate capability for lithium storage than V2O5 nanoparticles. The improved electrochemical performance indicates that the V2O5/mesoporous carbon composite could be used as a promising cathode material for lithium ion batteries