Catalytic role of Ge in highly reversible GeO2/Ge/C nanocomposite anode material for lithium batteries.

GeO2/Ge/C anode material synthesized using a simple method involving simultaneous carbon coating and reduction by acetylene gas is composed of nanosized GeO2/Ge particles coated by a thin layer of carbon, which is also interconnected between neighboring particles to form clusters of up to 30 µm. The GeO2/Ge/C composite shows a high capacity of up to 1860 mAh/g and 1680 mAh/g at 1 C (2.1 A/g) and 10 C rates, respectively. This good electrochemical performance is related to the fact that the elemental germanium nanoparticles present in the composite increases the reversibility of the conversion reaction of GeO2. These factors have been found through investigating and comparing GeO2/Ge/C, GeO2/C, nanosized GeO2, and bulk GeO2.

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).

Reversible sodium storage via conversion reaction of a MoS2-C composite.

An exfoliated MoS2-C composite (E-MoS2-C) was prepared via simple chemical exfoliation and a hydrothermal method. The obtained E-MoS2-C was tested as an anode material for sodium ion batteries. High capacity (~400 mA h g(-1)) at 0.25 C (100 mA g(-1)) was maintained over prolonged cycling life (100 cycles). Outstanding rate capability was also achieved with a capacity of 290 mA h g(-1) at 5 C.

Electrospun P2-type Na(2/3)(Fe(1/2)Mn(1/2))O2 hierarchical nanofibers 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. Accordingly, the present study reports the first example of the preparation of Na2/3(Fe1/2Mn1/2)O2 hierarchical nanofibers by electrospinning. The nanofibers with aggregated nanocrystallites along the fiber direction have been characterized structurally and electrochemically, resulting in enhanced cyclability when compared to nanoparticles, with initial discharge capacity of ∼195 mAh g(-1). This is attributed to the good interconnection among the fibers, with well-guided charge transfers and better electrolyte contacts.

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

A novel hierarchical star-like Co(3)O(4) 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. Co(3)O(4) 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 Co(3)O(4) 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.