Wrapping SnO2 with porosity-tuned graphene as a strategy for high-rate performance in lithium battery anodes

The previous studies on SnO2 as electrode materials convey a message that the inevitable pulverization of SnO2 particles can be resolved by carbon-based materials. Since graphene has also proved effective for the harmful decrepitation of the particles with an advantage of electronic conductivity, wrapping SnO2 by sufficient amount of graphene seems to be an answer to enhancing its cycle life. On the other hand, severe wrapping of SnO2 by graphene is deleterious to its rate capability due to the sluggish motion of Li+ through the stacked graphene layers. Thus, in order to make graphene sheets favorable for Li-ion diffusion, they were modified to have large porosity with 3-D architectures, by a simple heating-rate control. The porous graphene-wrapped SnO2, having direct diffusion channels for Li+, outperforms the SnO2 with less-porous graphene. Consequently, the excellent performances are fulfilled, showing both stable cyclability (???1100 mAh g-1 up to 100 cycles) and high rate capability (???690 mAh g-1 under 3600 mA g-1). This strategy using porosity-tuned graphene sheet furnishes a valuable insight into the effective encapsulation of active materials, especially for those undergoing pulverization during cycling.close5

Electronic Effect in Methanol Dehydrogenation on Pt Surfaces: Potential Control during Methanol Electrooxidation

Establishing a relationship between the catalytic activity and electronic structure of a transition-metal surface is important in the prediction and design of a new catalyst in fuel cell technology. Herein, we introduce a novel approach for identifying the methanol oxidation reactions, especially focusing on the effect of the Pt electronic structure on methanol dehydrogenation. By systematically controlling the electrode potential, we simplified the reaction paths, excluding other unfavorable effects, and thereby obtained only the methanol dehydrogenation activity in terms of the electronic structure of the Pt surface. We observed that the methanol dehydrogenation activity of Pt decreases when the position of the d-band center relative to the Fermi level is lower, and this fundamental relation provides advanced insight into the design of an optimal catalyst as the anode for direct methanol fuel cells

Optimum Morphology of Mixed-Olivine Mesocrystals for a Li-Ion Battery

In this present work, we report on the synthesis of micron-sized LiMn_0.8Fe_0.2PO₄ (LMFP) mesocrystals via a solvothermal method with varying pH and precursor ratios. The morphologies of resultant LMFP secondary particles are classified into two major classes, flakes and ellipsoids, both of which are featured by the mesocrystalline aggregates where the primary particles constituting LMFP secondary particles are crystallographically aligned. Assessment of the battery performance reveals that the flake-shaped LMFP mesocrystals exhibit a specific capacity and rate capability superior to those of other mesocrystals. The origin of the enhanced electrochemical performance is investigated in terms of primary particle size, pore structure, antisite-defect concentration, and secondary particle shape. It is shown that the shape of the secondary particle has just as much of a significant effect on the battery performance as the crystallite size and antisite defects do. We believe that this work provides a rule of design for electrochemically favorable meso/nanostructures, which is of great potential for improving battery performance by tuning the morphology of particles on multilength scales