Beads-Milling of Waste Si Sawdust into High-Performance Nanoflakes for Lithium-Ion Batteries.

Nowadays, ca. 176,640 tons/year of silicon (Si) (>4N) is manufactured for Si wafers used for semiconductor industry. The production of the highly pure Si wafers inevitably includes very high-temperature steps at 1400-2000 °C, which is energy-consuming and environmentally unfriendly. Inefficiently, ca. 45-55% of such costly Si is lost simply as sawdust in the cutting process. In this work, we develop a cost-effective way to recycle Si sawdust as a high-performance anode material for lithium-ion batteries. By a beads-milling process, nanoflakes with extremely small thickness (15-17 nm) and large diameter (0.2-1 µm) are obtained. The nanoflake framework is transformed into a high-performance porous structure, named wrinkled structure, through a self-organization induced by lithiation/delithiation cycling. Under capacity restriction up to 1200 mAh g-1, the best sample can retain the constant capacity over 800 cycles with a reasonably high coulombic efficiency (98-99.8%).

Real Understanding of the Nitrogen-Doping Effect on the Electrochemical Performance of Carbon Materials by Using Carbon-Coated Mesoporous Silica as a Model Material.

The main aim of the present work is to precisely understand the sole effect of nitrogen doping on the electrochemical performance of porous carbon materials. To achieve this objective, the whole surface of mesoporous silica (SBA-15) was coated with a thin layer of carbon (about 0.4 nm) with and without N-doping by using acetonitrile and acetylene chemical vapor deposition, respectively. The resulting N-doped and nondoped carbon-coated silica samples have mesopore structures identical to those in the original SBA-15, and they are practically the same in terms of not only the pore size and pore structure but also the particle size distribution and particle morphology, with the exception of N-doping, which makes them unique model materials to extract the sole effect of nitrogen on the performances of electrochemical capacitors and electrocatalytic oxygen reduction. Moreover, the outstanding features of the carbon-coated silica samples allow even a quantitative understanding of the pseudocapacitance induced by nitrogen functionalities on the carbon surface in an acidic aqueous electrolyte.