A Facile Path to Graphene-Wrapped Polydopamine-Entwined Silicon Nanoparticles with High Electrochemical Performance

Graphene-coated silicon nanoparticles with polydopamine buffers have been designed and successfully fabricated as anodes for lithium ion batteries, where the polydopamine was grown on the silicon nanoparticles and then coated with graphene layers. The expansion cavities for silicon nanoparticles during charging and discharging process are provided by the polydopamine buffer layers. The outermost graphene coating layers not only keep the pulverized silicon particles together without disintegration, but also improve the electric conductivity of silicon nanoparticles. Silicon nanoparticles of an industrial product level with different size distributions and oxidation layers were used in this work. High electrochemical performances with specific capacities of 1100 mAh g^-1 were achieved by the designed silicon composites with polydopamine and graphene after 550 cycles at a current rate of 200 mA g^-1 .

Mechanochemical synthesis of Si/Cu3Si-based composite as negative electrode materials for lithium ion battery

Mechanochemical synthesis of Si/Cu₃Si-based composite as negative electrode materials for lithium ion battery is investigated. Results indicate that CuO is decomposed and alloyed with Si forming amorphous Cu-Si solid solution due to high energy impacting during high energy mechanical milling (HEMM). Upon carbonization at 800 °C, heating energy induces Cu₃Si to crystallize in nanocrystalline/amorphous Si-rich matrix enhancing composite rigidity and conductivity. In addition, residual carbon formed on outside surface of composite powder as a buff space further alleviates volume change upon lithiation/delithiation. Thus, coin cell made of C-coated Si/Cu₃Si-based composite as negative electrode (active materials loading, 2.3 mg cm⁻²) conducted at 100 mA g⁻¹ performs the initial charge capacity of 1812 mAh g⁻¹ (4.08 mAh cm⁻²) columbic efficiency of 83.7% and retained charge capacity of 1470 mAh g⁻¹ (3.31 mAh cm⁻²) at the end of the 100^th cycle, opening a promised window as negative electrode materials for lithium ion batteries.

Mesoporous NiCo2O4 networks with enhanced performance as counter electrodes for dye-sensitized solar cells

The performance of a dye-sensitized solar cell (DSSC) is strongly influenced by the catalytic performance of its counter electrode (CE) materials. Platinum (Pt) is conventionally used as the CE for DSSCs, but it is precious and is readily corroded by the iodide/triiodide electrolyte. Herein, mesoporous NiCo₂O₄ networks with different types of building blocks were prepared by electrospinning of a composite solution followed by annealing in air, and their performances as CEs in DSSCs were investigated. The honeycomb-like NiCo₂O₄ exhibited better performance than the nanotube ones, showing a photoelectric conversion efficiency of 7.09% which is higher than that of a standard Pt CE (7.05%) under the same conditions. The enhanced electrode performance was attributed to the relatively larger surface area and higher conductivity. The preparation methods demonstrated in this study are scalable and would pave the way for practical applications of Pt-free DSSCs.