Zhang Jinli

Self-assembly of cetyl trimethylammonium bromide in ethanol-water mixtures

The critical micelle concentration (CMC) of cetyl trimethylammonium bromide (CTAB) in both water and ethanol-water-mixed solvent was determined using steady-state fluorescence techniques in order to investigate the effect of the self-assembling properties of the surfactant on the template synthesis of porous inorganic materials. Results indicated that the CMC increased with the increase of ethanol concentration in the mixed solvent. The CMC of CTAB is 0.0009 mol/L in water, while it is 0.24 mol/L in ethanol. Furthermore, the dissipative particle dynamics (DPD) was adopted to simulate the aggregation of CTAB in water and ethanol/water mixtures, and the energy difference was calculated for the surfactant tail groups after mixing with the solvent. The simulation results reflected a regularity similar to the experimental data, i.e., tail groups of CTAB interacted more strongly with ethanol than with groups of CTAB interacted more strongly with ethanol than with water, which elucidates the reason that the micelle is difficult to form in ethanol.

High-performance lithium iron phosphate with phosphorus-doped carbon layers for lithium ion batteries

A novel composite of LiFePO4 with phosphorus-doped carbon layers has been prepared via a simple hydrothermal method using glucose as the carbon source to generate a carbon coating and triphenylphosphine as the phosphorus source. The effects of phosphorus doping on the phase purity, morphology and electrochemical performance of the materials are studied by the characterizations using X-ray diffraction, Raman spectroscopy, scanning electron microscopy, high resolution transmission electron microscopy and electrochemical techniques. It is indicated that phosphorus doping into the carbon layers is beneficial for the graphitization of the carbon. Phosphorus in the carbon layers exists in the form of P–C bonds and its concentration depends on the second calcination temperature. Moreover, the phosphorus-doped carbon layers on the particle surface make the charge transfer resistance decrease remarkably from 156.5 Ω to 49.1 Ω, which can be ascribed to the free carriers donated by phosphorus. The as-prepared LiFePO4 with phosphorus-doped carbon layers calcined at 600 °C shows the best electrochemical performance with a discharge capacity of 124.0 mA h g−1 at a high rate of 20 C and an excellent retention rate of 91.4% after 50 cycles. The LiFePO4 with phosphorus-doped carbon layers exhibits excellent electrochemical performances, especially at high current rates; thus, it is a promising cathode material for high-performance lithium ion batteries.