Enhanced electrochemical performance of Si/C electrode through surface modification using SrF_(2) particle

The silicon-based material exhibits a high theoretical specific capacity and is one of the best anode for the next generation of advanced lithium-ion batteries(LIBs).However,it is difficult for the silicon-based anode to form a stable solid-state interphase(SEI)during Li alloy/de-alloy process due to the large volume change(up to 300%)between silicon and Li4.4Si,which seriously limits the cycle life of the LIBs.Herein,we use strontium fluoride(SrF_(2))particle to coat the silicon-carbon(Si/C)electrode(SrF_(2)@Si/C)to help forming a stable and high mechanical strength SEI by spontaneously embedding the SrF_(2) particle into SEI.Meanwhile the formed SEI can inhibit the volume expansion of the silicon-carbon anode during the cycle.The electrochemical test results show that the cycle performance and the ionic conductivity of the SrF_(2)@Si/C anode has been significantly improved.The X-ray photoelectron spectroscopy(XPS)analysis reveals that there are fewer electrolyte decomposition products formed on the surface of the SrF_(2)@Si/C anode.This study provides a facile approach to overcome the problems of Si/C electrode during the electrochemical cycling,which will be beneficial to the industrial application of silicon-based anode materials.

Nanosized complex fluorides based on Eu^(3+) doped Sr_2LnF_7(Ln=La, Gd)

A simple co-precipitation approach taking place between Ln3＋, Sr2＋ cations and F anions, led to the formation of nanocrystalline Eu3＋ doped Sr2LnF7 （Ln-La and Gd） complex fluorides. The reaction was carried out in the presence of polyeth- ylene glycol, PEG 6000 as a surfactant/surface modifier, providing small size and homogeneity of the products. The synthesized compounds were composed of small nanoparticles with an average size of 15 nm. All obtained Eu3＋ doped compounds exhibited an intensive red luminescence. In the case of gadolinium based compounds, the energy transfer phenomena could be observed from Gd3＋ ions to Eu3＋ ions. In order to study the structure and morphology of the synthesized fluorides, powder X-ray diffraction （XRD） and transmission electron microscopy （TEM） measurements were performed. Also FT-IR spectra of the products were re- corded, revealing the presence of PEG molecules on the nanoparticles suN＇ace. A spectrofluorometry technique was applied to examine optical properties of the synthesized nanoparticles. Excitation and emission spectra as well as luminescence decay curves were measured and analysed. The performed analysis revealed a red luminescence, typical for the Eu3＋ ion situated in the inorganic, highly symmetric matrix. Concentration quenching phenomena and lifetimes shortening, together with an increasing of the Eu3＋ doping level, were observed and discussed. Judd-Ofelt analysis was also performed for all doped samples, in order to support the registered spectroscopic data and examine in details structural and optoelectronic properties of the synthesized nanomaterials.