The Influence Of Silicon Sources And Sulfur Sources On Sulfur Modified Lithium Iron Silicate

Sulfur substitute lithium iron silicate(Li2FeSiO3S),which can reduce the high delithiated voltage and the large volume change rate when the second lithium ions embedded in Li2FeSiO4,so realize the second lithium ion de-intercalation and reach the theoretical capacity of 330mAh/g.It is still not clear how to prepare Li2FeSiO3S,so it is meaningful to explore the influence of silicon sources and sulfur sources on the Li2FeSiO3S,especially whether it can realize Si-S bond when change silicon sources and sulfur sources.This work explored tetraethoxysilane(TEOS),methyl triethoxy silane(MTES)and Mercaptopropropyl trimethoxysilane(MPTMS)as silicon sources,as well as thiourea,1-dodecanethiol and sublimed sulfur as sulfur sources,respectively,and the sulfur modified Li2FeSiO4 were prepared using different sulfur contents and synthetic parameters.The effects of sulfur sources on the structure,morphology,surface species and properties of sulfur modified materials with different silicon source were analyzed by X-ray diffraction,scanning electron microscopy,Raman spectroscopy and performance test.The influence of the reaction temperature of the silicon source on the synthesis of the sulfur modified Li2FeSiO4 was investigated by thermal analysis,and the existence form of sulfur was analyzed.The results show that a series of different sulfur content of sulfur modified Li2FeSiO4 using tetraethoxysilane as silicon source and thiourea or 1-dodecanethiol as sulfur source are synthesis,the phase structure did not shift to Li2FeSiO3S diffraction peak.The silicon oxygen bond is difficult to break at the synthesis temperature of Li2FeSiO4,sulfur is difficult to bond with silicon,TEOS is not suitable for as the silicon source of sulfur modified;the sulfur was mainly coating on the surface of particles when using 1-dodecanethiol as sulfur source.The sulfur modified Li2FeSiO4 with a sulfur content of 25%was prepared by MTES as silicon source,the reaction temperature of Si-CH3 is higher than 500?,and 170? of thiourea,270? of 1-dodecanethiol,300? of sublimed sulfur,Sulfur is generally lost before the reaction of silicon source,sulfur can't bond with silicon,MTES is also not suitable as the silicon source for sulfur modified.The sulfur modified Li2FeSiO4 using MPTMS as silicon and sulfur source,the reaction temperature of-sh is almost the same as si-functional groups.The sulfur-modified Li2FeSiO4 with a sulfur content of 25%using MPTMS as silicon source and sublimated sulfur as sulfur source,there exists S2-,%S4+,S6+,the existence of high-valence sulfur indicates that sulphur is oxidized,there maybe a small amount of Si-S bond,most of the sulfur still exists in the form of coating on the material surface.