Prepatation And Properities Studies Of Si-based Anode Materials For Lithium Ion Batteries

Lithium ion batteries are of great interest as a green energy storage device. New typeof lithium ion batteries of higher specific capacity, longer cycle life and better safetyperformance have become the pursuit of people. Silicon triggers much attention ofresearchers because of its highest theoretical capacity (4200mAh/g). But the pulverizationof silicon caused by huge volume expansion during lithiation/delithiation process, resultsin decrease of conductivity and poor cycling performance.In this paper, nanoscale silicon fume and CNTs@Si composites were prepared byst ber method and magnesiothermic reduction method. Si/C composites were prepared byhigh temperature pyrolysis method, where glucose was introduced as the source ofpyrolytic carbon. CNTs@Si@C composites were prepared by st ber method,magnesiothermic reduction method and high temperature pyrolysis method. The physicalproperties of these materials were characterized by the means of XRD, SEM, TEM, TGA,et al. The electrochemical performance of the composites was investigated bycharge/discharge test and electrochemical impedance spectroscopy. The research resultsare shown as follows:As-prepared nanoscale silicon fume is pure without impurities and the size ofparticles is about50nm. The reversible capacity and capacity retention rate of the samplesis respectively135.6mAh/g and13.5%after50cycles at the current density of100mA/g.Cycling performance of nanoscale silicon fume has been improved compared with micronsilicon fume，but far away to the requirements of commercial production. It is difficult toprepare silicon anode materials with excellent electrochemical just by reducing the particlesize of silicon fume.Si/C composites have improved the electrochemical performance of pure siliconfume. The higher of carbon content, the better of cycling performance and rateperformance. When carbon content is71%, Si/C composites exhibit the best cyclingperformance and rate performance. A reversible capacity of413.1mAh/g is recorded after50cycles at the current density of100mA/g and350.1mAh/g is obtained at the currentdensity of4000mA/g. Both CNTs@Si composites and CNTs@Si@C composites have improved theelectrochemical performance of pure silicon fume and CNTs@Si@C composites exhibitthe best cycling performance and rate performance. A reversible capacity of594.6mAh/gis recorded after50cycles at the current density of100mA/g and464.1mAh/g is obtainedat the current density of4000mA/g.