Nanocrystalline CoSn2-carbon composite electrode prepared by using sonochemistry

Abstract

A sonochemical method has been used to prepare negative electrode materials containing intermetallic nanoparticles and polyacrylonitrile (PAN). The ultrasound irradiation is applied to achieve small particle size. After annealing at 490 °C under Ar-flow, the polymer PAN is partially carbonized and the metallic nanoparticles are surrounded by a carbonaceous matrix. The main metallic phase is CoSn(2). The carbonaceous coating and the surface oxides have been explored by using XPS. The resulting CoSn(2)-carbonaceous phase electrode (CoSn(2)@C) shows improved electrochemical behavior (ca. 450 mAh/g after 50 cycles) in comparison with previous reports on pure crystalline CoSn(2). The reaction between CoSn(2)@C and Li has been studied by using XRD and (119)Sn Mössbauer spectroscopy. The formation of large grains of crystalline Li(x)Sn phases after the first discharge is discarded. The small particle size which is achieved by using ultrasonication and the carbonaceous matrix contribute to maintain the Co-Sn interactions during the electrochemical cycling. The aggregation of the nanosized metallic particles upon electrochemical cycling can be suppressed by the carbonaceous matrix (pyrolytic PAN).