Synthesis and electrochemical properties of Sn87Co13 alloys by NaBH4 and sodium naphthalenide reduction methods

Sn87Co13 alloys are prepared by two different reduction methods and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and electrochemical cycling. One method, using NaBH4 as a reducing agent, obtains aggregated particles with particle sizes from 20 to 200 nm. The second method, using sodium naphthalenide as a reducing agent, shows a well-dispersed nanoalloy coated with amorphous carbon, with a particle size of 15 nm. Although electrochemical results shows that the charge capacity of the two alloys is quite similar, 662 mAh/g, the capacity retention of the nanoalloy prepared using sodium naphthalenide was 427 mAh/g, which is two times higher after 30 cycles than the bulk analogue obtained using NaBH4. This is due to the uniform particle size and amorphous carbon layer that effectively reduces anisotropic volume expansion and also minimizes particle aggregation and pulverization that causes a direct electrical disconnection with the copper current collector. (c) 2006 Elsevier Ltd. All rights reserved.