Optimization of tin intermetallics and composite electrodes for lithium-ion batteries obtained by sonochemical synthesis

The optimization of active electrode materials for advanced lithium batteries obtained by sonochemically promoted reactions is discussed. Composites containing amorphous CoSn intermetallic compound and exfoliated graphite are prepared by a combination of graphite mechanical exfoliation followed by the reduction of Co2+ and Sn2+ solutions in tetraethyleneglycol with NaBH4 with simultaneous high-intensity ultrasonication. X-ray diffraction and electron microscopy reveal relevant similarities with the negative electrode of the commercial Nexelion (TM) battery. The resulting nanocomposite is tested as an electrode material using a lithium polyacrylate binder. The electrochemical cycling in lithium test cells shows capacities around 400 mAh/g after 400 cycles, and the ac impedance spectra reveal low resistance values. In the first discharge, nanocrystalline Li (x) Sn is formed. After cycling, the metallic nanoparticles (ca. 7-20 nm) remain to be X-ray amorphous and embedded in the binder.