Hiroyuki Uono

Cyclic Properties of Si-Cu/Carbon Nanocomposite Anodes for Li-Ion Secondary Batteries

Si/carbon nanocomposites with different Si distribution were prepared to the anode of Li-ion batteries for better cyclic properties. Si particles were milled by a high-energy multi-ring-type mill to decrease the crystallite size to 15 nm. Nanocomposite particles with controlled inhomogeneous spatial Si distribution were obtained by co-grinding with Cu powder. Heterogeneity of the Si distribution exhibited better cyclability than those with homogeneous Si distribution prepared from well-dispersed Si nanoparticles. We attribute the better cyclability to two factors, reduction of mechanical stress developed by electrochemical volume change of Si and networking of Si particles for maintaining conductive paths in the electrode.

Fabrication of nano-sized Si powders with a narrow size distribution by two-step milling

By the combination of two successive dry milling processes (i.e., by using a multiring mill and subsequently a pin-type disintegrator), downsizing of Si powders was achieved to 30 nm crystallites and their aggregated meanvolume diameter about 100 nm, with the top size less than 400 nm. Combination of the two dry milling processes proved to be effective to reduce the particle size and sharpen the size distribution of the aggregates without using any additives, tedious wet processes, or subsequent classification. Increase in the impurity due to milling was <0.1% for Fe and <0.4% for Zr, being well within a tolerable limit for most of the technological purposes.

Formation of Sn-dispersed Si Nanoparticles by Co-grinding

An immiscible Si/Sn (=7/3 by volume) powder mixture was subjected to simple grinding and subsequent leaching process to give Sn nanopowder reinforced or dispersed in Si powder. Crystallite and their agglomerates of Si were ca. 15 nm and 100 ㎚, respectively. Sn remained at 4.5 vol% in Si powder after aqueous HCl leaching, dispersively occluded in Si matrix as confirmed by ICP analysis and cross sectional TEM observation.