Abstract
Two kinds of tin-based nanopowders were fabricated and applied in microelectronic packaging and Li-ion rechargeable batteries, respectively. One was the lead-free solder with Sn-Ag-Cu nanopowder in microelectronic packaging, and the other was nano tin-based alloy/carbonaceous composite anode material in Li-ion rechargeable batteries. In this study, lead-free solders with Sn-3.5Ag-xCu (x = 0.2, 0.5, 1.0) nanoparticles were synthesized by chemical precipitation with NaBH4. XRD patterns revealed that the Ag3Sn phase was formed due to the alloying process. Only Cu6Sn5 was formed when Cu concentration was as high as 1.0 wt% in the derived nanopowders. TEM observation revealed that the isolated particle was in ovoid shape and the sizes of powders were approximately 5 nm. FE-SEM examination revealed that the majority of size of Sn-Ag-Cu nanoparticles was in the range of 40 nm. It was evident from the DSC profile that the Sn-Ag-Cu nanoparticles were melted successfully. Thus, the nanoparticles produced by chemical reduction method in this study can be potentially used as solder powders in electronic packaging. The microstructural characteristics of particle growth of the Sn-3.5Ag-0.5Cu nanoparticle synthesized by chemical precipitation with NaBH4 were examined by X-ray diffraction, transmission and scanning electron microscopy. The results indicated that the primary particles after precipitation were (Ag,Cu)4Sn with a size of 4.9 nm. The (Ag,Cu)4Sn phase particle was then transformed into (Ag,Cu)3Sn phase particle, when the total amount of Sn contributed from both (Ag,Cu)4Sn and Sn covering the (Ag,Cu)4Sn overtook that of (Ag,Cu)3Sn. The final particle size of polycrystalline particles was 40 nm owing to the depletion of Sn atoms in the solution. The nucleation and growth mechanism of Sn-3.5Ag-0.5Cu nanoparticles was discussed and proposed. Tin-based alloy/carbonaceous composite materials are highly attracted for Li-ion rechargeable batteries because of the high capacity. A novel Ni-Sn-P/mesophase carbon micro beads (MCMBs) composite material for lithium-ion batteries was prepared by an electroless plating method. On the basis of X-ray color mapping analysis by electron probe microanalyzer, the nanosize Ni-Sn-P was precipitated not only on the surface but in the interior of MCMB powders. The Ni-Sn-P/MCMB composite anode exhibited large capacity (418 mAh/g in the tenth cycle) and high coulombic efficiency (98 %) even after the twenty-fifth cycle. In addition, the Ni-Sn-P/MCMB composite anode showed a significant improvement in electrochemical performance. Therefore, the Ni-Sn-P/MCMB provides a new type of anode material for lithium-ion batteries with enhanced capacity.