Sn/SnOx Core-Shell Nanospheres: Synthesis, Anode Performance in Li Ion Batteries, and Superconductivity

Sn/SnOx core-shell nanospheres have been synthesized via a modified polyol process. Their size can be readily controlled by tuning the usage of surface stabilizers and the temperature. Anode performance in Li ion batteries and their superconducting properties is detailed. As anode materials, 45 nm nanospheres outperform both larger and smaller ones. Thus, they exhibit a capacity of about 3443 mAh cm(-3) and retain about 88% of after 10 cycles. We propose a model based on the microstructural evolution to explain the size impact on nanosphere performance. Magnetic measurements indicate that the nanospheres become superconducting below the transition temperature T-C = 3.7 K, which is similar to the value obtained in bulk tin. Although Tc does not significantly change with the size of the Sn core, we determined that the critical field H-C of nanospheres can be as much as a factor of 30 larger compared to the bulk value. Alternating current measurements demonstrated that a transition from conventional to filamentary superconducting structure occurs in Sn/SnOx particles as their size increases. The transition is determined by the relationship between the particle size and the magnetic field penetration depth.