Influence of the diffusion-layer thickness during electrodeposition on the synthesis of nano core/shell Sn-O-C composite as an anode of lithium secondary batteries

Electrodeposition was conducted from an organic carbonate solvent via the potentiostatic technique through three consecutive steps in order to synthesise Sn-O-C composite, which delivered a discharge capacity of 596 mA h g of Sn-1 after 50 cycles. However, the composite anode suffered from a significantly low initial discharge capacity, delivering a discharge capacity of 79 mA h g of Sn-1 until the 5th cycle. It was deduced that the improbably low initial capacity was induced by the deposition of Li-rich compounds, which were formed by electrolyte decomposition accompanied by the reduction product of supporting electrolyte salts during the electrodeposition process, on the surface layer. In order to improve the poor initial capacity, we modified the chemical composition of the surface layer by means of implementing the agitation of the electrolyte during the deposition process. This gave rise to varying the diffusion-layer thickness during the deposition process due to the enhancement of convection by movement of the electrolyte itself. As a result, we achieved improvement of the initial discharge capacity, delivering 572 mA h g of Sn-1 at the 1st cycle and 586 mA h g of Sn-1 at the 50th cycle. It was revealed that the surface layer was composed of a decomposition product of the organic carbonate solvent. Furthermore, a smaller particle size of the Sn-O-C composite was obtained via electrolyte agitation, giving rise to homogeneous shell formation on the Sn compound core. Herein, we thoroughly examined the influence of varying diffusion-layer thickness during the deposition process on the properties of the Sn-O-C composites from an electrochemical standpoint.