Sn-carbon core-shell powder for anode in lithium secondary batteries

Spherical Sn-carbon core-shell powder was synthesized through a resorcinol-formaldehyde (RF) microemulsion polymerization performed in the presence of hydrophobized Sn nanoparticles. The Sn-carbon core-shell structure was found to greatly enhance the cycle life compared to the mixture of Sn and spherical carbon when evaluated as the anode in lithium-ion batteries. A core-shell powder containing 20 wt % Sn showed 69% capacity retention at the 40th cycle when cycled between 0 and 2.0 V (vs Li/Li⁺) at a constant current of 40 mA g^-1. The mixture of 20 wt % Sn nanopowder and 80 wt % spherical carbon powder exhibited only 10% capacity retention in the same test condition. It is believed that the improved cyclability achieved with the core-shell powder is largely attributed to the inhibition of aggregation between Sn nanoparticles. The marginal polarization due to an intimate electrical contact made between Sn core and carbon shell is an additional advantageous feature achieved with this electrode.