Structural and electrochemical characterization of tin-containing graphite compounds used as anodes for Li-ion batteries

Two tin–graphite composites (“core-shell” structures) with different metal content (80 wt% and 20 wt%) as well as their structural and electrochemical characteristics are presented. Mitsubishi's synthetic carbon was used as starting material for the modification experiments. Chemical reduction was applied for the coating process, which was carried out under inert argon atmosphere. Although a homogeneous film of the nanoscale tin particles (∼60 nm) have been achieved, the electrochemical performance improvement strongly depends on the thickness of the “shell’ layer and the progressively increased active surface area together with the tin metal contents. The electrode with low metal concentration displayed both improved cycling performance and stable discharge capacity of 435 Ah kg−1 compared with untreated graphite electrode. The tin-rich composite shows a higher medial discharge capacity (540 mAh g−1) but increased capacity fading, while higher metal contents lead to bulk-coated film with disassociated and agglomerated tin nanoparticles as well as higher surface area and likely presence of oxide impurities.The obtained electrochemical results lead to the assumption, that there is a critical metal ratio up to which good cycling behavior can be achieved. Moreover, the properties of the coating film are closely related with the synthesis conditions and the type of the graphite. In this case, the optimal amount for tin–graphite composite with improved electrochemical performance is about 20 wt%.