Tin-graphite materials prepared by reduction of SnCl4 in organic medium:: Synthesis, characterization and electrochemical lithiation

Tin-graphite materials were prepared by chemical reduction of SnCl4 by t-BuONa-activated NaH. TEM imaging showed that the crude material is composed of an. amorphous organic matrix containing tin present either as nanosized particles deposited on the graphite surface or as free aggregates. Subsequent washings with ethanol and water allow removal of side products as well as most part of the organic matrix. Electrochemical insertion of lithium occurred in graphite and in tin. The initial reversible massic capacity of 630 mAh g(-1) decayed to a stable value of 415 mAh g(-1) after 12 cycles. This capacity value was lower than the expected maximum one of 650m Ah g(-1) corresponding to a Sn/12C molar composition and assuming the formation of LiC6 and Li22Sn5. Even if this massic capacity is not much improved by comparison with that of graphite, it must be pointed out that the volume capacity of this graphite/Sn material is much larger (2137 mAh cm(-3)) than that corresponding to graphite (837 mAh cm(-3)). It was hypothesized that the part of tin bound to graphite could be responsible for the stable reversible capacity. To the contrary graphite unsupported tin aggregates would contribute to the observed gradual decline in the storage capacity. Therefore, the improvement in cycleability, compared to that of massive metals, could be attributed both to the nanoscale dimension of the metal particles and to interactions between graphite and metal the nature of which remaining to be precised. (c) 2006 Elsevier B.V. All rights reserved.