The influence of the synthesis conditions of graphite/tin nanoparticle materials on their electrode electrochemical performance in Li-ion battery anodes

摘要

Electrochemical lithium insertion was carried out in tin-graphite composites obtained by two different preparation processes. In the first graphite was mixed with the products obtained by reduction of SnCl_4 with Na rerz-Butanoate (t-BuONa)-activated NaH (two-step synthesis). The second used materials synthesized by reducing SnCl_4 with a graphite and (t-BuONa)-activated NaH suspension in THF (one-pot synthesis). Both composites were characterized by X-ray diffraction and transmission electron microscopy. It appeared that the tin particle size was controlled by the reduction time of SnCl4. The stability of the electrochemical capacity of composites prepared by the two-step synthesis is dependent on the tin particle size: a stable capacity upon cycling was shown with subnanometer particles while a capacity fade was observed with larger nanoparticles. In materials prepared by the one pot synthesis, tin was present either as nanopart-cles supported on graphite or as free aggregates. An initial reversible capacity of 630 mA hg~(-1) decayed to a constant value of 415 mA hg~(-1) after 12 charge/discharge cycles. It was hypothesized that the fraction of tin bound to graphite contributed to the stable reversible capacity while free tin aggregates were responsible for its decay.