Synthesis, characterization and lithium electrochemical insertion into antimony-based graphite composites

There is a renewal of interest in the use of metals that are capable of alloying with lithium as negative-electrode materials for lithium-ion batteries. These metals can supply larger capacities than graphite but their main disadvantage consists in their very limited cycle life. Indeed, they present considerable volume variations during alloying, which lead to a mechanical degradation of the electrode. The concept of an active phase stabilizing matrix was introduced. We propose in this study to associate a metal able to alloy lithium to graphite by using new preparation methods involving graphite intercalation compounds (GICs) as precursors. In one case, antimony pentachloride SbCl5 was reduced by the stage I KC8 GIC. In another case, C12SbCl5 and C24SbCl5 GICs were reduced either by gaseous caesium or by activated sodium hydride NaH. Actually, these methods led to the attention of antimony-based graphite composites in which antimony particles are deposited on the surface and edges of graphite layers or embedded in an organic matrix. Both morphological and structural characteristics of such composites were studied by transmission electron microscopy. Examination of their electrochemical properties as regards lithium insertion showed that they present interesting performances because the reversible capacity is increased by comparison with that of pure graphite and the stability of the metal is preserved throughout the cycling. The combination of graphite and antimony prevents the metal against cracking and pulverization that occur generally during alloying/dealloying cycles. Antimony-graphite composites prepared via SbCl5 reduction by KC8, via C12SbCl5 reduction by gaseous caesium or via C24SbCl5 reduction by activated NaH display improved reversible capacities of 420, 490 and 440 mAh g(-1), respectively. (C) 2004 Elsevier B.V. All rights reserved.