Evaluation of discharge and cycling properties of skutterudite-type Co1-2yFeyNiySb3 compounds in lithium cells

The preparation, structural characterization and study of the electrochemical behavior in lithium cells of Co1-2yFeyNiySb3 (0.125 < v less than or equal to 0.5) compounds is described, The refinement of X-ray diffraction (XRD) patterns evidenced the skutterudite-type structure for all compositions, with an increasing partial filling of 2a sites. The first discharge of lithium a-node cells shows two plateaus. The plateau at higher potential, which occurs at ca. 0.8 V and extends from ca. 150 to 250 Ah/kg depending on "y", is mainly assigned to side reactions of lithium with the electrolyte, as confirmed by Li-7 NMR. The second plateau occurs at 0.5-0.6 V and is assigned to Li-Sb alloys formation. The charge of the cell shows that only the second step is reversible. Further discharge/charge cycles present a plateau at 0.8 V in the discharge and at 1.05 V in the charge, which agree well with the Li-Sb alloying/de-alloying process. Extended cycling results on a loss of capacity, to stabilize over 100 Ah/kg after 20 cycles. (C) 2002 Elsevier Science B.V. All rights reserved.