Differential capacity as a spectroscopic probe for the investigation of alkali metal insertion reactions

Detailed electrochemical measurements have been carried out on metallic Li cells utilizing composite cathodes derived from two batches of the non-stoichiometric lithium insertion compound, V6O13. Powder XRD of the as-made materials and particle size analysis of the electrode stocks revealed only minor differences between the two batches. The electrochemical analysis indicated that the lithium insertion reactions into V6O13 were far more complicated than have been suggested by the relatively simple three voltage plateau relationship described previously in the literature[21]. Electrochemical voltage spectroscopy studies revealed differential capacity profiles which included up to eight discrete peaks related to lithium insertion reactions at energetically inequivalent sites within the host lattice. There were also readily discernible differences between the differential capacity features from the two V6O13 batches. For instance, one batch had two additional features at cell potentials of 2.87V and 2.58V. Further, it was possible to detect distinct differences in the shapes and relative sizes of some of the peaks. The sensitivity (in terms of discharge capacity) of the differential capacity method was demonstrated to be better than 2% for the overall discharge reaction. It is concluded that the measurement of the differential capacity may be viewed as a true spectroscopic probe for alkali metal insertions reactions. Copyright (C) 1996 Elsevier Science Ltd.