X-Ray Study of Metal Oxide Based Anodes for Li-Ion Batteries

Cells were made from Co3O4 and Co2SnO4 and lithium metal and tested to determine reversible lithium capacity. Li is reversibly inserted into Co3O4 , as was observed by electrochemistry, coupled with changes of cobalt oxidation state as observed by Co K-edge EXAFS. On lithium insertion the Co3O4 is reduced to yield only metallic cobalt species, and then on lithium removal an oxide of Co is formed. The EXAFS data further showed that the initial reduction was to Co(II) and then to metallic Co, and that both the metallic and oxide phases were disordered, having low co-ordination numbers and large shell spacings. The electrochemical behaviour of the CozSnO(4) cells was closer to that of SnO2 than Co3O4 , but did exhibit changes obviously caused by the cobalt. EXAFS on Co2SnO4 cells revealed that the Co is reduced to metallic cobalt on the initial discharge, but does not convert back to an oxide on cycling.