Investigations of a Number of Alternative Negative Electrode Materials for Use in Lithium Cells

There is a considerable interest in the replacement of graphite as the negative electrode reactant in rechargeable lithium batteries by composite electrodes containing alloys or convertible oxides. Some such materials can have much higher theoretical specific capacities than graphite, more than a factor of ten in some cases. In addition it would be desirable to eliminate the irreversible loss of capacity during the first charging cycle that is characterisitic of graphite electrodes, as well to raise the operating potential somewhat in order to reduce the danger of the formation of elemental lithium during recharging. The several strategies that have been followed in the search for attractive alternatives will be briefly described. It has been found to be difficult to obtain the desired combination of high capacity, low first cycle loss and capacity retention upon cycling. Investigations of the electrochemical behaviour of elemental boron and borides (B4C, CaB6, LaB6, AIB(2), SiB3), elemental silicon and silicides (Mg2Si, FeSi2, CoSi2, NiSi2, TiSi2, VSi2) and of siliconmonoxide, SiO, will be reported. The galvanostatic cycling method was used, with thick layer electrodes (30 mu m) deposited upon copper foil in coffee bag-type cells with a liquid electrolyte. Lithium foil was used for the counter and reference electrodes. The results of the investigation of the morphological changes upon cycling, as observed by the use of SEM, will also be presented.