Copper–tin anodes for rechargeable lithium batteries: an example of the matrix effect in an intermetallic system

Lithium batteries are typically constructed from a lithium cobalt oxide cathode and a carbon anode. We have investigated intermetallic anode materials based on tin, which can provide a high theoretical capacity at a slightly higher voltage (0–400 mV) than metallic lithium and thus reduce the safety concerns associated with the carbon anode. In particular, we have investigated the copper–tin system at around the composition Cu6Sn5 and have determined the effect on cycling and capacity of electrodes with various ratios of copper to tin. Anode compositions that are slightly copper rich (Cu6Sn4) were found to exhibit greater utilization of the tin than those with the stoichiometric bronze ratio (Cu6Sn5) or those having a slight excess of tin (Cu6Sn6). The differences in electrochemical behavior are explained in terms of an inert matrix model.