Electrochemistry of Cu3N with lithium -: A complex system with parallel processes

Cu3N was examined as a candidate negative electrode material for rechargeable Li-ion batteries. Cu3N electrodes exhibited good cycle life and excellent rate capabilities. The investigation of the material's electrochemical reaction mechanism revealed that the electrochemistry of Cu3N is rich with several parallel processes. In addition to a reversible lithium/copper nitride conversion process and the formation/decomposition of an organic layer at the surface of the nanocomposite, large cycle number and elevated temperature were found to promote a reversible lithium/copper oxide conversion process. Although the lithium/metal nitride conversion process was found to exhibit poor cycling stability, it constituted a fundamental step in the electrode chemistry as it generated highly active Cu nanoparticles which may have activated the formation of an organic layer and the formation of copper oxide. The oxidation of Cu metal into Cu2+ to form CuO and its reduction contributed to the increase in capacity with cycle number. However, the maximum capacity obtained at high rate and elevated temperature far exceeded the theoretical capacity associated to the reduction of pure Cu2+ into Cu metal. These results suggest that the formation/decomposition of an electrolyte interface layer, which may become more substantial with cycling, and other reaction processes, such as a Li-Cu alloying reaction, may provide the additional capacity during cycling. (C) 2003 The Electrochemical Society.