Antagonistic effects of copper on the electrochemical performance of LiFePO4

In the last few years, several strategies towards boosting the electrochemical performance of LiFePO4 cathodes have been envisaged. Copper addition to the phosphate seems to be a simple, inexpensive method for this purpose. However, it has a serious drawback: at voltages slightly higher than that required for lithium extraction from LiFePO4, the copper is oxidized to either Cu(I) or Cu(II) with partial decomposition of the electrolyte. XRD patterns are consistent with the disappearance of copper from pristine composites upon charging at up to 4.0 V Moreover, a copper deposit is formed on the lithium surface in the discharged state that creates a barrier hindering the release of Li ion from the electrode. Therefore, copper electroactivity strongly influences the capacity and cycling life of the cell. (C) 2007 Elsevier Ltd. All rights reserved.