A Functionalized Co₂P Negative Electrode for Batteries Demanding High Li-Potential Reaction

Co-P alloy films were electrodeposited on a titanium electrode. The controlled addition of phosphorous acid or sodium hypophosphite to a Co 2+ -containing solution leads to the formation of amorphous or crystalline CoP phases. Particularly, the orthorhombic Co 2 P phase is obtained at 80°C with a current density of 37.5 mA cm −2 during 10 and 20 min as determined by XRD and XPS analysis. The morphology of Co 2 P can be controlled from leopard-like spots to hexagonal symmetric particles as confirmed by SEM. This phase is for first time used as a negative electrode in rechargeable batteries. The electrochemical results in a lithium test cell of this unique product differ significantly from other metal phosphides reported in the literature. A high potential reaction at 1.3 V is observed in the first discharge. Successive charge/discharge branches are quite different to those reported so far. The preliminary results suggest that the Co to P ratio may affect the redox properties of the materials. In view of the limited amount of reports dealing with performances of cobalt phosphides in Li-cells, the properties presented here justify further effort to be done to evaluate their real potential application in Li-ion batteries with a predefined voltage operation.