Magnesium insertion into Mg0.5+y(FeyTi1-y)2(PO4)(3)

A series of transition metal phosphates, Mg0.5+y(FeyTi1-y)(3) (PO4)(3) (MFT P), modified from Mg0.5Ti2(PO4)(3) (MTP) were prepared by solgel method and evaluated as cathode materials for rechargeable magesium cells. The crysta l structure of MFTP at 0 less than or equal to y less than or equal to 0.5 was identical to that of MTP, while their unit cell volumes were smaller th an that of MTP due to introduced Mg2+ ions. Electrochemical magnesium inser tion into MFTP was found possible as observed for MTP. However, the Limitin g extent of magnesium insertion into MFTP at 0.1 less than or equal to y le ss than or equal to 0.5 was small compared with MTP and remarkably dependen t on the current density during discharge, suggesting that the insertion li mit is determined not by the number of available sites for Mg2+ or electron s but by the mobility of Mg2+ in the host varying with the unit cell volume . (C) 2001 Elsevier Science B.V. All rights reserved.