High potential positive materials for lithium-ion batteries: transition metal phosphates

In the quest of a new material for high potential electrochemical cycling (about 5 V vs. Li+/Li), we have studied the LiMPO4/Li systems with M = Mn, Fe, Co and Ni. To explain the wide average potential range in the series (4, 3.5, 4.8 V, respectively, and probably much higher for Ni), a DFT calculation was done, tacking into account a possible spin-polarization effect. The obtained results rule out any possible bielectronic process for the highest potentials, as proposed in the literature. Some first electrochemical results are given for LiCoPO4, its voltage vs. Li being reasonable from the point of view of high potential electrolyte stability. In optimized conditions, a reproducible electrochemical capacity of 110 mAh/g could be reached during the first discharge. (C) 2003 Elsevier Ltd. All rights reserved.