Hydrated iron phosphates FePO4•nH2O and Fe4(P2O7)3•nH2O as 3 V positive electrodes in rechargeable lithium batteries

Hydrated Fe-III phosphates were investigated as positive electrode materials in lithium batteries. Reversible lithium insertion into amorphous and crystalline FePO4.nH(2)O and Fe-4(P2O7)(3).nH(2)O compositions was found at potentials between 3.5 and 2.5 V vs. Li+/Li. The roles of (i) specific surface area, (ii) amorphous vs. crystalline state, (iii) H2O content, and (i v) electronic contact between particles in the composite positive electrode, on the electrochemical performances of these materials are discussed. Very stable cycling was obtained for optimized FePO4.1.6H(2)O and Fe-4(P2O7)(3).4H(2)O electrodes at an average voltage of 3.0 and 3.2 V vs. Li+/Li, respectively. (C) 2002 The Electrochemical Society.