Hydrated Iron Phosphates FePO[sub 4]⋅nH[sub 2]O and Fe[sub 4](P[sub 2]O[sub 7])[sub 3]⋅nH[sub 2]O as 3 V Positive Electrodes in Rechargeable Lithium Batteries

Abstract

Hydrated Fe111 phosphates were investigated as positive electrode materials in lithium batteries. Reversible lithium insertion into amorphous and crystalline FePO4·nH2O and Fe4(P2O7)3·n H2O 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 (iv) 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 FePO4·1.6H2O and Fe4(P2O7)3·4H2O electrodes at an average voltage of 3.0 and 3.2 V vs. Li+/Li, respectively.