Olivine LiCoPO4–carbon composite showing high rechargeable capacity

Abstract

A LiCoPO₄ positive electrode material with an extremely high discharge capacity, 145 mA h (g-phosphate)⁻¹, is reported. Seeking high capacity, we examined three kinds of precursors, Co₃O₄, Co₃(PO₄)₂·2H₂O, and NH₄CoPO₄·H₂O. In combination with a thermal gravimetric study, we found that simple the dehydration of the first two precursors is related to the formation of LiCoPO₄–acetylene black carbon composites (hereafter referred as C–LiCoPO₄). Meanwhile, the formation of the C–LiCoPO₄ composite is somewhat different. That is, generation of NH₃ gas and dehydration of the NH₄CoPO₄·H₂O precursor occurs spontaneously, and the NH₃, which decomposes to N₂ and H₂ gases, provides a more reductive environment during calcination, leaving a small quantity of metallic Co nanoparticles (<10 nm). Distribution of the added acetylene black carbon network is important for proper electron transfer, resulting in good rate capability and capacity retention at 25 °C and 55 °C, which has never been reported.