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, Co-3(PO4)(2)center dot 2H(2)O, and NH4CoPO4 center dot 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 center dot H2O precursor occurs spontaneously, and the NH3, which decomposes to N-2 and H-2 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 degrees C and 55 degrees C, which has never been reported.