J. Phys. Chem. C 2010, 114, 587–592
587
Theoretical Study of a New Cathode Material of Li-Battery: Iron Hydroxyl-phosphate Shaorui Sun, Zhongli Wang, and Dingguo Xia* EnVironmental Electrochem Laboratory, EnVironment and Energy College, Beijing UniVersity of Technology, Beijing, 100124, China ReceiVed: September 9, 2009; ReVised Manuscript ReceiVed: NoVember 10, 2009
The charge/discharge process and electronic structure of iron hydroxyl-phosphate (Fe2-y0y(PO4)(OH)3-3y(H2O)3y-2) are investigated by density functional theory (DFT) calculation under the GGA+U scheme. The calculation results show that the intermediate phase LixFe1.25(PO4)(OH)0.75(H2O)0.25 does not separate into the two end phases, Fe1.25(PO4)(OH)0.75(H2O)0.25 and Li1.25Fe1.25(PO4)(OH)0.75(H2O)0.25, during lithium insertion/ extraction. The most striking feature of voltage-composition curve is the presence of a sloping voltage curve on charge and discharge, which is a characteristic of a single-phase charge/discharge behavior. It is attributed to the high concentration vacancy defects and the different topological and chemical local structures around the defects. No obvious band gap is observed, and unoccupied states locate around the Fermi level for the LixFe1.25(PO4)(OH)0.75(H2O)0.25 (0 < x
