First-principles calculation of atomic structure and electrochemical potential of Li1+xV3O8

Interest in the gamma-bronze, Li1+xV3O8, as a possible electrode material in rechargeable Li batteries has stimulated several experimental studies on this system. Detailed interpretation of the electrochemical and physical-property measurements is complicated by uncertainties regarding the structural arrangement of Li atoms as a function of x and by a phase transition between two monoclinic structures (gamma(a), gamma(b)) during intercalation. To elucidate the atomic structures and the phase transition, first-principles calculations are performed with the local-density-functional-theory (LDFT) planewave pseudopotential method for both gamma(a) and gamma(b) as a function of lithiation. Calculations for the compositions 1 + x = 1.5 and 1 + x = 4 confirm that the Li configuration determined in the existing X-ray diffraction structure refinements (at 1 + x = 1.2 and 1 + x = 4, respectively), coincide with the predicted low-energy configurations. Structure predictions were made at intermediate compositions, for which no experimental structure measurement is available. The order in which the tetrahedrally coordinated Li sites are filled at equilibrium as a function of x in gamma(a) was predicted. Calculated electrochemical potentials as a function of composition agree well with experimental data. (C) 1999 Elsevier Science S.A. All rights reserved.