To study the important role played by metastable phases during electrode’s charging and discharging cycling, we simulated the lithiation process of the Co₃O₄ and NiO using DFT calculations. The studies are started with creating supercells for Co₃O₄ and NiO. Li-ions were put into the unoccupied interstitial sites for a series of stoichiometries (Li_xM_aO_b, x = 0.5, 1.0, 1.5... and M=Co, Ni). For Co₃O₄, to investigate the energetic influence of the Co migration, initial structures are created with Cos moved from tetrahedral sites to the octahedral sites. For each composition, all the geometrically different derivative structures were generated and selected to be relaxed in DFT. Convex hulls are built with all formation energies of different stoichiometries. Voltage profiles are calculated using the energetics of the phases on the hull. Six and two metastable phases are identified for Co₃O₄ and NiO. Structures evolution predicted for Co₃O₄ are confirmed with the former experimental studies. The simulated voltage profiles resulted from the prediction of the metastable phases fit much better with the experimental measurements. The results indicate that the lithiation process of Co₃O₄ and NiO occur through a series of metastable phases.

Acknowledgements

Z.Y., Q.L., J.W., V.D., and C.W. were supported as part of the Center for Electrochemical Energy Science (CEES), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of the Science, Basic Energy Science. S.K. was supported by Northwestern-Argonne Institute of Science and Engineering (NAISE). M.A. was supported by the Dow Chemical Company. This research used resources of the National Energy Research Scientific Computing Center, a DOE Office of Science User Facility supported by the Office of Science of the U.S. Department of Energy under Contract DE-AC02-05CH11231.