First Principles Investigation of Stable LiMn2O4 Surfaces for Lithium-Ion Batteries

  The spinel LiMn₂O₄ (LMO) has been widely studied as a lithium-ion battery cathode to replace the currently-used LiCoO₂ materials due to its low cost and fast Li⁺ diffusivity.^[1]  However, a severe capacity fading during LMO cycling occurs because of the Mn dissolution, possibly initiating from the cathode surface. Thus, it is essential to completely understand the stable LMO surface structure to overcome current limitations and further to suppress the Mn dissolution in LMO.

  In this work, we investigate the effects of surface termination, slab reconstruction, relaxation schemes, magnetic ordering, and different U value for Mn to determine the relative stabilities of the LMO surfaces. We find that it is necessary to relax all atomic positions with symmetry-broken DFT calculations to fully capture the local variation of Mn-O and Li-O polyhedral clusters to obtain the most consistent surface energies. We finally comment on the possible implication of our work on the future surface studies of the mixed-valence transition metal complex oxides such as the LMO system.

Acknowledgement: This work has been supported by Northwestern-Argonne Institute of Science and Engineering (NAISE) and by The Dow Chemical Company.

Reference: [1] R. J. Gummow, A. Kock, M.M. Thackeray, Solid State Ionics 1994, 69, 59.