title: Revealing the Reconstructed Surface of Li[Mn2]O4.
abstract: The spinel Li[Mn2]O4 is a candidate cathode for a Li-ion battery, but its capacity fades over a charge/discharge cycle of Li1-x[Mn2]O4 (0 < x < 1) that is associated with a loss of Mn to the organic-liquid electrolyte. It is known that the disproportionation reaction 2Mn(3+) = Mn(2+) + Mn(4+) occurs at the surface of a Mn spinel, and it is important to understand the atomic structure and composition of the surface of Li[Mn2]O4 in order to understand how Mn loss occurs. We report a study of the surface reconstruction of Li[Mn2]O4 by aberration-corrected scanning transmission electron microscopy. The atomic structure coupled with Mn-valence and the distribution of the atomic ratio of oxygen obtained by electron energy loss spectroscopy reveals a thin, stable surface layer of Mn3O4, a subsurface region of Li1+x[Mn2]O4 with retention of bulk Li[Mn2]O4. This observation is compatible with the disproportionation reaction coupled with oxygen deficiency and a displacement of surface Li(+) from the Mn3O4 surface phase. These results provide a critical step toward understanding how Mn is lost from Li[Mn2]O4, once inside a battery.
authors.affiliation: Materials Science and Engineering Program, The University of Texas at Austin , Austin, Texas 78712, United States.
authors.forename: Charles D
authors.initials: CD
authors.lastname: Amos
authors.affiliation: The STEM Group, Materials Science and Technology Division, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States.|Universidad Complutense de Madrid , Madrid 28040, Spain.
authors.forename: Manuel A
authors.initials: MA
authors.lastname: Roldan
authors.affiliation: The STEM Group, Materials Science and Technology Division, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States.|Universidad Complutense de Madrid , Madrid 28040, Spain.
authors.forename: Maria
authors.initials: M
authors.lastname: Varela
authors.affiliation: Materials Science and Engineering Program, The University of Texas at Austin , Austin, Texas 78712, United States.
authors.forename: John B
authors.initials: JB
authors.lastname: Goodenough
authors.affiliation: Materials Science and Engineering Program, The University of Texas at Austin , Austin, Texas 78712, United States.
authors.forename: Paulo J
authors.initials: PJ
authors.lastname: Ferreira
keywords: EELS; HAADF STEM; LiMn2O4; Mn-disproportionation; surface reconstruction