May.28, 2015. Holl 202 in Lu-Jiaxi Building.
Seminar Title: Cation Mobility and Charge Dislocation in Lithium Transition Metal

               Oxides
Dr. Zonghai Chen (Argonne National Laboratory, USA)

Abstract
 
  Lithium transition metal oxides are dominant cathode materials for lithium-ion batteries that power the modern portable electronics, and as well as the emerging hybrid electric vehicles and electric vehicles.  The research effort to understand the structural stability, the mobility of cations and charge dislocation in this class of materials has been dramatically boosted due to their emerging application for the electrification of the transportation system. In lithium transition metal oxides, the oxygen atoms generally adopt a face centered cubic (FCC) structure, forming the supporting framework to host lithium ions and transition metal ions in its tetrahedral sites and/or octahedral sites.  Different type of materials, ranging from rock slat structure, to spinel and classical layered structure, can be formed by filling vacancies with different ratio of cations with different filling patterns. The common feature of this class of materials is that their lithium ions are mobile in the oxygen framework while the transition metal ion has extremely low or no mobility in the framework, offering the desired reversible charge storage mechanism for long-life and high energy-density lithium-ion batteries. In this work, in situ synchrotron probes were utilized to unveil the migration mechanism of transition metal ions in oxygen framework.  The application of this mechanism to guide the design of next generation high-energy density cathode materials will also be discussed.