Xiankai Yu


Major: Materials Science and Engineering
Office: Cook 4088B
Phone: (847) 491-7805
Email: xiankaiyu2014@u.northwestern.edu

2014-Present Ph.D. Student, Materials Science and Engineering, Northwestern University
2010-2014 B.S., Mechanical Engineering, Tsinghua University

Research: Hetero-structural Thin Films for Lithium Ion Batteries
LiMn2O4 (LMO) as one of the most promising cathode material for lithium ion batteries (LIBs) receives extensive researches on critical challenges, such as capacity fading, calendar life and cyclic reversibility. Those phenomena are directly associated with electrode surface & interface chemistry. Progress of fundamental understanding interfacial physics and chemistry between electrodes and electrolytes in LIBs has been pursued by architecting model ultrathin films as characterization tools. Using advanced thin film technology such as pulsed laser deposition (PLD) and radio-frequency (RF) magnetron sputtering, hetero-epitaxial thin films of LMO (~10nm) are constructed layer-by-layer on single crystal substrates SrTiO3 with electrical conductive back contact layer of (La,Sr)CoO3 (LSCO). The highly oriented LMO/LSCO bilayer of continuous atomic stacking provides well defined 2D cathode interface and surface with sub-nano flatness. Advanced in-situ and ex-situ characterizations such as synchrotron XRD, XRR, AFM and high resolution TEM are used to study crystal structural and chemical properties change during cycling of LMO. Furthermore, solid-solid interfacial resistance is great challenge concerning the state of the art concept of all-solid-state LIBs. Engineering ideal epitaxial cathode/solid electrolyte hetero-structure mitigates those challenges. Ultrathin films by PLD can also serve as a dense barrier layer on LMO cathode to prevent Mn dissolution and improve electron & Li+ conductivity.