Abstract
To meet surging demands for sustainable energy and clean environment, one critical requirement is to develop high-energy, safe and low-cost rechargeable batteries for electric transportation and grid storage. At the foundation of these batteries are innovative material designs to control the behaviors of ions, electrons, and redox reactions.
In the first part of this presentation, I will show our recent work using an interlayer expansion approach to overcome the large Mg2+ ion diffusion barrier to significantly enhance the diffusivity in Mg rechargeable batteries. Theory, synthesis, electrochemical measurements, and kinetic analysis are combined to improve Mg diffusion behavior in MoS2, which is a poor Mg transporting material in its pristine form. The expansion boosts Mg conductivity by two orders of magnitude, effectively enabling the otherwise barely active MoS2 to approach its theoretical storage capacity as well as to achieve one of the highest rate capabilities. The discovery will lead to novel mechanisms and material designs for multivalent ion storage and open the way to high-energy-density, low-cost and safe batteries.
In the second part, I will demonstrate a “π-conjugated redox polymer” simultaneously featuring a π-conjugated backbone and integrated redox sites, which can be stably and reversibly n-doped to a high doping level of 2.0 with significantly enhanced electronic conductivity. P(NDI2OD-T2) delivers 95% of its theoretical capacity at a high rate of 100C (72 s per charge?discharge cycle) under practical measurement conditions as well as 96% capacity retention after 3000 cycles of deep discharge?charge. Electrochemical, impedance, and charge-transport measurements unambiguously demonstrate that the ultrafast electrode kinetics of P(NDI2OD-T2) are attributed to the high electronic conductivity of the polymer in the heavily n-doped state. Further modification on chemical structures improves specific capacity over 200 mAh/g while maintaining faster electrode kinetics.

Biography
Yan Yao is the Robert A. Welch Assistant Professor in the Department of Electrical and Computer Engineering and Texas Center for Superconductivity at the University of Houston. He studied Materials Science (B.S. and M.S.) from Fudan University (1996- 2003) and Materials Science and Engineering  (Ph.D.) at the University of California, Los Angeles (UCLA, 2003-2008). He worked at Polyera Corporation as a Senior Scientist and Stanford University as a Postdoc Scholar before joining the faculty at the University of Houston in 2012. His current research focuses on designing materials and architectures for electrochemical energy storage. His research has been supported by governmental agencies including the National Science Foundation, Department of Defense, and Department of Energy. Notably he has received the Office of Naval Research Young Investigator Award and he was one of 22 awardees in the Department of Energy’s ARPA-E RANGE program for his aqueous battery technology and a team member as one of 41 awardees in ARPA-E OPEN 2015 for developing all-solid-state-batteries. His research has been widely cited in the scientific community (~12,000 total citations and h-index = 31) and extensively covered by the media.