Wenxiang Chen, Ph.D.

Postdoctoral Research Associate, University of Illinois at Urbana-Champaign Email address: wxchen@illinois.edu

Presented: November 19 and 20, 2020

“Strain-Induced Electrochemical Inhomogeneity in Cathode Nanoparticles Revealed at Atomic Level”

Chemomechanical coupling, a concept commonly used to describe energy conversion in molecular motors, has emerged in the field of insertion electrochemistry to illustrate the interplay between electrochemical processes and mechanical deformation in energy storage materials, catalysts, and reconfigurable architectures. In rechargeable ion batteries, chronic or acute mechanical failures originate from shuffling of guest ions in and out of host structures, which impacts ion insertion pathways and undermines battery performance. Understanding chemomechanical coupling in insertion chemistry is thus critical to inform the design of electrode materials with high capacity, long life-time, and safety. In this talk, I will discuss new strategies to probe and engineer the chemomechanical coupling and electrochemical responses in cathode materials at the atomic level. Using crystalline cathode particles in Mg ion batteries as a model system, we first identify distinctive structural phase transition pathways in particles of different sizes during Mg ion intercalation as characterized by X-ray and electron microscopy. Small, nanoscopic cathode particles exhibit a solid-solution phase transition pathway while their micron-sized counterparts undergo conventional multiphase evolution. Next, we examine the chemomechanical coupling in cathode nanoparticles by integrating scanning electron nanodiffraction microscopy with collocated atomically resolved scanning transmission electron microscopy images. We map the strain and phase in a correlative manner in the intercalated nanoparticles at an unprecedented spatial resolution of 2 nm, achieving the first direct “visualization” of the chemomechanical coupling. Assisted by density functional theory, we elucidate atomic-scale strain relaxation mechanisms as the origin of the spatial heterogeneities of strains and phases in cathode materials, which impacts macroscopic cathode performance. The engineering implications could be on designing nanomaterials of high strain tolerance by tailoring the particle size as well as atomic-scale ion diffusion processes, which we envisage are applicable for various applications in insertion electrochemistry.

Wenxiang Chen, Ph.D., Postdoctoral Research Associate, University of Illinois at Urbana-Champaign

Wenxiang has been a postdoctoral researcher with Professor Qian Chen in the Department of Materials Science and Engineering at the University of Illinois at Urbana-Champaign since 2017. Prior to that, he received his Ph.D. in electrical and systems engineering at the University of Pennsylvania with Professor Cherie R. Kagan in 2017, awarded with the S. J. Stein Prize at Penn Engineering for his Ph.D. thesis. His research efforts focus on designing and understanding new generations of electrochemical and optical nanomaterials, by integrating colloidal synthesis, device fabrication, characterization, and simulation methods in both materials science and electrical engineering on length scales from atomic level all the way to meters. These approaches allow comprehending the chemomechanical coupling and engineering the strain in the electrode materials towards rationally optimizing energy technology and constructing reconfigurable, highly efficient metamaterials with unconventional optical properties.