Abstract

The presentation will discuss the interplay between core level spectroscopies and lithium electrochemistry,in pursuit of improvedenergy efficiency and storageapplications (i.e., electrochromic smart windows and lithium ion batteries).Electrochromic devices and lithium ion batteries are “rocking-chair”devices, where lithium ions shuttle between cathodic and anodic electrodes upon electrochemical cycling. The intercalation of lithium ions into electrode materialsinduces simultaneous changes in the crystal/electronic structures and optical properties of the hosts, which are strongly correlated and can be probed by several spectroscopic and microscopic tools. Core level spectroscopies, including synchrotron X-ray absorption spectroscopy (XAS), X-ray photoelectron spectroscopy (XPS) and electron energy loss spectroscopy (EELS), are intensively applied in our studies by taking advantage of their high sensitivity to the local geometric and electronic structuresof matters. With regards to electrochromic smart windows, we found that, in multicomponent nickel oxide-based electrochromic materials (e.g., Li_2.34NiZr_0.28O_x), the electrochromism originates from the reversible formation of hole states in the NiO₆ octahedral cluster accompanied with the reversible formation of Li₂O₂ at the electrode surfaces.Consequently, improved electrochromic performance was achieved through high-concentration “hole doping” during the materials fabrication using radio frequency magnetron sputtering. With respect to lithium ion batteries, we investigated the structural evolution of theprominent stoichiometric layered cathode materials (LiNi_1-x-yMn_xCo_yO₂) under high-voltage operation conditions, and determined that the anisotropic phase transition from an R m structure to Fm m/Fd m structures at the particle surfacesis primarily responsible for the performance degradationof batteries (e.g., capacity fading, impedance rise). Applying this knowledge, we employed modifiedsynthetic protocols, i.e.,spray pyrolysis and aliovalent substitution,for accessing those cathode materials, and improved battery performances were achieved.In brief, state-of-the-art core level spectroscopies could provide rich fundamental understandings of the electrode materials, which may lead to a better design of materials for advanced energy efficiency and storage applications.

Bio

Dr. Feng Lin is currently a Postdoctoral Fellow in Dr. Marca Doeff’s group at Lawrence Berkeley National Laboratory. His current research topics include rechargeable batteries and electrocatalysis. He holds a Bachelor’s degree in Materials Science and Engineering from Tianjin University, and an MSc degree and a PhD degree in Materials Science from Colorado School of Mines. His graduate research was co-supervised by Prof. Ryan Richards, Dr. Anne Dillon and Dr. Chaiwat Engtrakul at Colorado School of Mines andNational Renewable Energy Laboratory, where he developed advanced materials for electrochromics and catalysis. Over the years of materials research, Dr. Feng Lin has acquired his expertise in templated sol-gel chemistry, thin film deposition, synthetic laser chemistry, surface science, and electron and X-ray spectroscopy. His research has been frequently highlighted by DOE national laboratories and public media, including a 2014's Top-10 Scientific Achievements at Brookhaven National Laboratory. Dr. Feng Lin served the electrochemistry community in Northern California as the Chair of The Electrochemical Society-San Francisco Section (22 Sections globally) during2013-2014.

Representative Publications:

1) He, K.; Xin, H. L.; Li, J.; Lin, F.;* Su, D. et al.,  Nano Letters2015, 1437-1444

2) Lin, F.*; Markus, I. M.; Nordlund, D. et al.,  Nature Communications 2014, 5: 3529

3) Lin, F.*; Nordlund, D.; Weng, T. -C. et al., Nature Communications 2014, 5:3358

4) Lin, F.; Nordlund, D.; Weng, T. -C. et al., ACS Applied Materials & Interface2013, 5, 3643–3649

5) Lin, F.*; Nordlund, D.; Markus, I. M. et al., Energy & Environmental Science2014, 7, 3077-3085

6) Lin, F.; Nordlund, D.; Moore, R. G. et al., Advanced Materials Interfaces2015 DOI: 10.1002/admi.201400523