Research

Research

Electrochemical Energy Conversion and Storage

  • Li-lon Batteries
  • Na-Ion & K-Ion Batteries
  • Li-S & Li-Se Batteries
  • Aqueous Rechargeable Batteries
  • All-Solid-State Batteries
  • Fuel Cells

Sustainable energy becomes more and more important because it can reduce air emission as well as avoid the rapid depletion of fossil fuel reserves. However, sustainable/renewable energies are usually uncertain and intermittent, so developing of efficient energy storages is urgently necessary to make these sustainable/renewable energies become a major contribution to the future energies. In addition, to keep pace with development of portable electronic devices and electrical vehicles, development of energy storages with high energy and power densities is required. We are interested in designing and developing new materials to be applied to electrochemical energy devices. These include but are not restrained to electrode in secondary batteries (Li-ion, Na-ion, K-ion, Mg-ion, Li-S and Li-Se batteries, Zn aqueous batteries and all-solid-state batteries) and electrocatalysts for the oxygen reduction reaction in fuel cells.

Stable Li Metal Anode

Lithium, the lightest metal with the lowest standard reduction potential, has been long considered as the ultimate anode material for next‐generation high‐energy‐density batteries. However, an unexpected Li dendrite formation, which causes poor reversibility of electrochemical reactions and safety concerns, is a major problem that has to be solved for the commercialization of Li metal anodes. We are interested in understanding reaction mechanism of Li deposition/dissolution during plating/stripping and developing stable Li metal anodes.

Material Design for Reversible Anionic Redox in Cathodes

To date, rechargeable batteries have been mainly based on the cationic redox activity of transition metal (TM) ions. Recently, attention has been drawn to the anionic redox activity of oxygen, which can be exploited to prepare high‐energy‐density cathodes for lithium and sodium ion batteries. However, the irreversible structural disorder and voltage fading accompanying oxygen release are major problems preventing commercial use. We are interested in studying on relationship between structural stability and anionic redox activity to find solutions for these limitations.

Operando/In-Situ Analyses Based on Synchrotron X-ray

  • Operando X-ray Diffraction and X-ray Microscopy
  • X-ray Tomography

There are three types of measurements to analyze the reactions: ex-situ, in-situ and operando measurements (A. Franco, Rechargeable Lithium Batteries: From Fundamentals to Applications, Woodhead. P184). For ex-situ measurement, the cells are stopped at the desired potential, followed by extraction of the electrode from the electrochemical cell in order to analyze it with the desired technique. For in-situ measurement, the cells are stopped to measure directly the electrode inside the cell at OCV. Operando measurement is performed while the cell is cycling. Most results from in-situ and operando measurements are similar, but the results from ex-situ measurement can be very different, since the state can be changed through relaxation process once cell is stopped. Operando/in-situ (especially, synchrotron based) X-ray techniques are very powerful to obtain important information for revealing reaction mechanisms of electrodes. Our research focuses on mechanistic studies of rechargeable battery electrodes using operando synchrotron X-ray based methods such as X-ray absorption spectroscopy and X-ray diffraction. In particular, we are interested in direct visualizing the evolution of the morphology of materials during the entire battery cycling process.

Material Design for High-Performance Energy Storage

High capacity materials store large amount of Li ions/electrons, which always accompanies with huge volume expansion. This normally causes low cycle stability. Properly designed nanostructures effectively accommodate the volume changes during cycling. In addition, nanostructure provides short lithium/electron transport paths, resulting in high rate capability. We have developed a variety of nanomaterials for battery applications.