Research

Lithium-ion batteries (LIBs) are one of the most successful electrochemical devices. Modern electronic devices demand lithium-ion batteries with high energy density. In addition, growing interest in high power applications such as plug-in hybrid and power tools requires both high energy density as well as high power density. Currently our group focuses on cathode and anode for lithium ion batteries using novel nanocrystalline materials. With regards to research on the cathode, our current interest has been to explore olivine-based phosphate as well as silicate materials. These materials are known to be both electronically as well as ionically insulating at room temperature. Attempts are made to reduce the transport length for the charge carriers by reducing the particle size to nanometers. Extra efforts are made in decorating the surfaces by carbon coating to improve the electronic connectivity to the current collectors.

As for the anode, we aim to explore the conversion reaction where deep lithium incorporation into a transition metal oxide reduces it to a metal along with in-situ formation of nanocrystalline/ amorphous lithium oxide. Upon extraction of lithium this metal/lithium oxide composite transforms to nanocrystalline/amorphous transition metal oxide. Although this conversion reaction has been successful in increasing the energy density, 1000-1200 mAh/g (which is nearly 3 times higher than conventional graphite as anode material), the reversibility of such conversion reaction during first charge cycle is limited to about 70-80%. Attempts are made to increase this coulombic efficiency to above 90% with a stable cyclic performance. We also aim to increase the storage capacity due to interfacial storage mechanism by increasing the interfacial area of metal/lithium oxide

Intermittency of renewables such as solar and wind necessitates the need for the development of large scale renewable energy storage systems for micro-gird applications. Though lithium-ion batteries are front-runners, their high cost ($/kWh) is a matter of concern if such batteries are to be deployed on a large scale. Further, confinement of Li resources to specific geographies could lead to economic monopoly in the near future. In this regard, sodium-ion batteries (NIBs) have re-captured the attention of the scientific community as sodium is cheap and available in abundance. Most importantly, this research direction provides an opportunity to explore new chemistries and intercalation hosts which have not been successful with lithium counterparts.

Despite several advantages, this technology still remains in its nascent stage as appropriate sodium storage hosts have not been completely identified yet. In our group, we are investigating a family of novel cathode and anode materials that could store sodium. On the cathode front, we are currently developing a low cost nano-engineering process to produce a variety of phosphate based cathode materials which show ultra-long cycle life. Recent studies also suggest fast diffusion of sodium ions with relatively less polarization compared to lithium ions at high current rates. On the anode front, we are investigating new materials that store sodium by either insertion or conversion reaction. We also investigate new binders for sodium-ion batteries as our initial findings show a strong influence of the binder on the sodium storage performance. With the above solutions, we hope to support intermittent renewables using our low cost nano-engineered electrode materials for sodium-ion batteries.