Projects in Battery are:

• Battery-Supercapacitor Hybrid System
• Li-ion Batteries - Calendar Life Studies

Conventional battery systems (Lead acid, Ni-Zn, Ni-Fe, and Ni-Cd) do not address important issues needed for electronic appliances such as long life, low weight, the use of nontoxic materials and high power. In the last decade focus has shifted to a new class of cells such as Lithium ion and Nickel Metal Hydride batteries. This laboratory is set up to synthesize different chemicals, which can be used as battery electrodes for Li-ion cells and Ni-MH batteries. Further, the facility has capacity to study the charge-discharge behavior, utilization and capacity fade of different batteries and supercapacitors. We also have the capability to cut open batteries and perform diagnostic tests to determine the causes of battery failure.

For the past 2 years, my group has been involved in studying the cause of failure of Nickel-Metal Hydride and Lithium-ion batteries. This program has been funded by both private and government funds. The National Reconnaissance Office and the Office of Basic Research, Department of Energy have been supporting this effort. To perform extensive cycle life studies we have 3 Arbin cyclers with more than 100 channels and 4 Bitrode cyclers with more than 150 channels. Using these cyclers it is possible to study the cycle life characteristics of the batteries under various charging protocols. The Arbin BT2000 Charger shown on right has the capability to perform both cycle life and 3 electrode characterization studies. With Potentiostatic and Galvanostatic capability, the channels in the charger can be coupled to achieve higher currents if needed. Further, the charger can be used for doing GSM and CDMA discharge and pulse charging for very small durations (milliseconds) to the battery.

Apart from capacity fade, our other main thrust is on developing new materials, which possess superior capacity and cycle life as compared to presently used electrode materials. Other characteristics desired include low self-discharge, uniform operation at high temperatures and corrosion resistance. Since, chemicals used in the Li-ion batteries are highly reactive in atmosphere, the entire synthesis procedure is carried out in an inert atmosphere.

Subsequent to synthesis, characterization of the electrode materials is carried out using a three electrode setup shown on right. The T-cell is assembled in an inert atmosphere. Various electrochemical studies are carried out on these cells. Based on the data collected the synthesis procedure is further refined. The following electrochemical characterization studies are done on new materials and also on material obtained from cycled batteries:

1.  Electrochemical Impedance Spectroscopy studies on the anode and cathode materials using Li/Li+ as reference and counter electrodes. EIS gives information on individual electrode resistances and resolves them to specific components which can be monitored as the battery ages.
   
2.  Determine specific capacity and the reversibility of the processes, which occur at the electrode-electrolyte interface, for both electrode materials using slow scan cyclic voltammetry.
   
3.  Determine rate capability (capacity at different discharge rates for carbon and LiCoO2), during discharge using galvanostatic techniques.
   
4.  Study change in the equilibrium potential and exchange current density as a function of state of charge for both carbon and LiCoO2 using linear polarization

The rate capability and cycle life of these electrode materials are determined next using a multi-channel cycling station. Data obtained from these studies will reveal how long the material will last during normal operation.Gathering all the data for a given experiment, the results from the cycling station are plotted to study the performance of different electrode materials. This is then compared to industry standards. Prototype industrial cells of materials that show promise are subsequently done and tested similarly.