Investigations related to rechargeable lithium and magnesium batteries:

Among various rechargeable batteries, lithium-ion batteries occupy a special place in terms of energy density and also several applications anticipated. Research activities on important electrode active materials have been under progress. Positive electrode materials, which are capable of providing high specific capacity with good structural stability over prolonged charge-discharge cycle life, are considered important for future generation lithium-ion batteries. These compounds need to provide safety and reliability for the battery. Lithiated mixed transition metal oxide, namely, LiNi1/3Co1/3Mn1/3O2, LiMnO2, LiMn2O4, and LiFePO4 have emerged as a promising material for the positive electrodes. These compounds are prepared as sub-micron size particles for imparting high rate capability. Various surface modifications, such as coating with inert oxide layers, carbon coatings, conducting polymer coatings, etc., are studied. The compounds are characterized by several physicochemical techniques, which are useful to study the phase purity, particle size and oxidation state of the metal ions. Electrochemical cells in non-aqueous electrolytes are assembled in an argon filled glove box and evaluated for various electrochemical properties. The properties include specific discharge capacity, rate capability, temperature dependence on capacity, ac impedance behavior, diffusion coefficient and cycle-life test.

It is now well recognized that Li-ion batteries are the batteries for future. These batteries are projected for various applications including electric vehicles (EVs) and hybrid electric vehicles (HEVs). Intense research activities on various aspects of Li-ion batteries are underway in many laboratories around the world. However, it has to be noticed that the global raw material resources of lithium are very limited, which is likely to hamper a wide dependence of the society on Li-ion batteries. Although it too early to envision a battery system which is alternate to Li-ion battery, it is intended to start research programme on rechargeable magnesium batteries. It is obvious that the resources of magnesium are plentiful, Mg is safe to handle and environmental friendly. Although the electrical performance characteristics of Mg based batteries are likely to be inferior to the batteries based on Li, merits of the former battery system overweigh the limitations.

Electrochemical Supercapacitors can withstand to higher power than batteries, and deliver higher energy than the conventional electrostatic and electrolytic capacitors. Electronically conducting polymers are interesting class of materials studied for supercapacitor application because of the following merits: high electronic conductivity, environmental friendliness, ease of preparation and fabrication, high stability, high capacitance and low cost. polyaniline and poly(3,4-ethylenedioxythiophene) are studied in this category. Among the transition metal oxides, MnO2 with a theoretical specific capacitance of 1370 F g-1 is an attractive material for supercapacitor studies. However, a maximum specific capacitance of about 240 F g-1 is usually reported in the literature. Experimental investigations are taken up to study various aspects to enhance specific capacitance. In view of this, attempts are made to enhance specific capacitance of MnO2 by electrochemical deposition in presence of surfactants. Nano-structured MnO2 synthesized by inverse microemulsion route is also studied for electrochemical Supercapacitors. The effect of crystallographic structure of MnO2 on the capacitance properties, studies on electrochemical deposition of MnO2 in acidic and neutral medium using electrochemical quartz crystal microbalance and capacitance characteristics of MnO2-polyaniline composites are studied. From EQCM data of mass variation during cycling, it is observed that the rate of electrodeposition of MnO2 is higher in the neutral medium than in the acidic medium. Specific capacitance of MnO2 deposited from the neutral medium is higher than that deposited from acidic medium owing to different crystallographic structures. Reversible insertion/deinsertion of hydrogen in to the layers of -MnO2 is observed in hydrogen evolution region. Electrochemically precipitated Mn(OH)2 is also found electrochemically active for Supercapacitors studies in aqueous electrolytes.

Electrochemistry of conducting polymers is an important area of research in view of various applications. Electrooxidation of methanol, formic acid, formaldehyde and ethanol on nanocluster of Pt and Pt-Ru deposited on PEDOT/C electrode are studied in view of their promising applications in fuel cells. Films of PEDOT are electrochemically deposited in carbon paper. Nanoclusters of Pt and bimetallic Pt-Ru catalysts are potentiostatically deposited on PEDOT/C electrodes. Catalysts are also prepared on bare carbon paper for studying the effect of PEDOT. The presence of PEDOT film on carbon paper allows the formation of uniform, well dispersed nanoclusters of Pt as well as Pt-Ru catalysts. TEM studies suggest that the nanoclusters of about 50 nm consist of nanoparticles of about 5 nm in diameter. Electrooxidation of methanol, formic acid, formaldehyde and ethanol are studied on Pt-PEDOT/C and PtRu-PEDOT/C electrodes by cyclic voltammetry and chronoamperometry. The data for oxidation of these small organic molecules reveal that PEDOT imparts a greater catalytic activity for the Pt and Pt-Ru catalysts. PEDOT - coated stainless steel electrodes are used to investigate phenol oxidation and also for Supercapacitors studies.