Lithium-ion batteries are the forerunners in today's energy storage sector, with an energy density
close to 280 Wh kg-1
. However, the cost and abundance of raw materials, safety, and the demand for
higher energy density from electric vehicles and the renewable energy sector provide further impetus
for developing batteries "beyond lithium-ion." Even though a single technology can not comply with
all these requirements, several promising alternative technologies are being explored. The present
work deals with the development of electrolyte and positive electrode materials for sodium-ion, LiO2, and Na-S batteries.
In the first segment of the work, a high entropy, O3 type positive electrode material is developed for
sodium-ion batteries. The electrochemical properties and various phase transitions during sodium-ion
intercalation are studied. A 'full cell' with the developed positive electrode material is demonstrated
by coupling it with sodium titanate negative electrode. In the second segment of the work, solid and
liquid phase reaction promoters are developed for Li-O2 batteries. The role of oxygen vacancies
created by the topotactic reduction of CaMnO3 perovskite in Li2O2 oxidation is examined. A novel
entropy stabilized spinel oxide material, and a liquid phase CoI2 based redox mediator is also
developed, and their role as solid and liquid phase Li2O2 oxidation reaction promoters is studied.
Finally, sodium superionic conductor ceramics are discussed in the third segment of the work. The
brittle ceramic is made flexible and mechanically robust by coupling with a gel polymer electrolyte.
The developed solid electrolyte is applied in room temperature Na-S batteries, with an aim to bring
down the cost factor and increase energy density and safety simultaneously.