Li–O2 batteries are considered as one of the promising beyond Li-ion battery technologies owing to their high energy density. But, their poor cycle life due to sluggish oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) hinder the commercialization of this technology. Hence, fabrication of highly efficient ORR and OER catalysts is of paramount importance in order to improve the cyclic stability and longevity of this device. Herein, we discuss systematically the synthesis and electrochemical analysis of such bifunctional perovskite catalysts, namely, pristine CaMnO3 and its defect induced counterpart. When evaluated as a cathode catalyst in a Li–O2 battery along with a redox mediator LiI, the oxygen deficient CaMnO3 gives an improved cycle life reported at a high current rate of 500 mA g–1 with a capacity of 500 mA h g–1 in comparison with similar catalysts reported in the literature. Introduction of defects in the pristine framework predominantly improves the catalytic activity by lowering the overpotential. The presence of oxygen vacancies creates mixed-valence states of Mn3+/Mn4+ which modify the electronic structure, resulting in the improved catalytic activity. Comprehensive phase and compositional analysis confirm the formation of the desired defect-induced structure with improved catalytic activity toward ORR and OER which is elaborated with electrochemical analysis.

A method to produce a thin and flexible “polymer in ceramic” type sodium ion conductor film from an erstwhile brittle Na3Zr2Si2PO12 ceramic film is reported and its application in room temperature sodium-sulfur batteries is demonstrated.

Charge transport limitations at the Li2O2 discharge product‐electrode interfaces hinder the rechargeability of Li−O2 batteries. Herein, we introduce entropy stabilized oxides (ESO) as reaction ′promoters′ in positive electrodes that can facilitate charge transport by reducing the binding energy of the intermediates. In this work, we developed a rock‐salt type entropy stabilized oxide. We show that the rock salt phase transforms into a pure, equimolar, quinary spinel on heat treatment. A Li−O2 battery with the developed ESOs at the positive electrode is cycled with an areal capacity of 1 mAh cm−2 at a current rate of 0.25 mA cm−2 to study its role as a reaction promoter. The surface, bulk, and morphological characterization are carried out for both materials. The presence of multiple cations and defects on the surface of the ESO is found to benefit the discharge product oxidation and improve the cyclic stability.

Out of all the anode materials available for sodium ion batteries, sodium metal itself offersthe highest theoretical capacity. However, the direct use of sodium metal as anode is hindered by the challenges involved in processing the material, dendrite formation and high volume expansion. “Anode free” batteries are one of the most promising strategies to address these issues. In anode free sodium batteries, the sodium ions from the cathode are directly deposited on the anode current collector thorough the electrolyte and hence eliminate the use of sodium metal during the cell fabrication. Solid state electrolytes (SSE), on the other hand, are proposed to deal with the dendrite formation issues. Therefore, anode free sodium battery with a solid electrolyte is a fascinating electrochemical system which not only aims to solve majority of the issues with Na-metal batteries but also provides high volumetric energy density, safety and ease of fabrication.For a successful anode free battery, the behavior of sodium plating and stripping processes in different electrolytes/current collectors must be comprehended. Additionally, interfacial impedance is an area of major concern for solid electrolytes as well. Keeping this in mind, this work focusses on the study of the interfaces between solid electrolytes and anode current collectors. Interfacial properties of inorganic sodium super ionic conductor (NASICON) in combination with a polymer electrolyte (PVDF-HFP/NaPF6/TEGDME) are studied with respect to copper/3D carbon cloth current collector using electrochemical impedance spectroscopy. Sodium stripping and plating processes are studied with respect to both sodium electrodes and Na2S based cathodes and an anode free Na-S battery is demonstrated with the optimized combinations of SSEs and current collectors.