Advancements in energy storage technologies need to keep pace with the accelerating transition to renewable energy sources. Li metal anodes and high voltage cathode materials are widely considered to be the path into next generation Li-ion batteries, while the scare amounts of lithium in the earth's crust has prompted research into other battery materials. Of these, Sodium-ion batteries are extremely interesting due to the abundance of Na, similar insertion chemistry to Li as well as the possibility of using aqueous electrolytes due to higher redox potential. Next generation Li-ion batteries are currently held back due to issues like - dendrite formation at the metal anode which may lead to internal short circuiting and thermal runaway of the organic electrolyte. Similarly, Na-ion systems have issues with organic electrolytes due to the limited solubility of Na electrolyte salts. Solid state electrolytes (SSEs) have rapidly garnered interest as a potential alternative. SSEs vastly improve battery safety due to their superior thermal stability and mechanical strength. However, there are still limitations for SSEs in both these systems that need to be resolved prior to implementing these electrolytes in commercial batteries.In this study, alginate salts, which are natural polysaccarides extracted from brown algae, have been examined as a solution to the problems in these systems. Initially, sodium and lithium salts (NaAlg and LiAlg) of alginic acid were synthesized followed by their physical characterization. Conductivity for sodium and lithium alginate (with 0% water) were both promising at 0.2 mS/cm. Additionally, both LiAlg and NaAlg exhibit excellent performance as binders in anode systems compared to PVdF (polyvinylidene difluoride) binders.For utilizing the LiAlg in Li solid-state batteries, NaSICON-based LAGP electrolyte was synthesized and characterized for this study. The degradation of LAGP on Li contact has already been well researched. To combat the issue, we try to utilize a layer of LiAlg as protective layer at the LAGP surface. The coated LAGP remains stable against Li without undergoing degradation. The Li cyclability and electrochemical performance of LiAlg was further analysed by coating it on a various electrodes and studying their rate capabilities against Li. LiAlg displayed excellent performance as a secondary polymer electrolyte on the surface and in the bulk of the electrodes. These tests show exceptional cycling performances and establish a proof of concept for LiAlg as a polymer electrolyte.NaAlg which was chosen as the electrolyte in Na-ion batteries, displays better gelation properties. The effects of water content and operating temperature on Na conductivity were investigated. For a fixed water content, increasing the temperature results in improved conductivity - though this effect is more prominent at higher water concentrations and within the margin of error at lower water concentrations. At a fixed temperature, the conductivity shows linear improvement in at low (<25%) and high (>90%) water concentrations, while remaining constant between 25% and 90%. Additionally, the performance of NaAlg electrolytes (2w% NaAlg aq. solution) and GPE (20w% NaAlg Gel Polymer Electrolyte) was compared with the conventional Na2SO4 electrolyte. During these tests, the electrolyte underwent degradation possibly caused due to cross-linking induced by the dissolution of Mn2+ from the cathode on de-sodiation. Nevertheless, as a proof of concept, the NaAlg showed promise as an electrolyte (aq. and GPE) but further system optimization needs to be done to fully establish its scope as electrolytes for Na batteries.

Large scale stationary energy storage is becoming the need of the hour as the world transitions to a renewable economy. For this, there is a necessity of higher energy density batteries that can cope well both in storing excess energy and minimizing fluctuations on the grid. Solid polymer electrolyte batteries can be extremely safe and reduce packaging while also preventing dendrite formation in Lithium-ion batteries. Sodium ion movement is seen from one oxygen atom to another for an arbitrary Na+ ion. This thesis shows that MD simulations can be a promising method to study the mechanisms involved in alginate polymer electrolytes. Further work is necessary to enable rigorous analysis by incorporating both mannuronates and guluronates. Neutron Magnetic Resonance (NMR) can be carried out to validate the results obtained through MD simulations. MD simulations on sodium alginate (primarily of guluronate) as a solid polymer electrolyte appear to indicate the interaction of Na+ ion with O2 atom of the polyguluronate residue is in preference to interaction of Na+ ion with carboxylate oxygen atoms. Diffusion constant of Na+ ion is seen to drop in MD simulations with increase in Ca2+ ion concentrations both at temperatures 300 K and 373 K.

Metal anode based batteries, considered the ideal upgrade to Lithium ion batteries in terms of energy density, are currently held back by the non-homogeneous deposition phenomenon that leads to the formation of dendrites that short circuit the cell. The solution to this problem is twofold: while it is important to come up with solutions that mitigate/resist dendrite formation, it is more important to fully understand the deposition phenomena in metal anodes through experiments and theoretical analyses. This study aimed to first understand the deposition mechanism in Zinc and Lithium metal anodes, and then study the feasibility of polymer coatings based on Sulfonated Poly Ether Ether Ketone (SPEEK) as a solution to mitigating the dendrites. The electrochemical performance of Zinc in ZnSO4 electrolyte systems was studied for a wide range of current densities and for different operating conditions with the help of operando microscopy and ex-situ SEM. Further, the mechanism of initial Zinc deposition was visualized with the help of in-situ TEM. The origins of the different types of morphology observed at these conditions were explained on the basis of competition between the mass transfer and the kinetics for control over the overall process. Further, a proof of concept was established for the use of SPEEK based coatings on Zinc metal, and the electrochemical performance of polymer coated Zinc electrodes was analyzed. In the case of Lithium, the deposition in carbonate based electrolytes was first studied with the help of operando microscopy for Bare Lithium. Operando microscopy was also carried out to study the influence of the SEI, the separator and a standard polymer coating (PVDF) on Lithium deposition. Further, Lithiated SPEEK was used as a polymer coating on Lithium, and itwas observed that a more even Lithium deposition takes place with the Li-SPEEK coating on Lithium. Slight improvements were observed in the Li+ conductivity of the coating with the addition of TiO2 nanofiller to the polymer. However, performance issues were observed with long term cycling, possibly due to the instability of the polymer coating in carbonate electrolytes over long periods.