Research Projects

Non-aqueous lithium-ion batteries (LiBs), despite their excellent energy and power density, are unlikely to meet the stiff scale-up targets concerning performance, cost, and safety expected in electric mobility and the grid. Additionally, with the increased awareness of sustainability, there has been a paradigm shift toward developing alternative battery systems beyond LiBs. Using earth-abundant and low-cost materials coupled with aqueous electrolytes can lead to novel and cost-effective batteries. Higher-valent-ion (Zn2+, Al3+, Ca2+, and Mg2+) aqueous batteries (HVABs) provide a significant edge over monovalent ions like Li+/Na+ due to higher energy density, attributed to the higher valency. These metals, part of India’s Energy Roadmap (2019-2032), are abundant in India (compared to Li) and will provide economic rechargeable batteries for the electric grid, rooftop PVs, and remote installations. Despite these advantages, HVABs are plagued by several fundamental and technological challenges. Due to their high charge-to-size ratios, a large solvation (hydration) shell exists around the ‘active ions.’ This inhibits rapid diffusion in both liquid and solid electrode materials. The increased size of the ‘active ion’ limits the choice of electrodes to only a few chemical compositions. The operation voltage is limited ( 1.23 V). As a result, the HVABs are plagued by water splitting, parasitic side reactions, and corrosion, thus limiting the battery's performance and life. This proposal will systematically investigate the solvated HV-ions ( molecular-ions) of Zn2+, Al3+, Ca2+, and Mg2+, which directly participate in the energy storage mechanism, using experiments and theory. Conclusive evidence depicts the direct participation of water and proton-mediated chemical reactivities/intermediates on charge transport and electrochemical storage. This warrants a systematic probing of the role of water in various environments (liquid electrolyte, electrolyte-electrode interface, and solid-electrode) and apriori predictions of the molecular-ion structures. The molecular ions, whose properties are distinctly different from the free-ion, will change in size and composition depending on their composition and environment. The energy landscape of the interface and within the solid will decide the chemical coordination within the solid electrode. Apart from the ion structure, the dynamics and chemical reactivity will also play a significant role. We plan to study here the physical characteristics of liquid electrolytes ranging from conventional (salt-in-water) to super-concentrated (water-in-salt) to binary solvents (water + non-aqueous solvent). Systematic operando experiments and theoretical modeling will establish the role of the solvated HV-ion in electrochemical storage and performance. The fundamental studies as part of the proposal will have profound implications on both materials design and the development of practical HVABs.