Engineering cathode and anode for rechargeable aluminum-ion aqueous battery

• Main Author: Sonal, Kumar
• Other Authors: Madhavi Srinivasan
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2021
• Subjects: Engineering::Materials::Energy materials
• Online Access: https://hdl.handle.net/10356/154135
• Institution: Nanyang Technological University

Rechargeable aluminum-ion aqueous battery (AIAB) is extremely attractive from the prospects of developing environmentally and economically sustainable battery energy storage systems. The usage of water as an electrolyte solvent in AIAB makes it inherently non-flammable and presents opportunities for open-air fabrication, making it safer and cheaper. At the same time, AIAB presents opportunities of getting rid of lithium while harnessing aluminium’s (Al’s) high volumetric capacity (~8000 mAh cm-3) and low cost because of the high abundance in the earth’s crust. Hence, AIAB is a strong contender for futuristic energy storage applications, challenging established commercial battery chemistries. However, the AIAB battery research is nascent and presents challenges on both the cathode and anode front, often raising questions about the feasibility and practicality of such viable battery chemistry. This thesis is an effort towards to studying Al-ion batteries and answering this feasibility question by testing novel cathodes and anodes in water-based electrolyte. The thesis starts with a deep dive into the existing AIAB literature. Further, the research gaps are identified and problem statements are defined. The main objective is to study the feasibility of AIAB, essentially by demonstrating working AIAB cell. Hence the scope of the thesis includes (i)engineering new cathode materials which allow for reversible accommodation of Al-ion or its complexes in an Al-salt based aqueous electrolyte, (ii) engineering the surface of Al-metal to enable its usage as an anode in an Al-salt based aqueous electrolyte without significant electrolyte decomposition, and (iii) implementing electrochemical and materials characterization techniques to develop an understanding of the concomitant cell reactions. The thesis can be broadly divided into two parts, one focusing on cathode and the other on anode development. FeVO4, VO2, and HCFs have been explored as potential cathode materials. FeVO4 is reported by us for the first time as a host material showing Al-ion intake by a conversion type mechanism; VO2 is shown to have excellent long-term cycling stability in an optimized electrolyte, and HCF has been developed as a standard cathode material with stable cycling properties to complement anodic studies. On the anodic front, AlCl3 based eutectic formulations have been proposed, which can be used to engineer an artificial protective layer on Al-metal. These layers protect Al from oxidation in ambient and improve the conductivity and kinetics at anode/electrolyte interface, making usage of Al-metal as an anode possible in aqueous electrolyte. A combination of in-house and synchrotron characterization techniques has also been used to understand the structural and compositional evolution in the cathode and study the evolution of Al anode surface chemistry under various conditions. The thesis concludes that an aluminum-ion battery chemistry is possible in an aqueous electrolyte. However, such chemistry is currently limited by low cell voltage, which can be overcome by developing high voltage cathodes and new coating formulations which can exploit the actual reduction potential of Al-metal (-1.66 V vs SHE). The developments made in the thesis serve as a collection of important preliminary studies in the AIAB field and will be beneficial for researchers working in multivalent aqueous chemistry and metal surface engineering.