Cathode material investigation towards high-performance aluminum batteries

• Main Author: Gong, Xuefei
• Other Authors: Lee Pooi See
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2020
• Subjects: Engineering::Materials::Energy materials; Engineering::Materials::Nanostructured materials
• Online Access: https://hdl.handle.net/10356/137034
• Institution: Nanyang Technological University

Aluminum (Al) batteries, with merits of cost effectiveness, safe handle, high capacity and dendrite-free formation of Al anode and utilization of non-flammable ionic liquid electrolyte, has been considered as promising alternative to lithium ion batteries. However, Al batteries suffer from sluggish kinetics of ion intercalation/de-intercalation and inferior cycling performance. It is due to the large electrostatic interactions between trivalent Al3+ and the framework of cathode materials, thus resulting in the destruction of the lattices of cathode materials, trapping Al3+ ions into the framework of cathode materials and hindering the subsequent Al3+ intercalation. It is hypothesized that cathode materials with enhanced electrical conductivity, porous and hierarchical structures and appropriate lattices can ensure sufficient pathways for Al3+ ion diffusion and charge transfer, accommodate volume expansion and mitigate structural collapse during trivalent Al3+ ion intercalation/de-intercalation, which are beneficial to delivering improved electrochemical performance during charge/discharge process. Particularly, Al-S battery systems with enhanced energy density are attracting tremendous attentions. However, the issues are the sluggish redox reactions of insulating sulfur/polysulfides and the dissolution of polysulfides into electrolyte, leading to inferior cycling stability. Thus, this research employed the following approaches, namely, preparing metal oxides to chemically anchor soluble polysulfide species via a surface oxidation process, synthesizing porous and conductive carbon framework to physically confine sulfur, and developing metal sulfides to chemically bond soluble polysulfides. The strategies are demonstrated to be effective in mitigating the shuttling of polysulfides from cathode to anode and improving the kinetics of redox reactions. Additionally, hybrid Al-Li-ion batteries, with Li+ intercalation/de-intercalation participation in the cathode materials and Al stripping/deposition at anode, is proposed to enhance kinetics, increase capacities and prolong cycling life as well as maintain dendrite-free . The improved electrochemical performance can be ascribed to the less electrostatic interactions between monovalent Li+ with the framework of cathode materials and the faster mobility of Li+ insertion/extraction into/from host materials.